Light Quality Modulates Plant Cold Response and Freezing Tolerance.

The cold acclimation process is regulated by many factors like ambient temperature, day length, light intensity, or hormonal status. Experiments with plants grown under different light quality conditions indicate that the plant response to cold is also a light-quality-dependent process. Here, the role of light quality in the cold response was studied in 1-month-old Arabidopsis thaliana (Col-0) plants exposed for 1 week to 4°C at short-day conditions under white (100 and 20 µmol m-2s-1), blue, or red (20 µmol m-2s-1) light conditions. An upregulated expression of CBF1, inhibition of photosynthesis, and an increase in membrane damage showed that blue light enhanced the effect of low temperature. Interestingly, cold-treated plants under blue and red light showed only limited freezing tolerance compared to white light cold-treated plants. Next, the specificity of the light quality signal in cold response was evaluated in Arabidopsis accessions originating from different and contrasting latitudes. In all but one Arabidopsis accession, blue light increased the effect of cold on photosynthetic parameters and electrolyte leakage. This effect was not found for Ws-0, which lacks functional CRY2 protein, indicating its role in the cold response. Proteomics data confirmed significant differences between red and blue light-treated plants at low temperatures and showed that the cold response is highly accession-specific. In general, blue light increased mainly the cold-stress-related proteins and red light-induced higher expression of chloroplast-related proteins, which correlated with higher photosynthetic parameters in red light cold-treated plants. Altogether, our data suggest that light modulates two distinct mechanisms during the cold treatment - red light-driven cell function maintaining program and blue light-activated specific cold response. The importance of mutual complementarity of these mechanisms was demonstrated by significantly higher freezing tolerance of cold-treated plants under white light.

Effect of Seed Coating and PEG-Induced Drought on the Germination Capacity of Five Clover Crops.

The effect of coating the seed of clover crops by water absorbing seed process (WASP) technology pelletization on its germination capacity was studied in conditions of diverse drought intensities simulated by different concentrations of polyethylenglycol (PEG) 8000 solution. Drought resistance was monitored in the seed of five fodder clover species: Anthyllis vulneraria L., Medicago lupulina L., Trifolium repens L., Melilotus albus Medik. and Onobrychis viciifolia Scop. In the seed of given plant species, germination capacity was determined along with the share of dead and hard seeds. Although the coating significantly (p < 0.05) affected the drought resistance of seeds, the germination capacity increased only in conditions of milder drought (simulation with PEG: 0.1-0.3 mol). With the increasing intensity of drought induced by higher PEG concentrations (0.4-0.7 mol) the number of germinable seeds demonstrably decreased and the number of dead seeds increased in the coated seed as compared with the uncoated seed. The coated seed can be appropriate for use in M. lupulina, M. albus and T. repens, while the uncoated seed can be used in A. vulneraria and O. viciifolia.

Arabidopsis Response to Inhibitor of Cytokinin Degradation INCYDE: Modulations of Cytokinin Signaling and Plant Proteome.

Cytokinins are multifaceted plant hormones that play crucial roles in plant interactions with the environment. Modulations in cytokinin metabolism and signaling have been successfully used for elevating plant tolerance to biotic and abiotic stressors. Here, we analyzed Arabidopsis thaliana response to INhibitor of CYtokinin DEgradation (INCYDE), a potent inhibitor of cytokinin dehydrogenase. We found that at low nanomolar concentration, the effect of INCYCE on seedling growth and development was not significantly different from that of trans-Zeatin treatment. However, an alteration in the spatial distribution of cytokinin signaling was found at low micromolar concentrations, and proteomics analysis revealed a significant impact on the molecular level. An in-depth proteome analysis of an early (24 h) response and a dose-dependent response after 168 h highlighted the effects on primary and secondary metabolism, including alterations in ribosomal subunits, RNA metabolism, modulations of proteins associated with chromatin, and the flavonoid and phenylpropanoid biosynthetic pathway. The observed attenuation in stress-response mechanisms, including abscisic acid signaling and the metabolism of jasmonates, could explain previously reported positive effects of INCYDE under mild stress conditions.