The effects of aluminium on nodulation and symbiotic nitrogen fixation in Casuarina cunninghamiana Miq.

In order to investigate the effects of Al on nodule formation and function in the Casuarina-Frankia symbiosis, inoculated plants were grown in sand culture at five nominal Al concentrations (0-880 M Al) at pH 4.0. There was an Al-free control at pH 6.0 to assess the effects of pH 4.0 treatments. Mean N concentration of nodules was significantly less at pH 4.0 (1.83%) than at pH 6.0 (2.01%). There were nodulated plants at all Al levels, though there were fewer nodulated plants at 440 and 880 M Al. Dry weights of nodules, shoots and roots were not reduced by Al concentrations at or below 220 M Al, but were decreased by Al concentrations at or above 440 M Al. Nodule weight expressed as a percentage of total weight did not differ significantly with respect to an Al-free control at pH 4. N concentrations of shoots and whole plants were significantly reduced at 440 M Al. Nodular specific acetylene reduction activity (ARA) did not differ significantly among Al treatments. However, N₂-fixation efficiency was decreased from 0.20 to 0.10 mg N fixed mg nodule dry weight^–1 at 880 M Al.     

A circadian rhythm in the level of carbon dioxide compensation in Bryophyllum fedtschenkoi with zero values during the transient

Summary Detached shoots of Bryophyllum fedtschenkoi maintained in a closed system in the light exhibited an endogenous circadian rhythm in CO₂ compensation. The rhythm was sensitive to changes in light intensity and temperature. At 15° C it damped rapidly in light of 78 J m^-2 s^-1, but at 10° C a rhythm of considerable amplitude was evident at this same light intensity. During the transient (i.e. the temporary state of the rhythm before it acquired its steady state) low compensation values between 0 and 5 ppm CO₂ were achieved. When the plants were maintained at a higher light intensity prior to the measurements, the period of low compensation during the transient was extended, and zero values were obtained under some conditions.Studies of gas exchange at opposite phases of the rhythm revealed: (i) that the rate of uptake of ¹⁴CO₂ differed, both in light and darkness (the epidermis was removed during these observations to avoid interference from stomatal rhythms); (ii) photorespiration, estimated by extrapolation of the graph relating photosynthetic rate and CO₂ concentration, was highest during the peaks of the rhythm in CO₂ compensation; (iii) estimates of the capacity for photorespiration by the glycine-1-¹⁴C assay indicated highest values during the troughs of the rhythm. These findings are discussed in relation to the C₄-acid metabolism of this species. Low CO₂ compensation is probably due to the activity of phosphoenolpyruvate carboxylase and not to the absence of processes involving CO₂ evolution.     

Photosynthetic pathways and the ecological distribution of the chenopodiaceae in Isreal

Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, ¹³C values, habitat and phytogeographical distribution. 17 species have ¹³C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C₃ plants. 37 species have ¹³C values between -10 and -18 and Kranz or C₄-Suaeda type anatomy and are therefore considered as C₄ plants. Some C₄ plants have leaf structure which seems to be intermediate between the Kranz and the C₄-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C₃ Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C₄ Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.     

Biomass production of C3- and C4-plant species in pure and mixed culture with different water supply

Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C₃ plant) and Amaranthus retroflexus L (C₄) on the one hand and of the grasses Avena sativa L (C₃) and Panicum miliaceum L. (C₄) on the other hand were maintained in a standard soil with different ground water tables. After 12 weeks the length, dry weight and nitrogen-content of the aboveground and belowground parts of the plants, and in addition the carbon-and ash-content and the ¹³C value of the aboveground parts were determined. It turned out that the length and the dry weight of the shoots of the C₃ species showed on increasing tendency with increased water supply, while the values of the C₄ species were drastically diminished at the highest water level only. The roots showed in most cases an increased length and dry weight at drier conditions, more pronounced in the C₄ than in the C₃ species. The nitrogen content of the shoots was mostly higher in the shoots of the C₃ plants and in the roots of the C₄ plants; it changed in a non-regular manner with variations in water supply. Since the carbon content did not change markedly, the C/N ratio was variable. There was a slight tendency for a higher carbon content and mostly also for a higher C/N-ratio in the shoots of C₄ plants. The ¹³C values of both C₃ as C₄ plants were in general not at all influenced by the water supply; they were fixed genetically. The ash content of the analyzed species did not show a clear relationship to the type of photosynthetic CO₂-fixation or to the water regime.The influence of light intensity was studied with mixed cultures of all four plant species, again with different water supply. There was a strong effect of light intensity on the competitive behaviour of the C₃ and C₄ plants under modified water conditions. The wild C₃ plant Atriplex hortensis was most successful under conditions of relatively low light intensity and high water availability, while the cultivated artificial species Avena sativa showed much less differences between full-light grown and shadow plants. The C₄ plant Amaranthus retroflexus is most successful under competitive conditions at high water stress in full light. The C₄ grass Panicum miliaceum showed maximum shoot growth in light, but was successful under competitive conditions especially also with good water supply. The light intensity had no effect on the ¹³C values. — There was no indication that the soil-type as such has a distinct influence on the success of C₃ or C₄ plants in mixed cultures.Dedicated to Prof. Dr. M. Evenari, Jerusalem, and to Dr. K.F. Springer, Heidelberg     

Simultaneous oxygen production and nitrogenase activity of an ammonia-excreting mutant of the cyanobacterium Anabaena variabilis in a co-culture with wheat

Summary A mutant strain of Anabaena variabilis, strain SA-1 that supported growth of wheat plants in a hydroponic co-culture in nitrogen (N) free medium also produced enough oxygen (O₂) to support root respiration. The steady-state concentration of net O₂ in the co-culture was dependent on incident light intensity. At an incident photosynthetic photoflux (PPF) of 1000 mol photons·m^–2·s^–1, net O₂ evolution by the co-culture in the root zone reached a maximum value of about 220 mol O₂ evolved·h^–1·mg chlorophyll (Chl)^–1. The O₂ concentration in the rhizosphere of the co-culture stayed above the ambient air level. O₂ uptake in the dark by strain SA-1-supplemented wheat roots washed free of cyanobacterium was higher than the root respiration of nitrate-grown plants. Nitrate-grown plants required aeration for maximum growth while the wheat-cyanobacterial co-culture can be cultured without aeration. These results show that O₂ produced by strain SA-1 can be used to supply the O₂ needs for root respiration of wheat. Respiration reduced net O₂ evolution by the mutant SA-1, decreasing the partial pressure of O₂ at the sites of cyanobacterial attachment to the roots. This led to an increase in the specific activity of nitrogenase of the co-culture at the high light intensities used to support wheat growth. This activity of about 30 mol ethylene produced·mg Chl^–1·h^–1 was three-fold higher than the activities obtained with the free-living strain SA-1 assayed at the same light intensity. In the co-culture, ammonia produced by the mutant strain SA-1 was not detectable. The NH _inf4 ^sup+ produced by strain SA-1 was used by the wheat plants and, under these conditions, the total N content of the plants reached as high as 85% of the total N content of nitrate-grown plants. In the co-culture system the metabolism of wheat and the cyanobacterium complemented each other, leading to higher plant growth in N-free medium. Offprint requests to: M. Gunasekaran     

Photorespiration studies in Cycas circinalis L. and Cycas beddomei Dyer

Photosynthetic carboxylating enzymes and the effects of light and temperature on ¹⁴CO₂ efflux in two species of gymnosperm leaves were studied. The activity of RuBP carboxylase was high and that of PEP carboxylase was very low when compared to C₄ plants. The CO₂ compensation point was high. ¹⁴CO₂ efflux was greater in light than in darkness and the ratio (L/D) increased with increase in temperature and light intensity. The inhibitors of glycolate metabolism showed decreased ¹⁴CO₂ evolution in light while dark respiration was unaffected. It is concluded that both Cycas circinalis, L. and Cycas beddomei Dyer are C₃ plants.     

