Preliminary studies of the growth and development of Phaseolus vulgaris (cv. The Prince) pods and seeds were carried out to determine the sequence of change in dry matter and water, in seed germinability and desiccation tolerance, and to establish the pattern of ultrastructural development in the cells of the embryonic primary leaf during seed growth and ripening. Subsequent work involved the artificial induction of ripening in immature seeds to further investigate the ripening process. Developing P. vulgaris seeds became capable of germination at approximately 27 days after anthesis and tolerant of rapid desiccation (D.T.) at approximately 40 days. Detached immature seeds developed D.T. progressively during 3-5 days incubation at high relative humidity (R.H.). Five days incubation enabled seeds as small as 0.1g desiccated weight (approximately 16% of full size) to be successfully dried and germinated. Incubation at lower humidities enabled only older seed to develop D.T. such that 50% survived by 28.5 day old seed at 75% R.H., by 33.5 day old seed at 32% R.H. and 36 day old seed at 0% R.H. Both natural and induced ripening, in addition to increasing D.T., involved a loss of seed chlorophyll, and reduced post-desiccation leakage of total electrolytes, K+, sugars and amino acids during imbibition. Acquisition of the ability to retain solutes after desiccation -was temperature-sensitive, being inhibited at 10°C and delayed at 15°C (Q10 from 15 to 25°C being approximately 2.5). Incubation under humidified N2 inhibited acquisition of solute retention after desiccation but the effect was reversible, even after seven days. An ultrastructural study of the primary leaf tissues of immature seeds during induced acquisition of D.T. showed that a period of enhanced cellular activity, followed by organelle regression resembling normal maturation, took place although seed water content remained high. It is proposed that development of D.T. may require active processes to initiate the orderly modification of membranes and organelles and the decline in cellular activity characteristic of ripening.
|Date of Award||1981|