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1.
The gross and net O2 evolution together with O2 uptake, CO2assimilation, transpiration, shoot dark respiration, root respirationand ion uptake of a soybean plant were studied during 19 d whichincluded two periods of water stress. O2 uptake was measuredusing 18O2 as a tracer. Short term water stress induced immediateand lasting effects: (1) reduction of light interception bywilting, (2) limitation of the total reducing equivalent producedby the electron transport chain, (3) decrease of stomatal conductancereducing both losses of water and the entry of CO2 for assimilation,(4) relative stimulation of O2 uptake. The ratio of O2 uptaketo CO2 assimilation changed from 1.0 before stress to 1.4 forseveral days after. Root respiration was less affected by thestress than ion uptake and shoot gas exchanges. Key words: Photosynthesis, Photorespiration, Transpiration, Shoot and root respiration, Ion uptake, Water stress, Glycine max. L.  相似文献   

2.
A technique used for hydroponics was adapted to measure instantaneousroot water uptake from the soil for a leaf succulent CAM species,Agave deserti. Comparisons were made to previously modelledwater fluxes for A. deserti and to Encelia farinosa, a non-succulentC3species. Net CO2uptake and transpiration forA. deserti underwell-watered conditions occurred primarily at night whereasroot water uptake was relatively constant over 24 h. Leaf thicknessdecreased when transpiration commenced and then increased whenrecharge from the stem and soil occurred, consistent with previousmodels. A drought of 90 d eliminated net CO2uptake and transpirationand reduced the water content of leaves by 62%. Rewetting theentire root system for 7 d led to a full recovery of leaf waterstorage but only 56% of maximal net CO2uptake. Root water uptakewas maximal immediately after rewetting, which replenished rootwater content, and decreased to a steady rate by 14 d. Whenonly the distal 50% of the root system was rewetted, the timefor net CO2uptake and leaf water storage to recover increased,but by 30 d gas exchange and leaf water storage were similarto 100% rewetting. Rewetting 10 or 20% of the root system resultedin much less water uptake; these plants did not recover leafwater storage or gas exchange by 30 d after rewetting. A redundancyin the root system of A. deserti apparently exists for dailywater uptake requirements under wet conditions but the entireroot system is required for rapid recovery from drought.Copyright1999 Annals of Botany Company Agave deserti Engelm., desert, drought, gas exchange, rewetting, roots, succulent, water uptake.  相似文献   

3.
Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 4–0 parts 10–6 NO2, and0.1, 0.2, and 0.4 parts 10–6 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 10–6 NO2 and 0.1 parts 10–6 O3.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 10–6 NO2 and 0.1 parts 10–6 O3. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O3 exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O3 with NO2 significantlydecreased the assimilation of NO2 by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 10–6NO2 and 0–2 parts 10–6 O3. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O3 exposure. Key words: NO2, O3, Phaseolus vulgaris, Growth, Sugars, Root respiration  相似文献   

4.
Correlation of Water Uptake and Root Exudation   总被引:1,自引:0,他引:1  
ERREDE  L. A. 《Annals of botany》1983,52(3):373-380
Water uptake in systems consisting of a potted plant and twoembedded reservoirs were monitored over test intervals thatlasted more than a year. One reservoir was fitted with a microporousbottom that allowed water uptake to occur only after permeationthrough the thin microporous barrier, whereas the other wasfitted with a microporous bottom that allowed water to reachthe roots directly. In each study the patterns for water uptake,F1 and F2, from the alternate sources fluctuated in synchrony,such that the ratio F1/F2 on any given day was essentially constant.It was concluded that the cyclic actions that control wateruptake and water permeation (i.e. root exudation of bio-surfactants)occur simultaneously or sequentially within a short time period.Both responses, therefore, are appropriate means for studyingplant-water relationships. water uptake, autonomic cycle, synchrony, root growth, root exudates, rhizosphere, artificial membranes, permeability  相似文献   

