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1.
Nuclear volumes and cell areas were determined for seven regionsof the meristem of roots of Zea mays. Roots were fixed in 10per cent neutral buffered formalin, in 3 per cent glutaraldehydeor in acetic acid/alcohol; they were prepared as sections oralls were teased apart. Mean volumes of interphase nuclei weresimilar in all regions of the root except the vascular tissueof the stele. Mean nuclear volumes and the overall range ofvolumes were similar in sub-populations of cells with differentproportions of G1, S and G2 cells, e.g. in row I of root capinitials, whose cells lack a G1 phase, and in quiescent centrecells, which are mainly in G1. Nuclear volume does not appearto be closely correlated with DNA content. Nuclear volumes covereda 6 to 12-fold range within a meristem and even within specificregions, in which cells are part of the same cell lineages,there was a 4- to 9-fold range. Nuclear volumes were comparedin sister cells in rows I and II of the root cap initials. In10 per cent of the pairs, sister nuclei had identical volumes;the other pain had different volumes and mean difference was68 µm3. Mechanisms by which this variability could begenerated are discussed, particularly asymmetry, at mitoses,of factors that regulate nuclear growth. Zea mays L., nuclear volume, cell size, root mcristem, DNA content, mitosis 相似文献
2.
Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s1 m2 photon flux density in a16 h photoperiod. The rate of CO2 output per fruit increasedquickly from 0.005 to 0.018 mg CO2 min1 during fruitelongation and subsequently more slowly to 0.030 mg CO2 min1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO2 g1 min1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO2 g1 min1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g1 d. wt day1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg1 d. wt day1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg1 nitrogen day1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g1growth (equivalent to a conversion efficiency, YG, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration 相似文献
3.
The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 714-dayperiod of vegetative growth varied between 10 and 17 mg CO2g1 (dry weight) h1. This mean value consistedof two components: a specific root respiration rate of 69mg CO2 g1 h1 and a specific nodule respirationrate of 2246 mg CO2 g1 h1. Nodule respirationaccounted for 4270 per cent of nodulated root respiration;nodule weight accounted for 1240 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 2030per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation 相似文献
4.
KEYS A. J.; SAMPAIO E. V. S. B.; CORNELIUS M. J.; BIRD I. F. 《Journal of experimental botany》1977,28(3):525-533
Wheat plants were grown in a controlled environment with daytemperatures of 18 ?C and with 500 µ Einsteins m281 of photosynthetically active radiation for 16 h. Beforeanthesis and 2 to 3 weeks after, rates of net photosynthesiswere measured for leaves in 2 or 21% O2 containing 350 vpm CO2at 13, 18, 23, and 28 ?C and with 500 µEinsteins m2s1 of photosynthetically active radiation. Also, underthe same conditions of light intensity and temperature, therates of efflux of CO2 into CO2-free air were measured and,for mature flag leaves 3 to 4 weeks after anthesis, gross andnet photosynthesis from air containing 320 vpm 14CO2 of specificactivity 39?7 nCi µmol1. When the O2 concentration was decreased from 21 to 2% (v/v)the rate of net photosynthesis increased by 32 per cent at thelowest temperature and 54 per cent at the highest temperature.Efflux of CO2 into CO2-free air ranged from 38 per cent of netphotosynthesis at 13 ?C to 86 per cent at 28 ?C. Gross photosynthesis,measured by the 14C assimilated during 40 s, was greater thannet photosynthesis by some 10 per cent at 13 ?C and 17 per centat 28 ?C. These data indicate that photorespiration was relativelygreater at higher temperatures. 相似文献
5.
