Effect of ethylene and culture environment on rice callus proliferation

Modifications to the gaseous envelope by callus during culture in Petri dishes were shown to reduce growth and promote necrosis of several rice (Oryza sativa L.) cultivars. Incubating callus under a continuous flow of gas mixtures of known composition suggested that the inhibition of growth was caused by the accumulation of ethylene, the depletion of oxygen and, to a lesser extent, the accumulation of carbon dioxide. In order to evaluate the importance of ethylene accumulation aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-carboxylic acid (ACC) and silver nitrate (AgNO3), were added to the nutrient medium and ethylene measurements performed during callus culture. Ethylene restricted callus growth particularly under high (35 degrees C) as compared to moderate (25 degrees C) temperatures and under illuminated as compared to darkened incubation. Under illuminated incubation at 25 degrees C AVG (5 mmol m(-3)) and AgNO3 (50 mmol m(-3)) significantly improved callus growth (100 and 60%, respectively) while ACC (200 mmol m(-3)) significantly decreased growth (40%). AVG and AgNO3 were less effective under dark incubation at 25 degrees C where ethylene production was lower. Furthermore, callus growth was significantly better in large as compared to small culture vessels since the ethylene concentration was diluted and more oxygen was available for respiration. Better control of ethylene and increased oxygen availability could be a way of producing healthy callus for the formation of embryogenic tissues of otherwise recalcitrant cultivars of rice (e.g. Indica IR42) and may be a way of improving manipulation of other cereal species