AUTHOR=Yan Guochao , Fan Xiaoping , Peng Miao , Yin Chang , Xiao Zhuoxi , Liang Yongchao 

TITLE=Silicon Improves Rice Salinity Resistance by Alleviating Ionic Toxicity and Osmotic Constraint in an Organ-Specific Pattern

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00260

DOI=10.3389/fpls.2020.00260

ISSN=1664-462X

ABSTRACT=Salinity stress severely inhibits the growth of plant via ionic toxicity and osmotic constraint. Exogenous silicon (Si) can alleviate salinity stress but the mechanisms behind remain unclear. To investigate the role of Si in alleviating ionic and osmotic components of salinity, rice (Oryza sativa L.) seedlings were grown hydroponically in iso-osmotic stress conditions developed from NaCl or polyethylene glycol (PEG). The effects of Si on the growth of shoot and root of rice under salinity and PEG-derived osmotic stress were evaluated and further compared using Principal Coordinate Analysis (PCoA). We also analyzed the concentrations of Na, K and compatible osmolytes, tissue sap osmotic potential, antioxidant enzymes activities and the expression of aquaporin genes. Generally, Si significantly promoted shoot and root growth in rice exposed to both NaCl and PEG. PCoA shows that the Si-induced distance change under NaCl treatment was larger than that under PEG treatment in shoot, while the Si-induced distance changes under NaCl and PEG treatments were at an equal level in root. Under salinity, Si decreased Na concentration and Na/K ratio in shoot but not in root. However, Si decreased net Na uptake and increased root Na accumulation content. Osmotic potential was increased in shoot but decreased in root by Si addition. Si decreased soluble sugar and proline concentrations in shoot but increased soluble sugar and soluble protein concentrations in root. Besides, Si promoted shoot transpiration rate and root morphological traits. Although, both NaCl and PEG treatments up-regulated aquaporin genes expression, Si addition maintained the expression of OsPIPs under NaCl and PEG treatments at same levels as control treatment. Furthermore, Si alleviated oxidative damages under both NaCl and PEG by regulating antioxidant enzymes activities. In summary, our results show that Si improves salt stress tolerance in rice by alleviating ionic toxicity and osmotic constraint in an organ-specific pattern. Si ameliorates ionic toxicity by decreasing Na uptake and increasing root Na reservation. Si alleviates osmotic constraint by regulating root morphological traits and root osmotic potential but not aquaporin genes expression for water uptake, and promoting transpiration force but not osmotic force in shoot for root-to-shoot water transport.