A Comparative Molecular-Physiological Study of Submergence Response in Lowland and Deepwater Rice

Abstract

Survival of rice (Oryza sativa) upon an extreme rise of the water level depends on rapid stem elongation, which is mediated by ethylene. A genomic clone (OS-ACS5) encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, which catalyzes a regulatory step in ethylene biosynthesis, has been isolated from cv IR36, a lowland rice variety. Expression was induced upon short-and long-term submergence in cv IR36 and in cv Plai Ngam, a Thai deepwater rice variety. Under hypoxic conditions, abscisic acid and gibberellin had a reciprocal opposite effect on the activity of OS-ACS5. Gibberellin up-regulated and abscisic acid down-regulated OS-ACS5 mRNA accumulation. Growth experiments indicated that lowland rice responded to submergence with a burst of growth early on, but lacked the ability to sustain elongation growth. Sustained growth, characteristic for deepwater rice, was correlated with a prolonged induction of OS-ACS5. In addition, a more pronounced capacity to convert ACC to ethylene, a limited ACC conjugation, and a high level of endogenous gibberellin 20 were characteristic for the deepwater variety. An elevated level of OS-ACS5 messenger was found in cv IR36 plants treated with exogenous ACC. This observation was concomitant with an increase in the capacity of converting ACC to ethylene and in elongation growth, and resulted in prolonged survival. In conclusion, OS-ACS5 is involved in the rapid elongation growth of deepwater rice by contributing to the initial and long-term increase in ethylene levels. Our data also suggest that ACC limits survival of submerged lowland rice seedlings.

Submergence tolerance conferred by Sub1A is mediated by SLR1 and SLRL1 restriction of gibberellin responses in rice

“…2). Consistent with our results, submergence reduced the endogenous ABA content to a similar extent within 1 day in seedlings of both deepwater and submergence-intolerant lowland rice (20). This shows that the tolerance of prolonged inundation provided by Sub1A is mediated downstream of ABA catabolism and upstream of GA responses.…”

Epidermal Cell Death in Rice Is Regulated by Ethylene, Gibberellin, and Abscisic Acid

“…GA 1 is the major bioactive GA in rice (Kobayashi et al, 1989). A similar increase in GA levels was shown to occur in rice seedlings upon submergence (Van Der Straeten et al, 2001), indicating that the hormonal change was neither restricted to the adult stage nor to one particular stem part at that stage. Even though data on endogenous GA levels in nodes of adult plants are missing, we showed that a specific set of epidermal cells and adventitious roots at the nodes are competent to respond to elevated GA levels in the presence of ethylene.…”

“…Submergence causes accumulation of ethylene, a decrease in ABA, and an increase in bioactive gibberellic acids (Hoffmann-Benning and Kende, 1992;Azuma et al, 1995;Van Der Straeten et al, 2001). The alteration in GA to ABA balance is induced by submergence in seedlings (Van Der Straeten et al, 2001) as well as in adult deepwater rice plants (HoffmannBenning and Kende, 1992). It can also be brought about by application of ethylene (Hoffmann-Benning and Kende, 1992), indicating that ethylene may be responsible for these changes in GA and ABA levels.…”

Examination of two lowland rice cultivars reveals that gibberellin-dependent early response to submergence is not necessarily mediated by ethylene

“…It is known that in the case of deepwater rice stem elongation under submergence is due to the increase of ethylene content in the tissues (due to less diffusion under water but also to enhanced new synthesis), [2][3][4]12 that stimulates GA biosynthesis. A similar conclusion was obtained in the case of the tall lowland rice cultivar IR36.…”

“…A similar conclusion was obtained in the case of the tall lowland rice cultivar IR36. 4 We therefore investigated whether ethylene was also active in enhancing lowland rice seedling elongation of the Bomba and Senia cultivars. Interestingly, while Bomba seedling elongated in response to ethylene or 1-aminocyclopropane-1-carboxylic-acid (ACC; an ethylene precursor) application, as expected, Senia seedlings did not.…”