Influence of 9-β-l(+)-adenosine on malate dehydrogenase activity in rice

The activity of malate dehydrogenase (MDH, EC 1.1.1.37) in rice ( Oryza sativa L. cv. California M-201) roots was increased within 25 min by a foliar application of 37 n M of 9-β- l (+)-adenosine [ l (+)-adenosine]. A similar concentration of 9-β- d (-)-adenosine [ d (-)-adenosine] did not affect MDH. Triacontanol (2.7 n M ) which elicits l (+)-adenosine in plants also increased MDH activity in roots of rice seedlings. whereas neither octacosanol nor a mixture of equimolar concentrations of triacontanol and octacosanol had any effect on MDH activity. l (+)-Adenosine increased MDH activity of rice seedlings grown at 10.20 and 40°C. The effect was measurable 24 h after application at 10 and 20°C, but not 6 h after treatment at 40°C. Ninety minutes after l (+)-adenosine was applied to the foliage of plants grown at 10, 20 and 40°C, MDH activity in the roots was 40, 30 and 9% more, respectively, than in the untreated controls. The concentration of water soluble protein was also increased by l (+)-adenosine and was positively correlated with MDH activity. When measured 90 min after application of l (+)-adenosine at different times of day, MDH activity and dry weight were increased most when l (+)-adenosine was applied 9 and 12 h after the lights came on in a 16-h photoperiod. The optimum light intensity for the response of rice to l (+)-adenosine, as measured by MDH activity, was 450 μmol m⁻² s⁻¹.