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1.
Five ecotypes of Arabidopsis thaliana, from widely dispersed origins, were grown under combinations of ambient and elevated atmospheric CO 2 concentrations and ambient and elevated temperatures within solardomes. Total above-ground plant biomass was measured when the majority of plants across all ecotypes and treatments had formed seed pods. There were substantial differences in biomass between the ecotypes across all treatments. Temperature had no effect on biomass whilst CO 2 had a significant effect both alone and in interaction with ecotype. The CO 2 x ecotype interaction was mostly due to the enhancement of a single ecotype from the Cape Verde Islands. 相似文献
2.
Summary Within the widespread species Solanum dulcamara, contrasting ecotypes were found which are physiologically adapted to the light intensities prevailing in their natural habitats. When grown under a high light intensity, an ecotype from a shaded habitat exhibits signs of damage. Another one from an exposed habitat has higher rates of photosynthetic CO 2 uptake when grown under strong as compared to weak light and does not show damage. This differential response becomes even more evident when leaves of both ecotypes are grown to maturity under weak light and are subsequently subjected to strong light for some time. The quantum requirement for photosynthesis increases in the shade-, but not in the sun-ecotype. The sun type increases its rate of photosynthesis under saturating light intensities after a few days in strong light.No significant difference in physical resistances to gas diffusion could be found to explain the highly differing rates of photosynthesis. With the increase in photosynthetic capacity in leaves of the sun type, protein content, activity of RuDP carboxylase, and concentration of Fraction I protein increased likewise. It is suggested that de novo synthesis of photosynthetic enzymes in fully expanded leaves of the sun ecotype following treatment with strong light is the cause of its increased capacity for CO 2 fixation. 相似文献
3.
Summary Populations of Geranium carolinianum, a winter annual plant common in disturbed habitats, vary in their foliar response to sulfur dioxide, and pollution resistance is characteristic of populations sampled from areas in which SO 2 has been a prominent stress. The physiological basis of this ecotypic response was investigated using a whole-plant gaseous exchange system in which leaf resistance to H 2O efflux and SO 2 influx were concurrently monitored. Individual plants of distinct SO 2 susceptibility were exposed to pollutant concentrations of either 0.4, 0.6 or 0.8 l 1 -1 in both the dark and light. Total SO 2 flux (g cm -2 h -1) to the plant, which is the sum of leaf adsorptive and absorptive loss, varied as an inverse function of leaf resistance (s cm -1), and the relationship was modeled using linear regression techniques. Total SO 2 flux was partitioned to leaf surface and internal fractions using estimation procedures with the regression analysis. SO 2 flux into the leaf interior, the pollutant fraction responsible for causing foliar injury, was strikingly similar for resistant and sensitive plants at each concentration. Resistant plants must absorb 30% more SO 2 than their sensitive counterparts in order to exhibit comparable levels of foliar injury. Therefore, in G. carolinianum the predominant explantation for genetically controlled and quantitatively inherited differences in plant résponse to SO 2 is not variable pollutant flux but rather disparate physiological-biochemical processes affecting pollutant toxicity, cellular perturbation and repair. This conclusion is relevant to understanding how populations of G. carolinianum respond over time to elevated levels of SO 2 and may explain the inherent susceptibility of this species compared with plants with which it co-exists. 相似文献
4.
The concurrent exchange of SO 2 and H 2O vapor between the atmosphere and foliage of Geranium carolinianum was investigated using a whole-plant gas exchange chamber. Total leaf flux of SO 2 was partitioned into leaf surface and internal fractions. The emission rate of SO 2-induced H 2S was measured to develop a net leaf budget for atmospherically derived sulfur. Stomatal resistance to SO 2 flux was estimated by two techniques: (a) R sSO2′ from SO 2 data using analog modeling techniques and (b) R sSO2 from analogy to H 2O ( i.e. 1.89 R sH2o). 相似文献
5.
Leymus chinensis (Trin.) Tzvel is a perennial grass in the tribe Gramineae and important forage in Northern China. Knowledge of its genetic
diversity is a prerequisite for using modern breeding techniques. Amplified fragment length polymorphism (AFLP) was first
used to evaluate the genetic relationship among and within three ecotypes. Distinct clusters were produced based on AFLP markers.
