Showing papers on "Photosynthesis published in 1974"

Regulation of Soybean Net Photosynthetic CO2 Fixation by the Interaction of CO2, O2, and Ribulose 1,5-Diphosphate Carboxylase

Abstract: Kinetic properties of soybean net photosynthetic CO(2) fixation and of the carboxylase and oxygenase activities of purified soybean (Glycine max [L.] Merr.) ribulose 1, 5-diphosphate carboxylase (EC 4.1.1.39) were examined as functions of temperature, CO(2) concentration, and O(2) concentration. With leaves, O(2) inhibition of net photosynthetic CO(2) fixation increased when the ambient leaf temperature was increased. The increased inhibition of CO(2) fixation at higher temperatures was caused by a reduced affinity of the leaf for CO(2) and an increased affinity of the leaf for O(2). With purified ribulose 1,5-diphosphate carboxylase, O(2) inhibition of CO(2) incorporation and the ratio of oxygenase activity to carboxylase activity increased with increased temperature. The increased O(2) sensitivity of the enzyme at higher temperature was caused by a reduced affinity of the enzyme for CO(2) and a slightly increased affinity of the enzyme for O(2). The similarity of the effect of temperature on the affinity of intact leaves and of ribulose 1,5-diphosphate carboxylase for CO(2) and O(2) provides further evidence that the carboxylase regulates the O(2) response of photosynthetic CO(2) fixation in soybean leaves. Based on results reported here and in the literature, a scheme outlining the stoichiometry between CO(2) and O(2) fixation in vivo is proposed.Oxygen competitively inhibited carboxylase activity with respect to CO(2), and CO(2) competitively inhibited oxygenase activity with respect to O(2). Within the limits of experimental error, the Michaelis constant (CO(2)) in the carboxylase reaction was identical with the inhibition constant (CO(2)) in the oxygenase reaction, and the Michaelis constant (O(2)) in the oxygenase reaction was identical with the inhibition constant (O(2)) in the carboxylase reaction. The Michaelis constant, (ribulose 1,5-diphosphate) was the same in both the carboxylase and oxygenase reactions. This equality of kinetic constants is consistent with the notion that the same enzyme catalyzes both reactions.

Energy Conservation in Photosynthetic Electron Transport of Chloroplasts

Abstract: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 ELECTRON ACCEPTOR OF PHOTOSYSTEM I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 Endogenous Electron Acceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 Localization of the Acceptor Site of Photosystem I in the Membrane. . . . . . . . . . . . 428 ELECTRON DONOR OF PHOTOSYSTEM I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Endogenous Electron Donor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Artificial Electron Donors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 Cyclic Electron Flow Around Photosystem I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 Localization of the Donor Site of Photosystem I in the Membrane . . . . . . . . . . . . . . 433 ELECTRON ACCEPTOR OF PHOTOSYSTEM II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 Endogenous Electron Acceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 Artificial Electron Acceptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 Localization of the Acceptor Site of Photosystem II in the Membrane . . . . . . . . . . . 437 ELECTRON DONOR OF PHOTOSYSTEM II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Endogenous Electron Donor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Artificial Electron Donors ............................. : . . . . . . . . . . . . . . . . . . 439 Localization of the Donor Site of Photosystem II in the Membrane . . . . . . . . . . . . . 440 FURTHER EVIDENCE FOR THE SIDED NESS OF THE MEMBRANE ................ 441 NONCYCLIC AND CYCLIC ELECTRON FLOW ACROSS THE THYLAKOID MEMBRANE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 ENERGY CONSERVATION IN PHOTOSYNTHETIC ELECTRON FLOW.............. 451

Composition of the Photosynthetic Apparatus of Normal Barley Leaves and a Mutant Lacking Chlorophyll b

