Screening some pine species from North America and dried zones of western Asia for drought stress tolerance in terms of nutrients status, biochemical and physiological characteristics.

Drought due to climate change or reduced precipitation is one of the main factors limiting the growth and establishment of plants and is one of the most critical challenges facing humans. To investigate the effect of different levels of drought stress on some pine species, this research was carried out as a factorial experiment using two factors and a completely randomized design. It included five populations of four pine species (Pinus brutia Ten. var. eldarica, P. nigra Arnold, P. mugo, and P. banksiana Lamb (including populations 8310055 and 8960049), and three levels of irrigation (100%, 75%, or 50% FC, denoted as normal, mild or intense drought stress, respectively) with three replicates. The findings showed that, photosynthetic pigments, relative water content, visual quality, the content of nutrients, protein content, and fresh and dry weight all decreased significantly when plants were exposed to intense drought stress. However, raised proline levels, electrolyte leakage percentage, soluble sugars levels, and antioxidant enzyme activity. We detected a decline in most growth traits when comparing mild drought stress conditions to normal irrigation, yet acceptable quality seedlings when compared to intense drought stress. Intense drought stress had a substantial impact on many pine seedlings. PCA results showed that among different pine species, the level of resistance to drought is as follows: P. mugo> P. brutia var. eldarica> P. nigra> P. banksiana 8310055> P. banksiana 8960049. Our novel finding was that, P. mugo is a resistant species in arid and semi-arid regions, and P. banksiana species, especially its population of 8960049, is sensitive.

Salt stress triggers augmented levels of Na+, K+ and ROS alters salt-related gene expression in leaves and roots of tall wheatgrass (Agropyron elongatum).

In turfgrass breeding, competent grass ecotypes are preferably identified for their resistance to salinity condition. This research was designed to explore genes that induce salt resistance (NHX1, NHX2, HKT1;4, SnRK2.4 and NAC9) and their role in physiological modifications of six tall wheatgrass ecotypes (Agropyron elongatum L.). The sites of sample collection were characterized by different levels of salinity, i.e. low (EC: 4 dS m-1 and pH: 6.5), moderate (EC: 7 dS m-1 and pH: 6.5) and high (EC: 12 dS m-1 and pH: 7.5). This study was designed as a split-plot in a randomized complete block where salinity treatments served as the whole-plot factor and ecotypes served as the subplot factor. The ecotypes were screened for their resistance to salinity, based on visual symptoms, salt injury index, physiological features and biochemical parameters. The results revealed that ecotype 'AE5' was most resistant to salinity than other ecotypes, whereas 'AE3' was the most susceptible. To understand why these differences occurred, measurements were aimed at revealing mRNA levels that resulted from genes responsible for salt resistance. Our results demonstrated that salinity-resistant ecotypes showed high expression levels of several genes, i.e. NHX1, NHX2, HKT1;4, SnRK2.4 and NAC9 in the leaves and roots. These results were corroborated by a decrease (by 1.5-2.5 times) in stress markers, namely, superoxide anion (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA), as well as an increase (by 0.5-7 times) in enzymatic and non-enzymatic antioxidant activity in salinity-resistant ecotypes when the plants were exposed to salinity. We observed higher values of initial root length and lateral root density (21% and 18%, respectively) in salinity-resistant ecotypes under salinity condition, compared to other ecotypes. There were lower expression levels of NHX1 and NHX2 in the roots, which were 3.2 and 2.1 times less, respectively, compared to the leaves. This implied that NHX1 and NHX2 expressions can lead to the sequestration of Na+ in the leaves during salinity condition. The current research revealed that HKT1;4 was more able to restrict Na + accumulation, compared to the actions of NHX1 and NHX2 genes. The over-expression of HKT1;4 in 'AE5' allowed a better maintenance of root growth during salinity condition. The expression of NAC9 had an increase of 2.1-fold which correlated with an increase in the amount of antioxidant enzymes. In general, the location of sample collection explained the differences in gene expression, especially regarding the extent to which plants respond to salinity condition. Ultimately, these differences can define physiological features in salinity-resistant and salinity-susceptible ecotypes of tall wheatgrass.

Global identification of long non-coding RNAs involved in the induction of spinach flowering.

