Changes in activities of antioxidant enzymes in radish (Raphanus sativus) seedlings in response to allelopathic effect of safflower (Carthamus tinctorius)

Abstract ROS (Reactive Oxygen Species) production is a usual plant reaction to environmental stresses such as allelopathy. Plants possess antioxidant enzymes to scavenge cells and resist against the ROS. This study was conducted to evaluate changes in antioxidant enzymes (CAT, GPX, APX) in radish seedlings in response to allelopathic effect of safflower root and shoot residues grown under normal irrigation and drought stress. Safflower allelopathic effect led to an increase in antioxidant enzymes activities. GPX activity increased more than CAT and APX. Radish seedlings exposed to safflower residue grown under drought stress showed more antioxidant enzymes activities. Root residues enhanced the activities of antioxidant enzymes greater than shoot. Seedlings exposed to root residues grown under drought stress had the highest level of antioxidant enzymes activities.

Comparative transcriptome analysis identifies genes associated with chlorophyll levels and reveals photosynthesis in green flesh of radish taproot.

The flesh of the taproot of Raphanus sativus L. is rich in chlorophyll (Chl) throughout the developmental process, which is why the flesh is green. However, little is known about which genes are associated with Chl accumulation in this non-foliar, internal green tissue and whether the green flesh can perform photosynthesis. To determine these aspects, we measured the Chl content, examined Chl fluorescence, and carried out comparative transcriptome analyses of taproot flesh between green-fleshed "Cuishuai" and white-fleshed "Zhedachang" across five developmental stages. Numerous genes involved in the Chl metabolic pathway were identified. It was found that Chl accumulation in radish green flesh may be due to the low expression of Chl degradation genes and high expression of Chl biosynthesis genes, especially those associated with Part Ⅳ (from Protoporphyrin Ⅸ to Chl a). Bioinformatics analysis revealed that differentially expressed genes between "Cuishuai" and "Zhedachang" were significantly enriched in photosynthesis-related pathways, such as photosynthesis, antenna proteins, porphyrin and Chl metabolism, carbon fixation, and photorespiration. Twenty-five genes involved in the Calvin cycle were highly expressed in "Cuishuai". These findings suggested that photosynthesis occurred in the radish green flesh, which was also supported by the results of Chl fluorescence. Our study provides transcriptome data on radish taproots and provides new information on the formation and function of radish green flesh.

Transcriptome-based gene expression profiling of diploid radish (Raphanus sativus L.) and the corresponding autotetraploid.

Polyploidy is an important evolutionary factor in most land plant lineages which possess more than two complete sets of chromosomes. Radish (Raphanus sativus L.) is an economically annual/biennial root vegetable crop worldwide. However, the expression patterns of duplicated homologs involved in the autopolyploidization remains unclear. In present study, the autotetraploid radish plants (2n = 4x = 36) were produced with colchicine and exhibited an increase in the size of flowers, leaves, stomata and pollen grains. The differential gene expression (DGE) profiling was performed to investigate the differences in gene expression patterns between diploid and its corresponding autotetraploid by RNA-Sequencing (RNA-Seq). Totally, 483 up-regulated differentially expressed genes (DEGs) and 408 down-regulated DEGs were detected in diploid and autotetraploid radishes, which majorly involved in the pathways of hormones, photosynthesis and stress response. Moreover, the xyloglucan endotransglucosylase/hydrolase (XTH) and pectin methylesterases (PME) family members related to cell enlargement and cell wall construction were found to be enriched in GO enrichment analysis, of which XTH family members enriched in "apoplast" and "cell wall" terms, while PME family members enriched in "cell wall" term. Reverse-transcription quantitative PCR (RT-qPCR) analysis indicated that the expression profile of DEGs were consistent with results from the RNA-Seq analysis. The DEGs involved in cell wall construction and auxin metabolism were predicted to be associated with organs size increase of autotetraploid radishes in the present study. These results could provide valuable information for elucidating the molecular mechanism underlying polyploidization and facilitating further genetic improvements of important traits in radish breeding programs.

Effect of expanded variation in anther position on pollinator visitation to wild radish, Raphanus raphanistrum.

Background and Aims: Plant-pollinator interactions shape the evolution of flowers. Floral attraction and reward traits have often been shown to affect pollinator behaviour, but the possible effect of efficiency traits on visitation behaviour has rarely been addressed. Anther position, usually considered a trait that influences efficiency of pollen deposition on pollinators, was tested here for its effect on pollinator visitation rates and visit duration in flowers of wild radish, Raphanus raphanistrum . Methods: Artificial selection lines from two experiments that expanded the naturally occurring phenotypic variation in anther position were used. In one experiment, plant lines were selected either to increase or to decrease anther exsertion. The other experiment decreased anther dimorphism, which resulted in increased short stamen exsertion. The hypothesis was that increased exsertion would increase visitation of pollen foragers due to increased visual attraction. Another hypothesis was that exsertion of anthers above the corolla would interfere with nectar foragers and increase the duration of visit per flower. Key Results: In the exsertion selection experiment, increased exsertion of both short and long stamens resulted in an increased number of fly visits per plant, and in the dimorphism experiment bee visits increased with increased short stamen exsertion. The duration of visits of nectar feeders declined significantly with increasing long stamen exsertion, which was opposite to the hypothesis. Conclusions: Until now, anther position was considered to be an efficiency trait to enhance pollen uptake and deposition. Anther position in wild radish is shown here also to have an ecological significance in attracting pollen foragers. This study suggests an additional adaptive role for anther position beyond efficiency, and highlights the multiple ecological functions of floral traits in plant-pollinator interactions.

