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Photocontrol of Peanut (Arachis hypogaea L.) Embryo and Ovule Development in Vitro

Smithsonian Environmental Research Center, Rockville, Maryland 20852-1773, Faculty of Agriculture, Hebrew University, Jerusalem, Rehovot 76100, Israel

The purpose of the present study was to determine the nature of the photoreceptor that controls the light-dependent development of the peanut ovule and embryo, and to determine whether this photoreceptor activity is located in the ovular or the embryonic tissue. Peanut ovules were aseptically excised from surface sterilized gynophores (pegs) and cultured in darkness, continuous far red (FR), or given 15 minutes daily irradiations with white (W), red (R), blue (B); FR, R/FR, FR/R light for 21 days. Increases in the volume of ovules cultured in dark, continuous FR, FR, or R/FR were significantly greater than for ovules cultured in W, R, FR/R, or B radiation. Halving the ovule or removing the micropyle did not affect the relative change in ovule volume in response to different light treatments. When the light sources were altered after the first 10 days of culture, the ovules exposed first to darkness or FR radiation began to increase in ovule volume which then ceased after subsequent exposure to W, R, or B radiation. Likewise, if W, R, or B radiation was given during the first 10 days, ovule development was inhibited, and could be stimulated by exposure to darkness or FR light. Growth of embryos, when removed from the influence exerted by ovular tissue, was unaffected by the light. However, when embryos remained attached to the ovular tissue, their growth was stimulated in darkness or by FR light and inhibited by W, R, or B light. The R/FR reversibility indicates that the photoreceptor that regulates ovular growth is phytochrome and that the maternal ovular tissue appears to be the site of photoreception, which may then transmit some developmental signal to the embryo.