The Interdependence of Tillers in Lolium multiflorum Lam.--a Quantitative Assessment 总被引:5,自引:0,他引:5
Experiments were made to determine the extent of reciprocaltransfer of products (derived from the assimilation of 14CO2)between various parts of the young vegetative grass plant (Loliummultiflorum Lam.). When individual laminae on different tillerswere supplied with 14CO2, 4764 per cent of the fixedcarbon was exported after 24 h. The principal sinks were theroot system and the shoot or tiller to which the fed leaf wasattached. Other tillers also received significant quantitiesof radiocarbon. When whole tillers were supplied with 14CO2the percentage of fixed radiocarbon exported within 24 h rangedfrom 1431 per cent. Of this, 5074 per cent wasrecovered from the root system (except in the case of exportfrom the youngest tiller) but exchange of material between tillersalso occurred.A reciprocity diagram is presented and it is concludedthat despite the magnitude of the exchange no tiller showedan over-all net gain or loss. The main shoot and the tillersdiffered in the extent of their carbon exchange and in theirdegree of independence. The oldest daughter tiller of the mainshoot was the most independent and the main shoot most interdependent. 相似文献
6.
Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth 总被引:1,自引:0,他引:1
In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO2 g1h1, of which nodule growth and maintenanceaccounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule growth and maintenancerespiration by 6070 per cent, and rate of N2 fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N2,fixation: 9.1 µmol CO2 µmol1N2. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO2 µmol1 C2H4;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N2 fixation increased with plant growthfrom 1 to 22 µmol N2 per plant h1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.52.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.51 h at a rate about 50 per cent of that initiallyobserved. Regression of peak rate of ethyleneproduction on rate of N2 fixation indicated a value of 2.9 µmolC2H4 µmol1 N2, for rates of N2 fixation between1 and 22 µmol N2 per plant h1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN2 fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N2, fixation, nitrogenase 相似文献
7.
Lung endothelial cell proliferation with decreased shear stress is mediated by reactive oxygen species 总被引:4,自引:0,他引:4
Milovanova T Chatterjee S Manevich Y Kotelnikova I Debolt K Madesh M Moore JS Fisher AB 《American journal of physiology. Cell physiology》2006,290(1):C66-C76
Acute cessation of flow (ischemia) leads to depolarization of the endothelial cell (EC) membrane mediated by KATP channels and followed by production of reactive oxygen species (ROS) from NADPH oxidase. We postulated that ROS are a signal for initiating EC proliferation associated with the loss of shear stress. Flow cytometry was used to identify proliferating CD31-positive pulmonary microvascular endothelial cells (mPMVECs) from wild-type, Kir6.2/, and gp91phox/ mice. mPMVECs were labeled with PKH26 and cultured in artificial capillaries for 72 h at 5 dyn/cm2 (flow adaptation), followed by 24 h of stop flow or continued flow. ROS production during the first hour of ischemia was markedly diminished compared with wild-type mice in both types of gene-targeted mPMVECs. Cell proliferation was defined as the proliferation index (PI). After 72 h of flow, >98% of PKH26-labeled wild-type mPMVECs were at a single peak (PI 1.0) and the proportion of cells in the S+G2/M phases were at 5.8% on the basis of cell cycle analysis. With ischemia (24 h), PI increased to 2.5 and the ratio of cells in S+G2/M phases were at 35%. Catalase, diphenyleneiodonium, and cromakalim markedly inhibited ROS production and cell proliferation in flow-adapted wild-type mPMVECs. Significant effects of ischemia were not observed in Kir6.2/ and gp91phox/ cells. ANG II activation of NADPH oxidase was unaffected by KATP gene deletion. Thus loss of shear stress in flow-adapted mPMVECs results in cell division associated with ROS generated by NADPH oxidase. This effect requires a functioning cell membrane KATP channel. cell signaling; ischemia; mechanotransduction; KATP channels; NADPH oxidase 相似文献
8.
Respiratory Efflux of Carbon Dioxide from Mature and Meristematic Tissue of Uniculm Barley During Eighty Hours of Continuous Darkness 总被引:1,自引:0,他引:1
Young plants of uniculm barley were grown singly in pots ina growth room at 23/21 °C, and an irradiance of 655 µEm2s1 during each 12 h photoperiod. At the fifth leaf stage,they were subjected to 80 h of continuous darkness during whichthe rates of CO2 efflux of vegetative shoot meristems, and maturefully expanded leaves, were separately monitored. Respiratoryefflux from the meristematic tissue was initially high, 1215mg CO2 g1 h1, equivalent to a daily loss in weightof 2025 per cent. It remained high, or even rose slightly,during what would have been the normal dark period, but thenfell sharply. Even so, it was still three times that of themature tissue at the end of the experimental period. The rateof CO2 efflux of the mature tissue began low, and fell evenfurther during the first 12 h of darkness. It then levelledoff at a rate of 2·02·5 mg CO2 g1h1, equivalent to a daily loss in weight of about 3 percent. It is suggested that the rate of mature tissuerespiration, established after 1224 h of darkness, mightbe a useful selection criterion to employ in attempts to increasethe total dry matter yield of the grass crop by breeding. Hordeum vulgare L., barley, respiration, synthetic respiration, maintenance respiration, meristem, mature tissue respiration, simulated sward 相似文献
9.
