Selenium Absorption by Excised Astragalus Roots

Absorption of selenate and selenite by excised roots of Astragalus Crotalariae, a selenium accumulator, and of A. lentiginosus, a non-accumulator, was favored by CaCl(2) and a pH of 4.0. The uptake of selenate and possibly selenite, is metabolically linked. Roots of a number of Astragalus species were examined, and in all cases selenate entered the roots much faster than selenite. In these short-term experiments there was no relation between uptake of the 2 ions and classification of a species as selenium-accumulator or non-accumulator.     

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 Presence of Gibberellins in Excised Tomato Roots

Substances having similar physiological properties to the gibberellins(located by the ‘Meteor’ dwarf pea bio-assay) havebeen detected in extracts from excised tomato root. The chromatographicbehaviour of the most active zone is similar to that of gibberellinA₁. Experiments using the d-1 and d-5 mutants of mazie did not indicatethe presence of substances with differential effects on thesetwo mutants.     

Metabolism of Some Indole Auxins in Excised Tomato Roots

Indolylacetylaspartic acid (IAAsp) and possibly indolylacetylglutamicacid (IAG) are formed by exposure of excised tomato roots toIAA. Little ‘free’ IAA accumulates in the tissue.An unidentified substance reacting pink with nitricnitrite reagentis also formed. These substances are metabolized when IAA-treatedroots are transferred to auxin-free medium. IAAsp and IAA aresimilarly inhibitory to the growth of excised tomato roots.Excised tomato roots do not interconvert IAA and IAN. IAN-feedingleads to IAN accumulation and the appearance of indolylcarboxylicacid (ICA); transference to auxin-free medium causes a declinein the IAN activity but the ICA spot persists. The inhibitoryactivity of IAN is not due to its conversion to ICA. Excisedtomato and wheat roots respond very differently to externall-tryptophane but in neither case is there evidence of the conversionof tryptophane to ethyl acetate-soluble auxins.     

Interactions in the Absorption of Monovalent Cations by Excised Radish Roots

Preferential absorption of potassium over sodium has been observedwith excised radish roots using a wide range of concentrationsin the bathing medium. This result is contrary to the situationobserved in most other plants which have been investigated,where it is found that at high external concentrations (>1·0mM) the uptake of potassium is less specific and the rate ofsodium absorption exceeds that of potassium. In radish rootscalcium does not interact with the monovalent cation absorptionin the higher range of concentration and the sodium absorptionis not sensitive to chloride-sulphate substitution. These resultsare discussed in relation to salinity-tolerance and potassium:sodiuminteractions.     

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: 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.     

Sucrose Leakage from Isolated Parenchyma of Sugar Beet Roots

The kinetics of sugar efflux from slices of sugar beet rootswas investigated using washing solutions of different osmoticpressure and calcium concentration. The leakage of sucrose isstrongly reduced in solutions of high osmotic pressure (>0·8MPa) or high calcium concentration (10 mM). Turgor-dependentnecrosis of parenchyma cells (plasmoptysis) is the main causeof sucrose efflux from the tissue in hypotonic media with lowcalcium activity. This was shown by good correlation betweenthe percentage of leaked sucrose and the percentage of tissuewater, which was in the free space after the washing procedure.The kinetics of sugar leakage from beet root parenchyma is nobasis for the estimation of the sugar contents of the free spaceor the cytoplasm in situ.     

Some Effects of Sucrose Concentration on Primordium Development in Excised Primary Roots

The effects of varying the amount of sucrose used to supplementthe culture medium maintaining the growth of excised roots ofPisum sativum L., Vicia faba L., Zea mays L. and Phaseolus vulgarisL., on the rates of primordium initiation and subsequent emergenceas lateral roots and on the duration of the interval betweenprimordium inception and emergence as a secondary root throughthe tissues of the primary have been investigated. Variation in the exogenous concentration of sucrose from 0.5to 8 per cent had little effect on the rate of primordium inceptionin Pisum and Vicia and the rates never reached the values obtainedfor the roots of the corresponding intact plants. Moreover,over the 6 day culture period lateral root emergence did notoccur in any of the excised roots of these two species. In contrast,each of the aspects of primordium development examined in theexcised roots of Zea and Phaseolus was markedly affected bythe amount of sucrose used to supplement the culture medium.In addition, in the presence of about 6 per cent sucrose, primordiumdevelopment in these cultured roots was very similar to thatin roots of the corresponding intact plants. The results indicate either that some factor necessary for primordiumdevelopment is present in adequate amounts in excised rootsof Zea and Phaseolus, but not in those of Pisum and Vicia, orthat the factors controlling such development are differentin the former and latter two species. Vicia faba L., Pisum sativum L., Zea mays L., Phaseolus vulgaris L., broad bean, garden pea, maize, dwarf bean, primordium development, sucrose concentration, cultured roots