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1.
Temperature dependence of longitudinal relaxation times (T1)of water protons in flower buds of six azalea species differingin cold hardiness and ecological distribution was investigatedby pulse nuclear magnetic resonance spectroscopy. Thermal hysteresiswas observed for T1 following a slow freeze-thaw cycle. TheT1 ratio (the ratio obtained from the difference between theoriginal T1 value in an unfrozen sample and the final T1 aftera freeze-thaw treatment, both at 20C, divided by the originalT1) was closely correlated with the viability of florets innon-acclimated buds of R. kiusianum. If the buds were frozento a lethal temperature and then thawed to 20C, the T1 ratioincreased. The T1 ratios of acclimated winter buds for the sixspecies used were correlated with the level of cold hardiness(supercooling ability of florets determined by differentialthermal analysis). The T1 ratio of deacclimated spring buds,especially those from hardier species, markedly increased uponcooling to a lethal temperature. Species differences observedin acclimated winter buds disappeared upon deacclimation. TheT1 ratio appears to be related to the viability of florets andthe degree of freezing damage (membrane disruption) in florets. (Received December 28, 1984; Accepted May 24, 1985) 相似文献
2.
Barradas Victor L.; Jones Hamlyn G.; Clark Jerry A. 《Journal of experimental botany》1994,45(7):931-936
The effects of air temperature (To), leaf-air vapour pressuredifferences [VPD) and water deficit on stomatal responses tochanging irradiance were studied in Phaseolus vulgaris L. Responseswere approximately sigmoidal, with rates of closure being fasterthan the rates of opening. The mean half-time for closure was5.4 min and for the opening 9.2 min. Under water deficit, bothstomatal opening and closing were faster than in well-wateredconditions. Stomata were more sensitive to VPD and water stressthan to To. The higher the VPD or To the more rapid was thestomatal response, except in stressed plants where there wasno significant effect of To. Under water stress, stomata weremore sensitive to water potential ( 相似文献
3.
The longitudinal relaxation time (T1) of water protons in floretsof R. ? akebono flower buds was measured with a pulse NMR spectrometerto determine the relationship of T1 to water content and coldhardiness (supercooling ability). Seasonal changes of T1 inflorets were closely correlated with water content and supercoolingability of florets. T1 of florets was short for acclimated budshaving a low water content and long for non-acclimated budshaving a high water content. Flower buds collected in Novemberand stored at 0 and 5?C for 4 weeks had shorter T1 values thanbuds stored at 10?C even though the floret water content andsupercooling ability were similar. Thus, the short T1 of coldacclimated buds hardened naturally or by storage at low temperaturesis due to a combination of both reduced water content and temperature. (Received August 27, 1983; Accepted May 26, 1984) 相似文献
4.
COVELL S.; ELLIS R. H.; ROBERTS E. H.; SUMMERFIELD R. J. 《Journal of experimental botany》1986,37(5):705-715
For a single seed population of each of four species of grainlegume positive linear relationships were shown between temperatureand rate of germination for different fractions (G) of eachpopulation, from a base temperature, Tb(G), at which germinationrate is zero, to an optimum temperature, To(G) at which germinationrate is maximal. At constant temperatures warmer than To(G)there were negative relations (probably linear) between temperatureand rate of germination to the maximum temperature for germination,Tm(G), Within each population Tb(G) did not differ, but it didvary between species, viz.0.0?C, 0.25?C, 4.and 8.5?C for chickpea(Cicer arietinum L.), lentil (Lens culinaris Medic.), soyabean(Glycine max [ Merr.) and cowpea (Vigna unguiculata [L.] Walp.),respectively. In contrast, To(G) varied both within each populationand also between the four species: 80% of seeds in each populationhad To(G) values within the range 31.8?C to 33.8 ?C, 24.0?Cto 24.4?C, 34.0?C to 34.5?C and 33.2?C to >40?C, respectively.Values of Tm(G) were much more vanable: the 80% population rangewas 48 .0?C to 60.8?C for chickpea, 31.8?C to 34.4?C for lentiland 46.8?C to 55.2?C for soyabean; reliable estimates couldnot be made for cowpea, but the results suggest higher and morevariable values of Tm(G) than in the other three species. Atsub-optimal temperatures the distribution of thermal time forthe different fractions of each population was normal, exceptfor lentil where it was log-normal. A single equation is proposedto describe the influence of sub-optimal temperatures on ratesof germination for whole seed populations. At supra-optimaltemperatures, variation in thermal time for the different fractionsof each population was only slight. The implications of thesefindings for the adaptation of grain legume crops to differentenvironments, and for the screening of germplasm, are discussed. Key words: Seed germination rate, temperature, grain legumes 相似文献
5.
