摘要:

Gas exchange characteristics were studied in two mangrove species,Aegiceras corniculatum(L.) Blanco andAvicennia marina(Forstk.) Vierh. varaustralasica(Walp.) Moldenke, grown under a variety of salinity and humidity conditions. The assimilation rate was measured as a function of the intercellular CO2concentration [A(ci) curve]. The photosynthetic capacity decreased with increase in salinity from 50 to 500 millimolar NaCl, as shown by decline in both the initial linear slope and the upper plateau of theA(ci) curve, withA. corniculatumbeing the more sensitive species. The decline in photosynthetic capacity was enhanced by increase in the leaf to air vapor pressure difference from 6 to 24 millibars, but this treatment caused a decrease in only the upper plateau of theA(ci) curve. Stomatal conductance was such that the intercellular CO2concentration obtaining under normal atmospheric conditions occurred near the transition between the lower linear and upper plateau portions of theA(ci) curves. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate, which declined with increasing salinity and decreasing humidity. The marginal water cost of carbon assimilation was similar in most treatments, despite variation in the water loss/carbon gain ratio.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Measurements of gas exchange characteristics were made on intact, attached leaves of hydroponically grown seedlings ofAvicennia marina(Forstk.) Vierh. varaustralasica(Walp.) Moldenke as the NaCl concentration of the culture solution was varied by step changes of 50 millimolar NaCl every 2nd day from 50 to 500 to 50 millimolar NaCl. The CO2assimilation rate, stomatal conductance, intercellular CO2concentration, and evaporation rate decreased at salinities above 250 millimolar NaCl and recovered substantially upon return to the original salinity.The assimilation rate was measured as a function of the intercellular CO2concentration [A(ci) curve]. The lower linear portion of this curve was insensitive to variation in salinity, whereas the upper nonlinear portion declined with increasing salinity, indicating a reduction in the capacity for CO2assimilation which recovered upon return to the original salinity. Stomatal conductance changed such that the intercellular CO2concentration measured under normal atmospheric conditions occurred in the transition between the lower, linear and upper nonlinear portions of theA(ci) curve. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate. The changes in gas exchange characteristics were such that water loss was minimal relative to carbon gain.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Illuminated flag leaves ofTriticum monococcum(2X),T. urartu(2X),T. dicoccum(4X),T. dicoccoides(4X), andT. aestivum(6X) were exposed to14CO2for 10 seconds and subsequently allowed to continue photosynthesis in the ambient air for periods of up to 2 minutes. The relative distribution of14C among water-soluble products in the leaves was similar for each species at each sampling time. After the 10-second pulse of14CO2, radioactivity was mainly in phosphate esters with less than 5% in C4acids. Subsequently, radioactivity increased in sucrose, glycine, and serine at the expense of that in phosphate esters. By 2 minutes, between 18% and 29% of the14C was in glycine plus serine. The results suggest rapid photorespiration in all species and an absence of C4photosynthesis.d-Ribulose 1,5-bisphosphate carboxylase (EC4.1.1.39) was partly purified from seedling leaves of each of the fiveTriticumspecies. Each preparation was assayed for simultaneous carboxylase and oxygenase activities in 2.1 millimolar NaHCO3and 265 micromolar O2at pH 8.2 and 25°C. The mean ratio of carboxylase to oxygenase activities was 6.11±0.16 (standard error); differences between values for different species were not statistically significant. The results do not explain the faster rates of photosynthesis per unit leaf area reported for diploid and tetraploid species ofTriticumcompared to the hexaploi

