Inactivation Of Photosynthesis Research Articles

Changes in H(+)-ATP Synthase Activity, Proton Electrochemical Gradient, and pH in Pea Chloroplast Can Be Connected with Variation Potential.

Local stimulation induces generation and propagation of electrical signals, including the variation potential (VP) and action potential, in plants. Burning-induced VP changes the physiological state of plants; specifically, it inactivates photosynthesis. However, the mechanisms that decrease photosynthesis are poorly understood. We investigated these mechanisms by measuring VP-connected systemic changes in CO2 assimilation, parameters of light reactions of photosynthesis, electrochromic pigment absorbance shifts, and light scattering. We reveal that inactivation of photosynthesis in the pea, including inactivation of dark and light reactions, was connected with the VP. Inactivation of dark reactions decreased the rate constant of the fast relaxation of the electrochromic pigment absorbance shift, which reflected a decrease in the H+-ATP synthase activity. This decrease likely contributed to the acidification of the chloroplast lumen, which developed after VP induction. However, VP-connected decrease of the proton motive force across the thylakoid membrane, possibly, reflected a decreased pH in the stroma. This decrease may be another mechanism of chloroplast lumen acidification. Overall, stroma acidification can decrease electron flow through photosystem I, and lumen acidification induces growth of fluorescence non-photochemical quenching and decreases electron flow through photosystem II, i.e., pH decreases in the stroma and lumen, possibly, contribute to the VP-induced inactivation of light reactions of photosynthesis.

Photosynthetic Oxygen Generator for Bioartificial Pancreas

Immunoisolation of pancreatic islets interrupts their vascular connections and results in severe cell hypoxia and dysfunction. This process is believed to be the major obstacle to a successful cure of diabetes by implantation of bioartificial pancreas. Here we describe a new technology for microalga-based, photosynthetic oxygen supply to encapsulated islets, in which a thermophylic strain of the unicellular alga Chlorella was used as a natural photosynthetic oxygen generator. Following determinations of the optimal number of alga cells required for compensation of islet respiration, an appropriate number of islets and algae were co-encapsulated in alginate and perifused with oxygen-free medium at increasing glucose concentrations. No insulin response to glucose was obtained in islets alone, or upon inactivation of photosynthesis by darkness. However, under illumination, photosynthetic- dependent oxygen generation induced higher glucose-stimulated insulin response when compared to normoxic perifusion. Such photosynthetic oxygen generation may have a potential application in development of various bioartificial tissues, in particular the endocrine pancreas.

Effects of nitrogen availability on pigmentation and carbon assimilation in the cyanobacterium Synechococcus sp. strain SH-94-5

Because pigments of phototrophs can be involved either in photosynthesis or photoprotection, pigmentation changes in response to nutrient availability can affect how cells interact with their solar environment. We investigated the impact of nitrogen availability both on pigmentation of the cyanobacterium Synechococcus sp. strain SH-94-5 and on carbon assimilation by this strain in the presence or absence of UV radiation. Pigmentation changes in strain SH-94-5 due to ammonium exhaustion included phycobiliprotein degradation, an exponential decline in chlorophyll a content, and a net increase in beta-carotene. Following its replenishment, ammonium stimulated non-photosynthetic carbon assimilation for several hours prior to the resumption of photosynthesis and growth. Carbon fixation during this lag phase was concurrent with the metabolism of glycogen reserves, and it is likely that inorganic carbon was incorporated into glycogen-derived carbon skeletons primarily for amino acid synthesis. In contrast, carbon fixation was almost exclusively photosynthetic during exponential growth. UV-A radiation (320-400 nm) inhibited photosynthetic but not non-photosynthetic carbon assimilation. Only growing cells were inhibited, and the disappearance of inhibition following nitrogen depletion appeared to result from the reduction of cellular photosensitizing targets below a threshold level rather than from the inactivation of photosynthesis.

