Impact of suboptimal temperature on growth, photosynthesis, leaf pigments and carbohydrates of domestic and high-altitude wild Lycopersicon species

The impact of near-optimal (25/20 degrees C) and suboptimal (16/14 degrees C) day/night temperatures on growth, photosynthesis, pigment composition an d carbohydrate content was compared between domestic and high-altitude wild Lycopersicon species. When related to the relative shoot growth rate (RSGR ) measured at optimal temperature, genotypes of the domestic tomato (L. esc ulentum (L.) Mill. cv. Abunda and cv. Large Red Cherry (LRC) showed a stron ger inhibition of RSGR at suboptimal temperature than the high-altitude wil d species L. peruvianum Mill. LA 385 and L. hirsutum Humb. & Bonpl. LA 1777 . The initiation rare of new leaves was 2.1-fold faster in all species at 2 5/20 degrees C than at 16/14 degrees C. In contrast to the other genotypes, the leaf area of suboptimally grown Abunda plants was 28 % smaller than th e area of leaves that were fully expanded at optimal temperature. In all sp ecies, specific leaf area (SLA) at 16/14 degrees C was 17-26 % lower than a t 25/20 degrees C. The percentage of leaf dry matter increased in response to growth ar suboptimal temperature. This increase was higher in L. esculen tum genotype Abunda (99 %) than in genotype LRC (38 %), and the wild specie s L. peruvianum (50 %) and L. hirsutum (38 %), which could be attributed to inter- and intra-specific differences in starch accumulation of 16/14 degr ees C-grown leaves. Only in both L. esculentum genotypes, net photosyntheti c rate at growth irradiance (A(225)) and at light saturation (A(sat)) was 1 4 to 30 % lower in leaves grown and measured at suboptimal temperature, com pared with leaves grown and measured at optimal temperature (25 degrees C). Chlorophyll (Chl) a fluorescence measurements indicated that the decrease of A225 in leaves of suboptimally grown L. esculentum plants was paralleled by a decrease in the quantum yield of photosystem II electron transport (P hi(PSII)), which could be mainly attributed to a decrease in the photochemi cal quenching component (q(P)). In all species, the nonphotochemical quench ing component (NPQ) was 2 to 4-fold higher at 16/14 degrees C. Growth tempe rature hardly affected Chi content on a leaf area basis, whereas the conten t of xanthophyll cycle pigments (violaxanthin + antheraxanthin + zeaxanthin ) on a Chi basis was ca. 1.5-fold higher in 16/14 degrees C-grown leaves. T he epoxidation state of the xanthophyll cycle pool was only slightly lower in suboptimal leaves due to the moderate growth irradiance.