Day-Night Periodicity of Exudation in Detopped Tobacco

Wallace, A.; Ashcroft, R. T.; Lunt, O. R.

doi:10.1104/pp.42.2.238

Cited by 15 publications

(10 citation statements)

References 7 publications

(13 reference statements)

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“…An enhancing effect of nitrate over chloride on exudation volumes has been previously reported (3,31). Nitrate also enhanced the exudation volumes relative to other forms of nitrogen (27,28).…”

Section: Discussionsupporting

confidence: 51%

Nitrate Translocation by Detopped Corn Seedlings

Ezeta¹,

Jackson²

1975

Plant Physiol.

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Five-day-old seedlings of corn (Zea mays L.) grown without nitrate were decapitated and exposed to 0.5 mM KNOs or 0.5 mM KCI in aerated solutions at 30 C. Uptake of nitrate, chloride, and potassium was determined by replacing solutions hourly and measuring their depletion. Translocation of these ions and of organic nitrogen was determined by hourly analysis of the vascular exudate. Nitrate reduetion was estimated by the difference between nitrate uptake and nitrate recovered in the tissue and exudate. Nitrate uptake exhibited its usual pattern of apparent induction resulting in the development of an accelerated uptake phase. Chloride uptake remained fairly constant throughout the experimental period. Translocation of nitrate increased progressively for at least 7 hours whereas chloride translocation reached a maximum about the 3d hour and then declined to a lower rate than nitrate translocation. Nitrate uptake and translocation were restricted by anaerobiosis, by 20 and 40 C relative to 30 C, and by 0.05 mM 6-methylpurine, an RNA-synthesis inhibitor. Accumulation, reduction and translocation of nitrate had different sensitivities to all these factors. (17,18). Data are presented to support the concept that continuous nitrate uptake is required to maintain significant translocation of nitrate. In addition, the translocation of organic nitrogen was strongly dependent upon continuous nitrate uptake. MATERIALS AND METHODSThe procedures were, in general, similar to those described by Jackson et al. (17). All experiments were conducted with corn (Zea mays L.) hybrid DeKalb XL45. Four days after germination in darkness with 0.1 mm CaSO, the secondary roots were excised and five seedlings were assembled in a Plexiglas holder especially designed to fit the top of a 75-ml Taylor tube. Seedlings were then placed in a pretreatment solution for 24 to 36 hr in darkness prior to initiating the experiment. The pretreatment solutions contained per liter 0.25 mM (NH)2SO,, 0.6 mmY K2SO4, 0.4 mM KH2PO4, 1.6 mM MgSO4, 0.8 mm CaSO4, and 250 mg CaCO,. Iron was supplied as Fe-EDTA at 1.8 mg per liter; the remaining five micronutrients were present at one-fifth the concentration of Hoagland's solution (13).The standard uptake solution contained 0.5 mM KNO or 0.5 mM KCl plus 0.25 mm CaSO4, pH 6. For the experiments involving temperature, 6-methylpurine, or anaerobiosis variables, the uptake solutions also contained 1 mm Na 2-[Nmorpholino]ethanesulfonate as a buffer and the bactericide chloramphenicol at 20 jtg mP. Except where indicated, solutions were continuously aerated and the temperature was maintained at 30 C. Solutions were changed hourly and nitrate, chloride, and potassium uptake determined from depletion of the solutions. Five plants per 70 ml were employed for each replication. Four of these five-seedling units were used as replicates for each treatment and the data presented are the averages of the four replicates.Immediately after placing the plants in the uptake solutions, the mesocotyls were excised below the firs...

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Section: Discussionsupporting

confidence: 51%

Nitrate Translocation by Detopped Corn Seedlings

Ezeta¹,

Jackson²

1975

Plant Physiol.