Synergistic effect of high-light and low temperature on cell growth of the Delta12 fatty acid desaturase mutant in Synechococcus sp. PCC 7002.

The effect of polyunsaturated fatty acids on photosynthesis and the growth of the marine cyanobacterium Synechococcus sp. PCC 7002 was examined using wild-type and Delta12 fatty acid desaturase mutant strains. Under a light intensity of 250 mumol m(-2) s(-1), wild-type cells could grow exponentially in a temperature range of 20-38 degrees C, but growth was non-exponential below 20 degrees C and ceased at 12 degrees C. The Delta12 desaturase mutant cells lacking polyunsaturated fatty acids had the same growth rate as wild-type cells in a temperature range of 25-38 degrees C but grew slowly at 22 degrees C, and no cell growth took place below 18 degrees C. Under a very high-light intensity of 2.5 mmol m(-2) s(-1), wild-type cells could grow exponentially in a temperature range of 30-38 degrees C, although the high-light grown cells became chlorotic because of nitrogen limitation. The temperature sensitive phenotype in the Delta12 desaturase mutant was enhanced in cells grown under high-light illumination; the mutant cells could grow at 38 degrees C, but were killed at 30 degrees C. The decrease of oxygen evolution and nitrate consumption by whole cells as a function of temperature was similar in both wild type and the Delta12 desaturase mutant. No differences were observed in either light-induced damage of oxygen evolution or recovery from this damage. No inactivation of oxygen evolution took place at 22 degrees C under the normal light intensity of 250 mumol m(-2) s(-1). These results suggest that growth of the Delta12 desaturase mutant at low temperature is not directly limited by the inactivation of photosynthesis, and raise new questions about the functions of polyunsaturated membrane lipids on low temperature acclimation in cyanobacteria.

Acclimation to the growth temperature and the high-temperature effects on photosystem II and plasma membranes in a mesophilic cyanobacterium, Synechocystis sp. PCC6803.

High-temperature effects on Photosystem II and plasma membranes, temperature dependence of growth, and acclimation to the growth temperature were studied in a mesophilic cyanobacterium, Synechocystis sp. PCC6803. The following results were obtained. (1) Small but distinct temperature acclimation of the PSII reaction center activity was shown for the first time when the activity was measured at inhibitory high temperatures. However, the reaction center activity showed no apparent acclimation when it was measured at growth temperatures after heat stress. (2) Oxygen-evolving activity and the permeability of plasma membranes showed higher resistance to heat when PCC6803 cells were grown at higher temperatures. (3) Acclimation of photosynthesis to the growth temperature seemed to occur so as to maintain photosynthesis activity not at a maximum level but in a certain range at the growth temperatures. (4) Neither sensitivity to high-temperature-induced dissociation of phycobilisomes from the PSII reaction center complexes nor degradation of phycocyanin were altered by changes in the environmental temperature. (5) A close relationship between the viability of cells and the structural changes of plasma membranes (but not the inactivation of photosynthesis) was observed. The denaturation process of PSII complexes and the relationship between the temperature dependence of the growth of Synechocystis PCC6803 cells and that of the photosynthetic activity are also discussed.

Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of Vicia leaves.

Guard cell protoplasts isolated from Vicia leaves showed a strong suppression of the photosynthesis under hypotonic conditions, as reflected by changes in the chlorophyll fluorescence characteristics. The response was reversible as well. Mesophyll cell protoplasts did not show any lowering of photosynthetic activity under hypo-osmotic conditions. This result indicates that the response was guard cell specific.

