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2.
Among C 4 species, sorghum is known to be more drought tolerant than maize. The objective was to evaluate differences in leaf gas exchanges, carbohydrates, and two enzyme activities of these nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME) C 4 subtype monocots in response to water deficit and CO 2 concentration ([CO 2]). Maize and sorghum were grown in pots in sunlit environmental-controlled chambers. Treatments included well watered (WW) and water stressed (WS) (water withheld at 26 days) and daytime [CO 2] of 360 (ambient) and 720 (elevated) μmol mol −1. Midday gas exchange rates, concentrations of nonstructural carbohydrates, and activities of sucrose-phosphate synthase (SPS) and adenosine 5′-diphosphoglucose pyrophosphorylase (ADGP) were determined for fully expanded leaf sections. There was no difference in leaf CO 2 exchange rates (CER) between ambient and elevated [CO 2] control plants for both maize and sorghum. After withholding water, leaf CER declined to zero after 8 days in maize and 10 days for sorghum. Sorghum had lower stomatal conductance and transpiration rates than maize, which resulted in a longer period of CER under drought. Nonstructural carbohydrates of both control maize and sorghum were hardly affected by elevated [CO 2]. Under drought, however, increases in soluble sugars and decreases in starch were generally observed for maize and sorghum at both [CO 2] levels. For stressed maize and sorghum, decreases in starch occurred earlier and were greater at ambient [CO 2] than at elevated [CO 2]. For maize, drought did not meaningfully affect SPS activity. However, a decline in SPS activity was observed for drought-stressed sorghum under both [CO 2] treatments. There was an increase in ADGP activity in maize under drought for both [CO 2] treatments. Such a response in ADGP to drought, however, did not occur for sorghum. The generally more rapid response of maize than sorghum to drought might be related to the more rapid growth of leaf area of maize. 相似文献
3.
Maize, in rotation with soybean, forms the largest continuous ecosystem in temperate North America, therefore changes to the biosphere‐atmosphere exchange of water vapor and energy of these crops are likely to have an impact on the Midwestern US climate and hydrological cycle. As a C 4 crop, maize photosynthesis is already CO 2‐saturated at current CO 2 concentrations ([CO 2]) and the primary response of maize to elevated [CO 2] is decreased stomatal conductance ( gs). If maize photosynthesis is not stimulated in elevated [CO 2], then reduced gs is not offset by greater canopy leaf area, which could potentially result in a greater ET reduction relative to that previously reported in soybean, a C 3 species. The objective of this study is to quantify the impact of elevated [CO 2] on canopy energy and water fluxes of maize ( Zea mays). Maize was grown under ambient and elevated [CO 2] (550 μmol mol ?1 during 2004 and 2006 and 585 μmol mol ?1 during 2010) using Free Air Concentration Enrichment (FACE) technology at the SoyFACE facility in Urbana, Illinois. Maize ET was determined using a residual energy balance approach based on measurements of sensible ( H) and soil heat fluxes, and net radiation. Relative to control, elevated [CO 2] decreased maize ET (7–11%; P < 0.01) along with lesser soil moisture depletion, while H increased (25–30 W m ?2; P < 0.01) along with higher canopy temperature (0.5–0.6 °C). This reduction in maize ET in elevated [CO 2] is approximately half that previously reported for soybean. A partitioning analysis showed that transpiration contributed less to total ET for maize compared to soybean, indicating a smaller role of stomata in dictating the ET response to elevated [CO 2]. Nonetheless, both maize and soybean had significantly decreased ET and increased H, highlighting the critical role of elevated [CO 2] in altering future hydrology and climate of the region that is extensively cropped with these species. 相似文献
4.
The enhanced dark CO 2 uptake after a preillumination period under varying O 2 concentrations has been measured with maize, a C 4 plant. For comparison the same study has been conducted with tomato, a C 3 plant. Increasing the O 2 concentration during preillumination inhibits by 70% the subsequent dark CO 2 uptake in tomato but stimulates 2-fold this CO 2 uptake in maize. The O 2 enhancement of CO 2 uptake in maize is due to the enhancement of malate and aspartate synthesis. The percentages of radioactivity incorporated in the C-4 of malate and aspartate vary from 74 to 87% when O 2 concentration during preillumination is increased from 0 to 100%. 相似文献
5.
