Galactomannan hydrolyzing activity develops during priming in the micropylar endosperm tip of tomato seeds

Development of galactomannan hydrolyzing activity was followed in seeds of tomato [Lycopersicon esculentum (L.) Mill. cv. Toyonishiki] during priming and germination. The activity developed in seeds that were being primed in polyethylene glycol (‐0.8 MPa). The activity was detected exclusively in the endosperm portion just adjacent to the radicle tip. Part of the activity remained active after desiccation of the primed seeds. After transfer to water, the activity in the primed seeds immediately began to increase, while in unprimed seeds the beginning of the increase in activity was delayed by about 1 day. In scanning electron microscopy, the inner surface of the cell walls of the micropylar endosperm portion appeared eroded in primed seeds that had been imbibed in water for 16 h (before germination), but not in unprimed seeds imbibed for the same period. These results support the hypothesis that galactomannan hydrolyzing enzyme, which is believed to be responsible for breakdown of tomato endosperm cell walls and hence for the weakening of mechanical restraint against radicle growth, may be involved in the improved germination of primed tomato seeds.