V. Goltsev

Low temperature tolerance of tobacco plants transformed to accumulate proline, fructans, or glycine betaine. Variable chlorophyll fluorescence evidence

Tobacco (Nicotiana tabacum L.) has been transformed to accumulate different compatible solutes (proline, fructans, or glycine betaine) in order to improve its tolerance to abiotic stress. Photosynthetic activity of wild Type (wt) and transformed tobacco plants before and after freezing stress was studied by measuring chlorophyll (Chl) fluorescence. The JIP test of Chl fluorescence induction was used to analyze in details the functional activity of photosystem 2. No significant differences were found among wild Type and transgenic plants after 12 h of freezing. Both plant Types maintained the same values of the measured parameters [FV/FM, PI(CSM), ABS/RC, TR0/RC, ET/RC] after recovery of stress. The studied Chl fluorescence parameters decreased only for the wild Type plants, stressed for 24 h at −2 °C. The strong inhibition of photosynthetic reactions in the wt plant after 24 h of freezing could not be restored. The evaluated parameters of transgenic plants did not change significantly after 24 h at −2 °C and successfully survived freezing stress.

Advances on Photosystem II Investigation by Measurement of Delayed Chlorophyll Fluorescence by a Phosphoroscopic Method

A method for data acquisition based on recording of light signal from a conventional phophoroscope fluorometer with high‐speed digitalization is proposed to extract more information from a delayed chlorophyll a fluorescence (DF) signal. During the signal processing from all points registered by the fluorometer, we obtain simultaneously a large number of induction curves of DF decaying at different time ranges. In addition, it is possible to register a series of dark relaxation kinetics of DF, recorded at different moments during the induction period or at different temperatures. This allows the evaluation of the contribution of DF kinetic components during the induction period or at different temperatures and the comparison between DF signals registered with different phophoroscopes. With the phosphoroscope system used in this study, we have shown that the contribution of the millisecond components (with lifetimes 0.6 and 2–4 ms) predominates during the first second of the induction period. After 1 s of illumination, the amplitudes of the 0.6 ms and 2–4 ms components and of the slower one (with lifetime more than 10 ms) become approximately equal. The change in lifetime of the different components during the induction and during gradual heating is also observed. It is shown that all registered DF kinetic components have different temperature dependences.

High-temperature damage and acclimation of the photosynthetic apparatus I. Temperature sensitivity of some photosynthetic parameters of chloroplasts isolated from acclimated and non-acclimated bean leaves

The thermosensitivity of delayed fluorescence, the relative values of variable chlorophyll fluorescence and the degree of quenching of 9-aminoacridine fluorescene were studied in the chloroplasts from heat-acclimated and non-acclimated (treated 6 h at 52,5°C) young bean plants. The temperature sensitivity of each parameter studied was defined by that temperature at which chloroplast activity decreased by 50% (T50) of its maximum value. There was appreciable increase in the thermostability of membrane energization in chloroplasts isolated from acclimated and non-acclimated plants compared with the controls. The photosynthetic parameters differed according to the suspending medium and the preacclimation treatment. When chloroplast were suspended in phosphate buffer with the addition of stabilizing compounds (2 M sucrose or 0.5% human serum albumin) the thermostability of the thylakoid membranes increased, as was evident by the increases in T50 of about 8–10° C (sucrose) and 2–5° C (human serum albumin) for all the parameters investigated. Photoinduced quenching of 9-aminoacridine fluorescence decreased to some extent in the presence of protective compounds, but in chloroplasts from acclimated plants the T50 was practically equal to that for their long-lived luminescence under the same conditions. At the thylakoid membrane level, acclimation was clearly manifested as an increased thermostability of photoinduced proton-gradient formation.

Effects of exogenous polyamines applied separately and in combination with simulated acid rain on functional activity of photosynthetic apparatus

Summary Ten-day-old bean seedlings (Phaseolus vulgaris L.) were grown in a greenhouse and sprayed with spermidine or spermine. After 24 h they were treated with a cocktail of simulated acid rain (pH 5.6 and 1.8). Polyamines were applied separately or in combination with acid rain. Their protective effect on the functional activity of the photosynthetic apparatus in the acid rain-treated plants was investigated. It was found that acid rain with pH 1.8 applied separately decreased strongly the photosynthetic rate, the oxygen evolution, as well as the PS2 activity. Polyamines (spermidine and spermine) applied 24 h the before the acid rain treatment partially diminished the inhibitory effect of acid rain on the photosynthetic apparatus. The results showed also that the favourable effect of spermine was higher than that of spermidine. The protective action of polyamines could be explained by their polycationic nature, their ability to bind with photosynthetic membranes, resulting in conformational changes and stabilization, of the membrane and by their ability to act as free radical scavengers.

Influence of short-term osmotic stress on the photosynthetic activity of barley seedlings

Oxygen evolution and chlorophyll a fluorescence transients of two barley (Hordeum vulgare L) cultivars subjected to polyethylene glycol induced osmotic stress was examined. The relative water content of the plants was used as a measure of their water status. The results suggested that although dehydration was considerable, photosystem 2 was weakly affected by the osmotic treatment.