The rising concentration of atmospheric carbon dioxide (CO 2) is known to increase the total aboveground biomass of several C3 crops, whereas C4 crops are reported to be hardly affected when water supply is sufficient. However, a free‐air carbon enrichment (FACE) experiment in Braunschweig, Germany, in 2007 and 2008 resulted in a 25% increased biomass of the C4 crop maize under restricted water conditions and elevated CO 2 (550 ppm). To project future yields of maize under climate change, an accurate representation of the effects of eCO 2 and drought on biomass and soil water conditions is essential. Current crop growth models reveal limitations in simulations of maize biomass under eCO 2 and limited water supply. We use the coupled process‐based hydrological‐plant growth model Catchment Modeling Framework‐Plant growth Modeling Framework to overcome this limitation. We apply the coupled model to the maize‐based FACE experiment in Braunschweig that provides robust data for the investigation of combined CO 2 and drought effects. We approve hypothesis I that CO 2 enrichment has a small direct‐fertilizing effect with regard to the total aboveground biomass of maize and hypothesis II that CO 2 enrichment decreases water stress and leads to higher yields of maize under restricted water conditions. Hypothesis III could partly be approved showing that CO 2 enrichment decreases the transpiration of maize, but does not raise soil moisture, while increasing evaporation. We emphasize the importance of plant‐specific CO 2 response factors derived by use of comprehensive FACE data. By now, only one FACE experiment on maize is accomplished applying different water levels. For the rigorous testing of plant growth models and their applicability in climate change studies, we call for datasets that go beyond single criteria (only yield response) and single effects (only elevated CO 2). 相似文献
6.
Carbon dioxide gas production in maize, mixed with 0, 5 or 10% broken corn and foreign material (BCFM), and 0 or 100 adult maize weevils at 13, 16 or 19% moisture content (mc) was studied in 1.8 liter thermos containers which were held at 26.6°C and 60±5% r.h. for 80 days. CO 2 was measured at 7 day intervals using an infrared gas analyzer. At 13 or 16% mc, higher CO 2 production was measured in infested maize than in uninfested maize, and BCFM did not significantly affect CO 2 production. At 19% mc, CO 2 production was greatly increased regardless of the presence of insects and BCFM. CO 2 produced over 12 weeks was 110–166g/kg. The number of live maige weevils after 80 days was 538 in 13% mc, 344 in 16% mc and 48 in the 19% mc Therefore, respiration of fungi such as Aspergillus glaucus, Aspergillus candidus and Aspergillus terreus other than that of insects appeared to more greatly influence CO 2 production than did the insects at 19% mc The moisture content and presence of maize weevils were major factors affecting respiration during storage, but level of BCFM did not significantly affect CO 2 production. The CO 2 produced over 12 weeks was 135–147 g/kg in infested maize at 13% and 136–144 g/kg at 16% mc. 相似文献
7.
Use of the gas chromatograph and a mercury-to-glass sealed respirometer adapted for gas syringe sampling, allowed the rapid, accurate characterization of CO 2 evolution rates from live and from dead-sterile Zea mays L. grain dried to moisture levels of 12.6 to 1.4%. The live grain at the lowest moisture level showed an elevated rate inconsistent with the exponential increase in rate of CO 2 evolution with increasing moisture found for maize with moisture contents from 4 to 12.6%. At the lowest moisture level, rates of CO 2 evolution from dead-sterile grain were greater than for live grain. Moisture had no effect on CO 2 evolution from dead-sterile grain. Increasing temperature and increasing levels of O 2 in the storage atmosphere resulted in increased rates of CO 2 evolution from both live and dead-sterile maize. CO 2 production rates from live and from dead-sterile grain decreased with increasing storage time, even though respirometer CO 2 concentrations were less than 1% at the end of the experiment. Our results indicate that CO 2 production is not a dependable measure of respiration in dry seeds. Other experiments indicate that oxygen absorption also is not reliable in maize grain. 相似文献
8.
