The relationships between gibberellin and organ size in colored Zantedeschia cv. 'Calla Gold'

Involvement of gibberellin in the regulation of size and shape of different plant organs (leaf, floral stem, and tuber) were studied in colored Zantedeschia cv. 'Calla Gold' (CG). The effect of gibberellin on allometric relationships between these organs was also examined. Tubers were dipped in solutions of GA₃ (0.6 mM) or of the gibberellin biosynthesis inhibitor Uniconazole (3.4 mM) prior to storage, prior to planting, or twice-before storage and before planting. The effects of the growth regulators were followed in plants grown in pots in a screen house under 50% shade. Tuber weight was reduced by both GA₃ and Uniconazole, but by different processes. GA₃ increased the number of the floral stems per plant, but did not affect floral stem length or blade and petiole length. Uniconazole reduced the proportion of flowering plants, and inhibited leaf and stem elongation. Co-application with GA₃ canceled the inhibitory action of Uniconazole on leaf and peduncle elongation. This suggests that gibberellin is involved in the regulation of organ elongation, despite lack of direct effect of exogenous GA₃ application. Linear positive relationships were found across the different treatments between tuber weight vs. leaf area, petiole length vs. blade length, petiole length vs. floral stem length, and blade length vs. floral stem length. The constancy in size relationships suggests that the action of the growth regulators on the growth of the different organs were according to intrinsic allometric relationships among them. The differential action of GA₃ on flowering and on stem and leaf elongation is discussed.