Effect of assimilate utilization on photosynthetic rate in wheat

Summary Two weeks after anthesis, when the grain is filling rapidly, the rate of photosynthesis by flag leaves of wheat cv. Gabo was between 20 and 30 mg CO₂ dm^-2 leaf surface hour^-1 under the conditions used. About 45% of flag-leaf assimilates were translocated to the ear, and only about 12% to the roots and young shoots.On removing the ear, net photosynthesis by the flag leaves was reduced by about 50% within 3–15 hours, and there was a marked reduction in the outflow of ¹⁴C-labelled assimilates from the flag leaves.Subsequent darkening of all other leaves on plants without ears led to recovery of flag-leaf photosynthesis, as measured by gas analysis and ¹⁴CO₂ fixation, and to increased translocation of assimilates to the roots and young shoots. Minor changes in the rates of dark respiration accompanied these major, reversible changes in photosynthetic rate.After more than a week in continuous, high-intensity light, the rate of photosynthesis by flag leaves of intact plants had fallen considerably, but could be restored again by a period in darkness, or by inhibiting photosynthesis in the ears by spraying them with DCMU. The inhibition of ear photosynthesis increased translocation of labelled assimilates from the flag leaf to the ears, without affecting leaf sugar levels.The application of TIBA to the culm below the ear inhibited auxin movement throught the culm, but had no influence on flag-leaf photosynthesis.These results suggest that, at least in this system, photosynthesis by the flag leaf is regulated directly by the demand for assimilates from the flag leaf and not indirectly through action in the leaf of auxins produced by the sink organs.     

Inorganic carbon assimilation in the Isoetids,Isoetes lacustris L. and Lobelia dortmanna L.

Summary The inorganic carbon fixation patterns of Isoetes lacustris and Lobelia dortmanna from an oligotrophic Scottish loch have been examined by following titratable acidity changes in plant sap and light/dark ¹⁴CO₂ incorporation by roots and shoots. The diurnal pattern of titratable acidity changes in I. lacustris suggests crassulacean acid metabolism (CAM) while the lack of any change in titratable acidity in L. dortmanna suggests C₃ metabolism. Of the carbon fixed by L. dortmanna, 99.9% was taken up through the roots and fixation occurred primarily during the day. In Isoetes, CO₂ was taken up by both roots and shoots and during both day and night. Regardless of the site of CO₂ uptake, fixation occurred only in the shoots of both plants. Analysis of carbon isotope ratios of plant organic material was used to further investigate the photosynthetic mechanisms of these Isoetids. Considering the absence of a nighttime peak in titratable acidity in L. dortmanna, the ¹³C (=¹³C plant-¹³C source) value of the shoots of L. dortmanna (-14.2) is indicative of C₃ photosynthesis limited by the rate of CO₂ diffusion. The less negative of I. lacustris (-6.0) is consistent with both dark acidification of CAM and CO₂ limited C₃ photosynthesis. This is in contrast to the terrestrial Isoetes durieui which is shown to have a value which is similar to a terrestrial C₃ plant. The carbon fixation patterns of these Isoetids suggest that the CO₂ concentration in the loch may be growth limiting, and that root uptake and/or dark acidification are means of optimising CO₂ supply. However, in view of the relatively high levels of CO₂ in sediment and bulk water, it is suggested that low levels of nutrients may also limit growth in these plants.     

The use of C14O2 canopy techniques for measuring carbon transfer through the plant-soil system

Summary Methods for labelling growing plants by exposing them to C¹⁴O₂ under a cellulose acetate-butyrate canopy have been developed for laboratory and field use. The length of labelling ranged from 2 to 33 days and the C¹⁴O₂ content of the atmosphere was automatically controlled. This made it possible to measure carbon assimilation by the plants, transfer of photosynthates beneath ground and respiration of the roots.In the laboratory, root respiration of wheat plants was measured by separating the above and beneath ground plant parts using a RTV rubber partition. Half to two thirds of the assimilated carbon was found above ground, 15 to 25 per cent in the roots and shoot bases below the partition and 17 to 25 per cent was lost by underground respiration. The variability of these proportions was related to the stage of maturity of the plants.On native grassland, the relative above and beneath ground productivity was 50 per cent. The time required for the photosynthates to reach the roots at various depths ranged from 1 to 5 days and the amount of material deposited in the roots changed with time and soil moisture content. The use of tubes inserted at various depths beneath the canopy permitted sampling of soil air for C¹⁴ and CO₂ measurements. The soil C¹⁴O₂ flux indicated that root respiration during 8 days accounted for 24 per cent of the labelled carbon translocated to the roots after a two days labelling period.     

