Showing papers on "Photosynthesis published in 1973"

Chlorophyll a fluorescence in marine centric diatoms: Responses of chloroplasts to light and nutrient stress

Abstract: Observations at sea of large variations in the cellular fluorescence of phytoplankton prompted a study of the fluorescence responses in marine diatoms to light and nutrient stress. When older cultures of Lauderia borealis were exposed to intense light, the in vivo fluorescence of chlorophyll a declined within the first 2 min of exposure. This initial response to light stress appeared to be correlated with a contraction of the chloroplasts. Continued exposure led to a second decline in fluorescence, which required 30 to 60 min for completion. A movement of chloroplasts to the valvar ends of the cell caused this secondary response. Both the contraction and intracellular movement of chloroplasts appeared to be related to both photoinhibition of photosynthesis and diel fluctuations in cellular fluorescence. An investigation of continuous cultures of Cyclotella nana showed that in vivo chlorophyll a fluoresced more strongly in nitrogen-starved cells than in enriched ones. Photoinhibition of cellular fluorescence also increased with the cell's state of nitrogen deficiency.

Hydrogen evolution by a chloroplast-ferredoxin-hydrogenase system.

Abstract: Spinach chloroplast preparations were mixed with Clostridium kluyveri hydrogenase and ferredoxin. Hydrogen evolution could be measured in the light in the absence of any added electron donors. Inhibition of the water-splitting reaction or of photosystem II reduced the amount of H2 evolved more than 95%, indicating that H2O was the electron donor in this reaction. The rates of H2 evolution observed were up to 20% of those measured in the presence of an oxygen-consuming reaction or of photosystem I electron donors. These findings indicate that hydrogen evolution from water and sunlight by photosynthetic processes could be a method for solar energy conversion.

Photosynthetic phosphoenolpyruvate carboxylases: characteristics of alloenzymes from leaves of c(3) and c(1) plants.

Abstract: A detailed comparison of green leaf phosphoenolpyruvate carboxylases from the C4-species Atriplex spongiosa and the C3-species Atriplex hastata revealed significant physical and kinetic differences. The two alloenzymes can be separated by anion exchange chromatography but have comparable molecular weights (350,000). Maximal velocity estimates were 38.0 and 1.48 micromoles per minute per milligram of chlorophyll for the carboxylases of A. spongiosa and A. hastata, respectively. Km phosphoenolpyruvate estimates were 0.49 and 0.08 mm for the C4A. spongiosa and C3A. hastata and the Km Mg estimates were 0.33 mm for the C4 species and 0.017 mm for the C3 species. The activity of the phosphoenolpyruvate carboxylase of A. spongiosa is more sensitive to chloride and phosphate than the phosphoenolpyruvate carboxylase of A. hastata, but both are equally sensitive to Mg chelating substances such as ATP, ADP, and citrate if assayed at their respective Km Mg values. A survey of the phosphoenolpyruvate carboxylases from 18 C4 and C3 species resulted in mean maximal velocity estimates of 29.0 ± 13.2 and 1.50 ± 0.57 micromoles per minute per milligram of chlorophyll for the C4 species and C3 species, respectively. Km phosphoenolpyruvate estimates were 0.59 ± 0.35 mm and 0.14 ± 0.07 mm for the C4 and C3, and Km Mg estimates were 0.50 ± 0.30 and 0.097 ± 0.057 mm for C4 and C3. All differences between means were significant at the 0.01 confidence level, supporting our hypothesis that the phosphoenolpyruvate carboxylase alloenzymes of C4 and C3 plants are functionally different and are associated with different photosynthetic roles. Both function in the photosynthetic production of C4 acids, the phosphoenolpyruvate carboxylase of C4 species largely producing malate or aspartate (or both) as a photosynthetic intermediate and the phosphoenolpyruvate carboxylase of C3 species producing malate or aspartate (or both) as a photosynthetic product.

