首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The hydraulic architecture of the secondary hemiepiphyte Monstera acuminata was examined in native plants from Los Tuxtlas, Veracruz, Mexico, to determine how it compared to better-known growth forms such as trees, shrubs, lianas and primary hemiepiphytes. Monstera acuminata starts its life cycle as a prostrate herb. As it ascends a tree or other vertical support, the stem becomes thicker, produces larger leaves, and may die back from the base upwards until only aerial feeding roots serve to connect the stem to the soil. Unlike the pattern of vessel-size distribution along the stems of woody dicotyledons, M. acuminata has its wider vessels at the top of the stem, decreasing in diameter towards the base. Also peculiar is the fact that Huber values (axis area/distal leaf area) tend to increase exponentially at higher positions within the plant. Based on the hydraulic conductivity ( k h) and leaf-specific conductivity (LSC, k h/distal leaf area), the base of the stem potentially acts as a severe hydraulic constriction. This constriction is apparently not limiting, as aerial roots are produced further up the stem. The plants have remarkably strong root pressures, up to 225 kPa, which may contribute to the maintenance of functional vessels by refilling them at night or during periods of very high atmospheric humidity, as in foggy weather and rain. In common with dicotyledonous plants, vessel length, vessel diameter, k h, specific conductivity ( k s, k h/axis area) and LSCs were all positively correlated with axis diameter. The features of the hydraulic architecture of M. acuminata may be an evolutionary consequence of an anatomical constraint (lack of vascular cambium and therefore of secondary growth) and the special requirements of the hemiepiphytic growth form.  相似文献   

2.
Downwardly-growing grapevine shoots have smaller and more frequent vessels than upwardly-growing ones and, as a consequence, a lower hydraulic conductivity. Here, grapevine (Vitis vinifera L.) shoot growth orientation was manipulated to test whether downward shoot orientation negatively affects vessel growth in the apex via a shortage of water and nutrients. The orientation of the central vine shoot portion was inverted by two consecutive 135 degrees bends, resulting in double-bent N-shaped vines; the central downward shoot portion was of different lengths in the experimental treatments to induce increasing reductions of shoot conductivity. These treatments reduced shoot conductivity and water flow, but had no effects on vessel development and frequency in the apex. In a second experiment, auxin concentration was assessed in shoots of upwardly- and downwardly-growing plants. IAA concentration at the apical internodes was higher in downwardly-oriented shoots than in shoots growing upwards. In addition, a higher density and a lower vessel diameter were observed in the lower, than the upper side, of the downwardly-oriented shoot, suggesting increased accumulation of auxin in the lower side. These results suggest that the downward orientation induces accumulation of auxin in the apex, which in turn affects the density and the size of the xylem vessels, causing reduction of hydraulic conductivity.  相似文献   

3.
4.
Five evergreen subtropical tree species growing under identical environmental conditions were investigated to establish which hydraulic properties are genotypically rigid and which show phenotypic plasticity. Maximum xylem-specific conductivity ( k s) correlated well with the anatomical characteristics (conduit diameter and density) for the four angiosperms Tecomaria capensis , Trichilia dregeana , Cinnamomum camphora and Barringtonia racemosa ; the anatomy of the gymnosperm Podocarpus latifolius was not assessed. Huber values (functional xylem cross-sectional area : leaf area) varied inversely with k s among species. Maximum leaf-specific conductivity was similar in the five unrelated species. Vulnerability of xylem to cavitation differed between species, as did the relationship between transpiration and water potential. Models of these parameters and isolated midday readings confirm that these trees operate at similar maximum leaf-specific conductivity ( k l) values. The data are consistent with the hypothesis that conductivity characteristics ( k l, k s) are influenced by environment, whereas vulnerability to cavitation is genetically determined.  相似文献   