BACKGROUND: Spinach is a beneficial annual vegetable species and sensitive to the bolting or early flowering, which causes a large reduction in quality and productivity. Indeed, bolting is an event induced by the coordinated effects of various environmental factors and endogenous genetic components. Although some key flowering responsive genes have been identified in spinach, non-coding RNA molecules like long non-coding RNAs (lncRNAs) were not investigated yet. Herein, we used bioinformatic approaches to analyze the transcriptome datasets from two different accessions Viroflay and Kashan at two vegetative and reproductive stages to reveal novel lncRNAs and the construction of the lncRNA-mRNA co-expression network. Additionally, correlations among gene expression modules and phenotypic traits were investigated; day to flowering was chosen as our interesting trait. RESULTS: In the present study, we identified a total of 1141 lncRNAs, of which 111 were differentially expressed between vegetative and reproductive stages. The GO and KEGG analyses carried out on the cis target gene of lncRNAs showed that the lncRNAs play an important role in the regulation of flowering spinach. Network analysis pinpointed several well-known flowering-related genes such as ELF, COL1, FLT, and FPF1 and also some putative TFs like MYB, WRKY, GATA, and MADS-box that are important regulators of flowering in spinach and could be potential targets for lncRNAs. CONCLUSIONS: This study is the first report on identifying bolting and flowering-related lncRNAs based on transcriptome sequencing in spinach, which provides a useful resource for future functional genomics studies, genes expression researches, evaluating genes regulatory networks and molecular breeding programs in the regulation of the genetic mechanisms related to bolting in spinach.

Transcriptome architecture reveals genetic networks of bolting regulation in spinach.

BACKGROUND: Bolting refers to the early flowering stem production on agricultural and horticultural crops before harvesting. Indeed, bolting is an event induced by the coordinated effects of various environmental factors and endogenous genetic components, which cause a large reduction in the quality and productivity of vegetable crops like spinach. However, little is known about the signaling pathways and molecular functions involved in bolting mechanisms in spinach. The genetic information regarding the transition from vegetative growth to the reproductive stage in spinach would represent an advantage to regulate bolting time and improvement of resistant cultivars to minimize performance loss. RESULTS: To investigate the key genes and their genetic networks controlling spinach bolting, we performed RNA-seq analysis on early bolting accession Kashan and late-bolting accession Viroflay at both vegetative and reproductive stages and found a significant number of differentially expressed genes (DEGs) ranging from 195 to 1230 in different comparisons. These genes were mainly associated with the signaling pathways of vernalization, photoperiod/circadian clock, gibberellin, autonomous, and aging pathways. Gene ontology analysis uncovered terms associated with carbohydrate metabolism, and detailed analysis of expression patterns for genes of Fructose-1, 6-bisphosphate aldolase, TREHALOSE-6-PHOSPHATE SYNTHASE 1, FLOWERING PROMOTING FACTOR 1, EARLY FLOWERING, GIGANTEA, and MADS-box proteins revealed their potential roles in the initiating or delaying of bolting. CONCLUSION: This study is the first report on identifying bolting and flowering-related genes based on transcriptome sequencing in spinach, which provides insight into bolting control and can be useful for molecular breeding programs and further study in the regulation of the genetic mechanisms related to bolting in other vegetable crops.

Gamma radiation negatively impacted seed germination, seedling growth and antioxidant enzymes activities in tall fescue infected with Epichloë endophyte.

