Regulation and subcellular localization of auxin-induced lipoxygenases

Auxin [α-naphthaleneacetic acid (NAA) or indole-3-acetic acid (IAA)] can induce the expression of two lipoxygenases (LOXs) in cultured immature zygotic embryo cotyledons of soybean (Glycine max L.). One of the IAA/NAA-induced LOX isozymes in cultured embryo cotyledons has been demonstrated to be seedling LOX4 (pI 5.09) and another appears to be LOX5 (pI 5.23). The effects of jasmonic acid (JA), methyl jasmonate (MJ), abscisic acid (ABA) and triiodobenzoic acid (TIBA) on the expression of NAA-induced LOXs were investigated in the cultured embryo cotyledons. Among tested plant regulators, only NAA can induce the expression of LOX4 and LOX5, whereas MJ, JA or ABA did not induce LOX expression in the absence of NAA. However combination of NAA with JA significantly increases the expression of NAA-induced LOXs compared with NAA alone. TIBA, an inhibitor of auxin transport, blocks the expressions of the NAA-induced LOXs in the cultured embryos. Immunogold labeling showed that NAA-induced LOXs are located in vacuoles. Our results suggest that auxin may directly or indirectly trigger the expression of soybean seedling LOXs during soybean germination. We also report that seedling LOX4 and/or LOX5 are located in vacuoles.