Carbon Isotope Discrimination in Photosynthesis of CAM Plants

Abstract: SUCCULENT plants capable of Crassulacean acid metabolism (CAM) show extremely variable carbon isotope discrimination ratios1,2. This ratio, usually expressed as a δ13C value referred to a standard3, has emerged as a useful diagnostic criterion to determine photosynthetic pathways in higher plants3–5. Species with the C4 photosynthetic pathway6 show less negative δ13C values than do species with the C3 photosynthetic pathway. The difference in isotope discrimination is believed to be a result of the different fractionation characteristics of the primary phosphoenolpyruvate (PEP) carboxylase of C4 plants and primary ribulosediphosphate (RuDP) carboxylase of C3 plants7. Within a species, the δ13C value for total carbon does not usually vary by more than ±0.5‰ and it is largely insensitive to environmental conditions during growth8, although the soluble components within a particular leaf may show some variation9. Examples of the constancy of δ13C values are shown in the genus Atriplex, where C4 species have less negative values (for total carbon) of −8 to −12‰ than C3 species which range between −25 and −27‰ (ref. 8).

Comparative studies on photosynthesis in higher plants.

Abstract: Publisher Summary This chapter discusses the localized altered regions or the damaged strands of DNA that are altered by ultraviolet (UV) irradiation. If there is some denaturation of DNA during irradiation, there will be an enhancement of forming certain photoproducts in these denatured regions. It is reasonable that localized denatured regions should occur in irradiated DNA as many of the photoproducts will alter internucleotide spacings, disrupt normal hydrogen bonding, and cause a loss of base stacking. Hence, as the radiation dose increases, the likelihood of forming photoproducts favored by single-stranded DNA increases. The mechanisms of detection that are used to determine and locate the altered strands of DNA can be broken down into two broad categories—qualitative detection, which can be achieved through physical method, chemical analysis, and biochemical means, and quantitative measures like thermal melting analysis and kinetic formaldehyde method.

Plant Photorespiration—An Inevitable Consequence of the Existence of Atmospheric Oxygen

Abstract: THE primary event in the glycollate pathway1, the metabolic sequence responsible for the phenomenon of photorespiration in plants2, is the oxygenation of ribulose 1,5-diphosphate (RuDP) to phosphoglycollate and 3-phosphoglycerate3–5. This reaction appears to be catalysed by the enzyme RuDP carboxylase4. When 18O2 is supplied, incorporation of one atom of 18O into the carboxyl group of one of the products only, namely phosphoglycollate, is observed. The other atom of the oxygen molecule is exchanged with the medium5. Similarly, intact spinach leaves incorporate isotopic oxygen, supplied as O2, into the carboxyl groups of the glycollate-pathway intermediates, glycine and serine6. The purpose served by photorespiration has remained an enduring riddle7. Superficially, it would seem that oxygenation of RuDP must be deleterious to the photosynthetic process, necessitating the glycollate pathway to recoup as much of the phosphoglycollate carbon as possible with one quarter of it being lost as CO2 at the glycine→serine conversion. Observations that net photosynthesis and plant growth in general are stimulated in oxygen-depleted atmospheres concomitantly with a suppression of photorespiration8,9 reinforce this concept.

Structure of Foliage Canopies and Photosynthesis

Abstract: All living things on the earth, including plants, rely principally upon the photosynthate produced by plants for their daily food, and accordingly are strongly affected by the variation of plant photosynthesis over the globe. The distribution of solar energy with latitude determines to a great extent the geographic variation of photosynthetic activity of plants. Its latitudinal change in turn sets broad geographic limits to the different forms of terrestrial life, affecting the energy flow and the cycle of materials in ecosystems. On the other hand, the morphological and physiological characteristics of plants are thought to result from their evolutional adaptation to environmental conditions during the geological past. The morphological features as characterized by the geometrical structure (or architecture) of plant canopies have a great influence upon the processes of action and reaction between plants and their environment through the modification and interception of fluxes of radiation, heat, carbon dioxide, etc. Consequently it is obvious that the canopy structure is determinant of the photosynthetic productivity of plant canopies. The canopy structure as well as the physiological properties of leaves with respect to photosynthesis and respiration, therefore, can play an important role in the competition between plants. Since the relation between the photosynthetic activity and the structure of plant canopies was elucidated by Monsi & Saeki (100) in 1953, a great number of both theoretical and experimental studies have been done on this problem. Studies in this field have been greatly stimulated by the activities of the International Biological

