Showing papers in "Functional Plant Biology in 1976"

Relation between Acid Proteinase Activity and Redistribution of Nitrogen during Grain Development in Wheat

Abstract: Accumulation of grain nitrogen was studied in the wheat cultivars Argentine IX and Insignia. The pattern of nitrogen removal from several tissues of each cultivar was compared with the pattern of acid proteinase activity. There was a highly significant relation between the rate of nitrogen loss from the tissues and the rate estimated from the enzyme activity measurements. This suggests an important role for acid proteinase enzymes in leaf senescence. Redistribution of nitrogen present in the plant at anthesis accounted for 78.5 and 80.6 % of the final grain nitrogen yield of Argentine IX and Insignia respectively.

Alcoholic Fermentation and Activity of Some Enzymes in Rice Roots Under Anaerobiosis

Abstract: Rice was initially grown in aerated solutions. When tillering commenced, anaerobiosis was imposed by flushing nitrogen gas through nutrient solutions for up to 6 days ('adapted plants'); plants which remained in aerated solutions are referred to as 'non-adapted plants'. Under anaerobiosis, CO2 evolution and ethanol production by excised apical root tissues were five times greater for adapted than for non-adapted plants. For excised tissues from adapted plants, carbon lost as CO2 and ethanol approximately equalled that of aerobic CO2 evolution, i.e. CO2(N2) / CO2(air) = 0.30. This ratio was only 0.06 for apical tissue from non-adapted plants. Ethanol was not produced under aerobic conditions, even by tissue from adapted plants. Anaerobiosis of the root environment caused rapid increases in activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC). Cycloheximide largely inhibited the increases in activities of these enzymes under anaerobiosis. Elevated activities of ADH and PDC persisted for several days after transfer of adapted plants to aerated solutions. Despite these high activities of PDC and ADH, ethanol was not produced in root tissue from adapted plants under aerobic conditions, which indicates that either PDC or ADH is under fine control. Experiments in vitro suggest that this control is afforded at least partly by activation of PDC by NADH and inhibition by NAD+. It is suggested that NADH can replace thiamin pyrophosphate in promoting PDC activity via effects on conformation of the enzyme.

Membrane Phase Changes in Chilling-Sensitive Vigna radiata and Their Significance to Growth

Abstract: Changes in the growth response of mung bean hypocotyl were studied as a function of temperature and related to structural and functional changes in membranes. The temperature coefficient for growth increased abruptly below 28°C and again below 15°C. The Arrhenius activation energy of mitochondrial succinate oxidase also increased below these same temperatures. Changes in molecular ordering were detected in the membrane lipids of both mitochondria and chloroplasts at about 28 and 15°C by electron spin resonance spectroscopy. The results demonstrate a precise relationship between changes in the molecular ordering of membrane lipids and the physiological response of plants to changes in temperature.

Physiology of Grain Yield in Wheat Growing on Stored Water

Abstract: The grain yield of wheat plants grown in the glasshouse on a fixed and limiting supply of water can be substantially increased by forcing the plants to use water slowly when young so that they have more water available while filling their grains. Water use was manipulated either (1) by providing the entire water supply at sowing and allowing the plant to develop only one root (instead of the usual 5-20) or (2) by metering the water to the plants at varying rates. With a water supply of 1800 ± 50 g per plant (equivalent to 180mm transpiration from a canopy containing 100 plants m-2), the grain yield ranged from zero, for plants uncontrolled in water use, to 3.5 g per plant for plants left with at least 400 g water to use after anthesis. Plants which used less than 200 g water after anthesis had yields approximately proportional to the amount of water used, giving about 1 g grain per 80 g water (compared with 1 g dry matter per 200 g water for the whole plant). The high efficiency of water use for grain growth was apparent rather than real. It arose because the grain of severely stressed plants was filled largely (up to two-thirds) from reserves, rather than largely from current photosynthate.