Abstract: Comparison of the composition of the energy-trapping apparatus of normal barley photo-synthetic membranes and those lacking chlorophyll b shows that not only is chlorophyll b absent from the mutant, but all constituents (chlorophyll a, chlorophyll b, carotenoids and the protein moiety) of the major chlorophyll-protein complex of normal higher plant chloroplast membranes are also missing; other chlorophyll-containing components, as far as can be ascertained, are essentially unaffected by the mutation. The nuclear gene which codes for the protein moiety of this complex is suggested as a possible site of the mutation in this barley mutant. This chlorophyll α/β-protein complex which accounts for such a large proportion of the chlorophyll and protein of the photosynthetic apparatus of higher plants is thus not essential for a plant to grow photosynthetically, and therefore a new name, light-harvesting chlorophyll-protein, is proposed for the complex, which was formerly termed the photosystem II chlorophyll-protein. The biosynthetic machinery in the mutant is unable to compensate for the loss of the light-harvesting chlorophyll-protein by adding extra chlorophylls into alternative sites in the membrane, thus the chlorophyll/P700 ratio in the mutant is two-thirds that of the normal plant. The light-harvesting chlorophyll-protein is the major location for chlorophyll b in higher plant membranes. The function of the complex is thought to be analogous to that of the algal biliproteins, i.e. light energy absorbed by the complex is fed preferentially, but not exclusively, to the photosystem II reaction-center or trap. It is reasoned that the complex exerts a strong influence on the organization of photosynthetic lamellae in higher plant chloroplasts by maintaining lamellae in contact with each other.

Influence of assimilate demand on photosynthesis, diffusive resistances, translocation, and carbohydrate levels of soybean leaves.

Abstract: Rates of net photosynthesis and translocation, CO 2 diffusive resistances, levels of carbohydrates, total protein, chlorophyll, and inorganic phosphate, and ribulose 1,5-diphosphate carboxylase activity were measured in soybean ( Glycine max L. Merrill) leaves to ascertain the effect of altered assimilate demand. To increase assimilate demand, the pods, stems, and all but one leaf (the “source leaf”) of potted plants were completely shaded for 6 or 8 days and the responses of the illuminated source leaf were monitored. Rate of net photosynthesis in the source leaf of the shaded plants was found to increase curvilinearly to a maximum on the 8th day. The source leaf of the control plants (no sink shading) maintained a constant photosynthetic rate during this period. Vapor-phase resistance to CO 2 diffusion did not vary with treatment, but mesophyll (liquid phase) resistance was significantly lower in the source leaf of the shaded plants. Starch concentration in the source leaf of shaded plants decreased more than 10-fold during the 8-day shading period. In this same period, sucrose concentration rose nearly 3-fold. Conversely, in the source leaf of the unshaded plants, starch concentration remained high (23% of leaf dry weight) and sucrose concentration remained very low (1.2%). When measured on the 8th day of treatment, translocation rate, ribulose 1,5-diphosphate carboxylase activity, and inorganic phosphate concentration were found to be significantly higher in the source leaf of the shaded plants than in the control source leaf. When shaded plants were again illuminated, all measured response trends in the source leaf were reversed. These data indicate that assimilate demand has a marked influence on source-leaf photosynthesis and carbohydrate formation and export.

Nitrogen assimilation of an oceanic diatom in nitrogen-limited continuous culture1

Abstract: SUMMARY The oceanic diatom Thalassiosira pseudonana Hasle and Heimdal (formerly Cyclotella nana) was grown with 12L:12D illumination cycles in nitrogen-limited continuous culture with a mixture of ammonium and nitrate as the N source Measurements included, at 3 different growth rates (degrees of N limitation), cell concentration, cell carbon, nitrogen, and chlorophyll a contents, cell volume, photosynthetic carbon assimilation vs irradiance, short-term uptake of ammonium and nitrate vs their ambient concentrations, and in vitro activities of the assimilatory enzymes nitrate reductase and glutamic dehydrogenase The various parameters showed either an increase (pattern a) or a decrease (pattern b) with increasing N limitation Those following pattern a were nitrate reductase activity and the capacity to assimilate nitrate and ammonium Those following pattern b were glutamic dehydrogenase activity, photosynthetic rate, nitrogen:carbon and chlorophyll a:carbon composition ratios Results are discussed in terms of the interpretation such measurement for natural phytoplankton and effects of circadian periodicity

Products of photosynthesis by marine phytoplankton: the effect of environmental factors on the relative rates of protein synthesis

Abstract: A method is presented by which the gross pattern of photosynthetic carbon-dioxide fixation in marine phytoplankton can be determined. It depends on differential solvent extraction yielding an ethanol-soluble, a hot TCA-soluble (polysaccharide) and a residue (protein) fraction. Using this fractionation technique, the effects of various environmental factors on the pattern of photosynthesis by the marine diatom Phaeodactylum tricornutum (Bohlin) have been investigated. Low light intensities and increasing degrees of nitrogen limitation in a chemostat increase markedly the relative rates of protein synthesis. Growth of the alga at lower temperatures also increases the proportion of carbon incorporated into the protein fraction. This increased protein syntheses is generally at the expense of the polysaccharide fraction. Preliminary experiments have established the suitability of this fractionation method for natural populations of phytoplankton and have shown similar effects of light intensity on the relative rates of protein synthesis.