Leaf Properties Related to the Photosynthetic Response to Drought in Upland and Lowland Rice Varieties 总被引:1,自引:0,他引:1
Four upland and two lowland varieties were grown on floodedand dry soil in pots in a glasshouse. Photosynthetic rate (P),transpiration rate (T), and water content (W) of the secondexpanded leaf from the top of the main stem were measured undercontrolled aeration and illumination in a leaf chamber in thelaboratory, together with leaf area (La), dry matter content(DM), nitrogen content (N), stomatal frequency (Sf), and totalvessel cross-sectional area at the base of the leaf blade (Va).P/La was positively related to T/La and Sf/La among six varietieswhen they were grown on flooded soil. IR 8, a semidwarf indicalowland variety, showed the highest P/La with the highest Sf/Laand T/La. When grown on dry soil P/La was positively correlatedwith W/DM, the latter being negatively related to T/Va. Twoupland varieties, African Moroberekan and Brazilian IAC 1246,showed the highest P/La on dry soil, keeping a higher W/DM witha lower T/La and a lower T/Va. Daytime leaf diffusive conductance(l/rL) and leaf water potential (L) measured on the same orthe same stage leaf in the glasshouse were positively correlatedwith the W/DM measured in the laboratory among varieties grownon dry soil. Simultaneous observation of P, T and W in the laboratoryindicated nonstomatal reduction in P/La due to leaf water deficitin sensitive varieties, although these varieties also showeda markedly lower daytime l/rL in the glasshouse as comparedwith resistant varieties. Oryza sativa L., rice, drought resistance, photosynthesis, transpiration, water deficit, stomatal frequency, vessel size 相似文献
6.
Antitranspirant-induced Heat Stress in the Parasitic Plant Striga hermonthica--A Novel Method of Control 总被引:1,自引:0,他引:1
PRESS MALCOLM C.; NOUR JANE J.; BEBAWI FAIZ F; STEWART GEORGE R. 《Journal of experimental botany》1989,40(5):585-591
Leaf temperatures (T1) of the parasitic plant Striga hermonthicaare substantially below those of the air (Ta), [TaT1]reaching 7 ?C at Ta = 40 ?C. This results from high rates oftranspiration and the consequent evaporative cooling of theleaf. Application of an antitranspirant, which mechanicallyimpedes foliar loss of water vapour, reduced transpiration andstomatal conductance by 40% and 57%, respectively, and reduced[Ta T1] to 2 ?C at Ta = 40 ?C. The temperature sensitivityof photosynthesis in the host-parasite association differed,the optima (Topt) being 37.2 and 40.1 ?C for S. hermonthicaand sorghum, respectively. Once Topt had been exceeded in S.hermonthica net photosynthesis declined rapidly, reaching thelethal limit (Tmax) at 42.6 ?C. S. hermonthica is particularlysensitive to high temperatures and antitranspirant-induced overheatingleads to blackening and shrivelling of the leaf after as littleas 4 h at Ta = 40 ?C. Application of an antitranspirant underfield conditions in the Sudan at Ta = 40 ?C resulted in 28%and 67% reductions in transpiration and stomatal conductance,together with a 5 ?C increase in T1, and subsequent leaf death.In addition to these short-term physiological responses, antitranspirantspraying of the arasite increased the grain and straw yieldof the crop by factors of 3.4 and 2.6, respectively. Antitranspirantsmay have potential use as a method of controlling Striga inthe field. Key words: Striga hermonthica, sorghum, photosynthesis, transpiration, high temperature stress, anti-transpirant 相似文献
7.