5.
Xylem maturation in elongating leaf blades of tall fescue ( Festuca arundinacea ) was studied using staining and microcasting. Three distinctive regions were identified in the blade: (1) a basal region, in which elongation was occurring and protoxylem (PX) vessels were functioning throughout; (2) a maturation region, in which elongation had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function; (3) a distal, mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic conductivity ( K h) was measured in leaf sections from all these regions and compared with the theoretical axial hydraulic conductivity ( K t) computed from the diameter of individual inner vessels. K t was proportional to K h throughout the leaf, but K t was about three times K h. The changes in K h and K t along the leaf reflected the different stages of xylem maturation. In the basal 60 mm region, K h was about 0.30±0.07 mmol s−1 mm MPa−1. Beyond that region, K h rapidly increased with metaxylem element maturation to a maximum value of 5.0±0.3 mmol s−1 mm MPa−1, 105 mm from the leaf base. It then decreased to 3.5±0.2 mmol s−1 mm MPa−1 near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.  相似文献   

6.
Abstract. This paper describes studies on trees of Pisonia grandis , bushes of Argusia argentea , and the perennial herb Melanthera biflora , growing on One Tree Island, a coral cay of the Great Barrier Reef with 'soil' of coarse coral rubble. Water potential (Ψb, measured on small shoots with a pressure chamber), sap flow, stomatal conductance, vapour pressure deficit and photon flux density were monitored over day/night cycles. Sap flow and Ψb responded to changes in light and humidity. From these experiments good linear correlations were found between sap flow in a shoot and Ψb of similar adjacent shoots. The linearity suggests that the resistance to sap flow is constant as Ψb varies. The correlation, however, does not indicate a causal relationship between Ψb of an individual shoot on the plant and its sap flow. Ψb was only slightly different in shaded shoots from those in sunshine, although sap flow would be expected to differ between them. Enclosing shoots and so reducing their transpiration and sap flow to very low rates resulted in only small changes in Ψb of the enclosed shoots; Tb of such enclosed shoots should closely approximate that of the xylem at the point of shoot attachment. From these results it is suggested that the resistance to water flow in shoot and leaf xylem is small compared to the resistance further down the plant, in the root or at the root/soil interface. Shoot xylem water potential would be similar for all parts of the plant, and in such plants the water potential of shoots in the shade would be determined by the overall water use of the plant.  相似文献   

7.
Abstract. Phloem sap was collected from petioles of growing and fully expanded leaves of lupins exposed to 0–150 mol m−3 [NaCl]ext, for various periods of time. Sap bled from growing leaves only after the turgor of the shoot was raised by applying pneumatic pressure to the root. Increased pressure was also needed to obtain sap from fully expanded leaves of plants at high [NaCl]ext. Exposure to NaCl caused a rapid rise in the Na+ concentration in phloem sap to high levels. The Na+ concentration reached 20 mol m−3 within a day of exposure and reached a plateau of about 60 mol m−3 in plants at 50–150 mol m−3 [NaCl]ext, after a week. There was a slower, smaller increase in the Cl concentration. K+ concentrations in phloem sap were not affected by [NaCl]ext. Cl concentrations in phloem sap collected from growing leaves were similar to those from old leaves while Na+ concentrations were somewhat increased, suggesting that there was no reduction in the salt content of the phloem sap while it flowed within the shoot to the apex. Calculations of ion fluxes in xylem and phloem sap indicated that Na+ and Cl fluxes in the phloem from leaves of plants at high NaCl could be equal to those in the xylem. This prediction was borne out by observations that Na+ and Cl concentrations in recently expanded leaves remained constant.  相似文献   

8.
In order to manipulate the shoot demand for mineral nutrients per unit root weight, maize ( Zea mays L.) seedlings were grown in nutrient solution with different temperatures in the root zone and at the shoot base. The aerial temperature was kept uniform at 24/20°C day/night. At a root zone temperature (RZT) of 24°C, shoot growth was reduced by decreasing the shoot base temperature (SBT) to 12°C; at a RZT of 12°C, shoot growth was increased by raising the SBT to 24°C. At both RZT root growth was not affected by the SBT. Thus, the shoot demand for nutrients per unit root was either increased by raising, or decreased by lowering the SBT. The net uptake rate of potassium (K), as determined from accumulation rates between sequential harvests, was not affected within the first 3 days after lowering the SBT, whereas net translocation rates of K into the shoot and translocation rates in the xylem exudate of decapitated plants were markedly reduced. Obviously, translocation of K into the shoot seems to be regulated independently from K uptake into the root cells. Translocation rates of K in the xylem exudate of decapitated plants were markedly reduced when the nutrient solution was replaced by CaCl2 solution during exudation. But, depending on the SBT before decapitation, significant differences remained in the translocation rates of K even when K uptake from the nutrient solution was prevented.
From the results it is suggested that xylem loading of K is regulated separately from K uptake from the external solution and that the adaptation of K translocation to shoot demand is coupled with an altered capacity of the root for xylem loading.  相似文献   

