Photomorphogenesis of the Gynophore, Pod and Embryo in Peanut, Arachis hypogaea L.

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Abstract
Darkened excized gynophores ceased to elongate after 8–10 days in vitro and started to form a pod. Gynophore elongation was inhibited to a greater extent in total darkness than under low irradiance, while pod and embryo growth was stimulated in darkness only. Intact gynophores, enclosed in transparent vials containing glass beads, continued to elongate in both light and darkness. In light the elongating gynophores thickened as they penetrated between the glass beads, forming a seedless pod at the bottom of the vials. In the dark the elongating gynophores produced small pods in which the seeds had started to grow. Excized gynophores elongated in vitro under continuous white light at a rate similar to that of intact exposed gynophores. The rate of elongation in vitro, was lower under continuous blue or red-enriched light, than under white light, and was further reduced under continuous far-red irradiation. Pods did not form during any of the continuous irradiation treatments but only after transfer to darkness, the largest pods forming after continuous far-red irradiation. As little as 10 min daily exposure to red or far-red irradiance had the same effect on gynophore elongation as continuous irradiation. Pods formed only when the daily periods of far-red irradiation were 30 min or less. Reducing the daily exposures to 2 min decreased the time to onset of pod formation from 30 to 16 days. Far-red following red irradiation was effective in inhibiting gynophore elongation stimulated by red irradiation. Pod formation in red/far-red irradiation was only 50 per cent of that observed in far-red irradiation. The involvement of light in continual gynophore elongation and in the concomitant inhibition of proembryo growth is discussed.