Root Carbohydrate Research Articles

Root soluble carbohydrates of Afzelia africana Sm. seedlings and modifications of mycorrhiza establishment in response to the excision of cotyledons

Stem length, number of secondary lateral roots, shoot dry weight and reducing sugar concentrations of root were significantly reduced when translocation of reserves from cotyledons to the roots of Afzelia africana seedlings was interrupted by complete or partial cotyledon excision. The sucrose but not the glucose concentration of lateral roots also decreased significantly after complete cotyledon excision. Hartig net development rather than fungal sheath formation was affected after inoculation with the early fungal isolate E1 and by both late-stage fungal isolates L1 and L2 after partial or complete cotyledon excision. However, mycorrhizal colonization by the early fungal isolate E2 was not affected by cotyledonary reserves, suggesting that this fungal isolate has a lower carbohydrate requirement than fungal isolates E1, L1 and L2. The late-stage fungal isolates L1 and L2 induced a hypersensitivity reaction by epidermal cell walls of the host plant after complete cotyledon excision, suggesting they are more dependent than the early fungal isolate E1 on available root carbohydrate substrates for ectomycorrhizal colonization. These results are discussed in the light of the hypothesis that early and late-stage fungi were different carbohydrate requirements, and that the time sequence of colonization was related to the root carbohydrate status, which increased with time.

Diurnal changes in net uptake rate of nitrate are associated with changes in estimated export of carbohydrates to roots.

The rate of NO3- uptake by soybean (Glycine max [L.] Merrill) roots generally declines during the night in association with progressive depletion of the nonstructural carbohydrate pool in the shoot as well as the concentration of carbohydrates in roots. To determine if NO3- uptake rate changes in response to variations in translocation rate of carbohydrates from shoot to roots per se or to carbohydrate status of the roots, the night period was interrupted with a low light level from incandescent lamps to alter the diurnal pattern of NO3- uptake by roots and export of carbohydrate from shoots of nonnodulated soybean. Depletion of NO3- from replenished, complete nutrient solutions containing 1 mM NO3- was measured by ion chromatography and rates of NO3- uptake were calculated. Changes in export of carbohydrates from shoot to roots during intervals of the night period were calculated as the differences between rates of disappearance in contents of nonstructural carbohydrates and their estimated rates of utilization in shoot respiration and growth. A positive, significant correlation occurred between changes in calculated rates of carbohydrate export from shoots and NO3- uptake rates. Conversely, there was no significant correlation between concentrations of nonstructural carbohydrates in roots and NO3- uptake rates. These results support the hypothesis that carbohydrate flux from shoot to roots has a direct role in regulation of nitrogen uptake by the whole plant.

Root and crown characteristics of alfalfas varying in fall dormancy

We compared root and crown characteristics of five alfalfa (Medicago sativa L.) entries which differed in fall dormancy. Alfalfas were subjected to bud or mid-bloom harvests. The most consistent entry effect occurred for root and crown dry weight and root total nonstructural carbohydrate (TNC) concentrations. Root TNC concentration was highest and root and crown weight were greatest for the nondormant and least in the most dormant entries. Entries did not consistently differ in crown bud numbers, shoot number, or shoot origin. In October, the number of elongated crown buds were greater for a non-fall dormant alfalfa Nitro than for the most fall dormant alfalfa. Key words: Alfalfa, root and crown morphology, fall dormancy, root carbohydrates

Phytophthora cryptogea root rot of tomato in rockwool nutrient culture:

SUMMARYThe effect of root temperature on growth and yield of rockwool‐grown tomato plants infected with Phytophthora cryptogea was investigated. Measurements of shoot and root growth were taken at high (25oC) and low (15oC) root temperatures during the generative phase of growth. The growth of roots of healthy and P. cryptogea‐infected tomato plants in rockwool blocks was higher in plants grown with roots at 25oC than at 15oC after 60 days and a similar effect was found in slabs after 98 days. Under sub‐optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature of c. 15oC and the response was greater in cv. Counter than cvs Calypso and Marathon. Water‐soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15oC and 25oC. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25oC. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25oC were taller than those with a root temperature of 15oC. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25oC were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25oC at the terminal harvest was higher than from healthy plants with roots maintained at 15oC.

