Time-Dependent Expression of Photosynthetic Genes in C3 and C4 Halophytes in Response to Osmotic and Ionic Components of Salinity

The temporal dynamics (3, 6 h, 1–4 days) of photosynthetic gene transcripts accumulation in response to salinity (400 mM NaCl) in C 3 halophyte Chenopodium quinoa Willd. and C 4 halophyte Salsola komarovii (Iljin) Akhani & Roalson were studied. Analysis of changes in water content, sodium accumulation, and antioxidant enzymes activity made it possible to separate the responses to the osmotic and ionic components of salinity in time. Three stages of response to salinity were identified: early response (3–6 h), sodium accumulation stage (1–2 days) and toxic ionic effect (3–4 days). At the early stage of salinity, osmotic stress was detected only in the C 3 halophyte, which led to a decrease in water content and in the expression of rbcL , psbA and PnsB5 genes. At the sodium accumulation stage, both species showed an increase in psbA expression, which was accompanied by increased PGR5 expression in C 3 species. The toxic effect of Na + led to an increase in expression of psbA , as well as PGR5 and PnsB5 genes of both pathways of cyclic electron transport (CET) photosystem I (PSI) in the C 3 halophyte with increased sodium flow through the leaf. Overall, genes encoding Rubisco, PSII components, and two CET PSI pathways were more sensitive to salinity in C. quinoa than in S. komarovii . This reflects differences in tolerance to osmotic and ionic stress in these species, possibly driven by both the C 4 carbon concentration mechanism in S. komarovii , which promotes more efficient water use, and the salt-excreting ability of C. quinoa , which results in high Na + flux through the leaf.