Carbohydrate metabolism in leaf meristems of tall fescue : I. Relationship to genetically altered leaf elongation rates

Kinematic Analysis of Cell Division and Expansion: Quantifying the Cellular Basis of Growth and Sampling Developmental Zones in Zea mays Leaves

Growth analyses are often used in plant science to investigate contrasting genotypes and the effect of environmental conditions. The cellular aspect of these analyses is of crucial importance, because growth is driven by cell division and cell elongation. Kinematic analysis represents a methodology to quantify these two processes. Moreover, this technique is easy to use in non-specialized laboratories. Here, we present a protocol for performing a kinematic analysis in monocotyledonous maize (Zea mays) leaves. Two aspects are presented: (1) the quantification of cell division and expansion parameters, and (2) the determination of the location of the developmental zones. This could serve as a basis for sampling design and/or could be useful for data interpretation of biochemical and molecular measurements with high spatial resolution in the leaf growth zone. The growth zone of maize leaves is harvested during steady-state growth. Individual leaves are used for meristem length determination using a DAPI stain and cell-length profiles using DIC microscopy. The protocol is suited for emerged monocotyledonous leaves harvested during steady-state growth, with growth zones spanning at least several centimeters. To improve the understanding of plant growth regulation, data on growth and molecular studies must be combined. Therefore, an important advantage of kinematic analysis is the possibility to correlate changes at the molecular level to well-defined stages of cellular development. Furthermore, it allows for a more focused sampling of specified developmental stages, which is useful in case of limited budget or time.

Carbohydrate concentrations in crown fractions from winter oat during hardening at sub-zero temperatures

BACKGROUND AND AIMS

Contradictory results in correlation studies of plant carbohydrates with freezing tolerance may be because whole crown tissue is analysed for carbohydrates while differences exist in the survival of specific tissue within the crown. The aim of this study was to see if carbohydrate changes in tissue within oat crowns during second phase hardening (sub-zero hardening) are tissue specific.

METHODS

The lower portion of oat (Avena sativa) crowns was exposed to mild grinding in a blender and the remaining crown meristem complex, consisting of tough root-like vessels, was ground in a device developed specifically for grinding cereal crown tissue. Carbohydrates were extracted by water and measured by HPLC. Carbohydrate concentrations were compared in the two regions of the crown before and after hardening at sub-zero temperatures.

KEY RESULTS

Fructan of all size classes except DP>6 decreased during sub-zero hardening in both stems (base of leaf sheath) and crown meristem complex. Total simple sugar increase, including sucrose, was significantly higher in the crown meristem complex than in the stem.

CONCLUSIONS

Results support the hypothesis that carbohydrate change in mildly frozen plants is tissue specific within crowns and underscore the need to evaluate specific tissue within the crown when correlating the biochemistry of plants with freezing tolerance.

Effects of elevated atmospheric CO2 on the nutritional ecology of C3 and C4 grass-feeding caterpillars

It is plausible that the nutritional quality of C3 plants will decline more under elevated atmospheric CO2 than will the nutritional quality of C4 plants, causing herbivorous insects to increase their feeding on C3 plants relative to C4 plants. We tested this hypothesis with a C3 and C4 grass and two caterpillar species with different diet breadths. Lolium multiflorum (C3) and Bouteloua curtipendula (C4) were grown in outdoor open top chambers at ambient (370 ppm) or elevated (740 ppm) CO2. Bioassays compared the performance and digestive efficiencies of Pseudaletia unipuncta (a grass-specialist noctuid) and Spodoptera frugiperda (a generalist noctuid). As expected, the nutritional quality of L. multiflorum changed to a greater extent than did that of B. curtipendula when grown in elevated CO2; levels of protein (considered growth limiting) declined in the C3 grass, while levels of carbohydrates (sugar, starch and fructan) increased. However, neither insect species increased its feeding rate on the C3 grass to compensate for its lower nutritional quality when grown in an elevated CO2 atmosphere. Consumption rates of P. unipuncta and S. frugiperda were higher on the C3 grass than the C4 grass, the opposite of the result expected for a compensatory response to the lower nutritional quality of the C4 grass. Although our results do not support the hypothesis that grass-specialist insects compensate for lower nutritional quality by increasing their consumption rates more than do generalist insects, the performance of the specialist was greater than that of the generalist on each grass species and at both CO2 levels. Mechanisms other than compensatory feeding, such as increased nutrient assimilation efficiency, appear to determine the relative performance of these herbivores. Our results also provide further evidence against the hypothesis that C4 grasses would be avoided by insect herbivores because a large fraction of their nutrients is unavailable to herbivores. Instead, our results are consistent with the hypothesis that C4 grasses are poorer host plants primarily because of their lower nutrient levels, higher fiber levels, and greater toughness.

