The appearance of a new molecular species of phosphoenolpyruvate carboxylase (PEPC) and the rapid induction of CAM in Sedum telephium L.

Abstract. When detached leaves of Sedum telephium are incubated in the absence of water, a rapid switch from C₃ photosynthesis to CAM (as indicated by the onset of day-to-night fluctuations in titratable acidity. ΔH⁺) occurs within the first dark period. The C₃-CAM switch in intact plants occurs within 3 5d. Extractable activity of phospho enol pyruvate carboxylase (PEPC) increases five-fold in intact plants during CAM induction; however, during rapid CAM induction in detached leaves, there is only a very small increase in PEPC activity. Fractionation by anion exchange chromatography of crude extracts from leaves of intact plants subjected to water deficit shows that CAM induction is associated with the appearance of a molecular species of PEPC termed PEPC I. PEPC I is barely detectable in well-watered plants which are not performing CAM. The major form in these plants is termed PEPC II. In leaves from intact plants, there is a significant positive correlation between PEPC I activity and ΔH⁺ during a period of increasing water deficit. PEPC I exhibits day to night fluctuations in malate sensitivity, being less sensitive during the dark period. In contrast, PEPC II is more sensitive to inhibition by malate and has no day to night fluctuation in sensitivity. In detached leaves deprived of water, a small increase in PEPC I capacity is detected at the end of the first dark period (20 h after the start of treatment). The results suggest that PEPC I is required for attainment of maximum nocturnal malic acid synthesis. There is a significant correlation between leaf water status (relative water content), ΔH⁺, total PEPC and PEPC I activity suggesting that the internal water status of the plant may be a trigger for CAM induction. Abscisic acid applied to detached leaves does not cause nocturnal acidification.     

Nocturnal citrate accumulation and its response to environmental stress in the CAM plant Kalanchoe pinnata (Lam.) Pers.

Abstract. Kalanchoe pinnata (Lam.) Pers., a plant having crassulacean acid metabolism (CAM), was grown in high light (16–23 mol photons m⁻² d⁻¹) and in the shade (0.8–2.1 mol photons m⁻² d⁻¹), respectively. Plants were stressed in three ways, i.e. by transfer from high light to shade or vice versa just before measurements, and by withholding nitrogen and/or water. During the day-night cycle of CAM, K. pinnata showed day-night changes of citrate levels (Δ citrate) in addition to malate changes (Δ malate). Changes of leaf-cell sap osmotic pressure. Δπ, were linearly correlated with these changes of organic-acid anion levels with a relation of Δπ/(Δ citrate +Δ malate) = 1/1. The environmental stressor, i.e. limited N-nutrition, drought and higher or lower irradiance than experienced during growth, affected the absolute and relative contributions made by Δ citrate and Δ malate to total nocturnal organic-acid accumulation. In the high-light-grown plants transferred to the shade, changes of citrate levels were much less affected than changes of malate levels by the generally decreased metabolic activity and inhibition of CO₂ uptake. In the shade-grown plants, Δ citrate increased in response to stress imposed by interactive effects of the three stressors.     

A behavioural test of the sensitivity of a nocturnal mosquito, Anopheles gambiae, to dim white, red and infra-red light

Abstract. A behavioural test was used to determine the light sensitivity of the nocturnal mosquito Anopheles gambiae Giles s.s. to low intensities of 'white' light (tungsten filament), 'red' light (white light filtered by a darkroom safelight filter) and 'infra-red' light) of two types (white light filtered by a λ>700 nm filter, and light-emitting diodes with λ>900 nm). Mosquitoes were placed in a 20 cm diameter flight-tunnel and their 'optomotor' response to a pattern of stripes moving across their visual field (at 14.5 cm s^-1) was recorded with infra-red-sensitive video. In free-flight, with ample light, the mosquitoes controlled their flight speed and direction in relation to the stripe movement, so that the stripes always appeared to move across their visual field from front to back. They did this by flying either with the moving stripes fast enough to overtake them (19.5 ± 0.7 cm s^-1), or against them more slowly (10.3 ± 0.7 cm s^-1)- The net ground speed of the mosquitoes was thus c. 4–5 cm s^-1. This response was significant down to 10^-5 W m^-2 in 'white' light, and 10^-3 W m^-2 in 'red' light. At light intensities below threshold and in infra-red light, however, they appeared to fly at random with respect to the stripe movement. The assumption commonly made, that mosquitoes do not 'see' in red light, may thus have to be revised.     