Plants and their accompanying microorganisms growing in contaminated sites with long-lived gamma-emitting radionuclides may be affected by radiation stress. The present study aimed to investigate the effects of gamma radiation on symbiotic relationship between Epichloë endophyte and Festuca arundinacea plant along with the radio-sensitivity of a pair of clones of tall fescue with (E+) and without (E-) symbiotic Epichloë endophyte exposed to different doses of gamma radiation including 25, 50, 75, 100, 150, 200, 300, and 400 Gray (Gy) from a Cobalt-60 source. Both irradiated and non-irradiated seeds of each status were grown under controlled conditions. Seed germination indices, seedling growth and certain physiological criteria associated with plant responses to oxidative stress were examined. The results revealed that low doses (up to 75 Gy) of gamma radiation stimulated seed germination indices and seedling growth. However, high doses (100-400 Gy) significantly reduced the final germination percentage, germination rate index, coefficient of velocity of germination, and the seed reserve depletion percentage, and enhanced the mean germination time. Further, high doses of radiation reduced root and shoot lengths, root and shoot fresh weights, and activities of antioxidant enzymes (especially catalase and superoxide dismutase), and increased the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) of the seedlings. The results showed that the endophyte was present in seeds after gamma ray irradiation. However, the presence of endophyte in seedlings started to be reduced significantly (18.45% reduction rather than the control) at 50 Gy of gamma radiation. High doses (100 Gy and above) dramatically declined the presence of endophyte down to zero in seedlings compared to the control. In this study, the E- clone had higher seed germination and seedling growth as well as lower H2O2 and MDA contents under radiation stress as compared with the E+ clone. Additionally, shoot tolerance index (STI) indicated more radiation tolerance in the E- clone. According to the results of the present study, it is concluded that biological impacts of gamma radiation stress and the harmful effects on endophyte viability may cause more radio-sensitivity and changes in the growth and physio-biochemical aspects of the host plant.

Physiological consequences of gamma ray irradiation in tall fescue with elimination potential of Epichloë fungal endophyte.

Perennial plants and their associated microorganisms grow in the areas that may be contaminated with long-lived gamma-emitting radionuclides. This will induce gamma stress response in plants and their accompanying microorganisms. The present work investigated the growth and physiological responses of Epichloe endophyte infected tall fescue to gamma radiation, as well as whether the endophyte could persist and infect the host plant once exposed to gamma radiation. Seeds of Iranian native genotype of 75B+ of tall fescue were exposed to different doses, including 5.0, 10.0, 15.0, 20.0, 30.0 and 40.0 krad of gamma ray from a 60Co source. Irradiated and unirradiated seeds were sown in pots and grown under controlled conditions in the greenhouse. The growth and physiological parameters associated with plant tolerance to oxidative stress of host plants, as well as endophytic infection frequency (% of plants infected) and intensity (mean number of endophytic hyphae per the field of view), were examined in 3 months-old seedlings. The results indicated that all gamma radiation doses (except 5.0 kr) significantly reduced the height and survival percentage of the host plant. Days to the emergence of seedling increased gradually as gamma doses rose. A dose-rate dependent induction was seen for photosynthetic pigments and proline content. Malondialdehyde (MDA) content grew with elevation of irradiation doses. Depending on the dose and time, the activities of antioxidant enzymes in the host plant responded differently to gamma radiation. Gamma radiation altered the enzyme activities with sever decline in SOD and CAT activities. However, it had barely any effect on in APX and POD activities. The results also revealed that the persistence and intensity of endophyte were affected after gamma-ray irradiation. The initial percentage of tall fescue seeds infected with the endophyte was 91% in un-irradiated seeds. Presence of the viable endophyte started to decline significantly (23%) at 5.0 kr of gamma radiation. A dramatic reduction in the presence and intensity of endophyte occurred at 10.0 to 40.0 kr intensities. Gamma radiation × trait (GT)-biplot analysis indicated positive correlations between the endophyte symbiosis and antioxidant enzyme activities. Also, negative correlations were observed between the endophyte and MDA content in the host plant. Our results suggest that radiation stress (doses over 5.0 kr) caused reduction in the growth and antioxidant enzyme activities of the host plant that accompanied by a dramatic reduction in the persistence and intensity of endophyte fungi. Our findings have provided the basic information for future studies on the effect of gamma irradiation on the interaction between endophytic fungi and its host plant.

Co-inoculation of Arizona cypress with arbuscular mycorrhiza fungi and Pseudomonas fluorescens under fuel pollution.

