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Diurnal fluctuations of antioxidative systems in leaves of field‐grown beech trees ( Fagus sylvatica ): Responses to light and temperature
Author(s) -
Peltzer Detlef,
Polle Andrea
Publication year - 2001
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2001.1110205.x
Subject(s) - fagus sylvatica , beech , apx , glutathione reductase , chemistry , antioxidant , botany , reductase , horticulture , biochemistry , enzyme , biology , glutathione peroxidase , superoxide dismutase
To test the hypothesis that antioxidant systems flexibly adjust to short‐term, diurnal fluctuations of ambient environmental conditions, ascorbate‐related systems were studied over several day/night cycles in mature sun‐acclimated leaves of field‐grown beech trees ( Fagus sylvatica ). Light‐dependent increases in the activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate radical reductase (MDAR, EC 1.1.5.4) and glutathione reductase (GR, EC 1.6.4.2) were not observed. Lowest activities of APX and MDAR were found on hot, sunny days. A strong negative correlation occurred between APX activities and ambient temperatures suggesting that this enzyme was temperature‐ rather than light‐regulated. In contrast to the enzymatic defences, ascorbate levels increased by about 30% under bright sunlight suggesting that protection from excess light is mediated via the adjustment of metabolites. Under these conditions the apparent electron transport rate exceeded the capacity for assimilation and the dehydroascorbate pool increased twofold. Since dehydroascorbate reductase activities were hardly detected, MDAR activities seemed to be the major enzyme to keep ascorbate in its reduced state. However, MDAR appeared to be insufficient to maintain the redox balance of the ascorbate pool under high light intensities in the field.