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1.
Van Donk E.; Faafeng B.A.; Hessen D.O.; Kallqvist T. 《Journal of plankton research》1993,15(7):761-769
Cells of the green alga Selenastrum capricomuxum were immobilizedin permeable alginate beads to prevent them from being grazedby zooplankton. Algae were able to grow in these beads and wereused as a new technique to estimate bioavailable phosphorus(P) released by zooplankton. P-limited algal cells were encapsulatedin alginate beads and used to measure P-release by Daphnia pulexfeeding on P-saturated and P-limited free algal cells. Daphnidsgrazing on P-saturated cells released 20 times more P availablefor the immobilized algae than animals grazing on P-limitedcells (0.06 versus 0.003 µg P mg1 Daphnia-DW h1). 相似文献
2.
The Interaction of Ultraviolet-B Radiation and Water Deficit in Two Arabidopsis thaliana Genotypes 总被引:2,自引:0,他引:2
Schmidt Anna-Mary; Ormrod Douglas P.; Livingston Nigel J.; Misra Santosh 《Annals of botany》2000,85(4):571-575
It has been demonstrated, in both herbaceous and woody species,that tissue hydration resulting from exposure to drought isless pronounced if plants are concurrently exposed to ultraviolet-Bradiation (UV-B). An explanation for the mechanisms underlyingthis phenomenon has been elusive. Arabidopsis thaliana(L.) Heynh.genotypes, defective in specific defences against UV-B exposure,may permit more insightful study of drought-UV-B interactionsthan is possible with genetically uniform plants. Arabidopsishas a rosette stature and has predominantly abaxial stomata.Thus, it is difficult to investigate its stomatal behaviourand gas exchange using conventional techniques and instrumentation.In this study, the relative abundance of13C and12C in leaf tissue(13C) was used as a means of determining water use efficiency(WUE) and the relative balance, at the site of carbon fixation,between CO2supply and demand. UV-B insensitive (L er) and sensitive(fah1)Arabidopsis genotypes were raised in a growth chamberand exposed to 6 kJ m-2 d-1UV-B irradiation and subjected todrought. In both genotypes, leaf desiccation was less pronouncedthan that of control plants that were subjected to drought butnot exposed to UV-B. The relatively low (more negative) leaf13C values (indicating low WUE), but high dry matter productionof the UV-B exposed plants suggest that their higher leaf watercontent was not primarily due to stomatal closure. We proposethat the mechanisms underlying the maintenance of higher leafwater content involved UV-B and water stress induced biosynthesisof stress proteins and compatible osmolytes. Copyright 2000Annals of Botany Company Arabidopsis thaliana, ultraviolet-B, water deficit, stable carbon isotopes, 13C, stomatal opening, tissue dehydration, dehydrin 相似文献
3.
The aim of this work was to test our hypothesis that pine needles protect themselves against UV-B radiation via anatomical changes in the epidermal layer. This could lead to needle growth reductions if large quantities of assimilates are allocated for the epidermal protective mechanisms at the expense of photosynthetic area. Effects of enhanced UV-B radiation on the needle ontogeny of mature Scots pines (Pinus sylvestris L.) were studied during the second season of a field experiment. Depending on the season and the time of the year (1996-1997), the enhanced UV-B irradiance varied from 0.92 to 5.09 kJ m-2 day-1 UV-BBE compared to 0.54-2.44 kJ m-2 day-1 UV-BBE of ambient radiation. It was found that UV-B treatment accelerated the early development of needles. In 6-day-old enhanced UV-B-treated needles, mesophyll and hypodermic cells were fully differentiated, whereas in ambient-treated needles, no lobate mesophyll cells were seen and hypodermic cells had not yet developed. In fully grown needles, no accelerated differentiation was seen, except that the epidermal cross-sectional area was smaller. The continuation of the experiment will show if such a significant difference only occurs irregularly and incidentally or if it is of consistent significance for needles. 相似文献
4.
