Abstract
The relationship between AA-metabolising enzymes and the AA pool was studied by subjecting tomato leaves to treatments up- or down-regulating the AA content. GalL feeding through leaf petioles increased the level of cellular ascorbate up to two-fold. This effect accompanied by a AA/total ascorbate ratio increase was observed after a 2-h incubation and remained constant during the following 4 days. Dark-incubated leaves showed a 56% decline in AA content concomitantly with DHA accumulation and significant ascorbate redox ratio decrease. Opposite changes were induced when the darkened leaves were transferred to light, as AA biosynthesis depends on light. The light-induced AA biosynthesis was partially inhibited by lycorine. Regardless of the pattern of AA pool changes the AA-related enzymes were similarly affected. Both the GalL/light-dependent AA increase and dark-induced AA depletion were accompanied by APX and MDHAR activity induction. No significant AA pool-dependent DHAR activity changes were found. The possible relevance of the AA system changes induced is discussed.
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