Characterization and expression analysis of WRKY genes during leaf and corolla senescence of Petunia hybrida plants.

Several families of transcription factors (TFs) control the progression of senescence. Many key TFs belonging to the WRKY family have been described to play crucial roles in the regulation of leaf senescence, mainly in Arabidopsis thaliana. However, little is known about senescence-associated WRKY members in floricultural species. Delay of senescence in leaves and petals of Petunia hybrida, a worldwide ornamental crop are highly appreciated traits. In this work, starting from 28 differentially expressed WRKY genes of A. thaliana during the progression of leaf senescence, we identified the orthologous in P. hybrida and explored the expression profiles of 20 PhWRKY genes during the progression of natural (age-related) leaf and corolla senescence as well as in the corollas of flowers undergoing pollination-induced senescence. Simultaneous visualization showed consistent and similar expression profiles of PhWRKYs during natural leaf and corolla senescence, although weak expression changes were observed during pollination-induced senescence. Comparable expression trends between PhWRKYs and the corresponding genes of A. thaliana were observed during leaf senescence, although more divergence was found in petals of pollinated petunia flowers. Integration of expression data with phylogenetics, conserved motif and cis-regulatory element analyses were used to establish a list of candidates that could regulate more than one senescence process. Our results suggest that several members of the WRKY family of TFs are tightly linked to the regulation of senescence in P. hybrida. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01243-y.

Genome-wide and comparative phylogenetic analysis of senescence-associated NAC transcription factors in sunflower (Helianthus annuus).

BACKGROUND: Leaf senescence delay impacts positively in grain yield by maintaining the photosynthetic area during the reproductive stage and during grain filling. Therefore a comprehensive understanding of the gene families associated with leaf senescence is essential. NAC transcription factors (TF) form a large plant-specific gene family involved in regulating development, senescence, and responses to biotic and abiotic stresses. The main goal of this work was to identify sunflower NAC TF (HaNAC) and their association with senescence, studying their orthologous to understand possible functional relationships between genes of different species. RESULTS: To clarify the orthologous relationships, we used an in-depth comparative study of four divergent taxa, in dicots and monocots, with completely sequenced genomes (Arabidopsis thaliana, Vitis vinifera, Musa acuminata and Oryza sativa). These orthologous groups provide a curated resource for large scale protein sequence annotation of NAC TF. From the 151 HaNAC genes detected in the latest version of the sunflower genome, 50 genes were associated with senescence traits. These genes showed significant differential expression in two contrasting lines according to an RNAseq assay. An assessment of overexpressing the Arabidopsis line for HaNAC001 (a gene of the same orthologous group of Arabidopsis thaliana ORE1) revealed that this line displayed a significantly higher number of senescent leaves and a pronounced change in development rate. CONCLUSIONS: This finding suggests HaNAC001 as an interesting candidate to explore the molecular regulation of senescence in sunflower.

Senescence-Associated Glycine max (Gm)NAC Genes: Integration of Natural and Stress-Induced Leaf Senescence.

Leaf senescence is a genetically regulated developmental process that can be triggered by a variety of internal and external signals, including hormones and environmental stimuli. Among the senescence-associated genes controlling leaf senescence, the transcriptional factors (TFs) comprise a functional class that is highly active at the onset and during the progression of leaf senescence. The plant-specific NAC (NAM, ATAF, and CUC) TFs are essential for controlling leaf senescence. Several members of Arabidopsis AtNAC-SAGs are well characterized as players in elucidated regulatory networks. However, only a few soybean members of this class display well-known functions; knowledge about their regulatory circuits is still rudimentary. Here, we describe the expression profile of soybean GmNAC-SAGs upregulated by natural senescence and their functional correlation with putative AtNAC-SAGs orthologs. The mechanisms and the regulatory gene networks underlying GmNAC081- and GmNAC030-positive regulation in leaf senescence are discussed. Furthermore, new insights into the role of GmNAC065 as a negative senescence regulator are presented, demonstrating extraordinary functional conservation with the Arabidopsis counterpart. Finally, we describe a regulatory circuit which integrates a stress-induced cell death program with developmental leaf senescence via the NRP-NAC-VPE signaling module.

