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951.
Abstract. The starch concentration in mature leaves of the halophyte Suaeda maritima increased from 4.7 to 7.3 mg mg−1 chlorophyll when sodium chloride (680 mol M−3 ) was added to the solution in which the plants were grown. This effect of salinity on the starch: chlorophyll ratio was greater in young than in old leaves. Electron micrographs showed the starch to be in the chloroplasts and this was confirmed by measurements on isolated chloroplasts. Total phosphorus concentration (mg mg−1 chlorophyll) in leaves of all ages from plants of S. maritima decreased on salinization of the growth medium suggesting an inverse relationship between phosphorus and starch concentrations. However, although leaf starch concentration varied with leaf age, phosphorus concentration did not. The cause of starch accumulation in chloroplasts at salinities which are optimal for growth (340 mol m−3 ) remains unclear. 相似文献
952.
To determine the sites of synthesis of chloroplast-envelope proteins, we have analysed several enzyme and translocator functions ascribed to the envelope membranes, and investigated the envelope polypeptide composition of plastids isolated from 70S ribosome-deficient leaves of rye (Secale cereale L.) generated by growing the plants at a temperature of 32°C. Since the ribosomedeficient plastids are also achlorophyllous in light-grown leaves, not only were chloroplasts from mature, green leaves used for comparison, but also those from yellowing, aged leaves as well as etioplasts from dark-grown leaves raised at a temperature of 22° C. A majority of the plastidenvelope polypeptides appeared to be of cytoplasmic origin. The envelopes of ribosome-deficient plastids possessed ATPase (EC 3.6.1.3) activity; this was not, however, dependent on divalent cations, in contrast to the Mn2+- or Mg2+-dependent ATPase which is associated with chloroplast envelopes. Adenylate kinase (EC 2.7.4.3) was present in the stromal fraction of ribosome-deficient plastids and the stromal form of this enzyme is, therefore, of cytoplasmic origin. In contrast to previous findings, adenylate kinase was not, however, specifically associated with the chloroplast-envelope membranes, either in rye or in spinach. Measurements of the uptake of l-[14C]-malate into ribosome-deficient plastids indicated the presence and cytoplasmic origin of the dicarboxylate translocator. Malate uptake into rye etioplasts was, however, low. The phosphate translocator was assayed by the uptake of 3-phospho-[14C]glycerate. While rapid 3-phosphoglycerate uptake was observed for rye chloroplasts and etioplasts, it was hardly detectable for ribosome-deficient, plastids and rather low for chloroplasts from aged leaves. A polypeptide of M
r approx. 30000 ascribed to the phosphate translocator was greatly reduced in the envelope patterns of ribosome-deficient plastids and of chloroplasts from aged leaves. 相似文献
953.
954.
955.
Detailed interpretation of triose phosphate isomerase (TPI) isozymes in seed plants has been restricted to only a few species. Three sets of TPI bands are regularly observed in the cherimoya(Annona cherimola), a primitive angiosperm. The slowest, set I, is expressed as one or three bands; the second-slowest set II, as one or two bands; and the fastest, set IV, as one or three bands. A faint set III, just cathodal to set IV, is detected rarely with overstaining. Set IV bands are expressed in macerated extracted pollen but not in pollen leachate. Dissociation-reassociation experiments reveal that the set II bands are heterodimers involving, in part, the enzymes involved in the set I bands. These data combined with those from full-sib progeny analysis lead us to propose a three-locus model to explain the TPI isozyme banding patterns in cherimoya. Sets I and IV consist of the allelic products of individual, single loci. Sets I and II occur in the cytoplasm. Set IV occurs in organelles. Set II isozymes are the intergenic heterodimers of the locus coding for set I and the locus coding for set III. Our results reported here are contrasted with the TPI isozyme patterns known for other vascular plants and suggest that the locus coding for set III may be a duplication of very ancient origin.This work was supported, in part, by funding from the Elvenia J. Slosson Endowment Fund. 相似文献
956.
Two experiments were carried out to study physiological effects of vesicular-arbuseular mycorrhizal infection on Plantago major L., ssp. pleiosperma (Pilger). In the first experiment, infection by the Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe increased growth, shoot to root ratio, P concentrations in both shoot and roots and total uptake of P per plant. The percentages of dry matter in both shoot and roots were lower in mycorrhizal plants.
In the second experiment different P treatments were applied to both mycorrhizal and non-mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants. 相似文献
In the second experiment different P treatments were applied to both mycorrhizal and non-mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants. 相似文献
957.
