CARBOHYDRATES MODULATE THE EXPRESSION OF THE SUNFLOWER CYTOCHROME-C GENE AT THE MESSENGER-RNA LEVEL

Changes in the steady-state mRNA levels of the gene encoding cytochrom e c were analyzed after feeding carbohydrates to detached leaves of su nflower (Helianthus annuus L.). Glucose, fructose and sucrose promoted an increase in mRNA levels, which was not observed with mannitol and other metabolites such as glycerol or acetate. The increase in mRNA le vels was proportionally higher in dark-treated leaves. The effect of s ugars could be mimicked by compounds that are phosphorylated by hexoki nase but not further metabolized, such as mannose or 2-deoxyglucose. T his may indicate that hexokinase is involved in the induction of the c ytochrome c gene by carbohydrates. The presence of potassium phosphate had no significant effect on the induction by sugars. Our results ind icate that the modulation of the expression of nuclear genes encoding mitochondrial components should be added to the list of known effects of carbohydrates on respiration.