Photosynthesis

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

Bacterial photosynthesis in surface waters of the open ocean

Abstract: The oxidation of the global ocean by cyanobacterial oxygenic photosynthesis, about 2,100 Myr ago, is presumed to have limited anoxygenic bacterial photosynthesis to oceanic regions that are both anoxic and illuminated. The discovery of oxygen-requiring photosynthetic bacteria about 20 years ago changed this notion, indicating that anoxygenic bacterial photosynthesis could persist under oxidizing conditions. However, the distribution of aerobic photosynthetic bacteria in the world oceans, their photosynthetic competence and their relationship to oxygenic photoautotrophs on global scales are unknown. Here we report the first biophysical evidence demonstrating that aerobic bacterial photosynthesis is widespread in tropical surface waters of the eastern Pacific Ocean and in temperate coastal waters of the northwestern Atlantic. Our results indicate that these organisms account for 2-5% of the photosynthetic electron transport in the upper ocean.

Relations between pigment content and photosynthetic characteristics in a blue-green alga

Abstract: 1. The blue-green alga Anacystis nidulans was cultured under steady state conditions at 25 and 39 degrees C. and under several different light intensities to give five different types of cells. 2. Cells were submitted to pigment analysis based upon acetone extracts and aqueous extracts obtained by sonic disintegration. The different cell types show a threefold range of chlorophyll content and a fourfold range of phycocyanin content with only minor changes in the chlorophyll/phycocyanin ratio. Cells of highest pigment content were estimated to contain 2.8 per cent chlorophyll a and 24 per cent phycocyanin, the latter on a total chromoproteid basis. 3. Light intensity curves of photosynthesis were obtained for each of the cell types at 25 and at 39 degrees C. The slopes of the light-limited regions of the curves are approximately linear functions of chlorophyll and phycocyanin contents. Maximum light-saturated rates of photosynthesis at 25 and 39 degrees show no simple relation to pigment content.

Low leaf-level response to light and nutrients in Mediterranean evergreen oaks: a conservative resource-use strategy?

Abstract: We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI = (maximum value - minimum)/maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems.

A cost-income model of leaves and roots with special reference to arid and semiarid areas

Abstract: The richness of plant-life forms, ranging from unicellular algae to large trees, from trailing herbs to large climbing vines, and from ephemerals to long-lived perennials, suggests that a variety of environmental factors exert important influences on plant shapes (Terborgh 1973). In this paper we describe a model in which the inevitable association between water loss and entrance of carbon dioxide through stomates, together with cell-morphological and physiological traits that affect these exchanges, prevent any one plant-life form from being the best adapted to more than a fraction of the earth's complex patterns of temperature and moisture availability. These relationships may also explain apparently stable mixtures of plants with different life forms in a single environment. The tight linking of water loss and carbon uptake affects all aspects of the total photosynthetic and materials uptake system of vascular plants, because reducing water loss lowers rates of carbon uptake and hence lowers rates of net photosynthesis per unit area of photosynthesizing surface. The combination of characters that yields maximum net photosynthesis per unit time under moist conditions reduces the maximum rate under drier conditions, and vice versa. There are, of course, mechanisms, such as C4 photosynthesis and opening stomata only when atmospheric humidity is high, which reduce water loss per molecule of carbon fixed, but these mechanisms are of limited effectiveness and have associated costs. Any model of natural selection assumes both some "goal" that is being optimized (or maximized) and the constraints within which the organisms operate. A reasonable short-range goal for plants might be the maximization of photosynthetic rate; a plant capable of increasing photosynthesis within the constraints of its available resources and the physical environment should gain advantages in competition with other plants, defenses against herbivores, and should have more energy to devote to reproduction. We assume in our model that total fitness is strongly correlated with net gain in calories and that it is reasonable to treat allocations of resources to leaves, stems, and roots in terms of calories. Thus, we ignore other potentially significant factors, e.g., nonuniform mortality risks due to herbivory or pathogens, which should influence the

Carotenoids in photosynthesis

Abstract: Carotenoids are usually considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen. Drawing upon recent work with photosynthetic bacteria, evidence is presented as to how the carotenoids are organized within both portions of the photosynthetic unit (the light harvesting antenna and the reaction centre) and how they discharge both their functions. The accessory pigment role is a singlet-singlet energy transfer from the carotenoid to the bacteriochlorophyll, while the protective role is a triplet-triplet energy transfer from the bacteriochlorophyll to the carotenoid.