Relationship of Ethylene Production to Elongation in Deepwater Rice¹

There is a need to unravel mechanisms controlling elongation and submergence tolerance in rice ( Oryza sativa L.) and to develop technology for improving rice for deepwater regions. Because of the reported involvement of ethylene in stem internode elongation of deepwater rice, we examined the relationship of seedling elongation to ethylene production. Fourteen rice cultivars/breeding lines with widely ranging differences in elongating capacity in deepwater were used in these studies. Ethylene production by intact 20 to 27‐day‐old seedlings was determined by submergence in 122 ✕ 6‐cm glass cylinders and related to leaf blade/sheath elongation. The floating rice, ‘TCA 177’, elongated largely by the leaf sheath supporting the youngest leaf. The elongating capacity of the rice seedling resided in the top two leaf blades and their sheaths. Elongation decreased with the duration of submergence and after 72 h little increase occurred. A 24‐h submergence enhanced the capacity of the seedlings to produce ethylene and the production was highest during the first hour after removal from water. Complete submergence caused greater production of ethylene than partial submergence. The capacity for ethylene production and elongation peaked at 24 to 36 h of complete submergence and then declined. Ethylene production following submergence generally followed the order: floating rice > deepwater rice > elongating modern cultivar > nonelongating modern cultivar. Elongation index correlated well ( r = 0.88**, significant at the 0.01 probability level) with ethylene producing capacity of seedlings in a population of 14 rice cultivars/breeding lines. The results show that ethylene production by young rice seedlings, following complete submergence, is a good measure of their elongating ability.