The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

The effects of NO-3 and NH+4 nutrition on hydroponically grown wheat (Triticum aestivum L.) and maize (Zea mays L.) were assessed from measurements of growth, gas exchange and xylem sap nitrogen contents. Biomass accumulation and shoot moisture contents of wheat and maize were lower with NH+4 than with NO-3 nutrition. The shoot:root ratios of wheat plants were increased with NH+4 compared to NO-3 nutrition, while those of maize were unaffected by the nitrogen source. Differences between NO-3 and NH+4-fed plant biomasses were apparent soon after introduction of the nitrogen into the root medium of both wheat and maize, and these differences were compounded during growth.Photosynthetic rates of 4 mM N-fed wheat were unaffected by the form of nitrogen supplied whereas those of 12 mM NH+4-fed wheat plants were reduced to 85% of those 12 mM NO-3-fed wheat plants. In maize supplied with 4 and 12 mM NH+4 the photosynthetic rates were 87 and 82% respectively of those of NO-3-fed plants. Reduced photosynthetic rates of NH+4 compared to NO-3-fed wheat and maize plants may thus partially explain reduced biomass accumulation in plants supplied with NH+4 compared to NO-3 nutrition. Differences in the partitioning of biomass between the shoots and roots of NO-3-and NH+4-fed plants may also, however, arise from xylem translocation of carbon from the root to the shoot in the form of amino compounds. The organic nitrogen content of xylem sap was found to be considerably higher in NH+4- than in NO-3-fed plants. This may result in depletion of root carbohydrate resources through translocation of amino compounds to the shoot in NH+4-fed wheat plants. The concentration of carbon associated with organic nitrogen in the xylem sap of maize was considerably higher than that in wheat. This may indicate that the shoot and root components of maize share a common carbon pool and thus differences induced by different forms of inorganic nitrogen are manifested as altered overall growth rather than changes in the shoot:root ratios.

Effects of flooding on carbohydrate and ABA levels in roots and shoots of alfalfa

ABSTRACTAlfalfa is sensitive to waterlogging, and its yields are significantly reduced under this condition. We investigated the effects of soil flooding on free abscisic acid (ABA) accumulation in shoots and roots of alfalfa in relation to plant growth and stomatal conductance responses. The production of dry matter in alfalfa was significantly affected by flooding mainly as a result of a rapid reduction in root growth. Shoot dry matter accumulation was maintained during the first 10 d of treatment and started to decline thereafter. Foliar concentration of the major mineral elements (N, P, K) was reduced by flooding, whereas only K concentration decreased in roots of flooded plants. Regrowth declined with duration of flooding and was less than 50% of controls after 2 weeks. While no changes in ABA concentration could be detected in flooded roots, an increase was noted within a few days in leaves when compared to unflooded controls. This increase in free ABA coincided with the accumulation of large quantities of starch in leaves and a rapid decline in leaf stomatal conductance. Our results support the suggestion that leaf ABA originates from the leaf itself and may be accumulating along with starch as a result of reduced translocation to the roots. Our observation of large accumulations of sucrose in flooded roots agrees with previous reports that supply of carbohydrates is not a limiting factor to root anaerobic metabolism in flooded alfalfa.

The development of endomycorrhizal root systems

SUMMARYConcentrations of phosphorus in shoot and soluble carbohydrates (fructose, glucose, sucrose and fructans) in root were measured in non‐mycorrhizal and vesicular‐arbuscular (VA) mycorrhizal (Glomus mosseae) leek plants (Allium porrum) raised at six concentrations of soil phosphate. In conditions when an increased concentration of soil phosphate reduced VA mycorrhizal infection, the concentrations of soluble carbohydrates in the root were at a maximum. Therefore the hypothesis that greater concentrations of soluble carbohydrates in roots favour VA mycorrhizal infection is discounted. There was a specific effect of VA mycorrhizas, in that infected roots contained a larger concentration of sucrose than did uninfected roots, in plants with similar phosphorus concentrations in dry matter of shoots.We conclude, first, that increased phosphorus supply from either phosphate addition to soil or VA mycorrhizal infection increases concentration of soluble carbohydrates in leek roots and, secondly, that the VA mycorrhizal root behaves as a particularly strong physiological sink when there is an excess concentration of sucrose in the host.

