The Carbohydrate Nutrition of Tomato Roots: V. The Promotion and Inhibition of Excised Root Growth by Various Sugars and Sugar Alcohols

Iron is only consistently present in an available form in White'sroot culture medium if the inorganic salts are autoclaved withthe sugar. The substitution of ferric ethylenediamine-tetra-acetatefor the inorganic ferric salt of White's medium ensures ironavailability when the carbon source of the medium is renderedsterile by ether treatment and subsequently added to the remainderof the constituents which have been sterilized by autoclaving. The biological activity of sugars, and particularly of dextroseand laevulose, is altered by autoclaving them in presence ofthe inorganic salt solution of White's medium. The only sugar which supports a considerable growth of excisedtomato roots is sucrose. The activity of this sugar is not affectedby alcohol-precipitation nor is it dependent upon the simultaneouspresence of traces of its constituent mono-saccharides. Dextrose or laevulose or a mixture of the two sugars supporta low but sustained level of excised-root growth. All othersugars and sugar alcohols tested were inactive as carbon sources. The addition of sucrose at low concentration (0–2 percent.) to a medium containing dextrose as the main carbon compounddoes not make possible a level of growth comparable with thatobtained with an adequate sucrose supply. It has not been possibleto enhance the growth-rate of excised roots supplied with dextroseby previous presentation of this sugar under conditions permittingactive growth. Using media containing 'etherized' sucrose anddextrose, no evidence was obtained of any competitive inhibitionof sucrose utilization by dextrose. Certain sugars when added to a medium, containing the optimumconcentration of sucrose₁, markedly inhibited excised root growth.Thus l-sorbose, l- and d-arabinose, and d-xylose caused notless than 80 per cent, inhibition at a concentration of 0-5per cent. d-mannose and d-galactose completely inhibited growthat o-1 per cent. The oligosaccharides, dextrose, laevulose,and the sugar alcohols tested had, by contrast, very low inhibitoryactivity.     

The Carbohydrate Nutrition of Tomato Roots: VIII. The Mechanism of the Inhibition by D-Mannose of the Respiration of Excised Roots

A study of certain aspects of the respiratory metabolism ofexcised tomato roots has been undertaken. Mitochondria derivedfrom such roots possess an active Krebs cycle. Neither the operationof the Krebs cycle nor the glucose-6-phosphate dehydrogenaseactivity of the preparations are inhibited by mannose. Tracerexperiments using mannose-U-¹⁴C indicate that mannose, on enteringthe root, is rapidly phosphorylated to mannose-6-phosphate whichaccumulates due to lack of phosphomannose isomerase activityin the tissues. The formation of mannose-6-phosphate is dueto the activity of a hexokinase, the presence of which has alsobeen demonstratedIn vitro. The participation of mannose in thehexo-kinase reaction implies its competitive interaction withthe natural substrates of this enzyme. Accumulated mannose-6-phosphateprobably also inhibits respiration through its demonstratedcompetitive inhibition of phosphoglucose isomerase. Certainobservations suggest that it may also inhibit respiration bydepleting the intracellular level of inorganic phosphate. Glucose antagonizes the mannose-inhibition of respiration. Oneeffect of glucose is to inhibit mannose uptake. An enhancedglucose level may also promote the formation of glucose-6-phosphaterather than mannose-6-phosphate by the hexokinase system.     

The Carbohydrate Nutrition of Tomato Roots: III. The Effects of. External Sucrose Concentration on the Growth and Anatomy of Excised Roots

Variation of the concentration of sucrose in White‘s mediummarkedly affects the increase in length of the main axis, andthe number and total length of the laterals developed by excisedtomato roots. Highest values for these three features are obtainedwith medium containing 1.5 per cent, sucrose. Root materialhas been analysed anatomically. Root diameter, cortical thickness,number of xylem vessels, and development of the cortical air-spacesystem increase with increase in sucrose concentration. Thedegree of vacuolation of extra-stelar meristematic cells increases,and protophloem differentiates further from the promeristemwith rising sucrose concentrations. The interpretation of theseresults is discussed.     