Mineral nutrient deficiency increases the sensitivity of photosynthesis to sulphur dioxide in needles of a coniferous tree,Abies nordmanniana

Summary Abies nordmanniana (Stev.) Spach was cultivated in rooting media either rich in nutrients (control) or low in magnesium (low Mg) or low in magnesium and nitrogen (low Mg-N), respectively. Intact, attached needles were exposed, in the light (460 mol photons m^-2 s^-1), to an atmosphere containing 1 ppm SO₂ for 5 h. Measurements of light- and CO₂-saturated rates of photosynthetic O₂ evolution, A _max, were performed before and after SO₂ treatments. In needles from well fertilized plants, A _max was high (about 50 mol m^-2 s^-1) and was not affected by SO₂. Needles from low-Mg and low-Mg-N plants had lower photosynthetic rates and showed a marked decline in A _max in response to the SO₂ treatment. Stomatal conductance was similar in the three groups of plants during SO₂ treatments.Abbreviations A _max photosynthetic capacity (CO₂- and light-saturated rate of O₂ evolution) - DW dry weight - F_o yield of dark level fluorescence - F_M maximum yield of fluorescence, induced in a pulse of saturating light - F_v yield of variable fluorescence (= F_M–F_O) - FW fresh weight; g, conductance to water vapor transfer     

In Vivo Nitrate Reduction in Roots and Shoots of Barley (Hordeum vulgare L.) Seedlings in Light and Darkness

In vivo NO₃⁻ reduction in roots and shoots of intact barley (Hordeum vulgare L. var Numar) seedlings was estimated in light and darkness. Seedlings were placed in darkness for 24 hours to make them carbohydrate-deficient. During darkness, the leaves lost 75% of their soluble carbohydrates, whereas the roots lost only 15%. Detached leaves from these plants reduced only 7% of the NO₃⁻ absorbed in darkness. By contrast, detached roots from the seedlings reduced the same proportion of absorbed NO₃⁻, as did roots from normal light-grown plants. The rate of NO₃⁻ reduction in the roots accounted for that found in the intact dark-treated carbohydrate-deficient seedlings. The rates of NO₃⁻ reduction in roots of intact plants were the same for approximately 12 hours, both in light and darkness, after which the NO₃⁻ reduction rate in roots of plants placed in darkness slowly declined. In the dark, approximately 40% of the NO₃⁻ reduction occurred in the roots, whereas in light only 20% of the total NO₃⁻ reduction occurred in roots. A lesser proportion was reduced in roots because the leaves reduced more nitrate in light than in darkness.     

The effect of O2 and CO2 concentration on photosynthesis and glycolate accumulation in bean leaves treated with α-hydroxy-2-pyridinemethanesulfonic acid (α-HPMS), the glycolate oxidase inhibitor

¹⁴CO₂ assimilation, ¹⁴C incorporation into glycolate and glycolate accumulation in -HPMS treated bean leaves at various O₂ and CO₂ concentrations were studied. In 1% CO₂ oxygen concentration had no significant effect on glycolate accumulation and ¹⁴C incorporation into glycolate. In the CO₂ concentration range of 0.03% to 0.01%, increased oxygen concentration decreased not only ¹⁴CO₂ assimilation but also glycolate accumulation and ¹⁴C incorporation into glycolate. In 1% and 0.1% CO₂, no matter what O₂ concentration was supplied, and in 0.03% CO₂ with 2% and 21% O₂, all of the glycolate accumulated was formed from newly assimilated carbon. In 0.01% CO₂ and 2%, 21% and 100% O₂, and in 0.03% CO₂ with 100% O₂, a substantial portion of the glycolic acid that accumulated in leaves originated from endogenous unlabelled substrates. These findings are discussed in terms of possible changes in the ratio of RuBP carboxylation to RuBP oxygenation and of changes of RuBP pool size, induced by changing O₂ and CO₂ concentrations.This work was supported by the Polish Academy of Sciences, Contract No. 10.2.10.     