Chloroplast Response to Low Leaf Water Potentials III. Differing Inhibition of Electron Transport and Photophosphorylation

Abstract: Cyclic and noncyclic photophosphorylation and electron transport by photosystem 1, photosystem 2, and from water to methyl viologen ("whole chain") were studied in chloroplasts isolated from sunflower (Helianthus annus L. var Russian Mammoth) leaves that had been desiccated to varying degrees. Electron transport showed considerable inhibition at leaf water potentials of -9 bars when the chloroplasts were exposed to an uncoupler in vitro, and it continued to decline in activity as leaf water potentials decreased. Electron transport by photosystem 2 and coupled electron transport by photosystem 1 and the whole chain were unaffected at leaf water potentials of -10 to -11 bars but became progressively inhibited between leaf water potentials of -11 and -17 bars. A low, stable activity remained at leaf water potentials below -17 bars. In contrast, both types of photophosphorylation were unaffected by leaf water potentials of -10 to -11 bars, but then ultimately became zero at leaf water potentials of -17 bars. Although the chloroplasts isolated from the desiccated leaves were coupled at leaf water potentials of -11 to -12 bars, they became progressively uncoupled as leaf water potentials decreased to -17 bars. Abscisic acid and ribonuclease had no effect on chloroplast photophosphorylation. The results are generally consistent with the idea that chloroplast activity begins to decrease at the same leaf water potentials that cause stomatal closure in sunflower leaves and that chloroplast electron transport begins to limit photosynthesis at leaf water potentials below about -11 bars. However, it suggests that, during severe desiccation, the limitation may shift from electron transport to photophosphorylation.

Effect of Cd on photosynthesis and transpiration of excised leaves of corn and sunflower

Abstract: Detached corn and sunflower leaves exposed to various concentrations of Cd, supplied as CdCl2, exhibit reduced photosynthesis and transpiration. The reduction is dependent on the concentration of CdCl2 solution and generally becomes more pronounced with time. In sunflower, net photosynthesis and transpiration are completely inhibited within 45 min after the introduction of 18 mM Cd. Within two hours net photosynthesis is reduced to 40% and 70% of maximum after the introduction of 9 and 4.5 mM Cd respectively. In corn the trend of photo-synthetic response to Cd is similar to that in sunflower except that the inhibition in corn is more pronounced at all treatment levels. A strong linear relationship between photosynthesis and transpiration inhibition is obtained in both species suggesting that Cd contamination induces stomatal closure.

Structure and function of developing barley plastids.

Abstract: Five different regions of the first foliage leaf of etiolated barley seedlings were studied with respect to leaf growth, plastid growth and replication, differentiation of etioplasts, and conversion of etioplasts into chloroplasts upon illumination. Ultrastructural changes of the plastids were correlated with chlorophyll synthesis and development of photosynthetic activity as measured by 14CO2 incorporation and O2 evolution. The first foliage leaf has greater linear growth over a longer period of time in the dark than in the light. Only the bottom two regions (4 and 5) are still growing in the 5-day etiolated leaf. Region 4 grows by cell elongation, and region 5 grows by both cell division and elongation. Plastids in all five regions of the leaf are capable of enlarging when exposed to light. This is true both for the intact plant and for excised sections. Plastid replication occurs predominantly in the younger regions of the leaf (regions 3, 4, and 5). The amount of chlorophyll synthesized by different regions in the intact plant is significantly higher (3-40 times) than that made by excised sections. Ultrastructural changes occurring in each region when excised sections are illuminated were classified into five stages involving increased membrane synthesis and appression into grana, and these changes were correlated with the first appearance of photosynthetic activity. The earliest detectable photosynthetic activity occurs in region 1 after 2 hours of illumination when chloroplasts show only a few overlaps in the thylakoids. Plastids in younger regions of the leaf require up to 24 hours of light to form grana and develop photosynthetic activity. Plastids in each region of the leaf are in different stages of development when photosynthesis is initiated, indicating that development of photosynthetic activity is not strictly correlated with a certain stage of plastid development. Membrane appression is not indicative of photosynthetic activity since overlaps are formed in the dark, but it was always present when photosynthetic activity was detectable. Likewise, there does not appear to be any strict correlation between the presence of chlorophyll and membrane appression. These results show that the particular structural and functional correlations that can be made depend to a large degree on age of the tissue.

