Plant Transpiration: The loss of water vapor by plants to the atmosphere. It occurs mainly from the leaves through pores (stomata) whose primary function is gas exchange. The water is replaced by a continuous column of water moving upwards from the roots within the xylem vessels. (Concise Dictionary of Biology, 1990)Plant Leaves: Expanded structures, usually green, of vascular plants, characteristically consisting of a bladelike expansion attached to a stem, and functioning as the principal organ of photosynthesis and transpiration. (American Heritage Dictionary, 2d ed)Plant Stomata: Closable openings in the epidermis of plants on the underside of leaves. They allow the exchange of gases between the internal tissues of the plant and the outside atmosphere.Plants, Genetically Modified: PLANTS, or their progeny, whose GENOME has been altered by GENETIC ENGINEERING.Plant Roots: The usually underground portions of a plant that serve as support, store food, and through which water and mineral nutrients enter the plant. (From American Heritage Dictionary, 1982; Concise Dictionary of Biology, 1990)Xylem: Plant tissue that carries water up the root and stem. Xylem cell walls derive most of their strength from LIGNIN. The vessels are similar to PHLOEM sieve tubes but lack companion cells and do not have perforated sides and pores.Water: A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Plant Proteins: Proteins found in plants (flowers, herbs, shrubs, trees, etc.). The concept does not include proteins found in vegetables for which VEGETABLE PROTEINS is available.Plant Shoots: New immature growth of a plant including stem, leaves, tips of branches, and SEEDLINGS.Acer: A plant genus of the family ACERACEAE, best known for trees with palmately lobed leaves.Plant Stems: Parts of plants that usually grow vertically upwards towards the light and support the leaves, buds, and reproductive structures. (From Concise Dictionary of Biology, 1990)Vapor Pressure: The contribution to barometric PRESSURE of gaseous substance in equilibrium with its solid or liquid phase.Genes, Plant: The functional hereditary units of PLANTS.Plant Epidermis: A thin layer of cells forming the outer integument of seed plants and ferns. (Random House Unabridged Dictionary, 2d ed)Xanthium: A plant genus of the family ASTERACEAE. The name "prickly burweed" is sometimes used but causes confusion with AMSINCKIA.Photosynthesis: The synthesis by organisms of organic chemical compounds, especially carbohydrates, from carbon dioxide using energy obtained from light rather than from the oxidation of chemical compounds. Photosynthesis comprises two separate processes: the light reactions and the dark reactions. In higher plants; GREEN ALGAE; and CYANOBACTERIA; NADPH and ATP formed by the light reactions drive the dark reactions which result in the fixation of carbon dioxide. (from Oxford Dictionary of Biochemistry and Molecular Biology, 2001)Droughts: Prolonged dry periods in natural climate cycle. They are slow-onset phenomena caused by rainfall deficit combined with other predisposing factors.Phaseolus: A plant genus in the family FABACEAE which is the source of edible beans and the lectin PHYTOHEMAGGLUTININS.Fabaceae: The large family of plants characterized by pods. Some are edible and some cause LATHYRISM or FAVISM and other forms of poisoning. Other species yield useful materials like gums from ACACIA and various LECTINS like PHYTOHEMAGGLUTININS from PHASEOLUS. Many of them harbor NITROGEN FIXATION bacteria on their roots. Many but not all species of "beans" belong to this family.Plants, Medicinal: Plants whose roots, leaves, seeds, bark, or other constituent parts possess therapeutic, tonic, purgative, curative or other pharmacologic attributes, when administered to man or animals.Light: That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.Gene Pool: The total genetic information possessed by the reproductive members of a POPULATION of sexually reproducing organisms.MissouriSunlight: Irradiation directly from the sun.Pesticides: Chemicals used to destroy pests of any sort. The concept includes fungicides (FUNGICIDES, INDUSTRIAL); INSECTICIDES; RODENTICIDES; etc.Epidermis: The external, nonvascular layer of the skin. It is made up, from within outward, of five layers of EPITHELIUM: (1) basal layer (stratum basale epidermidis); (2) spinous layer (stratum spinosum epidermidis); (3) granular layer (stratum granulosum epidermidis); (4) clear layer (stratum lucidum epidermidis); and (5) horny layer (stratum corneum epidermidis).