Hofmann Rainer W.; Swinny Ewald E.; Bloor Stephen J.; Markham Kenneth R.; Ryan Ken G.; Campbell Bruce D.; Jordan Brian R.; Fountain David W. 《Annals of botany》2000,86(3):527-537
This study aimed to quantify and identify flavonoids involvedin the response of nine populations of white clover (Trifoliumrepens L.) to ultraviolet-B radiation (UV-B). Plants were grownfor 12 weeks in controlled environment rooms with or withoutsupplemental UV-B radiation of 13.3 kJ m-2d-1. Methanolwaterextractable flavonoids were quantified using high performanceliquid chromatography (HPLC). Two major peaks showed significantenhancement in the HPLC chromatogram in response to supplementalUV-B. The structures of the compounds responsible were identifiedby1H and13C nuclear magnetic resonance (NMR) spectroscopy tobe the flavonols quercetin-3-O-ß- D -xylopyranosyl-(1 2)-ß- D -galactopyranoside and kaempferol-3-O-ß-D -xylopyranosyl-(1 2)-ß- D -galactopyranoside. Withsupplemental UV-B, quercetin glycoside levels increased on averageby 200% while the kaempferol glycoside response was much smaller.Significant differences in flavonol accumulation were foundamong T. repens populations, both constitutively and in responseto UV-B. Stress-adapted populations displayed particularly highflavonol levels under UV-B. There was an inverse correlationbetween plant productivity and quercetin accumulation. Furthermore,higher quercetin accumulation under UV-B was correlated withtolerance against UV-B-induced growth reduction. In conclusion,within-species comparisons in T. repens lend support to a distinctrole for ortho -dihydroxylated flavonoids in the adaptationto UV-B stress and suggest particular advantages in this UV-B-inducedbiochemical adaptation for populations characterized by lowhabitat and plant productivity. Copyright 2000 Annals of BotanyCompany Ultraviolet-B, Trifolium repens, white clover, HPLC, NMR, flavonoids, flavonols, quercetin, kaempferol, biomass, genetic variation, intraspecific 相似文献
5.
The Response of Bean Plants to UV-B Radiation Under Different Irradiances of Background Visible Light 总被引:14,自引:1,他引:13
Plants of Phaseolus vulgaris L. (cv. Stella) were grown in controlledconditions under three different irradiances of visible lightwith or without UV-B (280320nm) radiation. The biologicallyeffective UV-B radiation (UV-BBE) was 6.17 kJ m2 d1,and simulated a c. 5% decrease in stratospheric ozone at 55.7?N,13.4?E. The photon flux densities of the photosyntheticallyactive radiation (PAR, 400700 nm) were either 700 µmolm21 (HL), 500, µmol m2 s1(ML) or 230 µmol m2 s1 PAR (LL). Under highlight (HL) conditions plus UV-B radiation, bean plants appearedmost resistant to the enhanced levels of UV-B radiation, andresponded only by increasing leaf thickness by c. 18%. A smallincrease in UV screening pigments was also observed. Both thelower irradiances (ML and LL) increased the sensitivity of theplants to UV-B radiation. Changes in leaf structure were alsoobserved. Photosystem II was inhibited under ML and LL togetherwith UV-B radiation, as determined by Chi fluorescence inductionand calculation of the fluorescence half-rise times. Leaf reflectivitymeasurements showed that the amount of PAR able to penetrateleaves of UV-B treated plants was reduced, and that a possiblecorrelation may exist between the reduced PAR levels, loss ofChi and lowered photosynthetic activity, especially for LL +UV-Bgrown plants, where surface reflection from leaves was highest.Changes in leaf chlorophyll content were mostly confined toplants grown under LL + UV-B, where a decrease of c. 20% wasfound. With regard to protective pigments (the carotenoids andUV screening pigments) plants subjected to different visiblelight conditions responded differently. Among the growth parametersmeasured, there was a substantial decrease in leaf area, particularlyunder LL + UV-B (c. 47% relative to controls), where leaf dryweight was also reduced by c. 25%. Key words: Chlorophyll fluorescence induction, bean, flavonoids, Phaseolus vulgaris, reflectance, UV-B radiation 相似文献
6.
