Osmotic regulation and chlorophyll fluorescence characteristics in leaves of wheat seedlings under different salt stresses

Abstract

The damage mechanism of salt stress on plants has attracted much attention. In order to reveal the damage mechanism of different salt stresses, we compared osmotic regulation and photosynthetic characteristics of seedlings of wheat cultivar Xianhan 3 under sodium salt (150 mmol·L-1) and calcium salt (5, 30 mmol·L-1) treatments alone or in combination. The results showed that sodium salt or calcium salt stress alone significantly inhibited the growth of roots and stems, but increased the amount of soluble sugar and proline, regulatory energy-dissipated electron yield, non-photochemical quenching and relative content of zeaxanthin contents in leaves. In contrast, salt treatments alone significantly decreased the levels of chlorophyll a and chlorophyll b, maximum photochemical efficiency, PSⅡ photochemical efficiency, photochemical quenching and photosynthetic electron transport efficiency. Furthermore, the inhibition of wheat seedling growth was more sensitive to calcium salt than to sodium salt stress, whereas the decreases of chlorophyll content and chlorophyll fluorescence parameters were more prominent in response to sodium salt stress. Except for the amount of soluble protein, lutein and the relative level of zeaxanthin, the changes of other parameters in the leaves due to sodium salt stress were effectively blocked by the application of low calcium concentration, but further increased by the presence of high calcium salt concentration. Taken together, sodium or calcium salt stress alone significantly inhibited seedling growth. The toxicity of sodium salt to wheat seedlings was effectively alleviated by low calcium concentration, but was aggravated by high calcium concentration, which were associated with the changes of photosynthetic pigment content, light energy capture, and photosynthetic electron transport process in the leaves of wheat seedlings. Moreover, osmotic regulators played an important role in enhancing the resistance of wheat seedlings to sodium or/and calcium environment.