bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of transpiration from the upper canopy of a tropical forest: the role of stomatal, boundary layer and hydraulic architecture components
Authors: MEINZER F. C. , ANDRADE J. L. , GOLDSTEIN G. , HOLBROOK N. M. , CAVELIER J. , JACKSON P. 
Published: November 2003

ABSTRACTConcurrent, independent measurements of stomatal conductance (gs), transpiration (E) and microenvironmental variables were used to characterize control of crown transpiration in four tree species growing in a moist, lowland tropical forest. Access to the upper forest canopy was provided by a construction crane equipped with a gondola. Estimates of boundary layer conductance (gb) obtained with two independent methods permitted control of E to be partitioned quantitatively between gs and gb using a dimensionless decoupling coefficient (Ω) ranging from zero to 1. A combination of high gs (c. 300–600 mmol m−2 s−1) and low wind speed, and therefore relatively low gb (c. 100–800 mmol m−2 s−1), strongly decoupled E from control by stomata in all four species (Ω= 0.7–0.9). Photosynthetic water‐use efficiency was predicted to increase rather than decrease with increasing gs because gb was relatively low and internal conductance to CO2 transfer was relatively high. Responses of gs to humidity were apparent only when the leaf surface, and not the bulk air, was used as the reference point for determination of external vapour pressure. However, independent measurements of crown conductance (gc), a total vapour phase conductance that included stomatal and boundary layer components, revealed a clear decline in gc with increasing leaf‐to‐bulk air vapour pressure difference (Va because the external reference points for determination of gc and Va were compatible. The relationships between gc and Vc and between gs and Vs appeared to be distinct for each species. However, when gs and gc were normalized by the branch‐specific ratio of leaf area to sapwood area (LA/SA), a morphological index of potential transpirational demand relative to water transport capacity, a common relationship between conductance and evaporative demand for all four species emerged. Taken together, these results implied that, at a given combination of LA/SA and evaporative demand scaled to the appropriate reference point, the vapour phase conductance and therefore transpiration rates on a leaf area basis were identical in all four contrasting species studied.
The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don
Authors: WALCROFT A. S. , WHITEHEAD D. , SILVESTER W. B. , KELLIHER F. M. 
Published: November 2003

ABSTRACTResponses of photosynthesis (A) to intercellular CO2 concentration (ci) in 2‐year‐old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4‐fold increase in Vcmax, the maximum rate of carboxylation (10.7–43.3 μol m−2 s−1 and a 3‐fold increase in Jmax, the maximum electron transport rate (20.5–60.2 μmol m −2 s−1). The temperature optimum for Jmax was lower than that for Vcmax, causing a decline in the ratio Jmax:Vcmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg−1, and there were linear relationships between N concentration and both Vcmax and Jmax. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg−1 near the base to 1.54 mol kg−1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.
Heat shock temperature acclimation of normal secretory protein synthesis in barley aleurone cells
Authors: CAMPBELL J. D. , FIELDING L. A. , BRODL M. R. 
Published: November 2003

ABSTRACTExposure of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers to 40°C for a period of 3 h results in the selective suppression of the synthesis and secretion of hydrolytic enzymes; other normal cellular protein synthesis continues during heat shock. This suppression is correlated with secretory protein mRNA destabilization and the dissociation of stacked ER lamellae during heat shock (Belanger et al. 1986, Proceedings of the National Academy of Sciences USA 83, pp. 1354–1358). In this report we examined the effect of exposure to extended periods of heat shock. If exposure to 40°C was continued for a period of 18 h, the synthesis of α‐amylase, the predominant secreted hydrolase, resumed. This was accompanied by increased α‐amylase mRNA levels and the reformation of ER lamellae. Though initial exposure (3 h) to 40°C reduced protein secretion to ∼10% of that observed in aleurone cells maintained at 25°C, exposure for prolonged periods (16–20 h) permitted the resumption of protein secretion to ∼66% of non‐heat‐shocked control levels. The resumption of normal secretory protein synthesis during prolonged exposure to 40°C was correlated with an increase in the incorporation of [14C]glycerol into phosphatidylcholine and an increase in the ratio of saturated to unsaturated fatty acids in lipids isolated from ER membrane preparations. Increased fatty acid saturation has been demonstrated to enhance thermostability in biological membranes, and such changes in membrane composition may be important to the recovery of secretory protein synthesis at the ER.
Root respiration in citrus acclimates to temperature and slows during drought
Authors: BRYLA D. R. , BOUMA T. J. , EISSENSTAT D. M. 
Published: November 2003