Nitrate provision has been found to regulate the capacity forChara corallina cells to take up nitrate. When nitrate was suppliedto N sufficient cells maximum nitrate uptake was reached after8 h. Prolonged treatment of the cells in the absence of N alsoresulted in the apparent ability of these cells to take up nitrate.Chlorate was found to substitute partially for nitrate in theinduction step. The effects on nitrate reductionwere separated from those on nitrate uptake by experiments usingtungstate. Tungstate pretreatment had no effect on NO3uptake induced by N starvation, but inhibitedNO3 uptake associated with NO3 pretreatment. Chloridepretreatment similarly had no effect on NO3 uptake inducedby N deprivation, but inhibited NO3 uptake followingNO3 pretreatment. The data suggest that there are atleast two mechanisms responsible for the inductionof nitrate uptake by Chara cells, one associated with NO3reduction and induced by CIO3 or NO3and one associated with N deprivation. Key words: Nitrate, Chlorate, Chara corallina, Induction 相似文献
10.
The Carbon Economy of Rubus chamaemorus L. II. Respiration 总被引:1,自引:0,他引:1
Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO2 evolved dm2 h1 at 0 °Cto 4·6 rng CO2 evolved dm2 hh1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O2 uptake g1 fresh weight h1 at 0.7 ° C to10 µ10, uptake g1 f. wt h1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series. 相似文献
11.
The present study investigates the effects of triacontanol (CH3(CH2)28CH2OH),on plant growth (root and stem), peroxidase activity (apicalmeristem tissue), and auxin destruction (apical meristem tissue)in Little Marvel dwarf (LM) and Alaskapeas (AP). Triacontanol inhibited root growth in LM comparedto untreated controls. However, root growth in AP tissue wasenhanced by 1.0 mg I1 triacontanol and inhibited by allother treatments, in comparison to untreated controls. Wateruptake in triacontanol-treated AP plants was greater than inuntreated controls, with the converse being the case for LM.Triacontanol treatment caused an increase in peroxidase activityin both LM and AP plants compared to untreated controls. Interms of (114C)IAA destruction, GA3 + 0.01 mg 11triacontanol caused appreciable auxin breakdown (40%) in LMtissue, with GA3 + 0.1 mg 11 triacontanol giving a 43%decrease compared to untreated controls. In AP tissue, 10 µMGA3 increased auxin destruction by 188% whereas 0.1 mg I1triacontanol caused a 20% decrease compared to untreated controls.The effects of triacontanol on root and stem growth, peroxidaseactivity, and auxin destruction appear to be cultivar-specific,with respect to LM and AP varieties of peas. 相似文献
12.
SENGUPTA B.; NANDI A. S.; SAMANTA R. K.; PAL D.; SENGUPTA D. N.; SEN S. P. 《Annals of botany》1981,48(5):705-716
Of the 560 leaf samples belonging to 259 species of green plantsexamined more than 50 per cent of the Angiosperms and 25 percent of the Pteridophytes and Gymnosperms revealed the presenceof N2-fixing micro-organisms in their phyllosphere. Plants particularlyremarkable in this respect are orchids and several other epiphytes,Scindapsus officinalis, Ficus and cucurbits. Most of the isolatesappear to be biotypes of Klebsiella pneumoniae. The more activestrains fixed more than 5 mg N g1 glucose utilized andreduced more than 100 nmol C2H2 mg1 cell d. w h1. The efficacy of the phyllosphere N2-fixing isolates for N-nutritionof host plants was studied by spraying suspensions of the culturesgrown on N-free media on rice and wheat seedlings. In IR-26rice or Sonalika and Janak wheat grown on soil in wooden flatsor earthenware pots, 22 per cent of the 161 cultures studiedcaused increased height and about three-quarters of the culturesenhanced dry weight by more than 50 per cent; chlorophyll andN-contents were enhanced more than 50 per cent by about halfand two-thirds of the cultures respectively. In N-free sandculture 26 of the 50 promising strains doubled N-content, and30 doubled dry weight of the tested plants. In some cases dryweight, number of grains per panicle, and 1000 grain weightwere increased by 300, 7083 and 126158 per centrespectively; N-content of straw and seed was increased three-or fourfold. In several cases the beneficial effects were foundto match closely the performance of plants receiving ammoniumsulphate. Nitrogen-fixing micro-organisms, nitrogen nutrition, phyllosphere, rice, tropical plants, wheat 相似文献
13.
