Primary Investigation On The Effects Of EATP On Root Gravitropism In Arabidopsis Thaliana And Its Possible Mechanism

Gravitropism is a process that dictates the growth of plant organs along a special vector related to gravity, involving many aspects of plant growth. Gravitational stimuli generally is perceived by the columella cells in the root cap, through the sedimentation of amyloplasts, the signals of gravitational stimuli can be translated into the intracellular secondary signals, such as calcium signaling, cytoskeletal and so on. As a new extracellular signal, extracellular ATP (eATP) is receiving a growing concern. In this study, we discussed whether the extracellular ATP plays a role in plant gravitropism and also how does it realize this effect.We chose Arabidopsis heterotrimeric G protein mutants, null mutant of NADPH Oxidase, NO-associated protein as materials. By observing the changes of curvature of root cap and using CLSM to detect the morphological changes of cells in root tip, the effects of eATP on root gravitropism in Arabidopsis thaliana had been investigated. The results showed that:Two wild-types of Arabidopsis which had been treated by eATP had lost their gravitropism and the root tip began to grow along horizontal direction.Some reagents can also impair root gravitropism. Choose certain concentration of Ba²⁺ treatment impaired gravitropism of col ecotype, similarly to eATP. TEA has no effect on root gravitropism. We added certain concentration of Ba²⁺/ TEA to the medium which contained eATP, the results showed that neither Ba²⁺ nor TEA could reduce the inhibition of eATP on root gravitropism. Therefore it was supposed that potassium channel may not play a role in eATP-mediated signal transduction on root gravitropism.Calcium plays a significant role in plant growth, and it is also an important intracellular signaling molecules. In this research, we added certain concentration of EGTA to the medium which contained ATP, and found that EGTA can reduce the inhibition of eATP on root gravitropism. This further indicated that Ca²⁺ may play a role in eATP-mediated signal transduction on root gravitropism.In search of other possible components which may involve in the pathway of eATP-mediated signal transduction on root gravitropism, we made further investigations. By using Arabidopsis heterotrimeric G protein mutants, null mutant of NADPH Oxidase, NO-associated protein, we found that eATP can inhibit root gravitropism of all these mutant strains. It was indicated that eATP may influence other metabolism of the plant which related with root gravitropism.In order to study about the relationship between H+ -ATPase and gravitropism, we used Columbia as the material,and the results demonstrated that the appropriate concentration of Na₃VO₄ can relieve the inhibition of eATP on root gravitropism. This relust implied that H+-ATPase may play a regulatory role in the pathway of eATP-mediated signal transduction on root gravitropism.By using CLSM to detect the cell morphous of the bending part of root where had been treated by eATP, the result was different from the reference group. The lengths of the upperside and lowerside cells in the bending parts of elongation zones were almost the same in the experimental group, and in the reference group, the lengths of upperside cells were much longer than the lowerside (relative to the gravity vector).These results suggested that eATP could inhibit root gravitropism of Arabidopsis thaliana as a extracellular messenger, and Ca²⁺ and H+-ATPase played an important role in eATP-mediated signal transduction on root gravitropism. The effect of heterotrimeric G protein, NADPH Oxidase, NO-associated protein was not significant in the pathway of eATP-mediated signal transduction on root gravitropism.