954 resultados para marina mercante


Relevância:

20.00% 20.00%

Publicador:

Resumo:

尖尾藻细胞核的有丝分裂在涡鞭毛虫中间是非常独特的,可能对于了解有丝分裂的进化具有重要的意义。利用低速离心处理和低温(4℃)正常温度(19 ± 1℃)周期性自理相结合的办法,成功地实现了尖尾藻的同步化培养。以同步化培养的群体作为材料,用电子显微镜研究了尖尾藻细胞核有丝分裂过程中的超微结构变化。根据核中染色体的形态,间期细胞核可以分为两种类型-I型和II型。在II型间期核中,染色体比I型间期核中的染我体粗,其中的一部份呈棒状,另一部分形状不规则。在这两种类型的间期核中,细胞核和核仁都作园形。尖尾藻的分裂态Y形和U形染色体是出现在分裂间期细胞核中。前期时,核变成卵形,核仁伸长,在核膜上出现核小板(Nuclear Plaqes);从核小板向核内发出微管。我们的观察表明在尖尾藻的核分开明过程中,虽然没有赤道板出现,但中期仍然是存在的。与许多高等真核生物一样,类尾藻的后期也可以分成后期A和后期B。后期A时,核内染色体向两极度移动,细胞核没有显著的伸长。染色体的极度向运动可能是由于与染色体相连的牵引微管的缩短和位于正在移向两极度的两条染色体之是的微管的伸长两种因素相互协调地起作用而引起的。在后期A细胞核中,位于两极度的微管组织者是多个位于核膜上的核小板,它们并未融合成为统一的微管组织中心。在后期B时,在细胞核的中间共很少见到微管,细胞核伸长,到末期开始时,核的长度大约是后期A细胞核的两倍。这种伸长很可能是由于中间区核膜的生长。在整个核分裂过程中,始终有核膜存在。我们发现微管也会与分裂中的核仁相连,这表明微管在核仁分裂中可能起着重要的作用。根据已有的资料,讨论了有丝分裂的机制和有丝分裂的进化。

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Flowering and seed-bank development of annual Zostera marina L. and perennial Z. noltii hornem. were studied in the Zandkreek (S.W. Netherlands). Flowering of Z. noltii started at the end of June and continued until the end of September. A maximum of ca. 1000 flowering shoots (11% of the total amount of shoots per square metre) occurred in early August. Flowering of Z. marina started at the end of July and continued throughout October. Seed banks of both species appeared to be annual. Actual seed densities of Z. noltii were much lower than predicted on the basis of the amount of inflorescences.Germination was studied in the laboratory in relation to temperature (10, 20 and 30°C), salinity (1.0, 10.0, 20.0, 30.0 and 40.0‰) and stratification (at 4°C). Both species showed a maximal germination at 30°C and 1.0‰ salinity, decreasing with higher salinities and lower temperatures. Stratification stimulated germination only at salinities 20.0‰. Desiccation and anaerobia were lethal to Z. marina seeds. Seedlings of Z. marina survived best at 10°C and 10.0–20.0‰ salinity and those of Z. noltii survived best at 10°C and 1.0‰ salinity. Overall, seedlings of Z. marina survived better than those of Z. noltii.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

A new acylated iridoid glucoside, namely, 2'-O-(5-phenyl-2E, 4E-pentadienoyl)mussaenosidic acid, was isolated from the aerial parts of the mangrove plant Avicennia marina. The structure of the new compound was established on the basis of various NMR spectroscopic analyses, including 2D NMR techniques (H-1-H-1 COSY, HMQC, and HMBC) and HR-FAB-MS. This compound displayed moderate antioxidant activity.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Two new urostylid ciliates, Metaurostylopsis songi n. sp. and Metaurostylopsis salina n. sp. and Metaurostylopsis marina (Kahl 1932) are investigated using live observation and protargol impregnation. These species were isolated in Korea from intertidal sediments, saline ponds, and coastal waters. Metaurostylopsis songi is in vivo about 120 pm x 25 mu m, has a slenderly ellipsoidal body, colorless cortical granules in rows on ventral and dorsal body sides, about 54 macronuclear nodules, 28-47 adoral membranelles, five frontal, two or three frontoterminal and six or seven transverse cirri, and 9-12 midventral cirral pairs followed posteriorly by 1-3 single cirri. In vivo M. salina is about 60 pin x 25 mu m, has a pyriform body, colorless cortical granules irregularly arranged, about 45 macronuclear nodules, 18-23 adoral membranelles, three frontal, three to five frontoterminal and two to five transverse cirri, and four or five midventral cirral pairs followed posteriorly by five to seven single cirri. Both species have three marginal cirral rows on each body side and 3 long dorsal kineties. The Korean specimens of M. marina match the Chinese population in all main features. Metaurostylopsis songi differs from M. marina by the more slender body, the number of frontal cirri (invariably five vs. four), and the arrangement of cortical granules (in rows on dorsal and ventral cortex vs. only along dorsal kinetics and anterior body margin). Metaurostylopsis salina differs from its congeners by the distinctly smaller size, the pyriform body shape, the scattered cortical granules (vs. in rows), and number of frontal cirri. It differs from M. marina also by the number of midventral cirral pairs (four or five vs. seven to 11).

Relevância:

20.00% 20.00%

Publicador:

Relevância:

20.00% 20.00%

Publicador:

Relevância:

20.00% 20.00%

Publicador:

Relevância:

20.00% 20.00%

Publicador: