Abstract: Ray floret (rf) petals detached from inflorescences of Gerbera hybrida were cultured in vitro and the effects of exogenous ammonium on petal pigmentation and growth were investigated. NH₄⁺of 10.00mmol·L^-1 obviously blocked petal p igmentation and the petal expansion, the width, fresh weight and dry weight were also declined significantly. The anthocyanin content of the petals of ray floret cultured in vitro began to increase 36 h and accumulated greatly fast between 54 h and 84 h after the incubation, which was followed by a gradually decline. The application of NH₄⁺ within 36 h was completely effective on the inhibition of the p igmentation, while the effect was gradually decreased when NH₄⁺ was app lied after 36h. Moreover,stronger inhibition was observed when the working time of the NH₄⁺ was longer than 12 h. The anthocyanin accumulation was promoted by the increase of sucrose content in the present of NH₄⁺. Other sugars such as fructose, lactose, maltose and glucose in the media had little effect on the NH₄^+_-induced inhibition of pigmentation.

Key words: Gerbera hybrida, ammonium, ray floret, anthocyanin, growth