Early Products Of Photosynthesis Research Articles

Effects of Low Temperature and Abscisic Acid on the Expression of the Sorbitol-6-phosphate Dehydrogenase Gene in Apple Leaves

Sorbitol-6-phosphate dehydrogenase (S6PDH) is known to be a key enzyme in the biosynthesis of sorbitol, an early product of photosynthesis, common to fruit trees of the Rosaceae family. Effects of low temperature and abscisic acid (ABA) on the expression of the S6PDH gene were investigated in apple leaves. In leaf-disc experiments, the expression of S6PDH was enhanced by an ABA treatment, as well as by low temperature and high-salinity stresses. The level of S6PDH mRNA increased 8 h after the addition of ABA; the highest level of S6PDH mRNA resulted on exposure to 10 μM ABA. The level of S6PDH mRNA in leaves of apple trees growing in an orchard increased with a decrease in temperature in the fall while ABA content increased. This induction may partly be a stress-response to low temperature, a prerequisite for freezing tolerance during the coming winter. Southern blot analysis revealed that S6PDH is a single-copy gene in the apple genome, indicating that it is a unique, multifunctional one, for sorbitol biosynthesis under various stress responses, as well as for the translocation of photosynthates.

High CO2 partial pressure effects on dark and light CO2 fixation and metabolism in Vicia faba leaves

Stomatal opening on Vicia faba can be induced by high CO2 partial pressures (10.2%) in dark as well as in light. Stomatal aperture was measured in both cases with a hydrogen porometer. The distribution of (14)C among early products of photosynthesis was studied. Comparisons are made with carboxylations occurring when stomata were open in the dark with CO2-free air and in light with 0.034% CO2. Results showed that in high CO2 partial pressure in light, less radioactivity was incorporated in Calvin cycle intermediates and more in sucrose. β carboxylations and photorespiration seemed to be inhibited. In the dark in both CO2 conditions, (14)C incorporation was found in malate and aspartate but also in serine and glycerate in high CO2 conditions. In light these changes in metabolic pathways may be related with the deleterious effects recorded on leaves after long-term expositions to high partial pressure of CO2.

Phosphoserine as an early product of photosynthesis in isolated chloroplasts and in leaves of Zea mays seedlings

Phosphoserine as an early product of photosynthesis in isolated chloroplasts and in leaves of Zea mays seedlings

Die Differenzierung von Kristallidioblasten im Dunkeln und bei Hemmung der Glykolsäureoxidase

The epidermal cells of the leaves of jackbean, Canavalia ensiformis DC, partly differentiate into very specialized idioblasts. Each idioblast contains one crystal of calcium oxalate. Structure, development and the influence of calcium nutrition on the differentiation of these cells have been described earlier: Frank, 1965, 1967, 1969 a; Frank and Jensen, 1970; Frank, 1972). The two opposite leaflets of the trifoliate leaves of the young plant provide good material for comparisons. One of those leaflets got darkened. It then grows much slower than its opposite control leaflet but the number of crystals and specialized crystal cells per mm2 leaf area remains the same. Even though glycolic acid, presumably the precursor of oxalic acid, is an early product of photosynthesis, stopping of photosynthesis appears not to inhibit oxalate biosynthesis more than the general metabolism. Bisufite and α-hydroxysulfonates are known as inhibitors of glycolic acid oxidase the key enzyme of oxalate biosynthesis. Sodium bisulfite and α-hydroxy 2-pyridinemethane sulfonate were fed to intact plants. With both inhibitors the number of crystals per mm2 leaf area was greatly reduced. The number of idioblasts corresponded to the number of crystals. There were no idioblasts without crystals and no crystals outside idioblasts. Thus there seems to be a causal relationship between the metabolism of oxalic acid and the development of crystal cells. If the synthesis of the acid is inhibited less epidermal cells are differentiated into idioblasts. Die Blattepidermen der Jackbohne, Canavalia ensiformis DC, enthalten ausgeprägte Idioblasten mit Kristallen aus Calciumoxalat. Eine Seitenfieder des 3teiligen 3. Blattes der Jungpflanzen wurde verdunkelt. Diese Fieder blieb im Vergleich zur gegenständigen Kon-trollfieder im Wachstum stark zurück, bildete aber, bezogen auf mm2 Blattfläche, ebenso viele Kristalle und spezialisierte Kristallzellen wie die Kontrolle. Obwohl Glykolsäure, der wahrscheinliche Vorläufer des Oxalats, ein frühes Photosyntheseprodukt ist, wird die Biosynthese der Oxalsäure offenbar durch Ausschaltung der Photosynthese nicht stärker gehemmt als der allgemeine Stoffwechsel. Die Hemmstoffe der Glykolsäureoxidase, Natriumhydrogensulfit und 2 Pyridyl-hydroxy-methansulfosäure wurden intakten Pflanzen gefüttert. Die Zahl der Kristalle und ebenso der Idioblasten pro mm2 Blattfläche wurde dadurch stark herabgesetzt. Danach läßt sich vermuten, daß eine kausale Beziehung zwischen Oxalatbiosynthese und Idioblastendifferenzie-rung besteht.