Growth kinetic parameters of two planktonic desmid species under fluctuating phosphorus conditions in continuous-flow culture 总被引:1,自引:0,他引:1
Two planktonic desmid taxa, Staurastrum chaetoceras and Cosmariumabbreviatum var. planctonicum, were examined under pulsed phosphorus(P)-limited conditions in continuous culture. Two pulse regimeswere applied, i.e. 2.5 µM P twice a week and 10 µMP once every 2 weeks. Under both pulse regimes, S.chaetocerasshowed a higher maximum P uptake rate (Vmax) and affinity forP uptake (Vmax/affinity constant Km) than C.abbreviatum. Affinityfor P uptake in S.chaetoceras just before pulsing was higherthan shortly after pulsing, whereas C.abbreviatum did not showany significant difference. Cell densities and cellular P quotain S.chaetoceras and C.abbreviatum fluctuated in a comparableway, but fluctuations in C.abbreviatum were less pronouncedthan in S.chaetoceras. The mean cell volume of both specieswas greater under the bimonthly than under the biweekly pulseregime, and the lowest under continuous P-limited conditions.Competition between S.chaetoceras and C.abbreviatum under thebimonthly pulse regime was won by S.chaetoceras, but displacementwas less fast than under more frequent pulsing (equalling thesame total P supply). The above-mentioned results are discussedin relation to possible ecological strategies. 相似文献
7.
Zhen Yang Fanxiang Kong Xiaoli Shi Yang Yu Min Zhang 《Journal of applied phycology》2014,26(4):1669-1674
In this study, Microcystis aeruginosa was cultivated in a P-limited and P-replete culture medium and exposed to artificial UV-B radiation to investigate the interactive effect of UV-B exposure and phosphorus limitation on this harmful alga. After 15 days, both UV-B exposure and phosphorus limitation led to a significant decline in pigment content (phycocyanin and carotene) and photosynthetic activity (F v/F m and ETRmax), and the impact was most pronounced when the two conditions were combined. Due to the interactive effect, P-limited M. aeruginosa under UV-B exposure exhibited the lowest cell density compared to the other treatments. These results suggest that phosphorus limitation increases the stress of UV-B radiation in Microcystis. In other words, high-level UV-B radiation has higher growth inhibitory on Microcystis in P-limited lakes than in P-replete lakes. 相似文献
8.
Zoea I larvae of the brown shrimp Crangon crangon (Decapoda)were exposed to varying levels of UV radiation in a sunshinesimulator. Short-term exposures (08 h)were used to determine the highest UV dose with no significanteffect (NOEC; defined by limit of detection) and the lethaldose of 10 and 50% mortality (LD10 and LD50). Crangon crangonshowed a relatively high sensitivity to UVB radiation (NOEC= 10 kJ m2, LD10 = 15 kJ m2, LD50 = 24 kJ m2)compared to other crust-acean species. LD values (19971998)showed no adaptation to seasonal light regimes. Long-termexposures (010 days) were carried out to assessthe range where the law of reciprocity is valid.The larvae were exposed to UV levels of 0.2, 0.4 and 0.7 J m2for appropriate time intervals, always cumulating in a sublethaldose of 5 kJ m2 day1. Results reflect a possiblethreshold (0.20.4 J m2 UVB) in the effect of thedifferent UVB doses used; thus, a proportional relationshipof intensity and exposure time can only be shown at UVB levelsabove this threshold intensity. 相似文献
9.
