Relationship Between DNA Synthesis and Water Content During Ripening ofVicia FabaSeed

SUMMARYThe relation between cotyledon water content and following processes: i) DNA synthesis in cells of the radicle meristems, ii) mitotic activity in the meristems, iii) accumulation of storage material, has been studied during ripening of seeds in Vicia faba.It has been found that DNA synthesis stops when water content is still 75% of cotyledon fresh weight, while mitotic activity continues as long as water content is higher than 65%. This extended mitotic activity produces a progressive decrease in relative frequency of G2 cells, but not all G2 cells reach the G1 phase at full ripening stage.Accumulation of reserve material is less sensitive to decreased water supply; in fact it lasts as long as water content is higher than 55%.The data presented seem to indicate that each of the processes considered is limited by a critical level of water availability.