Stachyose: an Early Product of Photosynthesis in Squash Leaves

It was hypothesized that stachyose is translocated by squash because stachyose is supplied to the phloem loading system by the photosynthetic system. To test this hypothesis, (14)CO(2) was supplied to squash leaves. The nonphosphorylated sugars containing (14)C were studied. A large proportion of (14)C appeared in stachyose very early in the time sequence, tending to confirm the hypothesis.

The Rate of Photorespiration during Photosynthesis and the Relationship of the Substrate of Light Respiration to the Products of Photosynthesis in Sunflower Leaves

Single attached leaves of sunflower (Helianthus annus L. "Mennonite") were supplied (14)CO(2) of constant specific radioactivity in gas mixtures containing various CO(2) and O(2) concentrations. The (14)CO(2) and CO(2) fluxes were measured concurrently in an open system using an ionization chamber and infrared gas analyzer.The rate of photorespiration (5.7 +/- 0.3 mg CO(2).dm(-2).(-1)) during photosynthesis in 21% O(2) at 25 C and 3,500 footcandles was over three times the rate of dark respiration and was independent of CO(2) concentrations from 0 to 300 mul/l. The steady rate of CO(2) evolution into CO(2)-free air was about 30% lower. Low oxygen (1%) inhibited both (14)CO(2) and CO(2) evolution, both during photosynthesis and in CO(2)-free air in the light.At 300 mul/l CO(2) apparent photosynthesis was inhibited 41% by 21% O(2). Two-thirds of the inhibition was due to the inhibition of true photosynthesis by oxygen and one-third due to the stimulation of photorespiration. At 50 mul/l CO(2), where the percentage inhibition of apparent photosynthesis by 21% oxygen was 92%, photorespiration accounted for two-thirds of the total inhibition.The rate of (14)CO(2) uptake by the leaf decreased about 30 seconds after the introduction of (14)CO(2), indicating that (14)CO(2) was rapidly evolved from the leaf. The rate of (14)CO(2) evolution increased rapidly with time, the kinetics depending on the CO(2) concentration. The high specific radioactivity of the (14)CO(2) evolved during photosynthesis or in the early period of flushing in CO(2)-free air showed that the substrate for light respiration was an early product of photosynthesis. From the measurement of (14)CO(2) and CO(2) evolution into CO(2)-free air over a longer time period it was apparent that at least three compounds, each of decreased (14)C content, could supply the substrate for light respiration.Based on a consideration of the specific radioactivity of (14)CO(2) evolved under a variety of conditions, it is suggested that total CO(2) evolution in the light or photorespiration is composed of two processes, dark respiration and light respiration. Light respiration is a process that only occurs in the light, persists for some time on darkening, and metabolizes substrates that are quite different from those of dark respiration.

An open gas-exchange system for the simultaneous measurement of the CO2 and 14CO2 fluxes from leaves

An open gas exchange system that uses an infrared gas analyzer and an ionization chamber to measure CO2 and 14CO2 is described. The system will continuously measure the CO2 and 14CO2 exchange from a leaf within 30 s after the 14CO2 gas mixture is supplied to the leaf. Measurements are obtained under steady rate conditions since the 14CO2 gas mixture is supplied at a constant composition from pressurized cylinders. Methods of determining true photosynthesis, apparent photosynthesis, CO2 evolution, and the specific activity of the 14CO2 evolved are clearly described. The rate of CO2 evolution in the light was not affected by the CO2 concentration and the evolved CO2 was derived from the early products of photosynthesis.

