Identification of an Antifungal Compound in Unripe Avocado Fruits and its Possible Involvement in the Quiescent Infections of Colletotrichum gloeosporioides1

A new antifungal compound was isolated from peel and flesh of unripe avocado fruits and identified as 1-acetoxy-2,4-dihydroxy-n-heptadeca-16-ene. The maximal concentration of the anti-fungal monoene in unripe fruits was about 800 μg. g^?1 fr.wt. During ripening the monoene decreased to 40 μg. g^?1 fr.wt. concomitantly with the appearance of disease symptoms. The concentration of the previously described antifungal diene, 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene (Prusky et al. 1982), in avocado peel was 1,600 μg. g^?1 fr.wt. in unripe fruits, decreasing during ripening to 120 μg. g^?1 fr.wt. At 750 μg. ml^?1 the inhibition of germ tube elongation of germinated conidia by the antifungal monoene and the antifungal diene was 15 % and 44 %, respectively. A 1: 1 mixture of both antifungal compounds in concentrations ranging from 50 to 750 μg. ml^?1, showed synergistic activity and increased the percent of inhibited germ tubes of germinated conidia up to 15 % over the sum of activities of the separate compounds. The results are discussed in relation to the hypothesis that the antifungal diene and the antifungal monoene are involved in the quiescence of the germinated appressoria of Colletotrichum gloeosporioides in unripe avocado fruits.     

Contents of 1,4-benzoxazin-3-ones and 2-benzoxazolinone from Stenandrium dulce (Nees)

Secondary metabolites, DIBOA, HBOA, 7-OH-HBOA and BOA, were isolated and quantified from S. dulce (Nees), a native species in Chile belonging to the Acanthaceae family. The highest DIBOA and HBOA contents were determined in leaves (9.25 mmol kg(-1) fr. wt) and root (6.81 mmol kg(-1) fr. wt), respectively. Aglycones, 7-OH-HBOA and HBOA, were isolated together from root extracts of Acanthaceae species. Both, HBOA and 7-OH-HBOA should be direct precursors in the biosynthesis of DIBOA and DIMBOA, respectively.     

Involvement of Epicatechin in Cultivar Susceptibility of Avocado Fruits to Colletotrichum gloeosporioides after Harvest1

Avocado cultivars were defined as susceptible and resistant to Colletotrichum gloeosporioides depending upon the length of the incubation period of the disease after fruit softening. In the susceptible cultivars Fuerte, Horshim, Vurtz, Rincon, and Benik, epicatechin concentration of the peel decreased to 60-130 μg.g^?1, fr. wt. at fruit softening and symptoms appeared on the same or one day later. In the resistant cultivars Hass, Nabal, Netaim and Pinkerton, epicatechin concentration was still 632–1740 μg.g^?1 fr. wt. when fruit softening and symptoms appeared only 4-10 days later. When susceptible Fuerte fruits became soft the concentration of the antifungal compound 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15 diene, had decreased to 120 μg.g^?1 fr. wt. and symptoms appeared. In resistant Hass fruits, the antifungal diene was still 238 μg.g^?1 fr. wt. at fruit softening; and it had further decreased to 159 μg.g^?1 fr. wt. when symptoms appeared, four days later. A modified atmosphere and 0.2 M CaCl₂ infiltration both delayed softening of Fuerte fruits; but symptom appearance on these fruits was related to diene decrease and not to fruit softening. The results are discussed in relation to the hypothesis that the susceptibility of avocado cultivars to post-harvest decay by C. gloeosporioides is related to the degradation of the antifungal diene, catalyzed by avocado lipoxygenase, the activity of which is regulated by the decline of its inhibitor epicatechin.     

Photosynthetic characteristics and leaf carbon economy of a deciduous and an evergreen dwarf shrub: Vaccinium uliginosum L. and V. vitis-idaea L.

