Physiological changes in pea seeds during storage

Abstract

Pea seeds stored in humid or dry conditions showed deteriorative changes before loss of viability. This occurred over a period of weeks in 93% rh at 25°C and 1% rh at 10°C, or days in 94% rh at 45°C. Deterioration was seen in an increase in solute leakage from seed which maintained complete vital staining, and later, a further increase in solute leakage, the development of dead tissue on the cotyledons, and loss of viability. In early deterioration, the decline in the ability of seeds to retain solutes was attributed to changes in living cells, possibly, deterioration of cell membranes. This was presented as good evidence that membrane deterioration is one of the first stages of ageing. Analyses of seed phospholipid content following storage in 94% rh at 45°C, when increased leakage occurred from living seeds, showed changes in the proportions of different phospholipid classes. These changes were discussed as possible factors leading to increased membrane permeability. Seed lots stored for two years in conditions simulating warehouse storage showed deterioration, with increased leakage, reduced staining, and in some lots a decline in viability. Deterioration also occurred in commercially stored seed which remained viable, suggesting that one cause of vigour differences in pea seed lots could be prolonged storage. The similarity of deterioration in short and long term storage suggested that short term storage accelerated natural ageing. The response of seeds to storage was related to their initial embryo condition, seeds with good embryo condition deteriorated less rapidly. The response of seeds to accelerated ageing gave a more accurate prediction of seed storeability, rapid deterioration in accelerated ageing was associated with rapid deterioration during prolonged storage. A predictive test of pea seed store- ability, based on solute leakage following accelerated ageing for Id in 94% rh at 45°C was suggested. Vital staining of seeds imbibed minus the testa showed damage to outer layers of cells of the cotyledons within two minutes of contact with water. Damage was caused by rapid imbibition, possibly as a result of disruption of membranes by the inrush of water. The time course of early leakage from pea embryos was explained by membrane damage to outer cells and reformation of membranes of inner cells, during hydration. The different levels of solute leakage observed in seed lots of intact peas were ascribed to two causes: (1) the rate of imbibition, which was influenced by testa condition - seeds that imbibed rapidly had high leakage; (2) embryo condition, which influenced response to a given imbibition rate.