ABSTRACTCitrus seedlings were grown in soil columns in which the root system was hydraulically separated into two equal layers; this enabled us to maintain roots in the upper layer without water for 110 d. The columns were placed into waterbaths modified so that soil temperatures in the top layer could be maintained at 25°C or at 35°C, while temperature in the bottom layer was maintained at 25°C. We hypothesized that, if citrus plants were grown in dry soil for an extended period, root mortality would increase if the cost of maintaining the roots was increased by elevating the soil temperature. However, during the drought period we did not observe any root mortality, even at the higher soil temperature. Moreover, we did not find that root respiration was increased by prolonged exposure to drought and higher soil temperature. We did find that root respiration rates slowed in dry soil. Furthermore, when the soil columns were switched from one temperature treatment to another, root respiration rates in wet soil rapidly increased when moved to a higher temperature or rapidly decreased when moved to a lower temperature. But after only 4 d, respiration rates returned to their original level; root respiration in dry soil was not affected by either short‐or long‐term shifts in soil temperature. Root respiration in citrus appears to acclimate rapidly to changes in soil temperature.
The reflectance properties of plant internodes modify elongation responses to lateral far‐red radiation
Authors: SEAVERS G. P. , SMITH H. 
Published: November 2003

ABSTRACTThe quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied. Reflectance of incident light, which was either normal or longitudinal to the internode axis, was investigated. Increasing the angle of incidence caused a greater proportion of incident light to be reflected. Light striking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the reflected light quality. At larger angles, interactions with the internode were reduced. As a parallel investigation, the extension growth rate of light‐grown Sinapis alba L. seedlings was monitored continuously using sensitive linear displacement transducers. When the angle of illumination by fibre‐optic probes, presenting far‐red light to the growing internode, was changed from 0° to 45°, an increase was observed in stem extension rate. There is a possibility that this rate increase was the result of a fall in the red:far‐red ratio (R:FR) present inside the plant internode as the angle of incidence was altered. However, it is more likely that it was due to the larger surface area of stem being illuminated. The consequences of these observations are discussed in relation to the potential influence of such modified reflections on canopy light environments and resultant shade responses which may occur when light of known R:FR impinges on plant internodes at angles other than 0°. The possibility is discussed that plants may perceive the quality of reflected radiation from neighbouring plants to be substantially different dependent upon the angle at which it is reflected.
The responses of wild‐type and ABA mutant Arabidopsis thaliana plants to phosphorus starvation
Authors: TRULL M. C. , GUILTINAN M. J. , LYNCH J. P. , DEIKMAN J. 
Published: November 2003

ABSTRACTThe growth patterns of plants subjected to phosphorus starvation resemble those caused by treatment with ABA, suggesting that ABA could mediate the response of the plant to phosphorus starvation. We examined the role of ABA in phosphorus stress by comparing growth and biochemical responses of Arabidopsis thaliana ABA mutants aba‐1 and abi2‐1 to those of wild‐type plants. We first characterized acid phosphatase production of wild‐type Arabidopsis in response to phosphorus starvation. We found that several acid phosphatase isozymes are present in roots and shoots, but only a subset of these isozymes are induced by phosphorus stress, and they are induced in both organs. Production of acid phosphatase in response to phosphorus stress was not affected by the aba‐1 or abi2‐1 mutations. Low phosphorus also resulted in decreased growth of both wild‐type and ABA mutant plants, and the root‐to‐shoot ratio was increased in both wild type and mutants. Anthocyanins accumulated in response to phosphorus stress in both wild‐type and mutant plants, but the increase was reduced in the aba‐1 mutant. Thus, two different ABA mutants responded normally in most respects to phosphorus stress. Our data do not support a major role for ABA in coordinating the phosphorus‐stress response.
Rates of stomatal opening in conifer seedlings in relation to air temperature and daily carbon gain
Authors: PEPIN S. , LIVINGSTON N. J. 
Published: November 2003