Quantitative Assessment of Symplastic Transport of Pre-Nectar Into the Trichomes of Abutilon Nectaries

Abstract: The anatomy and ultrastructure of the stalk cell region of Abutilon megapotamicum var. variegatum floral nectary trichomes has been investigated and the observations related to estimates of the rate of secretion of nectar. Evidence was obtained that an apoplastic barrier exists in the anticlinal walls of the stalk cell, and is taken to indicate that a flow of pre-nectar, equivalent in volume to the nectar that is secreted from the apex of the trichome, passes through the stalk cell protoplast. In terms of volume of water, the plasma membrane of the stalk cell might have a large enough hydraulic conductivity to cope but, in terms of sugar transport, the required flux is 3-4 orders of magnitude greater than literature values for plant cell membranes. By contrast, the plasmodesmata in the distal periclinical wall of the stalk cell provide a low resistance pathway for a bulk flow of sugar solution. The desmotubules of the plasmodesmata are clearly connected to the endoplasmic reticulum of the adjacent cells. The cytoplasmic annulus between the desmotubule and the inner face of the plasma membrane is (in the majority of cases) parallel sided and non-constricted. The hydraulic conductivity of the cytoplasmic annulus route through the plasmodesmata is 1.4 × 10-5 m3 m-2 (of distal wall) s-1 bar-1; that of the hypothetical desmotubular route is about 2.3 × 10-6 in the same units. These conductivities are 4.5 and 45 times greater than corresponding values for root endodermal plasmodesmata reported in the literature. The results are discussed in relation to the physiology of nectar production in Abutilon.

Male Sterility in Sorghum bicolor (L.) Moench Induced by Low Night Temperature. I. Timing of the Stage of Sensitivity

Abstract: Male sterility was induced in grain sorghum (CK 60 × Tx 415) by exposure of plants to five low- temperature nights (25°C day/ 10°C night). Sensitivity was greatest at the late archesporial cell- pollen mother cell development period, up to the leptotene stage of meiosis. Female fertility was unaffected. For a complete inflorescence, the period of sensitivity extended from flag leaf ligule emergence until the flag sheath had elongated to about 20 cm, a period of 6-7 days under 25°C day/ 20°C night conditions. Pollen development proceeded in an apparently normal manner following low temperature treatment, but was arrested just prior to maturation at the vacuolate two-celled microspore stage. Sterile pollen at anthesis was devoid of starch and had low levels of free proline. Assays of anther proline levels proved to give a reliable index of pollen maturation.

Stress Metabolism. IX. The Significance of End-Product Inhibition of Proline Biosynthesis and of Compartmentation in Relation to Stress-Induced Proline Accumulation

Abstract: The rapid and extensive accumulation of proline during water stress in barley (cv. Prior) and tobacco (cv. White Burley) indicates that feedback inhibition of proline synthesis under these circumstances is unlikely. The incorporation into proline of radioactivity from administered L-[14C]glutamic acid was inhibited by the presence of proline in turgid but not in stressed tissues, suggesting that feedback inhibition of proline synthesis occurs in turgid but not in stressed tissues. An alternative explanation of the data, that the radioactivity in the L-glutamate pool of turgid tissue was diluted by non-labelled glutamate derived from the oxidation of the added proline, was not supported. Although rapid oxidation of added proline occurred, this did not appear to enter, to any significant extent, the glutamate pool concerned with proline synthesis. Neither aqueous nor non-aqueous isolation techniques demonstrated any specific enrichment with proline of specific cell fractions during stress. Moreover, in plants which had accumulated radioactivity in free proline during stress from administered L-[14C]glutamate, radioactivity accumul- ated in the proline incorporated in protein to an extent which suggested that the whole proline pool was equally available for protein synthesis. This does not favour the hypothesis that proline is accumulated exclusively in specific cellular organelles during stress.

Effect of Sulphur Supply on the Seed Globulin Composition of Lupinus angustifolius

Abstract: Seeds from L. angustifolius grown at three levels of applied sulphur contain similar amounts of protein whereas the ratio of total nitrogen to total sulphur in the whole seed and in the extracted protein is greatly increased under sulphur deficiency. This large change in nitrogen to sulphur ratio is accompanied by suppression of the synthesis of conglutins α and γ which usually contain most of the sulphur-containing amino acids found in these seeds. This is balanced by synthesis of an increased amount of conglutin β which normally contains no methionine and a lower proportion of cystine. Studies of the protein subunit composition show that the overall molecular weight distribution of the polypeptides is independent of the level of sulphur, but under sulphur deficiency the higher molecular weight subunits do not contain the disulphide linkages normally present. It is not known whether these higher-molecular-weight conglutin β subunits are normally absent or present only in trace amounts in the seeds.

