Effects of phosphate deficiency on acid phosphatase activities of
different maize genotypes tolerant to low-p stress

【Objectives】Acid phosphatases affects P acquisition and use efficiency of crops. In this study, seven maize inbred lines (five low-P tolerant and two low-P sensitive maize genotypes) were used to study their differences in acid phosphatase(APase)activities in maize leaves, root tissue and root exudation under low P stress, and to discuss relationship between the APase activities and P efficiency. These results may explain the physiological mechanism of low phosphorus tolerance in maize.【Methods】 A hydroponic experiment were designed in two P levels and used five low-P tolerant (99180T, 99239T, 99186T, 99327T and 99184T) and two low-P sensitive (99152S and 99270S) maize genotypes as materials. We determined the shoot dry weight, root dry weight, P accumulation in root and shoot, inorganic P content in leaves, APase in leaves and root exudation under the phosphorus deficiency treatments after 3 d, 8 d and 12 d, and APase in root was analyzed under the phosphorus deficiency treatments after 12d. 【Results】 1)The shoot dry weight was decreased, the root dry weight and root-shoot ratio of maize are significantly increased in the low-P tolerant maize genotypes with elongated treated time from 3 d to 8 d and 12 d in the low-P stress treatment. 2) There are significant differences in P uptakes and utilization efficiencies among different maize genotypes. Three low-P tolerant inbreds of 99239T, 99180T and 99327T have high uptake efficiency and 99186T and 99184T have high P-utilization efficiency, while both the P-sensitive inbreds 99152S and 99270S have low P-uptake and utilization efficiency. 3) The inorganic phosphorus (Pi) contents in leaves of maize are decreased significantly under the low-P stress, but the decreases in the low-P tolerant inbreds 99184T, 99327T and 99239T are less than in 99186T and 99184T under the low P, and the relative Pi contents in the leaves of the former three ones are higher than the latter two. 4) The APase activities in root exudation are increased in the low P level, and the activities in root exudation of the low-P tolerant inbreds, 99184T and 99186T, are higher than in other inbreds. The activities of root secreted APase are positively correlated with the P uptake efficiencies at the 3 and 8 d of low-P stress, and positively correlated with the P utilization efficiencies at the 12 d of low-P stress. These results indicate there are no significant correlations between the APase activities of root secreted and the P uptake and utilization efficiencies. 5) On the 12th day under low-P stress, changes of the root APase activities are consistent with root exudates in all the maize inbreds with the correlation coefficient r=0.755(P0.05). 6) Compared with the normal P treatment, the APase activities in leaves are significantly increased under the low-P treatment, and there are significant differences among seven maize inbreds. The increases of the APase activities in leaves are in order of 99184T and 99239T 99327T and 99186T 99180T, 99270S and 99152S after 8 d under the low-P stress. The APase activities in leaves of all maize inbreds are gradually increased after 12 d under the low-P stress, and the APase activities of 99239T, 99184T, 99327T and 99186T are higher than those of 99270S and 99152S. The APase activities in leaves of maize show no significant correlation with the P uptake and utilization efficiency. There is a significant positive correlation between the APase activity and the relative Pi content in leaves of maize under the P deficient condition. 【Conclusions】 The APase activities in leaves, roots and root exudation of all the tested inbreds are increased in response to the P deficiency. The low-P tolerance are significantly correlated with the APase activities in leaves of maize, but not those in the roots in the low P condition.