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1.
Low-K+ , high-Na+ cells of strain RL21a of Neurospora crassa , in steady state with 25 m M Na+ , were used to study K+ /Na+ exchanges in the presence or absence of Ca2+ and Mg2+ . In the presence of Ca2+ and Mg2+ , a low concentration of K+ (0.3 m M ) triggered a rapid exchange, but in the absence of the divalents, a high K+ concentration (30 m M ) was required to initiate the exchange at a rapid rate. In the absence of Ca2+ and Mg2+ , K+ uptake did not occur at low K+ concentration, internal K+ did not regulate Na+ influx in the presence of external K+ , and the efflux of Na+ proceeded at maximum activity at very low-K+ contents. 相似文献
2.
Influence of aluminium on phosphorus and calcium localization in roots of beech (Fagus sylvatica) 总被引:2,自引:0,他引:2
Beech plants ( Fagus sylvatica L. provenance Maramures) were grown in nutrient solution at low pH (4.2) and exposed to different concentrations of AlCl3 . Uptake and leakage of Ca2+ (45 Ca2+ ) and H2 PO4 -(32 P) were studied. A high external aluminium concentration (1.0m M ) reduced the uptake and export to the shoot of both calcium and phosphate, while 0.1 m M Al increased the phosphorus level in the roots. To determine the impact of aluminium on the localization of calcium and phosphate, leakage of the elements from both intact plants and plants frozen prior to the leakage experiment was studied. The leakage of Ca2+ from intact plants was not affected by prior exposure to 0.1 m M Al. Freezing of the beech plants before the leakage experiment increased leakage of calcium slightly more from roots of control plants than for roots exposed to 0.1 m M Al, indicating that even low concentrations of alminium may impede the influx of calcium across the plasma membrane in the roots. The patterns of Ca2+ leakage from roots previously exposed to 1.0 m M Al indicated that very little Ca2+ was located extracellularly. The extracellular fraction of phosphate increased with increasing Al concentration in the nutrient solution. Low Al concentration (0.1 m M ) only reduced the intracellular phosphate concentration to a minor extent, while 1.0 m M Al profoundly decreased it. It is concluded that 0.1 m M AlCl3 has a limited effect upon the localization of Ca2+ and phosphate in the roots. At higher levels of Al, 0.1–1.0 m M , there is a more dramatic change in nutrient localization in the free space and uptake over the plasma membrane. 相似文献
3.
Six cultivars of barley ( Hordeum vulgare L., cvs Salve, Nürnberg II, Bomi, Risø 1508, Mona and Sv 73 608) were exposed for three weeks to combinations of high and low mineral supply and differential root/shoot temperature. For all the parameters tested [fresh and dry weights, contents and levels of N, K+ , Ca2+ and Mg2+ , and influx of Rb+ (86 Rb)] the cultivar differences were influenced by the mineral supply, the root temperature and the age of the plants.
The cultivar differences in N nutrition of three-week-old plants could partly be attributed to variation in root size, uptake of N and in use-efficiency of the element. The cultivar variation in root-shoot partitioning of N was small, except when low mineral supply was combined with a low root temperature. Similarly, cultivar differences in contents of K+ , Ca2+ and Mg2+ were influenced by variation in uptake, use-efficiency and root/shoot partitioning of the elements. Low root temperature increased cultivar variation in K+ , Ca2+ and Mg2+ partitioning.
The modern cultivar Salve was compared with Nürnberg II, which is derived from a German land race. Nürnberg II performed better than Salve when low root temperature and restricted mineral supply were combined. Otherwise Salve grew better, partly due to a more efficient use of N.
Two high-lysine lines, Risø 1508 and Sv 73 608, were compared with their mother lines Bomi and Mona. The differences obtained revealed no general effect of the high-lysine genes on growth and mineral nutrition of up to three-week-old barley plants. 相似文献
The cultivar differences in N nutrition of three-week-old plants could partly be attributed to variation in root size, uptake of N and in use-efficiency of the element. The cultivar variation in root-shoot partitioning of N was small, except when low mineral supply was combined with a low root temperature. Similarly, cultivar differences in contents of K
The modern cultivar Salve was compared with Nürnberg II, which is derived from a German land race. Nürnberg II performed better than Salve when low root temperature and restricted mineral supply were combined. Otherwise Salve grew better, partly due to a more efficient use of N.
