We compared the responses of wild type (WT) and three mutants including npq1 (lutein-replete and violaxanthin deepoxidase-deficient), lut2 (lutein-deficient), and lut2-npq1 (double mutant) to high irradiance (HI, 2 000 μmol m-2 s-1) at both low (LT, 5 °C) and room (25 °C) temperature. Xanthophyll-dependent energy dissipation was highest in the WT, followed by the lut2, npq1, and npq1-lut2. At 25 °C the relative stress tolerance expressed by Fv/Fm was consistent with the energy dissipation capacity for the first 2 h of treatment. After 3-4 h, the Fv/Fm levels in lut2 and npq1 converged. Under combined LT and HI the relative tolerance sequence was in contrast to the energy dissipation capacity being WT > npq1> lut2 > lut2-npq1. There were little or no significant change in the contents of xanthophylls and carotenes or the chlorophyll (Chl) a/b ratio in any of the materials. Thus lutein (L) substitution possibly alters the conformation/organisation of L binding proteins to enhance damage susceptibility under HI at LT. The enhanced vulnerability is not compensated for the energy dissipation capacity in the lut2 background at LT. and Chang-Lian Peng, A. M. Gilmore.
Two cultivars of Capsicum annuum L. were acclimated for 5 d at sub-optimal temperature (14 °C) and irradiance of 250 µmol m-2 s-1. This cold-hardening resulted in some reduction in the extent of photoinhibition during an 8 h exposure to high irradiance at 4 °C. Obvious differences were observed between non-hardened leaves (NHL) and cold-hardened leaves (CHL) in the recovery under low irradiance at room temperature. The CHL of both cultivars recovered faster than NHL, especially during the initial fast phase of recovery. Compared with NHL, the total content of carotenoids (Cars), based on chlorophyll, Chl (a+b), and the proportions of xanthophyll cycle pigments referred to total Cars increased in CHL, mainly due to an increase of violaxanthin (V) + antheraxanthin (A) + zeaxanthin (Z) content per mol Chl (a+b). Faster development and a higher non-photochemical quenching (NPQ) of Chl fluorescence, related to a stronger deepoxidation of the larger xanthophyll cycle pool in NHL, could act as a major defence mechanism to reduce the formation of reactive oxygen species during severe chilling. This is suggested by higher content of Z or Z+A in photoinhibition as well as by its rapid decline during the initial fast phase of recovery. In contrast to the chilling-sensitive cv. 0004, the chilling-tolerant cv. 1141 did more easily acclimate its photosynthetic apparatus to low temperatures. and Peng Liu ... [et al.].
High irradiance (HI) effects on xanthophyll cycle pigments (XCP) and activity of violaxanthin de-epoxidase (VDE) in terms of de-epoxidation index (DEI) were studied in soybean calli. The calli from the hypocotyl segments of 5-d seedlings were induced on a solid (1.1 % agar) MS medium (pH 5.8) supplemented with 4.52 μM 2,4-dichloro-phenoxyacetic acid, 2.32 μM kinetin, and 3 % sucrose. After a 30 d cultivation, the green calli were irradiated for 24 h with "white light" (HI, 1 300 μmol m-2 s-1) and VDE was isolated from the photosystem 2 (PS2) particles. In the control (0 h irradiation) callus, the reaction of PS2 particles with VDE in the presence or absence of Tween 20 resulted in the decrease of VIO content and the increase of ZEA content. In the 24 h HI-callus, the reaction of PS2 particles in the absence of VDE led to the decrease of VIO and ANT contents and increase of ZEA content. In the control, DEIs in the presence of VDE with or without 0.1 %Tween 20 (1.04 and 1.06, respectively) were significantly higher than the DEI (0.76) in the absence of VDE. In the HI-callus, DEIs in the presence of VDE with or without 0.1 %Tween 20 (0.98 and 0.96, respectively) were similar to that (1.03) in the absence of VDE. and D. M. Pandey ... [et al.].
Foliage of Scots pine (Pinus sylvestris L.) and pedunculate oak (Quercus robur L.) was collected in a mixed pine/oak forest at canopy positions differing in radiation environment. In both species, chlorophyll (Chl) a/b ratios were higher in foliage of canopy positions exposed to higher irradiance as compared to more shaded crown layers. Throughout the growing season, pine needles exhibited significantly lower Chl a/b ratios than oak leaves acclimated to a similar photon availability. Hence, pine needles showed shade-type pigment characteristics relative to foliage of oak. At a given radiation environment, pine needles tended to contain more neoxanthin and lutein per unit of Chl than oak leaves. The differences in pigment composition between foliage of pine and oak can be explained by a higher ratio of outer antennae Chl to core complex Chl in needles of P. sylvestris which enhances the efficiency of photon capture under limiting irradiance. The shade-type pigment composition of pine relative to oak foliage could have been due to a reduced mesophyll internal photon exposure of chloroplasts in needles of Scots pine, resulting from their xeromorphic anatomy. Hence, the higher drought tolerance of pine needles could be achieved at the expense of shade tolerance. and U. Hansen, J. Schneiderheinze, B. Rank.