The Absorption of Ions by Excised Root Systems: III. OBSERVATIONS ON ROOTS OF PEA PLANTS GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Pea plants were grown in complete culture solution and in deficienciesof phosphorus, nitrogen, or potassium for a period of about5 weeks. Excised roots of these plants were treated with a complete,aerated culture solution for varying periods of time and thechanges in respiration rate, phosphorus, nitrogen, potassium,sugar, and starch contents measured.
2. There were changes infresh weight and dry weight of the excisedroots during treatment.The dry weight decreased with time butthe water content changeswere variable. Uptake of water wascorrelated with uptake ofpotassium and sucrose content in someinstances.
3. There wasno evidence of a ‘salt respiration’ inthose caseswhere active accumulation occurred.
4. The rates of gain or lossof phosphorus, nitrogen, or potassiumat 0 hours, 8 hours, and16 hours were calculated and it wasfound that the rate dependedboth on content of element in theroot and the sugar cotent.There was very little evidence thatone element affected therate of uptake of another. Simultaneousloss of one elementand gain of another occurred in some instances.
5. The observationsappear to be best explained on the assumptionthat the absorbedions are fixed in the cells in the form ofloosely bound compoundsand that these compounds are formedfrom sugars.

     

The Absorption of Ions by Excised Root Systems: I. APPARATUS AND PRELIMINARY EXPERIMENTS

1. An apparatus is described by means of which the absorptionofions from a complete nutrient solution of constant compositionby excised root systems of plants, grown under known nutrientdeficiencies, may be measured in standard conditions of aerationand temperature. Results of some prelimi nary experiments aredescribed.
2. It was found that the roots readily absorbed theelement inwhich they were deficient, but tended to lose thoseelementswhich were already present in normal amounts.
3. Therewas almost invariably a loss in fresh weight of the rootsafterthe absorption period and also a loss in dry weight. Thislossappears to be complex and is partly attributable to lossofrespiratory material.
4. The addition of 2 per cent. sucroseto the solution from whichthe root systems of phosphorus-deficientbarley plants wereabsorbing increased the nitrogen and phosphoruscontents ofthe roots and maintained the potassium content,while in absenceof sucrose only the phosphorus content increased,but this increasewas significantly less than in the presenceof sucrose.
5. It was shown that roots excised from plants growingin soilwere capable of absorbing phosphorus or nitrogen—elementsin which they were apparently deficient.
6. The interpretationof data obtained from excised roots is discussed,and it isconcluded that excised roots from plants grown incomplete nutrientare not likely to behave in the same way,as regards absorption,as corresponding roots of intact plants,but that roots grownunder conditions of deficiency will behaverather similarlywhether excised or intact. This fact providesa potential methodfor diagnosing and evaluating nutrient deficiencies.
7. The low-saltcondition of roots postulated by Hoagland and Broyeris notnecessarily the primary requisite for rapid absorptionof aparticular ion. It is rather that the roots should be deficientin that ion. The roots could be high in other salts.

     

STUDIES ON SUBMICROSCOPIC ASPECTS OF MINERAL DEFICIENCIES. II. NITROGEN,POTASSIUM, SULFUR,PHOSPHORUS, AND MAGNESIUM DEFICIENCIES IN THE SHOOT APEX OF BARLEY

Marinos, Nicos G. (Waite Agric. Res. Inst., Adelaide, S.A., Australia.) Studies on submicroscopic aspects of mineral deficiencies. II. Nitrogen, potassium, sulfur, phosphorus, and magnesium deficiencies in the shoot apex of barley. Amer. Jour. Bot. 50(10): 998–1005. Illus. 1903.—The elongation of the shoot apex of barley was retarded in the absence of N, P, or Mg, while the lack of S or K did not affect its growth as compared with the controls. Ultrastructural changes in cells of the terminal 100μ of the apical dome either appeared concurrently with, or preceded, measurable effects on apical elongation. These changes included: (1) formation of many dense intramitochondrial granules and a statistically significant reduction of the length of mitochondrial tubules; (2) accumulation in the cytoplasm of dense manganophilic inclusions which appeared to be formed by the Golgi bodies (dictyosomes); (3) starch accumulation, only in P-dcficient plants, in a region of the apex that is normally free of starch. The similarities in the symptoms induced by N, P, and Mg deficiencies reflect the metabolic interrelationships between these elements. On the basis of the time of appearance of these symptoms and their distribution in the longitudinal axis of the apical dome, it is concluded that altered mitochondrial function is an early response of cells to the lack of certain essential elements.     