Two high-lysine lines, Risø 1508 and Sv 73 608, were compared with their mother lines Bomi and Mona. The differences obtained revealed no general effect of the high-lysine genes on growth and mineral nutrition of up to three-week-old barley plants. 相似文献
4.
Martin G. Klotz Alajos Bérczi László Erdei Bernd Liebermann 《Physiologia plantarum》1989,75(3):405-410
Purified plasmalemma vesicles were isolated in the presence of 250 m M sucrose from roots of 14-day-old seedlings of winter wheat ( Triticum aestivum L. Martonvásári-8) by phase partitioning of salt-washed microsomal fractions in a Dextran-polyethylene glycol two-phase system, and both Mg2+ - and Ca2+ -ATPase activities were detected. Orthovanadate-sensitive Mg2+ -ATPase activity associated with the inside of right side-out plasmalemma (PM) vesicles (latency 98%) was inhibited 76% by 0.3 m M Ca2+ , Ca2+ -dependent ATPase activity located partly on the inside and partly on the outside of plasmalemma vesicles (latency 47%) was not affected by Mg2+ .
Mg2+ -ATPase activity was inhibited by 68% and inhibition of Mg2+ activation by 0.3 m M Ca2+ partly disappeared in the presence of 10 p M tentoxin, a fungal phytotoxin. Mg2+ -ATPase activity remained inhibited up to 10 n M tentoxin while at 1 μ M tentoxin Mg2+ activation was as high as without tentoxin. K+ -stimulation and vanadate inhibition was increased and decreased, respectively, by 100 p M -10 n M tentoxin. Ca2+ -dependent ATPase activity was continuously increased by 1 p M -10 n M tentoxin, but at 1 μ M tentoxin the stimulation disappeared. The effects of p M tentoxin on plasma-lemma Mg2+ -ATPase are discussed in relation to its influence on K+ transport in wheat seedlings. 相似文献
Mg
5.
The effects of abscisic acid (ABA) on growth, uptake and translocation of potassium ions, K+ ,Mg2+ -ATPase activity and transpiration were investigated in young wheat ( Triticum aestivum L. cv. Martonvásári-8) plants grown at different K+ supplies. Long-term treatment with ABA (10 μ M ) reduced growth in high-K+ plants, but had less effect under low-K+ conditions. K+ (86 Rb) uptake was inhibited by about 70 and 40% in low- and high-K+ plants, respectively. The stimulation by K+ of the Mg2+ -ATPase activity in the root microsomal fraction was lost with ABA treatment. It is suggested that the inhibitory effect of ABA on K+ uptake may be related to this effects on the K+ ,Mg2+ -ATPase. Translocation of K+ to the shoot was inhibited in low-K+ plants only, and it was not affected in high-K+ plants. In parallel to this, ABA treatment reduced transpiration by about 50% in low-K+ plants, whereas a much smaller effect was seen in high-K+ plants. These observations suggest that the regulation by ABA of the stomatal movements is strongly counteracted by high-K+ status. 相似文献
6.
Pb and Cd uptake in rice roots 总被引:9,自引:0,他引:9
Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb2+ and Cd2+ are affected by the presence of K+ , Ca2+ or Mg2+ . K+ had a little effect on uptake or toxicity of Pb2+ and Cd2+ . Ca2+ or Mg2+ blocked both Cd2+ transport into rice roots and Cd2+ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca2+ blocked both Pb2+ transport into the root and Pb2+ toxicity on root growth. The protective effect of Ca2+ on Pb2+ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb2+ toxicity. Mg2+ did not ameliorate the Pb2+ toxicity on root growth as much as Ca2+ did, although it decreased Pb2+ uptake into roots similarly as Ca2+ did. These results suggest that the protective effect of Ca2+ on Pb2+ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb2+ and Cd2+ may compete with divalent cations for transport into roots of rice plants. 相似文献
7.