9.
To study the effects of water-deficit stress on root water flow properties in trembling aspen ( Populus tremuloides Michx.), seedlings were grown in solution culture and subjected to water-deficit stress by placing their roots in sealed high humidity chambers. After 17 h of stress treatment, seedlings showed mild stress (MS) symptoms with a decline in shoot water potentials. Within 20 h, shoot water potentials rapidly declined, and severe stress (SS) symptoms were present. Root hydraulic conductivity ( L pr) increased more than two-fold and the relative concentration of apoplastic tracer dye trisodium 3-hydroxy-5, 8, 10-pyrenetrisulphonate (PTS3) in xylem exudate decreased by 73.6% in MS seedlings. Conversely, Lpr decreased (55.3%) and PTS3 increased (28.6%) in SS seedlings. Treatment of roots with 0.1 m M mercuric chloride decreased root volume flow density ( J v) by about 29.0% in control and MS plants with no decrease measured in SS seedlings. Mercuric chloride also increased PTS3 concentration in xylem exudate of control (59%) and MS (86%) seedlings with no change observed in SS plants. The results suggest that aquaporin-mediated transport is important in the regulation of root water flow under drought stress and that root water flow properties are strongly affected by the stress level. Regulation of root water flow may represent an important drought-stress resistance mechanism.  相似文献   

10.
By application of a recently developed method allowing analysis of gibberellins (GAs) in mg amounts of tissue, the effect of photoperiod on levels of GAs in shoot tips of individual seedlings of the woody species Salix pentandra was studied. In elongating long day-grown seedlings, maximum levels of GA1 were found 5–20 mm below the apex, approximately twice the levels in other segments. After exposure of plants to 5 or 15 short days, the levels of GA1 were about 50% lower within this specific region of the stem, as compared with seedlings grown under long days. Short day-induced cessation of shoot elongation also correlated with overall declines in the levels of GA53, GA19, GA20 and GA8, Within each photoperiodic treatment the levels of these GAs were generally relatively similar throughout the upper 35 mm of stems. No differences in internode lengths or in lengths of pith or epidermal cells were found in plants grown under long days compared with those exposed to 5 short days. In both cases, cells in mitosis were observed in the subapical stem tissues of shoot tips. After 15 short days, stem elongation was completed, and dividing cells were generally not found in the subapical part of the stem. However, short day exposure did not prevent elongation of internodes and cells differentiated before the treatment was started. Thus, the localised decrease in level of GA1 in shoot tips under short days precedes the morphological and anatomical changes connected with the short day-induced cessation of elongation growth. This supports the hypothesised role for GA1 in photoperiodic control of shoot elongation in S. pentandra .  相似文献   

11.
Changes in nodule growth and activity and in the concentrations of soluble N compounds in nodules, leaves and xylem sap under conditions of altered N nutrition in the actinorhizal plant Myrica gale L. are reported. Altering the N nutrition of symbiotic plants may alter the internal regulation of combined N which in turn may regulate nodule growth and activity. Flushing nodules daily with 100% O2 caused a decline in amide concentration and an increase in nodule growth although plants had recovered some nitrogenase activity within 4 h of exposure to O2. Samples of nodules, leaves and xylem sap were derivatized and amino acids identified and quantified using either reverse phase high performance liquid chromatography or gas chromatography-mass spectrometry in single ion monitoring mode. The ratio of asparagine in the nodules to that in the xylem was much higher in plants fed N (6.7 for NH+4-fed and 8.3 for NO3-fed plants) than for N2-fixing plants (2.5). Significant amounts of 15N added as 15NH+4 or 15NO3 accumulated in nodules following accumulation in the shoot which is consistent with the translocation of N to the nodules via the phloem. The uptake of 15NH+4 led to the synthesis and subsequent translocation of glutamine in the xylem sap. These results are discussed in terms of the feedback mechanisms that may regulate nitrogen fixation in Myrica root nodules.  相似文献   