Habitat selection by grayling-II. Preliminary results on larval and juvenile daytime habitats

Larval grayling were found along the shoreline at velocities <20 cm s^-1 depths <40 cm, shear stress <2 dyn m^-2 and over sand and silt. Juveniles were found in the river channel at currents of 20-40 cm s^-1 depths of 40-60 cm and shear stresses of 2-4 dyn m^-2, over gravel and pebbles.     

LIGHT-DEPENDENT GROWTH, DARK SURVIVAL, AND GLUCOSE UPTAKE BY CRYPTOPHYTES ISOLATED FROM A FRESHWATER CHEMOCLINE

Clones of Cryptomonas phaseolus Skuja , Cryptomonas rostratiformis ( Skuja ) Skuja in Huber-Pestalozi, and Cryptomonas undulata Gervais were isolated from the deep chlorophyll maximum near the oxic/anoxic boundary layer of the mesoeutrophic lake Schlachtensee, Germany. Different autecological features of these species were studied in batch culture experiments . Cryptomonas cf . ovata Ehrenberg and Chroomonas sp. that never dominated in the deep chlorophyll layer were also isolated from Schlachtensee to study their light-dependent growth in comparison to the deep-living species . Cryptomonas undulata, C. cf . ovata, and C. phaseolus had a very low light compensation point ( 5–7 μmol.m^-2.s^-1 ), whereas the growth rate of Chroomonas sp. and C. rostratiformis was positive above 16 and 24 μmol.m^-2.s^-1 . Cryptomonas phaseclus and Chroomonas sp. became photoinhibited above photon flux densities of 92 and 116 μmol.m^-2.s^-1 . Cryptomonas rostratiformis, C. cf . ovata, and C. undulata reached a maximum growth rate at a considerably higher photon flux density (198–250 μmol.m^-2.s^-1 ). Cryptomonas phaseolus grew fastest under light-limiting conditions . Chyptomonas phaseolus and C. undulata were best able to suruive prolonged periods of darkness . Cryptomonas phaseolus, C. rostratiformis, and C. undulata did not show any uptake of fluorescent latex beads. When labeled glucose was provided in naturally occurring concentrations, carbon uptake by C. phaseolus, C. rostratiformis, and C. undulata was negligibly small in comparison to cellular carbon content. I suggest that the adaptation to a low-light environment is an important preadaptation for the dominance of C. phaseolus and C. undulata near the freshwater chemocline .     

Development and accumulation of ABA in fluridone-treated and drought-stressed Vicia faba plants under different light conditions

The effects of fluridone on guard cell morphology, chloroplast ultrastructure and accumulation of drought stress-induced abscisic acid (ABA) were studied in Vicia faba L. plants grown under different light conditions. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. The appearance of defective and undeveloped stomata, and chloroplasts with a destroyed thylakoid membrane system was found in fluridone-treated plants grown at a photosynthetic photon flux (PPF) of 600 μmol m^-2 s^-1. Plants grown at a PPF of 40 μmol m^-2 s^-1 had diminished levels of ABA after imposition of dehydration. Fluridone treatment reduced the level of ABA in both unstressed and dehydrated leaves. Accumulation of ABA in the control plants was considerably reduced when they were exposed to dark periods of 24, 48 and 72 h just before imposition of the stress. Twenty-four hours after the dark treatment dehydration of the leaves resulted in a 3-fold decrease in the level of stress-induced ABA, and 72 h after dark treatment the amount of stress-induced ABA approximated the prestressed values. Fluridone-treated plants failed to accumulate ABA under water stress. In addition to functionally active chloroplasts, well-developed and functional stomata are required for drought stress to elicit a rise in ABA.     