Yoshikiyo Oji Masakazu Takahashi Yasuo Nagai Nariaki Wakiuchi 《Physiologia plantarum》1988,72(2):311-315
NADH-nitrate reductase (EC 1.6.6.1) was purified 800-fold from roots of two-row barley ( Hordeum vulgare L. cv. Daisen-gold) by a combination of Blue Sepharose and zinc-chelate affinity chromatographies followed by gel filtration on TSK-gel (G3000SW). The specific activity of the purified enzyme was 6.2 μmol nitrite produced (mg protein)−1 min−1 at 30°C.
Besides the reduction of nitrate by NADH, the root enzyme, like leaf nitrate reductase, also catalyzed the partial activities NADH-cytochrome c reductase, NADH-ferricyanide reductase, reduced methyl viologen nitrate reductase and FMNH2 -nitrate reductase. Its molecular weight was estimated to be about 200 kDa, which is somewhat smaller than that for the leaf enzyme. A comparison of root and leaf nitrate reductases shows physiologically similar or identical properties with respect to pH optimum, requirements of electron donor, acceptor, and FAD, apparent Km for nitrate, NADH and FAD, pH tolerance, thermal stability and response to inorganic orthophosphate. Phosphate activated root nitrate reductase at high concentration of nitrate, but was inhibitory at low concentrations, resulting in increases in apparent Km for nitrate as well as Vmax whereas it did not alter the Km for NADH. 相似文献
Besides the reduction of nitrate by NADH, the root enzyme, like leaf nitrate reductase, also catalyzed the partial activities NADH-cytochrome c reductase, NADH-ferricyanide reductase, reduced methyl viologen nitrate reductase and FMNH
958.
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
959.
Levels of nitrate reductase activity (N.R.A.) were measured in shoots and roots of P sufficient and P deficient rape plants
and changes in N.R.A. examined in relation to the onset of H ion efflux from the roots. Rates of xylem exudation were measured
and the sap analysed for nitrate, amino-N and phosphate content.
The optimum concentration of phosphate in the leaves for N.R.A. was about 0.7%. Both high and low concentrations of phosphate
within the leaves inhibited N.R.A in those leaves. This inhibition of N.R.A led to the accumulation of nitrate in the older
parts of the shoots of P sufficient plants. Less accumulation of nitrate occurred in the P deficient plants since nitrate
uptake by the plants decreased before any fall in N.R.A.
Xylem exudation rates halved within 18 hours of depriving the plants of phosphate, and, since the composition of the sap remained
constant, this indicated a reduced flux of nitrate into the xylem. The rate of xylem exudation continued to fall and by the
end of the experiment was approximately one tenth of the rate in the P sufficient plants.
The onset of H ion efflux from the terminal portions of the root preceded any effect on N.R.A by 2 days. 相似文献
960.
Phosphorus in the sediment of the Loosdrecht lakes and its implications for lake restoration perspectives 总被引:6,自引:3,他引:3
In 1984 the external phosphorus load of the shallow eutrophic Loosdrecht lakes was reduced from 3.3 to 1.0 mg m–2 d–1. The effect of phosphorus release from the sediment on lake restoration was investigated. Diffusive release under aerobic conditions (20 °C) decreased from 1 mg m–2 d–1 in 1984 to 0.3 mg m–2 d–1 in 1990. The generation of inorganic phosphorus due to mineralization during summer equals 3 mg m–2 d–1, which is much higher than the measured rate of diffusive release. Despite that, the phosphorus release is hardly stimulated by anaerobic conditions, which indicates that only a small amount of phosphorus is adsorbed by ferric iron in the top sediment layer. This apparent discrepancy is probably caused by the uptake of inorganic phosphorus uptake during resuspension and the loss of inorganic phosphorus with downward seepage.The estimated removal of phosphorus due to downward seepage of 0.8 mg m–2 d–1 agrees well with the average phosphorus retention in the lake. This indicates that sediment burial and diagenesis are unimportant mechanisms for withdrawing phosphorus from the nutrient cycle.Between 1982 and 1991 the total phosphorus content of the upper 2 cm of the sediment decreased from 0.94 to 0.60 g kg–1 DW. At present, about 20% of total phosphorus in this layer is potentially bioavailable, but largely incorporated in easily degradable organic matter. This pool is much smaller in deeper layers. Based on the estimated and measured rates and pool sizes, the annual average phosphorus cycle in the lakes was modelled to evaluate the effects of various restoration measures. The main predictions of the model are: 1) further reduction of the external load may cause a gradual decrease of the total phosphorus concentration in the lake water; 2) dredging and iron addition, without reduction of the external load, may give a rapid improvement followed by a slow return to the present situation; and 3) reduction of the external load, combined with a cut off of downward seepage will not improve the water quality. 相似文献