Interruption of Water Delivery at Physiological Maturity is Essential for Seed Development, Germination and Seedling Growth in Pea (Pisum sativum L.)

Abstract

flowering node, increase in fresh and dry weight until 75 d after planting (DAP); thereafter, dry weight and moisture content decrease rapidly. Seed development consists of three phases, all limited by low moisture content (MC). The first phase (PI) corresponds to the formation of the embryo and surrounding structure (MC is stable at 85%). During the second phase (P2) the cotyledons are filled (MC decreases from 84% to 55%). The third phase (P3) entails desiccation on the mother plant. Fresh and dry weight increase until 75 DAP (55% MC or physiological maturity, PM) and rapidly decrease during the third phase until 14% MC. Leakage conductivity of immature seeds reflects sap arrival in the testa and accumulation in the apoplast: it is important during PI and the onset of P2, but during P2 it decreases slowly until physiological maturity and rapidly thereafter. Immature seed germination is noted from 62 DAP, increases until 67 DAP, then decreases with a maximum at physiological maturity; some days after physiological maturity germination is complete (up to 100%). Seedling growth from immature seeds during P2 is low, but slowly increases until physiological maturity. When germination (up to 100%) is attained seedling growth is normal. Hydration of the immature seed indicates that 55% MC is a highly specific value at which a transition in the hydration rate is occurring. Moisture loss from pea seeds during the P2 filling stage appears to be necessary for seed adaptation to the abrupt desiccation which occurs at physiological maturity. Physiological maturity is attained when disruption of the vascular connection between the pod and the mother-plant occurs.