Silicon Supplementation Improves Tolerance to Water Deficiency in Sorghum Plants by Increasing Root System Growth and Improving Photosynthesis

Purpose This study was conducted to assess the effects of silicon treatments on architecture and morphometry of root systems of sorghum plants grown at two different soil water levels and to elucidate whether physiological improvements caused by silicon were related to morphometric modifications of the root system. Methods Plants of the sorghum genotype BRS332 which is sensitive to drought at pre-flowering stage were used in this study. These plants were grown in a greenhouse, either at field capacity or under water deficiency, and were treated with silicon or were untreated. Leaf water potential was evaluated at noon, and gas exchange, photosynthetic pigment levels, relative aquaporin expression, root system morphometry, and grain yield were assessed. Results Silicon treatments mitigated the effects of water deficiency on leaf potential, photosynthesis, instantaneous carboxylation efficiency, and morphometry of the root system. These positive effects contributed to a higher grain yield, and thus indicated higher tolerance to drought. The beneficial effects of silicon also occurred in plants grown at field capacity. Silicon treatments did not increase the relative expression of aquaporin genes. However, we observed that expression of aquaporin TIP4 responded more strongly to drought than that of aquaporins PIP1;6 and PIP1;3/1;4. Conclusion We conclude that silicon supplementation increases the tolerance of sorghum plants to drought by increasing growth of the root system and mitigating adverse effects of drought on photosynthesis.