Photosynthesis by carrot tissue cultures

Summary ¹⁴CO₂-fixation rates in green carrot callus cultres (about 35 g chlorophyll/g fresh wt) were determined in gaseous and liquid media using a range of light intensities and CO₂ concentrations. Main products of light-dependent CO₂-fixation were sucrose, alanine, glutamine, serine/glycine and malic acid. In darkness, glutamine and malic acid were formed.Light CO₂-fixation rates were about ten times higher than dark fixation rates and reached 50–90 mol/mg chlorophyll/h in 10000 lux, 1% CO₂ in air. Net O₂-evolution by the tissue was demonstrated polarographically under these conditions. Light CO₂-fixation rates were linearly related to chlorophyll levels while dark fixation was independent of chlorophyll content. Lowered O₂ partial pressures in gaseous conditions increased ¹⁴CO₂-fixation rates. Ribulose diphosphate carboxylase and phosphoenol pyruvate carboxylase activities and their distribution in subcellular fractions were examined.When carrot tissue cultures were grown for two or four weeks on agar media lacking a carbohydrate source, in 10000 lux and 1% CO₂ in either air or N₂, dry weight increases were obtained although chlorophyll levels eventually declined.     

Carbon dioxide exchange of C3 and C4 tree species in the understory of a Hawaiian forest

Summary Field measurements of photosynthetic CO₂ exchange were made on saplings of a C₄ tree species, Euphorbia forbesii, and a C₃ tree species, Claoxylon sandwicense, in a shaded mesic forest on Oahu, Hawaii. Both species had light responses typical of those generally found in shade plants. Light saturated photosynthetic rates were 7.15 and 4.09 mol m² s¹ and light compensation points were 6.3 and 1.7 mol m² s¹ in E. forbesii and C. sandwicense, respectively. E. forbesii maintained a higher mesophyll conductance and a higher water use efficiency than C. sandwicense as is typically found in comparisons of C₄ and C₃ plants. Under natural light regimes, both species maintained positive CO₂ uptake rates over essentially the entire day because of low respiration rates and light compensation points. However, photosynthesis during sunflecks accounted for a large fraction of the daily carbon gain. The results show that the carbon-gaining capacity of E. forbesii is comparable to that of a C₃ species in a moderately cool, shaded forest environment. There appears to be no particular advantage or disadvantage associated with the C₄ photosynthetic pathway of E. forbesii in this environment.     

Differential regulation by phytochrome of the appearance of plastidic and cytoplasmatic isoforms of glutathione reductase in mustard (Sinapis alba L.) cotyledons

An increase of glutathione reductase (GR; EC 1.6.4.2) activity during the transformation of mustard (Sinapis alba L.) cotyledons from storage organs to photosynthetically competent leaves was previously found to be controlled by light acting via phytochrome (Drumm, H., Mohr, H., Z. Naturforsch. 28c 559–563, 1973). Two isoforms of GR could be separated by disc electrophoresis. In the present study we have applied ionexchange chromatography to separate isoforms of GR during the development of the cotyledons. Furthermore, the technique of in situ photooxidation of plastids was used to distinguish between plastidic and cytoplasmatic isoforms. The isoform GR₂ is the plastidic enzyme, as shown by its sensitivity to photooxidative treatment, while GR₁ is a cytoplasmatic protein not affected by photooxidative treatment of plastids. Both isoforms are promoted by phytochrome but with different time courses. The appearance of GR₁ is independent of the integrity of the plastids, as one might expect. However, unexpectedly, the phytochrome-mediated re-appearance of GR₂ after a photooxidative treatment is much less affected by photooxidative destruction of the plastids, i.e. by the lack of a particular plastidic factor, than was to be expected from previous experience with typical plastidic proteins. An interpretation of this finding must await measurements at the level of GR₂ mRNA.Abbreviations c continuous - D darkness - FR far-red light (3.5 W·m^-2) - FPLC fast protein liquid chromatography - GR glutathione reductase (EC 1.6.4.2) - NF Norflurazon - R fed light (6.8 W·m^-2) - = Pfr/Ptot wavelength-dependent photoequilibrium of the phytochrome system     