Manuel Diaz de la Guardia José M. Fournier Manuel Benlloch 《Physiologia plantarum》1985,63(2):176-180
Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K+ levels (0.25 and 2.5 m M ) were used to study the effect of K+ content in the root on uptake and transport of K+ to the exuding stream of decapitated plants. Roots of plants grown in low K+ gave higher exudation flux, higher K+ concentration in exudate and higher K+ flux than high K+ roots. After 6 h of uptake the K+ flux in low K+ roots was about three times that in high K+ roots. When the roots were kept in a nutrient solution in which Rb+ replaced K+ , low K+ roots exuded much more Rb+ than K+ after the first 2 h, whereas high K+ roots exuded about similar amounts of K+ and Rb+ . In intact plants grown at three different K+ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K+ level in the nutrient solution and the Rb+ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes. 相似文献
8.
Two cultivars of wheat (Triticum aestivum L. cvs Kadett and WW 20299) were grown for 9 days with 20% relative increase in nutrient supply per day at pH 4.1. Aluminium at 50 μ M retarded the growth of roots more than that of shoots in both cultivars, thus decreasing the root/shoot ratio. The inhibition was largest in WW 20299. With long term Al treatment (9 days), Km for K+ (86 Rb) influx increased five times in both cultivars and Vmax decreased in WW 20299. Efflux of K+ (86 Rb) was little affected. When the roots were treated with aluminium for two days, only relative growth rate of roots was retarded, while growth of shoots was unaffected and influx of K+ (86 Rb) adjusted to the actual K+ demand of the plants. It is concluded that the effects of aluminium on K+ uptake in these wheat cultivars are not primary factors contributing to aluminium sensitivity. However, in soil with Al the demand for a comparatively high concentration of K+ to maintain an adequate K+ uptake rate, in combination with a slow growth rate of the roots, may secondarily lead to K+ deficiency in the plants. 相似文献
9.
KIYOTA GOSHIMA HACHIRO YAMANAKA GORO EGUCHI SHIGEO YOSHINO 《Development, growth & differentiation》1978,20(2):191-204
Increase in the extracellular Ca2+ concentration from low (≤ 10−7 M) to normal (10−3 M) caused morphological changes of cultured myocardial cells obtained from fetal mouse heart. The extracellular Na+ and K+ concentrations of the normal medium (10−3 M Ca2+ ) did not significantly affect the genesis of these morphological changes. Like Ca2+ , Ba2+ and Sr2+ , but not Mg2+ , Co2+ or Ni2+ , could induce morphological changes. Increase in the extracellular Ca2+ concentration from 10−8 M to 10−3 M also caused excess uptake of 45 Ca2+ by cultured myocardial cells. B–16CW 1 cells, which did not show these morphological changes, did not take up excess 45 Ca2+ on this treatment. Treatments, such as addition of verapamil or incubation at pH 6.3, which reduced the genesis of morphological changes, reduced the rate of 45 Ca2+ uptake by myocardial cells. These facts show that the morphological changes of myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal are due to excess uptake of Ca2+ by the myocardial cells.
The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal were reversed on further incubation of the cells in medium with or without Ca2+ . 相似文献
The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca
10.
Salt tolerance of the reed plant Phragmites communis 总被引:6,自引:0,他引:6
Reed plants ( Phragmites communis Trinius) were grown at NaCl concentrations up to 500 m M and their growth, mineral contents and leaf blade osmotic potential were determined. Addition of NaCl up to 300 m M did not affect growth significantly. Sucrose, Cl- and Na+ concentrations in the shoots increased with the salinity of the medium and the shoot water content decreased. K+ always contributed most to the leaf osmotic potential. Even in the presence of 250 m M NaCl in the rooting medium, the leaf blade contained only 50 mM Na+ , suggesting that the plants have an efficient mechanism for Na+ exclusion. 22 Na+ uptake experiments suggested that the retranslo-cation of absorbed Na+ from shoots to the rooting medium lowered the uptake of Na+ . 相似文献
11.
The K+ (86 Rb) uptake into the roots and the translocation to the shoots of 11-day-old intact wheat seedlings ( Triticum aestivum L. cv. Martonvásári 8) were investigated using plants grown with different K+ supplies. The effects of environmental conditions (darkness, humidity) and of metabolic and transport inhibitors (oligomycin, disalicylidene-propanediamine, 2,4-dinitriphenol, diethylstilbestrol, colchicine) were also studied. Plants with K content of about 0.2 mmol/g dry weight in the root and 0.5 mmol/g dry weight in the shoot (low K status) showed high K+ uptake into the roots and high translocation rates to the shoots. Both transport processes were very low in plants with K content of more than 1.5 and 2.2 mmol/g dry weight in the root and shoot, respectively (high K status).
