Genotypic Variations in Reproductive Organs of Rice Plants under Heat Stress

Abstract

Global warming is projected to impede significantly the world's rice(Oryza sativa L.) productivity within foreseeable future. In order to obtain a better insight into developing a new rice variety with enhanced tolerance to heat, morphological/anatomical observations were made in reproductive organs of a number of rice cultivars including Korean traditional varieties after subjecting them to heat stress at pollen and flower developmental stage. The measured traits include apical pore size, filament length, lodicules length and width of the floral organ structure, as well as pollen diameter, fertility, viability and grain fertility. We were particularly interested in examining whether the progression of tapetum cell apoptosis in the developing pollen sacs is delayed or accelerated by heat stress, either of which could result in a defective pollen development. Apical pore size showed no correlation to varieties of different heat tolerance, but every variety showed increased apical pore size upon heat treatment. Lodicule width value was slightly increased after heat treatment, which was more apparent in plants treated at just before heading stage than those treated at reduction division stage. Pollen and grain fertility showed similar pattern of decrease upon heat treatment, but the magnitude of decrease was much less in the heat-tolerant varieties as compared with that in the heat-susceptible varieties, in which degeneration of tapetum cell layer was also found more accelerated upon heat treatment. Data obtained from this study could contribute to facilitate our efforts to develop a new heat-tolerant rice variety.