Optimization of heat and relative humidity conditions to reduce Escherichia coli O157:H7 contamination and maximize the germination of radish seeds.

We previously reported that a combination of heat and relative humidity (RH) had a marked bactericidal effect on Escherichia coli O157:H7 on radish seeds. Here, response surface methodology with a Box-Behnken design was used to build a model to predict reductions in E. coli O157:H7 populations based on three independent variables: heating temperature (55 °C, 60 °C, or 65 °C), RH (40%, 60%, and 80%), and holding time (8, 15, or 22 h). Optimum treatment conditions were selected using a desirability function. The predictive model for microbial reduction had a high regression coefficient (R(2) = 0.97), and the accuracy of the model was verified using validation data (R(2) = 0.95). Among the three variables examined, heating temperature (P < 0.0001) and RH (P = 0.004) were the most significant in terms of bacterial reduction and seed germination, respectively. The optimum conditions for microbial reduction (6.6 log reduction) determined by ridge analysis were as follows: 64.5 °C and 63.2% RH for 17.7 h. However, when both microbial reduction and germination rate were taken into consideration, the desirability function yielded optimal conditions of 65 °C and 40% RH for 8 h (6.6 log reduction in the bacterial population; 94.4% of seeds germinated). This study provides comprehensive data that improve our understanding of the effects of heating temperature, RH, and holding time on the E. coli O157:H7 population on radish seeds. Radish seeds can be exposed to these conditions before sprouting, which greatly increases the microbiological safety of the products.

Manipulation of the hypocotyl sink activity by reciprocal grafting of two Raphanus sativus varieties: its effects on morphological and physiological traits of source leaves and whole-plant growth.

To reveal whether hypocotyl sink activities are regulated by the aboveground parts, and whether physiology and morphology of source leaves are affected by the hypocotyl sink activities, we conducted grafting experiments using two Raphanus sativus varieties with different hypocotyl sink activities. Comet (C) and Leafy (L) varieties with high and low hypocotyl sink activities were reciprocally grafted and resultant plants were called by their scion and stock such as CC, LC, CL and LL. Growth, leaf mass per area (LMA), total non-structural carbohydrates (TNCs) and photosynthetic characteristics were compared among them. Comet hypocotyls in CC and LC grew well regardless of the scions, whereas Leafy hypocotyls in CL and LL did not. Relative growth rate was highest in LL and lowest in CC. Photosynthetic capacity was correlated with Rubisco (ribulose 1·5-bisphosphate carboxylase/oxygenase) content but unaffected by TNC. High C/N ratio and accumulation of TNC led to high LMA and structural LMA. These results showed that the hypocotyl sink activity was autonomously regulated by hypocotyl and that the down-regulation of photosynthesis was not induced by TNC. We conclude that the change in the sink activity alters whole-plant growth through the changes in both biomass allocation and leaf morphological characteristics in R. sativus.

Novel seed protection in the recently evolved invasive, California wild radish, a hybrid Raphanus sp. (Brassicaceae).

UNLABELLED: • PREMISE OF THE STUDY: Interspecific hybridization may have considerable effects on plant structural defenses that can contribute to the success of invasive hybrid lineages. Changes in fruit structural and material properties are predicted to have key effects on predispersal granivory.• METHODS: Here, we asked whether plant structure can increase the fitness of a hybrid invasive relative to its progenitors. We compared fruit traits of the hybrid-derived lineage, California wild radish, with its progenitors, cultivated radish and jointed charlock.• KEY RESULTS: The hybrid lineage is significantly different from one or both ancestors in fruit length, mass, diameter, volume, shape, wall strength, and internal seed distribution. We experimentally exposed the fruits of both hybrid and wild progenitor to avian granivores and found (1) different types and degrees of damage at the different fruit sections and (2) significant differences in the inflicted damage at different sections of the fruit.• CONCLUSIONS: Combining our descriptive and experimental data, we conclude that the novel seed protection of the hybrid California wild radish is an important defense mechanism. It offers differential protection to its seeds and according to our findings, better protection of seeds that have been found to be better competitors. We suggest then that the fruit has enabled, at least in part, the successful replacement of the parental species by the hybrid lineage.

Florivores prefer white versus pink petal color morphs in wild radish, Raphanus sativus.

