Polyethylene Glycol Induced Water Stress in Vicia faba Seedlings: Cell Division, DNA Synthesis and a Possible Role for Cotyledons

Abstract

Vicia faba seedlings with attached cotyledons were cultured in 20% polyethylene glycol 6000 (PEG). Under this condition the mitotic index and incorporation of thymidine into DNA of root tip cells decreased during the first 8 hours of treatment and remained lower than the control for 40 to 56 hours. After this period of time both parameters increased to near the levels of the control indicating a self-recovery response. Seedlings transferred out of PEG after 24 hours of treatment showed a recovery in mitotic index and incorporation, but not to the control levels. Those transferred after 48 or 72 hours recovered fully. PEG-stressed seedlings lacking cotyledons did not exhibit self-recovery, indicating a possible cotyledon role in this phenomenon. Roots of stressed seedlings with attached cotyledons exhibited a drop in water potential, solute potential and turgor pressure demonstrating a close relationship between cell cycle responses and the water relations of root cells.