Under elevated environmental carbon dioxide (CO 2), leaf chewers tend to compensate for decreased leaf nutritional quality with increased consumption; mortality and development times also increase and cause a reduction in the fitness of leaf chewers. However, the effect of elevated CO 2 on multiple successive generations of these and other insects is not well understood. Furthermore, information about the direct effects of increased environmental CO 2 on developmental time and consumption of herbivores is lacking. In this paper, we tested the hypothesis that cascade effects of elevated CO 2 through plants, rather than the direct effects of elevated CO 2, are the main factors decreasing the fitness of cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). We used two series of experiments to quantify the growth, development, and consumption of H. armigera fed on an artificial diet or C 4 plants (maize) grown under two CO 2 levels (ambient vs. double ambient). In the first series of experiments, elevated CO 2 had no effect on the population abundance or individual consumption for three successive generations of cotton bollworms fed on an artificial diet. In the second series of experiments, elevated CO 2 reduced population abundance of cotton bollworm larvae for two successive generations when they were fed maize milky grains. The specific effects were longer larval duration, lower fecundity, and decreased r m of cotton bollworms. Furthermore, elevated CO 2 increased individual consumption when cotton bollworm was fed maize milky grains for two successive generations and decreased the population’s total consumption in the first generation but increased it in the second generation. The results from this study indicate that: (1) The effects of elevated CO 2 on three successive generations of cotton bollworm fed on artificial diet were weak, or even non‐existent, and (2) elevated CO 2 increased the consumption when cotton bollworm were fed maize. Our study also suggests that the damage inflicted by cotton bollworm on maize (a C 4 plant) will be seriously affected by the increases in atmospheric CO 2, which is unlike our previous results for spring wheat (a C 3 plant). 相似文献
9.
碳捕集与封存(Carbon Capture and Storage,CCS)是应对全球气候变化、实现煤炭清洁利用的有效手段之一,但是地质封存的CO 2存在泄漏的风险,可能对农田生态系统产生重大威胁,影响我国粮食安全。根系生长是地上部和地下部相互作用、相互促进的统一过程,其形态特征对作物生产力有显著影响,但CCS泄漏对植物根系的影响评估尚不多见。本文以玉米为研究对象,采用盆栽底部通入CO 2的方法模拟不同CO 2泄漏情景,研究CK(0 g m -2 d -1)和G1000(1000 g m -2 d -1)和G2000(2000 g m -2 d -1)三种泄漏情景下CO 2对玉米根系形态的影响。结果表明:CO 2泄漏对玉米根系形态有明显的影响,随着泄漏量的增大总根长从40290.81 cm减少至21448.18 cm,减少46.77%,其中细根大幅减少;CO 2泄漏造成玉米明显减产,最大减产率达26.64%;玉米的地上部生物量较地下部生物量对CO 2泄漏更加敏感。综合来看,随着CO 2泄漏量增大,对玉米根的生长、地上部生物量、地下部生物量以及产量有显著的抑制作用。作物根系形态对封存CO 2泄漏的响应可为CCS泄漏监测和生态修复提供系统科学依据。 相似文献
10.
Maize and grain sorghum seeds were sown in pots and grown for 39 days in sunlit controlled-environment chambers at 360 (ambient) and 720 (double-ambient, elevated) μmol mol −1 carbon dioxide concentrations [CO 2]. Canopy net photosynthesis (PS) and evapotranspiration (TR) was measured throughout and summarized daily from 08:00 to 17:00 h Eastern Standard Time. Irrigation was withheld from matched pairs of treatments starting on 26 days after sowing (DAS). By 35 DAS, cumulative PS of drought-stress maize, compared to well-watered plants, was 41% lower under ambient [CO 2] but only 13% lower under elevated [CO 2]. In contrast, by 35 DAS, cumulative PS of drought-stress grain sorghum, compared to well-watered plants, was only 9% lower under ambient [CO 2] and 7% lower under elevated [CO 2]. During the 27-35 DAS drought period, water use efficiency (WUE, mol CO 2 Kmol −1 H 2O), was 3.99, 3.88, 5.50, and 8.65 for maize and 3.75, 4.43, 5.26, and 9.94 for grain sorghum, for ambient-[CO 2] well-watered, ambient-[CO 2] stressed, elevated-[CO 2] well-watered and elevated-[CO 2] stressed plants, respectively. Young plants of maize and sorghum used water more efficiently at elevated [CO 2] than at ambient [CO 2], especially under drought. Reductions in biomass by drought for young maize and grain sorghum plants were 42 and 36% at ambient [CO 2], compared to 18 and 14% at elevated [CO 2], respectively. Results of our water stress experiment demonstrated that maintenance of relatively high canopy photosynthetic rates in the face of decreased transpiration rates enhanced WUE in plants grown at elevated [CO 2]. This confirms experimental evidence and conceptual models that suggest that an increase of intercellular [CO 2] (or a sustained intercellular [CO 2]) in the face of decreased stomatal conductance results in relative increases of growth of C 4 plants. In short, drought stress in C 4 crop plants can be ameliorated at elevated [CO 2] as a result of lower stomatal conductance and sustaining intercellular [CO 2]. Furthermore, less water might be required for C 4 crops in future higher CO 2 atmospheres, assuming weather and climate similar to present conditions. 相似文献
11.