The seasonal course of photosynthetic rate, and light and temperature relations were studied in the dwarf shrubs Vaccinium uliginosum L., deciduous, and Vaccinium vitisidaea L., evergreen, at a subarctic site in northern Sweden, Using the photosynthetic characteristics and meteorological data from the site, the seasonal and life-span carbon dioxide gain was estimated. The photosynthetic capacity of V. uliginosum was at a maximum one month after the start of leaf expansion and declined rapidly in the beginning of September. The old V. vitis-idaea leaves needed about 2 wk to recover full photosynthetic capacity after snow-melt; the current-year V. vitis-idaea leaves needed the same time after bud-break to reach full capacity. The leaves of V. vitis-idaea showed no seasonal trend in photosynthetic capacity after the first two wk of recovery, but their capacity decreased by one third after the first winter and by approximately 10% yr^?1 over the following two yr. The seasonal variation in the photosynthetic response to temperature was more marked in V. uliginosum than in V. vitis-idaea. Light saturation occurred at approximately 3000 μmol m^?2 s^?1 in V. uliginosum and at 60 μmol m^?2 s^?1 in one-year-old V. vitis-idaea leaves. The leaves of both species had a positive carbon balance at photon flux densities above 5 μmol m^?2 s^?1. The calculated seasonal CO² gain was 21 g CO₂ g_?1 leaf in V. uliginosum and 6–8 g CO₂ g_?1 in V. vitis-idaea leaves. Life-span CO₂ gain for leaves of V. vitis-idaea was the same as in V. uliginosum, viz. 21 g CO₂ g_?1. One fifth of the CO₂ gain of V. vitis-idaea was assimilated during periods when V. uliginosum was leafless.     

1,4-benzoxazin-3-one, 2-benzoxazolinone and gallic acid from Calceolaria thyrsiflora Graham and their antibacterial activity

Secondary metabolites, DIBOA, HBOA, 7-OH-HBOA, BOA and gallic acid, were isolated and quantified from Calceolaria thyrsiflora Graham, a native medicinal plant of Chile belonging to the Scrophulariaceae family. The highest DIBOA contents were determined in leaves (145 mmol kg(-1) dry wt) and flowers (161 mmol kg(-1) dry wt). Antibacterial activities of DIBOA, HBOA, BOA, gallic acid and infusions of flowers and leaves were determined. The phytomedicinal properties attributed to C. thyrsiflora Graham could be understood on the basis of its antibacterial activity.     

UV-A Inhibition of Alternative Respiration in Pea Leaves and a Unicellular Green Alga Chlamydomonas reinhardtii

Total respiration (v_T) increased after exposure to UV, but a decrease in the capacity of SHAM-sensitive-alternative respiration (V_alt) was accompanied by an increase in residual respiration (v_res). The capacity for CN sensitive-cytochrome c respiration (V_cyt) was not inhibited by UV-A. After 4 h of irradiation of high-CO₂-grown cells of Chlamydomonas reinhardtii with UV-A (2 μW. CM^?2) in the presence of white light (300μE.m^?2.s^?1), the capacity of Vast was reduced from 10 to 4 μmol O₂. mg^?1Chl.h^?1, a 60 % reduction. After a similar exposure to UV-A, the capacity of V_alt in pea leaves was reduced from 13 to 5 μmol O₂.g^?1 fr wt.h^?1. Exposure to UV-C was not inhibitory, but UV-B caused up to 25% inhibition of the V^alt. Twenty to 48 h after exposure to UV-A radiation, the capacity of alternative respiration had recovered. UV-A inhibition of the alternative respiration was consistent with UV-A absorption by quinones, except that UV-A did not inhibit the cyt c pathway of electron transport that also involves the ubiquinones.     