All accessions from the same ecotype were grouped in a cluster except accessions 6. According to AFLP profile ecotype-specific bands differ from each other. The genetic differentiation within the ecotype
of the species was much smaller than that among ecotypes. Self-incompatibility in this species contributes to evident genetic
differentiation together with environment. These results indicate that ecotypes were distinguished visually similarly to genetic
variation.
Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 5, pp. 764–770.
The text was submitted by the authors in English. 相似文献
6.
The EICA hypothesis predicts that shifts in allocation of invasive plants give rise to higher growth rates and lower herbivore defense levels in their introduced range than conspecifics in their native range. These changes in traits of invasive plants may also affect ecosystem processes. We conducted an outdoor pot experiment with Chinese tallow tree ( Sapium sebiferum, Euphorbiaceae) seedlings from its native (Jiangsu, China, native ecotype) and introduced ranges (Texas, USA, invasive ecotype) to compare their relative performances in its native range and to examine ecotype effects on soil processes with and without fertilization. Consistent with predictions, plant (shoot and root) mass was significantly greater and leaf defoliation tended to be higher, while the root:shoot ratio was lower for the invasive ecotype relative to the native ecotype. Seasonal amounts of soil–plant system CO 2 and N 2O emissions were higher for the invasive ecotype than for the native ecotype. Soil respiration rates and N 2O emission increases from fertilization were also greater for the invasive ecotype than for the native ecotype, while shoot-specific respiration rates (g CO 2–C g −1 C day −1) did not differ between ecotypes. Further, soil inorganic N (ammonium and nitrate) was higher, but soil total N was lower for soils with the invasive ecotype than soils with the native ecotype. Compared with native ecotypes, therefore, invasive ecotypes may have developed a competition advantage in accelerating soil processes and promoting more nitrogen uptake through soil–plant direct interaction. The results of this study suggest that soil and ecosystem processes accelerated by variation in traits of invasive plants may have implications for their invasiveness. 相似文献
7.
The anaerobic bacterium Chlorobium assimilates carbon dioxide in the light with various sulfur compounds as electron donors. The well-known metabolic pathway proceeds from the oxidation of sulfide via sulfur to sulfate. In the dark the reaction is partially reversed when sulfur is reduced to hydrogen sulfide. The fermenting cells thereby release an excess of reductant. We have now found a hydrogen sulfide production from sulfur, which is light-dependent. It is more than ten times faster than the dark reaction. This appears in experiments where the cell suspension is illuminated in absence of CO 2 and flushed continuously with H 2 or Ar. The H 2S is trapped with ZnCl 2 and the S 2- titrated with iodine. The total amount of H 2S evolved in the light increases proportionally with the amount of sulfur added, and about one-half of the added sulfur is converted to H 2S. Another part of the metabolized sulfur appears at the same time as sulfate, but all the sulfur oxidized to sulfate does not account for the larger amount of sulfur reduced to hydrogen sulfide. Very likely other unanalyzed oxidized sulfur compounds must also have been produced. Use of H 2 instead of Ar as the anaerobic gas phase does not increase the amount of H 2S produced, nor does the addition of thiosulfate; sulfur itself is the preferred electron donor for the sulfur reduction. Up to a light intensity of 10000 ergs cm -2sec -1 CO 2 does not affect H 2S production. Without CO 2, saturation of the light-dependent evolution of H 2S is reached at about 40000 ergs cm -2sec -1. In contrast, presence of CO 2 at this light intensity makes the sulfide production disappear completely. On application of mass spectrometry to the gas exchange upon illumination, at high light intensity a H 2S gush is found during the first 3 min. This is followed by CO 2 fixation, while simultaneously the reductant H 2S is now taken up. With Rhodospirillum rubrum, the addition of sulfur leads to a moderate evolution of H 2S. In contrast to Chlorobium this reaction in R. rubrum is not light-sensitive, nor does it produce detectable amounts of sulfate. After addition of malate the rate of H 2S evolution does increase in the light, since the cells use malate as an electron donor during their photochemical metabolism. 相似文献
8.
