Influence of foliar application of silicon on chlorophyll fluorescence, photosynthetic pigments, and growth in water-stressed wheat cultivars differing in drought tolerance

The influence of foliar application of silicon (Si) on chlorophyll contents, chlorophyll fluorescence, and growth of four wheat cultivars differing in drought tolerance (Sirvan and Chamran, as relatively drought tolerant, and Shiraz and Marvdasht, as drought sensitive) was examined under water deficit (100% and 40% F.C.) created in a greenhouse. The results showed that water deficit decreased shoot and root lengths, shoot dry weight, root dry weight, water utilization efficiency, chlorophyll a and b, and chlorophyll stability index. In contrast, foliar application of Si improved plant growth parameters and chlorophyll pigment concentration under water deficit; however, it did not significantly affect wheat growth under control conditions. Limited water supply reduced the values of minimal fluorescence from dark-adapted leaf (F-o), maximal fluorescence from dark-adapted leaf (F-m), maximum quantum yield of PSII (F-v/F-m), effective quantum yield of PSII (Phi PSII), photochemical quenching (q(P)), and apparent photosynthetic electron transport rate (ETR). However, under water deficit, foliar application of Si application increased the earlier mentioned parameters. In contrast, nonphotochemical quenching (q(N)) and F-o/F-m increased under water deficit, and application of Si further improved these parameters. Chlorophyll fluorescence analysis suggested that Si alleviated water deficit-induced adverse effects by reducing nonphotochemical quenching, while increasing F-v/F-m and q(P), so that it improved the light use efficiency in the four wheat cultivars under stress. Overall, we concluded that drought-sensitive cultivars (Shiraz and Marvdasht) could resemble resistant cultivars upon foliar application of silicon.