Injury to Rice Plants Caused by Complete Submergence; A Contribution by Ethylerie (Ethene)

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Abstract
Complete submergence of rice plants (Oryza sativa L. cv. ‘IR42’) in dilute nutrient solution for 3–6 d almost stopped the accumulation of dry matter, depressed soluble carbohydrate concentration by over 75% and promoted chlorosis in fully expanded leaves. Increase in fresh weight by the shoots was not impaired. Extension by the youngest visible leaf was stimulated. Extension by the next leaf to appear was retarded by submergence. These growth responses to submergence were associated with a 1-5-fold increase in the partial pressure of endogenous ethylene (ethene). Applying ethylene (0.3–0.35 Pa) in the gas-phase to non-submerged plants reproduced some, but not all, of these effects of submergence. Thus, greater leaf extension and chlorosis of submerged plants could be attributable to accumulated ethylene but neither the slow relative growth rate nor the decreased extension of leaves emerging after the start of submergence could be so attributed. Two cultivars (‘FR13A’ and ‘Kurkaruppan’) already known to tolerate submergence, differed little from submergence-intolerant ‘IR42’ in their relative growth rate and soluble carbohydrate concentration during submergence. However, their underwater leaf extension was less than in ‘IR42’ and chlorosis was much less prevalent, especially in ‘FR13A’. Similarly, ethylene supplied to non-submerged plants was a less effective promotor of leaf extension and chlorosis in the two submergence tolerant cultivars. Application of 1.0 kPa carbon dioxide in the gas-phase prevented the chlorosis response to ethylene. The results indicate that accumulated ethylene is a likely cause of fast leaf extension and chlorosis in submergence intolerant forms of rice, particularly when amounts of dissolved carbon dioxide are minimal.