The influence of light of different spectral regions on the synthesis of phenolic compounds in gherkin seedlings, in relation to photomorphogenesis. V. The temperature dependence

The increase in the rate of synthesis of hydroxycinnamic acids in response to irradiation is greater at higher temperatures, but the length of the period of enhanced accumulation is shorter. This can be explained by the influence of the temperature on the photoinduced changes in the level of the enzyme phenylalanine deaminase (PADAse); at higher temperatures the enzyme increases more rapidly but the subsequent decline of its level begins sooner. In the range of 12.5 to 32°C the lower temperatures are optimal for phenol synthesis if the seedlings are continuously irradiated. In the case of irradiation programs of a light period followed by darkness a maximum amount of phenols is synthesized at higher temperatures: the shorter the inducing light period, the higher is the optimal temperature. It is shown that there is one particular combination – 2.5 hours of light followed by 21.5 hours of darkness – with which the apparent Qi„ for phenol production is close to unity in the whole temperature range of 18 to 32 °C.