The ATXN2 Orthologs CID3 and CID4, Act Redundantly to In-Fluence Developmental Pathways throughout the Life Cycle of Arabidopsis thaliana.

RNA-binding proteins (RBPs) are key elements involved in post-transcriptional regulation. Ataxin-2 (ATXN2) is an evolutionarily conserved RBP protein, whose function has been studied in several model organisms, from Saccharomyces cerevisiae to the Homo sapiens. ATXN2 interacts with poly(A) binding proteins (PABP) and binds to specific sequences at the 3'UTR of target mRNAs to stabilize them. CTC-Interacting Domain3 (CID3) and CID4 are two ATXN2 orthologs present in plant genomes whose function is unknown. In the present study, phenotypical and transcriptome profiling were used to examine the role of CID3 and CID4 in Arabidopsis thaliana. We found that they act redundantly to influence pathways throughout the life cycle. cid3cid4 double mutant showed a delay in flowering time and a reduced rosette size. Transcriptome profiling revealed that key factors that promote floral transition and floral meristem identity were downregulated in cid3cid4 whereas the flowering repressor FLOWERING LOCUS C (FLC) was upregulated. Expression of key factors in the photoperiodic regulation of flowering and circadian clock pathways, were also altered in cid3cid4, as well as the expression of several transcription factors and miRNAs encoding genes involved in leaf growth dynamics. These findings reveal that ATXN2 orthologs may have a role in developmental pathways throughout the life cycle of plants.

GmNAC81 Inversely Modulates Leaf Senescence and Drought Tolerance.

Glycine max NAC81 (GmNAC81) is a downstream effector of the DCD/NRP-mediated cell death signaling, which interacts with GmNAC30 to fully induce the caspase 1-like vacuolar processing enzyme (VPE) expression, the executioner of the cell death program. GmNAC81 has been previously shown to positively modulate leaf senescence via the NRP/GmNAC81/VPE signaling module. Here, we examined the transcriptome induced by GmNAC81 overexpression and leaf senescence and showed that GmNAC81 further modulates leaf senescence by regulating an extensive repertoire of functionally characterized senescence-associated genes (SAGs). Because the NRP/GmNAC81/VPE signaling circuit also relays stress-induced cell death signals, we examined the effect of GmNAC81 overexpression in drought responses. Enhanced GmNAC81 expression in the transgenic lines increased sensitivity to water deprivation. Under progressive drought, the GmNAC81-overexpressing lines displayed severe leaf wilting, a larger and faster decline in leaf Ψw, relative water content (RWC), photosynthesis rate, stomatal conductance, and transpiration rate, in addition to higher Ci/Ca and lower Fm/Fv ratios compared to the BR16 control line. Collectively, these results indicate that the photosynthetic activity and apparatus were more affected by drought in the transgenic lines. Consistent with hypersensitivity to drought, chlorophyll loss, and lipid peroxidation were higher in the GmNAC81-overexpressing lines than in BR16 under dehydration. In addition to inducing VPE expression, GmNAC81 overexpression uncovered the regulation of typical drought-responsive genes. In particular, key regulators and effectors of ABA signaling were suppressed by GmNAC81 overexpression. These results suggest that GmNAC81 may negatively control drought tolerance not only via VPE activation but also via suppression of ABA signaling.

Transcription Factors Associated with Leaf Senescence in Crops.

Leaf senescence is a complex mechanism controlled by multiple genetic and environmental variables. Different crops present a delay in leaf senescence with an important impact on grain yield trough the maintenance of the photosynthetic leaf area during the reproductive stage. Additionally, because of the temporal gap between the onset and phenotypic detection of the senescence process, candidate genes are key tools to enable the early detection of this process. In this sense and given the importance of some transcription factors as hub genes in senescence pathways, we present a comprehensive review on senescence-associated transcription factors, in model plant species and in agronomic relevant crops. This review will contribute to the knowledge of leaf senescence process in crops, thus providing a valuable tool to assist molecular crop breeding.

