植物的向性（Tropism of plants）.docVIP

植物的向性（Tropism of plants） A tropism for sexual activity. It is the directional movement of plants caused by gravity. Positive and negative. The direction of the reaction toward the gravity of the earth is called positive, such as the root is always downward growth; the direction of the reaction is contrary to the gravity of the earth, called negative, such as the growth of the stem, or rice and wheat after lodging, but also stand up. Relating to the causes of fertility, generally attributed to uneven distribution of auxin caused by gravity. When the stem flat when more auxin to rely on one side, so the cell growth speed, stem showed apogeotropic. In the root, while the auxin distribution too, but the root of auxin sensitive trace auxin promoting growth effect, and when the content of IAA is slightly long, the root growth was inhibited but, therefore the upper auxin content of fast growth, the roots, and show positive geotropism. . Recent studies have suggested that the root cap produces abscisic acid (abscisic, acid) to inhibit the growth of cells in the root of the root, and that the underside is slow to grow and that the upper side is growing fast, so that the root is bent toward the center of the earth. The root tip cell contains large, heavy starch plastids (amyloplast), which are stored in large central fluid cells (vacuoles), which sink and the cell moves to bend the roots. The reason may be that plastids contain very high concentrations of hormone (Root-inhibiting), which inhibit the elongation of cells in contact with plastids and, therefore, bend the roots. The directional movement of a plant caused by a single direction of gravity, as the root has a downward, positive growth; the stalk has a negative growth direction; the stem has a horizontal, horizontal, etc growth in the horizontal direction. Also called dampness. The characteristics of roots tending to grow wetter when soil moisture distribution is uneven. The roots of most higher plants are positively