Symbiotic Nitrogen Fixation by Coralloid Roots of the Cycad Macrozamia riedlei: Physiological Characteristics and Ecological Significance

Abstract: 'Coralloid' roots containing blue-green algae occur commonly on the upper root stocks of M. riedlei in natural habitat in Western Australia. Each coralloid mass persists for several seasons; replacement sets form at irregular intervals, especially after fire. 15N2 and acetylene reduction assays demonstrate that coralloid roots fix nitrogen at physiologically significant rates. C2H2 reduction rates by coralloid roots are higher in winter than in summer. Performance is positively correlated with rainfall; soil temperature appears to be of lesser importance. Diurnal fluctuations in nitrogenase activity occur. Calibration using 15N2 gives a molar ratio of C2H2 reduced : N2 fixed of 5.8 : 1. The seasonal average of C2H2 reduction of 14.8 nmol per g fresh wt coralloid root per min is then equivalent to 37.6 g N per kg fresh wt per year, a fixation rate potentially capable of doubling coralloid root nitrogen once in every 8 weeks, and whole plant nitrogen every 8-11 years. Returns of fixed nitrogen in two natural populations of Macrozamia are estimated by compounding measurements of biomass of host and symbiotic organs with the seasonal average for coralloid fixation rate. The values obtained (18.8 and 18.6 kg N ha-1 year-1) indicate that Macrozamia contributes significantly to the nitrogen economy of its ecosystem.

Electrolyte Leakage Induced by Chilling in Passiflora Species Tolerant to Different Climates

Abstract: A method was devised to measure chilling sensitivity in a series of species and hybrids of Passiflora having a range of climatic requirements. Leaves from plants which had been grown under 25°C day/18°C night were chilled at 0°C in the dark. At the same time, leakage of electrolyte from thin strips of these leaves was measured at 0°C using conductivity. Two main stages of leakage were found: a relatively slow rate (stage 1) which was followed by a high rate (stage 2), during which most of the electrolyte was lost from the tissue. Potassium was the principal cation lost from the tissue, and its leakage was proportional to that of total electrolyte during the time course of leakage. Stage 2 occurred at about the same time as obvious lesions appeared on whole leaves, and apparently signified lethal chilling injury. When different species were compared, those which had originated from the tropical lowlands (P. maliformis L. and P. edulis Sims forma flavicarpa Degener) were killed in less than 10 days, but those tolerant of cooler climates (P. caerulea L. and P. edulis Sims) survived much longer. From the behaviour of a number of species and hybrids, the rate of leakage during stage 1 was related to the time taken to reach stage 2. Resistance to chilling in the species and hybrids examined was not an all-or-nothing property, but showed a gradual increase in the series: P. edulis forma flavicarpa < P. maliformis < P. cincinnata Masters < P. edulis < P. caerulea, with some hybrids occupying intermediate positions.

Effect of Phosphorus Nutrition and Cytokinins on Flowering in the Tomato, Lycopersicon esculentum Mill

Abstract: Ten days of phosphorus deficiency results in a decrease in the number of flowers that develop on the first truss of tomato plants. This effect on flower number is accompanied by a decrease in the cytokinin activity of the root exudate. The involvement of cytokinins in flower development is further implicated by the fact that application of kinetin to the growing medium increased the number of flowers produced by the seedlings. Preliminary identification of cytokinins in root exudate has revealed the presence of compounds that cochromatograph with zeatin and zeatin riboside on Sephadex LH20.

Oxygen Inhibition of Photosynthetic Oxygen Evolution in Marine Plants

Abstract: The effect of oxygen concentration on oxygen exchange in six species of the Chlorophyta, one of the Cyanophyta, one of the Rhodophyta, three of the Phaeophyta, zooxanthellae from Tridacna maxima (clam) and Pocillopora damicornis (coral), and a marine angiosperm was investigated with a polaro- graphic oxygen electrode. The rate of photosynthesis in air-saturated sea water ranged from 14 to 248 micromoles of oxygen evolved per hour per milligram of chlorophyll. Photosynthesis was inhibited by 15-85% in sea water adjusted to between 65 and 90% of oxygen saturation. A post- illumination burst of oxygen uptake was observed on darkening and the size of this burst was in- fluenced by oxygen concentration. Steady-state rates of oxygen uptake in the dark were enhanced at higher oxygen tensions. The likelihood that the dissolved oxygen content of sea water may regulate the productivity of reef communities is discussed.