Exploring gene networks in two sunflower lines with contrasting leaf senescence phenotype using a system biology approach.

BACKGROUND: Leaf senescence is a complex process, controlled by multiple genetic and environmental variables. In sunflower, leaf senescence is triggered abruptly following anthesis thereby limiting the capacity of plants to keep their green leaf area during grain filling, which subsequently has a strong impact on crop yield. Recently, we performed a selection of contrasting sunflower inbred lines for the progress of leaf senescence through a physiological, cytological and molecular approach. Here we present a large scale transcriptomic analysis using RNA-seq and its integration with metabolic profiles for two contrasting sunflower inbred lines, R453 and B481-6 (early and delayed senescence respectively), with the aim of identifying metabolic pathways associated to leaf senescence. RESULTS: Gene expression profiles revealed a higher number of differentially expressed genes, as well as, higher expression levels in R453, providing evidence for early activation of the senescence program in this line. Metabolic pathways associated with sugars and nutrient recycling were differentially regulated between the lines. Additionally, we identified transcription factors acting as hubs in the co-expression networks; some previously reported as senescence-associated genes in model species but many are novel candidate genes. CONCLUSIONS: Understanding the onset and the progress of the senescence process in crops and the identification of these new candidate genes will likely prove highly useful for different management strategies to mitigate the impact of senescence on crop yield. Functional characterization of candidate genes will help to develop molecular tools for biotechnological applications in breeding crop yield.

Identification and expression analysis of NAC transcription factors potentially involved in leaf and petal senescence in Petunia hybrida.

Progression of leaf senescence depends on several families of transcription factors. In Arabidopsis, the NAC family plays crucial roles in the modulation of leaf senescence; however, the mechanisms involved in this NAC-mediated regulation have not been extensively explored in agronomic species. Petunia hybrida is an ornamental plant that is commonly found worldwide. Decreasing the rate of leaf and petal senescence in P. hybrida is essential for maintaining plant quality. In this study, we examined the NAC-mediated networks involved in regulating senescence in this species. From 41 NAC genes, the expression of which changed in Arabidopsis during leaf senescence, we identified 29 putative orthologs in P. hybrida. Analysis using quantitative real-time-PCR indicated that 24 genes in P. hybrida changed their transcript levels during natural leaf senescence. Leaf-expressed genes were subsequently assessed in petals undergoing natural and pollination-induced senescence. Expression data and phylogenetic analysis were used to generate a list of 10-15 candidate genes; 7 of these were considered key regulatory candidates in senescence because of their consistent upregulation in the three senescence processes examined. Altogether, we identified common and distinct patterns of gene expression at different stages of leaf and petal development and during progression of senescence. The results obtained in this study will contribute to the understanding of NAC-mediated regulatory networks in petunia.

Chloroplast Protein Degradation in Senescing Leaves: Proteases and Lytic Compartments.

Leaf senescence is characterized by massive degradation of chloroplast proteins, yet the protease(s) involved is(are) not completely known. Increased expression and/or activities of serine, cysteine, aspartic, and metalloproteases were detected in senescing leaves, but these studies have not provided information on the identities of the proteases responsible for chloroplast protein breakdown. Silencing some senescence-associated proteases has delayed progression of senescence symptoms, yet it is still unclear if these proteases are directly involved in chloroplast protein breakdown. At least four cellular pathways involved in the traffic of chloroplast proteins for degradation outside the chloroplast have been described (i.e., "Rubisco-containing bodies," "senescence-associated vacuoles," "ATI1-plastid associated bodies," and "CV-containing vesicles"), which differ in their dependence on the autophagic machinery, and the identity of the proteins transported and/or degraded. Finding out the proteases involved in, for example, the degradation of Rubisco, may require piling up mutations in several senescence-associated proteases. Alternatively, targeting a proteinaceous protein inhibitor to chloroplasts may allow the inhibitor to reach "Rubisco-containing bodies," "senescence-associated vacuoles," "ATI1-plastid associated bodies," and "CV-containing vesicles" in essentially the way as chloroplast-targeted fluorescent proteins re-localize to these vesicular structures. This might help to reduce proteolytic activity, thereby reducing or slowing down plastid protein degradation during senescence.