Comparative Photosynthetic Capacities of Intertidal Algae under Exposed and Submerged Conditions

Abstract: Photosynthetic rates were measured for five species of intertidal marine algae, in the air and submerged. Ulva expansa and Prionitis lanceolata from the lower intertidal show reduced photosynthetic capacity air in air compared to submergedrates. In contrast, species from the middle and upper littoral (Iridaea flaccida, Porphyra perforata, Fucus distichus, and Endocladia muricata) reach maximum photosynthesis after some degree of drying. For these latter species, photosynthetic rates can be 1.6 to 6.6 times greater in air than in water at the same illumination and temperature. Desiccation rates under natural conditions are slow enough that these algae are capable of continuing a high rate of photosynthetic activity for extended periods while exposed and may fix the bulk of their carbon at this time. The capacity of these algae for sustained photosynthesis in air vary according to their intertidal zonation. It is suggested that these relationships may be partially responsible for the vertical distribution of intertidal marine algae.

A Comparison of Potential Photosynthesis, Productivity and Yield of Plant Species with Differing Photosynthetic Metabolism

Abstract: Maximum recorded values of various parameters for the rate of photosynthetic CO2, fixation, from the biochemical level through the leaf level to crop growth rate, suggests that for two contrasting photosynthetic groups (C3 and C4 species) the large potential advantage of the C4 mechanism at the biochemical level is progressively attenuated in moving from the microscopic to the macroscopic parameters until, at the level of crop growth rate, there is no apparent difference between best examples of the two groups when grown in their own preferred natural environments.

Influence of Partial Defoliation on Photosynthesis, Photorespiration and Transpiration by Lucerne Leaves of Different Ages

Abstract: A study was made of the short- and long-term effects of partial defoliation (cutting at 15 cm above the crown) of lucerne plants (Medicago sativa L. cv. Hunter River) on the net photosynthesis, transpiration, photorespiration and CO2 transfer resistances of remaining leaves. The response in gas-exchange properties of leaves of different ages to partial defoliation of the plant was also investigated. Partial defoliation always induced rejuvenation in photosynthetic rate of remaining leaves. Young and middle-aged leaves rejuvenated to rates comparable to those of recently expanded leaves but old leaves only partially rejuvenated. Time after defoliation to attain peak rates increased as leaves aged; values were 5, 9 and 12 days for plants partially defoliated on days 16, 30 and 65 of regrowth respectively. Peak rates were maintained for only 3 or 4 days before declining. Rates of photorespiration and photosynthesis were closely coupled. Transpiration rates varied over time in a similar but more erratic pattern to net photosynthetic rates. Changes in net photosynthetic rates associated with senescence, defoliation treatments and irradiance levels were largely attributable to changes in intracellular resistance to CO2 transfer. Intracellular resistances ranged from 2.6 to 30 s cm-1, constituting 67-95 % of the total resistance to photosynthesis. Stomatal resistance to CO2 diffusion remained low, 0.2 - 1.0 s cm-1, for all but very old leaves. Partial defoliation followed by continual removal of new crown and stubble shoots induced very high net photosynthetic rates, c. 15 days later. Highest net photosynthetic rate was 238 ng CO2 cm-2 s-1. Possible mechanisms responsible for photosynthetic rejuvenation following partial defoliation are discussed, together with ecological implications of this phenomenon.

Benthic Photosynthesis and Respiration in Char Lake

Abstract: Benthic photosynthesis and respiration was measured by in situ oxygen change and correlated with in situ radiation in ultraoligotrophic Char Lake Oat. 74°42′N). Photosynthesis by the moss and deep ...