Many hypotheses suggest that pollinators act to maintain or change floral color morph frequencies in nature, although pollinator preferences do not always match color morph frequencies in the field. Therefore, non-pollinating agents may also be responsible for color morph frequencies. To test this hypothesis, we examined whether Raphanus sativus plants with white flowers received different amounts of florivory than plants with pink flowers, and whether florivores preferred one floral color over the other. We found that white-flowered plants received significantly more floral damage than pink-flowered plants in eight populations over 4 years in northern California. Both generalists and specialists on Brassicaceae preferred white petals in choice and short-term no choice tests. In performance tests, generalists gained more weight on white versus pink petals whereas specialists gained similar amounts of weight on pink and white morphs. Because our results suggest that florivores prefer and perform better on white versus pink flowers, these insects may have the opportunity to affect the frequency of color morphs in the field.

Testing for conflicting and nonadditive selection: floral adaptation to multiple pollinators through male and female fitness.

Although conflicting selection from different resources is thought to play a critical role in the evolution of specialized species, the prevalence of conflicting selection in generalists is poorly understood. Plants may experience conflicting selection on floral traits by different pollinators and between genders. Using artificial selection to increase phenotypic variation, we tested for conflicting and nonadditive selection on wild radish (Raphanus raphanistrum) flowers. To do this, we measured selection by each of the major pollinator taxa through both male and female fitness, and tested for a single-generation response to selection by a subset of these pollinators. We found some evidence for conflicting selection on anther exertion--sweat bees exerted stabilizing selection and larger bees selected for increased exertion. Stamen dimorphism was only under selection by honey bees, causing a response to selection in the next generation, and flower size was under similar selection by multiple pollinators. Selection differed significantly between genders for two traits, but there was no evidence for stronger selection through male fitness or for conflicting selection between genders. Our results suggest wild radish flowers can adapt to multiple pollinators, as we found little evidence for conflicting selection and no evidence for nonadditive selection among pollinators.

Investigation of supplemental ultraviolet-B-induced changes in antioxidative defense system and leaf proteome in radish (Raphanus sativus L. cv Truthful): an insight to plant response under high oxidative stress.

Impact of supplemental UV-B (sUV-B) has been investigated on photosynthetic pigments, antioxidative enzymes, metabolites, and protein profiling of radish plants under realistic field conditions. Exposure of sUV-B leads to oxidative damage in plants. However, plants possess a number of UV-protection mechanisms including a stimulation of antioxidant defense system. It caused alteration in reactive oxygen species metabolism primarily by decreasing catalase activity vis-à-vis enhanced activities of other enzymatic (superoxide dismutase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbic acid) antioxidants. Qualitative analysis of samples also showed significant reductions in photosynthetic pigments and protein content. After sUV-B exposure, protein profile showed differences mainly at eight points--126.8, 84.8, 71.9, 61.5, 47.8, 40.6, 38.9, and 17.5 kDa, whereas protein(s) of 38.9 kDa showed increment. Results of the present investigation clearly showed the adverse effect of sUV-B on total biomass at final harvest.

Functional diversity of plant-pollinator interaction webs enhances the persistence of plant communities.

Pollination is exclusively or mainly animal mediated for 70% to 90% of angiosperm species. Thus, pollinators provide an essential ecosystem service to humankind. However, the impact of human-induced biodiversity loss on the functioning of plant-pollinator interactions has not been tested experimentally. To understand how plant communities respond to diversity changes in their pollinating fauna, we manipulated the functional diversity of both plants and pollinators under natural conditions. Increasing the functional diversity of both plants and pollinators led to the recruitment of more diverse plant communities. After two years the plant communities pollinated by the most functionally diverse pollinator assemblage contained about 50% more plant species than did plant communities pollinated by less-diverse pollinator assemblages. Moreover, the positive effect of functional diversity was explained by a complementarity between functional groups of pollinators and plants. Thus, the functional diversity of pollination networks may be critical to ecosystem sustainability.

Flower color microevolution in wild radish: evolutionary response to pollinator-mediated selection.

Evolutionary ecologists are fundamentally interested in how species interactions affect evolutionary change. We tested the degree to which plant-pollinator interactions affect the frequency of flower color morphs of Raphanus sativus. Petal color in R. sativus is determined by two independently assorting loci, producing four petal colors (yellow, white, pink, and bronze). We assessed the impact of pollinator discrimination on changes in flower color variation by comparing the frequency of colors produced in the presence (open pollination) versus absence (null pollination) of pollinator discrimination. We also assessed the impact of postpollination and developmental effects on progeny colors using equal pollinations with all four color morphs. Our results from open pollinations found an overrepresentation of yellow progeny in the next generation, when compared with both null pollinations and cumulative ratios based on Hardy-Weinberg and linkage equilibria assumptions. When these results were combined with those from equal pollinations, the overrepresentation of yellow could be attributed to selection from pollinators. Yet, surveys in the field the following year found no flower color frequency changes in the next generation. These results illustrate that flower color microevolution can be driven by both pollinator discrimination and other nonpollinator selective forces acting during the seed-to-adult transition, countering selection imposed by pollinators.