Seed germination is a critical phase in the establishment of crop plants in the field, or in the life cycles of wild annual plants. The overall quality of seed is closely related to the time taken for the seed to germinate after it is supplied with water, or the germination rate. The rate of germination slows as the temperature is lowered, as the water supply is restricted, or as the seeds deteriorate during storage. Species and varieties can also differ in their inherent rates of seed germination. The purpose of this project is to study the physiological basis for the differences in germination rates among species or seed lots in response to various environmental or physiological factors. We have modified a general model for the growth of plant tissues to adapt it to the description of seed germination rates. It is based upon water uptake in relation to plant cell growth, since the embryonic tissues must grow in order for germination to occur. By verifying this model and then applying it to seeds both the embryo inside the seed and the surrounding tissues such as the endosperm and seedcoat interact to determine when, or whether, germination occurs. This model should allow us to identify the mechanism(s) by which external (environmental) factors influence internal (physiological) parameters in specific tissues to either accelerate or delay germination. This model will serve as a framework or guide to lead to a better understanding of how the complex process of seed germination is regulated. From the practical viewpoint, the results will have utility in the production and marketing of higher quality seed for agricultural purposes. In many crops, particularly in the vegetables, the uniformity and timing of germination and seedling emergence through the soil are critical factors in the overall profitability of the crop. Through a quantitative understanding of how seed germination is regulated, techniques can be developed to enhance the performance of seeds under specific environmental conditions. Such enhanced seed are already being marketed in some crops, but the procedures used thus far have been developed by trial and error, rather than by application of a fundamental understanding of how seed germination is regulated. In addition, species and varieties differ in their seed quality characteristics. Knowledge of the physiological basis of such differences could identify specific selectable traits to use in breeding programs, or even specific genes to be transferred by biotechnical approaches, in order to improve seed quality. The fundamental information generated by this project will be readily absorbed by the seed industry and incorporated into their programs to improve the quality of seed available to farmers.