Gas exchange by pods and subtending leaves and internal recycling of CO(2) by pods of chickpea (Cicer arietinum L.) subjected to water deficits. (1/373)

Terminal drought markedly reduces leaf photosynthesis of chickpea (Cicer arietinum L.) during seed filling. A study was initiated to determine whether photosynthesis and internal recycling of CO(2) by the pods can compensate for the low rate of photosynthesis in leaves under water deficits. The influence of water deficits on the rates of photosynthesis and transpiration of pods and subtending leaves in chickpea (cv. Sona) was investigated in two naturally-lit, temperature-controlled glasshouses. At values of photosynthetically active radiation (PAR) of 900 micromol m(-2) s(-1) and higher, the rate of net photosynthesis of subtending leaves of 10-d-old pods was 24 and 6 micromol m(-2) s(-1) in the well-watered (WW) and water-stressed (WS) plants when the covered-leaf water potential (Psi) was -0.6 and -1.4 MPa, respectively. Leaf photosynthesis further decreased to 4.5 and 0.5 micromol m(-2) s(-1) as Psi decreased to -2.3 and -3.3 MPa, respectively. At 900--1500 micromol m(-2) s(-1) PAR, the net photosynthetic rate of 10-d-old pods was 0.9-1.0 micromol m(-2) s(-1) in the WW plants and was -0.1 to -0.8 micromol m(-2) s(-1) in the WS plants. The photosynthetic rates of both pods and subtending leaves decreased with age, but the rate of transpiration of the pods increased with age. The rates of respiration and net photosynthesis inside the pods were estimated by measuring the changes in the internal concentration of CO(2) of covered and uncovered pods during the day. Both the WW and WS pods had similar values of internal net photosynthesis, but the WS pods showed significantly higher rates of respiration suggesting that the WS pods had higher gross photosynthetic rates than the WW pods, particularly in the late afternoon. When (13)CO(2) was injected into the gas space inside the pod, nearly 80% of the labelled carbon 24 h after injection was observed in the pod wall in both the WW and WS plants. After 144 h the proportion of (13)C in the seed had increased from 19% to 32% in both treatments. The results suggest that internal recycling of CO(2) inside the pod may assist in maintaining seed filling in water-stressed chickpea.  (+info)

Leaf ureide degradation and N(2) fixation tolerance to water deficit in soybean. (2/373)

Accumulation of ureides in leaves is associated with the sensitivity of N(2) fixation in soybean to soil water deficit. Consequently, ureide degradation in leaves may be a key to increasing soybean tolerance to dry soils. Previous research indicated that allantoic acid degradation is catalysed by different enzymes in cultivars Maple Arrow and Williams. The enzyme found in Williams requires manganese as a cofactor. The first objective of this study was to determine if the two degradation pathways were associated with differences in N(2) sensitivity to soil water deficits. N(2) fixation of Williams grown on low-Mn soil was sensitive to stress, but it was relatively tolerant when grown on soil amended with Mn. N(2) fixation in Maple Arrow was relatively tolerant of soil drying regardless of the Mn treatment. The second objective of this study was to expand the study of the degradation pathway to nine additional genotypes. Based on ureide degradation in the presence and absence of Mn, these genotypes also segregated for the two degradation pathways. Those genotypes with the Mn-dependent pathway tended to have drought-sensitive N(2) fixation, but there was one exception. The genotypes not requiring Mn for ureide degradation were drought-tolerant except for one genotype. These results demonstrated the possibility for increasing N(2) fixation tolerance to soil water deficits in soybean by selection of lines with high ureide degradation rates, which were commonly associated with the Mn-independent pathway.  (+info)

Identification of causal relationships among traits related to drought resistance in Stylosanthes scabra using QTL analysis. (3/373)

