Shoot elongation and gibberellin contents in Cyclamen persicum are influenced by temperature and light intensity

Elongated petioles and wide leaf laminas decrease the ornamental quality of potted cyclamen (Cyclamen persicum). We determined the relationship between leaf petiole elongation and lamina expansion and endogenous gibberellins (GAs) of cyclamen as influenced by light intensity, daily light integral (DLI), and temperature. ‘Metis Scarlet Red’ cyclamen plants with five fully unfolded leaves were cultivated in growth chambers maintained at 14°C (low temperature, LT) and 26°C (high temperature, HT) and illuminated at 60 and 240 µmol·m^-2·s^-1 PPF [(low light (LL) and high light (HL), respectively] with 8 h (short day, SD) and 16 h (long day, LD) photoperiods by fluorescent lamps, giving a total of eight treatments. HT and LL increased petiole length, plant height, and leaf size. There was no significant effect of photoperiod on plant height or petiole length. ‘Metis Scarlet Red’ cyclamen had GA₁ and GA₄ as active GAs with a similar concentration. The concentration of active GAs was higher in plants grown at the HT compared to the LT. Concentrations of GA₂₀ and GA₁, products in the early C-13-hydroxylation pathway, and GA₉ and GA₄, products of the non C-13-hydroxylation pathway, were higher in plants grown under LL than HL. Petiole length increased linearly by about 6 cm (200%) in all eight treatments as the concentration of active GAs (GA₁ + GA₄) increased from 12 to 34 ng·g^-1. These results indicate that temperature and DLI regulated petiole length of cyclamen by controlling the content of active GAs.