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171.
Potato plants (Solanum tuberosum L.) were grown in water culture.About 14 d after tuber initiation no significant differenceswere found between apical and basal tuber parts in 14C-uptakeand partitioning into various fractions from 14C-labelled photosynthate.Thus, the fresh weight of these tubers could be used as a parameterfor the sink size. The 14C-content per tuber (sink strength)20 h after 14CO2-supply to the foliage was significantly correlatedwith the tuber fresh weight. No correlation was found betweenthe 14C-concentration of the tuber (sink activity; ct. ming fr. wt.) and tuber fresh weight. Consequently, tuberfresh weight (sink size) per se must have been a factor whichinfluenced sink strength. Stolon parameters characterizing theirgrowth prior to tuber initiation (e.g. stolon volume) and theircapacity for photosynthate transport (diameter, length) weremeasured at the time of tuber initiation. Significant correlationswere found between these stolon parameters and subsequent growthof individual tubers. Anatomical studies on the proportion ofvarious tissues in the cross sectional area of stolons supportthe idea of a negative relation between growth of individualtubers and transport resistance in the phloem of the stolons.It is concluded that in the initial phase of tuber growth, mainlyfactors outside of the tuber determine its growth rate. In laterstages of tuber growth, when the sink strength increases, thecompeting strength of individual tubers for photosynthate isdominated mainly by factors within the tuber itself, such astheir sink size and sink activity. Key words: Potato tuber, sink size, tuber initiation, transport resistance 相似文献
172.
Chromium VI Induced Structural and Ultrastructural Changes in Bush Bean Plants (Phaseolus vulgaris L.) 总被引:3,自引:0,他引:3
The effect of a growth reducing chromium VI concentration (9.6x 105M Cr as Na2CrO4) on the structure and ultrastructureof different organs of bush bean plants (Phaseolus vulgarisL.) grown on perlite was studied using light, transmission electronand scanning electron microscopy. The structural and ultrastructuralalterations observed were quite different in the various organsanalysed and did not always stay in direct relation to the averageCr content of the whole organ. The primary toxicity effect seemedto be membrane damage, due to the high oxidation power of CrVI. It is suggested that chromium is retained in vacuoles andcell walls of roots, and that the chromium reaching the leavesmay be principally Cr III and present in cell walls. The alterationsobserved in the upper plant parts seemed principally due toindirect Cr effects on the content of essential mineral nutrients. Phaseolus vulgaris L., bush bean, chromium VI toxicity, structure, ultranstructure, light microscopy, transmission electron microscopy, scanning electron microscopy 相似文献
173.
174.
The nucleotide sequences of the cow epsilon 2 and epsilon 4 globin genes
were determined. The sequences were 95% identical. These genes arose via a
four-gene block duplication that also gave rise to the bovine fetal (gamma)
and adult (beta) genes. Their deduced amino acid sequences are unlike any
previously reported fetal or adult globins; rather, comparison to other
mammalian globin genes indicates that they are embryonic in nature. The
sequence data indicate that these two genes have converted each other
during evolution. Pairwise comparison to the corresponding goat genes shows
greater similarity between paralogues than between more directly related
orthologues. This is in direct contrast to the situation between the cow
and goat fetal and adult genes. These observations suggest that the
frequency of DNA conversion or the fixation of conversion events may vary
in different locations of the cow beta-globin cluster.
相似文献
175.
JIÍ NEDOMA PETRA PORCALOVA JAROSLAVA KOMÁRKOVÁ VOJTCH VYHNÁLEK 《Freshwater Biology》1993,30(3):369-376
- 1 Seston elemental composition (C, N, P) and the orthophosphate uptake rate constant, k(upt), were measured in the epilimnion of the eutrophic ?ímov Reservoir in the period March-August 1989.
- 2 Seasonal series of log C/P, log N/P and log [k(upt)] values were highly correlated (r2 in the range 0.84–0.93), but, based on literature-derived criteria, k(upt) values indicated stronger P deficiency than did the C/P values.
- 3 The results showed moderate to strong phosphorus deficiency in summer, moderate deficiency at the end of the spring peak of phytoplankton, and no deficiency early in the spring or during the spring clear-water period.
176.
A NOVEL method for the phosphorylation of sugars by orthophosphate in the presence of cyanogen in dilute aqueous neutral or slightly alkaline solutions has been described, suggesting a plausible model of the prebiotic phosphorylation of sugars1–3. This reaction has now been applied to the synthesis of glucose 1,6-diphosphate, starting either from α-D-glucose 1-phosphate or from D-glucose 6-phosphate. The formation of α-D-glucose 1,6-diphosphate from α-D-glucose 1-phosphate would indicate a possible route for the synthesis of this compound on the primitive Earth. It is known that α-D-glucose 1,6-diphosphate is the coenzyme in the inter-conversion of α-D-glucose 1-phosphate with glucose 6-phosphate catalysed by phosphoglucomutase*. The formation of α-D-glucose 1,6-diphosphate seems to be interesting in view of our model for the chemical evolution of the metabolism of sugars5, as it may connect α-D-glucose 1-phosphate with the glycolytic pathway. 相似文献
177.
178.
Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth. 相似文献
179.
A. F. Gelb D. R. Aberle M. J. Schein D. P. Naidich J. D. Epstein D. P. Tashkin 《The Western journal of medicine》1990,153(4):385-389
We studied 8 adult patients with variable symptoms of cough, dyspnea, stridor, wheezing, or hemoptysis. Fiberoptic bronchoscopy in all showed complete or nearly complete endobronchial obstruction of a main-stem bronchus by neoplasm with a mean bronchial diameter of 1.9 mm +/- 1.6 mm (mean +/- standard deviation). In 4 patients, a lobar bronchus was also completely obstructed. No mass was visible on chest radiographs of any patient; however, computed tomography in each showed main-stem endobronchial obstruction, lobar obstruction (4 instances in 3 patients), and in 6 patients hypoperfusion of the involved lung. Computed tomographic scan showed additional abnormalities that were unsuspected on viewing chest radiographs or at bronchoscopy, including mediastinal adenopathy in 3 patients and an extraluminal tumor component in 4. After therapy with Nd-YAG laser, main-stem airway diameter increased to a mean of 9.6 mm +/- 1.0 mm (P less than .05) and pulmonary functions improved. Results suggest the complementary role of computed tomography and fiberoptic bronchoscopy in the detection and laser-treatment planning of chest radiographically occult severe neoplastic obstruction of the main-stem bronchus. 相似文献
180.