Osmoregulation in Rice Coleoptile Elongation as Promoted by Cooperation between IAA and Ethylene

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IAA-induced elongation of rice (Oryza sativa L. cv. Sasanishiki) coleoptiles is regulated by cooperation between IAA and ethylene produced in response to IAA. However, the presence of some solutes, such as K^+, Na^+, Rb^+, glucose and sucrose, in the incubation media was found to be indispensable for this cooperation. Without those solutes, the IAA-induced elongation was not sustaincd over a long time period. IAA caused increases in both the osmotic potentials of the coleoptile cells and the extensibility of their cell wall. In epidermal cells of IAA-treated coleoptiles, the osmotic potential increased from -0.87 to -0.62 MPa during a 4-h incubation with 1 mM KCl. More-over, IAA promoted the uptake of K^+ or Na^+ from the media into the coleoptiles. However, these effects of IAA were partially prevented by aminoethoxyvinylglycine (AVG), and all the AVG effects were completely nullified by ethylene applied simultaneously and exogenously. Both IAA and ethylene did not affect the wall yield stress. These results suggested that the long-term elongation induced by IAA in rice coleoptile segments results from inhibiting increases in osmotic potentials of their cells. The maintenance by IAA of low osmotic potentials may be partly due to the promotive action of ethylene produced in response to IAA on the solute uptake from the media.
日本植物生理学会の論文