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

As pea plants (Pisum sativum L.) cv. Finale and Solara developin the field, pods located at the second flowering node, increasein fresh and dry weight until 75 d after planting (DAP); thereafter,dry weight and moisture content decrease rapidly. Seed developmentconsists of three phases, all limited by low moisture content(MQ. The first phase (PI) corresponds to the formation of theembryo and surrounding structure (MC is stable at 85%). Duringthe second phase (P2) the cotyledons are filled (MC decreasesfrom 84% to 55%). The third phase (P3) entails desiccation onthe mother plant. Fresh and dry weight increase until 75 DAP(55% MC or physiological maturity, PM) and rapidly decreaseduring the third phase until 14% MC. Leakage conductivity ofimmature seeds reflects sap arrival in the testa and accumulationin the apoplast it is important during PI and the onset of P2,but during P2 it decreases slowly until physiological maturityand rapidly thereafter. Immature seed germination is noted from62 DAP, increases until 67 DAP, then decreases with a maximumat physiological maturity; some days after physiological maturitygermination is complete (up to 100%). Seedling growth from immatureseeds during P2 is low, but slowly increases until physiologicalmaturity. When germination (up to 100%) is attained seedlinggrowth is normal. Hydration of the immature seed indicates that55% MC is a highly specific value at which a transition in thehydration rate is occurring. Moisture loss from pea seeds duringthe P2 filling stage appears to be necessary for seed adaptationto the abrupt desiccation which occurs at physiological maturity.Physiological maturity is attained when disruption of the vascularconnection between the pod and the mother-plant occurs. Key words: Physiological maturity, germination, growth, pea