Ethylene inhibitors improve dry matter partitioning and development of late flowering spikelets on rice panicles

Abstract

Primary branch development of the rice panicle was in the order of a basipetal sequence from the top to the bottom at the time of anthesis. Delayed development of spikelets on the proximal branches of the panicle resulted in reduced grain filling. Two experiments were carried out to manipulate growth and development of the proximal spikelets with exogenous application of chemicals regulating formation or action of ethylene. In the first experiment, inhibitors of ethylene synthesis (cobalt) and action (silver) improved grain biomass and specific gravity of the basal spikelets, while 2-chloroethylphosphonic acid (CEPA) depressed these parameters significantly. In the second experiment, the ethylene synthesis inhibitor 1-aminoethoxyvinylglycine (AVG) promoted spikelet development on the basal primary branches and improved their survival and grain biomass. On the contrary, the ethylene precursor 1-aminocyclopropane-1- carboxylic acid (ACC) inhibited growth and development of these spikelets. The action of AVG was reversed when ACC was applied in combination with AVG. In both experiments, the chemicals did not influence growth and development of the superior spikelets on the apical primary branches of the panicle. Depression of growth and development by CEPA or ACC coincided with a concomitant rise in soluble carbohydrate concentration of the spikelets, whereas treatments with ethylene inhibitors decreased the concentration of the materials. The role of ethylene in metabolic dominance of the apical spikelets and its impact on grain yield of rice panicles is discussed.