Isolated bundle-sheath (BS) strands from leaves of mature maize plants show enhanced rates of CO 2 fixation in the presence of reduced intermediates of the photosynthetic cycle (R5P, DHAP, FruDP.) 3PGA is the major labelled product of 14CO 2 fixation whatever the substrate added. CO 2 fixation is much lower with PGA than with reduced intermediates, suggesting a limited capacity of the cells to regenerate RuDP (the CO 2-acceptor) from PGA. These two experimental facts, which are characteristic features of bundle-sheath photosynthesis for maize (a species with agranal bundle-sheath chloroplasts) indicate that phaotosystem II activity is a limiting factor for the evolution of the bundle-sheath photosynthetic process. Nevertheless, a reducing capacity arises as proved by sensitivity of CO 2 fixation to DCMU, particularly when PGA is added to the bundle-sheath. PGA synthesis occurs, in the presence of non-limiting amounts of CO 2, according to the equation: RuDP + CO 2→ 2 PGA; the oxygen effect on 14CO 2 fixation, at lower CO 2 concentration, is interpreted as a dilution effect of the internal pool of 14CO 2 by unlabelled CO 2 generated by photorespiration. 相似文献
12.
Summary Cotton and maize plants were grown under full sunlight in glass houses containing normal ambient partial pressure of CO 2 (330±20 bar) and enriched partial pressure of CO 2 (640 ±15 bar) with four levels of nitrogen nutrient. In 40 day old cotton plants grown in high CO 2, there was a 2-fold increase in day weight and a 1.6-fold increase in leaf area compared with plants grown in ambient CO 2. In 30 day old maize plants there was only 20% increase in dry weight in plants grown in 640 bar CO 2 compared with plants grown in 330 bar and no significant increase in leaf area. In both species, at both CO 2 treatments, dry weight and leaf area decreased in similar proportion with decreased nitrogen nutrient.The increase of leaf area in cotton plants at high CO 2 caused a reduction of total nitrogen on a dry weight basis. In cotton assimilation rate increased 1.5 fold when plants were grown with high nitrogen and high CO 2. The increase was less at lower levels of nitrate nutrient. There was a 1.2 fold increase in assimilation rate in maize grown at high CO 2 with high nitrate nutrient.Cotton and maize grown in high CO 2 had a lower assimilation rate in ambient CO 2 compared to plants grown in normal ambient air. This difference was due to the reduction in RuBP carboxylase activity. Water use efficiency was doubled in both cotton and maize plants grown at high CO 2 in all nutrient treatments. However, this increase in water use efficiency was due primarily to reduced transpiration in some treatments and to increased assimilation in others. These data show that plant responses to elevated atmospheric partial pressure of CO 2 depend on complex of partially compensatory processes which are not readily predictable. 相似文献
13.
