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151.
Alexander A. Bulychev Tijmen van Voorthuysen Wim J. Vredenberg 《Physiologia plantarum》1996,98(2):605-611
Electrochemical data obtained with TMPD+ -sensitive electrodes indicate that ammonium-uncoupled chloroplasts retain TMPD (N,N,N',N'-tetramethyl- p -phenylenediamine) mainly in the reduced form during illumination, whereas uncoupled DCMU-treated chloroplasts accumulate TMPD in the oxidized form (TMPD+ ). This observation indicates that the reduced plastoquinol is the preferred electron donor for photosystem I (PSI) and TMPD can only compete efficiently when plastoquinone reduction is blocked. After adding DCMU the formation of a transmembrane gradient for TMPD+ is reflected by a slow-down of the electrogenic electron transport and by the emerging of the overshoot of the membrane current in the light-off response. A light-dependent increase in photoelectric current generated by chloroplasts in the presence of NH4 Cl and TMPD is observed and considered to be caused by a reversible release of current limitation in the interfacial conductance barriers in the lumen. 相似文献
152.
Keitaro Kiyosawa 《Physiologia plantarum》1996,97(1):180-184
Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L-cell fragments) were prepared. The L-cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K+, Na+, Ca2+, Mg2+, Cl?, NO?3. and SO2?4. in the external electrolyte solutions in which L-cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 mM KCL + 0.1 mM CaCl2 solution, Chara L-cell fragments absorbed K+ and Cl? to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K+ On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca2+, SO2?4 and NO?3 showed much less permeability than K+ and Cl ?for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L-cells is limited by the permeability of the least permeable ion. 相似文献
153.
Experiments in laboratory stream channels compared the behaviour of Deleatidium mayfly nymphs in the absence of fish with that in the presence of either native common river galaxias (Galaxias vulgaris Stokell) or introduced brown trout (Salmo trutta L.). Galaxias present similar predation risks to prey during day and night but are more active at night. Whereas, trout present a higher predation risk during the day. Deleatidium maintained a fixed nocturnal drift periodicity that is characteristic of streams containing visually feeding fish regardless of the nature of the predation regime presented in the laboratory. However, the number on the substratum surface, and therefore able to graze algae, was lower when fish were present than when they were absent. The number was lower during the day in the presence of trout, when they present the highest predation risk, and lower during the night compared to the day in trials with galaxias when galaxias activity disturbs Deleatidium from the substratum. Increases in the probability of Deleatidium leaving a patch, reductions in the proportion of mayflies on high quality patches and reductions in the distance travelled from refuge also reflected variations in the predation regime. Similar differences in positioning were observed under the same predation regimes in in situ channels in the Shag River and these were associated with differences in algal biomass. Algal ash-free dry mass (AFDM) and chlorophyll a (chl a) were higher on the tops of cobbles when fish were present. Fish also affected the biomass and the distribution of algae on cobbles as AFDM and chl a were higher on the sides of cobbles from channels with trout compared to those with galaxias. Changes in grazing behaviour, caused by predator avoidance, are likely to have been responsible for differences in algal biomass because no significant differences were detected between treatments in the biomass of Deleatidium or of total invertebrates. 相似文献
154.
The effect of NH
4
+
on the regulation of NO
3
–
and NO
2
–
transport systems in roots of intact barley (Hordeum vulgareL.) seedlings grown in NO
3
–
or NO
2
–
was studied. Ammonium partially inhibited induction of both transport systems. The inhibition was less severe in NO
2
–
-fed than in NO
3
–
-fed seedlings, presumably due to lower uptake of NH
4
+
in the presence of NO
2
–
. In seedlings pretreated with NH
4
+
subsequent induction was inhibited only when NH
4
+
was also present during induction, even though pretreated roots accumulated high levels of NH
4
+
. This indicates that inhibition may be regulated by NH
4
+
concentration in the cytoplasm rather than its total accumulation in roots. L-Methionine sulfoximine did not relieve the inhibition by NH
4
+
, suggesting that inhibition is caused by NH
4
+
itself rather than by its assimilation product(s). Ammonium inhibited subsequent expression of NO
3
–
transport activity similarly in roots grown in 0.1, 1.0, or 10 mM NO
3
–
for 24 h (steady-state phase) or 4 d (decline phase), indicating that it has a direct, rather than general feedback effect. Induction of the NO
3
–
transport system was about twice as sensitive to NH
4
+
as compared to the NO
2
–
transport system. This may relate to higher turnover rates of membraneassociated NO
3
–
-transport proteins.Abbreviations Mes
2(N-morpholino)ethanesulfonic acid
- MSO
L-methionine sulfoximine 相似文献
155.