Acclimation of a mesophilic cyanobacterium, Synechocystis sp. PCC 6803 to the growth temperature

Photosynthetic organisms usually experience large changes of environmental factors, such as temperature, light intensity or light quality. Temperature is one of the most important factors which control the enzymatic reaction including photosynthesis. They may regulate the total reaction system to operate the photosynthesis maximally for their survival. In higher plants, acclimation to the surrounding temperature has been reported. Here, we analyzed the effect of temperature, especially that of high temperature, on the growth using a mesophilic cyanobacterium, Synechocystis sp. PCC 6803. The following results were obtained. (1) Photosynthesis seemed to be regulated so as to keep its rate in a certain range irrespective of the growth temperatures. (2) The oxygen-evolving activity and the intactness of plasma membranes showed larger tolerance to high temperatures when S. PCC 6803 cells were grown at higher temperatures. (3) The reaction center activity of photosystem II (PS II) showed similar sensitivity to the heat stress when the activity was measured at the growth temperatures irrespective of the growth temperature. However,small but distinct temperature acclimation of the PSII reaction center activity was shown for the cells grown at different temperatures when the activity was measured at inhibitory high temperatures. (4) A close relationship was observed between the viability of cells and the structural changes of plasma membranes (not the inactivation of photosynthesis). We will discuss how the S. PCC 6803 cells acclimate to the environmental temperature.

Osmotic and Atmospheric Dehydration Effects in the Lichens Hypogymnia Physodes, Lobaria Pulmonaria, and Peltigera Aphthosa: An in vivo Study of the Chlorophyll Fluorescence Induction

Inactivation of photosynthesis during atmospheric and osmotic (highly concentrated NaCl or sucrose solutions) dehydration was monitored by measurement of chlorophyll fluorescence induction (OIP-phase, Kautsky-curves) in three lichen species. The induction curves were changed in a very similar way by all three treatments. All dehydration effects were rapidly reversible after rehydration. At relatively mild water stress, the rise time to the transient peak Fp was prolonged, and the variable part of fluorescence was diminished. In addition, at severe water stress, a considerable decline of the F0 value was observed. For NaCl treatment this effect started at water potentials <-8.5 MPa in P. aphthosa, <-12 MPa in H. physodes, and <-21 MPa in L. pulmonaria. Above these water potentials, our observations are in agreement with values from desiccation-tolerant algae, higher plants, and lichens, where an inactivation on the photosystem 2 (PS2) donor side has been postulated. At very low water potentials, the decrease in F0 probably monitors changes in the organization of the antenna apparatus of PS2.

Metabolic engineering of rice leading to biosynthesis of glycinebetaine and tolerance to salt and cold.

Genetically engineered rice (Oryza sativa L.) with the ability to synthesize glycinebetaine was established by introducing the codA gene for choline oxidase from the soil bacterium Arthrobacter globiformis. Levels of glycinebetaine were as high as 1 and 5 micromol per gram fresh weight of leaves in two types of transgenic plant in which choline oxidase was targeted to the chloroplasts (ChlCOD plants) and to the cytosol (CytCOD plants), respectively. Although treatment with 0.15 M NaCl [corrected] inhibited the growth of both wild-type and transgenic plants, the transgenic plants began to grow again at the normal rate after a significantly less time than the wild-type plants after elimination of the salt stress. Inactivation of photosynthesis, used as a measure of cellular damage, indicated that ChlCOD plants were more tolerant than CytCOD plants to photoinhibition under salt stress and low-temperature stress. These results indicated that the subcellular compartmentalization of the biosynthesis of glycinebetaine was a critical element in the efficient enhancement of tolerance to stress in the engineered plants.

Inactivation of the clpP1 gene for the proteolytic subunit of the ATP-dependent Clp protease in the cyanobacterium Synechococcus limits growth and light acclimation.