Spinach plunts ( Spinacia oleracea L. cv. Monosa) were exposed to air with and without 0.25 μl l -1 H 2S. Effects of H 2S exposure for up to 18 days on photosynthesis, dark respiration and on chlorophyll a fluorescence were studied. Dark respiration was not affected by H 2S fumigation. Photosynthetic CO 2 fixation decreased linearly with time in both control and fumigated plants. The rate of decrease in CO 2 fixation was faster in the fumigated plants; after 14 days of exposure the fumigated plants showed a decrease in CO 2 fixation of 23%äs compared with the control plants. The H 2S-induced decrease in CO 2 fixation was accompanied by a decrease in quenching of the chlorophyll fluorescence. The most characteristic change in chlorophyll fluorescence was a decreased difference between maximum and steady-state fluorescence [(P-T)/P), suggesting a reduced efficiency in the use of photochemical energy in photosynthesis. Differences in CO 2 fixation were more pronounced whcn measured at high light intensity; the maximum rate of CO 2 fixation at light saturation decreased significantly with time in the H 2S-exposed plants; after 14 days of H 2S exposure a decrease of more than 70% was noted. The decrease in CO 2 fixation could not be attributed to a decreased chlorophyll content; on the contrary, chlorophyll content even slightly increased during fumigation. The initial increase in CO 2 fixation rate with increasing light intensity was also reduced by prolonged H 2S fumigation, indicating an effect of H 2S fumigation on photosynthetic electron transport. Finally, the phytotoxicity of H 2S is discusscd in relation to the H 2S-induced changes in photosynthetic CO 2 fixation and chlorophyll a fluorescence, and the effect of H 2S on leaf development observed in earlier studies. 相似文献
9.
The mechanisms controlling the photosynthetic performance of C 4 plants at low temperature were investigated using ecotypes of Bouteloua gracilis Lag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700 μ mol m ?2 s ?1 and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO 2 assimilation rate ( A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO 2‐saturated rate of photosynthesis to decline to a greater degree than the initial slope of A versus the intercellular CO 2 response, thereby reducing the photosynthetic CO 2 saturation point. As a consequence, A in normal air was CO 2‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higher A; however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum, A in high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, while A in low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adapted Fv/ Fm. In both ecotypes, the activity of Rubisco was equivalent to A below 17 °C but well in excess of A above 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco and A, we propose that Rubisco is a major limitation on C 4 photosynthesis in B. gracilis below 17 °C. Based on these results and for theoretical reasons associated with how C 4 plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C 4 photosynthesis at low temperature. 相似文献
10.
In seedlings of the tropical tree species Erythrina variegata Lam. and Hardwickia binata Roxb. exposed to different acidic mist (H 2SO 4, pH 5, 3 and 2) for 5 d significant reduction in seedling growth, biomass accumulation and 14CO 2 fixation were determined. In isolated chloroplasts a decrease in the activities of photosystem 2 and whole electron transport
chain was observed only at pH 3 and 2, but no significant change in photosystem 1 activity was observed. SDS-PAGE analysis
of crude leaf extracts of ribulose 1,5-bisphosphate carboxylase (RuBPC) indicated a significant loss of 55 and 15 kDa polypeptides
at pH 2 in Erythrina. The reduction in the RuBPC activity in seedlings grown under acidic mists correlated well with CO 2 fixation. 相似文献
11.
Summary In altitudinal ecotypes of Trifolium repens L. the oxygen inhibition of photosynthesis, the CO 2 compensation point and the sugar content were examined. Excised leaves were exposed to 14CO 2 for 20 s and 60 min periods and the radioactivity in different photosynthetic products was studied. In all experiments the temperature during growth and measurement was varied.To some extent, the differences between the ecotypes and the differences between the plants grown under different temperature conditions are similar. These ecotypic differences appear to reflect long-term adaptation to the general temperature conditions at each site. Alpine ecotypes and plants grown at low temperatures show an increased photorespiration. The 14C-labeling of certain photosynthetic products also changes with the ecotypes and the temperatures during growth. Other differences between the ecotypes are interpreted as adaptations to the partial pressure of Co 2 and to the length of the growing season, both of which change with altitude.The metabolism of photosynthesis depends greatly on temperature. The 14C-experiments and the study of photorespiration suggest that, to a certain degree, adaptation can compensate for this dependence on temperature. 相似文献
12.