5.
Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown for 71 d in flowing nutrient solutions containingN as 10 mmol m–3 NH4NO3, under artificial illumination,with shoots at 20/15°C day/night temperatures and root temperaturereduced decrementally from 20 to 5°C. Root temperatureswere then changed to 3, 7, 9, 11, 13, 17 or 25°C, and theacquisition of N by N2 fixation, NH4+ and NO3 uptakewas measured over 14 d. Shoot specific growth rates (d. wt)doubled with increasing temperature between 7 and 17°C,whilst root specific growth rates showed little response; shoot:root ratios increased with root temperature, and over time at11°C. Net uptake of total N per plant (N2 fixation + NH4++ NO3) over 14 d increased three-fold between 3 and 17°C.The proportion contributed by N2 fixation decreased with increasingtemperature from 51% at 5°C to 18% at 25°C. Uptake ofNH4+ as a proportion of NH4+ + NO3 uptake over 14 d variedlittle (55–62%) with root temperature between 3 and 25°C,although it increased with time at most temperatures. Mean ratesof total N uptake per unit shoot f. wt over 14 d changed littlebetween 9 and 25°C, but decreased progressively with temperaturebelow 9°C, due to the decline in the rates of NH4+ and NO3uptake, even though N2 fixation increased. The results suggestthat N2 fixation in the presence of sustained low concentrationsof NH4+ and NO4 is less sensitive to low root temperaturethan are either NH4+ or NO3 uptake systems. White clover, Trifolium repens L. cv. Huia, root temperature, nitrogen fixation, ammonium, nitrate  相似文献   

6.
The CO2-, H2O- and 16O2/18O2 isotopic-gas exchange and the fluorescencequenching by attached leaves of the wild-type and of the phytochrome-deficienttomato aurea mutant was compared in relation to water stressand the photon fluence rate. The chlorophyll content of aurealeaves was reduced and the ultra-structure of the chloroplastswas altered. Nevertheless, the maximum rate of net CO2 uptakein air by the yellow-green leaves of the aurea mutant was similarto that by the dark-green wild-type leaves. However, less O2was produced by the leaves of the aurea mutant than by leavesof the wild-type. This result indicates a reduced rate of photosyntheticelectron flux in aurea mutant leaves. No difference in bothphotochemical and non-photochemical fluorescence quenching wasfound between wild-type and aurea mutant leaves. Water stresswas correlated with a reversible decrease in the rates of bothnet CO2 uptake and transpiration by wild-type and aurea mutantleaves. The rate of gross 16O2 evolution by both wild-type andaurea mutant leaves was fairly unaffected by water stress. Thisresult shows that in both wild-type and aurea leaves, the photochemicalprocesses are highly resistant to water stress. The rate ofgross 18O2 uptake by wild-type leaves increased during waterstress when the photon fluence rate was high. Under the sameconditions, the rate of gross 18O2 uptake by aurea mutant leavesremained unchanged. The physiological significane of this differencewith respect to the (presumed) importance of oxygen reductionin photoprotection is discussed. Key words: Water stress, gas exchange, fluorescence quenching, Lycopersicon esculentum, mutant (tomato, aurea), energy dissipation  相似文献   

7.
The xylem exudation of detopped 7-d-old seedlings of Zea maysL. doubled when KCI was present in the root medium comparedto seedlings maintained on water. It was further enhanced whenKCI was replaced by nitrogen compounds such as nitrate, ammoniumand glutamine. The role of the nitrate assimilation pathwayon the enhancement of xylem exudation rate was investigatedusing tungstate, an inhibitor of nitrate reductase (NR) activity,and phosphinothricin or methionine sulphoximine, inhibitorsof glutamine synthetase (GS) activity. The sap levels of NO3,NH4+, glutamine, and asparagine was used to ascertain the invivo inhibition of both enzymes. The tungstate effects werealso checked by measuring leaf in vitro NA activity and NR proteincontent. Xylem exudation rate of detopped seedlings fed withKNO3 decreased when the nitrate assimilation pathway was blockedeither at the NR or at GS sites. This decrease was preventedwhen urea (acting as NH4+ supply) was given simultaneously withtungstate. KNO3 does not act directly on exudation, but throughthe involvement of NH4+. The involvement of glutamine was alsoshown since GS inhibition resulted in a cancellation of theenhancing effect of KNO3 on exudation. As change of exudationrate was not linked to change in sap osmolarity, it is assumedthat the assimilation chain could modify root water conductance.The role of glutamine was discussed. Key words: Exudation, maize, nitrate, conductance, NR, GS  相似文献   