Papain-like cysteine protease encoding genes in rubber (Hevea brasiliensis): comparative genomics, phylogenetic, and transcriptional profiling analysis.

MAIN CONCLUSION: 43 HbPLCPs representing nine subfamilies or 20 orthologous groups were found in rubber, where paralogs were resulted from the recent WGD and local duplication. Several senescence-associated genes were also identified. Papain-like cysteine proteases (PLCPs) comprise a large family of proteolytic enzymes involved in plant growth and development, seed germination, organ senescence, immunity, and stress response. Despite their importance and the extensive research in the model plant Arabidopsis thaliana, little information is available on rubber tree (Hevea brasiliensis), a rubber-producing plant of the Euphorbiaceae family. This study performed a genome-wide identification of PLCP family genes in rubber, resulting in a relatively high number of 43 members. The phylogenetic analysis assigned these genes into nine subfamilies, i.e., RD21 (6), CEP (4), XCP (4), XBCP3 (2), THI (1), SAG12 (18), RD19 (4), ALP (2), and CTB (2). Most of them were shown to have orthologs in Arabidopsis; however, several members in SAG12, CEP and XBCP3 subfamilies form new groups as observed in other core eudicots such as Manihot esculenta, Ricinus communis, Populus trichocarpa, and Vitis vinifera. Based on an expert sequence comparison, 20 orthologous groups (OGs) were proposed for core eudicots, and rubber paralogs were shown to be resulted from the recent whole-genome duplication (WGD) as well as local duplication. Transcriptional profiling showed distinct expression pattern of different members across various tissues, e.g., root, leaf, bark, laticifer, flower, and seed. By using the senescence-specific HbSAG12H1 as the indicator, the transcriptome of senescent rubber leaves was deeply sequenced and several senescence-associated PLCP genes were identified. Results obtained from this study provide valuable information for future functional analysis and utilization of PLCP genes in Hevea and other species.

Identification and characterization of contrasting sunflower genotypes to early leaf senescence process combining molecular and physiological studies (Helianthus annuus L.).

Leaf senescence is a complex mechanism ruled by multiple genetic and environmental variables that affect crop yields. It is the last stage in leaf development, is characterized by an active decline in photosynthetic rate, nutrients recycling and cell death. The aim of this work was to identify contrasting sunflower inbred lines differing in leaf senescence and to deepen the study of this process in sunflower. Ten sunflower genotypes, previously selected by physiological analysis from 150 inbred genotypes, were evaluated under field conditions through physiological, cytological and molecular analysis. The physiological measurement allowed the identification of two contrasting senescence inbred lines, R453 and B481-6, with an increase in yield in the senescence delayed genotype. These findings were confirmed by cytological and molecular analysis using TUNEL, genomic DNA gel electrophoresis, flow sorting and gene expression analysis by qPCR. These results allowed the selection of the two most promising contrasting genotypes, which enables future studies and the identification of new biomarkers associated to early senescence in sunflower. In addition, they allowed the tuning of cytological techniques for a non-model species and its integration with molecular variables.

Network and biosignature analysis for the integration of transcriptomic and metabolomic data to characterize leaf senescence process in sunflower.