The effects of some amino acid analogues (o-, m- and p-fluorophenylalanineand azetidine-2-carboxylic acid) on uptake of42K and 45Ca intothe roots and transport to the shoots of whole wheat and mungbean seedlings were measured. The effect of each analogue oneither K+ or Ca2+ movement could be placed into one of fourcategories: (1) No effect on either ion uptake or transport;(2) No effect on ion uptake, but a reduction in transport; (3)Similar reductions in ion uptake and transport; (4) A relativelygreater reduction in ion transport than in uptake. At leasttwo independent sites of protein involvement in ion movementwere required to account for all four types of analogue effectobserved; one site of protein involvement was probably at theplasmalemma of root cortex cells and the second site, involvinga protein that turned over more quickly, was within the stele.Some evidence was found that Ca2+ transport is a passive process.Light did not stimulate uptake. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis 相似文献
10.
Effects of Intermittent Desiccation on Nutrient Economy and Growth of Two Ecologically Contrasted Mosses 总被引:2,自引:0,他引:2
The mossesBrachythecium rutabulum (Hedw.) B., S. & G. andPseudoscleropodiumpurum (Hedw.) Fleisch. were cultivated for more than 50 d ina growth cabinet with or without weekly drying interludes of24 h. Some plants also received applications of a dilute NPKnutrient solution at weekly intervals. The continuously hydratedplants showed appreciably more biomass production than thosereceiving intermittent desiccation. Desiccation led to somebleaching of the green tissues inB. rutabulum but not inP. purumwhich appeared more desiccation-tolerant. NPK addition causeda further significant growth stimulation in continuously hydratedplants, but not in intermittently desiccatedB. rutabulum. Pseudoscleropodiumpurum showed NPK-induced growth stimulation even when intermittentlydesiccated. Net uptake of N was similar in desiccated and hydratedplants in both species. Considerable net uptake of P and K+occurredin continuously wetB. rutabulum , but uptake was much reducedin intermittently desiccated plants. Net uptake of P and K+byP.purum was similar in desiccated and hydrated samples. IntracellularK+, leaked from the cells during the desiccation treatment,was retained by cation exchange on the negatively charged cellwalls in both species. Levels of intracellular K+and Mg2+inthe new growth were maintained at the expense of the pool ofexchangeable cations. The growth stimulation and the net uptakeof nutrients under intermittent desiccation was greatest whenthe NPK application was made at the start of rehydration, possiblybecause of accentuated uptake in the early stages of recovery.The results support the hypothesis thatP. purum has a lowernutrient requirement thanB. rutabulum and highlight the importanceof continuous hydration for the latter's more productive plantlife strategy. The data also show that considerable new growthof bryophyte tissues is possible without additional nutrientabsorption. Brachythecium rutabulum ; Pseudoscleropodium purum ; mineral nutrition; desiccation; solute leakage; plant life strategies 相似文献
11.
BREEZE V. G.; WILD A.; HOPPER M. J.; JONES L. H. P. 《Journal of experimental botany》1984,35(8):1210-1221
The effect of phosphate concentration in flowing solution cultureat a range between 0.04 and 32 mmol m3 P on the growthof perennial ryegrass was studied in two experiments, each lastingabout 45 d after sowing. Phosphorus contents of seedlings wereaffected by the concentration in solution within about 5 d fromgermination, and dry weight differences were first observedat about 6 d after this. The rate of uptake of phosphate byseedlings was affected by the concentration in solution beforethe root fresh weight or root/emdash shoot ratio had changed.Young plants (less than 4 weeks old) were more sensitive tophosphate concentration in solution than older ones. In conditionsof high rate of growth, older plants required a solution concentrationbetween 0.1 and 0.4 mmol m3 P to achieve maximum potentialgrowth rate, whereas for plants of similar age but less dryweight, 0.04 mmol m3 P was adequate. Towards the endof the experimental period, plants growing at a nominal solutionconcentration of 0.04 mmol m3 P were able to obtain phosphatefrom a solution of about 0.01 mmol m3P. Phosphate toxicity was not observed, nor were there visual symptoms(other than reduced growth) of phosphate deficiency in plantswhose growth was limited by phosphate concentration in solution. Key words: Lolium perenne, Phosphate uptake 相似文献
12.
Ritchie Raymond J.; Trautman Donelle A.; Larkum A.W.D. 《Plant & cell physiology》1997,38(11):1232-1241
Phosphate uptake rates in Synechococcus R-2 in BG-11 media (anitrate-based medium, not phosphate limited) were measured usingcells grown semi-continuously and in continuous culture. Netuptake of phosphate is proportional to external concentration.Growing cells at pHo 10 have a net uptake rate of about 600pmol m2 s1 phosphate, but the isotopic flux for32P phosphate was about 4 nmol m2 s1. There appearsto be a constitutive over-capacity for phosphate uptake. TheKm and Vmax, of the saturable component were not significantlydifferent at pHo 7.5 and 10, hence the transport system probablyrecognizes both H2PO4and HPO24. The intracellularinorganic phosphate concentration is about 3 to 10 mol m3,but there is an intracellular polyphosphate store of about 400mol m3. Intracellular inorganic phosphate is 25 to 50kJ mol1 from electrochemical equilibrium in both thelight and dark and at pHo 7.5 and 10. Phosphate uptake is veryslow in the dark ( 100 pmol m2 s1) and is light-activated(pHo 7.51.3 nmol m2 s1, pHo 10600 pmol m2s1). Uptake has an irreversible requirement for Mg2+in the medium. Uptake in the light is strongly Na+-dependent.Phosphate uptake was negatively electrogenic (net negative chargetaken up when transporting phosphate) at pHo 7.5, but positivelyelectrogenic at pHo 10. This seems to exclude a sodium motiveforce driven mechanism. An ATP-driven phosphate uptake mechanismneeds to have a stoichiometry of one phosphate taken up perATP (1 PO4 in/ATP) to be thermodynamically possible under allthe conditions tested in the present study. (Received June 16, 1997; Accepted September 4, 1997) 相似文献
13.
Ethylene evolution and ABA and polyamine contents in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> during UV-B stress 总被引:2,自引:2,他引:0
V. Yu. Rakitin O. N. Prudnikova V. V. Karyagin T. Ya. Rakitina P. V. Vlasov T. A. Borisova G. V. Novikova I. E. Moshkov 《Russian Journal of Plant Physiology》2008,55(3):321-327
Changes in plant growth, membrane integrity, ethylene evolution, ABA content, and the content of free polyamines were examined in 14-day-old Arabidopsis thaliana (L.) Heynh., strain Columbia (Col-0) plants after a single UV-B irradiation with low (3 kJ/m2), moderate (6–9 kJ/m2), high (18 kJ/m2), and lethal (27 kJ/m2) doses. The UV-B treatment caused dose-dependent suppression of plant growth. One hour after irradiation, the membrane damage was evident from the increased leakage of electrolytes. The low-dose and moderate-dose irradiation caused a transient increase in evolution of ethylene and in the content of putrescine (spermidine and spermine precursor) with the peaks of these parameters attained at 5 and 24 h, respectively. The high-and lethaldose irradiation induced a smaller rise in ethylene evolution, with a slight trend to its decrease, especially, after the exposure to the lethal dose. The high and lethal doses of UV-B suppressed putrescine accumulation, depleted spermidine and spermine pools, and caused severe injuries and plant death. During the first day after irradiation, the ABA content increased in proportion to the irradiation dose. On the second day, the accumulation of ABA was observed in plants irradiated with moderate doses. The accumulation was arrested after a high-dose irradiation and was diminished by 45% after a lethal dose treatment. The results provide evidence for the involvement of ethylene, ABA, and polyamines in plant responses induced by UV-B irradiation. 相似文献
14.