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

The tissue accumulation of sucrose, glucose, and fructose has been studied in cultured cotton (Gossypium hirsutumL.) roots and leaf discs. Sucrose uptake by both tissues from high apoplastic concentrations was independent of pH but has a slightly acidic pH optimum from low concentrations. Like other higher plant tissues, cotton root cells accumulate sucrose via a `saturable,' inhibitor-sensitive mechanism and a linear, inhibitor-resistant mechanism. The linear mechanism of sucrose uptake is not as pronounced in leaf disc data as it is in root data. Further, sucrose uptake by cotton leaf discs is more resistant than uptake by root cells to pH alterations, inhibitors, and monosaccharides in the uptake medium. The saturable phase of sucrose influx into cotton root is eliminated by glucose, fructose, and high pH. Sucrose influx into both tissues is not altered by osmotica up to 200 milliOsmolar. Sucrose accumulated by both tissues is rapidly converted to other chemical forms, especially in root tissue where only approximately 50% remains as neutral sugars 1 hour following the start of radiolable exposure. Although the entry of radiolabeled sucrose is faster in abraded leaf discs, they give the same response patterns to pH, inhibitors, and monosaccharide as do unabraded discs.The sucrose accumulation kinetics of cotton roots and leaf discs differ. These differences may be related to the physiological roles (sourceversussink) of the two tissues in the intact plant.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Upon rehydration of desiccatedTortula ruralis, RNA synthesis is immediately resumed; this resumption is quicker in moss recovering from slow drying than from rapid drying. Newly synthesized RNA enters the protein synthetic complex almost immediately upon rehydration, reaching control steady state levels within 2 hours after slow drying and 6 hours after rapid drying. RNA synthesized in the 1st hour following the readdition of water enters into polysomes much earlier after slow drying than after rapid drying. The RNA components of the protein synthetic complex are stable to desiccation at either slow or rapid speeds, although more so following the former drying regime. Immediately upon rehydration, these conserved RNA are readily utilized for protein synthesis, and continue to be so at least 4 hours thereafter. Hence, the speed of desiccation affects the rate at which RNA is synthesized upon subsequent rehydration, as well as the mode of utilization of that RNA.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Cells from reproductive soybean (Glycine max[L.] Merr.) plants were isolated using a mechanical-enzymic technique that produced a high yield of uniform, physiologically active cells. Cells were incubated in a pH 6.0 buffered solution and subjected to various treatments in order to determine the nature of net amino acid efflux. Total net amino acid (ninhydrinreactive substances) efflux was not affected by the following conditions: (a) darkness, (b) aeration, (c) K+concentrations of 0.1, 1.0, 10, or 100 millimolar and (d) pH 4, 5, 6, 7, or 8. The Q10for net amino acid efflux between 10°C and 30°C was 1.6. Thus, it seems that net amino acid efflux requires neither current photosynthetic energy nor a pH/ion concentration gradient. Amino acid analyses of the intra-and extracellular fractions over time showed that each amino acid was exported linearly for at least 210 minutes, but that export rate was not necessarily related to internal amino acid pools. Amino acids that were exported fastest were alanine, lysine, leucine, and glycine. Addition of the inhibitorp-chloromercuriphenyl sulfonic acid, 3(3,4-dichlorophenyl)-1,1-dimethylurea, or carbonylcyanidep-trifluoromethoxyphenylhydrazone increased the rate of total amino acid efflux but had specific effects on the efflux of certain amino acids. For example,p-chloromercuriphenyl sulfonic acid greatly enhanced efflux ofγ-aminobutyric acid, which is not normally exported rapidly even though a high concentration normally exists within cells. The data suggest that net amino acid efflux is a selective diffusional process. Because net efflux is the result of simultaneous efflux and influx, we propose that efflux is a facilitated diffusion process whereas influx involves energy-dependent carrier protei

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Fruits ofLycopersicon esculentumMill cv Sonatine stored in 6% CO2, 6% O2, and 88% N2for 14 weeks at 12°C, exhibited a temporal separation of certain biochemical events associated with ripening.The specific activity of two citric acid cycle enzymes, citrate synthase and malate dehydrogenase, fell substantially during the first 2 weeks of storage when changes in organic acid concentration also occurred. During this period, lycopene, polygalacturonase, and ethylene were undetectable.When fruit were removed from store, ethylene was evolved and polygalacturonase and invertase activity were rapidly initiated as was synthesis of lycopene.To determine whether the changes in organic acid metabolism were affected by ethylene, fruit was kept at 22°C in either a normal atmosphere or a normal atmosphere supplemented with 27 microliters per liter of ethylene, and it was shown that in both atmospheres similar quantitative changes to those described above occurred in the citric acid cycle enzymes specific activities before any detectable increase in the specific activities of invertase and polygalacturonase. These latter changes, together with pigment changes, occurred between 2 and 3 days earlier in fruit exposed to ethylene, compared with those kept in a normal atmospher

