Effect of the Interaction Between N and Zn on Active Oxygen Metabolism and Chloroplast Ultrastructure of White Clover Leaves

Sand culture experiment was carried out to study the effect of interaction between N and Zn on active oxygen metabolism and chloroplast ultrastructure of white clover leaves.The main results indicated that the dry matter weight,the content of chlorophyll,SOD and carotinoid of leaves significantly decreased and MDA content of leaves remarkably increased with the increase of N rate;N and Zn combined application showed antagonism effect in the condition with deficient Zn,while,in the condition with sufficient Zn,the dry matter weight,the content of chlorophyll,SOD and carotinoid of leaves were higher and MDA content of leaves was lower at moderate N rate than those at high and low N rates,suggesting that N and Zn combined application showed synergism effect;at high amount of N supply,the dry matter weight,the content of chlorophyll,SOD and carotinoid of leaves significantly decreased and MDA content of leaves remarkably increased compared with those at moderate and low N rate,implying that N and Zn combined application showed antagonism effect.The chloroplast ultrastructure of mesophyll cell of white clover leaves showed that in the condition of Zn deficiency,with the increasing rate of applied N,the inner structure of chloroplast ruined,in which the number of the grana and grana lamellae as well as stroma lamellae decreased and disintegrated,which resulted in the low photosynthesis capacity of chloroplast.In the condition with sufficient supply of Zn,the numbers of the grana,grana lamellae and stroma lamellae as well as the order of the combination of them in chloroplast were the highest at moderate rate of N application,the volume of chloroplast reduced and the system of lamellae swelled and couldn't form grana at high rate of N application.The change of chloroplast ultrastructure was correspondent with that of chlorophyll,SOD and carotinoid content.