CHILLING SENSITIVITY OF PHOTOSYNTHESIS - ECOPHYSIOLOGICAL STUDIES IN 2 LYCOPERSICON SPECIES OF DIFFERENT CHILLING TOLERANCE

The cultivated tomato, Lycopersicon esculentum, and high-altitude line s of its wild relative, L. peruvianum, differ significantly in their s ensitivity towards long-term chilling stress under non-photoinhibiting conditions. While the latter species is hardly affected by such stres s treatments and rather shows symptoms of acclimation to suboptimal te mperatures, the cultivated tomato reacts with a permanent partial inhi bition of photosynthesis in the chilling-exposed leaves. This inhibiti on ultimately results in a severe drawback of biomass accumulation, ev en during recovery under favourable circumstances after the chilling s tress. It is caused by an oxidation of cystein residues of ribulose-1, 5-bisphosphate carboxylase/oxygenase (RubisCo), leading to RubisCo-lim itation of photosynthesis in chilled L. esculentum plants, whereas in L. peruvianum a limitation by ribulose-1,5-bisphosphate regeneration s eems more probable. Possible reasons for the differential in vivo-sens itivity of RubisCo in the two species during chilling have been found in different temperature dependences of Q(A) reoxidation and of energy dissipation by the q(E) mechanism. With respect to both processes, th e probability of formation of reactive oxygen species by Mehler reacti on and by increasing lifetime of excited singlet chlorophyll appears m uch higher in L. esculentum than in L. peruvianum.