8.
Relationships between nitrate (NO-3) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (15–30%) with increased applied NO-3concentrationfrom 0 to 5–20 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH+4) or 5 mMNO-3but NH+4did not affect the rate of mobilization of seedreserves. Chloride (Cl-) was similar to NO-3in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO-3or Cl-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH+4did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO-3or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO-3did not affect total seedling water or residualseed water content until 10–14 DAS. The effects of seedN and NO-3on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO-3is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization  相似文献   

9.
The effects of root age, temperature, and soil water statuson root hydraulic conductivity (LP) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, LP at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 10–7m s–1 MPa–1 for F. acanthodes and 5.2 ? 10–7m s–1 MPa–1 for O.ficus-indica at 11 to 17 weeksof age; LP subsequently declined with increasing root age forboth species. LP was maximal at a temperature of about 10 ?Cfor the youngest roots (1–3 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), LP increased with temperature from 0?C to 50 ?C, with a Q10 of 1.3 between 20 ?C and 30 ?C. At asoil water potential (soil) of –0.016 MPa, root LP wasindependent of the direction of water flow for both species.Depending on root age, LP declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as soil was reduced from–0.016 to –1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow  相似文献   

10.
研究了外源一氧化氮(nitric oxide, NO)对盐胁迫下黑麦草幼苗根生长和氧化损伤的影响。结果表明,5~100 μmol·L-1的NO供体硝普钠(sodium nitroprusside, SNP)处理显著减轻100mmol·L-1 NaCl胁迫对黑麦草幼苗根生长的抑制效应,其中50 μmol·L-1的SNP效果最明显,150 μmol·L-1以上的SNP处理则抑制根的生长。50 μmol·L-1 SNP处理提高了100 mmol·L-1 NaCl胁迫下黑麦草幼苗根组织中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)及液泡膜上H+-ATP酶(H+-ATPase)和H+焦磷酸酶(H+-PPase)的活性,使谷胱甘肽(GSH)、抗坏血酸(ASA)和脯氨酸含量及K+/Na+、(Spd+Spm)/Put比值和根干物质积累量增加,超氧阴离子(O-2)、H2O2和丙二醛(MDA)含量降低,而1mmol·L-1NO清除剂PTIO和1 μmol·L-1 NaNO2处理(对照)的效果则不明显。由此推断,NO通过提高根组织的抗氧化和渗透调节能力,促进根系对K+的选择性吸收及Put向Spd和Spm的转化,降低Na+的吸收并加强在液泡中的区隔化缓解盐胁迫对黑麦草幼苗根生长的抑制和膜脂过氧化损伤。  相似文献   

11.
Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown as simulated swards for 71 d in flowing nutrientsolutions with roots at 11 C and shoots at 20/15 C, day/night,under natural illumination. Root temperatures were then changedto 3, 5, 7, 11, 13, 17 or 25 C and the total N2, fixation over21 d was measured in the absence of a supply mineral N. Alltreatments were subsequently supplied with 10 mmol m–2NO2 in the flowing solutions for 14 d, and the relativeuptake of N by N2, fixation and NO3 uptake was compared.Net uptake of K+ was measured on a daily basis. Root temperature had little effect on root d. wt over the 35-dexperimental period, but shoot d. wt increased by a factor of3.5 between 3 and 25 C, with the sharpest increase occurringat 7–11 C. Shoot: root d. wt ratios increased from 25to 68 with increasing temperature at 7–25 C. N2-fixationper plant (in the absence of NO2 ) increased with roottemperature at 3–13C, but showed little change above13 C. The ratios of N2 fixation: NO2 uptake over 14d (mol N: mol N) were 0.47–0.77 at 3–7 C, 092–154at 11–17 C, and 046 at 25 C, reflecting the dominanceof NO3 uptake over N2 fixation at extremes of high andlow root temperature. The total uptake of N varied only slightlyat 11–25 –C (095–110 mmol N plant–1),the decline in N2 fixation as root temperature increased above11 C was compensated for by the increase in NO 3 uptake.The % N in shoot dry matter declined with decreasing root temperature,from 32% at 13 C to 15% at 3 C. In contrast, concentrationsof N expressed on a shoot water content basis showed a modestdecrease with increasing temperature, from 345 mol m–3at 3 C to 290 mol m–3 at 25 C. Trifolium repens L, white clover, root temperature, N2 fixation, potassium uptake, nitrate uptake, flowing solution culture  相似文献   

