Compatibility of glycinebetaine in rice plants: evaluation using transgenic rice plants with a gene for peroxisomal betaine aldehyde dehydrogenase from barley

Glycinebetaine is synthesized in plants by the two-step oxidation of cholin e, with betaine aldehyde as the intermediate. The reactions are catalyzed b y choline mono-oxygenase and betaine aldehyde dehydrogenase. Rice plants, w hich do not accumulate glycinebetaine, possess a gene encoding betaine alde hyde dehydrogenase, whose activity is detectable at low levels. To evaluate the compatibility in rice of glycinebetaine on growth and tolerance to sal t, cold and heat, we produced transgenic rice plants by introduction of a c DNA for betaine aldehyde dehydrogenase of barley, which is localized in per oxisomes unlike the chloroplast-specific localization of betaine aldehyde d ehydrogenase in spinach and sugar beet. The transgenic rice plants converte d high levels of exogenously applied betaine aldehyde (up to 10 mol m(-3)) to glycinebetaine more efficiently than did wild-type plants. The elevated level of glycinebetaine in transgenic plants conferred significant toleranc e to salt, cold and heat stress. However, very high levels of glycinebetain e, resulting from conversion of applied betaine aldehyde to glycinebetaine or from exogenous application, inhibited increases in length of rice plants but not increases in dry weight. Our results suggested that the benefits o f accumulation of glycinebetaine by rice plants might be considerable under high light conditions.