Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the va...Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.展开更多
该文基于英国国家语料库,对前缀pro-以及前缀pre-进行语义词源上的对比研究,以及两者所构成词的词性的对比。研究发现,前缀pro-拥有更多的语义。另外,前缀pro-所构成词的词汇往往有一个动作的倾向性,而前缀pre-构成的词往往在时间有一...该文基于英国国家语料库,对前缀pro-以及前缀pre-进行语义词源上的对比研究,以及两者所构成词的词性的对比。研究发现,前缀pro-拥有更多的语义。另外,前缀pro-所构成词的词汇往往有一个动作的倾向性,而前缀pre-构成的词往往在时间有一个提前。在语义相同的情况下,两个前缀均表示"before"时,pre-构成词的词性更多;而在前缀表示"front"时,两者相反,前缀pro-构成词的词性更多;在表示"in front of"时,两者构成词词性均为动词,且词汇量较少。展开更多
文摘Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.
文摘该文基于英国国家语料库,对前缀pro-以及前缀pre-进行语义词源上的对比研究,以及两者所构成词的词性的对比。研究发现,前缀pro-拥有更多的语义。另外,前缀pro-所构成词的词汇往往有一个动作的倾向性,而前缀pre-构成的词往往在时间有一个提前。在语义相同的情况下,两个前缀均表示"before"时,pre-构成词的词性更多;而在前缀表示"front"时,两者相反,前缀pro-构成词的词性更多;在表示"in front of"时,两者构成词词性均为动词,且词汇量较少。
