Kinetics and Energetics of Light-enhanced Potassium Absorption by Corn Leaf Tissue

Abstract. The effect of various periods of pretreatment in CaSO4 solutions (aging) on the absorption of Na and K by bean stem slices was investigated. Freshly sliced tissue absorbed Na over the entire range of concentrations studied (0.02-50 mM). Potassium absorption by fresh tissue was nil at concentrations below 0.5 mM but at higher concentrations was similar to that of Na. When tissue was aged 'by aerating slices for 20 hr in 0.5 mm CaSO4, K absorption was substantia,l over the entire range (0.01-50 mM), with evidence of a dual mechanism of absorption, whereas Na absorption was nil at concentrations below 0.2 mm. The formation of K-absorbing capacity with aging, and the loss of Na-absorbing capacity at low concentrations, were temperature-dependent and did not result from significant changes in rates of efflux of either ion. The absorption of Na by fresh tissue and K by aged tissue was sensitive to antimetabolites, with K uptake the more sensitive. Benzyladenine, an analog of kinetin, suppressed the formation of K-absorbing capability in aged tissue but did not prevent the 4loss of Naabsorbing oapacity. Possible mechanisms for this alteration in ion-specificity of transport mechanisms are discussed.

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confidence: 99%

“…Preparation of tissue for the experiments was as described previously (23,24,29) (29). The tissue was sliced transversely to give slices 400 ji thick.…”

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confidence: 99%

Sodium and Potassium Absorption by Bean Stem Tissue

Rains

1969

“…All treatments, including controls, contained 0.2 mm CaSO4. CaSO4 was supplied since calcium ions help maintain normal membrane function (6,22,27) in both root (6) and leaf (27) tissue.…”

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confidence: 99%

Loss of Ribulose 1,5-Diphosphate Carboxylase and Increase in Proteolytic Activity during Senescence of Detached Primary Barley Leaves

Peterson¹,

Huffaker²

1975

205

118

(5,12,13,14) and Perilla (10) leaves. Fraction I protein as usually isolated can probably be considered to be crude RuDPCase' since it often contains several other enzymatic activities in addition to that of RuDPCase (15,18,36). We recently reported that intact barley seedlings placed in extended darkness lost soluble protein, almost all of which was accounted for by the enzyme RuDPCase (9,25). The results of these investigations are not surprising, since this enzyme is considered to be the major storage protein of many plant leaves (18,26). Since RuDPCase is also principally responsible for net fixation of CO2 in plants, its fate during senescence is important. This study is a further extension to show the effects of some chemicals and light on the loss of RuDPCase and to correlate the concurrent development of proteases and esterases during senescence. Evidence is also presented for the turnover of RuDPCase under these conditions. The process of senescence has been studied in intact plants, detached leaves, and leaf discs in both light and dark (31, 37). In general, senescence is speeded by detaching the leaves and/or imposing darkness. Perhaps the most striking changes in senescence are losses of Chl, nucleic acids, and protein (39), accompanied by a general increase in proteolytic activity as measured in vitro. Cytokinins (32,33,37) or light (7)

“…That the mechanism involves chlorophyll was shown by van Lookeren Campagne (19) and by Kylin (17,18). Studies with inhibitors and anaerobic conditions indicated that light-stimulated transport derived its energy from cyclic photosynthetic phosphorylation (16,19,22,25). Kylin (17), however, concluded that although many data on the effects of inhibitors fit the phosphorylation theory, some effects fit a cytochrome theory better, and both mechanisms may be involved.…”

Section: Discussionmentioning

confidence: 99%

Effect of Potassium Deficiency upon Translocation of ¹⁴C in Detached Blades of Sugarcane

Hartt

1970

The translocation of radioactive photosynthate was studied in blades detached from plants which had been grown in nutrient solution with and without potassium. Basipetal translocation decreased in the blades of plants deprived of potassium, even when deficiency symptoms were not visible. In such slightly potassium-deficient leaves, translocation was decreased in the light but not in the dark. More severe potassium deficiency decreased translocation both in darkness and in light. Potassium deficiency decreased translocation at light intensities giving no difference in rate of photosynthesis between plus and minus potassium leaves and even at light intensities at which there was no net fixation of carbon dioxide. At all levels of deficiency, the relative decrease in translocation was greater than the relative decrease in photosynthesis. Translocation was affected at potassium deficiency levels which had no effect upon photosynthesis.Potassium deficiency decreased translocation relatively more than it decreased moisture content. There was a much better correlation between the decrease in potassium and translocation than between the decrease in moisture and translocation.An experiment with radioactive phosphorus indicated an upset in phosphorylation in the stems of potassium-deficient plants.Experiments reported in the preceding paper (9) led to the conclusion that K may exert a direct effect upon translocation of photosynthate. This conclusion was confirmed and strengthened by studies with detached blades reported herein.K is not the only nutrient required for translocation, since deficiencies in N and P also decrease the transport of sugar in the sugarcane plant (6, 11). MATERIALS AND METHODSThe varieties of sugarcane studied in these experiments were previously described (9).Shoots grown from stem cuttings cultured in volcanic black sand for 2.5 months were transplanted to tap water culture, two plants per 16-liter pot or one per 8-liter pot. After about 1 month in tap water, the plants were supplied with nutrient solutions prepared with distilled or deionized water. The complete solution contained K; the -K solution contained no K (9).All of the methods of application of "CO2, sampling, analysis, and radioactivity counting were the same as with attached blades, the only difference being that the system under investigation was a detached blade rather than an entire plant, a system with several advantages (12).Blades were cut from the plant at about 8 AM, recut twice under water, and taken to the air-conditioned room. The cut end of the blade remained in water during the entire test. After preillumination, measured doses of 14CO2 were supplied to portions of the blades for 5 min in artificial light. The feeding chamber (6, 15) was quickly removed, and the blade was placed under the illumination desired for translocation. The portion of the blade above the fed part is called the apex; that below the fed part, the base.Translocation took place for 6 or 24 hr, after which each blade was cut into measured sect...