Performance of a generalist grasshopper on a C3 and a C4 grass: compensation for the effects of elevated CO2 on plant nutritional quality

The increasing CO2 concentration in Earth's atmosphere is expected to cause a greater decline in the nutritional quality of C3 than C4 plants. As a compensatory response, herbivorous insects may increase their feeding disproportionately on C3 plants. These hypotheses were tested by growing the grasses Lolium multiflorum C3) and Bouteloua curtipendula C4) at ambient (370 ppm) and elevated (740 ppm) CO2 levels in open top chambers in the field, and comparing the growth and digestive efficiencies of the generalist grasshopper Melanoplus sanguinipes on each of the four plant x CO2 treatment combinations. As expected, the nutritional quality of the C3 grass declined to a greater extent than did that of the C4 grass at elevated CO2; protein levels declined in the C3 grass, while levels of carbohydrates (sugar, fructan and starch) increased. However, M. sanguinipes did not significantly increase its consumption rate to compensate for the lower nutritional quality of the C3 grass grown under elevated CO2. Instead, these grasshoppers appear to use post-ingestive mechanisms to maintain their growth rates on the C3 grass under elevated CO2. Consumption rates of the C3 and C4 grasses were also similar, demonstrating a lack of compensatory feeding on the C4 grass. We also examined the relative efficiencies of nutrient utilization from a C3 and C4 grass by M. sanguinipes to test the basis for the C4 plant avoidance hypothesis. Contrary to this hypothesis, neither protein nor sugar was digested with a lower efficiency from the C4 grass than from the C3 grass. A novel finding of this study is that fructan, a potentially large carbohydrate source in C3 grasses, is utilized by grasshoppers. Based on the higher nutrient levels in the C3 grass and the better growth performance of M. sanguinipes on this grass at both CO2 levels, we conclude that C3 grasses are likely to remain better host plants than C4 grasses in future CO2 conditions.

CKS1At overexpression in Arabidopsis thaliana inhibits growth by reducing meristem size and inhibiting cell-cycle progression

The SUC1/CKS1 proteins associate with cyclin-dependent kinases (CDKs) and play an essential role in the regulation of the cell cycle. Recently, an Arabidopsis thaliana SUC1/CKS1 homologous gene, designated CKS1At, has been cloned. Here, overexpression of CKS1At in Arabidopsis is shown to reduce leaf size and root growth rates. Reduced root growth resulted primarily from an increase of the cell-cycle duration and a shortening of the meristem. Endoreduplication was unaffected. The increased cell-cycle duration was associated with an equal extension of both the G1 and G2 phases. This inhibition was due to the binding of CDK subunits with CDKs. The reduced growth rates in response to altered cell-cycle gene expression demonstrates a direct dependence of plant growth rates on cell-cycle regulation.

