Significance of rooting depth in mire plants: Evidence from natural <Superscript>15</Superscript>N abundance

Variation in stable nitrogen isotope ratios (¹⁵N) was assessed for plants comprising two wetland communities, a bog-fen system and a flood plain, in central Japan. ¹⁵N of 12 species from the bog-fen system and six species from the flood plain were remarkably variable, ranging from –5.9 to +1.1 and from +3.1 to +8.7, respectively. Phragmites australis exhibited the highest ¹⁵N value at both sites. Rooting depth also differed greatly with plant species, ranging from 5cm to over 200cm in the bog-fen system. There was a tendency for plants having deeper root systems to exhibit higher ¹⁵N values; plant ¹⁵N was positively associated with rooting depth. Moreover, an increasing gradient of peat ¹⁵N was found along with depth. This evidence, together with the fact that inorganic nitrogen was depleted under a deep-rooted Phragmites australis stand, strongly suggests that deep-rooted plants actually absorb nitrogen from the deep peat layer. Thus, we successfully demonstrated the diverse traits of nitrogen nutrition among mire plants using stable isotope analysis. The ecological significance of deep rooting in mire plants is that it enables those plants to monopolize nutrients in deep substratum layers. This advantage should compensate for any consequential structural and/or physiological costs. Good evidence of the benefits of deep rooting is provided by the fact that Phragmites australis dominates as a tall mire grass.     

Measurement of formaldehyde and some fully N-methylated substances in tissue cultures of Datura innoxia

Formaldehyde (HCHO) and choline, trigonelline and N-trimethyl-L-lysine (TML) were detected and measured in tissue cultures of Datura innoxia Mill. by TLC and OPLC. The higher level of HCHO in young tissues appears to originate from the methylation reactions. This is in correlation with the high level of fully N-methylated substances. In spite of this the level of the fully N-methylated substances decreased with the aging of tissue. HCHO level also decreased with aging. However, in old tissues the amount of HCHO again increased. This HCHO originates mainly from demethylation reactions. It seems that there is a dynamic relationship between methylation/ demethylation processes based on HCHO reactions and cell proliferation.Abbreviations HCHO formaldehyde - HPTLC high-performance thin-layer chromatography - HS heat shock - OPLC overpressured layer chromatography - SAM S-adenosyl-L-methionine - TML N-trimethyl-L-lysine - TLC thin-layer chromatography This work was supported by National Science Foundation grant (OTKA T-14141, -17394, -17351 and ETT-119, AMFK-465).     

The Determination of Total Concentration and Activity of Antioxidants in Foodstuffs

We developed a new method for the analysis of active antioxidants that is based on their reactions with the BTS⁺ cation radical obtained by oxidation of ABTS, 2,2"-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt. The feasibility of this method was confirmed by electrochemical and kinetic studies of model antioxidants. BTS⁺ was shown to react rapidly with active and slowly with weak antioxidants, which allows it to be used as a model radical for the quantitative determination of the total content of natural antioxidants (antioxidant equivalent) in natural extracts and wines. Another analytical method based on the competitive oxidation of Pyrogallol Red (a detecting molecule) and the examined antioxidants by radicals derived from peroxynitrite was used for measuring the relative activity of antioxidants. A combination of both methods helped measure the total concentration of antioxidants and their average specific activities (per molecule of active compound) in extracts from grape, olive, and tomato and in various popular beverages (wines, beers, and juices), as well as in the commercial concentrated food product Kréto-A^®, made from grape, red wine, tomato, and olive. Red wine and red grape juice were shown to be the most rich in antioxidants (up to 20 mM), with their activity being similar to that of polyphenols.     

Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria

Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The ¹³C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (¹³C between-25.3 and-27.8) were significantly less depleted in ¹³C than needles (¹³C between-27.3 and-29.1), and ¹³C in twigs increased consistently with age. The ¹⁵N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles ¹⁵N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in ¹⁵N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. ¹⁵N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. ¹⁵N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The ¹⁵N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.     