Summary After 10 min illumination of segments of bean ( Phaseolus vulgaris L.) or maize ( Zea mays L.) leaves in air with 14CO 2, the atmosphere was changed to CO 2-free O 2 or N 2 and conversion of photosynthetic products in the light was investigated. The experiments have shown that after the 14CO 2 assimilation period the bean leaves contain the pool of weakly fixed 14C (WF- 14C) which is converted into stable products during the subsequent period of illumination in CO 2-free N 2. In O 2 atmosphere the WF- 14C pool is initially the main source of CO 2 evolved. The marked decrease in radioactivity of sucrose and starch during illumination of bean leaves in O 2 atmosphere indicates that these compounds were also the source of CO 2 evolved in the light. The total amount of previously fixed 14C remained almost on the same level during illumination of maize leaves in N 2 as well as in O 2. However, oxygen changed the distribution of 14C in photosynthetic products, which is suggested to be the consequence of the photorespiration process in maize.Abbreviation WF- 14C
weakly fixed 14C 相似文献
14.
Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO 2 enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize ( Zea mays L.) and alfalfa ( Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000 ppm CO 2, the second at 700 ppm CO 2, and the third at ambient greenhouse CO 2 environment (i.e. 435 ppm). Three water stress treatments HWS (200 ml per week), MWS (400 ml per week), and CWS (600 ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO 2 concentrations. Stomatal lengths were higher in enriched CO 2 environments under water stress. At 700 ppm CO 2, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO 2 environments, stomatal densities decreased compared to ambient CO 2 environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO 2 environments, even though a slight increase was noticed. 相似文献
15.
Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat, and maize) are the largest source of human calories, and it is estimated that world cereal production must increase by 1.3% annually to 2025 to meet growing demand. Sustainable intensification of cereal production systems will require maintaining high yields while reducing environmental costs. We conducted a meta‐analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the global warming potential (GWP) of CH 4 and N 2O emissions from rice, wheat, and maize, when expressed per ton of grain (yield‐scaled GWP), is similar, and that the lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH 4 and N 2O emissions from rice (3757 kg CO 2 eq ha ?1 season ?1) was higher than wheat (662 kg CO 2 eq ha ?1 season ?1) and maize (1399 kg CO 2 eq ha ?1 season ?1). The yield‐scaled GWP of rice was about four times higher (657 kg CO 2 eq Mg ?1) than wheat (166 kg CO 2 eq Mg ?1) and maize (185 kg CO 2 eq Mg ?1). Across cereals, the lowest yield‐scaled GWP values were achieved at 92% of maximal yield and were about twice as high for rice (279 kg CO 2 eq Mg ?1) than wheat (102 kg CO 2 eq Mg ?1) or maize (140 kg CO 2 eq Mg ?1), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21%, and 1.06% of N applied was emitted as N 2O, respectively. In rice systems, there was no correlation between CH 4 emissions and N rate. In addition, when evaluating issues related to food security and environmental sustainability, other factors including cultural significance, the provisioning of ecosystem services, and human health and well‐being must also be considered. 相似文献
16.
The course of respiration of attached maize ( Zea mays L.) leaves was measured by infrared gas analysis of CO 2 efflux in the dark following illumination in atmospheres of 300 microliters of CO 2 per liter of air, CO 2-free air, and CO 2-free N 2 containing 400 microliters of O 2 per liter. CO 2 efflux from control leaves started 3 to 4 minutes after darkening, increased to a maximum after about 20 minutes, and returned to a steady minimum after 2 to 3 hours. Respiration was quantitatively related to prior illumination, independent of net CO 2 fixation in the light, and depressed by N 2. Light, but not air, was required to produce a substrate for respiration in the subsequent dark period; air was required for oxidation of the substrate to CO 2. The stimulation of respiration by prior illumination in maize leaves differs in its slower onset and greater duration from the postillumination burst of photorespiration. 相似文献
17.