Darkness and a relative humidity of the air of 100% did not influence K+ uptake by roots, but did inhibit upward translocation and water transport. Inhibition of photosynthesis and treatments with diethylstilbestrol (10−5 mol/dm3 ), as well as with colchicine resulted in inhibition of translocation in plants of low K status, but these inhibitors had little effect on K+ uptake by the roots. Oligomycin, 2,4-dinitrophenol and diethylstilbestrol (10−4 mol/dm3 ), however, inhibited K+ uptake by the roots. In general, K+ transport processes were almost unchanged in plants of high K status. It is concluded that only plants of low K status operating with active K+ transport mechanisms are responsive to environmental factors. In high K+ plants the transport processes are passive and are uncoupled from the metabolic energy flow. 相似文献
Darkness and a relative humidity of the air of 100% did not influence K
12.
Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd2+ was excreted by plants exposed for 1–10 days to 9 or 45 μ M Cd2+ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na+ and Cl− was positively correlated with NaCl concentration (1.5, 10, 50 m M ) of the medium. The Na+ /Cl− ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca2+ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K+ and Mg2+ was only little affected by NaCl. Excretion of Li+ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li+ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla . 相似文献
13.
Influence of aluminium on phosphate and calcium uptake in beech (Fagus sylvatica) grown in nutrient solution and soil solution 总被引:3,自引:0,他引:3
The effects of AICI3 on uptake of Ca2+ and phosphate in roots of intact beech ( Fagus sylvatica L. provenance Maramures) plants were studied in nutrient solution and soil solution. Aluminium reduced the concentrations of Ca, Mg and P in plants and increased that of K. In short term experiments, uptake of Ca2+ (45 Ca) was reduced by exposure of the roots to Al. The effect of aluminium on Ca2+ (45 Ca) uptake was immediate and primarily of a competitive nature, preventing Ca2+ from being adsorbed. Uptake of 32 P-phosphate increased with increasing Al concentration up to 0.1 m M and then decreased at higher Al concentrations. The effect of Al on 32 P-phosphate uptake was most pronounced during the first hours of exposure. Growth of plants for 15 days in soil solution, collected from the upper A horizon of a beech forest soil, had no effect on uptake of Ca2+ (45 Ca) and 32 P-phosphate, probably because of a low concentration of labile bound monomeric Al and binding of Al to organic compounds. Soil solution from the deeper B horizon reduced Ca2+ (45 Ca) uptake and increased 32 P-phosphate uptake in a manner similar to that with Altreatment in nutrient solution. It is concluded that in soil solution from the deeper regions of the soil, mineral uptake by roots was affected by Al. 相似文献
14.
Plants of Sinapis alba L. were induced to flower by either a single long day or a single displaced short day. The levels of three cations. Ca2+ , Mg2+ and K+ , were measured by atomic absorption spectrophotometry in exudates from roots, leaves and apical stem tips. The export of all three cations out of the root system (root exudate) was increased in induced as compared to non-induced plants. No changes were observed in cation export out of the mature leaves (leaf exudate). The supply of cations to the apical bud (apical exudate) did not originate from the phloem and, so, should mainly be of apoplastic origin. Only the supply of Ca2+ to the apical bud was increased, not the supply of Mg2+ or K+ . The increase in Ca2+ supply was transient and occurred at about the same time as a conspicuous stimulation of cell division, previously detected in the apical bud. 相似文献
15.