12.
采用水培方法,研究了外源一氧化氮(NO)供体硝普钠(SNP)对300 μmol·L-1 LaCl3胁迫下黑麦草幼苗生长和根系活性氧代谢的影响。结果表明:在LaCl3胁迫下,喷施50 μmol·L-1 SNP能够抑制镧(La)从黑麦草根系向地上部的转运,缓解La对幼苗生长的抑制作用;提高幼苗根系超氧化物歧化酶和抗坏血酸过氧化物酶活性,降低过氧化物酶活性及谷胱甘肽、脯氨酸、H2O2、丙二醛含量、超氧阴离子产生速率和质膜相对透性,对过氧化氢酶活性和抗坏血酸含量无显著影响。表明NO可通过活性氧代谢的调节,缓解高浓度La胁迫对黑麦草幼苗生长的抑制作用。  相似文献   

13.
Barley plants (Hordewn vulgare L. cv. Atem) were grown fromseed for 28 d in flowing solution culture, during which timeroot temperature was lowered decrementally to 5?C. Plants werethen subjected to root temperatures of 3, 5, 7, 9, 11, 13, 17or 25 ?C, with common air temperature of 25/15 ?C (day/night).Changes in growth, plant total N, and NO3 levels, andnet uptake of NH4+ and NO3 from a maintained concentrationof 10 mmol m–3 NH4NO3 were measured over 14 d. Dry matterproduction increased 6-fold with increasing root temperaturebetween 3–25 ?C. The growth response was biphasic followingan increase in root temperature. Phase I, lasting about 5 d,was characterized by high root specific growth rates relativeto those of the shoot, particularly on a fresh weight basis.During Phase I the shoot dry weight specific growth rates wereinversely related to root temperature between 3–13 ?C.Phase 2, from 5–14 d, was characterized by the approachtowards, and/or attainment of, balanced exponential growth betweenshoots and roots. Concentrations of total N in plant dry matterincreased with root temperature between 3–25 ?C, moreso in the shoots than roots and most acutely in the youngestfully expanded leaf (2?l–6?9% N). When N contents wereexpressed on a tissue fresh weight basis the variation withtemperature lessened and the highest concentration in the shootwas at 11 ?C. Uptake of N increased with root temperature, andat all temperatures uptake of NH4+, exceeded that of NO3,irrespective of time. The proportions of total N uptake over14 d absorbed in the form of NH4+ were (%): 86, 91, 75, 77,76, 73, 77, and 80, respectively, at 3, 5, 7, 9, Il, 13, 17,and 25 ?C. At all temperatures the preference for NH4+ overNO3 uptake increased with time. An inverse relationshipbetween root temperature (3–11 ?C) and the uptake of NH4+as a proportion of total N uptake was apparent during PhaseI. The possible mechanisms by which root temperature limitsgrowth and influences N uptake are discussed. Key words: Hordeum vulgare, root temperature, ammonium, nitrate, ion uptake, growth rate  相似文献   

