AUTHOR=Shuyskaya Elena , Rakhmankulova Zulfira , Prokofieva Maria , Saidova Luizat , Toderich Kristina , Voronin Pavel 

TITLE=Intensity and duration of salinity required to form adaptive response in C4 halophyte Kochia prostrata (L.) Shrad

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.955880

DOI=10.3389/fpls.2022.955880

ISSN=1664-462X

ABSTRACT=Plant adaptation to salinity is a highly multifaceted process harnessing various physiological mechanisms depending on the severity and duration of salt stress. This study focuses on the effect of 4- and 10-days treatments with low (100 mM NaCl) and moderate (200 mM NaCl) salinity on growth, CO2/H2O gas exchange, stomatal apparatus performance, the efficiency of photosystems I and II (PS I and II), content of key C4 photosynthesis enzymes, the accumulation of Na+, K+ and proline in shoots of widespread forage C4 halophyte Kochia prostrata. Our data show that 4 days of low salinity treatment resulted in a decrease in biomass, intensity of apparent photosynthesis and cyclic electron transport around PS I. It was accompanied by the increase in transpiration, and Rubisco and PEPC contents, while the Na+ and proline contents were low in K. prostrata shoots. By the 10th day of salinity, Na+ and proline have accumulated, PS I function got stabilized, while PS II efficiency decreased due to the enhanced non-photochemical quenching of chlorophyll fluorescence (NPQ). Thus, under low salinity conditions, Na+ accumulated slowly and the imbalance between light and dark reactions of photosynthesis was observed. These processes might be induced by an early sodium signaling wave that affects cellular pH and ion homeostasis ultimately disturbing the photosynthetic electron transport. Another adaptive reaction more ‘typical’ of salt-tolerant species was observed at 200 mM NaCl treatment. It proceeds by two stages. First, during the first 4 days, dry biomass and apparent photosynthesis decrease, whereas stomata sensitivity and dissipation energy during dark respiration increase. In parallel, an active Na+ accumulation and decreased K+/Na+ ratio take place. Second, by the 10th day, a fully-fledged adaptive response was formed, when growth and apparent photosynthesis got stabilized and stomata closed. Decreased dissipation energy, increased WUE, stabilization of Rubisco and PEPC contents, and decreased proline content testify to completion of the adaptation and stabilization of the physiological state of plants. The obtained results allowed us to conclude that the formation of full-fledged salt-tolerant response common for halophytes in K. prostrata occurs by the 10th day of moderate salinity.