Internal Factors Regulating Nitrate and Chloride Influx in Plant Cells 总被引:14,自引:0,他引:14
The primary factor determining the observed decrease in activeC1 influx during salt accumulation in carrot and barleyroot cells has been shown to be the concentration of C1+ NO3 in the vacuole. The relationship between C1 influx and the vacuolar concentrationsof various substances was examined after the tissues had accumulatedions from various salt solutions. After accumulating K+ malate,C1 influx was not reduced, but after accumulating C1or NO3 salts, C1 influx was reduced by up to 90per cent. Considering all treatments, C1 influx was notcorrelated with the vacuolar concentration of K+, Na+, (K++Na+),reducing sugars, malate, C1, or NO3, nor withthe cellular osmotic pressure. The correlation coefficient betweenCl influx and log (C1 + NO3 concentrationin the vacuole) was highly significant, and accounted for allthe variation in C1 influx in this experiment. Net NO3 influx is similarly reduced by a high C1concentration in the vacuole. External Cl and NO3have quantitatively different, apparently competitive, effectson C1 influx. These differ from the apparently negative-feedbackeffects of C1 and NO3 in the vacuole, which arequantitatively similar. Decreasing the internal hydrostatic pressure by raising theexternal osmotic pressure increased active K+ influx in Valoniaventricosa, but had no effect on C1 or K+ influx in carrotor maize root cells. Cl influx is not related to thereducing sugar concentration during ageing drifts in excisedcarrot root tissue. Acetazolamide did not inhibit C1 influx to carrot tissue. The implications of this type of negative feedback regulation,and the relationship between C1 and NO3 transportare discussed. 相似文献
14.
The respiratory losses of 14CO2 from whole plants of uniculmbarley and maize were measured following exposure of the wholeplant or a single leaf to air containing a uniform specificactivity of 14CO2 for 3060 min during normal photosynthesis.The total respiratory efflux of 14CO2 could be described interms of two main components: an intense efflux characterizedby a half-life of 48 h, which was identified with thebiosynthesis of new tissue in meristems; and a much less intenseefflux characterized by a half-life of 26120 h, whichwas primarily identified with the maintenance of metabolic activity.The (bio)synthetic efflux of 14CO2 totalled between 25 and 35per cent of the labelled assimilate (14C: 14C), and was generallyinsensitive to temperature and light intensity. The maintenanceefflux totalled between 12 and 27 per cent of the labelled assimilateor its derivatives: the total generally increased with hightemperature and low light intensity. The rate of the maintenanceefflux showed a normal temperature response (Q102). It is concludedthat the efficiency of conversion of assimilate into new growthis unlikely to exceed 65 per cent in the long term, and willgenerally be less. 相似文献
15.