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s^-1 m^-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s^-1 m^-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.     

Effects of light and temperature on the cell size and some biochemical components in two freshwater cryptophytes

The effects of light and temperature on cell size and cellular composition (chlorophyll, protein, carbohydrate) of two freshwater cryptophytes were studied with batch cultures. Neither of the species had a constant cell size but the size varied with growth conditions. At each temperature the smallest cells were recorded at the lowest experimental photon flux density. The smallest cells of Cryptomonas 979/67 had an average volume of 232 μm³ and the largest ones 1 020 μm³. In Cryptomonas 979/62 the smallest and largest cells measured 4 306 μm³ and 12 450 μm³. Both species increased their cellular chlorophyll content when PFB dropped below 110–120 μmol m^-2 s^-1. The highest and lowest chlorophyll contents of 979/67 were 7.45 fg μm^-3 and 0.55 fg μm^-2 respectively. For 979/62 the corresponding values were 10.23 fg μm^-3 and 0.93 fg μm^-3. In both species the protein content remained stable at PFDs higher than 110–120 μmol m^-2 S^-1. The highest content of protein measured in 979/67 was 638 fg μm^-3 and the lowest 147 fg μm^-3. For 979/62 these values were 1 036 fg μm^-3 and 148 fg μm^-3 respectively. The carbohydrate results were less clear and no pattern either in response to photon flux density or temperature was obvious. The lowest and highest contents recorded for 979/67 were 62 fg μm^-3 and 409 fg μ^-3 and for 979162, 36 fg μm^-3 and 329 fg μm^-3     

Kinetic changes with temperature of phosphoenolpyruvate carboxylase from a CAM plant

Abstract. Purified and crude phosphoenolpyruvate carboxylase from the CAM plant Kalanchoë daigremontiana Hamet et Perrier ( Bryophyllum diagremontianum ) was assayed at temperatures between 10 and 45° C. The optimum temperature of the enzyme activity changed with substrate availability and effector concentration in the assay. l -malate inhibited the enzyme activity and lowered the optimum temperature. Glucose-6-phosphate raised the optimum temperature to 43°C. K _m values for phosphoenolpyruvate increased with assay temperature from 0.12 mol m^-3 at 15° C to 0.36 mol^m−3 at 35° C. Inhibition by malate increased with temperature and acidity of the assay. In the crude enzyme 50% of control activity was inhibited by 1.65 mol m^-3 malate at 15° C and by 0.5 mol m^-3 at 35° C (at pH 7.0). With purification malate sensitivity was lost ( K _i values for malate at least 10 times higher). The shift in optimum temperatures for PEP-carboxylase activity thus results from changes in the kinetic parameters with temperature and allosteric effectors. The often low optimum temperatures for CO₂ fixation observed in nature may thus be the result of substrate and effector concentrations in the cytoplasm and the antagonistic effect of temperature on substrate affinity and effector efficiency on phosphoenolpyruvate carboxylase.     

Leaf Gas Exchange Characteristics in Relation to Leaf Canopy Position of Myrica faya in its Native Environment (Tenerife, Canary Islands)