The oxidation of organic compounds with elemental sulfur or thiosulfate as electron acceptor was studied in the anaerobic hyperthermophilic archaea Thermoproteus tenax and Pyrobaculum islandicum. T. tenax was grown on either glucose or casamino acids and sulfur; P. islandicum on peptone and either elemental sulfur or thiosulfate as electron acceptor. During exponential growth only CO 2 and H 2S rather than acetate, alanine, lactate, and succinate were detected as fermentation products of both organisms; the ratio of CO 2/H 2S formed was 1:2 with elemental sulfur and 1:1 with thiosulfate as electron acceptor. Cell extracts of T. tenax and P. islandicum contained all enzymes of the citric acid cycle in catabolic activities: citrate synthase, aconitase, isocitrate dehydrogenase (NADP +-reducing), oxoglutarate: benzylviologen oxidoreductase, succinyl-CoA synthetase, succinate dehydrogenase, fumarase and malate dehydrogenase (NAD +-reducing). Carbon monoxide dehydrogenase activity was not detected. We conclude that in T. tenax and P. islandicum organic compounds are completely oxidized to CO 2 with sulfur or thiosulfate as electron acceptor and that acetyl-CoA oxidation to CO 2 proceeds via the citric acid cycle. 相似文献
13.
The potential for gibberellins (GAs) to control stem elongation and itsplasticity (range of phenotypic expression) was investigated in Stellaria longipes grown in long warm days. Gibberellinmetabolism and sensitivity was compared between a slow-growing alpine dwarfwithlow stem elongation plasticity and a rapidly elongating, highly plastic prairieecotype. Both ecotypes elongated in response to exogenous GA 1,GA 4 or GA 9, but surprisingly, the alpine dwarf wasrelatively unresponsive to GA 3. Endogenous GA 1,GA 3, GA 4, GA 5, GA 8, GA 9and GA 20 were identified and quantified in stem tissue harvested atcommencement, middle and end of the period of most rapid elongation. Theconcentration of GAs which might be expected to promote shoot elongation washigher during rapid elongation than toward its end for both ecotypes. Whilethere was a trend for certain GAs (GA 3, GA 4,GA 9, GA 20) to be higher in stems of the alpine ecotypeduring rapid elongation, that result does not explain the slower growth of thealpine ecotype and the faster growth of the prairie ecotype under a range ofconditions. To determine if the two ecotypes metabolized GA 20differently, plants were fed [ 2H]- or[ 3H]-GA 20. The metabolic products identified included[ 2H 2]-GA 1, -GA 8, -GA 29,-GA 60, -3-epi-GA 1, GA 118(-1-epi-GA 60) and -GA 77. The concentration of[ 2H 2]-GA 1 also did not differ between the twoecotypes and metabolism of [ 2H 2]- or[ 3H]-GA 20 was also similar. In the same experiments thepresence of epi-GA 1, GA 29, GA 60,GA 118 and GA 77 was indicated, suggesting that these GAsmay also occur naturally in S. longipes, in addition tothose described above. Collectively, these results suggest that while stemelongation within ecotypes is likely regulated by GAs, differences in GAcontent, sensitivity to GAs (GA 3 excepted), or GA metabolism areunlikely to be the controlling factor in determining the differences seen ingrowth rate between the two ecotypes under the controlled environmentconditionsof this study. Nevertheless, further study is warranted especially underconditions where environmental factors may favour a GA:ethylene interaction. 相似文献
14.
Spruce ( Picea Abies L.) trees from the same clone were supplied with different, but low, amounts of plant available sulfate in the soil (9.7-18.1 milligrams per 100 grams of soil). Branches attached to the trees were enclosed in a dynamic gas exchange cuvette and analyzed for the emission of volatile sulfur compounds. Independent of the sulfate supply in the soil, H 2S was the predominant reduced sulfur compound continuously emitted from the branches with high rates during the day and low rates in the night. In the light, as well as in the dark, the rates of H 2S emission increased exponentially with increasing water vapor flux from the needles. Approximately 1 nanomole of H 2S was found to be emitted per mole of water. When stomata were closed completely, only minute emission of H 2S was observed. Apparently, H 2S emission from the needles is highly dependent on stromatal aperture, and permeation through the cuticle is negligible. In several experiments, small amounts of dimethylsulfide and carbonylsulfide were also detected in a portion of the samples. However, SO 2 was the only sulfur compound consistently emitted from branches of spruce trees in addition to H 2S. Emission of SO 2 mainly proceeded via an outburst starting before the beginning of the light period. The total amount of SO 2 emitted from the needles during this outburst was correlated with the plant available sulfate in the soil. The diurnal changes in sulfur metabolism that may result in an outburst of SO 2 are discussed. 相似文献
15.
