The changes in thermoluminescence (TL) signals induced by short-term ozone exposure of leaves are characterized by a down-shift of the peak-temperature of the TLB-band and an increase of a TL band at 55°C. We investigated the relationship of these changes to photosystem 2 (PS2) photochemistry. The changes were not only detectable in the presence of ozone, but also after irradiation of dark-adapted leaves and after aging of irradiated detached leaf segments. The opposite effect on TL, an up-shift of the peak-temperature of the B-band and the decrease of the intensity of the band at 55°C were found after infiltration of leaves with nigericin, antimycin A, and diphenyleneiodonium chloride (DPI). Propyl gallate down-shifted the peak-temperature of the B-band. 2,5-dimethyl-1,4-benzoquinone up-shifted the peak-temperature of the B-band and decreased the intensity of the 55°C band. The intensity of the 55°C band did not change significantly in the presence of oxygen in comparison to that in nitrogen atmosphere. It decreased with time of dark adaptation (50% intensity was observed after 3 h of dark adaptation at room temperature), however, it was reactivated to its initial value (at 5 min of dark adaptation) after 1 single-turnover flash. The 55°C band was not significantly changed in the presence of DCMU. Thus the ozone-induced band at 55°C is assigned to charge recombination in PS2. Changes in the electron transport chain at the acceptor side of PS2, probably related to the cyclic electron transport around photosystem 1 and/or chlororespiration, could play an important role in the increase of the 55°C band and the down-shift of the B-band. The changes at the acceptor side indicated by TL can be an ex pression of a physiological regulatory mechanism functional under stress conditions. and J. Skotnica ... [et al.].
Melatonin is a well-known bioactive molecule able to mitigate photooxidative damage caused by excess light. Here we have shown that mutant Arabidopsis lines with disrupted genes for melatonin putative receptor CAND2/PMTR1 and GPA1 encoding the α-subunit of heterotrimeric G-protein were partially insensitive to melatonin treatment under high light stress. They exhibited a higher degree of photodamage due to a significantly decreased photosynthetic activity and diminished expression of chloroplast and nuclear-encoded genes and the corresponding proteins. A possible mechanism for melatonin-dependent regulation of chloroplast genes is associated with a change in the activity of the genes for chloroplast RNA polymerases. We conclude that under high light stress, melatonin may act as a hormone-like signaling molecule via the CAND2/PMTR1-mediated signaling pathway.
Synechococcus is one of the most abundant photoautotrophic picoplankton in the marine ecosystem. However, it is not clear how Synechococcus assemblages respond to light intensity variation in a genus group. Here, enriched Synechococcus assemblages from in situ coastal seawater were subjected to light intensity simulation experiments in a range of 9-243 μmol(photon) m-2 s-1. Characteristics concerning physiology, genomics, and metatranscriptomics were analyzed. Physiologically, the fitting model predicted photosynthesis indications and pigment contents increased with different trends following the light intensity. Genomic sequencing demonstrated that both the phylogenetic and phenotypic compositions of Synechococcus assemblage exhibited population succession. Especially, the proportion of Synechococcus pigment type 2 was changed significantly. In metatranscriptomics, most genes were downregulated in the high-light intensity group, while photosynthesis-related genes were entirely upregulated. The high upregulation of photosynthesis-related genes, such as psbO, psbA, apcB, and cpcB, corresponded to the succession of Synechococcus genotype and was responsible for the physiological shift in response to light intensity.
