Intraspecific Photosynthetic Diversity and Differences in Stress-Induced Plasticity in C3-C4Sedobassia sedoides under Drought Stress

Research into organization and peculiarities of carbon-concentrating mechanism (CCM) functioning in plants with intermediate C-3-C-4 (C-2) photosynthesis type characterized by resistance to arid climate is of paramount importance given the global climate changes. In this study two populations (P1 and P2) of C-3-C(4)Sedobassia sedoides (Chenopodiaceae) different in productivity were investigated under PEG-induced osmotic stress. As a result of our studies, a less productive P1 population was classified as the Type II of C-2 photosynthesis, since there was a relatively low efficiency of cyclic electron transport around PSI, and high glycine decarboxylase (GDC) content. On the contrary, P2 population was more productive and based on type of photosynthesis was classified as C-4-like plants. It exhibited a higher efficiency of cyclic electron transport around PSI and lower GDC content. Plants in each population also demonstrated heterogeneity in terms of the degree of dehydration under osmotic stress and fell into two groups: stress-tolerant (ST) and not stress-tolerant (NST) plants. NST plants from both populations showed a significant increase in proline content and a decrease of maximum quantum yield of PSII (F-v/F-m) evidencing a severe osmotic stress. P1 and P2 plants showed differences in mechanisms ensuring drought tolerance, more pronounced in NST plants. NST plants from P1 showed a decrease in K+/Na+ ratio, an increase in cyclic electron flow around PSI and a decrease in efficiency of PSII (due to NPQ), presence of oxidative stress (an increase in catalase and SOD activity), increase in content of C-4 CCM enzymes PEPC and NAD-Me. NST plants from P2 retained considerable dry biomass and shoot length (which were formed before stress), demonstrated a decline in Na+ accumulation, an increase in K+/Na+ ratio, and a decrease in activity of cyclic electron flow around PSI and PSII efficiency (due to NPQ), absence of oxidative stress, a decrease in Rubisco content and content of C-4 CCM enzymes PEPC and NAD-Me. The complexity of determining the specific mechanisms of biochemical response of plants to stress is discussed, as well as the high stress-induced plasticity of this type of photosynthesis, i.e. the possibility of switch from one type of C-3-C-4 photosynthesis to another under drought, either towards enhancing C-4 characteristics or towards their weakening.

Automated summary

Research on the carbon-concentrating mechanism (CCM) in plants with intermediate C-3-C-4 (C-2) photosynthesis type and resistance to arid climate is important due to global climate changes. This study investigated two populations of C-3-C(4)Sedobassia sedoides under osmotic stress and found differences in photosynthesis type and stress tolerance mechanisms between the populations.