Net photosynthesis and dark respiration (CO 2 flux) of Antarctic mosses were measured at Langhovde, East Antarctica, from 9 to 17 January 1988. Moss blocks were taken
from communities in the Yukidori Valley (69°14′30″S, 39°46′00″E) at Langhovde. Each block was composed of Ceratodon purpureus and Bryum pseudotriquetrum, or B. pseudotriquetrum. The upper part of the block was used to measure net photosynthesis and dark respiration. The net photosynthesis of each
sample was measured in the field for one or three days with two infrared CO 2 gas analyzers and an assimilation chamber. The relationships of net photosynthetic rate and dark respiration rate, to the
water content of the sample, the intensity of solar radiation and the moss temperature were estimated from the field data.
The maximum rate of net photosynthesis was about 4 μmol CO 2 m −2s −1 at saturating radiation intensity and at optimum temperature, about 10°C. Environmental features of moss habitats in the
Yukidori Valley are discussed in relation to these results. 相似文献
16.
The potential of plant nutrients (such as sulphur, S) and phytohormones (such as salicylic acid, SA) has been explored in isolated studies by researchers in controlling the impact of abiotic stresses such as salinity in plants. However, information is scanty on the major mechanisms underlying the role of S and/or SA in modulation of enzymes involved in nitrogen (N) assimilation, GOGAT cycle, and antioxidant defence system; the cellular status of N-containing osmolyte proline, glucose, S-containing compounds; and their cumulative role in photosynthesis functions and growth in crop plants. The present study aimed to assess the role of cumulative effect of SA and S (SO42−) mediated induction of N assimilatory enzymes, GOGAT cycle, N-osmolyte proline and its metabolizing enzymes, glyoxylase enzymes, and antioxidant capacity in mungbean (Vigna radiata L.) exposed to NaCl with or without SO42− and SA. Salt-exposed V. radiate showed differential elevations in damage (O.2−, H2O2, lipid peroxidation; glucose) and defence (ascorbate peroxidase, APX; glutathione reductase, GR; superoxide dismutase, SOD; reduced GSH; proline) and inhibitions in the activities of NR and NiR; N content, photosynthesis, photosynthetic N-use-efficiency (NUE), and growth. The separate supplementation of SA and SO42− to 50 mM NaCl almost equally strengthened the antioxidant machinery and diminished NaCl-accrued damages. However, combined supply of SA and SO42− to NaCl-exposed cultivars led to significant improvements in NR and NiR activities, the accumulation of N, GSH, proline, enhanced activity of APX, GR, and reduced activity of SOD, and also decreases in O.2−, H2O2, lipid peroxidation and glucose. These observations were corroborated with SA, SO42− and NaCl-mediated changes in the traits of photosynthesis and growth, stomatal behaviour, and the polypeptide patterns of Rubisco in V. radiata. Overall, in V. radiata, SA-mediated higher enhancements in the activity of N assimilatory enzymes (NR, NiR, and GS), increase in the N and proline, and GSH; and decreases in the contents of Na+ and Cl− ions, and glucose (a photosynthesis repressor); maintenance of a fine tuning among SOD, APX, and GR enzymes; and higher minimization of ROS (O.2−, H2O2) and lipid peroxidation finally led to a higher promotion in photosynthesis and growth. 相似文献
17.
Fumigation of leaves with SO 2 can reduce the capacity for photosynthetic CO 2 uptake even in the absence of visible symptoms of damage. In vitro studies suggest that this invisible injury to intact leaves could be affected by damage to each of the main stages in the photosynthetic process. Reduced stomatal apertures may also reduce photosynthesis following SO 2 fumigation. The responses of CO 2 uptake by leaves to intercellular CO 2 concentration and to absorbed light provide information for quantitative separation of the in vivo contribution of the different stages of photosynthesis to reduction in overall rate. This study uses these techniques to examine the basis of reduction in CO 2 uptake in Zea mays cv. LG11 leaves following short-term fumigation with SO 2. Fumigation with 33 μmol m –3 SO 2 for 30 min reduced light saturated CO 2 uptake by about one-third. An even greater reduction in light limited CO 2 uptake was observed and with no significant change in light absorptance this was attributed to a reduced quantum yield of photosynthesis. The light saturated CO 2 uptake rate and the stomatal conductance decreased in parallel. However, the relationship of CO 2 uptake to the intercellular CO 2 concentration suggested that the reduced stomatal conductance did not account for the reduced rate of CO 2 uptake following fumigation. Both the initial slope and plateau of this relationship were significantly reduced, suggesting that both carboxylation efficiency and capacity for regeneration of CO 2 acceptor were diminished by SO 2 fumigation. The operating intercellular CO 2 concentration indicated that both processes were co-limiting, before and after fumigation. The time required for induction of photosynthetic CO 2 uptake on illumination was approximately doubled following SO 2 fumigation, showing that fumigation impairs the ability of the photosynthetic apparatus to adapt to fluctuations in light level. 相似文献
18.