14.
根系具有高度的形态和生理功能异质性, 在森林生态系统碳和养分循环中起重要作用。根系分枝的顺序构成根序,是根系最基本的构型特征, 根序代表根系不同的发育阶段。然而, 目前直接测定不同根序细根生理功能的研究很少。以落叶松(Larix gmelinii)和水曲柳(Fraxinus mandshurica)的细根为研究对象, 使用气相氧电极测定不同根序细根的呼吸速率, 探讨根系呼吸速率与其形态、结构和组织氮浓度的关系。结果表明: 落叶松和水曲柳细根的直径、根长和维管束直径均随着根序的增加(1–5级)而增加, 而比根长、组织氮浓度和呼吸速率随着根序的增加而降低, 各根序之间差异显著(P < 0.05); 1级根比根长最大、皮层组织发达、组织氮浓度最高且呼吸速率也最高, 其呼吸速率分别为17.57 nmolO2·g–1·s–1(落叶松)和18.80 nmolO2·g–1·s–1(水曲柳), 比5级根分别高148%(落叶松)和124%(水曲柳); 并且, 落叶松根的呼吸速率几乎有96%与根系组织氮浓度相关, 而水曲柳根的呼吸速率则有89%与根系组织氮浓度相关。上述结果说明, 细根的形态和生理功能异质性是紧密相连的, 低级根的形态、结构决定其功能是吸收养分和水, 而高级根的形态、结构决定其功能是运输和贮存养分。  相似文献   

15.
外源亚精胺可缓解荇菜镉毒害   总被引:2,自引:0,他引:2  
研究了外施浓度为0.01 mmol.L-1的亚精胺(Spd)对不同浓度镉(Cd2+)胁迫下荇菜(Nymphoides peltatum)叶片的叶绿体结构、叶绿素含量、可溶性蛋白含量、超氧阴离子(O2-.)产生速率和丙二醛(MDA)含量, 以及保护酶——超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT) 活性的影响。结果表明, (1) Cd2+胁迫可使荇菜细胞的叶绿体结构遭到破坏,叶绿素含量减少。外施Spd则可有效地保护叶绿体结构, 减少叶绿素的流失。(2) 在单一Cd2+处理条件下, 随着Cd2+浓度的升高, 叶绿素含量呈现先升后降的趋势, 可溶性蛋白含量则逐渐下降。外源Spd处理显著提高了二者的含量, 并延缓了它们的下降速度。(3) 在单一Cd2+处理条件下, SOD、POD和CAT活性分别在Cd2+浓度为1、 1和2 mg.L-1时达到最高值, 而后随着Cd2+浓度的增加其活性逐渐下降。外施Spd使它们的活性分别提高了5.8%、37.5%和3.3%, 并降低了O2-.产生速率和MDA的含量。上述结果表明, Spd增强了荇菜对Cd2+毒害的抗性, 并在一定程度上缓解了Cd2+对荇菜的毒害。  相似文献   

16.
This paper reports the effects of low O2 concentration (0–01,0–055, and 0.115mol m–3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (0–2mm) than in the expanding tissues (2–4 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (4–12 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (0–2mm) K + /Na+ selectivity was already reduced at 0.115 mol m–3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m–3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues  相似文献   

17.
COUTTS  M. P. 《Annals of botany》1982,49(5):661-668
Sitka spruce[Picea sitchensis(Bong.) Carr] seedlings were subjectedto varying degrees of root damage in a growth room, rangingfrom careful transplanting to exposure of the root system toair for up to 3 h. After replanting, transpiration (E), leafwater potential (1) and growth of the shoot and root were measuredand observations made on plant survival. Some plants in the root exposure treatments died 20–85days after planting. In plants which eventually died, E wasdepressed directly after treatment, but 1 showed a variableresponse. In some plants 1 decreased from —8·0x 105 to —30 x 105 Pa after only 10 days but in othersthere was little change in 1 for 50 days. In spite of the maintenanceof a high water potential in some of the latter plants for longperiods, no root or shoot growth occurred. In plants which lived, the root damage reduced root and shootgrowth relative to untreated controls, and most treatments stronglydepressed E but had little or no effect on 1. The changes of E and 1 in treated plants suggest that the suppressionof E was often independent of 1 although water stress eventuallydeveloped in some of the severely treated plants. Sitka spruce, Picea sitchensis (Bong.)Carr, water relations, root damage, transpiration, leaf water potential  相似文献   