Abstract: Diurnal courses of gas exchange were measured throughout one year in fully expanded current-year leaves in the uppermost canopy (sun leaves, 18 m above ground) and in the lower canopy (shade leaves, 12 m above ground) of Myrica faya Ait., a dominant component of the Canarian laurel forest in Tenerife, Canary Islands, Spain.
M. faya showed large differences between sun and shade leaves in gas exchange characteristics (about 50 % of maximum carbon assimilation rate (A_max) reduction in shade leaves, but this reduction can be higher on specific days) that were modulated by strong light attenuation and high leaf area index (LAI) of the stand. This species presented low A_max, about 10 μmol m^-2 s^-1, high maximum transpiration (E, 8 mmol m^-2 s^-1) and stomatal conductance (g_s, 750 mmol m^-2 s^-1) and very low instantaneous water use efficiency (WUE, mean maximum 1.1 mmol mol^-1) and A/g_s (mean maximum 23.5 μmol mol^-1). M. faya responded to high air vapour pressure deficit (VPD), decreasing its g_s but maintaining relatively high values of A and E during the studied period. Stomatal response to VPD showed a higher sensitivity than its congeners, M. cerifera, and Laurus azorica, tree species co-occurring in the Canarian laurel forest. In general, all these gas exchange characteristics lead us to consider this species more similar to subtropical plants of humid regions than to species of the Mediterranean region.     

Performance and Photosynthetic Ecophysiology of Three Photo-Types of Dioscorea zingiberensis under Differing Light Intensities

Abstract: The performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis were studied. The three types are designated DzTL, DzTM and DzTH, according to their adaptation to low (LL), medium (ML) and high (HL) light intensities, respectively. Under LL (23 - 55 μmol m^-2 s^-1) and simulated natural light (SNL), DzTM grows well with increased longevity, and green leaves which are unspotted; while its leaves became small, light yellow and short-lived under HL (550 - 850 μmol m^-2 s^-1). In contrast, under LL the leaves of DzTH were very large, spotted, light yellow and short-lived; while they were small, green and long-lived under HL. Under HL, DzTH had a much higher chlorophyll content than DzTM. Under LL, DzTM and DzTL had a higher Chl content than DzTH. Among the three types, DzTM had the highest peroxidase activity. DzTL had a higher electron transport rate (ETR), maximal quantum yield (MQY) and effective quantum yield (EQY) than DzTH and DzTL under LL, while DzTH had higher ETR, MQY and EQY than the other two types under ML and HL. Therefore, three different photo-types can be characterized according to their adaptation to LL, ML and HL: DzTL, DzTM and DzTH, respectively.     

Chlorophyll fluorescence measured using the Fraunhofer line-depth principle and relationship to photosynthetic rate in the field

Abstract. A field study was conducted to determine the relationship of solar-excited chlorophyll a fluorescence to net CO₂ assimilation rate in attached leaves. The Fraunhofer line-depth principle was used to measure fluorescence at 656.3 nm wavelength while leaves remained exposed to full sunlight and normal atmospheric pressures of CO₂ and O₂. Fluorescence induction kinetics were observed when leaves were exposed to sunlight after 10 min in darkness. Subsequently, fluorescence varied inversely with assimilation rate. In the C₄ Zea mays , fluorescence decreased from 2.5 to 0.8 mW m^-2 nm^-1 as CO₂ assimilation rate increased from 1 to 8 μmol m^-2 s^-1 (r²= 0.520). In the C₃ Liquidambar styraciflua and Pinus taeda , fluorescence decreased from 6 to 2 mW m^-2 nm^-1 as assimilation rate increased from 2 to 5 or 0 to 2 μmol m^-2 s^-1 (r²= 0.44 and 0.45. respectively). The Fraunhofer line-depth principle enables the simultaneous measurement of solar-excited fluorescence and CO₂ assimilation rate in individual leaves, but also at larger scales. Thus, it may contribute significantly to field studies of the relationship of fluorescence to photosynthesis.     

GROWTH OF HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE) ON NITRATE AND AMMONIUM AT THREE PHOTON FLUX DENSITIES: EVIDENCE FOR N STRESS IN NITRATE-GROWING CELLS

