Excess salt affects about 955 million ha of arable land worldwide, and 49% of agricultural land is Zn-deficient. Soil salinity and zinc deficiency can intensify plant abiotic stress. The mechanisms by which Zn can mitigate salinity effects on plant functions are not well understood. We conducted an experiment to determine how Zn and salinity effects on rice plant retention of Zn, K and the salt ion Na affect chlorophyll formation, leaf cell membrane stability and grain yield. We examined the mechanisms of Zn nutrition in mitigating salinity stress by examining plant physiology and nutrition. We used native Zn-deficient soils (control), four salinity (EC) and Zn treatments - Zn 10 mg·kg (Zn ), EC 5 dS·m (EC ), Zn +EC and Zn +EC , a coarse rice (KS-282) and a fine rice (Basmati-515) in the study. Our results showed that Zn alone (Zn ) significantly increased rice tolerance to salinity stress by promoting Zn/K retention, inhibiting plant Na uptake and enhancing leaf cell membrane stability and chlorophyll formation in both rice cultivars in native alkaline, Zn-deficient soils (P < 0.05). Further, under the salinity treatment (EC ), Zn inputs (10-15 mg·kg ) could also significantly promote rice plant Zn/K retention and reduce plant Na uptake, and thus increased leaf cell membrane stability and grain yield. Coarse rice was more salinity-tolerant than fine rice, having significantly higher Zn/K nutrient retention. The mechanistic basis of Zn nutrition in mitigating salinity impacts was through promoting plant Zn/K uptake and inhibiting plant Na uptake, which could result in increased plant physiological vigour, leaf cell membrane stability and rice productivity.
Athyrium wardii (Hook.) is a promising herbaceous plant species for phytostabilization of cadmium (Cd)-contaminated sites with large biomass and fast growth rate. However, little information is available on its tolerance mechanisms toward Cd. To further understand the mechanisms involved in Cd migration, accumulation and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in the mining ecotypes and corresponding non-mining ecotypes of A. wardii via greenhouse pot experiment. Subcellular fractionation of Cd-containing tissues demonstrated that the majority of the element was mainly located in soluble fraction in cell walls. This indicated that both the vacuoles and cell walls might be evolved the Cd tolerance mechanisms to protect metabolically active cellular compartments from toxic Cd concentrations. Meanwhile, Cd taken up by the plant existed in different chemical forms. Results showed that the majority of Cd in plant was in undissolved Cd-phosphate complexes (extracted by 2 % CH 3 COOH), followed by water-soluble Cd-organic acid complexes, Cd(H 2 PO 4 ) 2 , pectates and protein form (extracted by deionized water and 1 M NaCl), whereas only small amount of Cd in roots was in inorganic form (extracted by 80 % ethanol), which suggests low capacity to be transported to aboveground tissues. It could be suggested that Cd integrated with undissolved Cd-phosphate complexes in cell wall or compartmentalization in vacuole might be responsible for the adaptation of the mining ecotypes of A. wardii to Cd stress.
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