Delayed Chlorophyll Fluorescence as a Monitor for Physiological State of Photosynthetic Apparatus

ABSTRACT Intact plants emit light quanta called delayed fluorescence (DF). DF is result of radiative deactivation of secondary excited chlorophyll molecules in Photosystem II (PS II) antennae complexes. The excitations are produced by backward electron- transfer reactions both in the donor and acceptor sides of PS II. The poly-exponential dark decay of DF in a time interval of tens of nanoseconds to tens of seconds reflects the kinetics of different forward and backward reactions of the photosynthetic electron transfer. The current work reviews the mechanisms of the DF light quanta generation and the methodical approaches that allow us to obtain quantitative information about the photosynthetic machinery state using the DF signal from native objects. We examine an approach for the simultaneous record of DF and prompt chlorophyll fluorescence during the transition of the photosynthetic machinery from dark-adapted to light-adapted state. A new device (Senior PEA) built by Hansatech (Kings Lynn, UK) allows us to measure simultaneously the induction transients of prompt chlorophyll fluorescence, DF decaying in a time range 10 μs—240 ms, and the changes in transmission at 820 nm. The comparative analysis of the three types of signals and the application of a model-based description of the processes and reactions that determine the dynamics of the signals during the light-induced transitions (dynamic models and JIP-test) allow us to obtain, from a single few-seconds-long measurement, quantitative information for: a) energetic fluxes and efficiencies at different steps of energy transformation; b) rate constants of electron transfer in and between the two photosystems; c) energization of the thylakoid membrane. This illustrates that DF in combination with other optical and luminescent measurements is a highly informative method for investigation of the physiological state of the photosynthetic apparatus of plants in vivo and in situ, and is an indispensable tool for the purposes of the biophysical phenomics.

Effects of Grapevine Fanleaf and Stem Pitting Viruses on the Photosynthetic Activity of Grapevine Plants Grown in vitro

The effects of viral diseases on the photosynthetic activity of grapevine (Vitis rupestrisvar. Rupestris du Lot) leaves were investigated. The third and sixth leaves used for measurements were obtained from in vitrogrown healthy plants and plants affected by grapevine fanleaf and rupestris stem pitting viruses. The induction curves of prompt and delayed chlorophyll fluorescence, as well as the temperature characteristics of steady-state, prompt, and delayed emissions, were investigated. Age-dependent changes were found, which were related, on the one hand, to the acceleration of electron transport and the enhancement of thylakoid energization and, on the other hand, to a smaller extent of transmembrane ΔμH+in the younger sixth leaf compared to that in the third leaf. The infected plants characteristically showed faster electron transport, an elevated energetic efficiency of photosynthesis, and the suppression of CO2fixation owing to a presumable activation of the adenylate metabolism. An analysis of the thermograms of prompt and delayed fluorescence revealed the shifts in the position of the M1peak and a half-inhibition temperature T50towards a higher temperature in infected plants, which indicates a certain increase in the thermal tolerance of thylakoid membranes. The data suggest that the viral metabolism affects the functional activity and stability of thylakoid membranes.

High-temperature damage and acclimation of the photosynthetic apparatus : II. Effect of mono- and divalent cations and pH on the temperature sensitivity of some functional characteristics of chloroplasts isolated from heat-acclimated and non-acclimated bean plants.

The influence of mono- (K+) and divalent (Mg2+) cations and protons (pH) on the temperature sensitivity of thylakoid membranes was investigated in three groups of young bean plants (control, heat-acclimated and non-acclimated). Thylakoid-membrane function was monitored by second and millisecond delayed fluorescence and 9-aminoacridine fluorescence quenching. It was established that metal ions at investigated concentrations decreased the thermostability of the photosynthetic parameters — an increase of MgSO4 concentration from 0.1 to 20 mM decreased the temperature of their half-inactivation (T50) by 13°C. At the same time the pH dependence of the thermal stability of these parameters showed a maximum at pH 5.5–6.5. The half-inactivation temperatures of those photosynthetic parameters connected with the ability of the thylakoid membrane to form light-induced proton gradients increased by 6–7°C in the heat-acclimated plants compared with the control. It was assumed that the temperature inactivation of photosynthetic electron transfer and the energization of the thylakoid membrane was determined both by the thermoinduced dissociation of the light-harvesting chlorophyll a/b protein complex from PSII, leading to destruction of the excitation energy transfer to the reaction centres, and by the thermal denaturation of the membrane-protein components. The rate of these processes was probably controlled by the size of the negative surface charge and the viscosity of the thylakoid membrane.

Effect of Cholesterol and Benzyl Alcohol on Prompt and Delayed Chlorophyll Fluorescence in Thylakoid Membranes

Photosynthesis is one of most sensitive processes determining plant response to environmental stress. Possible stress-induced reaction is modification of fluidity of the chloroplast thylakoid membrane (TM). The TM physical state may plays an important role in controlling of the light reactions of photosynthesis (1 – 3). Artificial alteration of the TM fluidity reflects on the whole chain electron transport rate, proton uptake, oxidation of the primary electron acceptor of PS II (QA), cytochrome f reduction and parameters of cation-induced chlorophyll fluorescence (3). Cholesterol incorporation leads to a decrease of membrane fluidity, while the treatment with benzyl alcohol has opposite effect (4). The effect of both membrane perturbing agents on the fluorescent transients of pea thylakoids expressed as follows: a decrease of PS IIα centers and of the Fv/Fm ratio in cholesterol-treated TM; in benzyl alcohol-treated TM the chlorophyll a fluorescence induction parameters are influenced to a smaller extent. The level of QB-nonreducing centers seems not to be altered by either treatment (5). The artificial TM fluidity alteration would be reflected also on other luminescence characteristics of photosynthetic apparatus.

Delayed luminescence yield kinetics in flash illuminated green plants

Abstract Oscillations of a delayed light emission have been studied in Chlorella cells, pea leaves and isolated pea chloroplasts illuminated by series of short saturating flashes. The oscillation is determined by changes of S-state numbers of the O 2 -evolving system and by pH lowering inside the thylakoids after a flash. The rate of deactivation of the S-states drastically decreases upon temperature lowering to + 4°C, and its pH-dependence has a maximum at pH 6. In isolated chloroplasts, transitions between individual S-states are inhibited at some certain temperatures in the range from −17°C to −40°C.