Effects of lipoxygenase on the corm formation and enlargement in Gladiolus hybridus

To investigate the effects of lipoxygenase (LOX1) on the corm formation and enlargement in Gladiolus hybridus, the field and in vitro researches were conducted to detect the growth and development course, the LOX1 activity, the contents of endogenetic methyl jasmonate (MJ), sucrose, starch and cellulose, as well as LOX isozymes and the expression of its genes in 'Rose Supreme' and 'Advanced Red'. The field investigation showed that the highest activities of LOX1 activity and MJ content in stolons, but not detected in leaves, which were higher in 'RS' than in 'AR'. And the contents of sucrose, starch and cellulose in corm and cormels showed different increase during growth and development of Gladiolus corm. The in vitro investigation showed that the salicylhydroxamic acid (SHAM) treatment caused obviously delayed corm formation. decrease of fresh weight and diameter, and percentage of corm formation; reduced contents of total dissoluble protein, MJ and carbohydrates, and LOX1 activity. Additionally the activity of LOX isozymes became weaker, with two isozyme bands disappeared. In contrast, these physiological and biochemical indexes were increased under MJ treatment. RT-PCR also demonstrated that the expression of LOX1 gene was inhibited under SHAM treatment, induced under MJ treatment. These results suggested that LOX1 might regulate the growth and development of Gladiolus corm through affecting JAs biosynthesis cycles, and then resulting in carbohydrate accumulation. The corm formation could be improved by MJ, but suppressed by SHAM, in which, MJ 0.5 mmol/L was the optimum concentration for promoting corm formation and enlargement in Gladiolus. (c) 2008 Elsevier B.V. All rights reserved.