Transverse Relaxation Time of Leaf Water Protons and Membrane Injury in Wheat (Triticum aestivum L.) in Response to High Temperature 总被引:2,自引:0,他引:2
MAHESWARI M.; JOSHI D. K.; SAHA R.; NAGARAJAN S.; GAMBHIR P. N. 《Annals of botany》1999,84(6):741-745
The relationship between high temperature stress injury andtemperature dependence of the transverse relaxation time (T2)of leaf water was examined using NMR in four cultivars of wheatdiffering in their sensitivity to high temperature stress. TheT2declined with increasing temperature between 25 and 35 °C.A comparison of relative injury based on electrolyte leakageand T2, between 40 and 50 °C, indicated that while membranepermeability increased with increasing temperature there wasan increase in T2until 44 and 48 °C in susceptible and tolerantcultivars respectively, followed by a sharp decline. This patternof change in T2with increasing temperature was consistent whetherthe same or different samples were used for each treatment temperature.Loss of temperature dependence of T2after heat killing indicatedirreversible changes in T2, probably due to the loss of membraneintegrity. Heat tolerant varieties, which suffered less membraneinjury, had a higher T2compared to susceptible varieties. Tolerantvarieties also maintained the T2of leaf water protons to highertemperatures than did sensitive varieties. This NMR-based, non-invasive,rapid technique could be used to efficiently detect heat injuryin leaf tissues. Copyright 1999 Annals of Botany Company Membrane integrity, transverse relaxation time, high temperature stress, Triticum aestivum L. 相似文献
8.
Endogenous Gibberellins in the Vegetative Shoots of Tall and Dwarf Cultivars of Phaseolus vulgaris L. 总被引:2,自引:0,他引:2
Endo Kaoru; Yamane Hisakazu; Nakayama Masayoshi; Yamaguchi Isomaro; Murofushi Noboru; Takahashi Nobutaka; Katsumi Masayuki 《Plant & cell physiology》1989,30(1):137-142
A series of 13-hydroxygibberellins, gibberellin A1 (GA1), GA19,GA20, GA44 and GA53, were identified by GC/MS (full scan) fromvegetative shoots of tall (cv. Kentucky Wonder) and dwarf (cv.Masterpiece) Phaseolus vulgaris L. It is suggested that GA1is active per se in the control of shoot elongation of P. vulgarisL., and that dwarfism in Masterpiece is not due to shortageof the active GA, but to its low ability to respond to the bioactiveGA. (Received August 29, 1988; Accepted November 21, 1988) 相似文献
9.
Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T1 O2 0.21;CO2 270?106: T2; O2 0.05, CO2, CO2 270?106: T3;O2 0.21; CO2 550?106. Experiment 1 (T1 and T2) lasted2 weeks: Experiment 2 (T1 T2 and T3) only one week. Hourly estimatesof CO2 uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that
where dV/dt is the rate of CO2 uptake per plant, ßis the photosynthetic efficiency, I0 is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T2)was at least double ß(T1), whilst f(T2) was smallerthan f(T1) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T1)=fL(T2) at anygiven time, i.e. the treatment with the larger leaf area (T2)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T2 than T1. Over the relatively short period of the experiment the resultsare adequately described by U=btn, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T3 were similar to T2 suggestingthat increasing CO2 concentration decreases the growth inhibitionat 21 per cent O2. 相似文献
10.
准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(Pn)、蒸腾速率(Tr)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大Pn、 最大Tr及WUE分别为8.07~35.96 μmol CO2·m-2·s-1、3.16~29.64 mmol H2O·m-2·s-1、0.54~4.26 μmol CO2·mmol-1H2O;种间最大Pn与最大气孔导度(Stomatal conductance, Gs)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol-1;从光合速率对胞间CO2浓度及光量子通量密度的响应曲线来看,这类植物的表观CO2补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO2·m-2·s-1·Pa-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm2;单位叶面积干重为0.40~0.77 g·m-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m2·kg-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C3植物特征,相比其它类型的荒漠植物具有较高的单位叶面积Pn、高Tr及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。 相似文献
11.
