The State of Photosystem I Complexes in the Central Regions of Pea Granal Thylakoids

Grana-core and grana-margin fragments were obtained from pea (Pisum sativum L.) thylakoids, and both fractions contained photosystem I (PSI) complexes. The yield of these fractions exhibited variations for the plants grown during various periods of the summer season. Low-temperature fluorescence spectra, excitation spectra of long-wave fluorescence, and P700 kinetic characteristics were recorded for these fractions. PSI complexes in central granal regions were associated with PSII and the light-harvesting complexes of PSII, which followed from the excitation spectra of long-wave fluorescence and the kinetic characteristics of P700 light oxidation and dark reduction. The characteristics of the margin regions were changed depending on the fraction yield. If the yield was low, marginal fragments contained mainly PSI complexes. When the yield increased, PSI associates with PSII appeared. A spatial distribution and state of PSI complexes in granal thylakoids are discussed as related to the size and composition of the light-harvesting antenna.     

Features of Grana Organization in Pea Chloroplasts

Two fractions of membrane fragments—the pellets precipitated at 1300 and 20000 g (fractions G1.3 and G20, respectively)—were isolated from pea (Pisum sativum L.) chloroplasts after solubilization with digitonin. These fragments assigned to grana displayed the following differences: (1) in spectra of low-temperature fluorescence, the ratio of short-wave and long-wave band intensities, as well as integrated intensity of the whole spectrum, were higher for G1.3 than for G20 fraction; (2) in excitation spectra of long-wave fluorescence, the ratio of peaks at 650 and 680 nm and integrated intensity of the spectrum were higher for G1.3 than for G20 fraction; and (3) the shapes of fluorescence excitation spectra differed for G1.3 and G20. These results indicate that the two fractions examined differed in proportion of photosystem I and photosystem II complexes, as well as in organization of these complexes. The size of light-harvesting antenna was larger in PSI complexes of G1.3 fraction, owing, in particular, to a higher content of chlorophyll a/b-protein complexes in this fraction. After repeated digitonin fragmentation of G1.3 and G20 preparations, more than 80% of G1.3 fraction was decomposed into lighter fragments, whereas G20 fraction was resistant to fragmentation (it lost about 10% of its material). Analysis of the data suggests the presence of two structurally different types of thylakoids in grana. The yield of G20 fraction (about 20%) is comparable to the ratio between the number of intergranal thylakoids, connected to granum in pea chloroplasts, and the total number of thylakoids in this granum. Based on these data, we assume that G20 fraction represent the fragments of intergranal thylakoids that extend into the granum.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 499–506.Original Russian Text Copyright © 2005 by Kochubei, Shevchenko, Bondarenko.     

Use of a genetically labelled strain for the analysis of Yersinia pseudotuberculosis population dynamics in natural soils

The Rifr mutant of Y. pseudotuberculosis, capable of producing pure cultures in media with a high content of rifampicin, has been used for an accurate quantitation of this microorganism in various kinds of natural (nonsterile) soil in controlled laboratory and field experiments. The main biological characteristics of the mutant have been identical to those of the parent strain. The first experiments have shown that the initially high concentration of Y. pseudotuberculosis in the soil gradually decreases in 2 months. The share of this microorganism in the natural microflora of the soil seems to be rather small, which probably explains the cause of low indices of spontaneous contamination of the soil in nature.