THE EFFECT OF HEAT-SHOCK ON MORPHOGENESIS IN BARLEY - COORDINATED CIRCADIAN REGULATION OF MESSENGER-RNA LEVELS FOR LIGHT-REGULATED GENES AND OF THE CAPACITY FOR ACCUMULATION OF CHLOROPHYLL PROTEIN COMPLEXES

The effect of daily heat-shock treatments on gene expression and morphogenesis of etiolated barley (Hordeum vulgare) was investigated. Heat-shock treatments in the dark induced shortening of the primary leaves and the coleoptiles to the length of those in light-grown plantlets. In addition, the mRNA levels of the light-induced genes that were investigated were raised under these conditions and showed distinct oscillations over a period of at least 3 d. While the mRNA levels for chlorophyll a/b binding protein (LHC II), plastocyanin, and the small subunit of ribulose-1,5-bis-phosphate carboxylase had maxima between 8 and 12 PM (12-16 h after the last heat-shock treatment), the mRNA levels for thionin oscillated with a phase opposed to that of LHC II. Etiolated barley, the circadian oscillator of which was synchronized by cyclic heat-shock treatments, was illuminated for a constant interval at different times of the day; this led to the finding that greening was fastest at the time when the maximal levels of mRNA for LHC II were also observed. Whereas accumulation of chlorophyll a during a 4-h period of illumination oscillated by a factor of 3, chlorophyll b accumulation changed 10- to 15-fold. Similarly, accumulation of LHC II was highest when pigments accumulated maximally. Hence, greening or, in other words, thylakoid membrane assembly is under control of the circadian oscillator.