The Carbohydrate Nutrition of Tomato Roots: VII. Sugars, Sugar Phosphates, and Sugar Alcohols as Respiratory Substrates for Excised Roots

The respiratory responses of substrate-depleted excised roottips to a range of sugars, sugar phosphates, and sugar alcoholshave been determined by measuring oxygen uptake by the directmethod of Warburg. Sucrose, dextrose, and laevulose are the only sugars which promotea high level of oxygen uptake. The effects of azide and DNP on the oxygen uptake promoted bysucrose and by dextrose are described. Mannose is a strong inhibitor of respiration. This inhibitionis reversed by the simultaneous addition of those sugars whichalso reverse the growth inhibition caused by mannose. Mannoseinhibits the respiration of sucrose and of glycolytic intermediates.Galactose is slowly respired and does not, even at high concentration,inhibit the respiration of sucrose. The results are discussed in relation to the growth effectsof the sugars tested.     

The Carbohydrate Nutrition of Tomato Roots: IV. The Nature and Distribution of Acid Phosphatases

The distribution of acid-phosphatase activity in sections ofembedded, excised, and seedling roots has been studied by theGomori technique. Evidence has been obtained for the presenceof two orthophosphatases and of a pyrophosphatase. The resultsare discussed in the light of the possible roles of these enzymesin carbohydrate metabolism.     

The Effects of Gibberellins on the Growth of Excised Tomato Roots

1. At appropriate concentrations both gibberellic acid (GA) and1-naphthalene-acetic acid (NAA) enhance the main axis growthof excised tomato roots grown in culture media containing sucroseat concentrations below 1 per cent. Lateral root extension growthis enhanced by GA at all sucrose concentrations tested; onlyat the lower sucrose concentrations is this effect observedwith NAA. Both GA and NAA increase the number of emergent lateralroots and this effect is most marked in media of low sucrosecontent. Both GA and NAA at higher concentrations inhibit rootgrowth but NAA exhibits its full range of growth effects overa much narrower concentration range than GA.
2. GA, like NAA,speeds up the loss of meristematic activity whichoccurs whenindividual meristems are repeatedly subculturedin media containing1 per cent, or higher concentrations ofsucrose.
3. The promotionof main axis growth by both GA and NAA involvesenhanced cellelongation and cell division. At a moderatelyinhibitory concentrationGA reduces both cell elongation andcell division; this is notthe case with NAA.
4. Gibberellins A₁, A₂, and A₄ resemble GA(gibberellin A₃) intheir growth effects. Allogibberic acidlike G A promotes lateralroot extension growth but causes markedinhibition of root growthat a much lower concentration thanGA.

     

The Effects of l-Naphthylacetic Acid on the Growth of Excised Tomato Roots

I-naphthylacetic acid (NAA) enhances main axis extension andlateral initiation of excised tomato roots cultured in 0.5 percent sucrose medium. NAA has a qualitatively similar effectupon the growth of root tips cultured in glucose medium or transferredafter 2 days' previous growth in standard (1.5 per cent sucrose)medium to a glucose medium containing NAA.NAA does not raisethe growth-rate of roots cultured in glucose medium to thatoccurring in presence of sucrose as carbon source. The enhancedgrowth resulting from addition of NAA to glucose medium is notdependent upon enhanced glucose uptake.The unique role of sucrosein the growth of excised tomato roots is discussed in the lightof the above observations and of studies on the ability of glucoseto maintain the growth of excised roots previously establishedby a period of culture in sucrose medium.     