15N natural abundance studies in Australian commercial sugarcane

The measurement of natural ¹⁵N abundance is a well-established technique for the identification and quantification of biological N₂ fixation in plants. Associative N₂ fixing bacteria have been isolated from sugarcane and reported to contribute potentially significant amounts of N to plant growth and development. It has not been established whether Australian commercial sugarcane receives significant input from biological N₂ fixation, even though high populations of N₂ fixing bacteria have been isolated from Australian commercial sugarcane fields and plants. In this study, ¹⁵N measurements were used as a primary measure to identify whether Australian commercial sugarcane was obtaining significant inputs of N via biological N₂ fixation. Quantification of N input, via biological N₂ fixation, was not possible since suitable non-N₂ fixing reference plants were not present in commercial cane fields. The survey of Australian commercially grown sugarcane crops showed the majority had positive leaf ¹⁵N values (73% >3.00, 63% of which were >5.00), which was not indicative of biological N₂ fixation being the major source of N for these crops. However, a small number of sites had low or negative leaf ¹⁵N values. These crops had received high N fertiliser applications in the weeks prior to sampling. Two possible pathways that could result in low ¹⁵N values for sugarcane leaves (other than N₂ fixation) are proposed; high external N concentrations and foliar uptake of volatilised NH₃. The leaf ¹⁵N value of sugarcane grown in aerated solution culture was shown to decrease by approximately 5 with increasing external N concentration (0.5–8.0 mM), with both NO₃ ^– and NH₄ ⁺ nitrogen forms. Foliar uptake of atmospheric NH₃ has been shown to result in depleted leaf ¹⁵N values in many plant species. Acid traps collected atmospheric N with negative ¹⁵N value (–24.45±0.90) from above a field recently surface fertilised with urea. The ¹⁵N of leaves of sugarcane plants either growing directly in the soil or isolated from soil in pots dropped by 3.00 in the same field after the fertiliser application. Both the high concentration of external N in the root zone (following the application of N-fertilisers) and/or subsequent foliar uptake of volatilised NH₃ could have caused the depleted leaf ¹⁵N values measured in the sugarcane crops at these sites.     

Effect of organic and inorganic fertigation on yields, δ15N values, and δ13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn)

We examined the effects of fertilizer application, especially the effects of fertigation and types of fertilizer (inorganic and organic) on yields and ¹⁵N and ¹³C values of tomato (Lycopersicon esculentum Mill. cv. Saturn). Fertigation is a method in which an appropriate diluted liquid fertilizer is applied to the plants each time they are drip-irrigated. We developed a method of organic fertigation using corn steep liquor (CSL) as the liquid fertilizer, because it is an industrial byproduct of cornstarch manufacture and can be used very effectively. We compared fruit yield, mineral content, ¹⁵N value, and ¹³C value of tomatoes grown under three different fertilizer treatments, basal dressing: basal dressing with granular chemical fertilizer; inorganic fertigation: fertigation with liquid chemical fertilizer; and organic fertigation: fertigaion with CSL. Mineral contents of tomatoes grown with basal dressing were generally lower than those grown under either fertigation treatment. These results indicated that yields and mineral contents were influenced more by the method of fertilizer application than by whether the fertilizers were inorganic or organic. There were, however, significant differences in the ¹⁵N values of tomato fruits grown under different types of fertilizer applications, especially between inorganic and organic fertilizers. The ¹⁵N value of the chemical fertilizer used for basal dressing was 0.81 ± 0.45{}, that of the chemical fertilizer for fertigation was 0.00 ± 0.04{}, and that of CSL was 8.50 ± 0.71{}. The ¹⁵N values of the soils reflected the ¹⁵N values of the fertilizers. Moreover, the ¹⁵N values of the fruits corresponded to the ¹⁵N values of the applied fertilizers. The ¹⁵N values were 3.18 ± 1.34{} in the fruits grown with a basal dressing of chemical fertilizer, 0.30 ± 0.61 in those grown under inorganic fertigation, and 7.09 ± 0.68 in those grown under organic fertigation. On the other hand, although the ¹³C values in the soil also reflected the ¹³C values of the applied fertilizers, there was no significant difference in the ¹³C values of fruits among the different treatments. In conclusion, because the ¹⁵N values of fertilizers correlated well with those of the fruits, it may be possible to use ¹⁵N values as an indicator of organic products.     

Variation in stable isotope signatures of seston and a zooplanktivorous fish in a eutrophic Chinese lake

Temporal and spatial changes in ¹³C and ¹⁵N of seston (mainly phytoplankton) and isotopic relationship between seston and the lake anchovy (Coilia ectenes) were studied in the large eutrophic freshwater Lake Chaohu in China. Much of the spatial and temporal variation in ¹³C of lake anchovies was explained by variation in seston, indicating a strong link between pelagic primary production and higher order consumers. Because the lake is shallow, there were no significant differences in ¹³C and ¹⁵N of seston between surface and overlying waters. Spatially, the relatively high ¹³C and ¹⁵N of seston in the western part of the lake might be due to high levels of anthropogenically derived N and C introduced from the surrounding cities through sewage drainage systems. The trophic position of the lake anchovy in the food web of Lake Chaohu was estimated to be 2.9–4.1 (3.5 ± 0.4), which agrees well with the previous stomach content analysis suggesting that the lake anchovy fed both on zooplankton and small planktivorous fishes.     

Molecular cloning and expression characterization of a rice K+ channel β subunit

K⁺ channel proteins native to animal membranes have been shown to be composed of two different types of polypeptides: the pore-forming subunit and the subunit which may be involved in either modulation of conductance through the channel, or stabilization and surface expression of the channel complex. Several cDNAs encoding animal K⁺ channel subunits have been recently cloned and sequenced. We report the molecular cloning of a rice plant homolog of these animal subunits. The rice cDNA (KOB1) described in this report encodes a 36 kDa polypeptide which shares 45% sequence identity with these animal K⁺ channel subunits, and 72% identity with the only other cloned plant (Arabidopsis thaliana) K⁺ channel subunit (KAB1). The KOB1 translation product was demonstrated to form a tight physical association with a plant K⁺ channel subunit. These results are consistent with the conclusion that the KOB1 cDNA encodes a K⁺ channel subunit.Expression studies indicated that KOB1 protein is more abundant in leaves than in either reproductive structures or roots. Later-developing leaves on a rice plant were found to contain increasing levels of the protein with the flag leaf having the highest titer of KOB1. Leaf sheaths are known to accumulate excess K⁺ and act as reserve sources of this cation when new growth requires remobilization of K⁺. Leaf sheaths were found to contain higher levels of KOB1 protein than the blade portions of leaves. It was further determined that when K⁺ was lost from older leaves of plants grown on K⁺-deficient fertilizer, the loss of cellular K⁺ was associated with a decline in both KOB1 mRNA and protein. This finding represents the first demonstration (in either plants or animals) that changes in cellular K⁺ status may specifically alter expression of a gene encoding a K⁺ channel subunit.     

Estimation of symbiotic dinitrogen fixation in alder forest by the method based on natural15N abundance

Annual N₂-fixation in virgin forest ecosystems has been measured using a¹⁵N natural abundance (¹⁵N) procedure. This method was compared to a¹⁵N labelled fertilizer isotopic dilution method. For young alders (5–6 years old), ¹⁵N of leaves gave results in good agreement with the isotopic dilution of fertilizer method. Since ¹⁵N variability was expected according to plant physiology, for alder trees, leaves were collected at various heights after the end of the growing season, and, to take account of isotopic variations coming from derived inputs, ¹⁵N of leaves of a large number of other plants in the same are were measured to give control values. Following this procedure, the ¹⁵N method gave reliable evaluation of the nitrogen supply, by through N₂-fixation, to alders, which were found to maintain high nitrogen fixing capacity in a sequence ranging from first stage of establishment of climactic formation. Moreover, the same method is reported to discriminate various origins ofAlnus glutinosa grown in natural conditions, possibly in relation to the genetic diversity of this species.     

Short-term patterns in water and nitrogen acquisition by two desert shrubs following a simulated summer rain