THE INFLUENCE OF HIGH CONCENTRATIONS OF AMMONIUM AND SODIUM MOLYBDATES ON FLAX, SOYBEAN AND PEAS GROWN IN NUTRIENT SOLUTIONS CONTAINING DEFICIENT OR EXCESS IRON

Ammonium molybdate supplying 20 or 40 p.p.m. Mo prevented chlorosis caused by low iron supply in young flax plants, but sodium molybdate was effective only at the higher concentration. Temporary darkening of the green colour of the shoots was also produced by 40 p.p.m. Mo in iron-deficient soybean and pea plants, but was soon followed by more severe chlorosis. Symptoms of molybdenum toxicity always developed when 40 p.p.m. Mo were given, whether or not the intensity of chlorosis was reduced. With an increase in iron supply, a reduction in molybdenum toxicity symptoms was confirmed in soybean and peas. In flax the higher level of iron eventually proved excessive unless it was combined with 40 p.p.m. Mo. High molybdenum thus seemed able to counteract both iron deficiency and toxicity in this plant.
High iron reduced the molybdenum content (p.p.m./d.m.) of both shoot and root in soybean, peas and also in flax provided the iron was not excessive. High molybdenum usually reduced the iron content of the shoot, but markedly increased it in the root. Molybdenum-induced chlorosis could thus be partly attributed to inhibition in iron translocation, but the beneficial effect of high molybdenum or high iron on colour was not obviously correlated with the analytical data.     

Effectiveness of Lotus Root Nodules: III. EFFECT OF COMBINED NITROGEN ON NODULE EFFECTIVENESS AND FLAVOLAN SYNTHESIS IN PLANT ROOTS

When grown in a nutrient solution containing combined nitrogen(NH₄NO₃), Lotus pedunculatus and L. tenuis seedlings inoculatedwith a fast-growing strain of Rhizoblum (NZP2037) did neitherdevelop root nodules nor develop flavolans in their roots. Incontrast, the roots of nodulated seedlings growing in a nitrogen-freenutrient solution contained flavolans. Flavolan synthesis coincidedwith root nodule development on these plants. When added as a single dose, high concentrations of NH₄NO₃ (5and 10 mg N per plant) stimulated the growth of L. pedunculatusplants but suppressed nodulation and nitrogen fixation. In contrastthe continued supply of a low concentration of NH₄NO₃ (1?0 mgN d^–1 per plant) stimulated nitrogen fixation by up to500%. This large increase in nitrogen fixation was associatedwith a large increase in nodule fresh weight per plant, a doublingof nodule nitrogenase activity, and a lowering of the flavolancontent of the plant roots. The close relationship between nitrogendeficiency, nodule development, and flavolan synthesis in L.pedunculatus meant that it was not possible (by nitrogen pretreatmentof plants) to alter the ineffective nodule response of a Rhizobiumstrain (NZP2213) sensitive to the flavolan present in the rootsof this plant.     

ON GUAIACOL SOLUTIONS : I. THE ELECTRICAL CONDUCTIVITY OF SODIUM AND POTASSIUM GUAIACOLATES IN GUAIACOL

1. Measurements on the densities, viscosities, dielectric constants, and specific conductances of pure anhydrous and water-saturated guaiacol at 25°C. are reported. 2. The solubility of water in guaiacol at 25°C., and its effect on the electrical conductivity of a sodium guaiacolate solution is given. 3. Electrical conductivity measurements are reported on solutions of sodium and potassium guaiacolates in water-saturated guaiacol at 25°C. 4. The decrease of electrical conductivity with increasing concentration for these salts is explained on the basis of an ionic equilibrium combined with the interionic attraction theory of Debye and Hückel. 5. The limiting equivalent conductances of sodium and potassium guaiacolates in water-saturated guaiacol at 25°C., the corresponding limiting ionic mobilities, and the dissociation constants are computed from the conductivity measurements. The salts are found to be weak electrolytes with dissociation constants of the order of 5 x 10^–6.     