Previous studies have shown that a negative relationship exists between transpiration efficiency (TE) and carbon isotope discrimination (Delta) and between TE and specific leaf area (SLA) in Stylosanthes scabra. A glasshouse experiment was conducted to confirm these relationships in an F(2) population and to study the causal nature of these relationships through quantitative trait loci (QTL) analysis. One hundred and twenty F(2) genotypes from a cross between two genotypes within S. scabra were used. Three replications for each genotype were maintained through vegetative propagation. Water stress was imposed by maintaining plants at 40% of field capacity for about 45 d. To facilitate QTL analysis, a genetic linkage map consisting of 151 RAPD markers was developed. Results from this study show that Delta was significantly and negatively correlated with TE and biomass production. Similarly, SLA showed significant negative correlation with TE and biomass production. Most of the QTL for TE and Delta were present on linkage groups 5 and 11. Similarly, QTL for SLA, transpiration and biomass productivity traits were clustered on linkage groups 13 and 24. One unlinked marker was also associated with these traits. There were several markers coincident between different traits. At all the coincident QTL, the direction of QTL effects was consistent with phenotypic data. At the coincident markers between TE and Delta, high alleles of TE were associated with low alleles of Delta. Similarly, low alleles of SLA were associated with high alleles of biomass productivity traits and transpiration. At the coincident markers between trans-4-hydroxy-N:-methyl proline (MHP) and relative water content (RWC), low alleles of MHP were associated with high alleles of RWC. This study suggests the causal nature of the relationship between TE and Delta. Phenotypic data and QTL data show that SLA was more closely associated with biomass production than with TE. This study also shows that a cause-effect relationship may exist between SLA and biomass production.  (+info)

Abscisic acid induces a decline in nitrogen fixation that involves leghaemoglobin, but is independent of sucrose synthase activity. (4/373)

Sucrose synthase (SS) activity has been suggested to be a key point of regulation in nodule metabolism since this enzyme is down-regulated in response to different stresses which lead to decreased nitrogen fixation. In soybean, a dramatic decline of SS transcripts has been observed within 1 d from the onset of drought. Such a quick response suggests mediation by a signal transduction molecule. Abscisic acid (ABA) is a likely candidate to act as such a molecule as it mediates in a significant number of plant responses to environmental constraints. The hypothesis of ABA controlling nodule metabolism was approached in this work by assessing nodule responses to exogenous ABA supply in pea. Under the experimental conditions, ABA did not affect plant biomass, nodule numbers or dry weight. However, nitrogen fixation rate was reduced by 70% within 5 d and by 80% after 9 d leading to a reduced plant organic nitrogen content. Leghaemoglobin (Lb) content declined in parallel with that of nitrogen fixation. SS activity, however, was not affected by ABA treatment, and neither were the activities of the enzymes aspartate amino transferase, alkaline invertase, malate dehydrogenase, glutamate synthase, uridine diphosphoglucose pyrophosphorylase, isocitrate dehydrogenase, and glutamine synthetase. Nodule bacteroid-soluble protein content was reduced in nodules only after 9 d of ABA treatment. These results do not support the hypothesis that ABA directly regulates SS activity. However, they do suggest the occurrence of at least two different control pathways in nodules under environmental constraints, which include ABA being involved in a Lb/oxygen-related control of nitrogen fixation.  (+info)

Acclimation of plants to light gradients in leaf canopies: evidence for a possible role for cytokinins transported in the transpiration stream. (5/373)

