Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Photosynthetic control of chloroplast gene expression

Abstract: Redox chemistry—the transfer of electrons or hydrogen atoms—is central to energy conversion in respiration and photosynthesis. In photosynthesis in chloroplasts, two separate, light-driven reactions, termed photosystem I and photosystem II, are connected in series by a chain of electron carriers1,2,3. The redox state of one connecting electron carrier, plastoquinone, governs the distribution of absorbed light energy between photosystems I and II by controlling the phosphorylation of a mobile, light-harvesting, pigment–protein complex4,5. Here we show that the redox state of plastoquinone also controls the rate of transcription of genes encoding reaction-centre apoproteins of photosystem I and photosystem II. As a result of this control, the stoichiometry between the two photosystems changes in a way that counteracts the inefficiency produced when either photosystem limits the rate of the other. In eukaryotes, these reaction-centre proteins are encoded universally within the chloroplast. Photosynthetic control of chloroplast gene expression indicates an evolutionary explanation for this rule: the redox signal-transduction pathway can be short, the response rapid, and the control direct.

Oxidative stress in cyanobacteria.

Abstract: Reactive oxygen species (ROS) are byproducts of aerobic metabolism and potent agents that cause oxidative damage. In oxygenic photosynthetic organisms such as cyanobacteria, ROS are inevitably generated by photosynthetic electron transport, especially when the intensity of light-driven electron transport outpaces the rate of electron consumption during CO2 fixation. Because cyanobacteria in their natural habitat are often exposed to changing external conditions, such as drastic fluctuations of light intensities, their ability to perceive ROS and to rapidly initiate antioxidant defences is crucial for their survival. This review summarizes recent findings and outlines important perspectives in this field.

Carbon and nitrogen economy of 24 wild species differing in relative growth rate.

Abstract: The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.

Effects of water deficit on photosynthetic capacity

Abstract: Under drought, CO2 assimilation rates decrease already at small leaf water deficits. At least part of the inhibition is attributed to non-stomata1 effects at the chloroplast level, with electron transport and phosphorylation being main targets of inhibition. These findings are questioned by direct measurements of photosynthetic capacity with systems that are not Limited by stomata, e.g. leaf slices in solution or leaves at ex-ternal CO2 concentrations exceeding 5%. Here, photosynthesis was rather insensitive to dehydration down to 50–70% relative water content, and different plant species re-sponded in a very similar way. More severe dehydration affected not only pboto-synthesis, but also dark CO2 fixation and presumably also photorespiration. Rever-sible and unspecific inhibition is thought to be mediated mainly by increased concen-trations of solutes in dehydrated cells. Inhibition of photorespiration might favour photoinhibition when long-term water stress is coupled with full sunlight. Photo-inhibition, together with general senescence phenomena might be involved in long-term effects of water stress under natural drought conditions. This offers an explanation for the conflicting results of short-term water stress experiments and studies carried out under field conditions.