ON GUAIACOL SOLUTIONS : II. THE DISTRIBUTION OF SODIUM AND POTASSIUM GUAIACOLATES BETWEEN GUAIACOL AND WATER

1. Measurements are reported on the distribution of sodium and potassium guaiacolates between guaiacol and water at 25°C. 2. The variation of the partition coefficients with the concentration is explained with the aid of the Debye-Hückel interionic attraction theory and the assumption that the salts are strong electrolytes in water and weak electrolytes in guaiacol. 3. The dissociation constants of sodium and potassium guaiacolates in guaiacol previously computed from electrical conductivity determinations are shown to be in agreement with the corresponding values obtained from the distribution measurements. 4. From theoretical considerations an equation is derived with which it is possible to predict the magnitude of the limiting partition coefficients from the dielectric constants of the solvents, the size of the solute ions, and the temperature.     

Devlopmental Physiology of Sugar-Beet: II. EFFECTS OF TEMPERATURE AND NITROGEN SUPPLY ON THE GROWTH, SOLUBLE CARBOHYDRATE CONTENT AND NITROGEN CONTENT OF LEAVES AND ROOTS

Plants were grown at temperatures of 15 and 25 ?C with two ratesof nitrogen supply. The changes in dry weight, leaf area, cellnumber, mean cell volume, soluble carbohydrate, and total nitrogenconcentration of the cotyledons, the first and second pair oftrue leaves, and the storage root were measured. Changes incell number and cell volume of the first pair of true leavesand storage root of plants were also measured at 11, 18, 25,and 32 ?C. Leaf growth before unfolding was chiefly by increase in cellnumber and after unfolding by increase in mean cell volume,while the growth of the storage root was almost entirely byincrease in cell number. The rates of cell division and cellexpansion were fastest at 25 ?C, but the initially high ratesof cell division in the terminal bud and in individual leavesdecreased rapidly and greater rates were maintained at the sub-optimaltemperatures, i.e. 15 and 18 ?C. After an initial period ofslow growth, the first-formed leaves grew faster and becamelarger at 15 than at 25 ?C. Leaves were produced, unfolded,grew faster, and became larger with increase in the externalconcentration of nitrogen, because cells divided and expandedfaster, so that nitrogen increased the number and size of cells. Sugar concentration was greater at 15 than at 25 ?C in leavesbut not in the storage root. Sugar concentration in the petiolesof the first and second pair of true leaves increased to 1.2and 2.0 per cent fresh weight respectively. Decreased nitrogensupply temporarily increased the sugar concentration of cotyledonpetioles and the seedling hypocotyl, but later decreased itin the leaves and storage root. Nitrogen concentration was greaterin the leaves and storage root at 15 than at 25 ?C with thelarger nitrogen supply. Nitrogen concentrations were similarin young leaves of all treatments but as the size of leavesincreased nitrogen concentrations decreased most rapidly at25 ?C with the smaller nitrogen supply. It is suggested that when increased leaf production and storage-rootgrowth occurs at temperatures below the growth optimum (25 ?C),they may be due to an effect of increased carbohydrate supplyon cell division and sugar storage.     

GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE L.): IV. THE EFFECT OF NITROGEN, PHOSPHORUS AND POTASSIUM SUPPLY ON GROWTH DURING THE FIRST YEAR

In a sand-culture experiment lasting 21 weeks plants of timothy grown from seed were maintained at all combinations of three levels of nitrogen, phosphorus and potassium. The number and weight of tillers, leaves and ears, and the weight of roots, were determined at the end of the experiment, and for some of the treatments at intervals of 4 weeks. All three nutrients had significant effects, especially N which at its lowest level of supply tended to mask the effect of the other two elements. Potassium influenced tiller numbers least, especially those of primary tillers, but in the presence of high concentrations of N and P it had a large effect on leaf area and dry weight. Relative growth and net assimilation rates responded to varying nutrient supply only in the early stages of growth, so that in general variations in dry weight were associated with nutrient effects on leaf area.     