Response of roots to mechanical impedance

The response of roots to mechanical impedance has been addressed in the literature largely from the physical point of view. The properties of soils which cause them to become impenetrable by roots have been analysed in detail, with particular reference to soil texture. Factors such as high soil cohesion (in clay soils) and high angle of internal friction (in sandy soils) contribute to soil strength. However, root growth often involves radial deformation of the soil near the growing apex, requiring a consideration of soil compression as well. While soils of all textures can impede root growth, those with high clay content are thought to be most inhibitory. Predictions of soil strength can also be obtained from penetrometer probes with different diameters and tip shapes. A precise physical analogue of root growth is not possible but probes which penetrate soil by deformation around the tip give surprisingly good estimates of relative soil strength. The capacity of roots to minimize friction with the soil and expand radially is thought to account for the lower absolute resistance perceived by roots than by penetrometer probes. Roots oppose strong soil by forces of osmotic origin acting on both the soil and the expanding cell walls. The response of roots is, however, poorly understood. Cortical cells tend to become broader and shorter, causing the root axis to thicken. Root volumes and osmotic pressures changes as a result. The role of ethylene as a mediator of structural changes is in question. Root (and shoot) carbohydrate metabolism is also change by impedance in a way that produces a favourable balance of biomass above and below ground and prevents carbohydrate deprivation to growing tissues. However, the co-ordination of changes in anatomy and metabolism remains a mystery. The scope for selection of plants tolerant to mechanical impedance is discussed and there are reasons for optimism if new screening criteria are adopted.

Seasonal changes in the carbohydrate content of two cultivars of asparagus

The annual changes in carbohydrate content in the roots of two cultivars of asparagus ( Asparagus officinalis L. cultivar UC 157 and cultivar ‘Junon’) grown in the relatively mild winter climate of Israel were studied. During the autumn (August–November) when the ferns senesce and the subsequent winter dormant season (November–February) the roots were characterized by a constant and significant decrease in fructan content in both cultivars, contributing to a loss of over 30% of the stored fructans. During the harvest (February–April) there was a further decline in root fructan content. During the post-harvest period of fern growth, as the unharvested ferns develop and expand, the root fructan content declined to its lowest levels. Following this, there was a sharp and continuous increase in root fructan levels, as well as a transient increase in sucrose levels for the following three summer months (May–August). The general pattern of root carbohydrate changes was similar in the two cultivars, although there were differences of possible physiological significance.

Peach/myrobalan plum graft incompatibility in the nursery

Various peach/myrobalan graft combinations were compared in nursery trials. Two peach cultivars (Prunus persica L. Batsch) grafted on five myrobalan x myrobalan (Prunus cera- sifera L. Ehrh.) clones were observed during the first year of growth after budding. Graft combinations, comprising the same peach cultivars grafted on other myrobalan x myrobalan clones that had shown symptoms of ‘translocated’ graft incompatibility in some replicated trees during the first year, were observed during the second year of growth. The time taken for the appearance of symptoms of incompatibility was determined. The degree of incompatibility was determined from growth rates, leaf dry weight per unit area, and leaf pigment content. Root carbohydrate content was measured at leaf fall. The sanitary state of plant material was determined to explain differences in severity and/or time for symptom appearance, observed between some replicates. No relationship was found between the sanitary state of plant material and the severit...

Accumulation and partitioning of biomass and soluble carbohydrates in maize seedlings as affected by source of nitrogen, nitrogen concentration, and cultivar1

Abstract Seedlings of four maize hybrids were grown hydroponically to investigate the impact of different N sources (Ca(NO3)2, (NH4)2SO4 and a 1:1 mixture of both) on (i) production and partitioning of root and shoot dry matter, (ii) concentration of soluble carbohydrates in roots and shoots and their partitioning to these plant parts, (iii) concentration of starch in the shoot, and (iv) N uptake. During the main phase of the experiments (duration 14d), the plants were grown in a greenhouse at 25/22°C day/night temperatures and a photoperiod of 16h. Nitrogen was supplied at three concentrations (2.8, 28, and 280 ppm). The root‐zone pH was 6.5. Under the lowest N supply, the N sources produced similar root and shoot dry matters. At the highest N level (280 ppm), NO3‐fed plants were superior. In contrast, the mixture of NH4 and NO3 − was optimum at 28 ppm. More or less pronounced N form by N concentration interactions were also found in the concentration and distribution of soluble carbohydrates and in all ...

Carbohydrate Content, Fructan and Sucrose Enzyme Activities in Roots, Stubble and Leaves of Ryegrass ( Lolium perenne L.) as Affected by Source/Sink Modification after Cutting

Glucose, fructose, sucrose and fructans were the main non-structural carbohydrates of perennial ryegrass. Fructans accumulated predominantly in stubble, i.e. in the basal part of the leaves. Regrowth after defoliation involved two different phases. The first one (0–6 days) was characterized by the mobilization of carbohydrates in both roots and stubble to sustain foliage development in the absence of current photosynthate. During the second phase (6–29 days) carbohydrate content rose to the values observed prior to cutting. Concomitant with a decrease in soluble protein and in non-structural carbohydrate contents, sucrose-sucrose-fructosyltransferase (SST) activity decreased during the first 6 days in roots and stubble whereas fructan exohydrolase (FEH) activity increased and invertase activity was high. Prior to the subsequent increase in carbohydrate content, sucrose synthase activity increased sharply while sucrose phosphate synthase showed only slight variation. During the second period of regrowth FEH declined and SST increased. In regrowing leaves, however, fructan accumulation was not paralleled by an increase in SST activity. Results are interpreted and discussed in terms of source-sink relationships and carbohydrate partitioning.