The marine alga Heterosigma carterae Hulburt (Raphidophyta) was grown in N-limiting batch cultures using either nitrate or ammonium as the N source, at photon flux densities (PFDs) of 50, 200, and 350 μmol·m^-2·s^-1 in a 12:12 h LD cycle. Carbon content could be estimated from biovolume (μg C = 0.278 × nL; R = 0.98) but not reliably from pigment content. During exponential growth, ammonium-grown cells (in comparison with nitrate-grown cells at the same PFD) attained higher growth rates by at least 20%, contained more N, and had a lower C:N ratio, higher concentrations of intracellular free amino acids, and higher ratios of glutamine: glutamate (Gln: Glu) and asparagine: aspartate (Asn:Asp). Growth was nearly light-saturated on ammonium at 200 μmol·m^-2·s^-1 (cell-specific growth rate of 1.2 d^-1) but probably not saturated in nitrate-grown cells at 350 μmol·m^-2·s^-1. PFD did not affect Gln: Glu or Asn: Asp for a given N source. These results indicate that the nitrate-growing cells were more N-stressed than those using ammonium (which in contrast were relatively C-stressed) and that this organism would show an enhanced competitive advantage against other species when supplied with a transient supply of ammonium rather than nitrate .     

Differential effects of chilling on the activity of C4 enzymes in two ecotypes of Echinochloa crus-galli from sites of contrasting climates

Five-week-old plants of Echinochloa crusgalli (L.) Beauv. from Mississippi and from Québec grown under controlled conditions were subjected to dark chilling for 10 h at 5°C or light chilling treatments for 14 h at 7°C under hight light (1 000 μmol m⁻² s⁻¹). The activities of four C₄ enzymes of Québec plants, measured 4 h after the completion of the cold treatment, were not affected by the chilling treatment in the dark. The activities of pyruvate, P_i dikinase (PPDK; EC 2.7.9.1) and NADP⁺-malic enzyme (NADP⁺-ME; EC 1.1.1.40), were significantly reduced in dark-chilled Mississippi plants. Chilling under high light conditions elicited significant levels of reduction in the activities of the four enzymes from both ecotypes but the reductions were significantly less severe for Québec plants. The recovery of activities of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and PPDK for both ecotypes was completed within 36 to 60 hours following the chilling treatment, but NADP⁺-malate dehydro-genase (NADP⁺-MDH; EC 1.1.1.82) and NADP⁺-ME activities of chilled Mississippi plants remained below that of control plants at the end of the 5-day monitoring period. PPDK was inactivated in vitro at 0 and 10°C and the rates of cold inactivation were significantly higher for PPDK extracted from Mississippi plants. The activity of PEPC of Mississippi extracts was slightly, but significantly reduced by a 60 min treatment at 0°C.     

Influence of long photoperiods on plant development and expression of Crassulacean acid metabolism in Mesembryanthemum crystallinum

Abstract. In the natural habitat plants of Mesembryanthemum crystallinum are induced to perform Crassulacean acid metabolism (CAM) after 3 months, and reproductive growth begins after 5 months (Winter, Liittge & Winter, 1978, Oecologia (Berlin), 34, 225-237). The life cycle of M. crystallinum and the extent of growth required prior to induction of enzymes of Crassulacean acid metabolism (CAM) are dramatically shortened by growing seedlings with a long photoperiod (3=16h/8h light/dark). Reproductive growth begins as soon as five weeks after germination when plants are grown in continuous light (under 600μmol quanta m⁻² s⁻¹, 30°C). In plants grown under well-watered conditions, the activities of PEP carboxylase and NADP-malic enzyme begin increasing markedly 2 weeks after germination, with plants grown under longer photoperiods having higher enzyme activities. After 3 weeks of growth, leaves accumulated a large amount of malate, but the microequivalents of malate present were up to nine times greater than the total titratable acidities. Interestingly, plants from a 24h/0h or a 20h/4h photo-period showed no diurnal fluctuation of malate, but did produce malate in the light as a major photosynthetic end product. That is, under these environmental conditions, principal enzymes of CAM can be induced without the plants performing CAM. However, plants grown in a 16h/8h photoperiod did exhibit nocturnal accumulation of malate after 3 weeks of growth. In plants of all three growth conditions, the activities of NADP-malic enzyme and PEP carboxylase were further increased two- to live-fold by irrigating 3-week-old-plants with 350mol m⁻³ NaCl. Such early enhancement of these enzymes by salt and the shortened life cycle may be due to an accelerated development under the long photoperiods.     

