EnvReg213-page2

EnvReg213-page2 - surface of cells in roots and to the...

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Plant Environmental Regulators - 2 Tropisms and Other Plant Movements There are three common tropisms in plants: Phototropism (light) Gravitropism (gravity) Thigmotropism (pressure or touch) Other tropisms include Chemotropism (chemical) Traumotropism (wounding) Thermotropism (heat) Skototropism (dark) Aerotropism (oxygen) Geomagnetotropism (earth's magnetic fields) Heliotropism (sun tracking) Hydrotropism (water) Gravitropism Gravitropisms are plant growth responses to the forces of gravity. Roots are positively gravitropic and shoots are negatively gravitropic. Negative Gravitropism in shoots Positive Gravitropism in root Auxin is important in gravitropic responses in shoots, but auxin migration in roots is not obvious. Calcium is important in stimulating gravitropic responses in both shoots and roots. Prior to curvature growth, calcium migrates to the lower
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Unformatted text preview: surface of cells in roots and to the upper surface of cells in shoots. Calmodulin, a calcium binding protein, and secondary messenger in signal transduction pathways, mediates the calcium migration. Elongation occurs in the walls with the lowest calcium levels. Cytokinins are also important to gravitropism. Roots grown normally have uniform distribution of cytokinins in their root tips. Within minutes of placing a root tip horizontally, cytokinins are distributed asymmetrically in the root. Concentration of cytokinins on the lower side of the root inhibits elongation on that side, while lowered concentration of cytokinins on the upper side of the root favors elongation that will orient the growing tip back towards gravity....
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