The effect of heavy metals on photosynthesis and loss of cell potassium in two species of marine algae, Dunaliella tertiolecta and Phaeodactylum tricornutum

Abstract: The effects of various heavy metals on light-induced oxygen evolution and on net potassium release were studied in short-term experiments using the unicellular marine algae Dunaliella tertiolecta and Phaeodactylum tricornutum. Heavy metals, except for copper and 3, (3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) did not cause loss of potassium at concentrations similar to or less than those required for inhibition of photosynthesis. At the concentrations used, no significant loss of potassium was observed for Zn2+, Cd2+, Tl+, Pb2+ nor DCMU. With Cu2+, potassium release occurred at a marginally lower concentration than did inhibition of photosynthesis. The extreme sensitivity of light-induced oxygen evolution to inhibition by cadmium and lead found previously by the author (Overnell, 1974) with Chlamydomonas reinhardii was not found with the strains used here.

Ecophysiology of Ambrosia Artemisiifolia: A Successional Dominant

Abstract: Ambrosia arteinisiifolia L. dominates abandoned fields after spring plowing in many parts of the eastern United States. Its seeds germinate at or near the soil surface in early spring, and the cotyledons become green shortly after they emerge. They are photosynthetically active, with a net photosynthesis dark respiration ratio (P/R) of 1.9. The primary leaves are photosynthetically more active than the cotyledons with a P/R ratio of 3. Photosynthesis of young A. artemisiifolia seedlings is 21 mg C02 dm-2 hr-1 at 1,076 X 102 lux, 250 C, and 300 ppm CO2. They approach light saturation at 1,076 X 102 lux (1.1 cal cm-2 min-) and exhibit appreciable photosynthesis at temperatures from 5? to 350 C. Their rate of photosynthesis increases with an increase of the ambient C02 concentrations comparable to that measured near the soil surface in the field. Although seedling photosynthesis is quite sensitive to decreasing water potential (*J.) between 0 and -10 bars, there is no further decrease between -10 and -20 bars. Furthermore, at this range of 'P photosynthesis is about 20% of that at 0 bars. In a plowed field these seedlings experience high light intensities, appreciable variation in daily temperature, high CO2 concentrations due to its flux from the soil, and low water potentials since the roots are in the upper part of the soil. Field-grown, mature A. artemisiifolia plants do not light-saturate even at 1,076 X 102 lux. Their photosynthetic rate at optimum light intensity, temperature, ala, and 300 ppm C02 is about 35 mg C02 dm-2 hr-1. This high rate of photosynthesis is accompanied by a high rate of transpiration (3 g H20 dm-2 hr-1). Photosynthesis in these plants is sensitive to temperature and reaches a peak at 200 C. The effect of CO2 enrichment on the rate of photosynthesis is not as pronounced in mature plants as in seedlings. Photosynthetic rates decline sharply between -10 and -15 bars BILL; however, appreciable rates are maintained even at '' of -20 bars for several hours. Photosynthetic recovery from water stress is rapid after watering and is attributed to the very low total plant resistance to water transport (1 X 106 sec cm-1). Mature plants have moderate photorespiration since their CO2 compensation point is reached at 50 ppm C02. These data indicate that A. artemisiifolia can not only efficiently exploit the environmental resources of the field during seedling and mature plant stages of its life cycle but also effectively function under the sometimes extreme conditions encountered in the field. These ecophysio- logical attributes coupled with complex germination behavior and genetic plasticity enable the species to be a successful pioneer in early successional ecosystems where the environment can be severe and unpredictable.

Plant species intermediate for c3, c4 photosynthesis.

Abstract: Mollugo verticillata is the first plant species reported which has characteristics of both C(3) (Calvin-Benson pathway) and C(4) (Hatch-Slack pathway) plants. This plant species is intermediate between C(3) and C(4) plants in at least four features generally used to separate those two plant groups: leaf anatomy, cell ultrastructure, photorespiration, and primary photosynthetic products.

