GERMINATION‐REGULATING MECHANISMS IN CITRULLUS COLOCYNTHIS

Abstract

Koller, D., A. Poljakoff‐Mayber, A. Berg, and T. Diskin. (Hebrew U., Jerusalem, Israel.) Germination‐regulating mechanisms in Citrullus colocynthis. Amer. Jour. Bot. 50(6): 597–603. Illus. 1963.—Intact seeds from mature, dry fruits of Citrullus colocynthis, collected in the southern Negev desert, did not germinate under a wide variety of experimental conditions. This inhibition was imposed by the testa, since germination was made possible by mechanically forcing open the testa, or by its complete removal. However, various pretreatments, including some which modified or even pierced the testa, failed to effect germination. No inhibitors were found in the testa and the manner in which it inhibits germination is yet unknown. How this inhibition is overcome in nature is also unknown. Germination of decoated seeds was inhibited by continuous light in combination with temperatures below 25 C. Removal of the inner seed membrane removed this inhibition, but, growth of the naked embryos at all temperatures was greatly reduced by continuous light, which also strongly influenced early development. An intact inner seed membrane had no effect on germination in darkness, but inhibited it in light at temperatures below 25 C. Inhibitory effects of the inner seed membrane could be duplicated by enclosing the naked embryos in moist filter paper and are thus probably the result of an interference with exchange of respiratory gases between the embryo and the atmosphere. Very low light intensities sufficed to inhibit decoated seeds, but at least 12‐hr daily illumination was required to produce significant inhibition. The blue region of the visible spectrum, transmitted by green and blue cellophane filters, was the most inhibitory. The site of light perception was located in the radicular portions of the embryo.