Electron and proton transport in wheat exposed to salt stress: is the increase of the thylakoid membrane proton conductivity responsible for decreasing the photosynthetic activity in sensitive genotypes?

Abstract

Effects of salinity caused by 150 mM NaCl on primary photochemical reactions and some physiological and biochemical parameters (K+/Na+ ratio, soluble sugars, proline, MDA) have been studied in five Triticum aestivum L. genotypes with contrasting salt tolerance. It was found that 150 mM NaCl significantly decreased the photosynthetic efficiency of two sensitive genotypes. The K+/Na+ ratio decreased in all genotypes exposed to salinity stress when compared with the control. Salinity stress also caused lipid peroxidation and accumulation of soluble sugars and proline. The amounts of soluble sugars and proline were higher in tolerant genotypes than sensitive ones, and lipid peroxidation was higher in sensitive genotypes. The noninvasive measurements of photosynthesis-related parameters indicated the genotype-dependent effects of salinity stress on the photosynthetic apparatus. The significant decrease of chlorophyll content (SPAD values) or adverse effects on photosynthetic functions at the PSII level (measured by the chlorophyll fluorescence parameters) were observed in the two sensitive genotypes only. Although the information obtained by different fast noninvasive techniques were consistent, the correlation analyses identified the highest correlation of the noninvasive records with MDA, K+/Na+ ratio, and free proline content. The lower correlation levels were found for chlorophyll content (SPAD) and Fv/Fm values derived from chlorophyll fluorescence. Performance index (PIabs) derived from fast fluorescence kinetics, and F735/F685 ratio correlated well with MDA and Na+ content. The most promising were the results of linear electron flow measured by MultispeQ sensor, in which we found a highly significant correlation with all parameters assessed. Moreover, the noninvasive simultaneous measurements of chlorophyll fluorescence and electrochromic band shift using this sensor indicated the apparent proton leakage at the thylakoid membranes resulting in a high proton conductivity (gH+), present in sensitive genotypes only. The possible consequences for the photosynthetic functions and the photoprotection are discussed.

Assessing the Adaptive Mechanisms of Two Bread Wheat (Triticum aestivum L.) Genotypes to Salinity Stress

“…Failure to detect the HKT1;5 gene transcript in the leaves can be attributed to complete silencing of this gene in the leaves or very low, undetectable levels of expression. These results are in line with previous reports confirming that the TaHKT1;5-D gene expression occurs in the root rather than in the shoot [18,56]. Microchip-based expression analysis of the HKT1;5 gene performed under 22 different conditions showed its activation in the roots and weakening in the leaves of rice varieties with contrasting tolerance.…”

“…The objects of the present study were two Azerbaijan local wheat (Triticum aestivum L.) genotypes: Mirbashir 128 (MIR) and Fatima (FAT). However, as per confirmation of Ibrahimova et al [18], the variety MIR is salt tolerant and FAT is salt-sensitive. Seeds were surface sterilized with 10% NaOCl for 10 min and then washed three times with sterile distilled water.…”

“…According to some authors, the osmotic potential is an important parameter for the selection of plants for drought and salt tolerance [31,48,49]. The accumulation of proline and sugars under salt stress regulates the osmotic balance between the cytosol and vacuoles [18]. In the presented study, the accumulation of sugars and proline was observed in the leaves of salt-exposed plants, and the increase was higher in the salt-tolerant genotype MIR.…”

“…The study aimed to assess the physiological and biochemical responses to salt stress and expression level of the TaHKT1;5 gene in two bread wheat genotypes: salt-tolerant Mirbashir 128 (MIR) and salt-sensitive Fatima (FAT). Salt tolerance properties of these genotypes were presented in our previous research [18]. Responses to salt stress of these genotypes were evaluated based on multivariable biochemical and physiological analyses.…”

Photosynthetic and Ultrastructural Properties of Eggplant (Solanum melongena) under Salinity Stress

“…Thus, a reduction in CO 2 intake and Calvin cycle efficiency, caused by salinity stress, likely leads to a reduction in chlorophyll content [39], causing an overall reduction in the net photosynthetic rate [40] and an increase in shoot Na+/K+ ratio that inhibits photosynthesis [41]. Ibrahimova et al (2021) reported that the Na+/K+ ratio increased significantly in all five Triticum aestivum L. genotypes exposed to salinity stress (150 mM NaCl) inhibiting the photosynthetic efficiency [42].…”