Effects of Mechanical Impedance on Root Growth in Barley, Hordeum vulgare L.: II. EFFECTS ON CELL DEVELOPMENT IN SEMINAL ROOTS

Anatomical changes induced in the roots of barley plants (Hordeumvulgare cv. Proctor) by an applied pressure of 2 ? 10⁴ Pa (0.2bar) have been examined; previous studies had shown that thelength of roots grown under these conditions was about 50% ofthat of unimpeded roots. Cryomicrotomy/light microscopy andscanning electron microscopy were used. Mechanical impedanceincreased the diameter of roots, this being due largely to anincreased thickness of the cortex; the number of cells in transversesection was increased and the diameter of the outer cells wasgreater though that of the inner ones was reduced.     

Growth of Two Soybean Shoots on a Single Root: EFFECT ON NITROGEN AND DRY MATTER ACCUMULATION BY SHOOTS AND ON THE RATE OF NITROGEN FIXATION BY NODULATED ROOTS

Soybean stems were grafted between the first and second nodes6 weeks after planting. Three or 5 weeks after grafting, oneroot system was cut from grafted plants, doubling the shoot:root ratio. This technique was applied to plants grown in sandculture and supplied with an excess of water and minerals butwith no combined nitrogen so that doubling the shoot:root ratiogreatly increased the requirement for fixed nitrogen. When theshoot:root ratio was doubled during the flowering or seed formationstages, there was no statistically significant effect on totalnitrogen or dry matter of shoots compared to non-grafted controlsat maturity. The period between 2 and 21 d after doubling theshoot:root ratio was studied to determine changes in root weight,nodule weight, and rate of nitrogen fixation (acetylene reduction).Weight of roots and nodules increased relative to controls (graftedplants with one shoot per root) after about 1 week. The rateof acetylene reduction per gram of nodule was 75 per cent greaterwith roots having two shoots than with control roots 2 d afterdoubling the shoot:root ratio. Acetylene reduction per noduledeclined to near control rates as nodule weight increased, butroots with two shoots maintained a 60 to 70 per cent greaterrate of acetylene reduction per root for 2 weeks. The resultsindicated that nodulated soybean roots are capable of fixingnitrogen at rates greater than those which normally prevail.     

The Structure and Development of Trifolium subterraneum L. Root Nodules: II. IN PLANTS GROWN AT SUB-OPTIMAL ROOT TEMPERATURES

Cold root temperature affected infection thread proliferation,cell invasion, and release of Rhizobium and the subsequent developmentof this infection in Trifotium subterraneum. These events werealso modified by both host cultivar and bacterial strain. At7 °C bacteroid development was only substantial with strainTA1, with either sparsely or abundantly nodulating lines ofthe host. At 11 °C strain SU297 also readily formed effective,bacteroid-filled nodules with both lines. Strain 0403 formeda few bacteroids with the abundant line only at 7 °C andreadily formed bacteroids with the sparse line only at 19 °C.At 15 °C 0403 nodules were effective on abundant lines,but mostly ineffective on sparse lines. The development of Rhizobium rods into bacteroicis and theirsubsequent degeneration wa slower at low temperatures with bothstrains. Low root temperatures favoured the deposition of starchthroughout the nodule. At higher temperatures, when bacteroidswere more active in nitrogen fixation, starch was mostly confinedto a narrow band of the youngest bacteroid filled cells andto the zone of bacteroid degeneration.     

PROTOPLASMIC POTENTIALS IN HALICYSTIS : II. THE EFFECTS OF POTASSIUM ON TWO SPECIES WITH DIFFERENT SAPS

The potential difference across the protoplasm of impaled cells of two American species of Halicystis is compared. The mean value for H. Osterhoutii is 68.4 mv.; that for H. ovalis is 79.7 mv., the sea water being positive to the sap in both. The higher potential of H. ovalis is apparently due to the higher concentration of KCl (0.3 M) in its vacuolar sap. When the KCl content of H. Osterhoutii sap (normally 0.01 M or less) is experimentally raised to 0.3 M, the potential rises to values about equal to those in H. ovalis. The external application of solutions high in potassium temporarily lowers the potential of both, probably by the high mobility of K⁺ ions. But a large potential is soon regained, representing the characteristic potential of the protoplasm. This is about 20 mv. lower than in sea water. The accumulation of KCl in the sap of H. ovalis is apparently not due to the higher mobility of K⁺ ion in its protoplasm, since the electrical effects of potassium are practically identical in H. Osterhoutii, where KCl is not accumulated.     