Iwaya-Inoue Mari; Yoshimura Kazuhisa; Yamasaki Hideo; Kaku Shosuke 《Plant & cell physiology》1993,34(5):705-711
Water protons in hypocotyl tissues from etiolated seedlingsof Vigna radiata that were exposed to temperature stress showedcharacteristic relaxation behaviors for 1H-NMR. Cold stresstreatment (0C) caused gradual prolongation of NMR relaxationtimes (T1). After exposure of tissues to cold stress for 24h, T1 returned to the initial value as a result of subsequentincubation at normal temperature (20C). By contrast, heat stresstreatment (40C) induced a time-dependent decrease in T1, whichdid not return completely to the initial value upon subsequentincubation at 20C after exposure to heat stress for 4 h. Weexamined changes in various physical factors that influencethe response of T1 to temperature stress, namely, water contentand the concentrations of protein, diamagnetic (K+, Na+, Ca2+and Mg2+) and paramagnetic (Mn2+ and Fe2+) ions in the tissues.From the relationships between T1 and these factors in vitro,we could not interpret the responses of T1 to the temperaturestress only in terms of a change in water content. A synergisticeffect of an Mn2+ -protein complex and pH might be essentialfor the mechanism of changes in T1 that are due to cold stress.The influence of heat stress on structural water in tissuesis discussed in terms of water-protein interactions. (Received December 28, 1992; Accepted May 6, 1993) 相似文献
12.
Several parameters related to the water relations of eight woodyhemiepiphytes with different photosynthetic pathways were studiedin situ and in the laboratory on Barro Colorado Island, Panama.As a group, woody hemiepiphytes tended to have less conductivestems per unit leaf area (lower kL) and invested less wood cross-sectionper unit leaf area compared to free-standing trees, while theirspecific conductivity (Ks) was significantly higher. Among hemiepiphytes,there were significant differences between C3 and CAM (CrassulaceanAcid Metabolism) species in respect to leaf characteristics,transpiration rates, diel patterns of water flow through aerialroots, and in hydraulic architecture parameters. Average transpirationrates of the two Clusia species (C3-CAM) were lower by aboutan order of magnitude compared to the C3 species. In all C3species, sap flow through aerial roots (F) closely followedtranspiration (E), whereas E and F were decoupled in time inthe C3-CAM species Clusia uvitana: considerable long-distancewater flow occurred at night. The hydraulic efficiency of theother C3-CAM species, C. minor was the lowest of the five speciesinvestigated. Key words: Hemiepiphytes, water relations, hydraulic architecture, aerial roots, CAM 相似文献
13.
Anthocyanin Influence on Water Proton NMR Relaxation Times and Water Contents in Leaves of Evergreen Woody Plants During the Winter 总被引:1,自引:0,他引:1
An investigation was made to determine the effect of anthocyaninin red-colored evergreen leaves during the mid-winter on waterproton NMR relaxation times (T1). Water contents, anthocyanincontentsand histologic localization of red-coloration in mesophyllswere determined by using both red-colored and green leaves fromthe same branches of Rhododendron, Viburnum and Mahonia, respectively.Although the decrease of water contents in the red-colored leavesin Mahonia was insignificant, decreases in the former two specieswere clearly observable. T1 differences between red-coloredand green leaves for the three species were insignificant. Increasesof anthocyanin contents and histologic localization of red colorationin mesophylls for the red-colored leaves were more pronouncedin Rhododendron and Viburnum than in Mahonia. These observationssuggest that the pronounced increases of histologic localizationof red-colored mesophyll cells and anthocyanin contents in red-coloredleaves for the former two species contribute to maintenanceof T1 relaxation times in spite of the marked decrease of watercontents in leaves. It is assumed that the increase of localizationareas of red-colored parenchymatous cells in mesophylls is moreeffective than the total contents of anthocyanins in leavestowards the maintenance of the T1 level in red-colored leaves,and this appears to be dependent on the vacuolar compartmentationof anthocyanin in mesophyll cells. (Received August 3, 1991; Accepted December 12, 1991) 相似文献
14.
The objectives of this study were to quantify changes in leaffreezing resistance and carbohydrate concentrations caused bylong-term (6 years) exposure to elevated CO2(ambient: 360 µll-1, elevated: 600 µl l-1) in five dominant plant speciesgrowing in situ in a native temperate grassland. Across allfive species tested from three functional groups, the mean temperatureat which all leaves were damaged (T100) significantly (P = 0.016)increased from -9.6 to -8.5 °C under elevated CO2 , anda similar marginally significant (P = 0.079) reduction was observedfor the mean temperature that caused 50% leaf damage (T50),from -6.7 to -6.0 °C. The mean temperature at which initialleaf damage was observed (T0) was not significantly influencedby elevated CO2 . Although concentrations of soluble sugars(+25%,P = 0.042), starch (+53%, P < 0.001), and total non-structuralcarbohydrates (TNC, +40%, P < 0.001) were significantly higherunder elevated CO2 , leaf freezing resistance actually decreasedunder elevated CO2 . Concentrations of soluble sugars were positivelycorrelated with freezing resistance when viewed across all fivecommunity dominants, but within any individual species, no suchrelationships were found. We also found no evidence for ouroriginal hypothesis that increased concentrations of solublesugars increase freezing resistance. Thus, future atmosphericCO2levels may instead increase the risk of late spring freezingdamage. Furthermore, the strong differences in freezing resistanceobserved among the species, along with decreased freezing resistance,may increase the risk of losing species that have inherentlyweak freezing resistances from the plant community. Copyright2001 Annals of Botany Company CO2enrichment, frost hardiness, sugar, starch, total non-structural carbohydrates (TNC) 相似文献
15.