BACKGROUND: In recent years, high throughput technologies have led to an increase of datasets from omics disciplines allowing the understanding of the complex regulatory networks associated with biological processes. Leaf senescence is a complex mechanism controlled by multiple genetic and environmental variables, which has a strong impact on crop yield. Transcription factors (TFs) are key proteins in the regulation of gene expression, regulating different signaling pathways; their function is crucial for triggering and/or regulating different aspects of the leaf senescence process. The study of TF interactions and their integration with metabolic profiles under different developmental conditions, especially for a non-model organism such as sunflower, will open new insights into the details of gene regulation of leaf senescence. RESULTS: Weighted Gene Correlation Network Analysis (WGCNA) and BioSignature Discoverer (BioSD, Gnosis Data Analysis, Heraklion, Greece) were used to integrate transcriptomic and metabolomic data. WGCNA allowed the detection of 10 metabolites and 13 TFs whereas BioSD allowed the detection of 1 metabolite and 6 TFs as potential biomarkers. The comparative analysis demonstrated that three transcription factors were detected through both methodologies, highlighting them as potentially robust biomarkers associated with leaf senescence in sunflower. CONCLUSIONS: The complementary use of network and BioSignature Discoverer analysis of transcriptomic and metabolomic data provided a useful tool for identifying candidate genes and metabolites which may have a role during the triggering and development of the leaf senescence process. The WGCNA tool allowed us to design and test a hypothetical network in order to infer relationships across selected transcription factor and metabolite candidate biomarkers involved in leaf senescence, whereas BioSignature Discoverer selected transcripts and metabolites which discriminate between different ages of sunflower plants. The methodology presented here would help to elucidate and predict novel networks and potential biomarkers of leaf senescence in sunflower.

The Stress-Induced Soybean NAC Transcription Factor GmNAC81 Plays a Positive Role in Developmentally Programmed Leaf Senescence.

The onset of leaf senescence is a highly regulated developmental change that is controlled by both genetics and the environment. Senescence is triggered by massive transcriptional reprogramming, but functional information about its underlying regulatory mechanisms is limited. In the current investigation, we performed a functional analysis of the soybean (Glycine max) osmotic stress- and endoplasmic reticulum (ER) stress-induced NAC transcription factor GmNAC81 during natural leaf senescence using overexpression studies and reverse genetics. GmNAC81-overexpressing lines displayed accelerated flowering and leaf senescence but otherwise developed normally. The precocious leaf senescence of GmNAC81-overexpressing lines was associated with greater Chl loss, faster photosynthetic decay and higher expression of hydrolytic enzyme-encoding GmNAC81 target genes, including the vacuolar processing enzyme (VPE), an executioner of vacuole-triggered programmed cell death (PCD). Conversely, virus-induced gene silencing-mediated silencing of GmNAC81 delayed leaf senescence and was associated with reductions in Chl loss, lipid peroxidation and the expression of GmNAC81 direct targets. Promoter-reporter studies revealed that the expression pattern of GmNAC81 was associated with senescence in soybean leaves. Our data indicate that GmNAC81 is a positive regulator of age-dependent senescence and may integrate osmotic stress- and ER stress-induced PCD responses with natural leaf senescence through the GmNAC81/VPE regulatory circuit.

Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production / Relação entre as características morfogênicas do azevém anual cv. 'BRS Ponteio' com a produção de forragem e de sementes

This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.

O presente estudo teve o objetivo de verificar, de forma precisa e detalhada, as respostas da cultivar de azevém anual 'BRS Ponteio', às diferentes frequências de desfolha para a produção de forragem e de sementes. Realizou-se, para tanto, um experimento com delineamento de blocos casualizados com quatro repetições. Foram aplicadas quatro frequências de desfolhas (sem, uma, duas e três) baseando-se no acúmulo térmico, onde se avaliou a taxa de aparecimento de folhas (TApF), o filocrono (F), a taxa de expansão de folhas (TEF), taxa de senescência de folhas (TScF), taxa de expansão dos colmos (TEC), taxa de perfilhamento (TP), duração de vida da folha (DVF), produção de forragem, proporção de lâminas foliares, colmos mais bainhas, material senescente e inflorescências em cada tratamento, bem como a produção de sementes. A segunda desfolha alterou marcadamente as respostas morfogênicas da planta, reduziu as taxas de expansão e aparecimento de folhas e aumentou as taxas de perfilhamento e de expansão do colmo. Esta plasticidade fenotípica manteve a alta produção de sementes da planta e propiciou a colheita de massa de forragem 100% superior à massa colhida no primeiro corte. A terceira desfolha propiciou o aumento de 100% da massa de forragem colhida, todavia, promoveu alterações drásticas e negativas nas características morfogênicas e no rendimento de sementes.

