Physiological Characteristics of Delaying Leaf Senescence in Maize Inbred Lines Tolerant to Potassium Deficiency

Abstract

A field experiment was conducted using two maize inbred lines with significant difference in potassium sensitivity to investigate the effects of low potassium stress at grain filling stage on leaf stay-green,chlorophyll contents,photosynthetic gas exchange and chlorophyll fluorescence parameters,and various antioxidant enzymes activities related with senescence.The results showed that,under low potassium stress,the characteristics of leaf stay-green of 90-21-3 were better than that of D937.In addition to changes in stay-green,it was found that decreased more strongly in D937,the photosynthetic pigment level in 90-21-3 was remained nearly normal under K deficiency conditions.Moreover,compared with D937,90-21-3 showed a lower stomatal restriction and a higher electronic transition capacity after accelerated ageing by K deficiency.FPSII,Fv,Fm in 90-21-3 were higher than in D937,while Fo was lower than those in D937.In addition,under low potassium stress,activities of PEPC and NADK were less decreased and photo system was less damaged in 90-21-3.And the content of malondialdehyde(MDA)was lower in 90-21-3 than in D937 under low potassium stress.The activities of superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)in ear leaf of 90-21-3 were obviously higher than those of D937 under low potassium stress,indicating that the antioxidant enzymes could eliminate reactive oxygen species,inhibit the membrane lipid peroxidation and decrease the content of MDA more efficiently in 90-21-3.Therefore,compared with D937,the leaf senescence of 90-21-3 was relatively slower,which could prolong the functional period of leaves.The activity of NADK could provide NADP as electronic receptors for photoreaction,at the same time the increased activity of PEPC led to more effective fixation of CO2,and the synergistic effect of light and dark reactions contributed to the higher photosynthetic rate and yield in 90-21-3.