The Pectinesterase of the Pulp of the Banana Fruit.

Abstract: The pectinesterase (pectin pectyl-hydrolase, EC 3.1.1.11) of the pulp of the banana fruit is completely solubilized by buffers containing 0.5M sodium acetate, and the activity of the enzyme in the pulp remains constant during ripening. An apparent change in the ease of extraction as ripening progresses may be artefactual. The enzyme has been purified 200-fold from climacteric fruit. In either case, a molecular weight about 30 000 is indicated by chromatography through Sephadex G200. After isoelectric focusing, the enzyme was found in two peaks, at pH 8.8 - 8.9 and at pH 9.3 - 9.4. The enzyme in the two peaks is of the same molecular size, and shows only minor differences in responses to pH, salt and polyol concentration during assay. These results are discussed in relation to previous publications concerning changes in pectinesterase activity and properties during ripening of banana fruits.

Photosynthesis and Transpiration in Dicotyledonous Plants. II. Expanding and Senescing Leaves of Soybean

Abstract: The history of net photosynthesis and transpiration per unit leaf area was determined for intact soybean leaves from their unfolding to senescence during flowering and pod filling on untreated (podded) and partially depodded plants growing in a glasshouse. Leaf diffusive resistances to CO2 were calculated and a water use efficiency parameter was derived (net mass of carbon dioxide fixed per unit mass of water transpired per millibar vapour pressure deficit). Net photosynthesis and transpiration behaved similarly through all stages of leaf development. A number of peaks were evident in these parameters. The first was associated with leaf expansion and occurred when the leaf reached its maximum area. The second peak coincided with flowering of the plant and later peaks occurred during pod filling. Stomatal and mesophyll resistances also exhibited similar behaviour during the life of the leaf; the possible causes of this linkage are discussed. Water use efficiency increased rapidly up to the time of full lamina expansion. Thereafter, it rose slowly or remained stable until leaf senescence approached, when the efficiency declined. Net photosynthesis and transpiration of leaves were very similar in both podded and partially depodded plants. It appears that to prevent a shortage of assimilate during flowering and pod filling, photosynthesis may be maintained or increased in some leaves and the response is not related to the number of pods available for filling. The increases in photosynthesis were correlated with both higher stomatal and mesophyll conductances. Mechanisms by which the plant may control leaf photosynthesis are discussed.

Effect of Water Deficit on Carbon Dioxide Exchange and Leaf Elongation Rate of Panicum maximum Var. trichoglume

Abstract: The responses of carbon dioxide exchange and leaf elongation of potted P. maximum var. trichoglume plants to water deficits were investigated in controlled environments and outdoors during drying cycles down to -92 bars leaf water potential, The sensitivities of net photosynthesis and leaf elongation to water deficits were similar. The leaf water potentials at which net photosynthesis and elongation ceased (c. -12 bars), and stomatal resistance increased substantially (- 6 bars), were relatively unaffected by nitrogen supply, environmental conditions during growth, and whether plants had previously experienced stress. However, these factors influenced the rate of net photosynthesis, at high leaf water potentials by affecting stomatal resistance and at moderate water potentials by affecting both stomatal and intracellular resistances. Stomata1 resistance was more sensitive than intracellular resistance to water deficits. Dark respiration rate decreased with leaf water potential, and was higher in plants receiving additional nitrogen. At moderate leaf water potentials (-7 to -9 bars), net photosynthesis of this C4 grass exhibited light saturation and rates similar to C3 plants. We suggest that the difference in behaviour of controlled-environment-grown and field-grown plants to water deficits observed with some species is unlikely to be due to differences in the aerial environment, but may result from differences in the rate at which stress develops. The ecological significance and evolution of the C4 syndrome are discussed briefly.