ABSTRACTExperiments were conducted on well watered 1‐year‐old Douglas fir [Pseudotsuga menziesii(Mirb.) Franco], western hemlock [Tsuga heterophylla(Raf.) Sarg.] and western redcedar (Thuja plicataDonn) seedlings to determine the effects of temperature on whole‐plant photosynthetic and stomatal responses to short‐term fluctuations in irradiance (Q). Following a step change inQ, time constants (τ, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar τAdecreased from 30 ± 4 min at 5 °C to 10 ± 1 min at 25 °C. In all cases, τAwas within 10–15% of τgs. There was considerable variation in τ among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for τ accounted for 99% of the diurnal variability inAandgsfor seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of dailyAwere within 2% of those measured. Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3–4 episodes (≥1 h) of shade (200 or 500 μmol m−2s−1) or complete darkness during the day. In such cases, dailyAwas overestimated by up to 4 and 21%, respectively, if a function for τ was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in τ could lead to increases in daily carbon gains of almost 5% depending on the frequency and degree of shading. If these daily gains were translated into increased dry matter production and compounded, seasonal gains would be even larger.
Oxygen sensitivity of C4 photosynthesis: evidence from gas exchange and chlorophyll fluorescence analyses with different C4 subtypes
Authors: MAROCO J. P. , KU M. S. B. , EDWARDS G. E. 
Published: November 2003

ABSTRACTBecause photosynthetic rates in C4 plants are the same at normal levels of O2 (c, 20 kPa) and at c, 2 kPa O2 (a conventional test for evaluating photorespiration in C3 plants) it has been thought that C4 photosynthesis is O2 insensitive. However, we have found a dual effect of O2 on the net rate of CO2 assimilation among species representing all three C4 subtypes from both monocots and dicots. The optimum O2 partial pressure for C4 photosynthesis at 30 °C, atmospheric CO2 level, and half full sunlight (1000 μmol quanta m−2 s−1) was about 5–10 kPa. Photosynthesis was inhibited by O2 below or above the optimum partial pressure. Decreasing CO2 levels from ambient levels (32.6 Pa) to 9.3 Pa caused a substantial increase in the degree of inhibition of photosynthesis by supra‐optimum levels of O2 and a large decrease in the ratio of quantum yield of CO2 fixation/quantum yield of photosystem II (PSII) measured by chlorophyll a fluorescence. Photosystem II activity, measured from chlorophyll a fluorescence analysis, was not inhibited at levels of O2 that were above the optimum for CO2 assimilation, which is consistent with a compensating, alternative electron How as net CO2 assimilation is inhibited. At suboptimum levels of O2, however, the inhibition of photosynthesis was paralleled by an inhibition of PSII quantum yield, increased state of reduction of quinone A, and decreased efficiency of open PSII centres. These results with different C4 types suggest that inhibition of net CO2 assimilation with increasing O2 partial pressure above the optimum is associated with photorespiration, and that inhibition below the optimum O2 may be caused by a reduced supply of ATP to the C4 cycle as a result of inhibition of its production photochemically.
Heat stress affects the organization of microtubules and cell division in Nicotiana tabacum cells
Authors: SMERTENKO A. , DRÁBER P. , VIKLICKÝ V. , OPATRNÝ Z. 
Published: November 2003

