Abstract
The role of the endosperm in releasing embryo dormancy was investigated in 'Campbell Early' grape seeds. Embryos, with or without their endosperms, which were excised from seeds of maturing berries were cultured in vitro and their germination rates and growth monitored. Embryos without endosperms germinated best when berries were taken a week before veraison, but the germination percentage thereafter declined abruptly to a deep dormancy level 2 weeks after veraison. On the other hand, embryos with endosperms gradually increased the germination rate to reach a maximum percentage 2 weeks after veraison. After berry harvest, mature seeds were collected and their embryos with endosperms were incubated in vitro for 0, 6, 12, and 24 hours ; the embryos were isolated from endosperms and cultured. Those incubated for 0 or 6-hr neither germination nor rooted, whereas those incubated for 12-hr germinated slightly and some rooted. A 24-hr incubation greatly improved the germination and rooting percentages. Although the removal of endosperm portion surrounding cotyledons and epicotyl did not greatly reduce germination or rooting ; removal of the endosperm surrounding the root tip elicited no response. Microscopic observations revealed that the root tip on embryos with endosperms incubated for 24 hr began to elongate and the endosperm cells adjacent to the root tip became densely stained, indicating that the cells were physiologically active. Therefore, we conclude that the mature endosperm controls the release of embryo dormancy and that endosperm portion linked to the root tip plays an important role in regulating embryo dormancy in grape seeds.