Response of Fructan to Water Deficit in Growing Leaves of Tall Fescue

Changes in dry matter and water-soluble carbohydrate components, especially fructan, were examined in the basal 25 mm of expanding leaf blades of tall fescue (Festuca arundinacea Schreb.) to assess their roles in plant response to water deficit. Water was withheld from vegetative plants grown in soil in controlled-environment chambers. As stress progressed, leaf elongation rate decreased sooner in the light period than it did in the dark period. The decrease in growth rate in the dark period was associated with a decrease in local relative elongation rates and a shortening of the elongation zone from about 25 mm (control) to 15 mm. Dry matter content of the leaf base increased 23% during stress, due mainly to increased water-soluble carbohydrate near the ligule and to increased water-soluble, carbohydrate-free dry matter at distal positions. Sucrose content increased 258% in the leaf base, but especially (over 4-fold) within 10 mm of the ligule. Hexose content increased 187% in the leaf base. Content of total fructan decreased to 69% of control, mostly in regions farther from the ligule. Fructan hydrolysis could account for the hexose accumulated. Stress caused the osmotic potential to decrease throughout the leaf base, but more toward the ligule. With stress there was 70% less direct contribution of low-degree-of-polymerization fructan to osmotic potential in the leaf base, but that for sucrose and hexose increased 96 and 67%, respectively. Thus, fructan metabolism is involved but fructan itself contributes only indirectly to osmotic adjustment.

Photosynthate partitioning in Basal zones of tall fescue leaf blades

Elongating grass leaves have successive zones of cell division, cell elongation, and cell maturation in the basal portion of the blade and are a strong sink for photosynthate. Our objective was to determine dry matter (DM) deposition and partitioning in basal zones of elongating tall fescue (Festuca arundinacea Schreb.) leaf blades. Vegetative tall fescue plants were grown in continuous light (350 micromoles per square meter per second photosynthetic photon flux density) to obtain a constant spatial distribution of elongation growth with time. Content and net deposition rates of water-soluble carbohydrates (WSC) and DM along elongating leaf blades were determined. These data were compared with accumulation of (14)C in the basal zones following leaf-labeling with (14)CO(2). Net deposition of DM was highest in the active cell elongation zone, due mainly to deposition of WSC. The maturation zone, just distal to the elongation zone, accounted for 22% of total net deposition of DM in elongating leaves. However, the spatial profile of (14)C accumulation suggested that the elongation zone and the maturation zone were sinks of equal strength. WSC-free DM accounted for 55% of the total net DM deposition in elongating leaf blades, but only 10% of incoming (14)C-photosynthate accumulated in the water-insoluble fraction (WIF approximately WSC-free DM) after 2 hours. In the maturation zone, more WSC was used for synthesis of WSC-free DM than was imported as recent photosynthate.

Tansley Review No. 27 The control of carbon partitioning in plants

This review reports on the processes associated with carbon transfer and metabolism in leaves and growing organs and the role of long-distance transport and vascular links in the regulation of carbon partitioning in plants. Partitioning is clearly influenced by both the supply and demand for photosynthate and is moderated by vascular connections and the storage capacity of the leaves and pathway tissues. However there appears to be little more than circumstantial evidence either that short distance transfer of carbon within either the source or the sink, or that long-distance transport in the phloem, are limiting photosynthesis or growth directly. Although individual biochemical and physiological processes relating to photosynthesis and growth may be well understood, the factors primarily responsible for the control of carbon partitioning in plants have not been clearly identified. There is a need for a greater understanding of organ initiation and development (source and sink formation and potential size), the clear identification of whether growth is sink or source limited (including possible sink-controlled photosynthesis) and a detailed assessment of the role of storage in buffering developmental and environmental changes in sink and source activity. Also more information is needed on the role of hormonal and nutritional factors in regulating source and sink activity (organ interactions not directly associated with carbon transfer). CONTENTS Summary 341 I. Introduction 342 II. General source-sink relationships 342 III. Control at the source 345 IV. The utilization of photosynthate: sink characteristics and limitations 353 V. Vascular constraints and temporary storage 360 VI. Concluding comments 366 Acknowledgements 366 References 367.

Growth rates and assimilate partitioning in the elongation zone of tall fescue leaf blades at high and low irradiance

Tall fescue (Festuca arundinacea Schreb.) leaf blades elongated 33% faster at continuous low than at continuous high irradiance (60 versus 300 micromoles per second per square meter photosynthetic photon flux density) when temperature of the leaf elongation zone was held constant at 21 degrees C. Increased rate of elongation was associated with a near proportional increase in length of the elongation zone (+38%). In contrast, growth in width and thickness was decreased at low irradiance, resulting in only a 12% increase in leaf area production and 5% less total growth-associated water deposition than at high irradiance. At low irradiance dry matter (DM) import into the elongation zone was 28% less, and 55% less DM was used per unit leaf area produced. DM use in synthesis of structural components (i.e. DM less water-soluble carbohydrates) was only 13% less at low irradiance, whereas water-soluble carbohydrates (WSC) deposition was 43% less. The lower rate of WSC deposition at low irradiance was associated with a higher net rate of monosaccharide deposition (+39%), whereas net deposition rates for sucrose (-27%) and fructan (-56%) were less than at high irradiance. Still, at low irradiance, net fructan accumulation accounted for 64% of WSC deposition, i.e. 25% of DM import, demonstrating the high sink strength of the leaf elongation zone.