Carbon isotope ratio measurements of succulent plants in southern Africa

Summary Succulent plants representing 16 families and a variety of growth forms originating from winter, summer, and year-round rainfall regimes in southern Africa were analyzed for carbon isotope ratios. Most families had species with ¹³C values indicative of CAM, particularly those from winter and year-round rainfall regimes. Plants with ¹³C values intermediate between CAM and C₃, indicating flexible photosynthetic pathways, were generally leafy perennials subject to seasonal tissue dehydration. Reproductive tissue tended to have less negative ¹³C values than vegetative tissue on the same plant, indicating drought-season origin of the former.CIW-DPB Publication No. 609     

Modifications of the carbon and nitrogen allocations in the plant (Triticum aestivum L.) soil system in response to increased atmospheric CO2 concentration

The aim of this work was to examine the response of wheat plants to a doubling of the atmospheric CO₂ concentration on: (1) carbon and nitrogen partitioning in the plant; (2) carbon release by the roots; and (3) the subsequent N uptake by the plants. The experiment was performed in controlled laboratory conditions by exposing fast-growing spring wheat plants, during 28 days, to a ¹⁴CO₂ concentration of 350 or 700 L L^–1 at two levels of soil nitrogen fertilization. Doubling CO₂ availability increased total plant production by 34% for both N treatment. In the N-fertilized soil, the CO₂ enrichment resulted in an increase in dry mass production of 41% in the shoots and 23% in the roots; without N fertilization this figure was 33% and 37%, respectively. In the N-fertilized soil, the CO₂ increase enhanced the total N uptake by 14% and lowered the N concentration in the shoots by 23%. The N concentration in the roots was unchanged. In the N-fertilized soil, doubling CO₂ availability increased N uptake by 32% but did not change the N concentrations, in either shoots or roots. The CO₂ enrichment increased total root-derived carbon by 12% with N fertilization, and by 24% without N fertilization. Between 85 and 90% of the total root derived-¹⁴C came from respiration, leaving only 10 to 15% in the soil as organic ¹⁴C. However, when total root-derived ¹⁴C was expressed as a function of root dry weight, these differences were only slightly significant. Thus, it appears that the enhanced carbon release from the living roots in response to increased atmospheric CO₂, is not due to a modification of the activity of the roots, but is a result of the increased size of the root system. The increase of root dry mass also resulted in a stimulation of the soil N mineralization related to the doubling atmospheric CO₂ concentration. The discussion is focused on the interactions between the carbon and nitrogen allocation, especially to the root system, and the implications for the acquisition of nutrients by plants in response to CO₂ increase.Abbreviations N soil fertilization without nitrogen - N soil fertilization with nitrogen     

Gibberellins in dark- and red-light-grown shoots of dwarf and tall cultivars of Pisum sativum: The quantification,metabolism and biological activity of gibberellins in Progress no. 9 and Alaska

