Changes in OsXTH gene expression, ABA content, and peduncle elongation in rice subjected to drought at the reproductive stage.

Drought stress causes yield loss in rice by inhibiting panicle exsertion which is driven by peduncle elongation near flowering. To elucidate the mechanism of peduncle elongation, we examined the drought sensitivity of corresponding genes encoding xyloglucan endotransglycosylase/hydrolase (XTH), a cell wall-loosening enzyme essential for cell elongation in the peduncle elongation zone at heading stage. When drought was imposed 6 days before heading, peduncle elongation rate (PER) was inhibited significantly at heading and 1 day after heading. Eleven OsXTH genes were isolated and their expression in rice peduncle determined. The expression of 11 OsXTH genes showed different patterns of response to drought stress. OsXTH3 was completely suppressed by drought. Transcript levels for OsXTH19, -20, -24, -27 and -28 genes were markedly down-regulated at a series of drought stresses. By contrast, OsXTH5 was up-regulated. Also, the behavior of leaf gas exchange and peduncle abscisic acid (ABA) level was determined under drought conditions. The results indicated that stomatal conductance was 83% lower than that in control plants and peduncle ABA increased ninefold with drought stress. Peduncle ABA content correlated highly with leaf stomatal conductance and PER (r = 0.85** and 0.88**). The expression in OsXTH5, -19, -20, -24 and -28, corresponded to changes in PER and ABA. We conclude that ABA could be involved in inducing the retardation of PER and changes of expression of OsXTH genes. OsXTH5, -19, -20, -24 and -28 genes may play a role in rice peduncle elongation. In addition, interactions among genes may affect PER under drought.