Carbonate Dehydratase in Marine Organisms of the Great Barrier Reef

Abstract: Carbonate dehydratase (EC 4.2.1.1, other name 'carbonic anhydrase') activity was found in 28 of 29 species of marine algae and angiosperms and in a mixed culture of phytoplankton collected in the vicinity of Lizard Island on the Great Barrier Reef of Australia. The species included 13 member- of the Chlorophyta, 4 of the Phaeophyta, 7 of the Rhodophyta, 2 of the Cyanophyta and 3 subs merged marine angiosperms. One of the two blue-green algae showed no detectable enzymic activity. The levels of activity ranged from 100 to 4800 units per milligram chlorophyll and were generally comparable with those of terrestrial angiosperms based on chlorophyll content, but were only a small fraction when compared on the basis of fresh weight. Culture of the green alga Chlorodesmis fastigiata in 'CO2-free' sea water (1.4 mg CO2 per litre) for 4 h did not lead to an induction of carbonate dehydratase activity. Some of the species of algae producing calcium carbonate contained the highest activities recorded but others had low activities. A correlation between high carbonate dehydratase activity and calcium carbonate deposition could not be adduced. Symbiotic zooxanthellae (Gymnodinium microadriaticum) of the hard coral Pocillopora damicornis and the clam Tridacna maxima also contained carbonate dehydratase (940 and 340 units per milligram chlorophyll, respectively). The host tissues contained about five times the activity of their respective zooxanthellae.

Vine Response to Carbon Dioxide Enrichment During Heat Therapy

Abstract: Virus diseases which limit productivity in horticultural plants can be eliminated, or at least ameliorated, by propagating shoot tips from 'heat-treated' parent material. Grapevines (Vitis vinifera L.) undergoing heat therapy have to be grown at high temperature (37-40°C, day and night) for sustained periods (3-6 months) and the present paper reports how CO2 enrichment (1200-1300 ppm) can become an aid to their survival under these rigorous conditions. Vine growth rate more than doubled due to elevated CO2, and dry matter distribution was altered in favour of greater root growth. Nevertheless, stomatal resistance was increased (twofold), so that the ratio of assimilation to transpiration was substantially improved. Photosynthetic capacity of individual leaves was enhanced (laboratory measurement at 35°C and 950 ppm CO2) whereas photorespiration appeared depressed-a favourable combination for growth at elevated temperature. These physiological responses are discussed in relation to changes in both nitrate reductase and ribulosebisphosphate carboxylase activities and are compared with the behaviour of Leea brunoniana Clarke, a naturally occurring relative of V. vinifera from northern Australia.

Leaf Ultrastructure and δ13C Values of Three Seagrasses from the Great Barrier Reef

Abstract: Leaf anatomy, ultrastructure and 13C/12C ratios were studied in three species of seagrasses collected on the Great Barrier Reef: Cymodocea rotundata Ehrenb. & Hempr., C. serrulata (R. Br.) Aschers. & Magnus, and Thalassia hemprichii (Ehrenb.) Aschers. Although they belong to two different mono- cotyledonous families, the three species are quite similar in the characteristics studied. Cells of the epidermal layer of the leaves are extremely thick-walled and have abundant cytoplasm with large chloroplasts and numerous mitochondria. The chloroplast-microbody profile ratio is c. 4-5 : 1 and the mitochondrion-microbody ratio 10-15 : 1. The epidermal cells resemble transfer cells in having a pronounced development of ingrowths on the radial walls. The mesophyll cells have thin walls, a large central vacuole and a thin layer of cytoplasm with relatively few organelles. There is no specialization of mesophyll cells around the vascular bundles. The δ13C values for the three sea- grasses range from -6.90, to - 12.40, and thus are characteristic of C4 land plants, although the seagrasses do not conform to the C4 syndrome in leaf anatomy or ultrastructure. It is not possible to place the seagrasses in either the C3, C4 or crassulacean acid metabolism category of land plants, but whether they constitute yet a fourth group with respect to characteristics related to CO2 assimilation is not clear.