Characterization of fructan from mature leaf blades and elongation zones of developing leaf blades of wheat, tall fescue, and timothy

Water-soluble carbohydrate composition of mature (ceased expanding) leaf blades and the elongation zone of developing leaf blades was characterized in wheat (Triticum aestivum L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). These species were chosen because they differ in mean degree of polymerization (DP) of fructan in the mature leaf blade. Our objective was to compare the nature and DP of the fructan. Vegetative plants were grown with a 14-hour photoperiod and constant 21 degrees C at the leaf base. Gel permeation chromatography of leaf blade extracts showed that the apparent mean fructan DP increased in the order wheat < tall fescue < timothy. Apparent mean DP of elongation zone fructan was higher than that of leaf blade fructan in wheat and timothy, but the reverse occurred for tall fescue. Low DP (</=10) and high DP (>10) pools were found in both tissues of tall fescue and wheat, but concentration of low DP fructan was very low in either tissue of timothy. All three species have high DP fructan. Comigration with standards on thin-layer chromotography showed that wheat contained 1-kestose and a noninulin fructan oligomer series. Tall fescue contained neokestose, 1-kestose and higher oligosaccharides that comigrated with neokestose-based compounds and inulins. Thin-layer chromatography showed that small amounts of fructose-containing oligosaccharides were present in timothy.

Fructan Content and Synthesis in Leaf Tissues of Festuca arundinacea

The concentration of fructan in tall fescue (Festuca arundinacea Schreb.) changes during growth and in response to environment. The objective of this research was to compare the fructan concentration and fructosyl-transferase activity of tall fescue leaf tissues. Expanding leaves, inner and outer sheaths, and expanded blades of greenhouse-grown tall fescue plants were assayed for fructan concentration and fructosyl-transferase activity. Leaf sheaths contained significantly more nonstructural carbohydrate than did the expanded blade. Sheaths also contained a greater percentage of fructan with more than six sugar residues (long chain fructan), than either the expanded blade or expanding leaf. Expanding leaves contained a greater concentration of fructose and oligosaccharides than did sheath or blade tissues. Expanding leaves also had the greatest fructosyl-transferase activity measured either as radiolabel incorporated into fructans in tissue pieces or protein extracts. Activity of fructosyl-transferase was greater in expanding leaf tissue than in sheath tissues.

Diurnal growth of tall fescue leaf blades : I. Spatial distribution of growth, deposition of water, and assimilate import in the elongation zone

Tall fescue leaf blades elongate at near constant rates during most of the light and dark periods of the diurnal cycle, with the dark rate being higher by 60 to 65%. Our objective was to determine relationships among diurnal rates of leaf elongation, deposition of water and deposition of dry matter (DM) into the elongation zone. Two separate experiments were conducted, both with a 15-hour photoperiod and constant 21 degrees C at the growth zone. Increased rates of leaf elongation in darkness were due to proportionally increased rates of elongation of 4-millimeter segments of the elongation zone. Length of the total elongation zone was 30 millimeters in both light and darkness. The spatial distribution of water contents in the elongation zone varied little during the diurnal cycle. Thus, dark stimulation of leaf elongation rate (+65%) and of water deposition (+77%) into elongation zones were similar. Water content per unit leaf length increased by 50% between the basal and distal limits of the elongation zone, indicating that tissue also grew in the lateral and vertical dimensions. Longitudinal growth of tissue, however, allowed 5 to 7 times more water deposition into the elongation zone than growth in cross-sectional area. This relationship was similar in light and darkness. In both light and darkness net rates of DM deposition (microgram per millimeter leaf length per hour) increased from the zone of cell division towards the region of most active elongation, 10 to 15 millimeters from the ligule, then decreased towards the distal end of the elongation zone. Net DM deposition rates (microgram per hour) integrated over the 30-millimeter elongation zone were similar during light and darkness. Thus, DM in the elongation zone was diluted during darkness as a result of increased water deposition. Net DM deposition rates at and above the distal end of the elongation zone were clearly positive during the light, but were close to zero or negative in darkness. Thus, DM deposition into the elongation zone and the adjacent recently expanded tissue was differentially affected in the diurnal cycle, DM deposition occurred in both tissues in light, but was restricted to the elongation zone in darkness.