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“…The maximum rate of exudation usually occurred around noon and the minimum rate occurred around midnight (4,6,8,9,10) . Such diurnal change in the exudation rate can be reversed by changing the light-dark cycle under which the plants were grown (4,6).…”

Section: Discussionmentioning

confidence: 99%

Diurnal Changes of the Exudation Rate and the Mineral Concentration in Xylem Sap after Decapitation of Grafted and Non-grafted Cucumbers

Masuda

Gomi

1982

Engei Gakkai zasshi

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SummaryThe xylem sap in cucumbers (Cucumis sativus L.) which were or were not grafted onto figleaf gourd (Cucurbita ficifolia Bouche) was collected after decapitation from the cut end of the stems hourly. The exudation rate was highest in the first one hour collection regardless of grafting, and then decreased rapidly with time. However, there was a diurnal change in the exudation rate with the maxima occurring at 1 : 00 to 3 : 00 PM and the minima at 7 : 00 to 8 : 00 AM, irrespective of decapitation time. The grafted cucumbers were smaller in amplitude than the nongrafted ones.The rate of xylem exudation and the concentrations of N03-N, P, Ca and Mg in the first one hour exudate were higher in the grafted cucumbers than in the nongrafted ones.Only the K concentration was higher in the non-grafted cucumbers. The mineral concentration in the exudate changed remarkably with time after decapitation ; the N03-N, K and Ca concentrations decreased and the P concentration increased rapidly for the first several hours.The Mg concentration scarcely changed. Thereafter, the N03-N and K concentrations of the exudate in the grafted cucumbers fell below the N03-N and K concentrations in the nutrient solution, while in the non-grafted cucumbers the former was kept always above the latter. From these results, the grafted cucumbers were considered to be superior to the non-grafted ones, in water uptake and nutrient absorption except for K and also to depend more intensely in N03-N and K absorptions on some metabolities from the upper parts of the plants.

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“…These roots reduce little of the NO3-that is absorbed, and most of it is transported to the stems and leaves (3). As with tobacco (30,31), cucumber roots depleted of NO3-respond to a new supply of this ion with increased rates of exudation and salt transport. These properties make the cucumber root ideal for studying ion transport to the xylem.…”

mentioning

confidence: 99%

Accumulation and Radial Transport of Ions from Potassium Salts by Cucumber Roots

Cooil¹

1974

Plant Physiol.

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Accumulation of K+ is insensitive to the anion supplied with it at a solution concentration below 1 mM. Rates of K+ transport to the xylem from the same solutions are, however, dependent upon the anion present and decrease in the order NO3->> Cl-> SOI2-. Parallel effects on rates of exudation and anion transport result from kind and concentration of anion supplied and time of exposure to the solution. When high K salt concentrations are used, only linear relationships are found between solution concentrations and transport rates. However, ion concentration in the exudate increases more than external solution concentration, while exudation rate is unaffected. It is suggested that some of the ions transported are from compartments within the cells. At high solution concentrations KNO3 results in more exudation and in higher ion concentration in the exudate than is found with KCI.The processes involved in transport of ions from the external medium into the xylem of roots continue to evoke controversy and have been discussed in several recent reviews (1,18,19,27). Liittge and Laties (22) Cucumber roots can be induced to exude from the xylem profusely. These roots reduce little of the NO3-that is absorbed, and most of it is transported to the stems and leaves (3). As with tobacco (30, 31), cucumber roots depleted of NO3-respond to a new supply of this ion with increased rates of exudation and salt transport. These properties make the cucumber root ideal for studying ion transport to the xylem.This report compares patterns of accumulation and radial transport in cucumber roots of K salt ions supplied at concentrations below 1 mm, and transport at concentrations of 0.5 to 10 mM. MATERIALS AND METHODSPlant Culture. Seeds of Cucumnis sativus L. cv. Burpeeana Hybrid were soaked in deionized water with continuous aeration for 24 hr, then planted in moist vermiculite and allowed to germinate in the dark for about 65 hr at 23 to 25 C. The seedlings were next exposed to indirect light for about 24 hr. Single plants were then transferred to 4-liter glass jars of continuously areated nutrient solution consisting of 1 mM Ca (N03)

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Day-Night Periodicity of Exudation in Detopped Tobacco

Cited by 15 publications

References 7 publications

Nitrate Translocation by Detopped Corn Seedlings

Nitrate Translocation by Detopped Corn Seedlings

Diurnal Changes of the Exudation Rate and the Mineral Concentration in Xylem Sap after Decapitation of Grafted and Non-grafted Cucumbers

Accumulation and Radial Transport of Ions from Potassium Salts by Cucumber Roots

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