Endo Mycorrhizae

Endo Mycorrhizae

endomycorrhizae

Figure 5.16 Mycorrhizae. A. A diagram of a cross section of a root with ectomycorrhizae (visible on the outside of the root). B. Comparison, in longitudinal section, of a root without ectomycorrhizae and one with ectomycorrhizae. C. Photomicrograph of a cross section of a root around which ectomycorrhizae have formed a mantle. The fungal cells have not penetrated deeper than the outermost layers of root cells. D. A cross section of a few root parenchyma cells with endomycorrhizae. The endomycorrhizae develop and flourish within the parenchyma cells.

endomycorrhizae

Figure 5.16 Mycorrhizae. A. A diagram of a cross section of a root with ectomycorrhizae (visible on the outside of the root). B. Comparison, in longitudinal section, of a root without ectomycorrhizae and one with ectomycorrhizae. C. Photomicrograph of a cross section of a root around which ectomycorrhizae have formed a mantle. The fungal cells have not penetrated deeper than the outermost layers of root cells. D. A cross section of a few root parenchyma cells with endomycorrhizae. The endomycorrhizae develop and flourish within the parenchyma cells.

78 Chapter 5

78 Chapter 5

Endomycorrhizae
Figure 5.17 Root nodules on the roots of bur clover (Medicago polymorpha). The somewhat popcornlike nodules contain bacteria that convert nitrogen from the air into forms that can be used by the plant, x 5.

root nodules that are clearly visible when such plants are uprooted (Fig. 5.17). The nodules contain large numbers of nitrogen-fixing bacteria.

A substance exuded into the soil by plant roots stimulates Rhizobium bacteria, which, in turn, respond with another substance that prompts root hairs to bend sharply. A bacterium may attach to the concave side of a bend and then invade the cell with a tubular infection thread that does not actually break the host cell wall and plasma membrane. The infection thread grows through to the cortex, which is stimulated to produce new cells that become a part of the root nodule; here the bacteria multiply and engage in nitrogen conversion. (See also the discussion of the nitrogen cycle in Chapter 25.)

Root nodules should not be confused with root knots, which are also swellings that may be seen in the roots of tomatoes and many other plants. Root knots develop in response to the invasion of tissue by small, parasitic round-worms (nematodes). Unlike bacterial nodules, root knots are not beneficial, and the activities of the parasites within them can eventually lead to the premature death of the plant.

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  • mikko
    Is the flowering plants mycorrhiza?
    7 years ago

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