Light-quality and irradiance-level control of light-harvesting complex of photosystem 2 in maize mesophyll cells. Evidence for a low fluence-rate threshold in blue-light reduction of mRNA and protein

Levels of pigment-proteins and mRNA coding for proteins associated with the light-harvesting complex of photosystem 2 (LHCP2) were reduced in maize ( Zea mays L. cv. OP Golden Bantum) plants grown for 14 days in 8.0 nmol m^-2s^-1 of blue light compared to those in plants grown under an equal irradiance of red light. At the same time, there was a small increase in steady state levels of mRNA for the Dl protein of PS2 (psbA) in blue-grown plants. The reduction of LHCP2 mRNA and the increase in psbA mRNA were observed in both 5- and 10-day-old blue-light-grown leaves, but the degree of reduction or increase was much greater in 10-day-old leaves. Maize grown under 6 different mixtures of blue and red light, each with a total irradiance level of 8.0 μmol m^-2 s^-1, showed the same degree of LHCP2 mRNA reduction relative to red light. This is different from the behavior of psbA which increased in a linear manner with increasing amounts of blue light. The amounts of Chi a and Chi b in these mixed-light samples were not significantly different froi those found in pure red light. This indicates that a low fluence level of blue light, even when combined with red light, is sufficient to reduce equilibrium levels of proteins and mRNA of LHCP2, and this reduction is independent of pigment formation. It also suggests that the mechanisms of blue-light regulation of mRNA may operate differently at the nuclear and chloroplast levels.     

The effect of different growth conditions on dark and light carbon assimilation in Littorella uniflora

The effect of long-term exposure to different inorganic carbon, nutrient and light regimes on CAM activity and photosynthetic performance in the submerged aquatic plant, Littorella uniflora (L.) Aschers was investigated. The potential CAM activity of Littorella was highly plastic and was reduced upon exposure to low light intensities (43 μmol m⁻² s⁻¹), high CO₂ concentrations (5.5 mM, pH 6.0) or low levels of inorganic nutrients, which caused a 25–80% decline in the potential maximum CAM activity relative to the activity in the control experiments (light: 450 μmol m⁻² s⁻¹; free CO₂: 1.5 mM). The CAM activity was regulated more by light than by CO₂, while nutrient levels only affected the activity to a minor extent. The minor effect of low nutrient regimes may be due to a general adaptation of isoetid species to low nutrient levels.
The photosynthetic capacity and CO₂ affinity was unaffected or increased by exposure to low CO₂, irrespective of nutrient levels. High CO₂, low nutrient and low light, however, reduced the capacity by 22–40% and the CO₂ affinity by 35-45%, relative to control.
The parallel effect of growth conditions on CAM activity and photosynthetic performance of Littorella suggest that light and dark carbon assimilation are interrelated and constitute an integrated part of the carbon assimilation physiology of the plant. The results are consistent with the hypothesis that CAM is a carbon-conserving mechanism in certain aquatic plants. The investment in the CAM enzyme system is beneficial to the plants during growth at high light and low CO₂ conditions.     

Reduced irradiance and applied auxin influence carbohydrate relations in Pinus banksiana cuttings during propagation

