Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2006
Publication Date: 3/31/2007
Citation: Matsumoto Brower, T.K., Tsumura, T., Zee, F.T. 2007. Exploring the mechanism of potassium chlorate induced flowering in dimocarpus longan. Acta Horticulturae 738 pg. 451 - 457. Interpretive Summary: Potassium chlorate is able to induce flowering of longan trees regardless of season. Previous work on other plants have shown that chlorate is reduced by nitrate reductase to chlorite and hypochlorite by nitrate reductase. To determine if chlorate, chlorite and hypochlorite reduce nitrate reductase activity and induce longan flowering we treated longan plants with chlorate, chlorite and hypochlorite and monitored nitrate reductase activity. All of the trees treated with chlorate, chlorite and hypochlorite had reduced levels of nitrate reductase activity and flowered. The addition of nitrate to hypochlorite further reduced nitrate reductase activity but did not have an additive effect on flowering. The carbon to nitrogen ratio and ammonium nitrogen were not altered in the untreated and potassium chlorate treated trees indicating that the reduction of nitrate reductase may have alternative pathways or is possible not involved in potassium chlorate induced flowering in longan.
Technical Abstract: Flowering is vital stage of plant development since it is the precursor to fruit and seed production as well as the vehicle for genetic improvement by breeding. Understanding flower induction in tree crops is often difficult since trees are a long-term perennial crop that is subject to environmental and cultural changes over multiple seasons of growth. Unlike temperate fruit trees, where growth, dormancy and break of dormancy is determined by the seasons; sub-tropical and tropical fruit trees rely on more subtle changes in rainfall, temperature or nutrient availability. The discovery of potassium chlorate induced flowering in longan has provides an excellent opportunity to investigate the mechanism of flowering in longan. Preliminary experiments suggest that chlorate inhibits nitrate reductase activity in longan trees treated with potassium chlorate however, there is no significant difference in the total nitrogen and carbon:nitrogen ratio content in potassium chlorate treated and untreated trees. In addition to potassium chlorate, sodium chlorite and sodium hypochlorite are also able to effectively decrease nitrate reductase activity and induce flowering of longan trees. To identify genes that may be involved in potassium chlorate induced flowering we created a suppressive subtractive hybridization (SSH) library to longan cDNAs that are differentially expressed in vegetative buds or floral buds induced by potassium chlorate.