Assessment of heavy metal accumulation in Anzali wetland,Iran, using a submerged aquatic plant,Ceratophyllum demersum

The objective of this study in 2009 was to examine whether levels of cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb) and chromium (Cr) were higher in the leaves than in the stems of a submerged aquatic plant Ceratophyllum demersum in Anzali wetland. Cadmium, Pb and Cr concentrations were highest in the leaves. The mean concentrations of Cd and Cr in the leaves at all the sampling sites ranged between 0.94–1.26 μg g^?1 and 1.03–2.71 μg g^?1, respectively. Lead also had its highest concentrations in the leaves. The mean concentration of Pb in the leaves at all sampling sites ranged between 7.49–11.88 μg g^?1. Copper and Zn concentrations were highest in the stems. The mean concentrations of Cu and Zn in the stems at all sampling sites ranged between 10.79–17.91 μg g^?1 and 19.89–40.01 μg g^?1, respectively. Cadmium and Pb concentrations were higher in the leaves than in the stems, while Zn concentration was higher in the stems than in the leaves. Accumulation of Cu and Cr in the organs of C. demersum was in descending order of leaf ～ stem, since there was no significant difference between their mean concentrations in the leaves and stems.     

Direct and acclimatory responses of stomatal conductance to elevated carbon dioxide in four herbaceous crop species in the field

In order to separate the net effect of growth at elevated [CO₂] on stomatal conductance (g_s) into direct and acclimatory responses, mid‐day values of g_s were measured for plants grown in field plots in open‐topped chambers at the current ambient [CO₂], which averaged 350 μmol mol^?1 in the daytime, and at ambient + 350 μmol mol^?1[CO₂] for winter wheat, winter barley, potato and sorghum. The acclimatory response was determined by comparing g_s measured at 700 μmol mol^?1[CO₂] for plants grown at the two [CO₂]. The direct effect of increasing [CO₂] from 350 to 700 μmol mol^?1 was determined for plants grown at the lower concentration. Photosynthetic rates were measured concurrently with g_s. For all species, growth at the higher [CO₂] significantly reduced g_s measured at 700 μmol mol^?1[CO₂]. The reduction in g_s caused by growth at the higher [CO₂] was larger for all species on days with low leaf to air water vapour pressure difference for a given temperature, which coincided with highest conductances and also the smallest direct effects of increased [CO₂] on conductance. For barley, there was no other evidence for stomatal acclimation, despite consistent down‐regulation of photosynthetic rate in plants grown at the higher [CO₂]. In wheat and potato, in addition to the vapour pressure difference interaction, the magnitude of stomatal acclimation varied directly in proportion to the magnitude of down‐regulation of photosynthetic rate through the season. In sorghum, g_s consistently exhibited acclimation, but there was no down‐regulation of photosynthetic rate. In none of the species except barley was the direct effect the larger component of the net reduction in g_s when averaged over measurement dates. The net effect of growth at elevated [CO₂] on mid‐day g_s resulted from unique combinations of direct and acclimatory responses in the various species.     

Seasonal differences in isoprene and light-dependent monoterpene emission by Amazonian tree species

Whereas for extra‐tropical regions model estimates of the emission of volatile organic compounds (VOC) predict strong responses to the strong annual cycles of foliar biomass, light intensity and temperature, the tropical regions stand out as a dominant source year round, with only little variability mainly due to the annual cycle of foliar biomass of drought‐deciduous trees. As part of the Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA‐EUSTACH), a remote secondary tropical forest site was visited in the dry‐to‐wet season transition campaign, and the trace gas exchange of a strong isoprene emitter and a monoterpene emitter are compared to the wet‐to‐dry season transition investigations reported earlier. Strong seasonal differences of the emission capacity were observed. The standard emission factor for isoprene emission of young mature leaves of Hymenaea courbaril was about twofold in the end of the dry season (111.5 μgC g^?1 h^?1 or 41.2 nmol m^?2 s^?1) compared to old mature leaves investigated in the end of the wet season (45.4 μgC g^?1 h^?1 or 24.9 nmol m^?2 s^?1). Standardized monoterpene emission rate of Apeiba tibourbou were 2.1 and 3.6 μgC g^?1 h^?1 (or 0.3 and 0.8 nmol m^?2 s^‐1), respectively. This change in species‐specific VOC emission capacity was mirrored by a concurrent change in the ambient mixing ratios. The growth conditions vary less in tropical areas than in temperate regions of the world, and the seasonal differences in emission strength could not be reconciled solely with meteorological data of instantaneous light intensity and temperature. Hence the inadequacy of using a single standard emission factor to represent an entire seasonal cycle is apparent. Among a host of other potential factors, including the leaf developmental stage, water and nutrient status, and abiotic stresses like the oxidative capacity of the ambient air, predominantly the long‐term growth temperature may be applied to predict the seasonal variability of the isoprene emission capacity. The dry season isoprene emission rates of H. courbaril measured at the canopy top were also compared to isoprene emissions of the shade‐adapted species Sorocea guilleminiana growing in the understory. Despite the difference in VOC emission composition and canopy position, one common algorithm was able to predict the diel emission pattern of all three tree species.     

