Abstract
In this work, the changes in ACh-hydrolyzing activity and ACh content in plant tissues of Macroptilium atropurpureum cv. Siratro following leaf wilting and leaf recovery after heat stress and the effects of exogenous ACh, K+ or Ca2+ on detached and heat-stressed leaves to which the primary pulvinus was still attached were determined. The ACh-hydrolyzing activity was 75 nM ACh mg-1 dry weight in the primary pulvinus and 46 nM ACh mg-1 dry weight in the secondary pulvinus, and was 4∼12 fold higher than found in the leaf, petiole, stem or root. Heat stress increased the ACh-hydrolyzing activity about 4 fold and 2 fold in the primary and secondary pulvini, respectively. The ACh-hydrolyzing activity was inhibited about 96% by neostigmine bromide. The content of ACh in the primary and secondary pulvini also changed dramatically within 3 min after heat stress. The changes of ACh content and ACh-hydrolyzing activity in plant tissues were then found to be correlated with leaf drooping and leaf recovery. Additionally, the application of ACh together with K+ or Ca2+ salts remarkably enhanced leaf recovery from wilting in detached and heat-stressed primary pulvinus leaves. The results suggest that ACh may control ion or hormone fluxes regulating the opening of ion channel in pulvini.