In order to investigate the possible impacts of increased atmospheric CO 2 levels on algal growth and photosynthesis, the influence of CO 2 concentration was tested on three planktonic algae ( Chlamydomonas reinhardtii, Chlorella pyrenoidosa, and Scenedesmus obliquus). Increased CO 2 concentration enhanced significantly the growth rate of all three species. Specific growth rates reached maximal values at 30, 100, and 60 M CO 2 in C. reinhardtii, C. pyrenoidosa, and S. obliquus, respectively. Such significant enhancement of growth rate with enriched CO 2 was also confirmed at different levels of inorganic N and P, being more profound at limiting levels of N in C. pyrenoidosa and P in S. obliquus. The maximal rates of net photosynthesis, photosynthetic efficiency and light-saturating point increased significantly ( p < 0.05) in high-CO 2-grown cells. Elevation of the CO 2 levels in cultures enhanced the photoinhibition of C. reinhardtii, but reduced that of C. pyrenoidosa and S. obliquus when exposed to high photon flux density. The photoinhibited cells recovered to some extent (from 71% to 99%) when placed under dim light or in darkness, with better recovery in high-CO 2-grown C. pyrenoidosa and S. obliquus. Although pH and pCO 2 effects cannot be distinguished from this study, it can be concluded that increased CO 2 concentrations with decreased pH could affect the growth rate and photosynthetic physiology of C. reinhardtii, C. pyrenoidosa, and S. obliquus. 相似文献
19.
The influence of elevated CO 2 concentrations on growth and photosynthesis of Gracilaria sp. and G. chilensis was investigated in order to procure information on the effective utilization of CO 2. Growth of both was enhanced by CO 2 enrichment (air + 650 ppm CO 2, air + 1250 ppm CO 2, the enhancement being greater in Gracilaria sp. Both species increased uptake of NO 3
– with CO 2 enrichment. Photosynthetic inorganic carbon uptake was depressed in G. chilensis by pre-culture (15 days) with CO 2 enrichment, but little affected in Gracilaria sp. Mass spectrometric analysis showed that O 2 uptake was higher in the light than in the dark for both species and in both cases was higher in Gracilaria sp. The higher growth enhancement in Gracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO 2 in culture. 相似文献
20.
Abstract: The current view of sulfur nutrition is based on the source‐to‐sink relationship of carbohydrates. SO 42‐ reduction is thought to occur mainly in leaves. Surplus reduced sulfur must be transported out of the leaves, loaded into the phloem and transported to other tissues, in particular tissues assumed to be sink organs. However, it has not been proved that tissues which are sinks for carbohydrates are also sink organs for reduced sulfur. It is evident that sinks must communicate with sources, and vice versa, to signal demand and to transport the surplus of reduced sulfur that is produced. The demand‐driven control model of sulfur nutrition proposes that the tripeptide glutathione is the signal which regulates S nutrition of the whole plant at the level of SO 42‐ uptake. Acclimatization to environmental changes has been shown to result in several changes in S nutrition of deciduous trees: (i) Drought stress diminished SO 42‐ transport into the xylem, although the GSH content in lateral roots remained unaffected, possibly due to an overall reduction in water status. (ii) Flooding decreased APS reductase activity in the anoxic roots. This may be due to enhanced GSH transport to the roots, but it is more likely to be the result of a change in metabolism leading to diminished energy gain in the roots. (iii) Mycorrhization enhanced the GSH content in the phloem, while SO 42‐ uptake was not affected. This clearly goes against the demand‐driven control model. (iv) Under both short‐ and long‐term exposure to elevated pCO 2, the APS reductase activity in leaves and lateral roots did not correlate with the GSH contents therein. Therefore, it must be assumed that, under these conditions, regulation of S nutrition goes beyond the demand‐driven control model, and occurs within the network of other nutrient metabolism. (v) Atmospheric S in the form of H 2S enhanced the reduced sulfur content of the phloem and lateral roots. Under these conditions, the SO 42‐ loaded into the xylem decreased. It would appear that the demand‐driven control model of sulfur nutrition is not always valid in the case of deciduous trees. 相似文献
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