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81.
纯化酶经聚丙烯酰胺凝胶电泳显示单一蛋白带,SDS-PAGE显示一条蛋自带,其亚基分子量为39.8kD。用SephacrylS-200凝胶过滤测得全酶的分子量为79.4kD,该酶由两个相同亚基组成。其表观Km为12mmol/L,Vmax为99.5mg还原糖mg-1proteinh-1。 相似文献
82.
玉米种子萌发成苗不同阶段需水阈值的研究 总被引:7,自引:0,他引:7
用渗透势不同的聚乙二醇(PEG)6000模拟外界环境水分条件,对玉米不同品种的种子在萌动、萌发及成苗三个阶段需水的量化研究表明,种苗的抗旱性随吸水进程的推进而减弱;种子在萌动、萌发及胚芽伸长至一定长度的时间(t)与外界环境水势(w)之间存在着1/t=a+bw的关系,据此推算出不同品种在不同成苗阶段的需水阈值,发现不同品种在同一成苗过程中对环境水分条件的反应不同,它们的抗旱性也不同。 相似文献
83.
六种固氮蓝藻提取液对玉米的促长作用和提取液成分比较 总被引:4,自引:1,他引:3
本文用六种固氮蓝藻的提取液处理玉米种子,同时对其提取液氨基酸组成和碳水化合物与维生素B12的含量进行了分析。结果表明固氮鱼腥藻HB686(AnabaenaazoticaHB686)、球孢鱼腥藻HB1017(A.sphaericaHB1017)、多变鱼腥藻HB1058(A.variabilisHB1058)和小单歧藻HBTT(TolypothrixtenuisHBTT)的提取液中氨基酸、碳水化合物和维生素B12的含量高于鱼腥藻SP.HB1042(Anabaenasp.HB1042)和繁育管链藻HB38(AulosirafertilissimaHB38)。同时,促进玉米种子萌发和幼苗生长的效果前四种藻较好,后两种则较差。 相似文献
84.
85.
Using a combination of gas-exchange and chlorophyll fluorescence measurements, low apparent CO2/O2 specificity factors (1300 mol mol?1) were estimated for the leaves of two deciduous tree species (Fagus sylvatica and Castanea sativa). These low values contrasted with those estimated for two herbaceous species and were ascribed to a drop in the CO2 mole fraction between the intercellular airspace (Ci) and the catalytic site of Rubisco (Cc) due to internal resistances to CO2 transfer. Cc. was calculated assuming a specificity of Rubisco value of 2560 mol mol?1. The drop between Ci and Cc was used to calculate the internal conductance for CO2 (gi). A good correlation between mean values of net CO2 assimilation rate (A) and gi was observed within a set of data obtained using 13 woody plant species, including our own data. We report that the relative limitation of A, which can be ascribed to internal resistances to CO2 transfer, was 24–30%. High internal resistances to CO2 transfer may explain the low apparent maximal rates of carboxylation and electron transport of some woody plant species calculated from A/Ci curves. 相似文献
86.
The mechanism by which chemical energy is converted into an electrochemical gradient by P-type ATPase is not completely understood. The effects of ATP analogs on the canine kidney (Na++ K+) ATPase were compared to effects of the same analogs on the maize (Zea mays L. cv. W7551) root H+-ATPase in order to identify probes for the ATP binding site of the maize root enzyme and to determine potential similarities of ATP hydrolysis mechanisms in these two enzymes. Six compounds able to modify the ATP binding site covalently were compared. These compounds could be classed into three distinct groups based on activity. The first group had little or no effect on catalytic activity of either enzyme and included 7-chloro-4-nitrobenz-2-oxa-1.3-diazole. The second group, which included azido adenine analogs. fluorescein isothiocyanate and 5′-p-fluorosulfonylbenzoyladenine, were inhibitors of ATP hydrolysis by both enzymes. However, the sensitivity of the (Na++ K+) ATPase to inhibition was much greater than that exhibited by the maize root enzyme. The third group, which included periodate treated nucleotide derivatives and 2′,3′-o-(4-benzoylbenzoyl)adenosine triphosphate. inhibited both enzymes similarly. This initial screening of these covalent modifiers indicated that 2′,3′-o-(4-benzoylbenzoyl)adenosine triphosphate was the optimal covalent modifier of the ATP binding site of the maize root enzyme. Certain reagents were much more effective against the (Na++ K+) ATPase than the maize root enzyme, possibly indicating differences in the ATP binding and hydrolysis pathway for these two enzymes. Two ATP analogs that are not covalent modifiers were also tested: the trinitrophenyl derivatives of adenine nucleotides were better than 5′-adenylylimidodiphosphate for use as an ATP binding probe. 相似文献
87.