Composition and Ultrastructure of Leaf Cuticles From Fruit Trees, Relative to Differential Foliar Absorption

Abstract: Differential foliar absorption of chemicals by peach, apple and orange was related to cuticle thickness, weight, surface wax and embedded wax content and to surface wax wettability, ultrastructure and composition. Surface wax concentration, especially on abaxial leaf surfaces, correlated well with resistance to foliar absorption. The abaxial surface wax on peach leaves was built up in layers around and over the guard cells (which are preferred paths of spray entry into leaves) whereas apple and orange guard cells were relatively wax-free. Peach surface waxes were more difficult to wet than orange waxes and, although more polar than orange waxes, may be more resistant to water penetration as they were rich in hydrocarbons and triterpenoids. Enhancement of foliar absorption may require improved partitioning of sprays through the surface waxes or the bypassing of the waxes via stomatal penetration.

Glycine Decarboxylation in Mitochondria Isolated from Spinach Leaves

Abstract: Mitochondria isolated from spinach leaves contain at least two glycine decarboxylating systems. One system is stimulated by ADP and evidently couples to the electron transport chain. The other system, three times as active, is stimulated by NAD+ and oxaloacetate and is not coupled directly to electron transport; however, comparative studies with uncouplers and inhibitors indicate it may depend on a membrane potential generated by electron transport. In this system, the role of oxaloacetate appears to be the regeneration of NAD+, via mitochondrial malate dehydrogenase, as an electron acceptor during glycine decarboxylation. Mitochondria isolated from spinach leaves also catalyse a rapid glycine-dependent exchange of bicarbonate into acid-stable products. This reaction is stimulated by the addition of lipoamide dehydrogenase. The activity of the glycine decarboxylation and exchange reactions are irreversibly lost when mitochondria are broken. When corrections are applied to account for mitochondrial breakage, the rates of glycine decarboxylation and the exchange reaction are comparable to the rates of CO*2 evolution from leaves of C*3 plants in air. The role of these processes in vivo and relationship to other sources of CO*2 in the glycollate pathway are discussed.

Nitrogen Fixation by Blue-green Algae of the Lizard Island Area of the Great Barrier Reef

Abstract: Reduction of acetylene and 15N2 by blue-green algae and other organisms from the Lizard Island area of the Great Barrier Reef was measured. The effects of storage of the algae, the partial pressures of acetylene and oxygen, and light intensity were studied. The average ratio of acetylene to N2 reduced was 1.9. With this factor, it was calculated that 6.8 - 30.6 kg nitrogen was fixed annually per hectare of rock surface in the intertidal zone. Fixation of nitrogen by blue-green algae can contribute a substantial portion of the fixed nitrogen required for maintaining the flora and fauna of the coral reef community.

Influence of Oxygen Concentration on Photosynthesis in Marine Plants

Abstract: Photosynthesis was studied in various atmospheres of oxygen with marine plants grown on the Great Barrier Reef near Lizard Island, Australia. Inhibition of photosynthesis in a 100 % oxygen atmosphere ranged from 12 to 83 % in specific marine plants when compared to a nitrogen or helium atmosphere. The rates of photosynthesis in these marine plants were in general similar to those of terrestrial plants which fix CO2 via the reductive pentose phosphate cycle. We conclude that photo-respiration is present in specific marine plants at levels similar to those found in terrestrial plants with the reductive pentose phosphate cycle.

The Basis of Osmotic Pressure Maintenance During Expansion Growth in Helianthus annuus Hypocotyls

Abstract: In etiolated sunflower (H. annuus) hypocotyls, the intracellular osmotic pressure was maintained in spite of the dilution caused by growth. The principal osmotic substances present were hexoses (44 ± 6 mol m-3 glucose and 40 ± 5 mol m-3 fructose) and organic potassium salts (30 mol m-3). , Potassium fluxes in vivo (intact rooted seedlings) and in vitro (1 cm, peeled, cut sections in an aerated bathing solution) were similar, indicating that the sectioning had not affected cell fluxes. The uptake of 3-O-methyl glucose by cut sections from a bathing medium was lower than the uptake estimated using intact tissue (in vitro influx was 5 % of the net accumulation rate of intact tissue). This suggested that some pathway of hexose uptake other than from the extracellular spaces occurred in vivo. To explain this difference in reducing sugar accumulation rates the following pathway is suggested: (1) Transport of sucrose from the cotyledons via the phloem; (2) Direct unloading of the sucrose into the symplast; (3) Transport of the sucrose into the vacuole down a sucrose concentration gradient maintained by hydrolysis of sucrose to glucose and fructose; (4) Low hexose efflux from the vacuole (5 % of in vivo influx), preventing loss from the vacuole.