ABSTRACTTo investigate the effects of heat stress on the plant cytoskeleton, the structure of microtubule arrays in N. tabacum suspension cells incubated at 38 or 42°C was analysed. Whilst incubation at 42 °C resulted in the disruption of the majority of cellular microtubules after 30 min, in cells exposed to 38 °C all the microtubule arrays were preserved even after 12 h of incubation, although their organization was altered. The most susceptible were the microtubules of the mitotic spindle and the phragmoplast. Several abnormalities were observed: (i) splitting of the spindle into several parts; (ii) elongation of the spindles; (iii) formation of microtubule asters in mitotic cells, and (iv) elongation of phragmoplast microtubules. Exposure of cells to 38 °C caused a decrease in the mitotic index but an accumulation of telophase cells. The recovery of normal microtubule organization occurred after 12 h. Treatment of the cells subjected to heat stress conditions with an inhibitor of protein synthesis, cycloheximide, did not prevent either the alterations of microtubule organization or accumulation of cells containing phragmoplasts. Therefore, heat shock proteins do not seem to be directly responsible for the microtubule disorganization induced by heat stress.
Active oxygen species production in tobacco cells elicited by cryptogein*
Authors: SIMON‐PLAS F. , RUSTÉRUCCI C. , MILAT M.‐L. , HUMBERT C. , MONTILLET J.‐L. , BLEIN J.‐P. 
Published: November 2003

ABSTRACTWe analyse the relationship between active oxygen species (AOS) production and pH changes induced in tobacco cells by cryptogein, a fungal proteinaceous elicitor of defence mechanisms in plants. When tobacco cells were treated with cryptogein, an intracellular acidification, an alkalinization of the extracellular medium and a transient burst of AOS (H2O2) were observed. Treatment of elicited cells with either diphenyleneiodonium (DPI), an inhibitor of the neutrophil NADPH oxidase, or Tiron, which scavenges O2˙− abolished AOS production. These data suggest the involvement of a NADPH oxidase‐like enzyme leading to H2O2 production through O2˙− dismutation. Although H2O2 production could be, per se, the origin of the pH changes observed, we showed that it was not the main cause, since DPI and Tiron did not inhibit extracellular alkalinization. On the other hand, cryptogein‐induced changes in pH could be abolished using fusicoccin (FC), which is known to stimulate the plasmalemma H+ ATPase. Consequently, the observed changes in pH induced by cryptogein could be mainly due to the inhibition of the plasmalemma H+‐ATPase activity. Furthermore, changes in extracellular pH were shown to modulate the intensity of AOS production by elicited cells. The possible regulation of the NAD(P)H oxidase activity of plant cells by changes in pH is further discussed.
Two isoforms of the GBSSI class of granule‐bound starch synthase are differentially expressed in the pea plant (Pisum sativum L.)
Authors: DENYER K. , BARBER L. M. , EDWARDS E. A. , SMITH A. M. , WANG T. L. 
Published: November 2003

ABSTRACTIn addition to the GBSSI isoform of starch synthase described previously, the pea plant contains a second, granule‐bound isoform, GBSSIb. GBSSI is abundant in pea embryos and Rhizobium root nodules, is present at low levels in pods and is absent from leaves. Mutations at the lam locus eliminate GBSSI from all of these organs. GBSSIb is present in pods, leaves and nodules and is unaffected by mutations at the lam locus. GBSSI and GBSSIb are very similar in molecular mass, primary sequence, activity and antigenic properties. GBSSIb, like GBSSI, can synthesize amylose in the presence of malto‐oligosaccharides in isolated starch granules. However, its role in vivo is unclear. The lam mutation eliminates amylose from the starch of embryos but does not affect the relatively small amounts of amylose‐like material in the starch of pods, leaves and nodules. The significance of these results for understanding of the regulation of amylose synthesis is discussed.
Carbon isotope discrimination in irrigated and droughted potato (Solanum tuberosum L.)
Authors: JEFFERIES R. A. , MACKERRON D. K. L. 
Published: November 2003

