Gaseous factors involved in the enhanced elongation of rice coleoptiles under water

Abstract

Abstract. Elongation responses of intact coleoptiles of rice ( Oryza sativa L. ev. Sasanishiki) explants to various gases were examined under submerged conditions in continuously flowing gas‐saturated incubation media. Reduced O 2 tension (hypoxia). CO 2 and especially C 2 H 4 significantly stimulated coleoptile elongation; the optimal concentrations of O 2 , CO 2 and C 2 H 4 when applied singly were 0.07 m 3 m ‐3 , 0.10 m 3 m ‐3 , and 3 cm 3 , respectively. However, in addition to these gases other as yet unknown factors were involved in the enhanced elongation of rice coleoptiles under water. The actions of CO 2 and C 2 H 4 , unlike that of hypoxia, were accompanied by increases in dry weight of the coleoptiles. The effect of C 2 H 4 occurred independently of O 2 concentrations, whereas that of CO 2 occurred above 0.08 m 3 m ‐3 O 2 . Maximum elongation of rice coleoptiles under submerged conditions was obtained when the flowing medium was saturated with a gas mixture containing 0.10 m 3 m ‐3 O 2 , 0.10 m 3 m ‐3 CO 2 and 10 cm 3 m ‐3 C 2 H 4 , greatly surpassing elongation in static media. However, elongation in static media was greater than that in a closed atmosphere. The intercellular C 2 H 4 concentration in explants growing in static media was higher than that in a closed atmosphere. These results showed that the coleoptile elongation of rice seedlings under water may be regulated by the accumulation of CO 2 and C 2 H 4 in and around the seedlings under hypoxic conditions.