Fusarium Crown-Rot Development in Alfalfa Stressed by Threecornered Alfalfa Hopper (Homoptera: Membracidae) Feeding

Alfalfa, Medicago sativa L., plants were inoculated with Fusarium oxysporum Schlecht and infested with Spissistilus festinus (Say) nymphal populations for six harvest periods under greenhouse conditions. Significant interactions between insect populations and F. oxysporum were found for number of harvestable stems and percent acid detergent fiber. The main effect of inoculation did not significantly affect any of the plant parameters examined. Insect populations, however, reduced plant height, root carbohydrate concentration, forage yield, and forage quality. S. festinus nymphs also were found to cause a significant increase in Fusarium crown-rot severity after six harvest periods.

Embedded Wire in Tree Roots: Implications for Tree Growth and Root Function

Experiments with two-year-old seedlings of Fraxinus pennsylvanica and Celtis occidenlalis and two yearold whips of Populus angulata x plantierensis were designed to study the effect of root girdling by wire. Overall growth, foliar nutrient content, xylem anatomy, root carbohydrate content, xylem water potential, and rate of transpiration were studied six months after girdling. Neither greenhouse grown seedlings nor field grown whips subjected to root girdling by wire grew less than those without girdling wire. Full girdling significantly reduced foliage dry weight in Fraxinus and the rate of transpiration in Fraxinus and Celtis. A gradient of water potential was observed in the xylem across the wire girdle in seedlings of these two species. The amount of carbohydrate present in root tissue and its distribution in relation to the wire was slightly influenced by girdling in all three species.

Impacts of Pear Thrips Damage on Root Carbohydrate, Sap, and Crown Characteristics of Sugar Maples in a Pennsylvania Sugarbush

Abstract Fall root total nonstructural carbohydrate concentration (TNC), spring sap sugar concentration and volume, and summer crown condition were compared for 2 years among sugar maples (Acer saccharum Marsh.) that exhibited different degrees of crown damage following a 1989 attack of pear thrips (Taeniothrips inconsequens Uzel) in a Pennsylvania sugarbush. Trees with heavy damage had lower root TNC the fall following attack and greater crown transparency in both years following attack compared with trees with less damage. In the first year following attack, sap sugar concentration and volume were greater for trees with light damage than trees with moderate or heavy damage. In the second year following attack, sap volume was still greatest for trees with light damage while trees with heavy damage had the highest sugar concentration of all damage classes. Calculated syrup production based on sap sugar concentration and volume was greatest for trees with light damage and lowest for trees with heavy damage in both years. Trees with heavy damage in 1989 had earlier 1991 spring budburst than trees with light damage, and early budburst was associated with greater 1991 thrips infestation. The results indicate that pear thrips damage had a detrimental impact on tree health and syrup production for the next 2 years. For. Sci. 38(2):381-392.

Soluble Carbohydrates in Mycorrhized and Non-Mycorrhized Fine Roots of Spruce Seedlings

Abstract We present results on the compartmentation of carbohydrates such as sucrose, glucose, fructose, and mannose in different parts of an ectomycorrhiza established between Picea abies and Amanita muscaria and compare it with non-mycorrhized fine roots. Lyophilized mycorrhizas and fine roots (< 2 mm length) were dissected into about 0.5 mm thick slices which represent 4 zones of different physiological functions. The total amount of the analyzed carbohydrates was about 30% higher in non-mycorrhized (n-myc) compared to mycorrhized (myc) fine roots, with sucrose being the dominating sugar in both root types. A longitudinal distinction of sucrose pools showed lowest levels in the middle parts of a mycorrhiza, which represent areas of most intense symbiotic interaction. Fine roots without fungal infection did not show longitudinal variations in sugar content.

Effects of Nymphal Populations of Three cornered Alfalfa Hopper (Homoptera: Membracidae) on ‘Florida 77’ Alfalfa Plants

High (six nymphs per plant) and moderate (three nymphs per plant) infestations of three cornered alfalfa hopper, Spissistilus festinus (Say), nymphs were placed on greenhouse-grown ‘Florida 77’ alfalfa, Medicago sativa L., plants for three harvest periods. Higher populations of nymphs caused a corresponding increase in girdle numbers on the test plants. Nymphal populations significantly increased plant chlorosis and accelerated plant maturity. Although dry-weight yield was not affected, forage quality was reduced because of a decrease in protein concentration and an increase in neutral detergent fiber. Root carbohydrate levels and stem regrowth were both significantly lower under high population levels.

