Regulation of Submergence-induced Enhanced Shoot Elongation in Oryza sativa L.

Rice (Oryza sativa L.) is the only cereal that can be cultivatedin the frequently flooded river deltas of South-East and SouthAsia. The survival strategies used by rice have been studiedquite extensively and the role of several phytohormones in theelongation response has been established. Deep-water rice cultivarscan diminish flooding stress by rapid elongation of their submergedtissues to keep up with the rising waters. Other rice cultivarsmay react by mechanisms of submergence tolerance. Aerenchymaand aerenchymatous adventitious roots are formed that facilitateoxygen diffusion to prevent anaerobic conditions in the submergedtissues. This paper discusses the molecular aspects of the mechanismthat leads to shoot elongation (leaves of seedlings and internodes),the regulation of which involves metabolism of, and interactionsbetween, ethylene, gibberellins and abscisic acid. Finally,the importance of new techniques in future research is assessed.Current molecular technology can reveal subtle differences ingene activity between tolerant and non-tolerant cultivars, andidentify genes that are involved in the regulation of submergenceavoidance and tolerance.