Growth Inhibition by D-Mannosamine and Its Reversal by Glucose and Mannose in Bacillus subtilis

Growth of the Bacillus subtilis wild type strain was severelyinhibited by mannosamine. This inhibitory effect was reversedby the addition of glucose or mannose. Growth in peptone mediumwas accompanied by the consumption of the added glucose andby the accumulation of acetoin. Glucose utilization and acetoinproduction were markedly repressed in the cells grown in thepresence of mannosamine. Growth in the presence of mannosaminewas accompanied by a relative decrease in a protein with themolecular weight of 70,000 as revealed by SDS polyacrylamidegel electrophoresis. Our results indicate that mannosamine'sinhibition of growth is due primarily to low glucose utilizationalthough other cellular metabolic activity also may be involved. (Received August 15, 1983; Accepted April 2, 1984)     

The Auxin Activity Extractable from Excised Tomato Roots by Cold 80 per cent. Methanol

Extracts of excised tomato roots prepared with cold aqueousmethanol have been partitioned between ethyl acetate and waterand chromatograms of the two fractions bioassayed by an Avenacoleoptile straight growth test and sprayed with various reagentsincluding those giving colour reactions with indole compounds.The greater part of the auxin activity is in the aqueous fractionand chromatograms of this fraction give positive indole reactions. The aqueous fraction chromatographed with isopropanol/ammonia/watershows two zones of growth-promoting activity. The zone of lowerRf contains tryptophane and unidentified ninhydrin-positivematerial. Tryptophane accounts for the activity of the Ehrlich-positiveregion of this zone. The activity of the zone of higher Rf isassociated with ninhydrin-positive material; this activity can,by use of other solvents, be distinguished in Rf from that ofthe common amino-acids which would occur in this zone on theprimary chromatograms. Chromatograms of the aqueous fractionalso show the presence of urea and of a phenol, neither of whichare associated with the zones of growth-promoting activity. The ethyl acetate fraction, and particularly the acid fractionof this, contains growth-promoting activity which, in a rangeof solvents, always corresponds in Rf to IAA. The acid fractioncontains a growth inhibitor corresponding in Rf to the ß-inhibitorof other workers. A zone of growth-promoting activity near thesolvent front on isopropanol/ammonia/water chromatograms containsmore than one active component, but IAN appears to be absent.     

Effects of 3-Indolylacetic Acid and 3-Indolylacetonitrile on the Growth of Excised Tomato Roots

1. The inhibition by IAA (3-indolylacetic acid) and by IAN (3-indolylacetonitrile)of the growth of excised tomato roots cultured for 7 days at27 C. in a modified White's medium is described. 510^–9g./ml, IAA or 510^–6 g./ml, IAN cause approx, 50 per cent,inhibition of the linear growth of the main axis. With IAA decreasein number of laterals closely parallels the decrease in lineargrowth of the main axis; with IAN reduction in linear growthof the main axis occurs at concentrations above 10^–8 whereasnumber of laterals does not decrease until the concentrationexceeds 10^–6.
2. Study of the course of cell elongationin the exodermal cellsshowed that in the standard medium andin media containing 510^–9IAA or 510^–6 IAN theprocess takes about 7 hours; thefinal cell lengths in IAA andIAN media are lower than in standardmedium owing to a slowerrate of elongation. The decrease inlinear growth of the mainaxis in presence of IAA could be accountedfor by the decreasein cell length; this was not the case withIAN. The implicationsof this are considered.
3. Determinations of the distance (mm.)between, and of the numberof exodermal cells separating, theadjacent laterals in oneorthostichy showed that IAN enhancesthe frequency of lateralswhereas this is either unaffectedor decreased by IAA. The enhancementof lateral frequency inIAN arises from shortening of the cellsof the main axis anddecrease in the number of cells separatingadjacent laterals.
4. The results are considered to support the view that IAN haseffects on root growth different from those of IAA. Study ofthe degree of inhibition of main axis growth and of alterationsin lateral frequency resulting from treatment with mixturesof IAA and IAN provided data which could also be most easilyexplained on this hypothesis.