Quantitative Estimation of Aluminium Toxicity in Cultured Tobacco Cells: Correlation between Aluminium Uptake and Growth Inhibition 总被引:3,自引:0,他引:3
Yamamoto Yoko; Rikiishi Sanae; Chang Yi-Chieh; Ono Kanji; Kasai Minobu; Matsumoto Hideaki 《Plant & cell physiology》1994,35(4):575-583
The relationship between aluminium (Al) uptake and growth inhibitionwas studied in tobacco cells (Nicotiana tabacum L. cv. Samsun;nonchlorophyllic cell line) in suspension culture. Cells atthe logarithmic phase of growth were treated with 100 µMA1C13 in modified Murashige-Skoog medium prepared without Piand EDTA (pH 4.0) for up to 21 h. After treatment, the inhibitionof cell growth by Al was estimated from the growth of the Al-treatedcells relative to that of the control cells during post-treatmentculture. Neither Al uptake nor the inhibition of the growthoccurred with less than a 10-h exposure but then both parametersincreased rapidly, reaching maximum values after an 18-h exposure.When cells were treated with AlCl3 at various concentrationsfor 18 h, the extent of growth inhibition was found to be afunction of the Al content of the cells. The dose-response curve(Al uptake versus growth inhibition) resembled the curve expectedfor "single-hit" kinetics. Extrapolation from the curve suggestedthat the uptake of 1 x 1011 Al atoms per cell is the minimumdose that inhibits cell growth. Cells of stationary phase wereresistant to Al and did not take up Al, an indication that theuptake of Al depends on the active growth of cells. Resultsof several types of experiment (hematoxylin staining, washingwith chelators, digestion of cell walls) indicated that Al wasincorporated inside the cells. Together, therefore, our resultssuggest that the amount of Al absorbed by the cells is a determiningfactor in the inhibition of growth by Al.
1Present address: Department of Biology, Faculty of Science,Hirosaki University Hirosaki, Aomori, 036 Japan 相似文献
15.
Astle, M. and Rubery, P. 1987. Carrier-mediated ABA uptake bysuspension-cultured Phaseolus coccineus L. cells: Stereospecificityand inhibition by ionones and ABA esters.J. exp. Bot.38: 150163. The substrate for the abscisic acid (ABA) carrier in Phaseoluscoccineus L. suspension-cultured cells is shown to be the (S)ABAenantiomer, Km = 1?0 mmol m3. The methyl (MeABA) andphenyl (PheABA) esters of ABA inhibit carrier-mediated uptakeof ABA with half-maximal inhibition achieved at about 7?0 mmolm3 and 10 mmol m3 respectively: with (S)MeABAthis value is decreased to about 2?0 mmol m3. There isno demethylation of radioactive MeABA by the cells during 5min incubations. Although MeABA reversibly inhibits the ABAcarrier, it is not a transport substrate: association of radioactiveMeABA with living cells is unaffected by non-radioactive MeABAor ABA and, by comparison with frozen-and-thawed cells, it isshown that the radioactivity remains extracellular. It is proposedthat MeABA binds to the carrier to form an abortive complexthat is not translocated. The terpenoid ABA analogue LAB 144143also inhibits carrier-mediated ABA uptake. At concentrationsup to about 20 mmol m3 - and ß-ionone specificallyinhibit the ABA carrier with the half-maximal effect at about0?6 mmol m3 ß-ionone. However, at higher iononeconcentrations, the uptake of ABA, indol-3-yl acetic acid andof 5,5-dimethyloxazolidine-2,4-dione (DMO) are all stimulated:this may reflect general permeabilization of the membrane toweak acids by ionone. Key words: Uptake carrier, abscisic acid, methyl and phenyl esters of ABA, ionone, Phaseolus coccineus L. suspension culture 相似文献
16.