18.
Deepwater rice (Oryza sativa L.) responds to partial submergenceby rapid elongation of the internodes. The elongation of intactplants was measured during 7 days of submergence using angulartransducers. Growth rates began to increase within 3 to 4 hupon submergence and peaked after 3 days; they were higher inthe light than in the dark. The composition of the gas phasein the internodal air spaces was analyzed at different timesafter partial submergence. In the light, the O2 concentrationsin internal gas compartments of intact plants dropped initially,but recovered largely within 90 min. During longer periods ofsubmergence, the internal O2 concentration followed a diurnalpattern with O2 levels being lower during the night than duringthe day. An O2 gradient was found from the apical parts of theplant near the water surface to the basal parts of the shoot. Concentrations of CO2 changed with a pattern inverse to thatof the O2concentrations. The level of ethylene in the internodallacunae increased upon submergence and reached 1µl-liter–1after 72 h. It was higher at the end of the dark period thanduring the day. The gas exchange of the submerged parts of the plant seems todepend mainly on mass flow of air from the atmosphere to theroot system. Mass flow through this pathway was determined atdifferent pressure gradients and was compared to the intakeof air into plants as established in earlier investigations.A significant decrease in gas flow resistance found during 7days of submergence may constitute a long-term adaptation toflooding. (Received August 30, 1988; Accepted October 25, 1988)  相似文献   

19.
In a study on metabolic consumption of photosynthetic electronsand dissipation of excess light energy under water stress, O2and CO2 gas exchange was measured by mass spectrometry in tomatoplants using 18O2 and 13CO2. Under water stress, gross O2 evolution(EO), gross O2 uptake (UO), net CO2 uptake (PN), gross CO2 uptake(TPS), and gross CO2 evolution (EC) declined. The ratio PN/EOfell during stress, while the ratios UO/EO and EC/TPS rose.Mitochondrial respiration in the light, which can be measureddirectly by 12CO2 evolution during 13CO2 uptake at 3000 µll–1 13CO2, is small in relation to gross CO2 evolutionand CO2 release from the glycolate pathway. It is concludedthat PSII, the Calvin cycle and mitochondrial respiration aredown-regulated under water stress. The percentages of photosyntheticelectrons dissipated by CO2 assimilation, photorespiration andthe Mehler reaction were calculated: in control leaves morethan 50 % of the electrons were consumed in CO2 assimilation,23 % in photorespiration and 13 % in the Mehler reaction. Undersevere stress the percentages of electrons dissipated by CO2assimilation and the Mehler reaction declined while the percentageof electrons used in photorespiration doubled. The consumptionof electrons in photorespiration may reduce the likelihood ofdamage during water deficit.  相似文献   

20.
The cytoplasmic [MgATP]/[ATP]free ratios, free Mg2+ concentrations,and phosphorylation potentials in mung bean [Vigna mungo (L.)Hepper] root tip cells were investigated by 31P nuclear magneticresonance spectroscopy. 31P NMR spectra show well defined peaksdue to G6P, cytoplasmic Pi, vacuolar Pi, ATP, UDP-glucose andnicotinamide adenine nucleotides. The concentrations of phosphorusmetabolites were determined from quantitative 31P NMR spectra.The [MgATP]/[ATP]free ratio was 9.45. Accordingly, about 90%of the cytoplasmic ATP was complexed to Mg2+. Utilizing thedissociation constant (Kd) determined for MgATP, the cytoplasmicfree Mg2+ concentration was estimated to be 0.4mM. The NMR-derivedphosphorylation potential, [ATP]/([ADP][Pi]), was 960 M-1. Thesodium azide treatment decreased the [ATP]/[ADP] ratio and thephosphorylation potential, and increased the [Mg2+]free. Metabolicinhibition may have been enhanced by an increase in [Mg2+freeand a decrease in the free energy change for ATP hydrolysis,which resulted due to a decrease in the ATP level. 1Present address: National Food Research Institute, TsukubaCity, Ibaraki 305, Japan. (Received February 8, 1988; Accepted June 1, 1988)  相似文献   

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