Diallel analysis for sex-linked and maternal effects 总被引:40,自引:0,他引:40
J. Zhu B. S. Weir 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,92(1):1-9
Genetic models including sex-linked and maternal effects as well as autosomal gene effects are described. Monte Carlo simulations were conducted to compare efficiencies of estimation by minimum norm quadratic unbiased estimation (MINQUE) and restricted maximum likelihood (REML) methods. MINQUE(1), which has 1 for all prior values, has a similar efficiency to MINQUE(), which requires prior estimates of parameter values. MINQUE(1) has the advantage over REML of unbiased estimation and convenient computation. An adjusted unbiased prediction (AUP) method is developed for predicting random genetic effects. AUP is desirable for its easy computation and unbiasedness of both mean and variance of predictors. The jackknife procedure is appropriate for estimating the sampling variances of estimated variances (or covariances) and of predicted genetic effects. A t-test based on jackknife variances is applicable for detecting significance of variation. Worked examples from mice and silkworm data are given in order to demonstrate variance and covariance estimation and genetic effect prediction. 相似文献
156.
FRANS J M BONNIER RITSERT C JANSEN JAAP M VAN TUYL 《The Annals of applied biology》1996,129(1):161-169
Collections of lily genotypes are usually maintained by yearly planting, harvesting and storage of the bulbs. To facilitate this maintenance, a storage method has been developed for a collection of lily genotypes, including Asiatic hybrids, Oriental hybrids, Lilium longiflorum and L. henryi. Scale bulblets were stored either dry, sealed air-tight in polyethylene bags, or in moist vermiculite in open polyethylene bags for a period of 2 yr. The decrease in mass, sprouting proportion and ion leakage or sprouting proportion alone were determined for treatments carried out at -2°C, °C and 17°C. Sealing scale bulblets in polyethylene bags at -2°C resulted in the smallest decrease in mass, the least ion leakage and the highest sprouting proportion after 2 yr of storage. 相似文献
157.
S. K. Sharma 《Biologia Plantarum》1996,38(2):261-267
Plants of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance were grown in sand with nutrient solutions. 35-d-old plants were subjected to 5
levels of salinity created by adding NaCl, CaCl2 and Na2SO4. Growth reduction caused by salinity was accompanied by increased Na+ and Cl- concentrations, Na+/K+ ratio, and decreased concentration of K+. The salt tolerant cv. Kharchia 65 showed better ionic regulation. Salinity up to 15.7 dS m-1 induced increased uptake of Na+ and Cl- but higher levels of salinity were not accompanied by further increase in uptake of these ions. Observed increases in Na+ and Cl- concentrations at higher salinities seemed to be the consequence of reduction in growth. Uptake of K+ was decreased; more in salt sensitive cultivar. This was also accompanied by differences in its distribution. 相似文献
158.