Phytochemical Profiles and Antioxidant Activity of Rehmannia glutinosa from Different Production Locations

The chemical components and antioxidant activity of 16 Rehmannia glutinosa samples were investigated to reveal the high‐quality raw resource for pharmaceutical products. 22 main chemical components were detected with significant content differences (P<0.05). The contents of 14 substances reached the maximum in S1 sample such as catalpol (6.74 mg g^?1), rehmaionoside A (1.93 mg g^?1) and rehmannioside D (5.13 mg g^?1). However, the content distribution of the other eight substances had no obvious change regulation. Three antioxidant evaluation methods commonly showed that S1 sample had strong antioxidant activity with a low IC₅₀ value of 0.022 mg mL^?1, a high ABTS value of 524.196 μmol equiv. Trolox g^?1, and a high FRAP value of 200.517 μmol equiv. Trolox g^?1. Considered the medicinal value, S1 had high quality based on the present phytochemical profiles and antioxidant activity. These results also indicated that the root extracts of R. glutinosa could become useful supplement for pharmaceutical products as new antioxidant agents.     

Seasonal changes in the chlorophyll content and quantum efficiency of the moss Brachythecium rutabulum

Abstract

The concentration of chlorophyll a, b, and total chlorophyll have been monitored on a seasonal basis in Brachythecium rutabulum. Total chlorophyll increases during summer full canopy conditions from 1.70 mg chl g^?1 on 8 May to 11.1 mg chl g^?1 on 11 October. Photosynthetic-illumination curves show that during this period light saturation declines from 200 μmol m^?2s^?1 to 30 μmol m^?2s^?1 by 6 July, and light compensation falls dramatically from 65 μmol m^?2s^?1 to 4 μmol m^?2s^?1. The data also appear to support the conclusion that there is concurrently an increase in the density of photosynthetic units by the end of September.     

Exceptional Visible‐Light‐Driven Cocatalyst‐Free Photocatalytic Activity of g‐C3N4 by Well Designed Nanocomposites with Plasmonic Au and SnO2

In this work, plasmonic Au/SnO₂/g‐C₃N₄ (Au/SO/CN) nanocomposites have been successfully synthesized and applied in the H₂ evolution as photocatalysts, which exhibit superior photocatalytic activities and favorable stability without any cocatalyst under visible‐light irradiation. The amount‐optimized 2Au/6SO/CN nanocomposite capable of producing approximately 770 μmol g^?1 h^?1 H₂ gas under λ > 400 nm light illumination far surpasses the H₂ gas output of SO/CN (130 μmol g^?1), Au/CN (112 μmol g^?1 h^?1), and CN (11 μmol g^?1 h^?1) as a contrast. In addition, the photocatalytic activity of 2Au/6SO/CN maintains unchanged for 5 runs in 5 h. The enhanced photoactivity for H₂ evolution is attributed to the prominently promoted photogenerated charge separation via the excited electron transfer from plasmonic Au (≈520 nm) and CN (470 nm > λ > 400 nm) to SO, as indicated by the surface photovoltage spectra, photoelectrochemical I–V curves, electrochemical impedance spectra, examination of formed hydroxyl radicals, and photocurrent action spectra. Moreover, the Kelvin probe test indicates that the newly aligned conduction band of SO in the fabricated 2Au/6SO/CN is indispensable to assist developing a proper energy platform for the photocatalytic H₂ evolution. This work distinctly provides a feasible strategy to synthesize highly efficient plasmonic‐assisted CN‐based photocatalysts utilized for solar fuel production.     

