Effect of cadmium on photosynthesis parameters, leaf soluble sugar and plant growth in two rice cultivars

Contamination of the environment with toxic heavy metals due to anthropogenic activities is one of the major global environmental and human health problems.Cadmium severely inhibits plant growth and even causes plant death by disturbing the uptake of nutrients and inhibiting photosynthesis via degradation of chlorophyll.Two rice(Oryza sativa L.) cultivars: Wuyujing No.3,a Cd tolerant cultivar and Shanyou 63,a Cd susceptible cultivar,were grown hydroponically in this study to investigate the effects of Cd applied at realistic levels on photosynthetic parameters,soluble sugar and plant growth.Rice seedlings were grown in nutrient solutions with cadmium applied at the rate of Cd 0,1.0 or 5.0 (μmol/L).The results showed that the photosynthesis of the leaves was significantly inhibited under Cd stress.In comparison with the control,Cd treatment induced a decline in net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),stomatal limitation value(Ls) and transpiration efficiency(Te) in seedlings and this Cd-induced reduction was significantly dose-dependent. Cadmium treatment increased the concentration of soluble sugar significantly in both cultivars but decreased the content of leaf chlorophyll only in the susceptible cultivar at 5.0 Cd μmol/L.Shoot growth(length) was significantly reduced in the susceptible cultivar only at Cd 5.0 μmol/L,but root growth(length) was significantly inhibited at either Cd 1.0 or 5.0 μmol/L.In contrast,shoot and root growth(length) was unaffected in the tolerant cultivar compared to the control.These results suggested that there was significant genotypical difference in rice in response to Cd toxicity.