Plant lipoxygenases (LOX, EC 1.13.11.12) have been involved in processes such as stress responses and development. The levels of these enzymes and their corresponding mRNAs are modulated during these processes as well as by different effectors such as jasmonic acid (JA), its methyl ester (MeJA) or abscisic acid (ABA). A new lipoxygenase (LOX) cDNA clone, PvLOX2, was isolated from a Phaseolus vulgaris nodule library and used to study the LOX mRNA accumulation pattern in some developmental stages and in plants subjected to hormone and stress treatments. In nodules, LOX mRNA reaches a maximum level around day 14 to 16 after Rhizobium tropici inoculation, as compared with LOX mRNA present in uninoculated and inoculated roots at the same days. LOX antigen is detected in the nodule parenchyma and in the uninfected cells. During germination, bean LOX transcripts start to accumulate 48 h after imbibition, remains at the same level until 72 h after imbibition and then declines. In hypocotyl, LOX mRNA is abundant in the growing region and almost absent in the mature region. After water stress or ABA treatment, this mRNA increases in the mature region and decreases in the growing region. In bean seedlings, LOX mRNA is accumulated in response to some types of stresses such as cold and desiccation. Wounding, MeJA or ABA treatment of mature leaves also induces LOX mRNA accumulation. These results indicate that in common bean plants LOX is required during development and stress conditions.

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Mechanical wounding, infiltration with P. syringae or A. tumefaciens, and exposure to an H(2)O(2)-generating system (Glc/Glc oxidase) induce betacyanin synthesis in red beet (Beta vulgaris) leaves. These conditions also induced the expression of BvGT, a gene encoding a glucosyltransferase (GT) from Beta vulgaris. BvGT has a high similarity to Dorotheanthus bellidiformis betanidin-5 GT involved in betacyanin synthesis. Furthermore, the transient expression of a BvGT antisense construct resulted in the reduction of BvGT transcript accumulation and betanin synthesis, suggesting a role for this gene product in betacyanin glucosylation. In addition, the NADPH oxidase inhibitor, diphenylene iodonium (DPI), inhibited the accumulation of the BvGT transcript in response to infiltration with Agrobacterium tumefaciens. Hence, this result suggests that ROS produced by a plasma membrane NADPH oxidase may act as a signal to induce BvGT expression, necessary for betanin synthesis after wounding and bacterial infiltration.

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