Stomatal behaviour in a beech canopy: an analysis of Bowen ratio measurements compared with porometer data

On the basis of measurements or stand transpiration and microclimate, the bulk stomatal or bulk leaf conductance (g_L) of a beech forest in northern Germany was calculated for periods in which leaves were fully expanded and the canopy was dry. This conductance depends strongly on light and humidity conditions above the forest. During periods with photosynthetic photon flux densities Q > 1200 μmol m^?2s^?1, g_L was reduced from 1500mmol m^?2s^?1 at a vapour pressure deficit D= 0.5kPa to 500 mmol m^?2s^?1 at D= 2kPa. Light saturation of g_L was not reached until Q= 1200 μmol m^?2s^?1 at low D, or until even higher Q at higher D. The dependence of g_L, on Q and D was described mathematically by a non-linear equation that requires two empirical parameters. Values for g_L as simulated by this equation provided a satisfactory agreement with independent porometer data collected on single leaves and scaled up to the canopy. A comparison of stomatal and aerodynamic conductances showed a strong coupling between the forest canopy and the atmosphere, indicating that transpiration of the beech forest is controlled mainly by the stomata.     

Interaction between atmospheric CO2 concentration and water deficit on gas exchange and crop growth: testing of ecosys with data from the Free Air CO2 Enrichment (FACE) experiment

Soil water deficits are likely to influence the response of crop growth and yield to changes in atmospheric CO₂ concentrations (C_a), but the extent of this influence is uncertain. To study the interaction of water deficits and C_a on crop growth, the ecosystem simulation model ecosys was tested with data for diurnal gas exchange and seasonal wheat growth measured during 1993 under high and low irrigation at C_a= 370 and 550 μmol mol^?1 in the Free Air CO₂ Enrichment (FACE) experiment near Phoenix, AZ. The model, supported by the data from canopy gas exchange enclosures, indicated that under high irrigation canopy conductance (g_c) at C_a= 550 μmol mol^?1 was reduced to about 0.75 that at C_a= 370 μmol mol^?1, but that under low irrigation, g_c was reduced less. Consequently when C_a was increased from 370 to 550 μmol mol^?1, canopy transpiration was reduced less, and net CO₂ fixation was increased more, under low irrigation than under high irrigation. The simulated effects of C_a and irrigation on diurnal gas exchange were also apparent on seasonal water use and grain yield. Simulated vs. measured seasonal water use by wheat under high irrigation was reduced by 6% vs. 4% at C_a= 550 vs. 370 μmol mol^?1 but that under low irrigation was increased by 3% vs. 5%. Simulated vs. measured grain yield of wheat under high irrigation was increased by 16% vs. 8%, but that under low irrigation was increased by 38% vs. 21%. In ecosys, the interaction between C_a and irrigation on diurnal gas exchange, and hence on seasonal crop growth and water use, was attributed to a convergence of simulated g_c towards common values under both C_a as canopy turgor declined. This convergence caused transpiration to decrease comparatively less, but CO₂ fixation to increase comparatively more, under high vs. low C_a. Convergence of g_c was in turn attributed to improved turgor maintenance under elevated C_a caused by greater storage C concentrations in the leaves, and by greater rooting density in the soil.     

Contrasting stream water NO3− and Ca2+ in two nearly adjacent catchments: the role of soil Ca and forest vegetation

Two nearly adjacent subcatchments, located in the Adirondack Mountains of New York State, US, with similar atmospheric inputs of N (0.6 kmol ha^?1 yr^?1), but markedly different stream water solute concentrations, provided a unique opportunity to evaluate the mechanisms causing this variation. Subcatchment 14 (S14) had much greater stream water Ca²⁺ and NO₃^? concentrations (851 and 73 μmol_c L^?1, respectively) than Subcatchment 15 (S15) (427 and 26 μmol_c L^?1, respectively). To elucidate factors affecting the variability in stream water concentrations, soil and forest floor samples from each subcatchment were analyzed for total elemental cations and extractable N species. Mineral soil samples were also analyzed for exchangeable cations. Tree species composition was characterized in each subcatchment and potential differences in land use history and hydrology were also assessed. Compared with S15, soils in S14 had significantly higher total elemental Ca²⁺ in the forest floor (380 vs. 84 μmol g^?1), Bs horizon (e.g. 1361 vs. 576 μmol g^?1) and C horizon (1340 vs. 717 μmol g^?1). Exchangeable Ca²⁺ was also significantly higher in the mineral soil (64 μmol g^?1 in S14 vs. 8 μmol g^?1 in S15). Extractable NO₃^? was higher in S14 compared with S15 in both the forest floor (0.1 vs. 0.01 μmol g^?1) and Bs horizon (0.2 vs. 0.07 μmol g^?1) while extractable NH₄⁺ was higher in S14 vs. S15 in the forest floor (7 vs. 5 μmol g^?1). The total basal area of ‘base‐rich indicator’ tree species (e.g. sugar maple, American basswood, eastern hophornbeam) was significantly greater in S14 compared with S15, which had species characteristic of sites with lower base concentrations (e.g. American beech and eastern white pine). The disparity in stream water Ca²⁺ and NO₃^?, concentrations and fluxes between S14 and S15 were explained by differences in tree species composition and soil properties rather than differences in land use or hydrology. The marked difference in soil Ca²⁺ concentrations in S14 vs. S15 corresponded to the higher stream water Ca²⁺ and the larger contribution of base‐rich tree species to the overstory biomass in S14. Soil under such species is associated with higher net mineralization and nitrification and likely contributed to the higher NO₃^? concentrations in the drainage waters of S14 vs. S15. Studies investigating differences in spatial and temporal patterns of the effects of chronic N deposition on surface water chemistry need to account for changes in tree species composition and how vegetation composition is influenced by soil properties, as well as climatic and biotic changes.     

Chemical variation and defense of Encelia farinosa

Chemical analysis of leaves from 12 different localities of Encelia farinosa (including var. phenicodonta and var. radians) collected on the peninsula of Baja California (Mexico) revealed the presence of various chemotypes that differed with regard to the concentrations of chromenes and sesquiterpene lactones. Localities of E. farinosa collected in the northern part of Baja California were characterized by high concentrations of the chromene encecalin (up to 252 μmol g⁻¹ dry wt.), whereas the sesquiterpene lactone farinosin was not detected. Localities of E. farinosa collected at the southern tip of the peninsula lacked encecalin, but were shown to accumulate farinosin (up to 85 μmol g⁻¹ dry wt.) instead. On the mainland of Mexico, as well as in Arizona (U.S.A.), farinosin concentrations varied from 18 to 44 μmol g⁻¹ dry wt. for 10 different localities analyzed. Chromenes were not detected or present only in minor amounts (up to 13 μmol g⁻¹ dry wt.), when compared to the samples from northern Baja California. Chemical variation within localities was small when compared to variation between different localities. Accumulation of encecalin and aridity seem to coincide at least on the peninsula of Baja California, as localities of E. farinosa that receive the least amount of rainfall contained the largest amounts of encecalin in their leaves. Leaves of E. farinosa that contained sufficiently large amounts of either encecalin or farinosin were both detrimental to neonate larvae of the polyphagous pest insect Spodoptera littoralis as shown by addition of the respective crude leaf extracts to artificial diet. Possible advantages of the observed intraspecific chemical variability of E. farinosa with regard to adaptation by generalist insect herbivores are discussed.     

Seasonal variation in energy fluxes and carbon dioxide exchange for a broad-leaved semi-arid savanna (Mopane woodland) in Southern Africa

