DROUGHT STRESS Role of Carbohydrate Metabolism in Drought-Induced Male Sterility in Rice Anthers* G. N. Nguyen 1 , D. L. Hailstones 3 , M. Wilkes 2 & B. G. Sutton 2 1 Agricultural Science Institute of Northern Central Vietnam, Vinh City, Nghe An Province, Vietnam 2 Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW, Australia 3 Elizabeth Macarthur Agricultural Institute, NSW Department of Primary Industries, NSW, Australia Introduction Rice (Oryza sativa L.) is very susceptible to water deficit during reproductive phases. The conspicuous injury observed in rice plants exposed to water stress during meiosis of the pollen mother cell is the reduction of grain set, which is attributed to the decline of male fertility (Saini and Lalonde 1998). In spite of much research on drought-induced male sterility in rice, the underlying mechanisms of the problem remain to be identified. Recent results in our laboratory illustrated that water def- icit imposed for three consecutive days at a mild level ()0.5 MPa) caused significant impairment of early micro- spore development (Nguyen and Sutton 2009). Dead microspores were assumed to be caused by rising levels of reactive oxygen species (ROS) in conjunction with a down-regulation of antioxidant systems which later resulted in activation of a programmed cell death (Nguyen et al. 2009). However, there are some other clues indicating the involvement of carbohydrate metabolism in the fate of microspores under abiotic stresses (Saini and Westgate 2000). Abnormally high levels of non-reducing and reducing sugars in rice anthers subjected to water and chilling stress signal a disturbance of sugar metabolism. Of particular concern is the impairment of vacuolar and cell wall acid invertases that are proposed as the cause of energy shortages, in the form of sugars, for developing Keywords drought stress; in situ hybridization; rice anther; sugar metabolism Correspondence Giao Ngoc Nguyen Agricultural Science Institute of Northern Central Vietnam, Vinh City, Nghe An Province, Vietnam Tel.: +84 383 510 055 Fax: +84 383 851 981 Email: g.nguyen@vnn.vn *This article originated from a poster presentation at the American Association of Cereal Chemistry (AACC) International Annual Meeting, Hawaii, USA, September 21–24, 2008. Accepted February 25, 2010 doi:10.1111/j.1439-037X.2010.00423.x Abstract Rice plants exposed to three consecutive days of water stress ()0.5 MPa) show a reduction in male fertility and grain set, which is attributed to increased lev- els of reactive oxygen species (ROS) and activation of a programmed cell death. This current research was conducted to further investigate the association of sugar metabolism with microspore abortion in rice anthers. Biochemical assays showed that sucrose, glucose and fructose contents were found to be signifi- cantly increased in anthers from water stressed plants compared with the con- trol. qRT-PCR analyses and in situ hybridization of metabolic genes (sugar transporters, invertase and phosphotransferase/kinases) demonstrated that the supply of sugars for developing microspores and the initial steps of sugar utili- zation e.g. glycolysis, were not repressed. However, it appears that the accumu- lation of sugars in stressed anthers might involve a reduction of mitochondrial activity during the tricarboxylic acid cycle, which could result in excessive pro- duction of ROS and a depletion of the ATP pool. These results also suggest that higher levels of sugars at all stages of anther development seemed to be associated with some measure of protection to the anthers against oxidative stress. Induced expression of sugar transporter genes might have maintained the high levels of sugar in the tapetum and the locules, which alleviated oxi- dant damage caused by excessive ROS generation. Thus, the increased level of sugars might potentially be a natural response in providing protection against oxidant damage by strengthening the antioxidant system in anthers. J. Agronomy & Crop Science (2010) ISSN 0931-2250 346 ª 2010 Blackwell Verlag GmbH, 196 (2010) 346–357