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51.
52.
Summary The mechanism of water movement across roots is, as yet, not well understood. Some workable black box theories have already been proposed. They, however, assumed unrealistic cell membranes with low values of , or were based on a poor anatomical knowledge of roots. The role of root stele in solute and water transport seems to be especially uncertain. An attempted explanation of the nature of root exudation and root pressure by applying the apoplast canal theory (Katou andFurumoto 1986 a, b) to transport in the root stele is given. The canal equations are solved for boundary conditions based on anatomical and physiological knowledge of the root stele. It is found that the symplast cell membrane, cell wall and net solute transport into the wall apoplast are the essential constituents of the canal system. Numerical analysis shows that the canal system enables the coupled transport of solutes and water into a xylem vessel, and the development of root pressure beyond the level predicted by the osmotic potential difference between the ambient medium and the exudate. Observations on root exudation and root pressure previously reported seem to be explained quite well. It is concluded that the movement of water in the root stele although apparently active is essentially osmotic.Abbreviations J
v
ex
volume exudation per root surface
- J0
non-osmotic exudation
- Lr
overall radial hydraulic conductivity of an excised root
-
reflection coefficient
- Cs
difference in the osmotic concentration between the bathing medium and the exudate
- R
gas constant
- T
absolute temperature
- CK
molar concentration of K+
- CCl
molar concentration of Cl–
- Cj
molar concentration of ion species j
- Pj
membrane permeability of ion j
- zj
valence of ion j
- F
Faraday constant
- Vix
intracellular electric potential with reference to the canal 相似文献
53.
The free and N-acetyl glucosamine contents, serving as a measure of the amounts of chitosan and chitin respectively, were
determined in the chitinase hydrolysates of the cell wall of a wild strain ofNeurospora crassa. Chitinase, obtained from cultures ofSerratia marcescens, could hydrolyse the cell wall completely apart from being capable of hydrolysing preparations of chitin and chitosan. The
free and N-acetyl glucosamines, released by chitinase hydrolysis, were determined by a modified Morgan-Elson reaction carried
out in the presence and absence of acetic anhydride. The method is capable of estimating chitin and chitosan contents in as
little as 100 μg of cell wall material. 相似文献
54.
Scavenging of superoxide radical by ascorbic acid 总被引:1,自引:0,他引:1
Using acetaldehyde and xanthine oxidase as the source of suPeroxide radical, the second order rate constant for the reaction
between ascorbic acid and superoxide radical was estimated to be 8.2 X 107 M-1 s-1. In rats, the average tissue concentration of ascorbic acid was of the order of 10-3 M and that of superoxide dismutase was of the order of 10-6 M. So, taking together both the rate constants and the tissue concentrations, the efficacy of ascorbic acid for scavenging
superoxide radical in animal tissues appears to be better than that of suPeroxide dismutase. The significance of ascorbic
acid as a scavenger of superoxide radical has been discussed from the point of view of the evolution of ascorbic acid synthesizing
capacity of terrestrial vertebrates. 相似文献
55.
56.
The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae) 总被引:1,自引:1,他引:0
Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates
were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d−1) than detritus (mean = 1.8% wet wt. d−1). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased
over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth
of S. vicarium may be partially controlled by seasonal factors. 相似文献
57.
58.
Cell wall mannoproteins during the population growth phases in Saccharomyces cerevisiae 总被引:2,自引:0,他引:2
E. Valentín E. Herrero H. Rico F. Miragall R. Sentandreu 《Archives of microbiology》1987,148(2):88-94
Mannoproteins from cell walls of Saccharomyces cerevisiae synthesized at successive stages of the population growth cycle have been solubilized with Zymolyase and subsequently analyzed. The major change along the population cycle concerned a large size mannoprotein material; the size of the newly-synthesized molecules varied from 120,000–500,000 (mean of about 200,000) at early exponential phase to 250,000–350,000 (mean of about 300,000) at late exponential phase. These differences are due to modifications in the amount of N-glycosidically linked mannose residues, since the size of the peptide moiety was 90,000–100,000 at all growth stages and the level of O-glycosylation changed only slightly. After, incubation of the purified walls with concanavalin A-ferritin and subsequent analysis by electron microscopy, labelling was localized at the external and internal faces of the walls. The middle space of these was labelled after digestion of the glucan network with Zymolyase, which demonstrate the presence of mannoproteins in close contact with the structural glucan molecules throughout the wall.Abbreviations BSA
bovine serum albumin
- Con A
concanavalin A
- SDS
sodium dodecyl sulphate 相似文献
59.
人体单臂间歇运动对发汗调定点的影响 总被引:2,自引:0,他引:2
本工作系在微小气候相对恒定条件下,对10名健康男青年每人进行四项实验。实验 Ⅰ 为测定双侧腿足浸入43℃水中,诱发左前臂屈侧显现定量汗点时的口腔温度(舌下)阈值,作为发汗调定点参考值(ToSSP);实验 Ⅱ 为 Ⅰ 附加右臂间歇轻负荷运动(77W)时测定 ToSSP,部分对象还记录了皮肤电反应;实验 Ⅲ、Ⅳ 为 Ⅰ、Ⅱ 均附加4.5m/s 气流(22—25℃)直吹头面部,再分别测定 ToSSP。实验 Ⅰ 与 Ⅱ 同体对照22人次,Ⅲ 与 Ⅳ 同体对照24人次。结果表明,实验 Ⅱ、Ⅳ 的 ToSSP 均值及其潜伏期均值分别较 Ⅰ、Ⅲ 者降低(P<0.01)或缩短(P<0.001);Ⅰ、Ⅱ间的 ToSSP 均值差、潜伏期均值差,分别与 Ⅲ、Ⅳ 之间者无显著差异(P>0.2);Ⅱ、Ⅳ 的ToSSP 均值各与其实验开始前的口温均值亦无明显差异(P>0.5)。此结果支持运动时体温调定点下降的论点,并提示在研究体温调定点活动时,以 ToSSP 为指标较用发汗速率为优越,因 ToSSP 不为许多干扰因素所影响。 相似文献
60.