Analysis of Photoprotection and Apparent Non-photochemical Quenching of Chlorophyll Fluorescence in Tradescantia Leaves Based on the Rate of Irradiance-Induced Changes in Optical Transparence.

The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20 min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ = 10-28 min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150 µmol PAR·m-2·s-1. Irradiance tolerance correlated with the rate of "apparent NPQ" induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).

Effects of light environment on the induction of chlorophyll fluorescence in leaves: a comparative study of Tradescantia species of different ecotypes.

In this work, using a PAM-fluorimetry technique, we have compared effects of plant adaptation to the light or dark conditions on the kinetics of chlorophyll a fluorescence yield in Tradecantia leaves of several species (Tradescantia albiflora, Tradescantia fluminensis, Tradescantia navicularis, and Tradescantia sillamontana), which represent plants of different ecotypes. Two fluorescence parameters were used to assess photosynthetic performance in vivo: non-photochemical quenching (NPQ) of chlorophyll fluorescence (q(NPQ)) determined by energy losses in the light-harvesting antenna of photosystem 2 (PS2), and PS2 operating efficiency (Φ(PSII)). Comparative study of light-induced changes in q(NPQ) and Φ(PSII) has demonstrated that shade-tolerant Tradecantia species (T. albiflora Kunth, T. fluminensis Vell.) reveal higher capacities for NPQ and demonstrate slower transitions between the 'light-adapted' and 'dark-adapted' states than succulent species T. navicularis and T. sillamontana, which are typical habitats of semi-deserts. We analyze the photosynthetic performance of Tradescantia species in the context of their adaptabilities to variable environment conditions. The ability of shade-tolerant plants to retain a relatively long-term (∼40-60 min) 'memory' for illumination history may be associated with the regulatory mechanisms that provide the flexibility of photosynthetic apparatus in response to fluctuations of light intensity.

[Change in certain physical characteristics of cells at various stages of the cell cycle]. / Izmenenie nekorotykh fizicheskikh kharakteristik kletok na raznykh stadiiakh kletochnogo tsikla.

Experiments on semisynchronized cultures of animal and plant cells, performed in our laboratory approximately 30 years ago, have demonstrated that there exist regular changes of certain physical parameters of the cells during the cell cycle. In particular on yeast cultures there has been observed the appearance of specific electron paramagnetic resonance (EPR) signals with simultaneous change of the static magnetic susceptibility of the cultures in the period immediately preceding the beginning of the intensive budding. On chlorella cultures grown at certain regimes of light and darkness it is possible to observe characteristic changes of the kinetics of the photoconduction signal at the frequency of 10 HHz (SHR-photoconduction). It can be conjectured that these effects are of a similar nature linked to some changes of the intracellular structures at certain stages of the cell cycle. The work performed much later makes it possible to link these changes to the appearance of spin, glass-like structures in macromolecular intracellular bodies.

[Regularity of changes in magnetic characteristics of Saccharomyces cerevisiae yeast cells at various stages of culture growth]. / Zakonomernosti izmeneniia magnitnykh kharkteristik kletok drozhzhei Saccharomyces cerevisiae na raznykh stadiiakh rosta kultury.

Correlation between cell cycle of the synchronous yeast culture and ESR signal intensity at g 2.2 and 77 K was studied. It was shown that the maximal intensity of ESR signal was reached 10-15 min before the beginning of intensive cell division. The ESR signal with g 2.2 (77 K) is caused by the spin-glass like structure. The "freezing" temperature of these spin-glasses was measured.

[ESR spectra of DNA in the temperature range of 8-300 K]. / Spektry EPR preparatov DNK v intervale 8-300 K.

ESR spectra of DNA from different sources were studied in a wide temperature range. In has been shown that the structures like spin-glass exist in DNA samples and these structures manifest an ESR signal at g approximately 2.2 at room temperature, but after cooling in the magnetic field above 0.4 T they give the ESR signal at g approximately 3.0.

[Iron-sulfur centers in the mitochondrial respiratory chain at different stages of cell culture growth of the hamster Cricetulus griceus]. / Issledovanie zhelezosernykh tsentrov dykhatel'noi tsepi mitokhondrii na raznykh stadiiakh rosta kul'tury kletok khomiachka Cricetulus griceus.

The dramatic diminishing of the concentration of the N-2 iron-sulfur centre of NADH-dehydrogenase of mitochondria during the growth of cell culture of hamster fibroblasts with the subsequent recovery of concentration to the initial level was discovered by means of low-temperature ESR spectroscopy. It was concluded that the results obtained are due mainly to the decrease of the number of respiratory chains, but not to the change of the electron transport chain structure.

[Relation of growth and decay kinetics of the microwave photoconductivity signal of Chlorella to its culture state]. / Zavisimost' kinetiki narastaniia i spada signala mikrovolnovoi fotoprovodimosti khlorelly ot sostoianiia kul'tury

Signals of microwave photoconductivity (MPC) of Chlorella cells in various physiological states and at various illumination conditions have been studied. It was shown that cells of high photosynthetic activity and unruptured electron transfer system give MPC signals of the type I (nonmonotonic rise and decay kinetics). A decrease of photosynthetic activity leads to the appearance of MPC signals of the type II (monotonic rise and decay kinetics).

[Effect of long wave pre-illumination on the kinetic characteristics of microwave photoconductivity signals in Chlorella cells and the Emerson effect]. / Vliianie dlinnovolnovoi podsvetki na kineticheskie kharakteristiki signalov mikrovolnovoi fotoprovodimosti kletok khlorelly i éffekt Emersona

By the method of microwave photoconductivity the memory effects of far-red pre-illumination and Emerson effect (nonadditivity of action of radiation at two different wavelengths) for Chlorella cells were observed and studied.