     

Inhibition of Syncytia Formation and Root-knot Nematode Development on Cultures of Excised Tomato Roots

Two different defined growth media were used to culture aseptically the root-knot nematode, Meloidogyne incognita, on excised roots of tomato, Lycopersicon esculentum cv ''Marglobe.'' One of these media, STW, was a formulation by Skoog, Tsui, and White and the other, MS, a formulation by Murashige and Skoog. From 1 through 4 weeks, inoculated tissues were fractured to observe root infection, giant-cell formation, and nematode development with the scanning electron microscope (SEM). Four weeks after inoculation, the fresh weights of roots and developmental stages of nematodes were recorded. SEM observations indicated that roots cultured on the STW medium had normal growth and infection sites with galls that supported the development of mature females by 4 weeks. Roots cultured on the MS medium were less vigorous and had infection sites with galls containing only one to four syncytialike cells that did not support the development of mature females. Eighty percent of the larvae infecting roots cultured on the MS medium failed to develop into mature females. To determine which factor(s) affected root growth and nematode development, inoculated and uninoculated roots were grown on media consisting of different combinations of the organic and inorganic fractions of the STW and MS formulations. These experiments indicated that the organic fraction of STW was essential for normal root growth; however, the inorganic fraction of MS inhibited normal gall formation and nematode development. Further testing of the inorganic fractions revealed that the high concentration of ammonium nitrate in the MS medium was a factor that inhibited giant-cell formation and nematode development.     

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Shoot and root growth rate, carbohydrate accumulation (includingfructan), reducing sugar content and dry matter percentage weremeasured in six wheat cultivars, ranging from winter to springtypes, grown at either 5 or 25 °C. At 5 °C (comparedwith 25 °C), the relative growth rate (RGR) of shoots wassimilarly reduced in all cultivars, but the RGR of shoots wasmore affected in winter wheats. This difference resulted insmaller root:shoot ratios than in spring wheats, which alsodeveloped more first-order lateral roots. A direct relationshipbetween carbohydrate accumulation at low temperatures and reductionin root growth was established. These results suggest that differentialshootvs.root growth inhibition at low temperature may play akey role in carbohydrate accumulation at chilling temperatures.This differential response might lead to improvements in survivalat temperatures below 0 °C, regrowth during spring, andwater and nutrient absorption at low temperatures.Copyright1997 Annals of Botany Company Wheat; Triticum aestivum; low temperatures; root growth; root: shoot ratio; sugar accumulation     

Light-controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 10³ M Cycocel reversed the inhibition of seed germination by 6.8 × 10⁴ M coumarin. and 6.32 × lO^?4 M Cycocel reversed the inhibition of root elongation by 3.4 × 10³ M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far-red light or darkness. The red-far-red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A₃ and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.     

Carbohydrate Level and Growth of Tomato Plants: II. The Effect of Irradiance and Temperature

The growth response of tomato (Lycopersicon esculentum L.) to temperature and irradiance may be related to carbohydrate concentration. Plants in the exponential phase of vegetative growth were grown under temperatures ranging from 9 to 36°C and under low or high irradiances of approximately 110 or 370 microeinsteins per square meter per second photosynthetically active radiation for a 12 hour photoperiod. The relative growth rate, leaf area ratio, net assimilation rate and whole plant carbohydrate levels were measured. At high irradiance, relative growth rate was 43% faster and total nonstructural carbohydrate concentration was 41% greater than at low irradiance. The change in carbohydrate with irradiance could explain the growth response. Plant growth was fastest at 25°C and decreased parabolically at lower and higher temperatures with a half-maximal rate at 13 and 36°C. Total nonstructural carbohydrate decreased between 13 and 23°C and remained constant at higher temperatures. Soluble sugar concentrations varied little with temperature above 13°C except for sucrose, whose level rose above 30°C. The change in carbohydrate with temperature could not explain the growth response. Above 23°C tomato plants appeared to regulate growth rate to maintain a relatively constant nonstructural carbohydrate concentration.