Methionine sulfoximine caused ammonia accumulation and photosyntheticrate inhibition in leaf discs from two C4 species, Zea maysL. cv. F. M. Cross (Hybrid) and Sorghum bicolor L. Moench cv.NC-70X, as well as one C3 plant species, Datura stramonium L.cv. stramonium. Similar results were obtained earlier with theC3 species Spinacia oleracea L. The effect occurred in the absenceof inorganic nitrogen reduction and was light dependent. Ammoniaaccumulation rates were similar in all four species examined.The results support a role for glutamine synthetase in leafammonia recycling in both C4 and C3 leaves.
1 Current address: Cetus Madison Corporation, 2208 Parview Road,Middleton, WI 53562, U.S.A. (Received November 2, 1981; Accepted April 28, 1982) 相似文献
16.
Changes in NMR relaxation times (T1) of water protons and watercontents of leaves of woody plants affected by formation ofinsect galls were studied in Machilus, Zelkova and Cinnamomumparasitized with a gall-midge, an aphid and two different Triozinepsyllids, respectively. The presence of galls in Machilus leavesincreased both T1 and water contents in the galled leaf tissues,while such tissues in Zelkova showed only increases in T1. Similartrends for both parameters were also observed in gall-bearingleaf tissues of Machilus and Cinnamomum, with galls caused bytwo different psyllids. It seems that it is the particular characteristicsof leaf tissues of the host plant that determine whether thesystemic effect of the presence of galls is reflected both inT1 and in water content, or only in T1. Histologic features,including the presence of tannins in and leakage of electrolytesfrom these materials, were compared with those of normal (ungalled)leaves to determine possible causative factors involved in theprolongation of T1 relaxation times that were associated withthe presence of insect galls. The eco-physiological implicationof tannins with respect to the host-parasite relationship isalso discussed. (Received October 27, 1989; Accepted April 24, 1990) 相似文献
17.
Growth rates of dominant planktonic ciliates in two freshwater bodies of different trophic degree 总被引:3,自引:0,他引:3
Macek Miroslav; S{caron}mek Karel; Pernthaler Jakob; Vyhnalek Vojtech; Psenner Roland 《Journal of plankton research》1996,18(4):463-481
The in situ growth rates of dominant ciliate species were studiedduring and shortly after phytoplankton peaks in two water bodies:the eutrophic Rímov Reservoir (South Bohemia, Czech Republic)and the oligo-mesotrophic Piburger See (Tyrol, Austria). Growthrate estimates based on changes in ciliate abundances in incubatedpre-screened samples (EN) were compared with those derived fromthe ciliate cell volume and ambient temperatures (ET). The valuesof EN were always rather lower than those of ET. During thestudies, the food supply limited the ciliate growth dependingon the ciliate feeding mode. An ecological grouping into filterfeeding versus raptorial feeding (hunting) species,on the one hand, and attached/crawling (browsing) versus freeswimming species, on the other hand, clearly affected experimentalestimation. Both fine filter feeders (namely attached) and browsersexhibited a calculated EN closer to the theoretical (maximum)ET than did hunters and coarse filter feeders. It was apparent,for example, comparing EN and ET (day1) of the followingspecies: filter feeders Halteria grandinella (EN = 0.42; ET>1.4), Strobilidium hexakinetum (0.34;>1.9), Pelagohalteriaviridis (0.27;>0.9), Vorticella aquadulcis complex (0.75;>1.0);raptorial Balanion planctonicum (0.65;>1.5), Urotricha furcata(in Rímov Reservoir 0.65;>2.1; in Piburger See 0.20;>1.5),Rhabdoaskenasia minima (0.22;>1.0), Askenasia acrostomia(0.12;>0.6); opportunistic Cyrtolophosis mucicola (0.42;>1.6)and Cinetochilum margaritaceum (0.86;>1.4). Predation byrotifers apparently affected measurements in several samplescontaining {small tilde}400 rotifers l1 however, it seemedto be of little importance in the water column. 相似文献
18.
