Bradford K J
Department of Vegetable Crops, University of California, Davis, California 95616.
Plant Physiol. 1990 Oct;94(2):840-9. doi: 10.1104/pp.94.2.840.
Seed germination culminates in the initiation of embryo growth and the resumption of water uptake after imbibition. Previous applications of cell growth models to describe seed germination have focused on the inhibition of radicle growth rates at reduced water potential (Psi). An alternative approach is presented, based upon the timing of radicle emergence, to characterize the relationship of seed germination rates to Psi. Using only three parameters, a ;hydrotime constant' and the mean and standard deviation in minimum or base Psi among seeds in the population, germination time courses can be predicted at any Psi, or normalized to a common time scale equal to that of seeds germinating in water. The rate of germination of lettuce (Lactuca sativa L. cv Empire) seeds, either intact or with the endosperm envelope cut, increased linearly with embryo turgor. The endosperm presented little physical resistance to radicle growth at the time of radicle emergence, but its presence markedly delayed germination. The length of the lag period after imbibition before radicle emergence is related to the time required for weakening of the endosperm, and not to the generation of additional turgor in the embryo. The rate of endosperm weakening is sensitive to Psi or turgor.
种子萌发以胚生长的启动和吸胀后水分吸收的恢复为高潮。以往应用细胞生长模型描述种子萌发时，重点关注了在降低的水势（Ψ）下胚根生长速率的抑制情况。本文提出了一种基于胚根出现时间的替代方法，用于描述种子萌发速率与Ψ之间的关系。仅使用三个参数，即“水时常数”以及群体中种子最低或基础Ψ的均值和标准差，就可以预测在任何Ψ下的萌发时间进程，或者将其归一化到与在水中萌发的种子相同的时间尺度。完整的或去除胚乳包被的生菜（Lactuca sativa L. cv Empire）种子的萌发速率随胚膨压呈线性增加。胚根出现时，胚乳对胚根生长几乎没有物理阻力，但其存在显著延迟了萌发。吸胀后到胚根出现前的滞后期长度与胚乳弱化所需时间有关，而与胚中额外膨压的产生无关。胚乳弱化速率对Ψ或膨压敏感。
