Gibberellic Acid Stimulated Degradation of Endosperm in Pepper

Abstract

Abstract Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA4+7) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA4+7 showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.