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《志摩的诗》

《翡冷翠的一夜》

C ． 《猛虎集》

D ．《云游集》

Like animals, plants make extensive use of transmembrane cell-surface receptors—especially enzyme-coupled receptors to recognize the extracellular signal molecules that control their growth and development. The spindly weed Arabidopsis thaliana has hundreds of genes encoding receptor serine/threonine kinases.

These are, however, structurally distinct from the receptor serine/threonine kinases found in animal cells .

The plant receptors are thought to play an important part in a large variety of cell signaling processes, including those governing plant growth, development, and disease resistance.

In contrast to animal cells, plant cells seem not to use RTKs, steroid-hormone-type nuclear receptors, or cyclic AMP, and they seem to use few GPCRs.

The plant cell carries out the same processes that generate energy in animal cells (glycolysis, citric acid cycle, and oxidative phosphorylation).

It can generate hexoses from three- or fourcarbon compounds by gluconeogenesis.

It can oxidize hexose phosphates to pentose phosphates with the generation of NADPH (the oxidative pentose phosphate pathway).

I t can produce a polymer of (α1→4)-linked glucose (starch) and degrade it to generate hexoses.

it is not known exactly what functions the hormones perform

each hormone has various effects on plants

none of the hormones can function without the others

each hormone has different effects on different kinds of plants

each hormone works on only a small subset of a cell’s genes at any particular time

tight junction

plasmodesmata

gap junction

anchoring junction

罗马

伦敦

威尼斯

佛罗伦萨

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The mechanism of cytokinesis in higher plants is entirely different from that in animal cells, presumably because plant cells are surrounded by a tough cell wall. The two daughter cells are separated not by the action of a contractile ring at the cell surface but instead by the construction of a new wall that forms inside the dividing cell.

The positioning of this new wall precisely determines the position of the two daughter cells relative to neighboring cells. Thus, the planes of cell division, together with cell enlargement, determine the final form of the plant.

The new cell wall starts to assemble in the cytoplasm between the two sets of segregated chromosomes at the start of telophase. The assembly process is guided by a structure called the phragmoplast, which is formed by the remains of the interpolar microtubules at the equator of the old mitotic spindle.

Small membrane-enclosed vesicles, largely derived from the Golgi apparatus and filled with polysaccharides and glycoproteins required for the cell wall matrix, are transported along the microtubules to the phragmoplast. Here, they fuse to form a disclike, membrane-enclosed structure, which expands outward by further vesicle fusion until it reaches the plasma membrane and original cell wall, thereby dividing the cell in two. Later, cellulose microfibrils are laid down within the matrix to complete the construction of the new cell wall.

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