A field experiment was conducted at the Jornada Long-Term Ecological Research (LTER) site in the Chihuahuan Desert of New Mexico to compare the rapidity with which the shrubs Larrea tridentata and Prosopis glandulosa utilized water, CO² and nitrogen (N) following a simulated summer rainfall event. Selected plants growing in a roughly 50-m² area were assigned to treatment and control groups. Treatment plants received the equivalent of 3 cm of rain, while no supplemental water was added to the control plants. Xylem water potential (_x) and net assimilation rate (A_net) were evaluated one day before and one and three days after watering. To monitor short-term N uptake, soils around each plant were labeled with eight equally distant patches of enriched ¹⁵N before watering. Each tracer patch contained 20 ml of 20 mM ¹⁵ NH₄ ¹⁵NO³ (99 atom%) solution applied to the soil at 20 cm from the center of the plant at soil depths of 10 and 20 cm. Nitrogen uptake, measured as leaf ¹⁵N, was evaluated at smaller time intervals and for a longer period than those used for _x and A^net. Both A^net and ^x exhibited a significant recovery in watered vs. control Larrea plants within 3 days after the imposition of treatment, but no such recovery was observed in Prosopis in that period. Larrea also exhibited a greater capacity for N uptake following the rain. Leaf ¹⁵N was five-fold greater in watered compared to unwatered Larrea plants within 2 days after watering, while foliar ¹⁵N was not significantly different between the watered and unwatered Prosopis plants during the same period. Lack of a significant change in root ¹⁵ NO^{– 3} uptake kinetics of Larrea, even three days after watering, indicated that the response of Larrea to a wetting pulse may have been due to a greater capacity to produce new roots. The differential ability of these potential competitors in rapidly acquiring pulses of improved soil resources following individual summer rainfall events may have significant implications for the dynamic nature of resource use in desert ecosystems.     

Natural 15N abundance in shrub and tree legumes,Casuarina, and non N2 fixing plants in Thailand

The leaves and nodules from the shrub and tree legumes, particularly, Aeschynomene spp., Sesbania spp., Mimosa spp. and Leucaena spp., and Casuarina spp. and the leaves from neighbouring non-fixing plants were analyzed for their natural abundances of ¹⁵N ( ¹⁵N).The ¹⁵N in the leaves of non-fixing plants was +5.9% on average, whereas those from shrub legumes and Casuarina spp. were lower and close to the values of atmospheric N₂, suggesting the large contribution of N₂ fixation as the N source in these plants. The ¹⁵N values of the leaves from tree legumes except for Leucaena spp. were between the shrub legumes and non-fixing plants, which suggests that the fractional contribution of fixed N₂ in tree legumes may be smaller than that in the shrub legumes. Casuarina spp. was highly dependent on N₂ fixation. The ¹⁵N values of the nodules from most of the shrub legumes investigated were higher than those of the leaves.     

Development of insect resistance in tomato plants expressing the δ-endotoxin gene ofBacillus thuringiensis subsp.tenebrionis

A crystal -endotoxin gene ofBacillus thuringiensis subsp.tenebrionis (B.t.t.) encoding a coleopteran insect-specific toxin was used to construct a chimeric gene which expressed the toxin in plant cells. Via anAgrobacterium tumefaciens binary vector system, the toxin gene was transferred into tomato cells. From leaf disks recombinant plants were regenerated. Hybridization experiments demonstrated that these plants synthesized toxin-specific mRNA of the expected size. Transgenic tomato plants with the chimericB.t.t. toxin gene contained a 74 kDa protein which cross-reacted with toxin antibodies. The expression caused a significant insecticidal activity of the transgenic tomato plants against Colorado potato beetle larvae.     

Release of carboxylic anions and protons by tomato roots in response to ammonium nitrate ratio and pH in nutrient solution

The exudation of certain organic anions and protons by roots which may affect solubility of metals and P and uptake by plants, is affected by nitrogen form and pH. The objective of this work was to study exudation of carboxylates and H⁺/OH^– by tomato plants in response to NH₄/NO₃ ratio and pH in nutrient solution. Four NH₄/(NH₄+NO₃) ratios (R= 0, 0.33, 0.67 and 1) and constant vs. variable solution pH treatments were investigated. The sum of the exudation rates of all carboxylates tended to decline with increasing R, particularly tri- and dicarboxylates. The molar fraction of the exuded tri- and dicarboxylates, averaged over all treatments and plant ages, increased in the order tartarate 2%), malate (6%), succinate (15%), citrate (26%) and fumarate (46%). At R=1 the solution pH dropped from 5.2 to 3 and at R=0 increased to 8. The R corresponding to the pH stat of tomato plant was 0.3. For the constant solution pH treatment, the effect of solution pH on carboxylate exudation rate was small as compared to the effect of R. The exudation of citrate and H⁺ efflux which were initiated when NO₃ and NH₄ uptake rates per plant exceeded certain threshold values, increased with plant age.     