Diurnal Growth of Tall Fescue Leaf Blades : II. Dry Matter Partitioning and Carbohydrate Metabolism in the Elongation Zone and Adjacent Expanded Tissue

The spatial distributions of net deposition rates of water soluble carbohydrate-free dry matter (WSC-free DM) and WSC were evaluated within and above the elongation zone of tall fescue (Festuca arundinacea Schreb.) leaf blades during light and darkness. Imported DM used for WSC-free DM synthesis during darkness (67% of the total in experiment I and 59% in experiment II) was greater than during light (47% in both experiments), suggesting that the 65% higher leaf elongation rate during darkness was accompanied by higher rates of synthesis of cellular structural components. Deposition rates of WSC in the basal and central part of the elongation zone (0-20 mm from the ligule) were similar during light and darkness, but above 20 millimeters WSC deposition occurred during light and WSC loss occurred during darkness. WSC deposition and loss throughout the elongation zone and the recently expanded tissue were mostly due to net synthesis and degradation of fructan. Fructan was predominantly low molecular weight and contributed about 50% of the total osmotic partial pressure of WSC. In the most actively growing region, where fructan synthesis was most rapid, no diurnal change occurred in molecular weight distribution of fructan. WSC solute concentrations were diluted in the most actively growing tissue during darkness because net monosaccharide and fructan deposition were unaltered and sucrose deposition was decreased, but growth-associated water deposition was increased by 77%. Net rates of fructan synthesis and degradation were not related to tissue sucrose concentration, but appeared to respond to the balance between assimilate import and assimilate use in synthesis of cellular structural components (i.e. WSC-free DM) and deposition of monosaccharides. Fructan synthesized in tissue during most active elongation was degraded when the respective tissue reached the distal limit of the elongation zone where assimilate import in darkness was insufficient to maintain synthetic processes associated with further differentiation of cells.

Growth Rates and Carbohydrate Fluxes within the Elongation Zone of Tall Fescue Leaf Blades

Investigations were performed to better understand the carbon economy in the elongation zone of tall fescue leaf blades. Plants were grown at constant 21 degrees C and continuous 300 micromoles per square meter per second photosynthetic photon flux density where leaf elongation was steady for several days. Elongation occurred in the basal 20 mm of the blade (0-20 millimeters above the ligule) and was maximum at 9 to 12 millimeters. Eight 3-millimeter long segments were sampled along the length of the elongation zone and analyzed for water-soluble carbohydrates. Sucrose concentration was high in the zone of cell division (0-6 millimeters) whereas monosaccharide concentration was high at and distal to the location where cell elongation terminated (20 millimeters). Fructan concentration increased in the basal part, then remained constant at about 85% of the total mass of water-soluble carbohydrates through the remainder of the elongation zone. Data on spatial distribution of growth velocities and substance contents (e.g. microgram fructan per millimeter leaf length) were used to calculate local net rates of substance deposition (i.e. excess rates of substance synthesis and/or import over substance degradation and/or export) and local rates of sucrose import. Rates of sucrose import and net deposition of fructan were positively associated with local elongation rate, whereas net rates of sucrose deposition were high in the zone of cell division and those of monosaccharide were high near the termination of elongation. At the location of most active elongation imported sucrose (29.5 milligrams per square decimeter per hour) was used largely for synthesis of structural components (52%) and fructan (41%).