Integrating transcriptomic and metabolomic analysis to understand natural leaf senescence in sunflower.

Leaf senescence is a complex process, which has dramatic consequences on crop yield. In sunflower, gap between potential and actual yields reveals the economic impact of senescence. Indeed, sunflower plants are incapable of maintaining their green leaf area over sustained periods. This study characterizes the leaf senescence process in sunflower through a systems biology approach integrating transcriptomic and metabolomic analyses: plants being grown under both glasshouse and field conditions. Our results revealed a correspondence between profile changes detected at the molecular, biochemical and physiological level throughout the progression of leaf senescence measured at different plant developmental stages. Early metabolic changes were detected prior to anthesis and before the onset of the first senescence symptoms, with more pronounced changes observed when physiological and molecular variables were assessed under field conditions. During leaf development, photosynthetic activity and cell growth processes decreased, whereas sucrose, fatty acid, nucleotide and amino acid metabolisms increased. Pathways related to nutrient recycling processes were also up-regulated. Members of the NAC, AP2-EREBP, HB, bZIP and MYB transcription factor families showed high expression levels, and their expression level was highly correlated, suggesting their involvement in sunflower senescence. The results of this study thus contribute to the elucidation of the molecular mechanisms involved in the onset and progression of leaf senescence in sunflower leaves as well as to the identification of candidate genes involved in this process.

Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production

This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.

O presente estudo teve o objetivo de verificar, de forma precisa e detalhada, as respostas da cultivar de azevém anual 'BRS Ponteio', às diferentes frequências de desfolha para a produção de forragem e de sementes. Realizou-se, para tanto, um experimento com delineamento de blocos casualizados com quatro repetições. Foram aplicadas quatro frequências de desfolhas (sem, uma, duas e três) baseando-se no acúmulo térmico, onde se avaliou a taxa de aparecimento de folhas (TApF), o filocrono (F), a taxa de expansão de folhas (TEF), taxa de senescência de folhas (TScF), taxa de expansão dos colmos (TEC), taxa de perfilhamento (TP), duração de vida da folha (DVF), produção de forragem, proporção de lâminas foliares, colmos mais bainhas, material senescente e inflorescências em cada tratamento, bem como a produção de sementes. A segunda desfolha alterou marcadamente as respostas morfogênicas da planta, reduziu as taxas de expansão e aparecimento de folhas e aumentou as taxas de perfilhamento e de expansão do colmo. Esta plasticidade fenotípica manteve a alta produção de sementes da planta e propiciou a colheita de massa de forragem 100% superior à massa colhida no primeiro corte. A terceira desfolha propiciou o aumento de 100% da massa de forragem colhida, todavia, promoveu alterações drásticas e negativas nas características morfogênicas e no rendimento de sementes.

Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production

This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.