Sources of nitrate in rivers draining sixteen watersheds in the northeastern U.S.: Isotopic constraints

The feasibility of using nitrogen and oxygenisotope ratios of nitrate (NO₃ ^–) forelucidating sources and transformations ofriverine nitrate was evaluated in a comparativestudy of 16 watersheds in the northeastern U.S.A. Stream water was sampled repeatedly at theoutlets of the watersheds between January andDecember 1999 for determining concentrations,¹⁵N values, and ¹⁸Ovalues of riverine nitrate.In conjunction with information about land useand nitrogen fluxes,¹⁵N_nitrate and¹⁸O_nitrate values providedmainly information about sources of riverinenitrate. In predominantly forested watersheds,riverine nitrate had mean concentrations ofless than 0.4 mg NO₃ ^–-N L^–1,¹⁵N_nitrate values of lessthan +5, and ¹⁸O_nitratevalues between +12 and +19. This indicatesthat riverine nitrate was almost exclusivelyderived from soil nitrification processes withpotentially minor nitrate contributions fromatmospheric deposition in some catchments. Inwatersheds with significant agricultural andurban land use, concentrations of riverinenitrate were as high as 2.6 mg NO₃ ^–-NL^–1 with ¹⁵N_nitratevalues between +5 and +8 and¹⁸O_nitrate values generallybelow +15. Correlations between nitrateconcentrations, ¹⁵N_nitratevalues, and N fluxes suggest that nitrate inwaste water constituted a major, and nitrate inmanure a minor additional source of riverinenitrate. Atmospheric nitrate deposition ornitrate-containing fertilizers were not asignificant source of riverine nitrate inwatersheds with significant agricultural andurban land use. Although complementary studiesindicate that in-stream denitrification wassignificant in all rivers, the isotopiccomposition of riverine nitrate sampled at theoutlet of the 16 watersheds did not provideevidence for denitrification in the form ofelevated ¹⁵N_nitrate and¹⁸O_nitrate values. Relativelylow isotopic enrichment factors for nitrogenand oxygen during in-stream denitrification andcontinuous admixture of nitrate from theabove-described sources are thought to beresponsible for this finding.     

Evidence for growth ofSporothrix schenckii on dead but not on living sphagnum moss

When clinical isolates ofSporothrix schenckii were inoculated onto the apices of living or dead sphagnum moss plants maintained under growth chamber conditions, populations of the fungus, assessed by standard dilution plate methods, increased swiftly up to about 70-fold on moist, dead plants but did not increase on the live moss. Light and scanning electron microscopy revealed fungal growth and sporulation on and within dead plants, but no evidence of either on live plants. These data provide indirect support for the contention thatS. schenckii does not grow on living sphagnum in bogs, but rather that sporotrichosis epidemics associated with sphagnum moss are likely to result from contamination of the dead plants at some point(s) in the chain of events during or after harvest. One practical implication of our results is that precautions should be taken to insure that sphagnum moss is stored dry and that it is not wetted any sooner than necessary before use. We also report here improvement of the Mycose isolation medium by an increase in cycloheximide from 400 to 800 mg/l, chloramphenicol from 50 to 250 mg/l, and the addition of rifampicin at 20 mg/l.     

Steady state osmotic adaptation inUlva lactuca

The effects of hyper- and hypo-saline stresses on the levels of various inorganic and organic solutes inUlva lactuca have been recorded. Hypoosmotic stress decreased the tissue concentration of K⁺, Na⁺ and Cl^- while hyper-osmotic stress caused a transient increase in Na⁺ and a stable accumulation of K⁺ and Cl^-. The tissue content of -dimethylsulphoniopropionate (-dimethylpropiothetin) responded to changes in salinity. The time course of hypersaline stress showed the -dimethylsulophoniopropionate concentration rose as the Na⁺ level fell. The levels of free sugars and amino acids, including proline, were relatively low in this alga and did not appear to be important in osmotic adjustment. The possibility that tertiary sulphonium dipolar ions have an analogous role in some algae to glycinebetaine and possibly other quaternary nitrogen compounds in higher plants as cytoplasmic osmotica is discussed briefly.Abbreviations DMSP -dimenthylsulphomiopropionate - AFT apparent free space - TLE thin layer electrophoresis - NPS ninhydrin positive substances - TLC thin layer chromatography     

Emission of gaseous nitrogen oxides from an extensively managed grassland in NE Bavaria, Germany.