The mechanism of response of plants to vertical light intensity gradients in leaf canopies was investigated. Since shaded leaves transpire less than leaves in high light, it was hypothesized that cytokinins (CKs) carried by mass transport in the transpiration stream would be distributed over the leaf area of partially shaded plants parallel to the gradient in light intensity. It was also hypothesized that this causes the distribution of leaf growth, leaf N and photosynthetic capacity, and possibly chloroplast acclimation as observed in plants growing in leaf canopies. In a field experiment, the distribution of Ca, N and CKs in a bean leaf canopy of a dense and an open stand supported the concept of a role for CKs in the response of N allocation to the light gradient when a decreasing sensitivity for CKs with increasing leaf age is assumed. Both shading of one leaf of the pair of primary bean leaves and independent reduction of its transpiration rate in a growth cabinet experiment caused lower dry mass, N and Ca per unit leaf area in comparison to the opposite not treated leaf. Shading caused a parallel reduction in CK concentration, which supports the hypothesis, but independent reduction of transpiration rate failed to do the same. Application of benzylaminopurine (BA) counteracted the reduction caused by shade of leaf N, photosynthetic capacity and leaf area growth. The experiments show an important role for the transpiration stream in the response of plants to light gradients. Evidence is presented here that CKs carried in the transpiration stream may be important mediators for the acclimation of plants to leaf canopy density.  (+info)

Distribution and mobility of aluminium in an Al-accumulating plant, Fagopyrum esculentum Moench. (6/373)

Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) accumulates high concentrations of Al in the leaves without showing any toxicity. To understand the accumulation mechanism of Al in buckwheat, the distribution and mobility of Al in buckwheat were investigated. Relatively long-term treatment (28 d) with Al led to a decrease in Al concentration from old to young leaves, while a short-term (1 d) exposure to Al resulted in a uniform distribution of Al in the leaves. When the fourth leaf was wrapped inside a transparent plastic bag to suppress transpiration, the Al concentration of this leaf was only one-quarter of that in the corresponding leaf without wrapping. Within a leaf, the Al concentration at the margins was much higher than that in the centre. These results indicate that Al distribution in the leaves is controlled by both rate and duration of transpiration. The mobility of Al between old and new leaves was studied by first growing plants in a solution with Al, followed by culture in a solution without Al. The Al content in the two new leaves appeared after removal of external Al was very low, whereas that in the old leaves did not decrease but continued to increase. The increased Al content was found to be translocated from Al remaining in the roots. It is concluded that Al is not mobile once it is accumulated in the leaf.  (+info)

Boron supply into wheat (Triticum aestivum L. cv. Wilgoyne) ears whilst still enclosed within leaf sheaths. (7/373)

The present study investigates whether there is significant remobilization of (10)B previously loaded in the flag and penultimate leaves into the young, actively growing ear enclosed within the sheaths of flag and penultimate leaves. It also explores whether B transport into the enclosed ear declines when air humidity in the shoot canopy increases. After 5 d (10)B labelling during the period from early to full emergence of the flag leaf, the plants were transferred into nutrient solutions containing either 10 microM (11)B or no added B for 3 d. Regardless of the subsequent B supply levels to the roots, (10)B contents in the ear continued to increase by up to 5-fold 3 d after the end of (10)B supply in the nutrient solution. During these 3 d, the ear experienced a rapid increase in biomass. However, the majority of B in the ear during the 3 d treatment period was from the newly acquired (11)B from root uptake, rather than retranslocation of (10)B previously deposited in the leaves. By comparing the relative distribution of (10)B, Rb (xylem-to-phloem transfer marker) and Sr (xylem-marker) in the ear and the flag leaf, the distribution of (10)B resembled that of Rb more than Sr. Canopy cover treatment greatly suppressed leaf transpiration and decreased the amount of newly acquired (10)B in the flag leaf and the ear, but not in the upper stem segments. The results suggest that whilst the young ear was still fully enclosed within the leaf sheaths without any significant transpiration activity, B transport into the ear is predominantly dependent on the long-distance B transport in the xylem driven by leaf transpiration and, therefore, on concurrent B uptake from the roots.  (+info)

Transpiration rate. An important factor controlling the sucrose content of the guard cell apoplast of broad bean. (8/373)