Root Carbohydrate, Organic Acids, and Phenolic Chemistry in Relation to Sweetpotato Weevil Resistance

Methanol extracts of external (outer 3 mm) and interior root tissue of four sweetpotato [Ipomoea batatas (L.) Lam.] cultivars (`Centennial', `Jewel', `Regal', and `Resisto') having different levels of susceptibility to the sweetpotato weevil [Cylas formicarius elegantulus Summer] were analyzed for simple carbohydrates (fructose, glucose, sucrose, inositol) and organic acids (malic, citric, quinic) by gas chromatography and for phenolics (caffeic acid, caffeoylquinic acids, rutin) by high-performance liquid chromatography. There were significant differences among cultivars in the concentrations of total sugars and phenolics in the external tissue (P < 0.05). In addition, the distribution of carbohydrates, organic acids, and chlorogenic acid [3-O-caffeoylquinic acid] differed between external and interior tissues. Sucrose was the major water-soluble carbohydrate in all cultivars. With the exception of malic acid, the concentration of carbohydrates, organic acids, and phenolics did not correlate with cultivar susceptibility to the sweetpotato weevil.

Growth, Reproduction and Chemical Composition of Horsenettle (Solanum carolinense)

Horsenettle was described quantitatively in two grazed bermudagrass pastures for two years. Six times from April through October, plants were counted, phenologically documented, and tops were harvested for estimation of above-ground phytomass. Roots were sampled for carbohydrate, N fraction, and macronutrient analyses. Top growth, flowering, fruiting, and chemical composition were similar between sites within years, but differed between years. Starch and total non-structural carbohydrates in roots increased following reproductive periods both years. Root concentrations of protein and non-protein N increased and concentrations of P decreased in August and September in one year only. Analysis of the relationship between seasonal trends in carbohydrate fluctuation and pasture management practices suggests that systemic herbicide application in mid-summer may lead to more effective control than application in spring.

Effects of Salt Stress on Amino Acid, Organic Acid, and Carbohydrate Composition of Roots, Bacteroids, and Cytosol of Alfalfa (Medicago sativa L.)

Ethanol-soluble organic acid, carbohydrate, and amino acid constituents of alfalfa (Medicago sativa) roots and nodules (cytosol and bacteroids) have been identified by gas-liquid chromatography and high performance liquid chromatography. Among organic acids, citrate was the predominant compound in roots and cytosol, with malonate present in the highest concentration in bacteroids. These two organic acids together with malate and succinate accounted for more than 85% of the organic acid pool in nodules and for 97% in roots. The major carbohydrates in roots, nodule cytosol, and bacteroids were (descending order of concentration): sucrose, pinitol, glucose, and ononitol. Maltose and trehalose appeared to be present in very low concentrations. Asparagine, glutamate, alanine, gamma-aminobutyrate, and proline were the major amino acids in cytosol and bacteroids. In addition to these solutes, serine and glutamine were well represented in roots. When alfalfa plants were subjected to 0.15 m sodium chloride stress for 2 weeks, total organic acid concentration in nodules and roots were depressed by more than 40%, whereas lactate concentration increased by 11, 27, and 94% in cytosol, roots, and bacteroids, respectively. In bacteroids, lactate became the most abundant organic acid and might contribute partly to the osmotic adjustment. On the other hand, salt stress induced a large increase in the amino acid and carbohydrate pools. Within the amino acids, proline showed the largest increase, 11.3-, 12.8-, and 8.0-fold in roots, cytosol, and bacteroids, respectively. Its accumulation reflected an osmoregulatory mechanism not only in roots but also in nodule tissue. In parallel, asparagine concentration was greatly enhanced; this amide remained the major nitrogen solute and, in bacteroids, played a significant role in osmoregulation. On the contrary, the salt treatment had a very limited effect on the concentration of other amino acids. Among carbohydrates, pinitol concentration was increased significantly, especially in cytosol and bacteroids (5.4- and 3.4-fold, respectively), in which this cyclitol accounted for more than 35% of the total carbohydrate pool; pinitol might contribute to the tolerance to salt stress. However, trehalose concentration remained low in both nodules and roots; its role in osmoregulation appeared unlikely in alfalfa.