ClpP functions as the proteolytic subunit of the ATP-dependent Clp protease in eubacteria, mammals and plant chloroplasts. We have cloned a clpP gene, designated clpP1, from the cyanobacterium Synechococcus sp. PCC 7942. The monocistronic 591 bp gene codes for a protein 80% similar to one of four putative ClpP proteins in another cyanobacterium, Synechocystis sp. PCC 6803. The constitutive ClpP1 content in Synechococcus cultures was not inducible by high temperatures, but it did rise fivefold with increasing growth light from 50 to 175 micromol photons m(-2) s(-1). A clpP1 inactivation strain (delta clpP1) exhibited slower growth rates, especially at the higher irradiances, and changes in the proportion of the photosynthetic pigments, chlorophyll a and phycocyanin. Many mutant cells (ca. 35%) were also severely elongated, up to 20 times longer than the wild type. The stress phenotype of delta clpP1 when grown at high light was confirmed by the induction of known stress proteins, such as the heat shock protein GroEL and the alternate form of PSII reaction center D1 protein, D1 form 2. ClpP1 content also rose significantly during short-term photoinhibition, but its loss in delta clpP1 did not exacerbate the extent of inactivation of photosynthesis, nor affect the inducible D1 exchange mechanism, indicating ClpP1 is not directly involved in D1 protein turnover.

Relationship between Photosynthesis and Chlorophyll Content during Leaf Senescence of Rice Seedlings

Photosynthetic oxygen evolution, chlorophyll contents and chlorophyll a /b ratios of 3rd to 6th leaves of rice seedlings were measured to examine whether or not inactivation of photosynthesis during senescence is related to loss of chlorophyll. Photosynthetic activity decreased more rapidly than chlorophyll content during leaf senescence; as a result, the lower the leaf position, the lower was the rate of oxygen evolution determined on the basis of chlorophyll. Chlorophyll a⊘b ratio also decreased with advancing senescence. Electrophoretic analysis revealed that the decline in chlorophyll a⊘b ratio is due to more rapid degradation of the reaction center complexes than light-harvesting chlorophyll a⊘b proteins of photosystem II and that the photosystem I reaction center disappears in parallel with the inactivation of photosynthesis. A simple method was developed to estimate the amounts of chlorophyll a associated with the reaction center complexes of the two photosystems from the total chlorophyll contents and chlorophyll a⊘b ratios of leaves. Rates of oxygen evolution, determined on the basis of chlorophyll a bound to the reaction center complexes, remained constant throughout the course of senescence. Thus, inactivation of photosynthesis is closely related with loss of the reaction center complexes during leaf senescence of rice seedlings. The results suggest that loss of photosynthesis is mainly caused by loss of a functional unit of photosynthesis or by a decrease in the number of whole chloroplasts.

Freezing injury in cold-acclimated and unhardened spinach leaves

Spinach plants (Spinacia oleracea L.) were frost-hardened by cold-acclimation to 1° C or kept in an unhardy state at 20°/14° C in phytotrons. Detached leaves were exposed to temperatures below 0°C. Rates of photosynthetic CO2 uptake by the leaves, recorded after frost treatment, served as a measure of freezing injury. Thylakoid membranes were isolated from frost-injured leaves and their photosynthetic activities tested. Ice formation occurred at about-4° to-5° C, both in unhardened and cold-acclimated leaves. After thawing, unhardened leaves appeared severely damaged when they had been exposed to-5° to-8° C. Acclimated leaves were damaged by freezing at temperatures between-10° to-14° C. The pattern of freezing damage was complex and appeared to be identical in hardened and unhardened leaves: 1. Inactivation of photosynthesis and respiration of the leaves occurred almost simultaneously. 2. When the leaves were partly damaged, the rates of photosynthetic electron transport and noncyclic photophosphorylation and the extent of light-induced H(+) uptake by the isolated thylakoids were lowered at about the same degree. The dark decay of the proton gradient was, however, not stimulated, indicating that the permeability of the membrane to-ward protons and metal cations had not increased. 3. As shown by partial reactions of the electron transport system, freezing of leaves predominantly inhibited the oxygen evolution, but photosystem II and photosystem I-dependent electron transport were also impaired. 4. Damage of the chloroplast envelope was indicated by a decline in the percentage of intact chloroplasts found in preparations from injured leaves. The results are discussed in relation to earlier studies on freezing damage of thylakoid membranes occurring in vitro.