Evaporation of water from the guard cell wall concentrates apoplastic solutes. We hypothesize that this phenomenon provides two mechanisms for responding to high transpiration rates. First, apoplastic abscisic acid is concentrated in the guard cell wall. Second, by accumulating in the guard cell wall, apoplastic sucrose (Suc) provides a direct osmotic feedback to guard cells. As a means of testing this second hypothesized mechanism, the guard cell Suc contents at a higher transpiration rate (60% relative humidity [RH]) were compared with those at a lower transpiration rate (90% RH) in broad bean (Vicia faba), an apoplastic phloem loader. In control plants (constant 60% RH), the guard cell apoplast Suc content increased from 97 +/- 81 femtomol (fmol) guard cell pair(-1) to 701 +/- 142 fmol guard cell pair(-1) between daybreak and midday. This increase is equivalent to approximately 150 mM external, which is sufficient to decrease stomatal aperture size. In plants that were shifted to 90% RH before daybreak, the guard cell apoplast Suc content did not increase during the day. In accordance, in plants that were shifted to 90% RH at midday, the guard cell apoplast Suc content declined to the daybreak value. Under all conditions, the guard cell symplast Suc content increased during the photoperiod, but the guard cell symplast Suc content was higher (836 +/- 33 fmol guard cell pair(-1)) in plants that were shifted to 90% RH. These results indicate that a high transpiration rate may result in a high guard cell apoplast Suc concentration, which diminishes stomatal aperture size.  (+info)