O presente estudo teve o objetivo de verificar, de forma precisa e detalhada, as respostas da cultivar de azevém anual 'BRS Ponteio', às diferentes frequências de desfolha para a produção de forragem e de sementes. Realizou-se, para tanto, um experimento com delineamento de blocos casualizados com quatro repetições. Foram aplicadas quatro frequências de desfolhas (sem, uma, duas e três) baseando-se no acúmulo térmico, onde se avaliou a taxa de aparecimento de folhas (TApF), o filocrono (F), a taxa de expansão de folhas (TEF), taxa de senescência de folhas (TScF), taxa de expansão dos colmos (TEC), taxa de perfilhamento (TP), duração de vida da folha (DVF), produção de forragem, proporção de lâminas foliares, colmos mais bainhas, material senescente e inflorescências em cada tratamento, bem como a produção de sementes. A segunda desfolha alterou marcadamente as respostas morfogênicas da planta, reduziu as taxas de expansão e aparecimento de folhas e aumentou as taxas de perfilhamento e de expansão do colmo. Esta plasticidade fenotípica manteve a alta produção de sementes da planta e propiciou a colheita de massa de forragem 100% superior à massa colhida no primeiro corte. A terceira desfolha propiciou o aumento de 100% da massa de forragem colhida, todavia, promoveu alterações drásticas e negativas nas características morfogênicas e no rendimento de sementes.

Relationship between the morphogenesis of Italian ryegrass cv. "BRS Ponteio" with forage and seed production / 10.1590/0103-8478cr20150296 / Relação entre as características morfogênicas do azevém anual cv. "BRS Ponteio" com a produção de forragem e de sementes

This study aims to verify, accurate and precisely, the responses of Italian ryegrass "BRS Ponteio" cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.(AU)

O presente estudo teve o objetivo de verificar, de forma precisa e detalhada, as respostas da cultivar de azevém anual "BRS Ponteio", às diferentes frequências de desfolha para a produção de forragem e de sementes. Realizou-se, para tanto, um experimento com delineamento de blocos casualizados com quatro repetições. Foram aplicadas quatro frequências de desfolhas (sem, uma, duas e três) baseando-se no acúmulo térmico, onde se avaliou a taxa de aparecimento de folhas (TApF), o filocrono (F), a taxa de expansão de folhas (TEF), taxa de senescência de folhas (TScF), taxa de expansão dos colmos (TEC), taxa de perfilhamento (TP), duração de vida da folha (DVF), produção de forragem, proporção de lâminas foliares, colmos mais bainhas, material senescente e inflorescências em cada tratamento, bem como a produção de sementes. A segunda desfolha alterou marcadamente as respostas morfogênicas da planta, reduziu as taxas de expansão e aparecimento de folhas e aumentou as taxas de perfilhamento e de expansão do colmo. Esta plasticidade fenotípica manteve a alta produção de sementes da planta e propiciou a colheita de massa de forragem 100% superior à massa colhida no primeiro corte. A terceira desfolha propiciou o aumento de 100% da massa de forragem colhida, todavia, promoveu alterações drásticas e negativas nas características morfogênicas e no rendimento de sementes.(AU)

Características morfogênicas, estruturais e padrões demográficos de perfilhos em pastagem de capim-andropógon sob diferentes ofertas de forragem / Morphogenetic characteristics and demographic patterns of tillers on andropogon grass under different forage allowances

Objetivou-se avaliar as características morfogênicas, estruturais e os padrões demográficos de perfilhamento do capim Andropogon gayanus Kunth var. Bisquamulatus (Hochst) Hack. cv. Planaltina, submetido a três ofertas de forragem: 11, 15 e 19% do PV, sob lotação contínua de caprinos. O delineamento experimental para avaliação das características morfogênicas do pasto foi o de blocos ao acaso (dois), com seis repetições (touceiras) dentro do bloco. Para a avaliação da dinâmica de perfilhamento e densidade populacional adotou-se o delineamento experimental em blocos ao acaso (dois), em esquema de parcelas subdivididas. Nas parcelas, avaliou-se o efeito das ofertas de forragem e, nas subparcelas, os meses: abril, maio e junho. As ofertas de forragem não influenciaram as taxas de alongamento foliar, de senescência foliar e o número de folhas vivas. A taxa de aparecimento de folhas foi maior nas ofertas de 11 e 15% PV. O manejo do pasto com oferta de forragem 19% do PV proporciona aumento na taxa de alongamento do colmo, na duração de vida das folhas e no comprimento das folhas e colmos. O número de perfilhos vegetativos e as taxas de aparecimento e sobrevivência de perfilhos não são influenciados pela oferta de forragem de 11 a 19% do PV.(AU)