Effects of Nitrogen Fertilizer on the Distribution of Photosynthate during Grain Growth of Spring Wheat 总被引:1,自引:0,他引:1
The distribution of photosynthate labelled with 14C was studiedin spring wheat grown with different amounts of nitrogen fertilizerin the three years 19724, after exposing the flag leafor the leaf below the flag leaf to 14CO2 at 610 or 1926days after anthesis. The movement of 14C to ears was unaffectedby nitrogen fertilizer except after early exposure in 1973,when nitrogen increased the retention of 14C in stems at maturity The concentration of sugar in the top part of the shoot at theend of the day was unaffected by nitrogen in 1973, but at 22days after anthesis in 1974 the concentration of sucrose inthe glumes and rachis, and in the flag leaf lamina was increasedby nitrogen. Loss of sugar by translocation and respirationduring the night may explain why this increase in concentrationwas not reflected in the 14C distribution 24 h after supplying14C. The proportion of the total 14C content of the shoot that wasin the ear at maturity ranged from 68 to 95 per cent dependingon when and to which leaf the 14CO2 was supplied. Less than5 per cent remained in the leaf exposed to 14CO2. The proportionof the final ear weight contributed by the leaf below the flagleaf was about half that contributed by the flag leaf. In 1974 about 24 per cent of the 14C absorbed by the flag leaf,and 56 per cent of that absorbed by the second leaf, was lostby maturity, presumably by respiration. Most loss occurred inthe first 24 h. 相似文献
16.
Function and contribution of the root tip in the induction of NO3- uptake along the barley root axis
The seminal roots of N-free-grown barley seedlings were ableto take up NO3 immediately upon initial exposure; theuptake rate in the tip was half of that in the older root zones(middle and base). A lag of 60 min was required in all rootzones before the uptake rates started to increase during inductionwith external NO3. This increase could be prevented bythe addition of pFPA; we thus assume that additional NO3transport proteins were synthesized during NO3 induction.During the time-course of NO3 induction different uptakerates were measured in morphologically different regions ofthe tip (1 mm segments) indicating a regulation of NO3induction on a narrow local scale. In NO3 grown plants, NO3 uptake as well as NO3content increased basipetally along the root axis concomitantlywith increasing vacuolization of the cells. Although NO3uptake into the tip was only half of that into the older rootzones, this NO3 uptake was very important for the entireroot. Firstly, it provided the substrate for protein biosynthesisin the meristematic region: nitrate reductase activity and totalsoluble protein were highest in the first apical mm of the tip.Secondly, 3% of the NO3 taken up by the tip was foundin the base where it induced NO3 uptake: NO3 wastranslocated almost exclusively basipetally and as little as20nmolg1 root fr. wt. translocated from the tip weresufficient for acceleration of NO3 induction in the rootbase of N-free-grown plants. This clearly shows that the inductionof NO3 uptake does not depend exclusively on the availabilityof external NO3, but can be mediated also with internallytranslocated NO3.The root tip, therefore, may be consideredthe NO3 sensing region of the root. Key words: Barley, Hordeum vulgare L, internal NO3, NO3 uptake, root zones 相似文献
17.
The influence of salinity in the growing media on ribulose-1,5-bisphosphate (RuBP) carboxylase and on CO2 fixation by intactsugar beet (Beta vulgaris) leaves was investigated. RuBP carboxylase activity was mostly stimulated in young leavesafter exposure of plants for 1 week to 180 mM NaCl in the nutrientsolution. This stimulation was more effective at the higherNaHCO2 concentrations in the reaction medium. Salinity also enhanced CO2 fixation in intact leaves mostlyat rate-limiting light intensities. A 60 per cent stimulationin CO2 fixation rate was obtained by salinity under 450 µEm2 s1. At quantum flux densities of 150 µEm2 s1 (400700 nm) this stimulation was280 per cent. Under high light intensities no stimulation bysalinity was found. In contrast, water stress achieved by directleaf desiccation or by polyethylene glycol inhibited enzymeactivity up to fourfold at 1.2 MPa. Beta vulgaris, sugar beet, ribulose-1, 5-bisphosphate carboxylase, salt stress, water stress, carbon dixoide fixation, salinity 相似文献
18.