12.
Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard ( Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO3. The presence of 20 μ M AgNO3 or 5 μ M AVG in culture medium containing 5 μ M naphthaleneacetic acid and 10 μ M benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO3 greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 μ M 2-chloroethylphosphonic acid (CEPA), but AgNO3-induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC by 70–80%. In contrast, AgNO3 stimulated all 3 parameters of ethylene synthesis. Both AgNO3 and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO3. Leaf discs derived from plants grown with AVG or AgNO3 were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO3 in the medium was inhibitory to regeneration of those derived from plants grown with AgNO3.  相似文献   

13.
Abstract The effect of oxygen on the growth, metabolism, and leukotoxin production of Actinobacillus actinomycetemcomitans 301-b was examined using a chemostat equipped with a redox potential control system. Steady states were obtained with fructose-limited cultures grown at a dilution rate of 0.1 h−1 under strictly anaerobic ( E h=−460 mV) and microaerobic conditions ( E h≤ 150 mV) but not under highly aerated conditions ( E h≥ 100 mV). The optimum growth was recorded at E h=−300 to − 200 mV and the recorded Y fructose value was about 1.3 times the Y fructose of anaerobic cultures. Although the organism contains a respiratory chain, the increased Y fructose under the microaerobic conditions might result from the increased substrate-level phosphorylation at the site of acetate kinase but not from electron transport phosphorylation. After passing threshold aeration ( E h=−100 mV), the culture yielded a variant with transparent colony morphology. Under anaerobic conditions, the Y fructose of the variant was about 1.6 times that of the original opaque colony-forming cells. The optimum growth of the variant was also recorded at E h=− 300 to − 200 mV. In both types of cells, the production of leukotoxin reached a maximum at E h=−350 to − 200 mV. These findings suggested the microaerophilic nature of A. actinomycetemcomitans .  相似文献   

14.
Peanuts ( Arachis hypogaea L. cv. Shulamit) grown with NO3 and saline water in hydroponics responded positively to addition of nitrogen (N) in their vegetative growth, but not in desert dune sand. In order to clarify these conflicting results, peanut plants were grown in a greenhouse pot experiment with fine calcareous sand. The nutrient solution contained 0 or 50 m M NaCl and 2 or 6 m M N in the form of Ca(NO3)2, NH4NO3 or (NH4)2SO4. Three replicates were harvested after 48 days (beginning of reproductive stage) and three after 109 days (pod filling). In addition, gynophores were treated with 0, 50, 100, 150 or 200 m M NaCl outside the growth pot to check their sensitivity to salt. Shoot dry weight became greater with increasing NH4+/NO3 ratio. Increasing the N concentration from 2 to 6 m M did not change shoot dry weight of the NH4NO3 or NH4+-fed plants, but caused a reduction in shoot dry weight of NO3-fed plants. Shoot dry weight was not affected by increasing the NaCl concentration to 50 m M . Salt caused an increase in the number of gynophores per plant and a reduction of the mean pod weight. A NaCl concentration of 100 m M and above reduced gynophore vitality. It is concluded that the salt sensitivity of peanut plants resides mainly in the sensitivity of the reproductive organs.  相似文献   

15.
Eucalyptus pauciflora Sieber ex Sprengel. (snow gum) was grown under ambient (370  µ L L−1) and elevated (700  µ L L−1) atmospheric [CO2] in open-top chambers (OTCs) in the field and temperature-controlled glasshouses. Nitrogen applications to the soil ranged from 0.1 to 2.75 g N per plant. Trees in the field at high N levels grew rapidly during summer, particularly in CO2-enriched atmosphere, but suffered high mortality during summer heatwaves. Generally, wider and more numerous secondary xylem vessels at the root–shoot junction in CO2-enriched trees conferred fourfold higher below-ground hydraulic conductance. Enhanced hydraulic capacity was typical of plants at elevated [CO2] (in which root and shoot growth was accelerated), but did not result from high N supply. However, because high rates of N application consistently made trees prone to dehydration during heatwaves, glasshouse studies were required to identify the effect of N nutrition on root development and hydraulics. While the effects of elevated [CO2] were again predominantly on hydraulic conductivity, N nutrition acted specifically by constraining deep root penetration into soil. Specifically, 15–40% shallower root systems supported marginally larger shoot canopies. Independent changes to hydraulics and root penetration have implications for survival of fertilized trees under elevated atmospheric [CO2], particularly during water stress.  相似文献   