Nuclei were isolated from cotyledons of a range of accessionsfrom 14 species of Glycine. These were stained with ethidiumbromide and the relative fluorescence for each genotype wasmeasured by flow cytometry. The DNA content was estimated bycomparison of relative fluorescence with that from nuclei fromseedling leaves of Allium cepa, whose DNA content has been calculatedpreviously by chemical assay. The 4C amounts for diploid Glycineranged from 3.80 to 6.59 pg. Two groups of diploid species appearedfrom the analysis. The first consisted of species with amountsranging from 3.80 to 5.16 pg and included G. canescens (AA),G. argyrea (A1 A1), G. clandestina (A2A2), G. microphylla(BB),G. latifolia (B1B1), G. tabacina 2n=40 (B2B2), G. tomentella2n=38 (EE) and 2n=40 (DD), G. max and G. soja (GG), G. arenariaand G. latrobeana. A second group had higher DNA contents rangingfrom 5.27 to 6.59 pg, and consisted of G. curvata, G. cyrtoloba(CC), and G. falcata (FF). The polyploid species, G. tabacina2n=80 (AABB, BBB1B1), G. tomentella 2n=78 and 2n=80 (AAEE andDDEE, respectively) contained amounts approximating to the sumsof the respective parental diploid species thought to have givenrise to these allotetraploids. Intraspecific variation was detectedin the DNA content of G. canescens. Within the overall distributionof DNA amounts found in A genome species, each genome containeda range of DNA contents specific to that species. This phenomenonwas also detected amongst B genome species. 相似文献
19.
Mechanisms of Thermoregulation in Flying Bees 总被引:1,自引:0,他引:1
SYNOPSIS. Thermoregulation of elevated thorax temperatures isnecessary for bees to achieve the high rates of power productionrequired for flight, and is a key factor allowing them to occupywidely varying thermal environments. However, the mechanismsby which bees thermoregulate during flight are poorly understood.Thermoregulation is accomplished by balancing heat gain andheat loss via the following routes: convection, evaporation,and metabolic heat production. There appears to be a diversityof thermoregulatory mechanisms employed during flight amongbee species. Some species, particularly Bombus spp., activelyincrease the distribution of thoracic heat to the abdomen duringflight as air temperature (Ta) rises, and apparently thermoregulateby varying convective heat loss. However, thermal variationin convection has not been directly measured for any free-flyingbee. Above 33°C, flying Apis mellifera greatly increaseevaporative heat loss with Ta, and many other species "tongue-lash"during flight at high Tas or when artificially heated. Thus,evaporation seems to be important for preventing overheatingduring flight at very high Tas. Flying A. mellifera and Centrispallida strongly decrease metabolic rate as Ta increases, suggestingthat they are varying metabolic heat production for thermoregulationand not aerodynamic requirements. Variation in metabolic heatproduction appears to be mediated by changes in wingbeat kinematics,since wingbeat frequency decreases with Ta for A. melliferaand Centris spp. It is unknown if the decrease in flight metabolicrate at higher Tas occurs secondarily as a consequence of greaterefficiency or if it is truly an active response. 相似文献
20.
The grass Alloteropsis semialata (R.Br.) Hitchcock is uniquein that both Kranz and non-Kranz leaf anatomy has been reportedin this species. The present study investigates Kranz formsof A. semialata collected from a single ecological niche. Theseplants exhibit morphological and anatomical differences withrespect to leaf area, stomatal size and stomatal distribution.Carbon dioxide and water exchange measurements in the two formsshow the expected pattern of higher photosynthetic rate andhigher water utilization efficiency associated with Kranz anatomy.No intermediate physiological response or anatomical form wasobserved in this sample. Alloteropsis semialata (R.Br.) Hitchcock, C3 photosynthetic, C4 photosynthesis, water utilization, leaf anatomy, Kranz anatomy 相似文献