Apparent uptake and transport of H232PO4 from nutrientsolutions containing 100 mmol m3 phosphate were characterizedasfunctions of time, concentration and pH in ryegrass seedlings.On a log/log plot, concentration versus uptake to the root resolvedintotwo linear phases, suggesting a change in uptake mechanism orefflux at the break. These results were compared with thosefor 32P uptake and transport in solutions containing Al rangingfrom 0185 mmol m3. Al addition depressed pH, butbecauseuptake of P was unaffected by pH below 50, noadjustments were attempted. Uptake time-courses revealed clearlythe usualinitial adsorption shoulder in the uptake curve, increasingwith Al concentration up to 37 mmol m3. Beyond about2 h, P uptaketo the root became linear, at rates increasingwith external Al concentration up to 37 mmol m3. Concentrationsof Al muchabove 100 mmol m3 were toxic. Al treatmentsdid not affect P transport to the shoot and absorbed Al wasconfined to the root.The quantities of P and Al taken up intothe root indicated storage in cortex cell vacuoles, lockingup significant amounts of P.Experiments with tillering plantsshowed similar characteristics to those with seedlings. Sequesteringof P with Al within the rootcortex cells was evident, particularlyin plants which had been grown in nutrient containing Al fromsoon after germination. Aland P solution chemistry is discussedin the context of this work and the consequences of effectson P uptake for the economy ofphosphate poor upland soils wereconsidered. Key words: Phosphate, aluminium, adsorption, uptake, Lolium perenne L 相似文献
17.
Five-month-old Cleopatra mandarin (Citrus reticulata Blanco)(CM) and Volkamer lemon (Citrus volkameriana Ten. and Pasq.)(VL) seedlings were grown in a glasshouse in 2·3-1 potsof Candler fine sand. Plants were irrigated with either non-saline(ECe = 0·23 dS m-1) or saline (6·13 dS m-1) waterusing 3:1 NaCl:CaCl2 solution over a 4-week period. A singleapplication of K15NO3 (19·64 atom % excess 15N) at 212mg N1-1, was substituted for a normal weekly fertilization after3 weeks and plants were harvested 7 d later. The transpirationrate, uptake of nitrogen, growth and nitrogen-use efficiency(NUE) on a dry weight basis (mg d. wt mg-1 N) of both specieswas reduced by salinity. Based on growth, water-use and chloride(Cl) accumulation in leaves, VL was more salt-sensitive thanCM, but 15N uptake was equally reduced by salinity in both species.Salinity reduced 15N uptake relatively more than shoot growthover the 7-d period, such that the 15NUE (mg d. wt µg-115N) of new shoot growth of both species increased. There wasno evidence of Cl antagonism of nitrate (NO3) uptake but totalplant 15NO3 uptake was positively correlated with whole planttranspiration in both species. Thus, it appears that reductionsin NO3 uptake are more strongly related to reduced water usethan to Cl antagonism from salt stress.Copyright 1993, 1999Academic Press Sodium, chloride, salinity, calcium, nitrate, 15NO3 uptake, nitrogen allocation, nitrogen-use efficiency, water use, Citrus reticulata, Citrus volkameriana 相似文献
18.
The marine diatoms Lauderia annulata and Synedra planctonicaharvested during exponential growth were exposed to differentdoses of u.v.-B (286, 439 and 710 J m2 d1) for2 days. Uptake of 15N-nitrate was estimated before, during andafter u.v.-B radiation over 2 days. Exposure to high levelsof u.v.-B (710 J m2 d1) caused irreversible damageat the second daily irradiance. Lauderia cells were less affectedby u.v.-B stress than Synedra cells. 15N-nitrate uptake wasreduced under u.v.-B irradiance but could be reactivated within1 day following exposure to a low dose (286 J m2 d1).Higher levels of u.v.-B radiation (710 J m2 d1)led to irreversible damage. The pattern of 15N-incorporationinto several amino acids of Lauderia varied after 2 days ofu.v.-B radiation. 15N enrichment of glutamine increased markedlyafter u.v.-B stress (717 J m2 d1) whereas I5Nexcess of aspartic acid was significantly reduced. Results arediscussed with reference to the u.v.-B damage of the nitratetransport system. 相似文献
19.