  • However, if a plant cannot acquire sufficient water, its stomata will rapidly close to prevent wilting. (
  • Interestingly, even if kept in the dark, plants will open and close stomata on a regular, 24-hour cycle, due to an internal clock. (
  • The opening and closing of stomata are tightly regulated, allowing plants to respond to specific environmental conditions. (
  • In their function as gate-keepers, stomata efficiently balance gas exchange and transpiration. (
  • This study aimed at characterising the dynamics of transpiration, development, growth and carbon metabolism, as well as the expression of invertase genes, in response to drought during a dry-down cycle. (
  • Plants require ample carbon dioxide from the atmosphere to conduct photosynthesis. (
  • During photosynthesis, plants acquire the necessary carbon dioxide and release the produced oxygen back into the atmosphere. (
  • An oxidative C 1 pathway is known to exist in plants where intermediates with a single carbon atom beginning with methanol are oxidized to CO 2 . (
  • The team's results demonstrate that methanol activates the C 1 pathway in plants which provides an alternative carbon source for glycine methylation in photorespiration, enhance CO 2 concentrations within chloroplasts, and produce key C 2 intermediates (e.g. acetyl-CoA) for central metabolism. (
  • They confirm that methanol initiates the complete C 1 pathway in plants (methanol, formaldehyde, formic acid, carbon dioxide) by providing the first real-time dynamic 13 C-labeling data showing their interdependence. (
  • Cienciala E, Kučera J, Lindroth A, Čermák J, Grelle A, Halldin S (1997) Canopy transpiration from a boreal forest in Sweden during a dry year. (
  • The regulation of carbohydrate metabolism and source-sink relationships among organs play a key role in plant adaptation to drought. (
  • Čermák J, Palát M, Penka M (1976) Transpiration flow rate in a full grown tree of Prunus avium L. estimated by the method of heat balance in connection with some meteorological factors. (
  • In this study, scientists at Lawrence Berkeley National Laboratory evaluated the C 1 pathway and its integration with central metabolism using aqueous solutions of 13 C-labeled C 1 and C 2 intermediates delivered to branches of the tropical species Inga edulis via the transpiration stream. (
  • Granier A, Loustau D (1994) Measuring and modelling the transpiration of a maritime pine canopy from sap-flow data. (
  • The daily transpiration from the upscaling function was well correlated with the daily evapotranspiration by the Penman-Monteith equation (coefficient of determination R 2 ≥ 0.67), indicating the applicability of this upscaling function, a useful tool for managing and restoring sand-fixing vegetations. (
  • For most locations investigated, we calculated reductions in daily transpiration rates over the twenty-first century that became stronger under higher atmospheric CO 2 concentrations. (
  • For currently cold regions, global warming would, however, lengthen the growing seasons so that annual sums of transpiration could increase in those regions despite reductions in daily transpiration rates over the summer months. (
  • Consequently, transpiration processes affect the yield and survival of agricultural species, and impact on the global carbon and hydrological cycles. (
  • Transport of minerals, movement of sugars, plant rigidity (turgor) and other major processes rely on water to function. (
  • The most abundant compound in all plants, as in all life, is water which serves an important role in the various processes taking place. (
  • This online course covers the fundamental processes and key structures within a plant that are responsible for its growth. (
  • Plant biostimulants contain substance(s) and/or micro-organisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and crop quality. (
  • Because it is difficult to measure evaporation and transpiration separately, the combined processes are often referred to as evapotranspiration. (
  • We used integrated hydrologic simulations that couple vegetation and land-energy processes with surface and subsurface hydrology to study transpiration partitioning at the continental scale. (
  • Practicals set this material in the context of plant-environmental and agricultural interactions by direct observations and measurements of physiological processes. (
  • We considered observations ranging from short-term laboratory-based experiments with plants grown under different CO 2 concentrations to studies of plants exposed to the naturally increasing atmospheric CO 2 concentrations. (
  • Plants will also wilt when the temperature of the rooting medium is less than the atmospheric temperature, particularly when the atmospheric demand is high. (
  • Leaf transpiration of drought tolerant plant can be captured by hyperspectral reflectance using PLSR analysis. (
  • The results revealed that the PLSR model based on the first-order derivative spectra at wavelengths selected through stepwise regression analysis can closely trace leaf transpiration with a high accuracy (R 2 = 0.78, RMSE = 1.62 µmol g -1 s -1 ). (
  • The results also proved that the first-order derivative spectra within the shortwave infrared (SWIR) domain, especially at 2435, 2440, 2445, and 2470 nm, were critical for PLSR models to predict leaf transpiration. (
  • However, a straightforward relationship between leaf transpiration and reflected information has still to be verified, while it has already been done for other parameters related to the biological status of plants ( ). (
  • Leaf transpiration and stomatal control. (
  • The model showed that water table depth and lateral flow strongly affect transpiration partitioning, thus explaining the inconsistencies between observations and models. (
  • The results indicated that during the growing season, the total actual transpiration of the Salix gordejevii and Caragana microphylla communities was found to be 287 ± 31 and 197 ± 24 mm, respectively, implying that the Salix gordejevii community might consume 1.5 times more water than the Caragana microphylla community. (
  • The last stage in the transpiration stream is the water moving into the leaves, and then the actual transpiration. (
  • Simulation results indicated that the VPD-limited transpiration trait is most beneficial in hot and dry regions of production where crops are exposed to extended periods without rainfall during the season or to a terminal drought. (
  • in addition, thick M cell walls may be beneficial for plant drought tolerance. (
  • Conditions of drought, unusual variations in temperature or other climatic changes can cause the plant to pass through the physiological equivalent of two full growing seasons in one year. (
  • To control water loss, plants are covered with relatively water-impermeable surfaces that are punctuated by stomatal pores. (
  • Almost all of the CO 2 fixed by terrestrial plants and most of the water transpired pass through these stomatal pores. (
  • little cytoplasm, no nucleus : sieve plate with pores separating the sieve tube cell : allows the flow of dissolved food substances -Companion : only found in flowering plant cells : adjacent and closely associated with the sieve tube cells : has a nucleus, dense cytoplasm & many mitochondria : transport manufactured food(sucrose & amino acids) from the leaf cells into the sieve tubes. (
  • In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of optical microscopy and live cell imaging , electron microscopy , analysis of chromosome number , plant chemistry and the structure and function of enzymes and other proteins . (
  • The scientific study of plants is called botany. (
  • Roger Hull graduated in Botany from Cambridge University in 1960, and subsequently studied plant virus epidemiology at London University's Wye College, gaining a PhD in 1964. (
  • Botany originated in prehistory as herbalism with the efforts of early humans to identify - and later cultivate - edible, medicinal and poisonous plants, making it one of the oldest branches of science. (
  • Botany originated as herbalism , the study and use of plants for their medicinal properties. (
  • The early recorded history of botany includes many ancient writings and plant classifications. (