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91.
92.
Few tropical species have been tested for their flowering response under controlled conditions. Hyptis brevipes Poit, is an annual herb, commonly found in wet margins of streams and ponds, being considered a weed for some perennial plantations in Brazil. Under experimental glasshouse conditions, this species proved to be an obligate short-day plant. Flowering was delayed when photoperiods longer than 8 h were given, the critical photoperiod being between 12 and 13 h. When both temperature and photoperiod were controlled, at 20°C a longer protoperiod (by almost 1 h) is still inductive compared to 25 and 30°C. The number of short-day cycles required for full induction is relatively high and dependent upon temperature; at 20°C or above, 10 cycles are adequate, but at 15°C, more short-day cycles are needed. The number of inflorescences formed as well as the floral index vary according to daylength × temperature × inductive cycle number, allowing flowering to be assessed quantitatively. Long days are inhibitory to flowering, either suppressing it completely (when symmetrically intercalated among 24 inductive cycles) or preventing the floral index from increasing. 相似文献
93.
Structural changes of tissues in unpollinated ovaries of Pisum sativum L. cv. Alaska after treatment with different plant growth substances (gibberellic acid, 2,4-dichlorophenoxyacetic acid, and 6-benzyladenine) or decapitation of the plant were studied. All the treatments resulted in the prevention of cellular disorganization associated with ovary senescence. They effected the enlargement of mesocarp cells and the differentiation of endocarp cells in very similar patterns, suggesting a similar induction of the structural processes involved in fruit development. Ultrastructural changes in mesocarp cells after treatment with gibberellic acid showed that rapid enlargement of mesocarp cells was sustained mainly by a reorganization of the membrane systems directed to the sysnthesis of primary cell wall. Early changes in the subcellular components in mesocarp cells were observed as the first symptoms in ovary senescence. 相似文献
94.
Organogenesis in thin cell layers of Nicotiana tabacum L. was studied in relation to the effects of natural and synthetic auxins in combination with various cytokinins. All cytokinins tested, benzyladenine (BA), kinetin, zeatin (Z), zeatin riboside (ZR), N6 -Δ2 -isopentenyl) adenine (IPA), dihydrozeatin [(diH)Z] and dihydrozeatin riboside [(diH)ZR], seem to be active in flower bud formation. In addition to the initiation of flower buds, vegetative buds or roots were also formed on the explants in the presence of BA, Z or IPA as exogenous cytokinins. Only dihydrozeatin and its riboside stimulated the initation of flower buds alone (as is known for kinetin), especially if supplemented with indole-3-acetic acid (IAA) as exogenous auxin. A high number of explants with flower buds was also found with high cytokinin/2,4-D ratios. In these conditions the presence of (diH)Z yielded the higest number of flower buds per explant. 相似文献
95.
L. Romo-Parada L.-P. Vézina P. M. Charest F. Castaigne C. Willemot 《Physiologia plantarum》1991,83(4):664-674
Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower ( Brassica oleracea , L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O2 , 21% O2 + 15% CO2 or 3% O2 + 15% CO2 . In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati-dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O2 did not prevent phospholipid breakdown. Low O2 prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O2 atmosphere was lost under 3% O2 + 15% CO2 . The high CO2 atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO2 . 相似文献
96.
Daniel E. L. Promislow 《Evolution; international journal of organic evolution》1991,45(8):1869-1887
Here, I use published mortality data from 56 natural populations of mammals to examine evidence for senescence, an increase in the probability of mortality with age. Data on extent of senescence and life history characteristics are compared across taxa in an attempt to test theories for the evolution of senescence in natural populations. In accord with theoretical expectation, senescence is highest in short-lived species with short generation times. In contrast to theoretical expectation, however, senescent increases in mortality rate do not begin until well after age at maturity in most cases. I also present evidence in support of the hypothesis that senescence will be lower in large-brained taxa. 相似文献
97.
Temporal variability in certain morphological and taxonomically important features was quantified for Sargassum polyceratium Mont. from a population in the Content Keys, Florida (U.S.A.). Patterns of blade development, senescence, and loss caused pronounced seasonal changes in blade length-width ratios. Blade length and width were maximal early in the growing season (August-November) and decreased as the annual stems matured. Early in the growing season, plants had broader blades with randomly distributed cryptostomata. Late in the growing season (February-April), plants had more linear blades with cryptostomata approximately arranged in two rows, one on each side of the midrib. The length-width ratio of blades increased acropetally along the stems and were directly correlated to the size of the cryptostomatal opening and inversely correlated with the number of cryptostomata. The branching pattern of the annual stems ranged from short spur branches to well-developed, lateral axillary branches. The frequency of bifurcated blades increased significantly late in the growing season. Vesicle shape and size and pedicel length were temporally stable. Alated pedicels and mucronate vesicles occurred in low frequencies. The variability of the morphological features used to delineate species within the genus Sargassum on the tropical eastern coasts of the Americas is poorly understood. 相似文献
98.
Alexander Christmann Jacqueline Christmann Petra Schiller Burkhard Frenzel 《Trees - Structure and Function》1996,10(5):331-338
Levels of indole-3-acetic acid (IAA) were determined in needles from silver fir (Abies alba Mill.) trees in the northern Black Forest. IAA was quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-methylester
(HFB-IAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed
employing two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by combined gas chromatography-mass spectrometry in selected
samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest
concentrations in winter and lowest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels
was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) in the
field due to a local SO2 source. Levels of IAA increased with increasing needle age. This age dependency of IAA concentrations was most pronounced
in late autumn when IAA levels were high and nearly disappeared in spring when IAA levels reached their minimum. In needles
from declining fir trees or fir trees suffering from a strong S-impact in the field, IAA levels hardly increased with increasing
needle age. It is suggested that in healthy trees high levels of IAA protect older needles from abscission and that the considerable
losses of older needles of declining fir trees or of fir trees under S-impact are a consequence of the low levels of IAA found
in older needles of such trees.
Received: 4 May 1995 / Accepted: 29 August 1995 相似文献
99.
反义RNA技术在植物基因工程领域中的应用 总被引:3,自引:0,他引:3
周跃钢 《生物化学与生物物理进展》1996,23(4):297-301
反义RNA技术在植物基因工程领域中的应用包括:a.番茄和其他水果的成熟控制;b.植物的抗病性;c.改变花卉的颜色;d.植物淀粉合成的控制;e.油料植物种子中脂肪酸合成的控制;f.杂交种子生产中雄性不育性的控制;g.其他. 相似文献
100.
p21是近年来发现的一类调控细胞增殖的小分子,是依赖周期素的CDK抑制因子.这些蛋白因子可结合cyclin-CDK并抑制其激酶活性从而调节细胞周期p15、p16、p27均属该类分子,他们在G1期限制点及G1/S检查点调控中发挥作用.进一步的研究表明,p21为p53调控,在p53介导的DNA损伤诱发的细胞周期阻断中发挥作用p21在老化细胞中高表达、细胞分化的同时表达,表明其在细胞增殖、分化及老化中发挥调节作用. 相似文献