Silicon-mediated alleviation of cadmium stress in Pennisetum glaucum: insights from physiology and root...

The problem of cadmium (Cd) pollution in soil has attracted much attention. Although Pennisetum glaucum has developed tolerance mechanisms to heavy metals, the accumulation of excess Cd through the food chain threatens human health. Silicon (Si) has a beneficial role in alleviating environmental stress. However, the underlying physiological and molecular mechanisms for alleviating Cd toxicity in P. glaucum are still largely unknown. Therefore, experiments were conducted to explore the effects of Si on the photosynthetic system, antioxidant defense system, and the expression of in P. glaucum under Cd stress. The results showed that Si amendment increased the net photosynthetic rate and chlorophyll content of Cd-stressed P. glaucum by 19.7% and 13.8%, respectively. Moreover, DHAR and MDHAR activities in roots were significantly increased by 53.6% and 63.6% in the AsA-GSH cycle after Si application, while MDA concentration was significantly decreased by 14.6%. Importantly, exogenous Si application dramatically reduced Cd concentration in roots and shoots of P. glaucum by 52.7% and 21.5%, respectively under Cd stress. RNA-seq analysis showed that 6491 differentially expressed genes (DEGs) were identified, among which 4429 DEGs were down-regulated and 2062 DEGs were up-regulated. Root transcriptomic analysis revealed that gene expression differed between the Cd and Cd+Si treatments, particularly for genes related to photosynthesis and glutathione metabolism. Contrarily, the expression of genes involved in Cd uptake and transport, such as ABCG36, ABCB11, Nramp5, and Nramp4 (folds were -1.10, -2.52, -2.66, and -1.55, respectively) were down-regulated by the addition of Si. Overall, these above results demonstrate that Si supplementation offers a viable approach to reduce Cd accumulation and ensure the safe production of forage crops.