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Effect of potassium on diurnal variations in Pn, Hill reaction and SOD activities in rice plant

Jiang Dean, Weng Xiaoyi, Lu Qing, Xie Xuemin, R

Division of Basic Courses,Zhejiang Agricultural University.Hangzhou 310029,Zhejiang

Abstract

Two rice cultivars grown in pots with normal and low potassium supply were used to explore the cause of deeper midday depression of Pn under low-potassium condition.Maximum Pn occurred at about 8:30 when the photosynthetic photon flux (PPF) was about 1200#mu#mol m~(-2)s~(-1) and was slightly higher in low-potassium plants than in normal plants. Under low-potassium condition the midday depression of Pn was deeper, particularly,for cv.Erjiufeng,a cultivar more sensitive to potassium deficieny.Hill reaction rate stayed unchanged throughout the morning,fell at noon and rose again in late afternoon.The rate at noon was higher in the low-potassium plants. SOD activity was lower in early morning than at noon and afternoon and was also higher in low-potassium plants than in normal -potassium plants. Although a prolonged low Ci under strong irradiance can reduce PSⅡ activity reversibly, positive correlation of Pn with stomatal conductance and Ci from 8:30 to 14:30 indicats that midday depression results from the lowering of stomatal conductance rather than from the low ering of Hill reaction rate. At noon the higher SOD activity in the low-potassium plants may be a mechanisum of avoidance of the damage from excessive PPF.

Key words: Potassium nitrition;Rice;Pn;Hill reaction;SOD;Diurnal change

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Citing This Article：

Jiang Dean, Weng Xiaoyi, Lu Qing, Xie Xuemin, R. Effect of potassium on diurnal variations in Pn, Hill reaction and SOD activities in rice plant. Acta Physiol Sin 1996; 48 (1): (in Chinese with English abstract).