Questions on the Mechanism of Temperature Adaptation in Marine Phytoplankton

Abstract: The rate of light-saturated photosynthesis in 3 marine algae [Phaeodactylum tricornutum Bohlin, Nitzschia closterium (Ehrenberg) Smith and Dunaliella tertiolecta Butcher] varies during growth in batch culture. The photosynthetic rare declines most rapidly during growth at the higher temperatures. Because of these changes in photosynthesis rate, the previously reported enhanced photosynthetic abilities caused by growth at lower temperatures (generally interpreted as evidence for higher enzyme levels) can only be observed when measurements are made late in the exponential phase or after the onset of the stationary phase of growth. When allowance is made for the earlier peak of photosynthetic ability in cultures growing at higher temperatures, there is no evidence for adaptation to lower temperatures being caused by increased levels of the enzymes required for carbon-dioxide fixation. When the changes due to growth in batch culture are taken into account, certain effects of temperature can be recognized. the dry weight: chlorophyll ratio of all 3 algae increases with decreasing growth temperatures. For P. tricornutum and N. closterium, growth at lower temperatures reduces the cellular content of chlorophyll a, but has little effect on the chlorophyll content of D. tertiolecta. The dry weight: cell-number ratio of D. tertiolecta and P. tricornutum increases with lower growth temperatures, but growth temperature has little effect on the cell mass of N. closterium. Growth of the 3 algae at lower temperatures does not increase their ability to photosynthesize at these lower temperatures. Rather, it reduces their ability to assimilate carbon dioxide at the higher temperatures.

Photorespiration and productivity in submersed aquatic vascular plants1

Abstract: A 14C assay for photorespiration (the light-induced uptake of oxygen and release of carbon dioxide resulting from glycolate metabolism) was developed for use with submersed aquatic plants. Laboratory studies with axenic cultures of Najas flexilis (Willd.) Rostk. and Schmidt indicated that respired carbon dioxide is refixed extensively in the light and that the 14C assay is a measure of net, rather than gross, photorespiration. Analyses of leaf anatomy and early 14C fixation products of photosynthesis indicated that N. flexilis is a C3 plant with Calvin-Benson cycle photosynthesis and glycolate metabolism. Respiration in the light in axenic N. flexilis increased with increasing dissolved oxygen concentration, which indcated the presence and enhancement of photorespiration and that net photosynthesis would decrease with increasing oxygen concentration. In situ experiments with N. flexilis and Scirpus subterminalis demonstrated variations in photorespiration and dark respiration within a 1-day photosynthetic period and seasonally.

The temperature-related photosynthetic capacity of plants under desert conditions : I. Seasonal changes of the photosynthetic response to temperature.

Abstract: Temperature dependence of net photosynthesis under conditions of light saturation and maximum air humidity was measured throughout the season in the Central Negev Desert (Israel). Experimental plants were the wild growing Hammada scoparia and Prunus armeniaca cultivated in the runoff farm of Avdat.The optimum temperature for net photosynthesis and the upper temperature compensation point of CO2 exchange showed a characteristic seasonal variation with low values in spring and fall and high values in mid-summer. This shift was exhibited by plants growing under conditions of normal soil-water stress as well as by irrigated plants. There was no general correlation between the changes in temperature dependence of net photosynthesis of the plants, their maximum photosynthetic capacity under the experimental conditions, their daily photosynthesis maximum under natural conditions, and their rate of dark respiration. The seasonal shift of the photosynthetic response to temperature cannot be explained by changes in the temperature sensitivity of the stomata. It may be caused by seasonal changes of biochemical and/or biophysical properties.A number of observations made on other wild plants also showed, in all cases, seasonal shifts of the upper temperature compensation point, with an amplitude of 6.0°C-13.7°C.

Iron Deficiency in the Blue-Green Alga Anacystis nidulans: Changes in Pigmentation and Photosynthesis

Abstract: Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared from Anacystis nidulans, grown in complete and iron-deficient media. French press treatment and fractionated centrifugation were used. Absorption studies of the particles revealed an iron deficiency-induced shift of the main red chlorophyll a absorption peak from 679 to 673 nm as reported before for whole cells. The shift may reflect a changed distribution between different chlorophyll a forms. Action spectra for photo-oxidation of mammalian cytochrome c with photosynthetic lamellae revealed an iron deficiency-induced shift, corresponding to that found in the absorption spectra. As photo-oxidation of cytochrome c is mediated by PSI, it is believed that chlorophyll a also after the shift towards shorter wavelengths, is active in PSI. A decreased photosynthetic capacity of PSI, due to iron deficiency, was shown by time course studies of photosynthetic oxygen evolution, by photo-oxidation studies of P700 and mammalian cytochrome c, by photo-reduction studies of NADP and by combined studies of light-induced and chemical oxidation of P700. The ration chlorophyll a/700 was also determined for whole cells, lyophilized cells and PSI-particles. Iron deficiency caused an increased ratio in all studied fractions. The results of this work imply that energy is transferred with less efficiency within the photosynthetic units of PSI in iron-deficient A. nidulans than in iron-supplied algae.