Pathways of CO2 Fixation in the Cam Plant Kalanchoe daigremontiana. III. Correlation With δ13C Value During Growth and Water Stress

Abstract: Seedlings of K. daigremontiana were grown in the same controlled-environment room under nine different day temperature and light regimes. In each treatment, irrigated plants maintained dawn water potentials of approximately -5 bar whereas droughted plants ranged to -22 bar. Irrigated plants showed a characteristic stomatal opening on illumination, closure during deacidification and partial stomatal opening following deacidification. Stomata of droughted plants remained closed throughout the light period. Irrigated and droughted plants showed comparable dark acid synthesis. Low light levels and low day temperature resulted in lower dark acid synthesis and more protracted deacidification in the light. The δ13C value (total carbon) of old as well as newly formed leaves of irrigated plants tended to become less negative throughout the experiment except in low-light, low-day-temperature treatments. This trend was accentuated in the δ13C value (total carbon) of whole shoots of droughted plants. These data are consistent with an increase, with age, in the proportion of CO2 assimilated in the dark during growth of irrigated plants, and with the greater dependence on dark CO2 assimilation during the slower growth of droughted plants. Differences in the δ13C value of soluble and insoluble carbon from irrigated and droughted plants assayed at dawn appear to be consistent with the established starch to acid relationships in crassulacean plants.

Light-dependent Redistribution of Ions in Isolated Spinach Chloroplasts

Abstract: The Mg2+, K+ and Cl- contents of chloroplast pellets collected after centrifugation in light and dark conditions have been determined in a specific reaction medium at pH 7.8 and 6.6. It was found that the light-induced proton uptake by chloroplasts was electrically balanced mainly by Mg2+ efflux and to a lesser extent by K+ efflux. Unlike results in other studies, Cl- influx was rather small. A model for the ionic relations of envelope-free chloroplasts is considered. Light-induced changes in the ionic contents calculated from the model are in agreement with our observations. An attempt is made to apply similar considerations to another set of reported data.

The Action Potential in Chara corallina: Effect of Temperature

Abstract: An investigation has been made of the effect of temperature on excitation in cells of C. corallina. It was found that the duration both of the action potential and of the transient current during excitation under voltage clamp increased with decreasing temperature, from ~1 s at 40°C to ~30 s at 3.5°C. The form of the transient response, however, was independent of temperature. While the peak potential during an action potential was largely independent of temperature, the peak transient current during a voltage clamp increased with increasing temperature up to ~30°C. Beyond this temperature, the peak current decreased again with increasing temperature. The activation enthalphy (ΔH*) calculated from Arrhenius plots of the duration of the action potential or of the transient current under voltage clamp varied continuously with temperature, having the values of ~7 kJ/mol for T > 20°C and ~350 kJ/mol for T 20°C and ~145 kJ/mol for T 35°C), ΔH* for both the passive and excitation channels was about the same as that for diffusion in a free solution. This suggests a progressive change in the degree of dehydration required for ion permeation in the channels. In the light of the known frequency dependence of the membrane capacitance of this species (at low frequencies), considerations are also given to the implications of the similarity in their temperature dependence, of the duration of the action potential and the duration of the transient currents during voltage clamps.

Glycollate Oxidase and Glycollate Dehydrogenase in Marine Algae and Plants

Abstract: Glycollate : dichlorophenolindophenol reductase, or glycollate dehydrogenase, was present in 15 green marine algae and one blue-green alga collected around Lizard Island, Australia. No enzyme activity was found in red or brown algae or zooxanthellae. Glycollate dehydrogenase was also found in the marine grasses Cymodocea and Thalassia, and this is the first report of it in higher plants. However, glycollate oxidase was present in the particulate fraction from Halophila, another marine monocotyldonous plant. On Lizard Island, the C3 plants, the C4 salt plants Distichlis and Salsola, and a crassulacean acid metabolism plant, Sesuvium all contained glycollate oxidase.