Untreated and indole-3-butyrie acid-treated (IBA) cuttings from 90-day-old Pinus banksiana Lamb, stock plants were propagated under normal greenhouse irradiance (max. 900 $$mol m^-2 s^-1) and shade (max. 120 $$mol m^-2 s^-1) to determine effects on adventitious rooting and on reducing sugar and starch concentrations in needles and basal stems. In one experiment, cuttings were assessed at days 15 and 25 of propagation for basal 1-cm stem fresh weight, proportion rooted, number of roots and longest root length. In a second experiment with cuttings, basal 1-cm stem fresh weight and concentrations of reducing sugar and starch in needles and basal stems were measured each day for the first 10 days of propagation. Carbohydrate measurements were also made for seedling stock plants as controls for the second experiment. Carbohydrate data for cuttings were primarily evaluated based on net (cutting minus seedling) concentrations, to correct for changes in cuttings not related to adventitious rooting. Increase of basal stem fresh weight and rooting of cuttings, based on all measured variables, occurred in the order: light + IBA > light > shade + IBA > shade. The best rooting required the greater irradiance. Compared to results from cuttings in the light, shading resulted in lesser accumulations of reducing sugars and starch in needles and basal stems. Reducing sugar: starch concentration ratios were significantly greater in shade- vs light-propagated cuttings, IBA treatment did not offset the effects of shade on rooting or on reducing sugar and starch concentrations or ratios. Overall, the results suggested that decreased reducing sugar and starch concentrations and/or their increased ratios are associated with shade-induced poor rooting of P. banksiana cuttings.     

Properties of NADP+-malic enzyme from pod walls of chickpea (Cicer arietinum)

NADP⁺-malic enzyme ( l -malate: NADP⁺ oxidoreductase, decarboxylating EC 1.1.1.40) from pod walls of chickpea was purified 51-fold by ammonium sulphate fractionation, DEAE- cellulose chromatography and gel filtration through Sepharose 4B. The purified enzyme required a divalent cation, either Mn²⁺ or Mg²⁺, for its activity. K_m values at pH 7.8 for malate, NADP⁺ and Mn²⁺ were 4.0, 0.031 and 0.71 m M , respectively. Mn²⁺-dependent activity was inhibited by heavy metal ions such as Cd²⁺, Zn²⁺, Hg²⁺, and to a lesser extent by Pb²⁺ and Al³⁺. Among the organic acids examined, sodium salts of oxalate and oxaloacetate were inhibitory. Kinetics of the reaction mechanism showed sequential binding of malate and NADP⁺ to the enzyme. Products of reaction, viz. pyruvate, bicarbonate and NADPH, inhibited the enzyme activity. At limiting concentrations of NADP⁺, pyruvate and bicarbonate induced a positive cooperative effect by malate. It is proposed that the activity of NADP⁺-malic enzyme is controlled by intracellular concentrations of substrates and products.     

Mode of interference of chlorosis-inducing herbicides with peroxisomal enzyme activities

In rye leaves ( Secale cereale L. cv. Petkus "Kustro") bleached in the presence of the chlorosis-inducing herbicides aminotriazole, haloxidine, San 6706 or difunone in white light of 54.2 W m^-2 (5000 lx), catalase activity was very low. In addition, the activities of glycolate oxidase and hydroxypyruvate reductase were strongly diminished in treatments with San 6706 and difunone. The lowering of the peroxisomal enzyme activities was observed in red, but not in blue light and did not occur after treatment with the non-bleaching pyridazinone derivative San 9785. The deficiencies of the peroxisomal enzymes did not appear to be involved in the initiation of the chlorosis. Instead they are probably produced as secondary consequences of the bleaching. Low peroxisomal enzyme activities were also obtained without herbicide treatment by growing the leaves in an atmosphere of 2% O₂ and 3% CO₂, but in this case were not accompanied by an increased sensitivity of the Chl to photooxidative bleaching. The peroxisomal enzymes reached as high activities as in untreated controls when the herbicide-treated leaves were grown at a low light intensity of 0.106 W m^-2 (10 lx). After transfer of herbicide-treated leaves grown under 0.106 W m^-2 to 306 W m^-2 (30 000 lx), catalase was strongly inactivated, even at 0°C. In treatments with San 6706 and difunone the increase of the activities of glycolate oxidase and hydroxypyruvate reductase was either stopped, remaining unchanged, or the enzymes were slightly inactivated after exposure to 306 W m^-2 (30 000 lx). The observations suggest that the inactivation of peroxisomal enzymes results from photooxidative events in the chloroplasts.