Air pollution in metropolitan areas of Iran has negatively impacted establishment, growth, and development of many woody plant species, threatening the health of urban forest species. This study was designed to investigate the effects of artificial inoculation of seedlings of a major urban forest tree, Arizona cypress (Cupressus arizonica Greene) with beneficial microorganisms under the stress of air pollution caused by exhaust emissions from fuel pollutants (FP). We conducted this research as a completely randomized design in a form of split-factorial with three factors comprising arbuscular mycorrhizal fungi (AMF) inoculation with Rhizophagus irregularis or Funneliformis mosseae or a mixture of both species, bacterial inoculation with Pseudomonas fluorescens and non-inoculated controls, and two levels of FP (fuel pollutants and non-fuel pollutants) using three replications of each treatment. Fuel pollutants significantly reduced root colonization, shoot and root dry weight, nutrient concentrations (N, P, K, and Fe), glomalin-related soil protein (GRSP), and chlorophyll concentration, while increasing proline content, enzyme activity, malondialdehyde (MDA), and hydrogen peroxide (H2O2) concentrations in Arizona cypress seedlings. Nevertheless, adverse effects of FP in the inoculated plants (especially AMF plants) were less than in the non-inoculated plants. Inoculations of AMF especially the mixture of both mycorrhizal species effectively alleviated the negative effects of FP on Arizona cypress seedlings. This promising effect was related to increased GRSP content in the media which improved concentrations of N, P, and Fe in plants, enhanced chlorophyll concentration, and elevated enzymatic antioxidants such as ascorbate peroxidase and glutathione peroxidase which resulted in increased dry mass of the plants under air pollution stress.

Molecular and physiological responses of Iranian Perennial ryegrass as affected by Trinexapac ethyl, Paclobutrazol and Abscisic acid under drought stress.

Drought stress is the major limiting factor which affects turfgrass management in area with restricted rainfall or irrigation water supply. Trinexapac ethyl (TE), Paclobutrazol (PAC) and Abscisic acid (ABA) are three plant growth regulators (PGRs) that are commonly used on turf species for increasing their tolerance to different environmental stresses such as drought. However, little is known about the impact of PGRs on stress tolerance of Iranian Perennial ryegrass (Lolium perenne). The present study was conducted to examine the visual and physiological changes of Iranian Perennial ryegrass in response to foliar application of TE, PAC, and ABA under drought stress conditions. According to the obtained results, application of all three PGRs considerably restored visual quality of drought exposed plants. TE treatment increased chlorophyll content, proline content and resulted in less malondialdehyde (MDA) in drought stressed Perennial ryegrass. Application of all PGRs enhanced the relative water content (RWC) and decreased the electrolyte leakage (EL) and Hydrogen peroxide contents (H2O2 content) of plants under drought stress, though the impact of TE was more pronounced. Throughout the experiment, TE- and ABA-treated plant showed greater soluble sugar (SSC) content as compared to the control. Antioxidant enzymes activities of drought exposed plants were considerably increased by PGRs application. Catalase (CAT) and Superoxide dismutase (SOD) activities were greater in TE-treated grasses followed by PAC-treated plants. Ascorbate peroxidase (APX) and peroxidase (POD) activities were significantly enhanced by TE and ABA application. The results of the present investigation suggest that application of TE, ABA and PAC enhances drought tolerance in Perennial ryegrass. TE, PAC and ABA were all effective in mitigating physiological damages resulting from drought stress, however the beneficial effects of TE were more pronounced. The result obtained of real time-PCR suggested that regulation of CAT, APX, POD and SOD genes expression at translational levels highly depended on the application of TE, PAC and ABA. Also, the results showed that deletion mutation in SOD and POD genes were not leading to enzyme inactivation.

Assessment of genetic diversity of Bermudagrass (Cynodon dactylon) using ISSR markers.

Bermudagrass (Cynodon spp.) is a major turfgrass for home lawns, public parks, golf courses and sport fields and is known to have originated in the Middle East. Morphological and physiological characteristics are not sufficient to differentiate some bermudagrass genotypes because the differences between them are often subtle and subjected to environmental influences. In this study, twenty seven bermudagrass accessions and introductions, mostly from different parts of Iran, were assayed by inter-simple sequence repeat (ISSR) markers to differentiate and explore their genetic relationships. Fourteen ISSR primers amplified 389 fragments of which 313 (80.5%) were polymorphic. The average polymorphism information content (PIC) was 0.328, which shows that the majority of primers are informative. Cluster analysis using the un-weighted paired group method with arithmetic average (UPGMA) method and Jaccard's similarity coefficient (r = 0.828) grouped the accessions into six main clusters according to some degree to geographical origin, their chromosome number and some morphological characteristics. It can be concluded that there exists a wide genetic base of bermudograss in Iran and that ISSR markers are effective in determining genetic diversity and relationships among them.