| Abstract: | Cooling of the roots was shown here to cause marked and rapidinhibition of leaf growth in wheat seedlings, as in some otherspecies. The root-shoot signal involved in this response wasinvestigated. Displacement transducers were used for the simultaneousmonitoring of leaf growth rate and leaf thickness in individualseedlings. Leaf water status was inferred from leaf thickness.Kinetics of changing water status were compared with those ofchanging leaf growth rate in the same seedling. Leaf water statuswas found to decline markedly beginning immediately after rootcooling. This occurs because cooling reduces the hydraulic conductivityof roots almost to zero. Apparent leaf growth rate was extremelysensitive to small changes in leaf water status, and the initialdecrease in leaf water status after root cooling was sufficientto cause cessation of leaf growth. Complications arising fromleaf elasticity and other sources were considered. Prolongedroot cooling caused a sustained depression in both leaf waterstatus and leaf growth rate. The effects of root cooling onleaf thickness and growth rate were completely prevented ifwater was made freely available to the shoot. It is thereforeconcluded that hydraulic factors (signals) can explain the short-and(at least in part) the medium-term effects of root cooling onleaf growth rate in wheat. Key words: Triticum durum L., leaf growth rate, hydraulic signals, root cooling |
