Low levels of oxygen promote internodal elongation in floating rice independently of enhanced ethylene production

Submergence induces rapid elongation of internodes in floating rice (Oryza sativa L. cv. Habiganj Aman II). The initial signal for such internodal elongation has been considered to be the reduced partial pressure of oxygen in submerged internodal cavities, which promotes the elongation of internodes through the enhancement of ethylene synthesis. We examined the relationship between low oxygen pressure and ethylene production in the rapid elongation of floating rice internodes using ethylene biosynthesis inhibitors, aminooxyacetic acid (AOA) and CoCl2 When floating rice stem segments were incubated in an atmosphere of low O-2 internodal elongation accelerated and ethylene production increased. However, in stem segments treated with AOA or CoCl2 low O-2 still stimulated the elongation of internodes although the ethylene production by the internodes was less than by those in control stem segments where internodal elongation was not promoted. These results indicate that low O-2 is capable of causing rapid elongation of internodes of floating rice independently of enhanced production of ethylene. In addition to low O-2 submergence, ethylene and gibberellic acid each enhanced the production of ethylene by internodal tissues, suggesting that enhanced ethylene production is a common phenomenon accompanied by the acceleration of internodal elongation in floating rice.