Arthrospira maxima is unique among cyanobacteria, growing at alkaline pH (<11) in concentrated (bi)carbonate (1.2 M saturated) and lacking carbonic anhydrases. We investigated dissolved inorganic carbon (DIC) roles within PSII of A. maxima cells oximetrically and fluorometrically, monitoring the light reactions on the donor and acceptor sides of PSII. We developed new methods for removing DIC based on a (bi)carbonate chelator and magnesium for (bi)carbonate ionpairing. We established relative affinities of three sites: the water-oxidizing complex (WOC), non-heme iron/QA-, and solvent-accessible arginines throughout PSII. Full reversibility is achieved but (bi)carbonate uptake requires light. DIC depletion at the non-heme iron site and solvent-accessible arginines greatly reduces the yield of O2 due to O2 uptake, but accelerates the PSII-WOC cycle, specifically the S2-S3 and S3-S0 transitions. DIC removal from the WOC site abolishes water oxidation and appears to influence free energy stabilization of the WOC from a site between CP43-R357 and Ca2+., G. Ananyev, C. Gates, G. C. Dismukes., and Obsahuje bibliografické odkazy
In this work, the injuries caused by clethodim herbicide application as well as the use of exogenous salicylic acid (SA) as a protective agent against clethodim in Zea mays leaves were examined. Although the target for clethodim is the inhibition of acetyl coenzyme A carboxylase (ACCase) which is the key enzyme for fatty acid biosynthesis, it can indirectly affect the photosynthetic machinery, gaseous exchange and some biochemical parameters. Clethodim application caused chlorosis and yellowing of leaf-tip parts. Higher doses caused browning or reddening of leaves and sometimes dead parts of the leaf margins were observed. The rate of photosynthesis was significantly lowered and the pigments content was highly reduced as a response to clethodim spraying. Moreover, other gas-exchange properties were altered. Furthermore, accumulation of high amounts of carbohydrates, proteins and proline were detected. SA spraying three days prior clethodim application caused partially or totally disappearance of clethodim injuries and kept the leaves similar to those of control. Improved photosynthesis and enhanced pigments content were observed in leaves treated with SA. Other analyzed parameters showed values similar to those of the corresponding control. From the experimental work, an evidenced role of SA working against clethodim effects was suggested and discussed in this paper., D. E. M. Radwan, D. M. Soltan., and Obsahuje bibliografii
Floristic composition, morphological functional types, and altitudinal distribution pattern for C4 species were studied in Yunnan province, South-western China. 159 species, in 6 families and 60 genera, were identified with C4 photosynthesis. 93 % of these C4 species were found in Monocotyledoneae, e.g. Cyperaceae (18 species), Gramineae (129 species), and Commelinaceae (1 species), the other 7 % was in Dicotyledoneae, e.g. Amaranthaceae (5 species), Portulacaceae (4 species), and Chenopodiaceae (2 species). Hence C4 plants mainly occurred in very few families in the tropical region. Compared with those in semi-arid grasslands and arid deserts in North China, more C4 grasses and much less Chenopodiaceae C4 species occurred in the tropical region. This indicates the physiological responses of C4 plants from the two families are very different. Chenopodiaceae C4 species may be more fit semi-arid and arid environments, while C4 grasses are more fit the moist tropical conditions. There was a strong relationship between C4 distribution and altitude in the tropical region. Altitudinal distribution pattern for C4 species in the region was consistent with altitude, climate, and habitats.
Floristic composition, morphological functional types and habitat distributions for C4 species were studied in Xinjiang, North-western China. 89 species, in 9 families and 41 genera, were identified with C4 photosynthesis. 48 % of these C4 species were found in Monocotyledoneae, e.g. Cyperaceae (5 species), Gramineae (38 species), the other 52 % was in Dicotyledoneae, e.g. Chenopodiaceae (29 species), Amaranthaceae (7 species), and Polygonaceae (5 species). Compared with those in semi-arid grasslands in North China and tropical forests in South China, more plant families were found with the occurrence of C4 plants in this arid region. Relatively higher annual species (63 %), shrubs (18 %), and Chenopodiaceae C4 species (33 %) compositions were the primary characteristics for the C4 species occurring in Xinjiang, and this was remarkably related with its arid environment. More Chenopodiaceae C4 species occurring in the region suggested that this type of C4 species may have higher capacity to fit the air and soil droughts. There was a strong relationship between C4 occurrence and habitat distributions, more than half of the total 89 C4 species were found in disturbed and cultivated lands and early stages of vegetation successions, indicating C4 occurrence was not only related with climate changes, but also with land uses and vegetation dynamics.