Fragrance in rice has been shown to result from deletions that cause the loss of function of betaine aldehyde dehydrogenase 2 (BADH2). In many plant species, BADHs play a role in abiotic stress tolerance; in some plants the mechanism by which this occurs is the accumulation of glycinebetaine (GB) from betaine aldehyde. However, rice does not accumulate GB. Rice BADH2 has only moderate activity on betaine aldehyde, with much higher activity on gamma aminobutyraldehyde (GABald). It has been proposed that the primary role of rice BADH2 in vivo is the metabolism of gamma-amino butyric acid (GABA) from GABald. Gamma-amino butyric acid has been shown to perform a range of roles in plants, including assisting in the response to abiotic stress. Recently it has been shown that non-fragrant rice lines with specifically inhibited BADH2 are more susceptible to salt stress than wild type with normal BADH2 expression. This strongly suggests that BADH2 has a role in protecting rice from the effects of salt. To investigate whether cultivated fragrant rice varieties are less tolerant of salt than cultivated non-fragrant rice varieties due to the absence of functional BADH2, the growth to harvest of fragrant and non-fragrant rice plants under salt treatment was observed in a glasshouse-scale experiment. A highly statistically significant difference in the ability of rice plants to produce mature seed under salt treatment was observed between the fragrant and non-fragrant groups. On average, greater than 99% inhibition of mature seed production for fragrant rice plants exposed to 22 mM salt solution (from 11 weeks post-planting) was observed, which is a greater salt sensitivity than previously reported for any rice genotype. These results suggest that human preference for the desirable aroma of fragrant rice has selected plants with salt sensitivity.
Fitzgerald, TL, Waters, DLE, Brooks, LO & Henry, RJ in press, 'Fragrance in rice (Oryza sativa) is associated with reduced yield under salt treatment', Environmental and Experimental Botany, vol. 68, no. 3, pp. 292-300.
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