Environmental Parameters Affecting Dark Response of Rice Seedlings (Oryza sativa L.) to Triacontanol

Triacontanol applied to IR-8 rice (Oryza sativa L.) seedlings in nutrient solution caused an increase in dry weight during a 6-hour dark period. This increase was altered by atmospheric CO(2) and O(2) concentrations. The largest growth response occurred from 200 to 350 muliters/liter CO(2) with 5% O(2). The treated seedlings did not fix atmospheric CO(2) in the dark, and the immediate products of photosynthesis were not involved in the dry weight increase. The growth response was characterized by an increase in soluble and insoluble Kjeldahl-N, and soluble carbohydrates. The response curve for dry weight increase was a linear function of log presentation time of triacontanol. The response exhibited an apparent K(dose) of 25 minutes in 10 mug/liter triacontanol in the dark and 18 minutes in the light. Concentrations of 50 mug/liter and higher inhibited growth.