Multiple Forms of Plant Phosphoenolpyruvate Carboxylase Associated with Different Metabolic Pathways

Abstract: The physical and kinetic properties of multiple forms of phosphoenolpyruvate carboxylase were studied in leaves of C4 and C3 species, their F1 and F3 hybrids, in greening maize leaves, in Crassulacean acid metabolism plants, and in nongreen root tissues Four different forms are suggested: a C4 photosynthetic phosphoenolpyruvate carboxylase with high Km for phosphoenolpyruvate (∼059 mm), Km Mg (∼05 mm), and Vmax (∼29 micromoles per minute per milligram of chlorophyll); a C3 photosynthetic phosphoenolpyruvate carboxylase with low Km for phosphoenolpyruvate (∼014 mm), Km for Mg (∼0097 mm), and Vmax (15); a Crassulacean acid metabolism type with low Km for phosphoenolpyruvate (014 mm), and high Vmax (14 micromoles per minute per milligram of chlorophyll); and a nongreen or nonautotrophic type with low Km for phosphoenolpyruvate, Km for Mg, and low Vmax In closely related species or within species, the types can be differentiated by anion exchange column chromatography Each of the four forms is associated with a different metabolic pathway: the phosphoenolpyruvate carboxylase of C4 species for malate generation as a photosynthetic intermediate, the phosphoenolpyruvate carboxylase of C3 species in malate generation as a photosynthetic product, the phosphoenolpyruvate carboxylase of Crassulacean acid metabolism species in malate generation as a CO2 donor for photosynthesis during the subsequent light period, and a nongreen or root type producing malate for ionic balance and reduced nicotinamide adenine dinucleotide phosphate generation The data in this paper in conjunction with published information support the notion of different molecular forms of a protein functioning in different metabolic pathways which have common enzymic steps

Zinc Deficiency, Carbonic Anhydrase, and Photosynthesis in Leaves of Spinach

Abstract: A shortage in the zinc supply to spinach (Spinacia oleracea L.) drastically reduced carbonic anhydrase levels with little effect on net CO2 uptake per unit leaf area, except with the most severe zinc stresses. Under these conditions, carbonic anhydrase was below 10% and photosynthesis 60 to 70% of the control levels. When photosynthesis was measured at a range of CO2 supply levels, zinc-deficient leaves were less efficient at 300 to 350 microliters per liter CO2 and above, but the same as controls at lower CO2 levels. This suggests that carbonic anhydrase does not affect the diffusion of CO2, and that the effect of zinc deficiency was on the photosynthetic process itself. Our evidence does not support the hypothesis that carbonic anhydrase has some role in facilitating the supply of CO2 to the sites of carboxylation within the chloroplast.

Seasonal pattern of net photosynthesis of artemisia tridentata

Abstract: Gas exchange studies were carried out on Artemisia tridenztata during the course of a growing season using microclimatically controlled cuvettes and infrared gas analysis. A definite seasonal pattern of net photosynthesis emerged. This pattern was influenced by the interaction of four major factors: plant water potential, leaf temperature, irradiation, and stage of phenological development. In spring and early summer, when plant water stress was minimal, photosynthesis rate was mainly correlated with leaf temperature and irradiation. During mid and late summer, increased plant water stress and phenological changes assumed at least equal importance with temperature and irradiation in limiting net photosynthesis. Indeed, plant water potential, mainly through its influence on stomatal aperture, r,', was probably the single most important factor influencing assimilation rate of this species on a seasonal basis. However, variations in mesophyll resistance to CO2 flux, rm', in response to temperature, water stress, or phenological changes also were involved. Sagebrush photosynthesis under field conditions was highest in late May and early June, and declined thereafter, minimum rates occurring in August during the driest period. Optimal temperatures for net photosynthesis were higher later in the season, indicating a change in gas exchange capacity more suitable to the warmer temperatures later in the

