Influence of Temperature Stress on in Vitro Fertilization and Heat Shock Protein Synthesis in Maize (Zea mays L.) Reproductive Tissues

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Abstract
This study was conducted to investigate the response of maize (Zea mays) male and female mature reproductive tissues to temperature stress. We have tested the fertilization abilities of the stressed spikelets and pollen using in vitro pollination-fertilization to determine their respective tolerance to stress. The synthesis of heat shock proteins (HSPs) was also analyzed in male and female tissues using electrophoresis of 35S-labeled proteins and fluorography, to establish a relationship between the physiological and molecular responses. Pollen, spikelets, and pollinated spikelets were exposed to selected temperatures (4, 28, 32, 36, or 40.degree. C) and tested using an in vitro fertilization system. The fertilization rate is highly reduced when pollinated spikelets are exposed to temperatures over 36.degree. C. When pollen and spikelets are exposed separately to temperature stress, the female tissues appear resistant to 4 hours of cold stress (4.degree. C) or heat stress (40.degree. C). Under heat shock conditions, the synthesis of a typical set of HSPs is induced in the female tissues. In contrast, the mature pollen is sensitive to heat stress and is responsible for the failure of fertilization at high temperatures. At the molecular level, no heat shock response is detected in the mature pollen.