The objective of this study was to evaluate the morphogenetic and structural characteristics and the demographic patterns of tillering in the grass Andropogon gayanus Kunth var. Bisquamulatus (Hochst) Hack. cv. Planaltina subjected to three forage allowances: 11, 15 and 19% of the LW, under continuous grazing by goats. The experimental design for the evaluation of the pasture morphogenetic characteristics was set in (two) random blocks, with six replications (tussocks) within the block. To evaluate the tillering dynamics and population density, we adopted the experimental design of (two) random blocks, in a split-plot arrangement. In the plots, we evaluated the effect of forage allowances and in the subplots, the months of April, May and June. Forage allowances did not affect the leaf elongation rate, leaf senescence or the number of live leaves. The leaf appearance rate was highest at the masses of 11 and 15% of the LW. Managing the pasture with a forage allowance of 19% of the LW increases the stem elongation rate, leaf lifespan and the lengths of leaf and stem. The number of vegetative tillers and the tiller appearance and survival rates are not affected by the forage allowances from 11 to 19% of the LW.(AU)

Características morfogênicas, estruturais e padrões demográficos de perfilhos em pastagem de capim-andropógon sob diferentes ofertas de forragem / Morphogenetic characteristics and demographic patterns of tillers on andropogon grass under different forage allowances

Objetivou-se avaliar as características morfogênicas, estruturais e os padrões demográficos de perfilhamento do capim Andropogon gayanus Kunth var. Bisquamulatus (Hochst) Hack. cv. Planaltina, submetido a três ofertas de forragem: 11, 15 e 19% do PV, sob lotação contínua de caprinos. O delineamento experimental para avaliação das características morfogênicas do pasto foi o de blocos ao acaso (dois), com seis repetições (touceiras) dentro do bloco. Para a avaliação da dinâmica de perfilhamento e densidade populacional adotou-se o delineamento experimental em blocos ao acaso (dois), em esquema de parcelas subdivididas. Nas parcelas, avaliou-se o efeito das ofertas de forragem e, nas subparcelas, os meses: abril, maio e junho. As ofertas de forragem não influenciaram as taxas de alongamento foliar, de senescência foliar e o número de folhas vivas. A taxa de aparecimento de folhas foi maior nas ofertas de 11 e 15% PV. O manejo do pasto com oferta de forragem 19% do PV proporciona aumento na taxa de alongamento do colmo, na duração de vida das folhas e no comprimento das folhas e colmos. O número de perfilhos vegetativos e as taxas de aparecimento e sobrevivência de perfilhos não são influenciados pela oferta de forragem de 11 a 19% do PV.

The objective of this study was to evaluate the morphogenetic and structural characteristics and the demographic patterns of tillering in the grass Andropogon gayanus Kunth var. Bisquamulatus (Hochst) Hack. cv. Planaltina subjected to three forage allowances: 11, 15 and 19% of the LW, under continuous grazing by goats. The experimental design for the evaluation of the pasture morphogenetic characteristics was set in (two) random blocks, with six replications (tussocks) within the block. To evaluate the tillering dynamics and population density, we adopted the experimental design of (two) random blocks, in a split-plot arrangement. In the plots, we evaluated the effect of forage allowances and in the subplots, the months of April, May and June. Forage allowances did not affect the leaf elongation rate, leaf senescence or the number of live leaves. The leaf appearance rate was highest at the masses of 11 and 15% of the LW. Managing the pasture with a forage allowance of 19% of the LW increases the stem elongation rate, leaf lifespan and the lengths of leaf and stem. The number of vegetative tillers and the tiller appearance and survival rates are not affected by the forage allowances from 11 to 19% of the LW.