Noriko Usui Kouji Matsushima Anne M. Pilaro Dan L. Longo Robert H. Wiltrout 《Biotherapy》1996,9(4):199-208
Recombinant human interleukin 1α (rh IL-1α) and etoposide (VP-16) synergize for direct growth inhibition of several human
tumor cell linesin vitro. Our previous studies demonstrated that VP-16 increased the number of membrane-associated IL-1 receptors (IL-1Rs) and also
enhanced the internalization of receptor-bound rh IL-1α. The purposes of this study were to test our hypothess that these
events were critical to the synergy between rhIL-1α and VP-16, to determine whether rhIL-1α and VP-16 synergize to increase
superoxide (SO) anion radical productionin vitro since SO anion has been implicated in the toxic effects of IL-1, and to investigate the antitumor efficacy of the combinaton
against tumors in vivo. A375/C6 melanoma cells and OVCAR-3 ovarian carcinoma cells were tested with IL-1 receptor antagonist
(IL-1ra) before exposure to rhIL-1α, VP-16 and rhIL-1α plus VP-16. The synergistic or antagonistic effects were assessed by
MTT assay. SO production was measured by reduction of cytochrome C. Athymic female mice bearing the A375/C6 melanoma were
treated by rhIL-1α, VP-16, and rhIL-1α+VP-16. The antitumor effects were evaluated by quantitating tumor growth and survival
time. Pretreatment with the IL-1ra abrogated the synergistic effects of rhIL-1α and VP-16. The production of SO radical by
A375/C6 cells was increased 2.5 fold by the combination of rhIL-1α and VP-16, and the addition of exogenous SOD blocked the
synergy between rhIL-1α and VP-16. However, when A375/S0D15 cells which over-expressed manganese superoxide dismutase (MnSOD)
after MnSOD cDNA transfecton were exposed to rhIL-1α and VP-16, in vitro antagonism was observed. In vivo studies demonstrated
that the combination of rhIL-1α and VP-16 delayed tumor growth better than either agent alone, although long-term survival
was not improved because of substantial toxicity. Our results suggest that the synergistic antitumor effects of IL-1α and
VP-16 may be due to IL-1R modulation and increased internalization of IL-1-IL-1R complex by VP-16 treatment, as well as to
a subsequent increase in SO anion radical production from the tumor cells exposed to both drugs. Thus, the combnation of IL-1α
and VP-16 might prove useful for the treatment of malignant diseasein vivo, if the increased toxicity can be reduced or managed.
The US Government’s right to retain a non-exclusive royalty-free license on and to any copyright is acknowledged. 相似文献
159.
Plant growth and reproduction along CO2 gradients: non-linear responses and implications for community change 总被引:4,自引:0,他引:4
The effects of rising atmospheric CO2 concentrations on natural plant communities will depend upon the cumulative responses of plant growth and reproduction to gradual, incremental changes in climatic conditions. We analysed published studies of plant responses to elevated CO2 to address whether reproductive and total biomass exhibit similar enhancement to elevated vs. ambient CO2 concentrations, and to assess the patterns of plant response along gradients of CO2 concentrations. In six annual plant species, mean enhancement at double ambient vs. ambient CO2 was 1.13 for total biomass and 1.30 for reproductive biomass. The two measures were significantly correlated, but there was considerable scatter in the relationship, indicating that reproductive responses cannot be consistently predicted from enhancement of total biomass. Along experimental CO2 gradients utilizing three concentrations, there was a great diversity of response patterns, including positive, negative, non-monotonic and non-significant (flat) responses. The distribution of response patterns differed for plants grown in stands compared to those grown individually. Positive responses were less frequent in competitive environments, and non-monotonic responses were more frequent. These results emphasize that interpolation of plant response based on enhancement ratios measured at elevated vs. ambient CO2 concentrations is not sufficient to predict community responses to incremental changes in atmospheric conditions. The consequences of differential response patterns were assessed in a simulation of community dynamics for four species of annual plants. The model illustrates that the final community composition at a future point in time depends critically on both the magnitude and the rate of increase of atmospheric CO2. 相似文献
160.
实验中观察到,用MUG培养基对植物药中的大肠杆菌定量时多发生荧光猝灭现象,影响检测结果。本文对此现象产生的原因与克服方法进行了系统的考察,发现以一种简便的转接方法可排除植物药介质对菌检的干扰。该方法由两组检验系列构成,当怀疑正常稀释系列(第一系列)40h培养液的荧光结果可能因猝灭现象呈假阴性时,立即分别将该系列的1—3号管培养液以0.5ml的接种量转接入新鲜的MUG培养基(第二系列),重新培养24h,荧光猝灭现象即可克服。综合两系列的荧光、产气和吲哚三项生化特征得出检品中大肠杆菌含量。实际应用表明,此法能显著提高使用该培养基时菌检结果的可靠性。 相似文献