Influence of mechanical impedance on root exudation of maize seedlings at two development stages 总被引:4,自引:0,他引:4
Studies were undertaken to evaluate the effects of mechanical impedance on root exudation by maize (Zea mays L., var Dea) and to examine the importance of these effects in relation to the stage of plant development. Plants were grown under sterile and hydroponic conditions. Mechanical impedance was simulated using glass beads of 1 mm diameter. This treatment was compared with a control without beads. Results demonstrated that plant growth was influenced by mechanical impedance. Mechanical impedance markedly affected the growth of the shoot, whether this was measured as leaf area or total dry matter. Besides increasing root/shoot biomass ratios, mechanical impedances also stimulated root exudation of organic and inorganic compounds. Stressed plants lost more nitrogenous compounds than control plants. Otherwise, the percentage of released carbon decreased. Depending on the developmental stage of the plant, there was a large variation in the magnitude and time course on mechanical impedance effects. The effects of mechanical impedance persist and accentuate with time. 相似文献
88.
Effects of moderate drought on ascorbate peroxidase and glutathione reductase activities in mesophyll and bundle sheath cells of maize 总被引:2,自引:0,他引:2
Mesophyll and bundle sheath cells of maize leaves ( Zea mays L.) both contain the enzymes ascorbate peroxidase (AP; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) which are involved in hydrogen peroxide detoxification. Since bundle sheath cells of maize are deficient in photosystem II and have high CO2 levels, oxidative stress may be less severe in these cells than in mesophyll cells. The present study was conducted to determine if AP and GR activity levels preferentially increase in mesophyll cells relative to bundle sheath cells when plants are subjected to moderate drought. Although drought inhibited the growth of greenhouse-grown plants, it did not affect the levels of protein, chlorophyll or AP. GR was unaffected by drought in whole leaf tissue and mesophyll cells, but did increase slightly in bundle sheath cells. This slight increase is of questionable biological importance. AP and GR activity levels were similar in mesophyll cells, bundle sheath cells and in whole leaf tissue. The data suggest that moderate drought has little effect on enzymes of the hydrogen peroxide scavenging system and that mesophyll and bundle sheath cells may be exposed to similar levels of hydrogen peroxide. 相似文献
89.
Uptake kinetics of iron-phytosiderophores in two maize genotypes differing in iron efficiency 总被引:5,自引:0,他引:5
Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of 59 Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar Km (∼ 10 μM) in both genotypes. In contrast. Vmax was 5.5 μmol Fe-DMA g−1 dry weight [30 min]−1 in Alice, but only 0.6 μmol Fe-DMA g−1 dry weight [30 min]−1 in ysl . Uptake experiments with double-labeled 59 Fe-[14 C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters. 相似文献
90.
The influx and efflux of organic acids across the root-soil interface were investigated in intact, sterile maize (Zea mays L.) roots under a variety of experimental conditions. Under nutrient-sufficient conditions the efflux of organic acids was shown to constitute < 1% of the total C lost across the root-soil interface. Under severe nutrient stress, however, the rates of malate and citrate efflux from the root increased 33 and 12 fold respectively. Influx experiments indicated that roots could not directly reabsorb citrate-Fe3+ or other metal complexes from solution. Influx of citrate was observed only at high external citrate concentration ( 1 mM) or from solutions with low ionic strengths. It was postulated that citrate influx is of little importance in a soil environment. 相似文献