Regulation of NPA and ACC on H2O2-Induced Pea Primary Horizontal Bending Root

Existing reports have described a notable fact that 1-naphthylphthalamic acid (NPA) coupled with 1-aminocylopropane-1-carboxylic acid (ACC), a precursor of ethylene, can regulate gravitropism of pea primary root by altering the volume of indole-3-acetic acid (IAA) and gibberellin A3 (GA3) in the root. However, the mechanism behind this is not quite clear. In this study, various concentration setups of NPA and ACC were used during cultivation of pea seeds (exposed to H2O2) to study the effect of NPA and ethylene on contents of IAA and GA3 in curving pea primary roots. Results showed that generally the horizontal bending of pea primary roots induced by H2O2 could be alleviated by NPA and ACC. Alpha-amylase activity in pea primary roots declined gradually with the rise of NPA and ACC concentrations, consequently boosting the content of starch while reducing the content of soluble sugar. ACC instigated the ethylene triple response. In addition, IAA content in primary roots declined gradually with the rise of NPA concentration, but GA3 content did not show any consistent fluctuation. The inhibition of NPA on IAA polar transport in pea was only effective in primary roots, with no effect on the IAA transport from bud to other parts.