Effect of dark phases and temperature on the chlorophyll a/b binding protein mRNA level oscillations in tomato seedlings

Abstract

External parameters (e.g. light/dark alterations and temperature) were tested for their ability to influence the expression pattern of the chlorophyll a/b binding protein (cab) genes and the small subunit of RuBPC/Oase (rbcS) genes. Particular interest was focused on the alterations of diurnal/circadian oscillation patterns of cab mRNA levels. Chlorophyll a/b binding protein and small subunit of RuBPC/Oase mRNA oscillations were observed in tomato seedlings grown without environmental perturbations (constant illumination and temperature), indicating that these genes are controlled by an endogenous rhythm. The rhythmic fluctuation patterns revealed a period of about 32 hours and a weekly expressed amplitude. A several-fold increase of the cab mRNA amplitude and a reduction of the period to about 24 hours (circadian) was monitored after exposure of the tomato seedlings to 3, 6 or 9 hours of darkness. The elevated amplitude disappeared at consecutive days if seedlings were not exposed to further dark phases. A circadian rhythm with clearly expressed cab mRNA amplitudes was also present after the plants had been transferred to darkness at various circadian times. However, under those circumstances the time points of maximum and minimum transcript levels were shifted by respective hours. Alteration of the growth temperature from 24 degrees C to 10 degrees C or 30 degrees C at constant illumination or in a light/dark cycle resulted in a reduction of the amplitudes or of the steady-state mRNA levels. Such extreme temperature changes do not induce or enhance the diurnal cab mRNA oscillations.