We studied the seasonal variation in carbon dioxide, water vapour and energy fluxes in a broad‐leafed semi‐arid savanna in Southern Africa using the eddy covariance technique. The open woodland studied consisted of an overstorey dominated by Colophospermum mopane with a sparse understorey of grasses and herbs. Measurements presented here cover a 19‐month period from the end of the rainy season in March 1999 to the end of the dry season September 2000. During the wet season, sensible and latent heat fluxes showed a linear dependence on incoming solar radiation (I) with a Bowen ratio (β) typically just below unity. Although β was typically around 1 at low incoming solar radiation (150 W m^?2) during the dry season, it increased dramatically with I, typically being as high as 4 or 5 around solar noon. Thus, under these water‐limited conditions, almost all available energy was dissipated as sensible, rather than latent heat. Marked spikes of CO₂ release occurred at the onset of the rainfall season after isolated rainfall events and respiration dominated the balance well into the rainfall season. During this time, the ecosystem was a constant source of CO₂ with an average flux of 3–5 μmol m^?2 s^?1 to the atmosphere during both day and night. But later in the wet season, for example, in March 2000 under optimal soil moisture conditions, with maximum leaf canopy development (leaf area index 0.9–1.3), the peak ecosystem CO₂ influx was as much as 10 μmol m^?2 s^?1. The net ecosystem maximum photosynthesis at this time was estimated at 14 μmol m^?2 s^?1, with the woodland ecosystem a significant sink for CO₂. During the dry season, just before leaf fall in August, maximum day‐ and night‐time net ecosystem fluxes were typically ?3 μmol m^?2 s^?1 and 1–2 μmol m^?2 s^?1, respectively, with the ecosystem still being a marginal sink. Over the course of 12 months (March 1999–March 2000), the woodland was more or less carbon neutral, with a net uptake estimated at only about 1 mol C m^?2 yr^?1. The annual net photosynthesis (gross primary production) was estimated at 32.2 mol m^?2 yr^?1.     

The effect of acute high light and low temperature stresses on the ascorbate–glutathione cycle and superoxide dismutase activity in two Dunaliella salina strains

Dunaliella species accumulate carotenoids and their role in protection against photooxidative stress has been investigated extensively. By contrast, the role of other antioxidants in this alga, has received less attention. Therefore, the components of the ascorbate–glutathione cycle, along with superoxide dismutase (E.C. 1.15.1.1) and peroxidase (E.C. 1.11.1.11) activity were compared in two strains of Dunaliella salina. Strain IR‐1 had two‐fold higher chlorophyll and β‐carotene concentration than Gh‐U. IR‐1 had around four‐fold higher superoxide dismutase, ascorbate peroxidase and pyrogallol peroxidase activities than Gh‐U on a protein basis. Ascorbate and glutathione concentrations and redox state did not differ between strains and there was little difference in the activity of ascorbate–glutathione cycle enzymes (monodehydroascorbate reductase [E.C. 1.6.5.4], dehydroascorbate reductase [E.C. 1.8.5.1] and glutathione reductase [E.C. 1.8.1.7]). The response of these antioxidants to high light and low temperature was assessed by transferring cells from normal growth conditions (28°C, photon flux density of 100 μmol m^?2 s^?1)to 28°C/1200 μmol m^?2 s^?1; 13°C/100 μmol m^?2 s^?1; 13°C/1200 μmol m^?2 s^?1 and 28°C/100 μmol m^?2 s^?1 for 24 h. Low temperature and combined high light‐low temperature decreased chlorophyll and β‐carotene in both strains indicating that these treatments cause photooxidative stress. High light, low temperature and combined high light‐low temperature treatments increased the total ascorbate pool by 10–50% and the total glutathione pool by 20–100% with no consistent effect on their redox state. Activities of ascorbate–glutathione cycle enzymes were not greatly affected but all the treatments increased superoxide dismutase activity. It is concluded that D. salina can partially adjust to photooxidative conditions by increasing superoxide dismutase activity, ascorbate and glutathione.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

Auxin Synthesis in Crown Gall Tumor Tissue: A Comparison of Three Putative Precursors

Axenic crown gall tumor callus (from Vinca rosea L.) which is known to synthesize its own auxin is able to convert exogenous ¹⁴C-indole or tryptamine to indoleacetic acid [5.4 and 10 × 10⁻⁶μmol × h⁻¹× (g fr wt)⁻¹ respectively], but little or no ³H-tryptophan is converted [less than 6.4 × 10⁻⁸×μmol × h⁻¹× (g fr wt)⁻¹].