The effects of three oils on marine phytoplankton photosynthesis

Abstract: The effects of 3 oils (Venezuelan crude, No 2 fuel, and No 6 fuel) on the photosynthesis of natural phytoplankton communities from Bedford Basin, Nova Scotia (Canada), and the northwest Atlantic Ocean between Halifax and Bermuda were examined using a radiocarbon method The 3 oils can inhibit photosynthesis, and the degree of inhibition depends upon oil type and concentration The No 2 fuel oil was the most toxic Under certain conditions, low concentrations of Venezuelan crude oil can stimulate photosynthesis On the basis of these results, it is concluded that present levels of oil contamination in Bedford Basin could be inhibiting photosynthesis by a few percent, while present levels in open ocean water have no apparent deleterious effect on photosynthesis

Phototaxis in Chlamydomonas reinhardtii.

Abstract: Parameters which distinguish phototaxis from random motility in Chlamydomonas reinhardtii have been defined with quantitative assays The phototactic responses in photosynthetic, mixotrophic, and heterotrophic cultures were highest during exponential growth and declined rapidly as the cultures entered stationary phase In contrast, random motility was relatively constant throughout growth Phototaxis and motility also differ in their sensitivity to azide and antimycin A Both of these drugs inhibited phototaxis within 5 min, but motility was unaffected for at least 30 min Phototaxis and motility have different ion requirements Optimum motility was observed in the presence of either Ca++ or Mg++; phototaxis required Ca++ and either K+ or NH4+ Photosynthesis is not required for phototaxis, since phototaxis was not inhibited by dichlorophenyldimethyl urea, and a mutant lacking chlorophyll was phototactic

Bicarbonate Ion as a Critical Factor in Photosynthetic Oxygen Evolution

Abstract: Bicarbonate ion, not dissolved CO2 gas, is shown to increase 4- to 5-fold the rate of dichlorophenol indophenol reduction by isolated maize (Zea mays) chloroplasts. Glutaraldehyde fixed chloroplasts continue to exhibit bicarbonate-dependent 2,6-dichlorophenol indophenol reduction. Bicarbonate is shown to act close to the oxygen-evolving site, i.e. prior to the electron donation site of diphenyl carbazide to photosystem II. Dark incubation and light pretreatment of chloroplasts in various concentrations of bicarbonate, just prior to assay, indicate that bicarbonate binds to chloroplasts in the dark and is released again as the Hill reaction proceeds in the light. It is suggested that bicarbonate ions may play a critical role in the oxygen-evolving process in photosynthesis.

Chilling Injury in Cucumber Leaves

Abstract: When cucumber plants are chilled at 5 °C and 85 per cent, r.h. the leaves wilt rapidly and lose water. Chlorophyll is lost in the light, but not in the dark. If chilled leaves are placed in water, electrolytes leak out rapidly, the amount depending on the duration of chilling. There are marked reductions in the rates of respiration and photosynthesis; Q10 for respiration is 5 0 between 15 and 5 °C. Phospholipid levels decline, but more slowly than the rate of water loss. Leaves recover their initial fresh weight, rate of electrolyte leakage, and respiration and photosynthesis rates if the plants are returned to warm conditions within 1 to 2 d. When leaves are chilled at 100 per cent r.h. they do not lose water or phospholipids; electro lyte leakage is little more than in controls, but respiration and photosynthesis are reduced as at 85 per cent r.h. It is envisaged that the leaf cell membranes suffer a physical change at 5 °C which reduces the rates of respiration and photosynthesis, but allows the passage of water and electrolytes out of the cells; the water evaporates away but electrolytes become concentrated in the walls and can be leached out of the leaf. As water is lost from the leaf symptoms of dehydration appear. Phospholipid loss may be associated with enzyme action following the loss of compart mentation.