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Using standard microelectrode techniques, we measured the effects of fusaric acid (FA) on the membrane potential of tomato (Lycopersicon esculentumMill. cv New Yorker 870) incipient root hair cells. At pH 5.3, FA caused a hyerpolarization, the magnitude of which increased with FA concentrations from 0.05 to 0.50 millimolar. A depolarization followed, the rate and magnitude of which increased with the concentration of FA and exposure to FA. Partial repolarizations occurred after exposures to 1.0 millimolar FA for less than 8 to 10 minutes, after longer exposures to lower FA concentrations, or after longer exposures to 1.0 millimolar FA in a less concentrated nutrient solution. The amount of ATP in tomato root tips decreased by about 85% after incubation for 80 min in 1.0 millimolar FA.At pH 7.2 and 8.2, the depolarization caused by an 8-minute exposure to 1.0 millimolar FA was immediate and much more rapid than at pH 5.2 and 6.3, but its magnitude was not as great. At pH 6.3, 7.2, and 8.2, the depolarization was at least partially reversible. The data are consistent with FA having at least three effects that elicited changes in tomato root cell electrical potential differences between the cell's interior and the external solution.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Previous work showed that theseglmutant of barley (Hordeum vulgarecv Betzes) did not differ from normal Betzes in plant growth, photosynthesis, or fertility, but it produced only shrunken seeds regardless of pollen source. To determine whether defects in sucrose uptake or starch synthesis resulted in the shrunken condition, developing grains of Betzes andsegl were cultured in [14C]sucrose solutions after slicing transversely to expose the endosperm cavity and free space. In both young grains (before genotypes differed in dry weight) and older grains (17 days after anthesis, whensegl grains were smaller than Betzes), sucrose uptake and starch synthesis were similar in both genotypes on a dry weight basis. To determine if sucrose was hydrolyzed during uptake, spikes of Betzes andsegl were allowed to take up [fructose-U-14C]sucrose 14 days after anthesis and the radioactivity of endosperm sugars was examined during 3 hours of incubation. Whereas less total radioactivity entered the endosperm and the endosperm cavity (free space) ofsegl, in both genotypes over 96% of the label of endosperm sugars was in sucrose, and there was no apparent initial or progressive randomization of label among hexose moieties of sucrose as compared to the free space sampled after 1 hour of incubation. We conclude thatsegl endosperms are capable of normal sucrose uptake and starch synthesis and that hydrolysis of sucrose is not required for uptake in either genotype. Evidence suggests abnormal development of grain tissue of maternal origin during growth ofsegl grains.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

The possibility that differences in stomatal conductance between upper and lower surfaces of amphistomatous leaves are adaptations to differences in CO2exchange characteristics for the two surfaces was investigated. The ratio of upper to lower stomatal conductance was found to change little in response to light and humidity for well-watered sunflower (Helianthus annuusL.) plants. Stressing the plants (ψ=−17 bars) and rewatering 1 day before gas exchange measurements reduced upper conductance more severely than lower in both indoor- and outdoor-grown plants, and caused small changes in conductance ratio with light and humidity. A similar pattern was found using outdoor grown sunflower and cocklebur (Xanthium strumariumL.) plants. Calculated intercellular CO2concentrations for upper and lower surfaces were always close to identical for a particular set of environmental conditions for both sunflower and cocklebur, indicating that no differences in CO2exchange characteristics exist between the two surfaces. By artificially creating a CO2gradient across the leaf, the resistance to CO2diffusion through the mesophyll was estimated and found to be so low that despite possible nonhomogeneity of the mesophyll, differences in CO2exchange characteristics for the two surfaces are unlikely. It is concluded that differences in conductance between upper and lower stomates are not adaptations to differences in CO2exchange characteristi

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB