The Effect of Addition of Sucrose on the Energy Status and the Trans-Root Electrical Potential Difference of Excised Maize Roots

We present the results of our attempt to determine the metabolicstatus of excised maize roots (Zea mays L. cv. ZP SC704) andits effect on the trans-root electrical potential difference(TRP). Besides the electrical potential difference, we measuredoxygen consumption, sugar content and ¹⁴C-sucrose uptake anddistribution by supplying the cut end of root with sucrose.Our experiments show that sucrose added to the cut end of excisedroots was taken up by them, increasing the sugar content andmetabolic activity of such roots. These sugar-supplemented rootsexhibited approximately 60% higher internal sugar content andrespiratory rates, and 30% higher magnitudes of TRP, comparedto sugar-depleted roots. By optimizing the ionic composition(pH, K⁺, Ca²⁺) and sucrose concentration of the upper solutionfor sucrose uptake and translocation, maintenance of energeticstatus and transport functions of the excised root, closer tothat existing in situ, was ensured. (Received July 4, 1994; Accepted October 17, 1994)     

The effect of abscisic acid on sugar levels in seedlings of Phaseolus vulgaris L. cv. redland pioneer

Abscisic acid (ABA) caused an increase in total-sugar and a 3-fold increase in reducing-sugar content in the roots of intact bean seedlings. The level of reducing sugars was also increased in the stem but total sugar levels remained unaffected by ABA. ABA also increased reducing-sugar content of the root in seedlings with cotyledons removed but in this case the reducing- and total-sugar contents of the leaf were reduced. However, ABA did not affect reducing- and total-sugar levels in excised bean root systems. The observed increase in sugar content of the root of intact bean seedlings appears to be the consequence of an ABA-induced stimulation of sugar transport from the shoot to the root. It is proposed that a relationship may exist between the effect of ABA on sugar transport and its effect on ion transport in excised root systems and in intact seedlings.     

sh-2甜玉米F2籽粒营养品质遗传特点、杂种优势及其亲子回归关系分析

研究了25个sh-2甜玉米自交系及其组配的15个sh-2型F_2籽粒的5个品质性状的遗传特点、杂种优势、亲子回归关系．结果表明,亲本间,除籽粒还原糖含量外,可溶性总糖、蔗糖、淀粉、可溶性蛋白含量是否存在显著差异,对F_2籽粒品质有明显影响．F_2籽粒可溶性总糖、还原糖、淀粉、可溶性蛋白含量近低亲遗传,而蔗糖含量近高亲遗传．杂种F_2籽粒可溶性总糖、淀粉、可溶性蛋白含量普遍介于双亲之间,杂种优势不强;还原糖含量普遍表现为低亲,没有超亲优势;蔗糖含量以超亲为主,有明显杂种优势．亲本对F_2杂交籽粒可溶性总糖、还原糖、蔗糖、淀粉、可溶性蛋白含量均表现为正效应;除还原糖品质外,其他品质性状受父本的影响较大．研究表明,了解sh-2甜玉米亲本营养品质性状,能很好的预测其F_2籽粒营养品质性状,使育种更有目的性．     

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 influence of sugars on nitrate reductase induction by exogenous nitrate or nitrite in excised pisum sativum roots

Nitrate reductase (NR) induction is enhanced by exogenously supplied sucrose in excised pea roots exposed to both exogenous nitrate and exogenous nitrite. NR synthesis is preferentially supported by sugars transported to the cells at the moment, however NR induction can take place for some time without exogenous sugar influx if roots are saturated with sugars during precultivation. Steady high NR levels are dependent on steady sugar and nitrate influxes. NR induction is low in roots precultivated for 20 h without sucrose although sugar content is still high in them. This suggests that compartmentation of sugars in the cells is of major importance during NR induction. Total nitrate content in roots exposed to nitrate is not influenced by sucrose supplied together with nitrate. Some nitrite is oxidized to nitrate in roots exposed to exogenous nitrite ; we assume that this nitrate is responsible for NR induction. Our results indicate that sugars, besides many indirect effects on NR induction, may also directly influence NR synthesis either as coinducers or as derepressors of NR synthesis. Our results further show that NR is not a product-inducible enzyme.     

Influence of Potassium and Nitrogen Fertilization on Parasitism by the Root-knot Nematode Meloidogyne javanica

The influence of various c oncentrations of K⁺, nitrogen sources, and inoculation with root-knot nematode Meloidogyne javanica were evaluated in tomato plants. Increased potassium concentration increased top and root fresh weights of intact plants and fresh weights of excised roots. Nitrate-fertilized plants weighed more than plants receiving ammonium independent of the K level in the medium. Nematode counts on roots were not affected by nutritional differences in intact or excised roots. In intact roots a high percentage of males was recorded at low K⁺ levels, whereas in excised roots the proportion of males in the population rose as the K⁺ levels increased. Inoculated intact roots accumulated K⁺ when the level of potassium supply was low; infected excised roots contained less K⁺ than did nematode-free roots.     

Physiological,biochemical and molecular analysis of sugar-starvation responses in tomato roots

Two-month-old tomato plants were submitted to day/night cycles and to prolonged darkness in order to investigate the physiological and biochemical response to sugar starvation in sink organs. Roots appeared particularly sensitive to the cessation of photosynthesis, as revealed by the reduction of the growth rate and the decline of the carbohydrate and protein content. Therefore, excised tomato roots were used as a model to deepen the characterization of sugar starvation symptoms. In excised roots, the endogenous sugars were rapidly exhausted and significant degradation of protein was observed. Glutamine and asparagine accounted for most of the nitrogen released by protein breakdown. Respiration declined and proliferation- and growth-associated genes were repressed soon after the beginning of the sugar depletion. Among the genes studied, only the gene encoding asparagine synthetase was strongly induced. All the starvation symptoms were reversible when the roots were resupplied with sugar. When the culture conditions deteriorated, the metabolic and molecular changes led to the triggering of apoptosis of the root cells.     

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.

     

Differences in salt tolerance of three sugar beet genotypes

The effect of increasing NaCl concentrations (up to 150 m M ) on growth and mineral composition of three genotypes of sugar beet ( Beta vulgaris L., MONOHILL, ADA and FIA) has been studied. Growth was stimulated or little affected in water culture by 50 m M NaCl in all 3 genotypes. Further increase in NaCl concentration depressed growth in ADA more than in MONOHILL, whereas in FIA growth did not significantly differ from the untreated control. In all 3 genotypes, particularly in FIA, increasing NaCl concentrations decreased potassium content in the shoots more than in the fibrous and storage roots. Simultaneously, the accumulation of sodium and chloride in the shoots was considerably higher in FIA than in ADA, where in contrast larger proportions of these ions were retained in the roots. The results demonstrate considerable genotypic differences in salt tolerance of sugar beet and indicate a positive correlation between salt tolerance and accumulation of sodium and chloride in the shoots. FIA but not ADA may be suited for a breeding programme of sugar beet for improved salt tolerance.     

Efficacy of Bacillus subtilis,Moringa oleifera seeds extract and potassium bicarbonate on Cercospora leaf spot on sugar beet

Cercospora leaf spot caused by Cercospora beticola are among the most dangerous plant diseases on sugar beet plants. It causes heavy economic losses, whether on the yield of roots, the percentage of sugar in them, or the quality of sugar produced. In addition to the economic cost caused by chemical control, these chemical pesticides cause an imbalance in the ecosystem and harm the health of humans and animals. In an attempt to search for a safer method than pesticides and environmentally friendly, an evaluation of using biocontrol agents, Bacillus subtilis as cell suspension (10⁸ cell/ml), was conducted in this study. Seeds extract of Moringa oleifera with two concentrations (25 and 50 g/L) and potassium bicarbonate at (5 and10 g/L (compared to fungicide Montoro 30% EC (Propiconazole 15% + Difenoconazole 15%). The evaluation results for twenty-five sugar beet varieties showed a significant discrepancy between these varieties in the extent of their susceptibility to infection with the disease under investigation. In-Vitro, B. subtilis induced an antagonist to C. beticola, and both M. oleifera seeds extract and potassium bicarbonate significantly reduced the linear growth of this pathogen. Under field conditions, the treatments used have given positive results in controlling Cercospora leaf spots. They significantly decreased the severity of disease and prevented C. beticola from creating conidiophores and conidiospores, along with examining their cell walls with the formation of plasmolysis of the fungus cells and reducing both the number and diameter of the spots on the surface leaves; this was demonstrated using a scanning electron microscope (SEM). It is worth noting that the best results obtained were most often when treated with M. oleifera seeds extract, followed by potassium bicarbonate, then cell suspension of B. subtilis. In addition, the percentage of the content of beet roots from total soluble solids and sucrose has improved significantly due to spraying sugar beet plants with the substances mentioned earlier. These treatments also contributed to a significant improvement in the enzymes polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase.     

The influence of plasma membrane ion permeability modulators on superoxide formation and bioelectrical characteristics of wheat root cells

Changes in superoxide radical formation and bioelectrical characteristics of excised wheat root cells under modification of plasma membrane ion permeability were studied. It was shown that a 2 h treatment of excised roots with valinomycin (Val, 20 microM), N, N'-dicyclohexylcarbodimide (DCCD, 100 microM), gramicidin S (Gr, 20 microM), chlorpromazine (CPZ, 100 microM) caused an increased loss of potassium by cells, lowering of membrane potential (MP) and electrical input resistance (Rin) of the cells. The superoxide formation by excised root cells diminished (under DCCD) or remained at the control level (under Val), which was accompanied by a minor decrease of MP and Rin of the cells, a small increase in potassium loss by excised roots, and in no change of pH of incubation medium. Significant depolarization of plasma membrane, dropping of Rin and essential loss of potassium ions by the cells correlated with a rise in the medium alkalinization and superoxide formation by excised roots (in the presence of Gr, CPZ). Ion channel blocker gadolinium (Gd3+, 200 microM) caused an increase of MP and Rin reduction of potassium loss by cells, and a decrease of pH of the incubation medium, and also enhancement of superoxide formation by excised root cells. It is suggested that upon plasma membrane ion permeability modification the activity of superoxide generating systems depends on the specificity and mechanisms of action of modulators, and is determined by their influence on redox state of plasma membrane as well as by peculiarities of ion transport disturbance.     

A comparison of potassium translocation in excised roots and intact maize seedlings

Summary The water and potassium fluxes exuded by excised primary roots of maize seedlings are compared with the rate of wet weight increase and of potassium uptake by the growing tissue of the shoots of intact seedlings. The exuded potassium flux from 1 mM KCl solution as the bathing medium is found to correspond very closely to the potassium uptake by the shoots of seedlings of idenfical age and history as the excised roots.     

断根结合生长素和钾肥施用对烤烟生长及糖碱比、有机钾指数的影响

河南济源烟区存在着烟叶糖碱比高、有机钾指数较低的生产现状,通过田间试验研究了打顶时断根(C)、打顶时断根结合喷施IAA(C+I)、打顶时断根结合追施钾肥(C+K)、打顶时断根结合喷施IAA并追施钾肥(C+K+I)和对照(CK)5种处理对烤烟生物量及糖碱比、有机钾指数的影响。结果表明:不同调控措施在烟株成熟期较对照均能增加根部、叶片的干重,减少烟碱、总糖在中上部烟叶的累积。断根结合喷施IAA能降低各部位烟叶的糖碱比,且以C+K+I处理的降幅最大,在下、中、上叶位中较对照分别降低了19.12%、15.33%和8.15%。与对照相比,各处理均能提高不同部位烟叶K⁺含量,降低Cl^-和SO₄^2-含量。C+K+I处理能极显著提高各部位烟叶的有机钾指数,且在中上部烟叶中增幅最大,较对照分别提高了125.00%和209.43%。总的看来,打顶时断根结合喷施IAA并追施钾肥能促进烟叶中的干物质积累、降低糖碱比、提高有机钾指数,进而提高烟叶的内在品质。     

Calcium inhibition of potassium absorption in corn roots

Calcium (or magnesium) sulfate or chloride was found to inhibit energy dependent potassium transport in excised corn roots. This Ca²⁺ inhibition of K⁺ transport was most pronounced during the initial phases of transport. As the absorption periods were lengthened the effect of Ca²⁺ gradually changed from an inhibition to a typical promotion (after about 30-45 mins) of K⁺ transport. Kinetic analysis indicated the inhibition to be of a non-competitive nature.

Identical experiments with excised barley roots showed that CaSO₄ had no effect on K⁺ absorption whereas CaCl₂ had a typical stimulatory effect on K⁺ absorption. Kinetic analysis indicated that both corn and barley have efficient K⁺ transporting systems but barley roots are approximately 5 times more active (on a fr wt basis) than corn roots.

These results illustrate the hazards involved in applying results obtained with 1 (or even several) plant species to all species.

     

Transmembrane electropotential in barley roots as related to cell type, cell location, and cutting and aging effects

Transmembrane electropotential difference (PD) was measured in whole roots of barley (Hordeum vulgare L. cvs. Compana and Himalaya). Seedlings were grown 4 to 5 days in aerated 0.5 mm CaSO(4) or a nutrient solution. Measurements of PD were made with roots bathed in CaSO(4), KCl + CaSO(4), or the nutrient solution. The following results were found. (a) There was a radial PD gradient with epidermal cells being 10 to 58 millivolts less negative than cells in the third layer of the cortex (outside to inside). There was no longitudinal PD gradient in the region 0.5 to 4 cm from the root tip, nor was there any difference between the PD of young root hairs and other epidermal cells. (b) Cell PD in excised whole roots was not detectably different from that found in roots attached to the shoot, and was unchanged for 2 hours from excision. (c) In 1-centimeter sections of root, cell PD at the freshly cut surface was depolarized by 90 millivolts from that in the intact root; cells farther than 1 millimeter from the cut surface were not depolarized. The PD of cells at the cut surface became more negative upon aging the segment in 0.5 mm CaSO(4), eventually becoming greater by -25 millivolts than that in cells of intact roots. Cells in segments to which the root tips were attached had less negative PDs after aging than those in subapical segments, indicating a possible hormonal effect. PDs in aged, excised segments are not equivalent to those in intact roots. (d) Creeping of cytoplasm over electrode tips inserted into the vacuole gave measurements of vacuole-to-cytoplasm PD of + 9 millivolts in 0.5 mm CaSO(4) and + 35 millivolts in 1 mm KCl + 0.5 mm CaSO(4). Most of the cell PD was across the plasmalemma. (e) The reducing sugar content of roots in CaSO(4) solution was greater than that of roots in the nutrient solution in which ion uptake, particularly K(+) occurred.     

果蔗叶片生理生化指标与品质性状的典范相关分析

选用果蔗（Saccharum officinarum L．）14个品种,用典范相关分析法研究不同生育期叶片生理生化指标对果蔗品质性状的影响。结果表明：分蘖期类胡萝卜素含量与蔗茎蔗糖含量,可溶性总糖含量与蔗茎含水率,可溶性总糖含量与蔗汁还原糖含量均呈正相关;伸长初期叶绿素含量、CAT活性与蔗茎蔗糖含量,可溶性蛋白质含量与蔗茎纤维含量均呈正相关;伸长盛期Mg^2＋ -ATP酶活性与蔗茎纤维含量,可溶性总糖含量与蔗茎蔗糖含量呈正相关,C／N与蔗茎含水率呈负相关;成熟期类胡萝卜素含量与蔗茎蔗糖含量呈正相关,可溶性总糖含量与蔗汁还原糖含量呈负相关。     

THE EFFECT OF BENZIMIDAZOLE ON CATION UPTAKE BY PLANT ROOTS

Klingensmith , M. J. (Colgate U., Hamilton, N.Y.) The effect of benzimidazole on cation uptake by plant roots. Amer. Jour. Bot. 48(8): 711–716. Illus. 1961.—A number of benzazole compounds were examined for their effect on cation uptake. Benzimidazole was found to almost double the uptake of potassium by excised barley roots in a 6-hr period. Chlorobenzimidazole also enhanced the absorption of potassium but not to the same extent. This stimulation of potassium accumulation was found to be insensitive to cyanide but was dependent on the temperature of the ambient solution. There was also an increased accumulation of potassium by roots of intact barley plants with benzimidazole treatment without interference with subsequent transport of the potassium. Benzimidazole also stimulated uptake of sodium and calcium by excised barley roots but not at identical levels. Results are discussed in the light of various theories of ion absorption.     

Secondary effects of potassium and nitrogen nutrition of rice: Change in microbial activity and iron reduction in the rhizosphere

Summary In solution culture experiments with rice the effects of different potassium applications and of various nitrogen sources on some criteria of microbial activity were studied. The following results have been obtained:The number of bacteria in the rhizosphere depends on the form of nitrogen available to the plants and the potassium nutritional state. With ammonium as a nitrogen source a greater number of bacteria is found in the rhizosphere than with nitrate. The interruption of potassium nutrition results in an increase in the total number of bacteria.In accordance with the different bacterial colonisation, the oxygen content in the nutrient solution with nitrate remains higher than with ammonium nutrition. With an increase in bacterial number after K interruption, a corresponding depression of the oxygen content in the nutrient solution can be noted. This is due to the higher respiration rate of the roots and the bacteria adhering to them in K-deficient plants.K deficiency consequently results in an increased concentration of reduced divalent iron in the nutrient solution.From the above results it follows that optimum potassium nutrition makes an essential contribution towards counteracting highly reducing conditions in paddy soils.     

Circadian rhythm of root pressure in popular and its driving factors

Aims Our main purposes were to investigate root pressure and its circadian rhythm of excised roots in ‘84K’ popular (Populus alba × P. glandulosa) cultured in soil and solution, to explore the influencing factors and their relationships with root pressure systematically and to understand the generation and rhythm regulation of root pressure. Methods We investigated the root pressure of excised roots in ‘84K’ popular using the method of digital pressure transducer. The diurnal rhythm of excised roots was conducted through different experimental treatments including sampling in different time, defoliation and girdling, together with ambient condition like soil temperature, differential or consistant temperature during day and night. Then we discussed the effects of root respiration and hydraulic conductivity on root pressure by further using chemical inhibitor. Furthermore, diurnal variation of osmotic potential and ions content as well as soluble sugar content of exudation was determined in order to explore their relationships with root pressure rhythm. Important findings Root pressure of excised roots in popular had diurnal rhythm which was higher during daytime and lower overnight. It reached its peak value in the morning to noon and valley value at 20:00. Root pressure of excised roots sampled at different time and cultured in different medium had influence on the rhythm of root pressure to some degrees, but did not the general rhythm of high in daytime and low overnight. Defoliation, girdling and the inhibitors for root respiration or cytomembrane hydraulic conductivity could affect the maximum value of root pressure while have no significant influence on the daily rhythm. Defoliation, girdling and respiration inhibitor reduced the maximum value of root pressure, whereas the hydraulic conductivity inhibitor had little influence on root pressure. The maximum value of root pressure declined with the decrease in soil temperature which could change the rhythm of root pressure. The synchronous change in the maximum value of root pressure and root respiration rate with temperature indicated that root respiration contributed to the change of root pressure along with temperature. Osmotic potential of root exudation was higher during the daytime and lower at night. Diurnal variations of ions and soluble sugar content of exudation were consistant with that of osmotic potential. The peak of root pressure measured under the condition of differential temperature during day and night was significant higher than that measured under constant temperature. In conclusion, root pressure of the poplar ‘84K’ showed significant diurnal rhythm, i.e. higher during the daytime and lower at night. The maximum value of root pressure was mainly regulated by root respiration metabolism. The factors such as respiration inhibitor, respiration substrate and temperature influence the value of the maximum root pressure of poplar ‘84K’. Root hydraulic conductivity had no significant influence on root pressure.