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

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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 O2 tension (hypoxia). CO2 and especially C2H4 significantly stimulated coleoptile elongation; the optimal concentrations of O2, CO2 and C2H4 when applied singly were 0.07 m3 m‐3, 0.10 m3 m‐3, and 3 cm3, 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 CO2 and C2H4, unlike that of hypoxia, were accompanied by increases in dry weight of the coleoptiles. The effect of C2H4 occurred independently of O2 concentrations, whereas that of CO2 occurred above 0.08 m3 m‐3O2. Maximum elongation of rice coleoptiles under submerged conditions was obtained when the flowing medium was saturated with a gas mixture containing 0.10 m3 m‐3 O2, 0.10 m3 m‐3 CO2 and 10 cm3 m‐3 C2H4, greatly surpassing elongation in static media. However, elongation in static media was greater than that in a closed atmosphere. The intercellular C2H4 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 CO2 and C2H4 in and around the seedlings under hypoxic conditions.