Temperature, DIF and photoperiod effects on the rhythm and rate of stem elongation in Campanula isophylla Moretti

Abstract

Stem elongation of Campanula isophylla Moretti cv. Hvit was measured continuously in controlled environment cabinets under different temperature and light conditions, using an angular displacement transducer (ADT). The elongation showed a rhythmic pattern with a high stem elongation rate (SER) during the night (in darkness) and low SER during the day. The day was a period when the plants received a high irradiance level provided by fluorescent light (FL). The rhythm was retained under constant darkness, and showed free running cycles with periods of about 24 h. This rhythm is classified as an endogenous circadian rhythm. The growth rhythm was controlled by diurnal cycles of high and low temperatures as well as by alternations between light and dark and between high and low light levels. Plants grown with 12 h high irradiance level and a 12 h day- extension light with low irradiance level (2 μmol m −2 s −1) showed the same rhythmic pattern as plants grown with 12 h high irradiance level and 12 h darkness. The SER increased when the light changed from high irradiance level to day extension light and from high irradiance level to darkness. Increase in constant temperature (15, 20 and 25°C) caused an increase in SER, but the ratio between day and night SER was approximately the same. The temperature difference between day and night (DIF) changed the rhythmic pattern and affected the SER both at day and night. At positive DIF (24°/12°C) SER was high both during day and night, and the average SER was larger than at negative DIF (12°/24°C) and constant temperature (18°/18°C). Plants grown at negative DIF and constant temperature showed higher SER at night than at day, but the average SER during the night was significantly higher at constant temperature than at negative DIF.