Vitamin B6 is essential for cellular functions and growth due to its involvement in important metabolic reactions. Humans and other mammals cannot synthesize vitamin B6 and thus must obtain this micronutrient from exogenous sources via intestinal absorption. The intestine, therefore, plays a central role in maintaining and regulating normal vitamin B6 homeostasis. Due to the water-soluble nature of vitamin B6 and the demonstration that transport of other water-soluble vitamins in intestinal epithelial cells involves specialized carrier-mediated mechanisms, we hypothesized that transport of vitamin B6 in these cells is also carrier mediated in nature. To test this hypothesis, we examined pyridoxine transport in a model system for human enterocytes, the human-derived intestinal epithelial Caco-2 cells. The results showed pyridoxine uptake to be 1) linear with time for up to 10 min of incubation and to occur with minimal metabolic alteration in the transported substrate, 2) temperature and energy dependent but Na+ independent, 3) pH dependent with higher uptake at acidic compared with alkaline pHs, 4) saturable as a function of concentration (at buffer pH 5.5 but not 7.4) with an apparent Michaelis-Menten constant (Km) of 11.99 ± 1.41 µM and a maximal velocity (Vmax) of 67.63 ± 3.87 pmol · mg protein-1 · 3 min-1, 5) inhibited by pyridoxine structural analogs (at buffer pH 5.5 but not 7.4) but not by unrelated compounds, and 6) inhibited in a competitive manner by amiloride with an apparent inhibitor constant (Ki) of 0.39 mM. We also examined the possible regulation of pyridoxine uptake by specific intracellular regulatory pathways. The results showed that whereas modulators of PKC, Ca+2/calmodulin (CaM), and nitric oxide (NO)-mediated pathways had no effect on pyridoxine uptake, modulators of PKA-mediated pathway were found to cause significant reduction in pyridoxine uptake. This reduction was mediated via a significant inhibition in the Vmax, but not the apparent Km, of the pyridoxine uptake process. These results demonstrate, for the first time, the involvement of a specialized carrier-mediated mechanism for pyridoxine uptake by intestinal epithelial cells. This system is pH dependent and amiloride sensitive and appears to be under the regulation of an intracellular PKA-mediated pathway. vitamin B6; intestinal transport; transport regulation; Caco-2 cell 相似文献
20.
Effects of light intensity and quality on the relative N and P requirement (the optimum N:P ratio) of marine planktonic algae 总被引:2,自引:0,他引:2
The relative requirement of N and P (the optimum N:P ratio)by Dunaliella tertiolecta, Phaeodactylum tricornutum, Prymnesiumparvum and Thalassiosira pseudonana was studied under variouslight intensities and spectra. The ratio was determined as theratio of the minimum cell N and P concentrations (q0N and q0pwhen either nutrient was limiting. The ratio varied widely amongspecies; under light-saturation for growth (116 µEin m2s1 it ranged from 11.8 in D. tertiolecta to 36.6 in P.tricornutum. The ratio appeared to be higher at a sub-saturatingintensity (24 µEin m2 s1 in all except P.tricornutum, mainly because of higher qoN with little changein qoP. In T. pseudonana QoP also increased, resulting in aninsignificant change in the ratio. The ratio varied little withinthe range of saturation intensity. Light quality affected qoNand qoP as well as the ratio, and the pattern of change variedfrom species to species. The optimum ratio of individual specieswas linearly correlated to their qoN except in P. tricornutum.qoN for all species showed a linear correlation with cell proteinconcentrations irrespective of light conditions. The changeof optimum N:P ratios in the three species thus appears to berelated to changes in cell protein contents. The ratio of carbohydratesto protein remained constant regardless of light intensity orquality and was higher in P-limited cultures. We conclude thatchanges in light regime can strongly influence algal nutrientrequirements and species interrelationships by altering theoptimum cellular N:P ratio. 相似文献