Assessment of spatial distribution of growth in the elongation zone of grass leaf blades

Knowledge about the spatial distribution of growth is essential for understanding the leaf growth process. In grasses the elongation zone is located at the base of the leaf blade and is enclosed by sheaths of older leaves. Assessment of spatial growth distribution, therefore, necessitates use of a destructive method. We used a fine needle to make holes through bases of tillers at the location of the leaf elongation zone of tall fescue (Festuca arundinacea Schreb.), then measured the displacement of the holes after a 6 or 24 h interval. Needle holes caused a 22 to 41% decrease in daily leaf elongation so experiments were conducted to investigate if the spatial distribution of growth in the elongation zone was altered. Leaf elongation rate was reduced similarly when needle holes were made within or above the zone where cell elongation occurs. Distribution of elongation within the zone was the same when estimated by displacement of needle holes or ink marks placed on the epidermis of the elongation zone after surrounding tissue had been removed. Making holes at different locations within the elongation zone did not differentially affect the relative contribution of the damaged or undamaged parts to leaf elongation. These findings demonstrate that needle holes or ink marks in paired leaves can be used to estimate the relative distribution of growth in the elongation zone of undamaged tall fescue leaf blades.

Relationship between Fructose 2,6-Bisphosphate and Carbohydrate Metabolism in Darkened Barley Primary Leaves

Initial dark fructose 2,6-bisphosphate levels in 10-day-old barley (Hordeum vulgare L.) leaves increased when the photosynthetic period was lengthened, when the temperature during the prior photosynthetic period was reduced, and following leaf excision. These treatments also increased the leaf sucrose concentration. Conversely, a decrease in dark fructose 2,6,-bisphosphate occurred during extended darkness, with increasing leaf age and when photosynthate in the leaf was reduced by earlier low light treatments. These variations in fructose 2,6-bisphosphate content correlate with known changes in dark respiration. These findings suggest, but do not conclusively prove, a causal relationship between dark fructose 2,6-bisphosphate levels and dark respiration rates.

TANSLEY REVIEW NO. 5 FRUCTANS AND THE METABOLISM OF SUCROSE IN VASCULAR PLANTS

The occurrence, structure and metabolism of fructose polymers in tissues of vascular plants are discussed in relation to the metabolism of sucrose. Distinctions are made between long-term and short-term storage of such polymers and the regulatory mechanisms which govern accumulation are examined. The roles of various fructosyltransferases in the synthesis of the different fructan structures from sucrose are outlined. The potential selective advantages of the possession of fructan metabolism in different species are assessed with reference to possible roles as cryoprotectants, in osmotic control and as storage carbohydrates whose metabolism can continue at low temperatures (0 to 5°C). It is concluded that the complexity and variety of fructan structures and of the associated enzyme systems has resulted in an incomplete understanding of their physiology and biochemistry, but their significance as an alternative storage polysaccharide in both leaves and storage organs should not be underestimated. Contents I. Introduction II. The structure of fructans in vascular plants: variations on a theme 2 III. The enzymes of fructan synthesis: common elements and sources of structural diversity 5 IV. The comparative biology of fructan metabolism: diversity in occurrence and function 11 V. Concluding remarks 19 Acknowledgements 19 References 19.

Effects of CO(2) Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans

During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO(2) per liter air, was 1.45 milligrams CO(2) evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO(2) per liter air). There was a higher foliar nonstructural carbohydrate level (e.g. sucrose and starch) in the CO(2) enriched compared with CO(2) normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO(2) enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO(2) enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO(2) adapted plants, but not in the control plants.Mitochondria, isolated simultaneously from the leaves of CO(2) enriched and control plants, showed no difference in NADH or malate-glutamate dependent O(2) uptake, and there were no observed differences in the specific activities of NAD(+) linked isocitrate dehydrogenase and cytochrome c oxidase. Since the mitochondrial O(2) uptake and total enzyme activities were not greater in young enriched leaves, the increase in leaf respiration rate was not caused by metabolic adaptations in the leaf mitochondria as a response to long term CO(2) enrichment. It was concluded, that the higher respiration rate in the enriched plant's foliage was attributable, in part, to a higher carbohydrate status.

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O(2) consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.