The cell cycle in Silene coeli-rosa shoot apices was measuredto test whether or not early components of the floral stimulus,produced during the 2nd and 3rd long days (LD) of an inductiveLD treatment, resulted in an increase in the duration of G2phase in constant 2024 h cell cycles. Plants were grownat 20°C in short days (SD) of 8 h light and 16 h darknessfor 28 d (day 0). Starting on day 0, plants were given SD or3 LD each comprising an identical 8 h day and 16 h photo-extension,or 3 dark-interrupted (d.i.) non-inductive LD, interrupted at1700 h of each day with 1 h of darkness. The cell cycle (percentagelabelled mitoses method) and changes in cell number were determinedin the shoot apical meristem. During days 12 of the SDtreatment, the cell cycle and mean cell generation time (MCGT)was 18 and 32 h, respectively, giving a growth fraction of 56%.During days 23, the cell cycle and MCGT shortened to15 and 23 h, respectively (growth fraction = 65%). During days12 of the LD and d.i. LD treatments, cell cycles andMCGTs were 910 and 2729 h, respectively, resultingin smaller growth fractions (about 33%). Thus, shortened cellcycles and altered growth fractions occurred regardless of whetheror not the treatment was inductive. The LD treatment resultedin a marked shortening of G1 and, to a lesser extent, S-phase,whilst G2 remained constant. These changes were consistent withincreases in the proportion of cells in G2 during the photoextensionof each LD which were suppressed during the comparable periodsof the d.i. LD treatment. The latter treatment resulted in eachphase occupying virtually identical proportions of the cellcycle as in the SD treatment. Thus, the unique cell cycle responsesto the initial part of the inductive LD treatment were increasesin the proportion of cells in G2 coupled with G1 and G2 beingof similar duration. Cell cycle, mean cell generation time, shoot apex, Silene coeli-rosa 相似文献
19.
The fate of the carbon from photosynthetically assimilated 14CO2and the nitrogen of rootapplied 15NO3 was studied by harvestingplants at intervals after a week's feeding period, either early(3441 d after sowing) during vegetative growth, or late(11219 d) as plants were fruiting. Only 23 per cent of the early fed 14C but more than 90 per centof the early-fed 15N survived in plants until maturity (155d). Efficiency of transfer of early-fed 14C to seeds was 2 percent, that for early-fed 15N, 51 per cent. Assimilatory activitybefore flowering had little direct relevance to the carbon nutritionof seeds but provided approximately one-fifth of the seeds'requirement for nitrogen. Early or late-fed 15N was mobilized slowly for reproductivedevelopment, seeds at all 15 reproductive nodes deriving benefit,late-forming ones more so than those developing earlier. Vegetative organs on a young shoot lost previously acquired15N at rates within the range 0.52.4 per cent per day.The released nitrogen was first taken up by the root and youngerparts of the shoot, but much was later traced to the seeds. Late feeding of 14C or 15N resulted in a high (746 percent) efficiency of transfer to seeds, most of this appearingto be donated by, or cycled through, vegetative parts of thereproductive zone of the shoot. The significance of past and current assimilation in fruit nutritionis discussed. 相似文献
20.
The effect of morphactin (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate)on basipetal transport of auxin (Indol-3-ylacetic acid-2-14C)was studied in bean (Phaseolus vulgaris) hypocotyl with thedonor-receiver block method. Morphactin (5 x 106m) reduced IAA (5 x 106m) transportintensity by an average of 83 per cent and auxin transport capacityby 90 per cent, but transport velocity was not affected. Morphactin did not inhibit uptake of IAA into hypocotyl tissue,but it did prevent transfer of IAA from the tissue into receiverblocks. Chromatographic analysis of the tissue after 4 h IAA-2-14Ctransport showed that 54 per cent of the total activity wasin the form of IAA in the control and 42 per cent in the morphactintreated tissue. No difference was found in the rate of decarboxylationof IAA-1-14C between control and morphactin treated tissue sections.Nor could any difference between control and morphactin be shownin the radioactivity associated with a TCA ppt fraction. Ina study of the transportable auxin pool, morphactin decreasedthe size of the pool and increased the half-life of decay ofauxin transport from 122 h to 385 h. In a kineticanalysis of the reversal of morphactin (5 x 106m) inhibitionby increasing concentration of IAA-2-14C (5 x 106m to2 x 105m), it was shown that IAA transport resemblesMichaelis-Menten enzyme reaction kinetics, and that inhibitionby morphactin fitted a mixed type model. IAA hada dissociation constant of 85 x 106m and morphactinthat of 43 x 107m with a Km for the transport processof 85 x 106m. 相似文献