Der Einfluß von Licht verschiedener Wellenlänge auf die Akkumulation und den Umsatz von Anthocyan-3-monoglucosiden in isolierten Petalen von Petunia hybrida

Abstract

Summary The influence of different light qualities: far-red, red, blue, and dark on the accumulation and the turnover of the 3-monoglucosides of delphinidin, petunidin, and malvidin was studied in isolated petals of the delphinidin-genotype (L. M. ff K.) of Petunia hybrida by feeding and by pulse labelling experiments using acetate-2-14C. Radioactivity is randomly incorporated into the anthocyanins which differ only in the B-ring methylation pattern (fig. 1). The aim of the study was to see whether there is a specific influence of light of different qualities on the anthocyanin composition of the isolated petals, i.e. whether changes occur in the relative proportions of these anthocyanin-3-monoglucosides due to the light quality. Furthermore, by studying the turnover, it was attempted to elucidate whether the light control of anthocyanin accumulation is mediated by the regulation of synthesis alone or by the regulation of both synthesis and turnover. Since the physiological behaviour of the buds differs with the time of harvest and the age of the plants, the bud-half technique was employed. The buds were symmetrically bisected. In each experiment one half of the bud halves, chosen to serve as a reference, was given a standard red light treatment. The physiologically equivalent other corresponding half of the bud-halves received the experimental treatment. Tests showed that during the incubation period anthocyanin accumulation can be considered to be proceeding normally. The anthocyanin content of the lower half of the bud is highest at the beginning of bud development, then it stays constant. Later on, a distribution gradient is built up in the bud with the anthocyanin content increasing and becoming highest in the upper quarter of the petals. Malvidin-3-monoglucoside shows the steepest gradient, delphinidin-3-monoglucoside the smoothest. Independent thereof, the accumulation in the different parts is linear with bud length (fig. 2). In red light, concluded from a comparison of experiments run in white fluorescent light and dark (Steiner 1971) and the experiments in red and dark (table 5), the anthocyanin composition seems to be influenced in the same manner as in white fluorescent light. In far-red light compared to red no differences are observed in the anthocyanin composition (table 3). In blue light compared to red the malvidin-3-monoglucoside accumulation remains unchanged. However, the petunidin- and particularly the delphinidin-3-monoglucoside accumulation is markedly increased, thus leading to a specific change in the anthocyanin composition (table 4). In the dark compared to red the accumulation of delphinidin- and petunidin-3-monogluco-side seems to be unchanged. However, the accumulation of malvidin-3-monoglucoside is reduced (table 5). Thus, in the dark a similar change in the anthocyanin composition is observed as in blue light, though for an entirely different reason. In red light, concluded from a comparison of experiments in white fluorescent light and dark (Steiner 1971) and the experiments in red and dark (table 11), the turnover of the 3-monoglucosides on a relative basis seems to be similar to that found in white fluorescent light. In far-red light compared to red no differences could be observed with respect to the turnover of all 3-monoglucosides (table 9). In blue light compared to red the turnover of all 3-monoglucosides is unspecifically increased (table 10). In the dark compared to red no differences are found in the turnover of delphinidin- and petunidin-3-monoglucoside, but the turnover of malvidin-3-monoglucoside is higher in the dark than in red (table 11). The data clearly show that the light controlled linear accumulation of the anthocyanin-3-monoglucosides in isolated petals of Petunia is without exception the result of synthesis and turnover. Due to the specific light quality the rate of synthesis as well as the rate of turnover can differ for each of the 3-monoglucosides. Hence, the anthocyanin composition of the petals can change. Yet, a similar anthocyanin composition may, on the other hand, be the result of a different accumulation regulation. A simple hypothesis is given proposing a reasonable regulation model fitting the data. Red and far-red light show the same effect on the anthocyanin composition. Blue light specifically alters this composition. Accordingly, anthocyanin composition in Petunia belongs to those photomorphogenic responses in which blue light action is prominent.