16.
Gibberellins and photoperiodic control of shoot elongation in Salix   总被引:1,自引:0,他引:1  
Effects of exogenous gibberellins GA53, GA44, GA19, GA20 and GA1 on photoperiodically controlled shoot elongation in seedlings of Salix pentandra L. were studied. Gibberellins GA20 and GA1 induced shoot elongation under short days (SD) and could substitute for a transfer to long day (LD), while gibberellins A53, A44 and A19 were inactive. In seedlings exposed to a prolonged SD-treatment (30 days) there was a significant positive interaction between a transfer to LD and a treatment with GA20 and GA1 on shoot elongation. In addition, GA19 enhanced the growth promotive effect of LD in these seedlings. The results are compatible with the suggestion that conversion of GA19 to GA20 is blocked under SD. This effect is supposed to be an early process leading to the cessation of shoot elongation under SD. Responsiveness of the seedlings to LD and to a GA-treatment gradually decreased with an increasing length of exposure to SD.  相似文献   

17.
The external heat ratio method is described for measurement of low rates of sap flow in both directions through stems and other plant organs, including fruit pedicels, with diameters up to 5 mm and flows less than 2 g h−1. Calibration was empirical, with heat pulse velocity ( v h) compared to gravimetric measurements of sap flow. In the four stem types tested ( Actinidia sp. fruit pedicels, Schefflera arboricola petioles, Pittosporum crassifolium stems and Fagus sylvatica stems), v h was linearly correlated with sap velocity ( v s) up to a v s of approximately 0.007 cm s−1, equivalent to a flow of 1.8 g h−1 through a 3-mm-diameter stem. Minimum detectable v s was approximately 0.0001 cm s−1, equivalent to 0.025 g h−1 through a 3-mm-diameter stem. Sensitivity increased with bark removal. Girdling had no effect on short-term measurements of in vivo sap flow, suggesting that phloem flows were too low to be separated from xylem flows. Fluctuating ambient temperatures increased variability in outdoor sap flow measurements. However, a consistent diurnal time-course of fruit pedicel sap flow was obtained, with flows towards 75-day-old kiwifruit lagging behind evaporative demand and peaking at 0.3 g h−1 in the late afternoon.  相似文献   

18.
Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA3) on K+ (Rb+) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA3 was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K+ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb+ replaced K+, the GA3 effects were evident also on Rb+ uptake and transport. In intact plants, GA3 increased the Rb+ transported to the shoot but did not affect Rb+ accumulation in the root. It is suggested that these GA3 effects can be explained if it is assumed that GA3 acts on the transport of ions to the xylem vessels.  相似文献   

19.
Populus euramericana (Dode) Guinier cv. Robusta plants were cultivated at irradiances of 7.5, 15 and 30 W m−2 (32.5, 65 and 130 μmol m2 s−1), 400–700 nm at 22°C and a relative humidity between 40 and 60% on a gravel culture subirrigated with Hoagland's nutrient solution. The basal diameter of the growing shoot, a measure of the number of apical cells participating in growth, increased proportionally to irradiance and was correlated with mature leaf length. The development of the length of the growing shoot (Lgs) depended also on the nutritional status of the (young) shoot. Lgs was strongly correlated with the rate of height growth.  相似文献   

20.
The importance of xylem constraints in the distribution of conifer species   总被引:10,自引:0,他引:10  
Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (φ50) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi-arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides . Mean φ50 was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of φ50 was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO2 concentration (ci) in the leaves of these species during artificial drought was strongly correlated with φ50 suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade-off between xylem conductivity and xylem vulnerability was tested in a sub-sample of four species, but no evidence of an inverse relationship between φ50 and either stem-area specific (Ka) or leaf-area specific conductivity (K1) was found.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号