This connectivity is associated with the sigmoidicity

of the initial phase of fast fluorescence transient (Joliot and Joliot 1964) and it plays an important role in mathematical models estimating the redox poise of PSII electron acceptors on the basis of chlorophyll fluorescence measurements (Lavergne and Trissl 1995; Kramer et al. 2004). In this paper, we have examined the status of photosynthetic apparatus in mature barley plants grown in different light conditions. As a typical annual grass adapted to sunny habitats, barley can serve as an interesting model, this website as one can expect different acclimations to shade than in woody plants or sciophytic species. The main conclusion of our paper is based mostly on analyses

of fast and slow chlorophyll fluorescence. Up to now, there has been a lack of studies combining the two ChlF techniques (PAM and directly measured fluorescence transient) in light acclimation studies; our current studies, using both methods, contribute to a better understanding of light acclimation process of barley plants grown under sun and shade conditions. We also discuss the differences in PSII connectivity observed in sun and shade barley leaves, and present some ideas about possible role of differences in excitation energy transfer for Bleomycin chemical structure maintaining the redox poise of PSII electron acceptors under physiologically acceptable range. Materials and methods Plant material and see more experimental design Plants of spring barley (Hordeum vulgare L.), variety Kompakt, were grown in 10 liter plastic pots filled with humus soil substrate. We grew 45 plants per pot. Four pots were exposed to full sunlight during their entire growth period,

whereas 4 pots were placed in shade, provided with a non-woven textile cover over them; this reduced the photosynthetic active radiation (PAR) to ~13 % of the sunlight. Each pot represents one replication; i.e., there were four replications per treatment. From the central part of each pot, one healthy penultimate leaf with almost horizontal position of the leaf blade (corresponding to position of light sensor) was chosen for measurements, i.e., 4 leaves from each BCKDHA treatment (sun vs. shade) were used subsequently for all the analyses. Before the start of measurements, leaf development was observed and leaves were measured after the full length of leaf was achieved. All the measurements were completed within a few days under controlled conditions, in order to prevent changes due to leaf age. After each noninvasive measurement, plants were exposed to moderate light for recovery for at least 1 h; immediately after the last measurement, analysis of assimilation pigments was done from the same position of the same leaf.