BackgroundArchaea are important to the carbon and nitrogen cycles, but it remains uncertain how rising atmospheric carbon dioxide concentrations ([CO 2]) will influence the structure and function of soil archaeal communities. Methodology/Principal FindingsWe measured abundances of archaeal and bacterial 16S rRNA and amoA genes, phylogenies of archaeal 16S rRNA and amoA genes, concentrations of KCl-extractable soil ammonium and nitrite, and potential ammonia oxidation rates in rhizosphere soil samples from maize and soybean exposed to ambient (∼385 ppm) and elevated (550 ppm) [CO 2] in a replicated and field-based study. There was no influence of elevated [CO 2] on copy numbers of archaeal or bacterial 16S rRNA or amoA genes, archaeal community composition, KCl-extractable soil ammonium or nitrite, or potential ammonia oxidation rates for samples from maize, a model C 4 plant. Phylogenetic evidence indicated decreased relative abundance of crenarchaeal sequences in the rhizosphere of soybean, a model leguminous-C 3 plant, at elevated [CO 2], whereas quantitative PCR data indicated no changes in the absolute abundance of archaea. There were no changes in potential ammonia oxidation rates at elevated [CO 2] for soybean. Ammonia oxidation rates were lower in the rhizosphere of maize than soybean, likely because of lower soil pH and/or abundance of archaea. KCl-extractable ammonium and nitrite concentrations were lower at elevated than ambient [CO 2] for soybean. ConclusionPlant-driven shifts in soil biogeochemical processes in response to elevated [CO 2] affected archaeal community composition, but not copy numbers of archaeal genes, in the rhizosphere of soybean. The lack of a treatment effect for maize is consistent with the fact that the photosynthesis and productivity of maize are not stimulated by elevated [CO 2] in the absence of drought. 相似文献
18.
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO 2 in light in a rapid stream of CO 2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO 2 output in the dark. In maize, photorespiration is only 2% of that in tobacco. The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue. It was concluded that maize does not evolve appreciable quantities of CO2 in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities. 相似文献
19.
The net carbon incorporation in maize ( Zea mays) and tomato ( Lycopersicum esculentum) leaves was mainly the result of the carboxylation of ribulose 1,5-diphosphate. In both of these organisms synthesis of glycerate 3-phosphate was studied during short chase experiments (2 or 3 seconds in 14CO 2 then 8 to 27 seconds in unlabeled CO 2). Changes in the radioactivity in the individual carbon atoms of glycerate 3-phosphate, malate, and aspartate are consistent with the formation, in both leaves, of 2 molecules of glycerate 3-phosphate for each CO 2 molecule incorporated. The CO 2, before reacting with ribulose 1,5-diphosphate, is first incorporated in an intracellular CO 2 pool which has a different composition according to the species. This pool is constituted in tomato by volatile compounds (50 nanomoles per gram of fresh weight) more or less in equilibrium with atmospheric CO 2. In maize the pool consists of carbon atoms 4 of malate and aspartate (for at least 80% of the pool) and volatile compounds which correspond, in all, to 540 nanomoles per gram of fresh weight where atmospheric CO 2 enters through an irreversible reaction. 相似文献
20.
The net CO 2 assimilation by leaves of maize ( Zea mays L. cv. Adonis) plants subjected to slow or rapid dehydration decreased without changes in the total extractable activities of phospho enolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (ME). The phosphorylation state of PEPC extracted from leaves after 2–3 h of exposure to light was not affected by water deficit, either. Moreover, when plants which had been slowly dehydrated to a leaf relative water content of about 60% were rehydrated, the net CO 2 assimilation by leaves increased very rapidly without any changes in the activities of MDH, ME and PEPC or phosphorylation state of PEPC. The net CO 2-dependent O 2 evolution of a non-wilted leaf measured with an oxygen electrode decreased as CO 2 concentration increased and was totally inhibited when the CO 2 concentration was about 10%. Nevertheless, high CO 2 concentrations (5–10%) counteracted most of the inhibitory effect of water deficit that developed during a slow dehydration but only counteracted a little of the inhibitory effect that developed during a rapid dehydration. In contrast to what could be observed during a rapidly developing water deficit, inhibition of leaf photosynthesis by cis-abscisic acid could be alleviated by high CO 2 concentrations. These results indicate that the inhibition of leaf net CO 2 uptake brought about by water deficit is mainly due to stomatal closure when a maize plant is dehydrated slowly while it is mainly due to inhibition of non-stomatal processes when a plant is rapidly dehydrated. The photosynthetic apparatus of maize leaves appears to be as resistant to drought as that of C 3 plants. The non-stomatal inhibition observed in rapidly dehydrated leaves might be the result of either a down-regulation of the photosynthetic enzymes by changes in metabolite pool sizes or restricted plasmodesmatal transport between mesophyll and bundle-sheath cells. 相似文献
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