The K+ (86 Rb+ ) uptake and the growth of intact wheat seedlings ( Triticum aestivum L. cv. GK Szeged) grown in 0.5 m M CaCl2 solution and of seedlings grown on wet filter paper in Petri dishes were compared under different experimental conditions. Aeroponic (AP) and hydroponic (HP) conditions brought about striking differences in the growth of the roots, whereas the shoot growth was not influenced. The dry weight of the roots was higher for the AP plants than for the HP plants. The AP grown seedlings exhibit a low rate of K+ uptake, which seems to be a passive process. The effect of 2, 4–dinitrophenol (2, 4–DNP) clearly shows the absence of an active component of the K+ uptake in roots grown in air with a high relative humidity. In plants grown under AP conditions the effect of Ca2+ on the K+ uptake is unfavourable, i.e. there is an inhibition (negative Viets effect). Results relating to the effect of 2,4–DNP suggest that the "negative Viets effect" is a feature of the passive K+ uptake. The data suggest that the AP growth conditions play a very important role in the induction and/or development of the ion transport system(s), which becomes impaired under the AP conditions. 相似文献
16.
Removal of the shoot above the primary node (detopping) of 3-week-old bean plants ( Phaseolus vulgaris L. cv. Contender) altered the metabolism and development of the remaining leaves. An increase in levels of chlorophyll, protein, stomatal opening, photosynthesis and growth, i.e. rejuvenation of primary leaves, was established within 7 days of detopping. These levels were maintained while the primary leaves of equivalent intact plants senesced.
The flux of xylem solution (mineral ions, cytokinins and water) into leaves is related to the leaf area to be supplied and root supply capacity; it has been suggested that detopping leads to an increased availability of root-supplied solutes and hence rejuvenation of the remaining leaves. This assumes however that root output of solutes is not decreased by the defoliation treatment.
We found that root output of ions (electrical conductivity of passive xylem exudate) in detopped plants was 30% lower than in intact plants after 24 h and 60% lower after 7 days. The output of Ca2+ , Mg2+ and K+ were similarly reduced 7 and 14 days after detopping as were fresh and dry weights of roots. Furthermore, neither the calculated xylem flux of ions nor directly measured levels of Ca2+ , Mg2+ and K+ were significantly increased in leaves of detopped plants during their rejuvenation. We therefore conclude that root output is tightly coupled to shoot demand and that the apparent rejuvenation of primary leaves caused by detopping bean plants is not a consequence of increased xylem flux of mineral ions into the leaves. 相似文献
The flux of xylem solution (mineral ions, cytokinins and water) into leaves is related to the leaf area to be supplied and root supply capacity; it has been suggested that detopping leads to an increased availability of root-supplied solutes and hence rejuvenation of the remaining leaves. This assumes however that root output of solutes is not decreased by the defoliation treatment.
We found that root output of ions (electrical conductivity of passive xylem exudate) in detopped plants was 30% lower than in intact plants after 24 h and 60% lower after 7 days. The output of Ca
17.
Plasmalemma was isolated from the roots of 2-week-old cucumber plants ( Cucumis sativus L. cv. Rhensk druv) by utilizing an aqueous polymer two-phase system with 6.5%:6.5% (w/w) Dextran T500 and polyethylene glycol (PEG) 3350 at pH 7.8. The plasmalemma fraction comprised ca 6% of the membrane proteins contained in the microsomal fraction. The specific activity of the plasma membrane marker enzyme (K+ , Mg2+ -ATPase) was 14- to 17-times higher in the upper (PEG-rich) than in the lower (Dextran-rich) phase, and the reverse was true for marker enzymes (cytochrome c oxidase, EC 1.9.3.1, and antimycin A-resistant NADPH cytochrome c reductase) of intracellular membranes. The ATPase was highly stimulated by the addition of detergent (Triton X-100), so that the isolated plasmalemma vesicles appear tightly sealed and in a right-side-out orientation. Further characterization of the ATPase activities showed a pH optimum at 6.0 in the presence of Mg2+ . This optimum was shifted to pH 5.8 after addition of K+ . K+ stimulated the ATPase activity below pH 6 and inhibited above pH 6. The ATPase activity was specific for ATP and sensitive to N,N-dicyclohexylcarbodiimide and sodium vanadate, with K+ enhancing the vanadate inhibition. The enzyme was insensitive to sodium molybdate, NO− 3 , azide and oligomycin. No Ca2+ -ATPase was detected, and even as little as 0.05 m M Ca2+ inhibited the Mg2+ -ATPase activity. 相似文献
18.
