Evidence for a Direct Effect of Water Stress on Tracheid Cell Wall Metabolism in Pine

Tissues of developing xylem were excised from the main stems of 16-year-old Pinus sylvestris L. trees and incubated in solutions containing labelled glucose and varying concentrations of polyethylene glycol. Increase in water stress with polyethylene glycol caused a significant lowering of glucose incorporation. As water potential decreased from — 3.1 atm, a level common in stems under favorable growing conditions, to — 28.1 atm, a level common under conditions of environmental stress, incorporation of labelled glucose was reduced by over 50 percent. Water stress thus has a direct effect on the cell wall metabolism of cambial derivatives in pine, independent of regulation from the crown foliage.