Silicon-mediated changes in radial hydraulic conductivity and cell wall stability are involved in silicon-induced drought resistance in tomato

Plants frequently experience drought stress. It is well known that silicon (Si) facilitates recovery from drought stress by improving drought resistance in plants. However, the effects of Si on the roots associated with the drought resistance in plants remain elusive. In this study, tomato (cv. 'Jinpeng 1(#)') was adopted to study the silicon-mediated drought avoidance and drought tolerance. The results showed that exogenous Si evidently influenced the drought-induced changes of the related indicators. Roots added with Si were more adaptable to drought stress. Silicon was involved in improving hydraulic conductivity in radial direction, which enhanced water uptake of tomato roots. Si also maintained solute accumulation at a high level, such as proline, soluble sugar, and soluble protein, and the osmotic adjustment ability of root was improved. So silicon promoted the drought avoidance by improving water absorption and water situation in tomato root. In addition, silicon enhanced antioxidant activities, including SOD activity and CAT activity, and reduced O-2 (A<overline>) production rate, H2O2 content, and malondialdehyde content, which contributed to alleviate harmful effects of drought and mitigate drought-induced cell wall rupture. Therefore, via induction of antioxidant activities, detoxification of the ROS, and maintenance of cell wall stability in tomato roots, silicon contributed to the drought tolerance. Though the silicon-mediated drought avoidance and drought tolerance can maintain physiological activities of tomato at relatively lower water potential, the maximal duration at which Si induced drought resistance was 3 or 5 days. When drought stress was for too long time, which exceeded the self-regulation of the tomato, mitigative effects of Si were weakened.