Ecological studies of Chloroflexis , a gliding photosynthetic bacterium

Abstract: Chloroflexis, a gliding, filamentous, photosynthetic bacterium, is present in the stratified algal-bacterial mats which occur in the 50°–70°C temperature range of alkaline hot spring effluents. The organism is in association with the alga in the upper, algal layer, and also forms thick, orange mats beneath the algal layer. Natural populations of Chloroflexis from these mats demonstrated light-stimulated uptake of some 14C-labelled organic compounds. Photosynthetic 14CO2 fixation by natural samples of Chloroflexis was investigated with respect to temperature, light intensity and mat depth. Bacterial photosynthesis was determined in samples in which algae were present by use of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Bacterial photosynthesis was maximal at depths down to about 3 mm and then decreased rapidly to very low levels at greater depths. The greatest amounts of bacteriochlorophyll pigments were also concentrated in the top 3–4 mm of the mat. The optimum light intensity for bacterial photosynthesis (about 400 ft-c) was considerably lower than the normal summer light intensity at the surface of the mat (5000-8000 ft-c). The temperature optima for photosynthesis by the bacterial component of natural mat samples from several sites of different temperatures in a hot spring thermal gradient were determined. Temperature optima approximated the environmental temperatures, indicative of the occurrence of strains of Chloroflexis adapted to different temperatures. Although bacterial standing crop was greatest in the temperature range 50°–55°C, maximum photosynthetic efficiency was observed at about 45°C. Sulfide was stimulatory to photosynthetic 14CO2 fixation by naturally occurring populations of Chloroflexis under field conditions. These data are consistent with the hypothesis that Chloroflexis may utilize sulfide as an electron donor for photosynthetic CO2 reduction. However, it is also likely that Chloroflexis grows photoheterotrophically in these mats, obtaining organic compounds from algal excretory products.

Moderate‐term water stresses and associated changes in some photosynthetic parameters in cotton

Abstract: SUMMARY Cotton plants (Gossypium hirsutum L., var Deltapine smoothleaf) were subjected to 1- or 2-week periods of mild water stress using an osmotic soil cell. The treatments were severe enough to affect seriously several photosynthetic parameters, while good night-time recovery of plant water-potential minimized effects on development and leaf expansion. Most measurements were made soon after rewatering, owing to very high stomatal resistances in the stressed plants. The stressed plants had lower rates of potential photosynthesis and lower rates of actual photosynthesis (at normal ambient CO2 concentrations) than the controls. Both stomatal and intracellular resistances and the corresponding ‘photosynthetic limitations’ were greater in the stressed plants than the controls. Most of these parameters showed fairly complete recovery 24 hours after rewatering. Parallel changes were observed in the activities of carbonic anhydrase, ribulosediphosphate carboxylase and 14C fixation by leaf slices, all of which were lower in the stressed plants. Although activities of all the processes studied showed parallel changes, there was evidence that the major factor causing reduced photosynthesis in the stressed plants was stomatal closure. There was some evidence that the photosynthetic system adjusted itself to water stress over the periods studied.

Diurnal Trends in Net Photosynthetic Rate and Carbohydrate Levels of Soybean Leaves

Abstract: A study was made of diurnal trends in net photosynthetic rate and carbohydrate levels of unifoliolate leaves of soybean ( Glycine max L. Merrill) under constant environmental conditions (50,000-lux light intensity, 24.5 C air temperature, 60% relative humidity, and 300 microliters of CO 2 per liter of air). Net photosynthetic rate remained relatively constant between 4 and 10 hours after the lights were turned on but then gradually declined to 85% of this rate by the end of the 16-hour photoperiod. The decline in net photosynthetic rate was due to increases in both stomatal diffusion resistance and residual resistance to CO 2 . The decline in net photosynthetic rate began when the rate of starch accumulation began to decline rapidly. At this time, there also appeared to be an increase in soluble carbohydrate level. The results suggest that when a high starch level was reached, further starch synthesis was impaired, leading to an increase in soluble carbohydrate level and, consequently, a reduction in net photosynthetic rate.

Light intensity and photosynthetic rates in phytoplankton

Abstract: The physiological behavior of various phytoplankton species has been examined under increasing and decreasing light regimes. A marked asymmetry has been found, with photosynthesis rates under risin...