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

1. Barley plants were grown in complete culture solution and indeficiencies of phosphorus, nitrogen, or potassium for a periodof about 6 weeks. Excised roots of these plants were treatedwith a complete, aerated culture solution at 25? C. for varyingperiods of time, and the changes in respiration rate, phosphorus,nitrogen, potassium, sugars, and starch contents measured.
2. Therewere changes in fresh weight and dry weight of the excisedrootsduring treatment. The dry weight decreased with time butthewater-content changes were variable. There was a gain orlossof water by the roots according to the treatment.
3. In all casesthe deficient roots increased in content of theelement in whichthey were originally deficient. The roots ofthe plants suppliedwith full nutrient usually decreased incontent of phosphorus,nitrogen, and potassium, but exceptionsoccurred and the reasonsare discussed.
4. In most of the experiments described simultaneousloss of oneion and gain of another occurred.
5. Nitrogen-deficientroots accumulated nitrate when exposed toa complete nutrientsolution, and some of this was assimilatedwith formation ofprotein. Under similar conditions nitrogen-richroots decreasedin nitrogen content and proteolysis took place.
6. There wasa rapid fall in sucrose and reducing sugar contentof the excise'roots. The starch content was initially verysmall and showedlittle change with time.
7. The respiration rate declined withtime in all treatments exceptwhere a nitrogen deficiency existed.Here the respiration rateincreased to a maximum value at about8 hours and then fell.This increase in rate is attributed toprotein synthesis. Noevidence of a ‘salt respiration’was observed evenwhen active uptake of phosphorus or potassiumwas occurring.
8. In most instances the carbon dioxide evolvedin respirationgreatly exceeded the carbon dioxide equivalentof the sugarconsumed in the same period. Exceptions were foundwith thenitrogen-deficient roots where less carbon dioxidewas evolvedthan the equivalent of sugar consumed. It is probablethat apart, at least, of the sugar unaccounted for was usedin proteinsynthesis.
9. Where the carbon dioxide of respirationwas in excess of theequivalent of sugar consumed, protein oramino-acid is the mostprobable substrate. Respiration rateis found to be relatedboth to nitrogen and sugar content.

     

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.

     

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.     

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.     

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.     

GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE L.) III. ABSORPTION AND DISTRIBUTION OF NITROGEN, PHOSPHORUS AND POTASSIUM DURING THE FIRST YEAR OF GROWTH

Absorption of nitrogen, phosphorus and potassium by S48 timothy plants ran parallel to dry-weight increase, at an increasing rate until the autumn, almost completely ceasing in the winter, and increasing again in the spring.
Flowering tillers accumulated nutrients until ear emergence, after which the content per tiller of all nutrients decreased until death of the tillers during the winter.
Non-flowering tillers continued to accumulate nutrients steadily throughout the whole period of the experiment.
These observations are discussed in relation to the perennial habit of the plant.     

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

The structure of effective nodules on Trifolium subterraneumL. grown at a root temperature favourable for nitrogen fixationwas examined by light microscopy. Rhizobium were released intohost cells from vesicles on infection threads which were closelyassociated with the host cell nucleus. Enlargement into bacteroidforms was rapid and synchronous in similarly-aged host cells,but groups of rhizobia close to the nucleus sometimes did notdevelop into bacteroids. Rhizobium changed in shape from smallrods to more elongate and then to irregularly swollen formsbefore finally becoming coccoid. On degeneration clusters ofbacteroids became un evenly stained before coalescing at thecentre of the host cell and finally disintegrating. Small vegetativerods multiplied amongst the degenerating bacteroids and in thegreatly enlarged intercellular spaces; host cell walls becamefolded and distorted and sometimes broke before collapsing ontoeach other.     

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.     

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.     

THE ACCUMULATION OF ELECTROLYTES : III. BEHAVIOR OF SODIUM,POTASSIUM, AND AMMONIUM IN VALONIA

When 0.001 M NH₄Cl is added to sea water containing Valonia macrophysa there seems to be a rapid penetration of undissociated NH₃ (or NH₄OH) which raises the pH value of the sap so that the thermodynamic potential of KOH becomes greater inside than outside and in consequence K leaves the cell: NaOH continues to go in because its thermodynamic potential is greater outside than inside. NH₄Cl accumulates, reaching a much higher concentration inside than outside. This might be explained on the ground that NH₃, after entering, combines with a weak organic acid produced in the cell whose anion is exchanged for the Cl^- of the sea water, or (more probably) the organic acid is exchanged for HCl.     

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.     

STUDIES ON THE ANOMALOUS VISCOSITY AND FLOW-BIREFRINGENCE OF PROTEIN SOLUTIONS : III. CHANGES IN THESE PROPERTIES OF MYOSIN SOLUTIONS IN RELATION TO ADENOSINETRIPHOSPHATE AND MUSCULAR CONTRACTION

1. An investigation of the physicochemical properties of myosin has been carried out. Prepared under standard conditions, the ratio of flow-birefringence to protein concentration is uniform. The effect of electrolytes, pH, and urea on the flow-birefringence and viscosity (relative and anomalous) of myosin has been examined. 2. Decrease or abolition of flow-birefringence does not necessarily imply far reaching denaturation, since such effects can be reversed by a variety of means. 3. When a myosin solution is treated with adenosinetriphosphate, its flow-birefringence is decreased (average 48 per cent), its anomalous viscosity is retained, and its relative viscosity is decreased (average 14 per cent). The full effect of adenosinetriphosphate is obtained at 0.004 M; a molarity very much less than that of other substances which decrease the flow-birefringence of myosin. 4. The changes in the physicochemical properties of myosin brought about by adenosinetriphosphate are spontaneously reversible, and are connected with the enzymatic action of the protein as adenosinetriphosphatase. 5. Effects similar to those of adenosinetriphosphate on the physicochemical properties of purified myosin have been obtained so far only with inosinetriphosphate. 6. Inorganic phosphate is split off by myosin from inosinetriphosphate as well as from adenosinetriphosphate. Inorganic triphosphate is split by 1 to 2 per cent solution of three times precipitated myosin. 7. Adenosinediphosphate and inorganic triphosphate act as competitive inhibitors with adenosinetriphosphate, blocking the fall of flow-birefringence. 8. The implications of the results, and the conception of active enzymic groups attached to proteins participating in cell structure, whether contractile or non-contractile, are discussed in relation to present views on muscle physiology and other biological problems.