Evolution in the Tropics

The substance of this article was delivered as the Presidential Address to the Society for the Study of Evolution, December 30, 1969, in Boston, Massachusetts. Attention is drawn to evolutionary studies in the tropics which appear to be advancing the subject significantly. Then, detailed attention is given to the possible evolutionary bases of the most striking biological characteristic of the tropics: the extraordinary floristic and faunistic diversity of tropical ecosystems. Because most contributions to the discussion of this topic have come from zoologists, the emphasis here is placed on botanical aspects. It is concluded that each of several potential explanations for the diversity may be valid and that a great need for the future is synthesis rather than arbitration between theories. THERE ARE MANY reasons why, as we come to the end of the 1960's, we should pay attention to what is happening in the study of evolution in the tropics. After many years of neglect, the tropics are getting more study by ecologists-and where the ecologists find their stimulation and their information there is also material for evolutionists, provided that we are still interested, as they are, in adaptation. Despite recent claims by molecular biologists (e.g., King and Jukes 1969, Wilson and Sarich 1969) for nonselective biochemical evolution, I believe that adaptation, maintained by natural selection, is still the cornerstone of the evolutionary edifice-and the tropics provide superb opportunities for studying multifarious examples of adaptation in action. Quite recently there have been important advances, with evolutionary significance, in several areas of tropical biology, and I should like to draw attention to some of them. For example, one of the most exciting developments in plant physiology in the last few years has been the demonstration that there are at least two biochemical pathways along which photosynthesis by flowering plants may proceed. The conventional or Calvin pathway (Calvin and Bassham 1962) involves phosphorylated chemical compounds with three carbon atoms while the more recently discovered pathway (Hatch and Slack 1966) involves four-carbon, dicarboxylic acids as early products of photosynthesis. Plants using the four-carbon pathway can fix carbon dioxide at rates up to twice that of those using the conventional mechanism, at least partly because they waste nothing in photorespiration. Correspondingly, their carbon dioxide compensation points (the level of CO2 in the atmosphere at which respiration just balances photosynthesis) are extremely low. Furthermore, they have peculiarities in the bundle sheaths of the leaves (Laetsch 1968) by which they may be recognized, as well as leaf structures which reduce gaseous exchange. Accumulation of carbon dioxide is facilitated under certain dark circumstances and, because C4 photosynthesis is not inhibited by accumulating oxygen during illumination (Olle Bjorkman, pers. comm.), their photosynthetic rates continue to increase as light intensities up to the maximum experienced in daylight are reached. Photosynthesis also continues even when dissolved carbon dioxide concentrations in the cells are reduced to low levels

Carbon Metabolism of C14-Labeled Amino Acids in Wheat Leaves. II. Serine & its Role in Glycine Metabolism

Wang and Waygood (24) investigated the conversion of glycine to sugars in wheat leaves and proposed a glyoxylate-serine pathway in which serine occupies a key position as an essential intermediate. Rabson et al. (19) also have discussed the glycolate pathway for the production of precursors of hexoses. They have reviewed much of the literature on the metabolism by plants of glycolic acid, glyoxylic acid, glyceric acid, glycine, serine, and related intermediates. Glycolic acid is an early product of photosynthesis (1), and a substantial percentage of the total carbon of the photosynthetic cycle enters into glycolate (1,25). This was shown dramatically when Zelitch (27) blocked glycolate oxidation with an a-hydroxysulfonate and demonstrated that approximately half of the C14 fixed appeared in glycolic acid. Kearney and Tolbert (11) showed that C14-labeled glvcolate and phosphoglycolate appeared rapidly outside isolated chloroplasts photosynthesizing C1402, and they suggested that these compounds likely are of special importance in the transport of photosynthate between chloroplasts and cytoplasm. Glycine arises from glyoxylate and in turn serves as a precursor for serine. Rabson et al. (19) also have implicated glycerate as an intermediate between serine and hexoses, and have suggested that this glycerate formed by the glycolate pathway represents a precursor for hexoses independent of the phosphoglyceric acid formed from the carboxylation of ribulose diphosphate. In the present work, an attempt has been made to substantiate the role of serine in the metabolism of glycine as well as to investigate the glyoxylateserine pathway in general. Metabolic changes with time in a number of labeled substrates have been followed in an attempt to clarify the interrelationships between these simple organic acids and amino acids and their roles as precursors for sugar synthesis. Materials & Methods

Effect of Wave-Length on the Distribution of Carbon-14 in the Early Products of Photosynthesis

Effect of Wave-Length on the Distribution of Carbon-14 in the Early Products of Photosynthesis