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Tocopherols (vitamin E) are lipid soluble antioxidants synthesized by plants and some cyanobacteria. We have earlier reported that overexpression of the gamma-tocopherol methyl transferase (gamma-TMT) gene from Arabidopsis thaliana in transgenic Brassica juncea plants resulted in an over six-fold increase in the level of alpha-tocopherol, the most active form of all the tocopherols. Tocopherol levels have been shown to increase in response to a variety of abiotic stresses. In the present study on Brassica juncea, we found that salt, heavy metal and osmotic stress induced an increase in the total tocopherol levels. Measurements of seed germination, shoot growth and leaf disc senescence showed that transgenic Brassica juncea plants overexpressing the gamma-TMT gene had enhanced tolerance to the induced stresses. Analysis of the chlorophyll a fluorescence rise kinetics, from the initial "O" level to the "P" (the peak) level, showed that there were differential effects of the applied stresses on different sites of the photosynthetic machinery; further, these effects were alleviated in the transgenic (line 16.1) Brassica juncea plants. We show that alpha-tocopherol plays an important role in the alleviation of stress induced by salt, heavy metal and osmoticum in Brassica juncea.

A new instrument (M-PEA), which measures simultaneously kinetics of prompt fluorescence (PF), delayed fluorescence (DF) and modulated light reflection at 820nm (MR), was used to screen dark-adapted leaves of the resurrection plant Haberlea rhodopensis during their progressive drying, down to 1% relative water content (RWC), and after their re-watering. This is the first investigation using M-PEA, which employs alternations of actinic light (627-nm peak, 5000 micromol photons m(-2) s(-1)) and dark intervals, where PF-MR and DF kinetics are respectively recorded, with the added advantages: (a) all kinetics are recorded with high time resolution (starting from 0.01 ms), (b) the dark intervals' duration can be as short as 0.1 ms, (c) actinic illumination can be interrupted at different times during the PF transient (recorded up to 300 s), with the earliest interruption at 0.3 ms. Analysis of the simultaneous measurements at different water-content-states of H. rhodopensis leaves allowed the comparison and correlation of complementary information on the structure/function of the photosynthetic machinery, which is not destroyed but only inactivated (reversibly) at different degrees; the comparison and correlation helped also to test current interpretations of each signal and advance their understanding. Our results suggest that the desiccation tolerance of the photosynthetic machinery in H. rhodopensis is mainly based on mechanism(s) that lead to inactivation of photosystem II reaction centres (transformation to heat sinks), triggered already by a small RWC decrease.

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The light-induced/dark-reversible changes in the chlorophyll (Chl) a fluorescence of photosynthetic cells and membranes in the mus-to-several min time window (fluorescence induction, FI; or Kautsky transient) reflect quantum yield changes (quenching/de-quenching) as well as changes in the number of Chls a in photosystem II (PS II; state transitions). Both relate to excitation trapping in PS II and the ensuing photosynthetic electron transport (PSET), and to secondary PSET effects, such as ion translocation across thylakoid membranes and filling or depletion of post-PS II and post-PS I pools of metabolites. In addition, high actinic light doses may depress Chl a fluorescence irreversibly (photoinhibitory lowering; q(I)). FI has been studied quite extensively in plants an algae (less so in cyanobacteria) as it affords a low resolution panoramic view of the photosynthesis process. Total FI comprises two transients, a fast initial (OPS; for Origin, Peak, Steady state) and a second slower transient (SMT; for Steady state, Maximum, Terminal state), whose details are characteristically different in eukaryotic (plants and algae) and prokaryotic (cyanobacteria) oxygenic photosynthetic organisms. In the former, maximal fluorescence output occurs at peak P, with peak M lying much lower or being absent, in which case the PSMT phases are replaced by a monotonous PT fluorescence decay. In contrast, in phycobilisome (PBS)-containing cyanobacteria maximal fluorescence occurs at M which lies much higher than peak P. It will be argued that this difference is caused by a fluorescence lowering trend (state 1 --> 2 transition) that dominates the FI pattern of plants and algae, and correspondingly by a fluorescence increasing trend (state 2 --> 1 transition) that dominates the FI of PBS-containing cyanobacteria. Characteristically, however, the FI pattern of the PBS-minus cyanobacterium Acaryochloris marina resembles the FI patterns of algae and plants and not of the PBS-containing cyanobacteria.