δ13C Values in Marine Organisms from the Great Barrier Reef

Abstract: The carbon isotope composition of marine organisms collected on the Great Barrier Reef near Lizard Island, Australia, was determined. Emphasis was placed on photosynthetic organisms including algae, zooxanthellae, angiosperms and symbiotic systems. The photosynthetic organisms had δ13C values ranging from -5.1 to -32.40,. Symbiotic systems and non-photosynthetic organisms had δ13C values within this range. CO2 released by acid treatment from coral, shell and cone carbonates had δ13C values between + 3.9 and - 2.70,. The results with photosynthetic tissue generally are interpreted in comparison to terrestrial plants as showing a major assimilation of CO2 into organic compounds via ribulosebisphosphate carboxylase in the marine ecosystem. However, a few photosynthetic organisms exhibited δ13C values between - 5.10, and - 110, and could be assimilating CO2 via phosphoenolpyruvate carboxylase. A unified scheme is presented for the pathway of carbon assimilation in the reef from the sea water through both autotrophic and heterotrophic metabolism, and finally to calcification.

Variation of Stomatal Diffusive Resistance With Ambient Humidity in Sunflower (Helianthus annuus)

Abstract: Experiments with sunflower were set up to supply quantitative information on the relationship between transpiration diffusive resistance and evaporative demand as affected by changes in ambient humidity. The experiments were run on whole plants with the roots in nutrient solution to ensure an adequate supply of water. Particular attention was paid to relating calculated diffusive resistance values with measured diffusion values and visual observations of the stomata. The transpiration diffusive resistance of the stomata was found to increase in a linear manner as the water vapour concentration difference between leaf and surrounding air increased. Changes in calculated diffusive resistance were paralleled by changes in the diffusion of nitrous oxide through the stomata. Visual observation showed that the stomata closed as resistance increased and vice versa. Stomata from both adaxial and abaxial surfaces of the leaf demonstrated increases in diffusive resistance with increasing evaporative demand but the response of the adaxial surface change was not always concurrent with that of the abaxial surface. Leaf water content did not change as evaporative demand was changed, reflecting the observation that uptake of water through the roots equalled the amount lost by transpiration. It was concluded that changes in diffusive resistance were directly related to the stomatal aperture and that the primary response was at the level of the stomatal apparatus. There was no evidence of stomatal control resulting from lowered tissue water content. Anomalous results may be obtained in gas exchange experiments where a constant area of leaf is sealed into a cuvette. Tests indicate that errors arise where the leaf is held too firmly.

Photosynthesis and Transpiration in Dicotyledonous Plants. I. Expanding Leaves of Tobacco and Sunflower.

Abstract: The aims of this paper were (1) to determine if irradiance and nutrition influence the timing of peak photosynthesis (Fmax) in expanding tobacco Ieaves and (2) to assess the relative importance of stomatal (rs) and mesophyll (rm) resistances to CO2 uptake as leaves expand. Growth conditions affected rates of leaf expansion and final leaf areas (Amax) but not the time from leaf emergence to Amax (25 days). Patterns of photosynthesis with time were similar in all treatments-F rose rapidly to Fmax and then declined, and Fmax occurred on day 13 when the areas of leaves in different treatments were from 65-80 % Amax. We suggest that temperature may determine the timing of Fmax. Changes in both rs and rm were associated with changes in F prior to Fmax. Although changes in rm were up to five times greater than in rs during this period, the relative reduction in the two resistances was similar. Absolute changes in rs and rm were similar immediately after Fmax, and during this period of 7 days F declined by almost 50%. Thereafter, relative changes were closely matched. Possible mechanisms for the control of the resistances by the plant are discussed. We discuss the hypothesis that Fmax was maintained for only a limited period in expanding tobacco leaves because of the lack of a sink for assimilate. Expanding sunflower leaves maintained Fmax for a much longer period and reasons are presented for this different behaviour. Water use efficiency (ω) of tobacco leaves changed as they expanded and was greatest under good nutrition and poorest under low irradiance. Maximum ω for tobacco and sunflower was similar.