Shoichi Asano Toshio Matsuda Kazuhiro Takuma Hye Sun Kim Tomoaki Sato Takashige Nishikawa Akemichi Baba 《Journal of neurochemistry》1995,64(6):2437-2441
Abstract: The effects of nitric oxide (NO)-generating agents on 45 Ca2+ uptake in rat brain slices and cultured rat astrocytes were studied in the presence of monensin, which is considered to drive the Na+ -Ca2+ exchanger in the reverse mode. Sodium nitroprusside (SNP) at >10 µ M increased monensin-stimulated Ca2+ uptake in the slices, although it did not affect high K+ -stimulated Ca2+ uptake. Another NO donor, 3-morpholinosydnonimine, was effective. The effect of SNP was antagonized by hemoglobin (50 µ M ), a NO scavenger, and mimicked by 8-bromo-cyclic GMP (100 µ M ). In rat brain synaptosomes, SNP increased monensin-stimulated Ca2+ uptake, but it did not affect high K+ -stimulated Ca2+ uptake. 8-Bromocyclic GMP, but not SNP, increased Na+ -dependent Ca2+ uptake significantly in synaptic membrane vesicles in the absence of monensin. In cultured rat astrocytes, SNP and 8-bromo-cyclic GMP increased Ca2+ uptake in the presence of ouabain and monensin, which were required for the Ca2+ uptake in the cells. These findings suggest that NO stimulates the Na+ -Ca2+ exchanger in neuronal preparations and astrocytes in a cyclic GMP-dependent mechanism. 相似文献
19.
Talvinder S. Sihra Daniele Piomelli Robert A. Nichols 《Journal of neurochemistry》1993,61(4):1220-1230
Abstract: During K+ -induced depolarization of isolated rat brain nerve terminals (synaptosomes), 1 m M Ba2+ could substitute for 1 m M Ca2+ in evoking the release of endogenous glutamate. In addition, Ba2+ was found to evoke glutamate release in the absence of K+ -induced depolarization. Ba2+ (1–10 m M ) depolarized synaptosomes, as measured by voltage-sensitive dye fluorescence and [3 H]-tetraphenylphosphonium cation distribution. Ba2+ partially inhibited the increase in synaptosomal K+ efflux produced by depolarization, as reflected by the redistribution of radiolabeled 86 Rb+ . The release evoked by Ba2+ was inhibited by tetrodotoxin (TTX). Using the divalent cation indicator fura-2, cytosolic [Ca2+ ] increased during stimulation by approximately 200 n M , but cytosolic [Ba2+ ] increased by more than 1 μ M . Taken together, our results indicate that Ba2+ initially depolarizes synaptosomes most likely by blocking a K+ channel, which then activates TTX-sensitive Na+ channels, causing further depolarization, and finally enters synaptosomes through voltage-sensitive Ca2+ channels to evoke neurotransmitter release directly. Though Ba2+ -evoked glutamate release was comparable in level to that obtained with K+ -induced depolarization in the presence of Ca2+ , the apparent intrasynaptosomal level of Ba2+ required for a given amount of glutamate release was found to be several-fold higher than that required of Ca2+ . 相似文献
20.
Ears of wheat plants ( Triticum aestivum L. cv. Kolibri), which were given different and uniform K+ -nutrition in two experiments, were cut at 2, 4 and 6 weeks after anthesis at 15 cm below the ear. These detached ears were fed 30 m M (experiment 1) or 15, 30, 60 or 90 m M 86 Rb-K2 malate (experiment 2) and 146 m M [14 C]-sucrose. After a pulse period of 6 and 4 h, respectively, the ears were transferred to identical non-labeled solutions for additional 0, 4, 8 or 20 h.
About 50% of the K+ and sucrose supplied was absorbed by detached ears. This rate declined with plant age and decreasing transpiration. Within the 6 and 4 h uptake period less than 7% of the absorbed K+ , but 20% of the sucrose taken up were incorporated into the grain. During the chase period labeled K+ in the grain increased to 15% and 14 C even to 50% of total tracer uptake. Incorporation of labeled K+ into the grain was not affected by the previous K+ nutrition of the plant and was proportional to the K+ concentration in the uptake solution. Transition of K+ from xylem into phloem during its acropetal transport is assumed. No evidence was found that the grain itself could control its uptake of K+ . 相似文献
About 50% of the K