We analysed the stable isotope composition of emitted N₂O in a one-year field experiment (June 1998 to April 1999) in unfertilized controls, and after adding nitrogen by applying slurry or mineral N (calcium ammonium nitrate). Emitted N₂O was analysed every 2–4 weeks, with additional daily sampling for 10 days after each fertilizer application. In supplementary soil incubations, the isotopic composition of N₂O was measured under defined conditions, favouring either denitrification or nitrification. Soil incubated for 48 h under conditions favouring nitrification emitted very little N₂O (0.024 mol g_dw ^–1) and still produced N₂O from denitrification. Under denitrifying incubation conditions, much more N₂O was formed (0.91 mol g_dw ^–1 after 48 h). The isotope ratios of N₂O emitted from denitrification stabilized at ¹⁵N = –40.8 ± 5.7 and ¹⁸O = 2.7 ± 6.3. In the field experiment, the N₂O isotope data showed no clear seasonal trends or treatment effects. Annual means weighted by time and emission rate were ¹⁵N = –8.6 and ¹⁸O = 34.7 after slurry application, ¹⁵N = –4.6 and ¹⁸O = 24.0 after mineral fertilizer application and ¹⁵N = –6.4 and ¹⁸O = 35.6 in the control plots, respectively. So, in all treatments the emitted N₂O was ¹⁵N-depleted compared to ambient air N₂O (¹⁵N = 11.4 ± 11.6, ¹⁸O = 36.9 ± 10.7). Isotope analyses of the emitted N₂O under field conditions per se allowed no unequivocal identification of the main N₂O producing process. However, additional data on soil conditions and from laboratory experiments point to denitrification as the predominant N₂O source. We concluded (1) that the isotope ratios of N₂O emitted from the field soil were not only influenced by the source processes, but also by microbial reduction of N₂O to N₂ and (2) that N₂O emission rates had to exceed 3.4 mol N₂O m^–2 h^–1 to obtain reliable N₂O isotope data.     

Induction of crassulacean acid metabolism in Mesembryanthemum crystallinum increases reproductive success under conditions of drought and salinity stress

Summary Mesembryanthemum crystallinum L., an inducible crassulacean acid metabolism (CAM) plant, was grown for approximately 5 weeks following germination in well-watered, non-saline soil in a controlled-environment chamber. During this time, plants were characterized by C₃ photosynthetic carbon metabolism. After the initial 5 weeks, CAM was induced by a combination of high soil salinity and reduced soil water content. One group of plants was allowed to engage in CAM by being continuously exposed to normal CO₂-containing air (about 350–400 ppm). A second group of plants was deprived of ambient CO₂ each night (12 h dark period) until completion of their life cycle, thereby minimizing potential carbon gain via dark CO₂ fixation. The capacity to express CAM under conditions of drought and salinity stress markedly improved reproductive success: plants kept in normal CO₂-containing air produced about 10 times more seeds than plants kept in CO₂-free air during dark periods. Seeds from plants deprived of ambient CO₂ overnight had more negative ¹³C values than seeds from plants kept in normal air.     

Regulation of proline catabolism in Pseudomonas aeruginosa PAO

Mutants of Pseudomonas aeruginosa deficient in the utilization of l-proline as the only carbon and nitrogen source have been found to be defective either in proline dehydrogenase activity or in both proline dehydrogenase and ¹-pyrroline-5-carboxylate dehydrogenase activities of the bifunctional proline degradative enzyme. The latter type of mutants was unable to utilize l-ornithine, indicating that a single ¹-pyrroline-5-carboxylate dehydrogenase activity is involved in the degradation of ornithine and proline. Proline dehydrogenase and ¹-pyrroline-5-carboxylate dehydrogenase activities were strongly and coordinately induced by proline. It was excluded that ¹-pyrroline-5-carboxylate acted as an inducer of the bifunctional enzyme and it was shown that the low level induction observed during growth on ornithine was due to the intracellular formation of proline. The formation of the proline degradative enzyme was shown to be subject to catabolite repression by citrate and nitrogen control.Abbreviations EMS Ethylmethane sulfonate - NG N-methyl-N-nitro-N-nitrosoguanidine - P Minimal medium P - Pro-DH Proline dehydro-genase - P5C ¹-Pyrroline-5-carboxylate - P5C-DH ¹-Pyrroline-5-carboxylate dehydrogenase