Weight-Change Patterns in Cut and Intact Rose Shoots II. Floral and Foliar Contributions as Related to Competition for Water

Abstract

Foliar contributions to diurnal light/dark changes in total shoot weight were assessed, with the aid of non-destructive beta-ray gauging (see Part I, De Stigter 1982), in two cultivars of intact or cut roses, the cut ones in water or in glucose + Al(3+). Once the flower buds of the intact, single-stem plants had fully opened, weight changes in both cultivars were mainly due to the gradually senescing blooms, with a minor contribution of the foliage. In the cut roses cultivar differences were distinct in overall performance resulting from water or glucose treatment, and in relative resistance or sensitivity of the foliage to water stress. Flower and foliage were found to differ in their kinetics of weight loss in the light and of recovery in the dark. These results and cultivar differences are interpreted in terms of varying inter-organ competition for water between flower and foliage. In most cases the overall fresh-weight evolution of the foliage was remarkably linear and consisted of diurnal light/dark fluctuations of rather constant amplitude. It is concluded that, apart from beta-gauging as presented here, the early course of foliar fresh weight may also be estimated by backward extrapolation of the pattern found in the leafy shoot after petal shedding. In very poorly performing cut roses this procedure is permissible only with reservations, because too many factors are changing simultaneously: the general trends in both total-shoot and foliar weight, as well as their respective diurnal amplitudes. On balance, the respective floral and foliar contributions to weight pattern in the cut rose shoots did not show a fixed proportionality, but a continuous shift toward a decreasing floral, and an increasing foliar share, the actual levels depending on cultivar and organ sensitivity to water stress.