ABSTRACTCarbon isotope discrimination (Δ) was measured in irrigated and droughted potato. Under irrigation, Δ in leaflets at given nodes increased (P < 0.001) between 21 and 63 d after emergence (DAE), which was attributed to increasing stomatal conductance (gs) during leaf expansion. The effect of leaf position on Δ was non‐significant in mature leaves. Under drought, Δ decreased (P < 0.001) in successive leaves up the stem, reflecting changes in gs and water stress. At each node Δ remained constant or decreased, suggesting that effects of water stress were greater than changes with leaf expansion. There were significant differences in Δ between cultivars in both treatments, and in the progressive decrease in Δ up the stem under drought. Differences in Δ between cultivars were consistent with differences in stomatal control of leaf water status following water stress. Values for Δ in tubers were consistently lower than in stem and leaf, and decreased more rapidly.Differences in Δ between cultivars did not reflect dry matter production in either treatment, and differences in water use were non‐significant between cultivars under drought. So, plants can achieve similar dry matter production through different growth strategies when irrigated or droughted, and Δ does not provide a simple, indirect method of selecting for dry matter production under water stress.
Evidence that the induction of crassulacean acid metabolism by water stress in Mesembryanthemum crystallinum (L.) involves root signalling
Authors: EASTMOND P. J. , ROSS J. D. 
Published: November 2003

ABSTRACTThe aim of this study was to investigate whether the root system of Mesembryanthemum crystallinum (L.) plays a role in triggering the induction of crassulacean acid metabolism (CAM) during water stress. Depriving well‐irrigated plants of water, by allowing the soil surrounding the roots to dry, caused increased daily losses in leaf relative water content (RVVC) and mesophyll cell turgor pressure. The RWC of the roots also declined. Subsequently plants exhibited physiological characteristics of CAM photosynthesis (i.e. diurnal fluctuations in leaf titratable acidity and nocturnal net CO2 fixation). When the root system of plants was divided equally between two soil compartments and one half deprived of water, plants exhibited physiological characteristics of CAM without prior changes in leaf RWC content or mesophyll cell turgor pressure. Only the RWC of the water‐stressed portion of the roots was reduced. These data suggest that in water‐stressed plants daily changes in leaf water relations greater than those observed in well‐irrigated plants, are not essential to trigger CAM expression. It is probable that a reduction in soil water availability can be perceived by the roots of M. crystallinum and that this information is conveyed to the leaves triggering the transition from C3 to CAM photosynthesis.
Soil CO2 concentration does not affect growth or root respiration in bean or citrus
Authors: BOUMA T. J. , NIELSEN K. L. , EISSENSTAT D. M. , LYNCH J. P. 
Published: November 2003

ABSTRACTContrasting effects of soil CO2 concentration on root respiration rates during short‐term CO2 exposure, and on plant growth during long‐term CO2 exposure, have been reported. Here we examine the effects of both short‐ and long‐term exposure to soil CO2 on the root respiration of intact plants and on plant growth for bean (Phaseolus vulgaris L.) and citrus (Citrus volkameriana Tan. & Pasq.). For rapidly growing bean plants, the growth and maintenance components of root respiration were separated to determine whether they differ in sensitivity to soil CO2. Respiration rates of citrus roots were unaffected by the CO2 concentration used during the respiration measurements (200 and 2000 μmol mol−1), regardless of the soil CO2, concentration during the previous month (600 and 20 000 μmol mol−1). Bean plants were grown with their roots exposed to either a natural CO2 diffusion gradient, or to an artificially maintained CO2 concentration of 600 or 20 000 μmol mol−1. These treatments had no effect on shoot and root growth. Growth respiration and maintenance respiration of bean roots were also unaffected by CO2 pretreatment and the CO2 concentration used during the respiration measurements (200–2000 μmol mol−1). We conclude that soil CO2 concentrations in the range likely to be encountered in natural soils do not affect root respiration in citrus or bean.