呼吸活性的下降可解释水分亏缺对银合欢根瘤固氮酶活性的抑制(英)

在温室条件下研究了水分亏缺对银合欢根瘤的水分关系、固氮酶活性（乙炔还原活性）、呼吸活性以及蔗糖代谢有关酶活性的影响。随着土壤含水量的下降，根瘤水势也相继下降。土壤干旱不但显著地抑制了根瘤乙炔还原的活性，而且对根瘤的呼吸活性、ATP的产生以及催化蔗糖降解的碱性转化酶和蔗糖合成酶的活性也具强烈的抑制作用。然而，根瘤可溶性总糖含量则不受土壤干旱的影响。用呼吸抑制剂DNP处理根瘤后，其固氮酶活性、呼吸活性及ATPI含量都受到极显著的抑制。这都表明，水分胁迫对根瘤呼吸活性及ATP产生的抑制可解释干旱条件下固氮酶活性的下降。

Inhbition of Respiratory Activity may be Responsible for the Lowering of Nitrogenase Activity of Water-stressed Leucaena leucocephale Nodules

The effects of soil drying on water relations, nitrogenase activity (measured as acetylene reduction activity), respiration activity and sucrose metabolism of Leucane leucocephala nodules were investigated under greenhouse condition. Water potential of nodules decreased steadily with increasing soil water deficit. Soil drying had a substantial inhibitive effect on acetylene reduction achvity (ARA) of nodules meased with an open-flow gas exchange system, so did the respiration rate and ATP content of nodules. Both alkaline invertase and sucrose synthase activities decreased significantly after the imposition of soil drying, which could explain the increase in sucrose concentration at the early stage of soil drying Nevertheless, the total soluble sugar content in nodules on drought-treated plants showed no obvious difference from that in nodules on well-watered plants, indicating that soil drought lowers the nitrogen fixation activity through the lowering of the respiratory activities, which diminishes the supply of energy by respiration in the form of ATP. This deduction was substantiated in an experiment with detached nodules. Respiration the and ATP content of nodules isolated from well-watered L. leucocephala plants decreased sigificantly after treatment with DNP, a respiratory inhibitor, for 30 min, so did the ARA. These results suggest that it may be through the decrease in respiration rate and thereby that in the supply of ATP that drought stress inhibits ARA of nodules.