The Absorption and Utilization of Phosphate by Young Barley Plants: IV. THE INITIAL STAGES OF PHOSPHATE METABOLISM IN ROOTS

Organic phosphorus compounds have been extracted from the rootsof intact plants which have absorbed radioactive phosphate.The distribution of phosphorus between different organic fractionsof the root during a 24-hour absorption period is markedly influencedby the concentration of phosphorus supplied. Less than 1 minute after entry a significant proportion of theabsorbed phosphorus is found to be in organic compounds. Incorporationinto nucleotides is particularly rapid, whereas incorporationinto hexose phosphates occurs more slowly. The pattern of esterificationis influenced by the phosphate status of the plants. 2: 4-dinitrophenol (10^–4M.) reduces the uptake of phosphorusand also the extent of esterification, the latter effect beingdue solely to reduced incorporation into the nucleotide fraction. Although extensive esterification of phosphate occurs in roots,it appears to be transported to the shoot as inorganic phosphateaccompanied by only a small amount of a single organic compound.     

The Influence of Mineral Nutrition on the Root Development of Trees: II. THE EFFECT OF SECIFIC NUTRIENT ELEMENTS ON THE GROWTH OF INDIVIDUAL ROOTS OF SITKA SPRUCE

Sitka spruce seedlings were grown with divided root systemsin sand culture and the application of N, P, and K was variedwhile maintaining a complete supply of other nutrients. Therewas a localized stimulation of the growth of roots to whichnutrients were applied and N produced the greatest stimulation;P was also important but K did not enhance growth. Measurements of Ca and Mg concentrations in the roots showedthat differential root growth, which is influenced by the concentrationof N and P in the bathing medium, could not be adequately explainedby the effect of N or P on the uptake of the immobile cations. The two parts of the divided root system appeared to competefor assimilates; the enhanced growth of one root was accompaniedby reduced growth in the other, and vice versa.     

Studies on the Growth in Culture of Plant Cells: VII. EFFECTS OF KINETIN ON THE CARBOHYDRATE AND NITROGEN METABOLISM OF ACER PSEUDOPLATANUS, L CELLS GROWN IN SUSPENSION CULTURE

Aspects of the carbohydrate and nitrogen metabolism of Acerpseudcplatanus, L cell suspension cultures grown on a syntheticmedium containing 2 per cent glucose and 1.0 mg/l 2,4-dichlorophenoxyaceticacid and kinetin either at 0.25 mg/l (low kinetin) or at 2.5mg/l (high kinetin) are described. High kinetin inhibits growthas measured by increase in cell number, packed-cell volume,and cell dry weight. Although not inhibitory to glucose utdization,high kinetin inhibits the O₂ uptake of the cells. Such cellscontain only a trace amount of fructose and their rate of O₂uptake can be raised to that of the low kinetin cells by a periodof fructose feeding. The O₂ uptake of both kinds of cell issensitive to malonate but the stimulation of O₂ uptake inducedby bis(hexafiuoroacetonyl)-acetone (‘1799’) at 0.2mM is much less with the high-kinetin than the low-kinetin cells.The enzymes phosphoglucoseiseomerase and glucose-6-phosphatedehydrogenase are much less active in the high-kinetin cells.Mitochondria isolated from both kinds of cells show good respiratorycontrol although slightly lower values for Q_O2(N), ADP/O ratioand control ratio are recorded with mitochondria from the highkinetin cells. Kinetin at 2.5 mg/l slightly reduces the ADP/Oratio of isolated mitochondria but at 4.0 mg/l their responseto ADP is completely suppressed. Extracellular hemicelluloseformed in presence of high kinetin has a reduced content ofgalactose and xylose and an increased content of glucose. Theseobservations indicate that the inhibition of respiration byhigh kinetin is mainly due to suppression of glucose conversionto other sugars rather than to inhibition of glycolysis or terminalrespiration. High kinetin decreases the rate of protein but not of amino-acidsynthesis. Suppression of the synthesis of particular proteinsmay be an important factor responsible for the reduced cellyield of the cultures in presence of high kinetin. The significanceof these observations to our understanding of the critical metaboliceffects of cytokinina is discussed. Acer pseudoplatanus cells release amino acids into their culturemedium early in the period of batch culture and largely reabsorbthem as incubation proceeds.