The stem growth in darkness or in continuous red light of two pea cultivars, Alaska (Le Le, tall) and Progress No. 9 (le le, dwarf), was measured for 13 d. The lengths of the first three internodes in dark-grown seedlings of the two cultivars were similar, substantiating previous literature reports that Progress No. 9 has a tall phenotype in the dark. The biological activity of gibberellin A₂₀ (GA₂₀), which is normally inactive in le le geno-types, was compared in darkness and in red light. Alaska seedlings, regardless of growing conditions, responded to GA₂₀. Dark-grown seedlings of Progress No. 9 also responded to GA₂₀, although red-light-grown seedlings did not. Gibberellin A₁ was active in both cultivars, in both darkness and red light. The metabolism of [¹³C³H]GA₂₀ has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [¹³C³H]GA₂₀ is converted to [¹³C³H]GA₁, [¹³C³H]GA₈, [¹³C]GA₂₉, its 2-epimer, and [¹³C³H]GA₂₉-catabolite. [¹³C³H] Gibberellin A₁ was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [¹³C³H]GA₈, was detected. However results do indicate that the tall growth habit of Progress No. 9 in the dark, and its ability to respond to GA₂₀ in the dark may be related to its capacity to 3-hydroxylate GA₂₀ to give GA₁. In red light the overall metabolism of [¹³C³H]GA₂₀ was reduced in both cultivars. There is some evidence that 3-hydroxylation of [¹³C³H]GA₂₀ can occur in red light-grown Alaska seedlings, but no 3-hydroxylated metabolites of [¹³C³H]GA₂₀ were observed in red light-grown Progress. Thus the dwarf habit of Progress No. 9 in red light and its inability to respond to GA₂₀ may be related, as in other dwarf genotypes, to its inability to 3-hydroxylate GA₂₀ to GA₁. However identification and quantification of native GAs in both cultivars showed that red-light-grown Progress does contain native GA₁. Thus the inability of red light-grown Progress No. 9 seedlings to respond to, and to 3-hydroxylate, applied GA₂₀ may be due to an effect of red light on uptake and compartmentation of GAs.Abbreviations AMO-1618 2-isopropyl-4-(trimethylammonium chloride)-5-methylphenyl piperidine-1-carboxylate - cv. cultivar - GC-MS gas chromatography-mass spectrometry - GA_(n) gibberellin A_(n) - HPLC high-pressure liquid chromatography     

Decomposition of diethylstilboestrol in soil

Summary The rate of decomposition of DES-monoethyl-1-C¹⁴ in soil was followed by measurement of C¹⁴O₂ released. From 1.6 to 16% of the added C¹⁴ was recovered as C¹⁴O₂ during 3 months. After six months as much as 12 to 28 per cent was released as C¹⁴O₂.Determination of C¹⁴ in the soil samples after the experiments showed that the amount extractable with benzene decreased to a greater extent than would be expected from the production of C¹⁴O₂ and that the amount extractable with water was increased when compared with that found shortly after the addition of DES.Addition of large amounts of DES (8%) did not inhibit the CO₂ production from the soil.Experiments with -sterilized soil indicated that enzymes present in the soil are able to attack DES.     

Photorespiration Contributes to Stomatal Regulation and Carbon Isotope Fractionation: A Study with Barley,Potato and Arabidopsis Plants Deficient in Glycine Decarboxylase

The rates of respiration in light and darkness, C _i/C _a and carbon isotope fractionation were investigated in glycine decarboxylase-deficient plants of barley, potato and Arabidopsis thaliana grown in climate chambers with controlled light intensity, temperature, humidity, irradiation and different CO₂ concentrations (360, 700 and 1400 µl l^–1) and compared to the wild-type plants. All photorespiration-impaired plants exhibited higher C _i/C _a and corresponding lower apparent water-use efficiencies, which were more expressed under high irradiance and elevated temperature. The mutants were depleted in ¹³C as compared to the wild-type plants, with a difference of up to 6 following growth in 360 µl l^–1 CO₂. We determined the carbon isotope content at different CO₂ concentrations to calculate the contribution of both C _i/C _a and photorespiration for ¹³C/¹²C fractionation. The direct effect of photorespiration was in the range of 0.7–1.0, from which we calculated the value of fractionation at the site of glycine decarboxylation as being 10–13, which is in agreement with the previously reported carbon isotope discrimination exerted by the glycine decarboxylase. Respiratory rates, particularly in the light, were increased in the glycine decarboxylase mutants. The necessity of the maintenance of a high CO₂ concentration near the site of carboxylation in chloroplasts in plants deficient in photorespiratory enzymes, requires an increased opening of the stomata with a corresponding decrease in water-use efficiency. It is concluded that photorespiration participates in the regulation of C _i/C _a and contributes to carbon isotope fractionation, both via effects on stomata and via discrimination of ¹³C in the glycine decarboxylase reaction.This revised version was published online in October 2005 with corrections to the Cover Date.