Effect of temperature and light on the coloration of rose flowers

Abstract

Pigmentation of flowers in red is a very complex phenomenon. Various flower colors in many species have been shown to be due to genetic factors. Even if the necessary genes are present, however, synthesis of anthocyanin will not occur in a plant unless environmental conditions are favorable. Of environmental factors regulating anthocyanin formation, sunlight and temperature influence it directly in some plant tissues. To obtain flowers of good color under glasshouse conditions, temperature and light must be regulated by means of heating or cooling and supplementary lighting or shading, especially during the winter or summer season.
The authors attempted in the study to obtain an information on the effects of temperature and sunlight on the coloration of rose flowers. The influence of temperature on the form of epidermal cells in the petal is also presented in this paper. As the materials, two varieties of garden roses were used. Using a variety of Hybrid Tea, Crimson Glory, the authors have followed the formation of red pigments quantitatively at various temperatures in the phytotron. After the differentiation of flower buds about 3 weeks after pruning, the potted plants were treated at various temperatures. At 20° and 10°C petals became dark red and showed a velvet-like appearance. According to anatomical observations, anthocyanin distributed only in the epidermis on the adaxial and abaxial surface of the petal. In the vertical section, the thickness of the upper epidermis of the petal treated at 20° and 10°C is much greater than that treated at 30°C. On the other hand, the upper epidermis showed a flat structure and red color did not appear at noon-and/or night-temperature of 30°C.
In the experiment of the measurement of color, and the analysis of pigments in petals, the roses were treated at 13° and 23°C after the bud formation. At 23°C the petals have a purplish hue and become bluish purple red later. On the other hand, at 13°C they have a red hue and a lower luminosity, and become brown later. Paper chromatographic analysis showed that the anthocyanins in Crimson Glory variety are cyanin and chrysanthemin. Of these pigments, cyanin is the highest in content. The anthocyanin content of petals at 13°C is much higher than that treated at 23°C.
Using a variety of Floribunda, Masquerade, an attempt was made in this paper to elucidate the effect of sunlight on the development of flower color. The flowers of the variety change their color ranging from yellow to red as the age of petals advances. Flower buds were covered with colored cellophane prior to their opening, which was removed after two weeks. Although the flowers bloomed, red color did not develop in their petals. Regardless of light quality, the anthocyanins were not formed at lower light intensity. It therefore appears that the flowers of Masquerade require high intensity of sunlight for development of their red color. There was a rise in anthocyanin content in the petals as the time advanced after flowering. In the petals of Masquerade, the anthocyanins are cyanin and chrysanthemin. Of the two anthocyanins, chrysanthemin has highly increased in content with advancing age of flowers.