Mycorrhizae is a symbiotic relationship that is shown by fungi and the Gymnosperms. Mycorrhiza shows a mutually beneficial relationship between the fungus and the roots of higher plants such as that of Gymnosperms and Angiosperms. The mycorrhizal fungi get the nourishment from the root cortical cells of the plant and in turn, these mycorrhizal fungi provide surface area for the plant so that its absorption capacity increases. The mycorrhizal association is seen in the roots of Pinus and Orchid plants. After learning about mycorrhizae meaning we will study it in more detail below. Also, the mycorrhizae are mainly made from fungi and associated with gymnosperms so we will study them too.
Fungi is one of the important parts of this mycorrhizal association. Fungi is the third kingdom after the Monera and Protista. The body of fungi is haploid. They have a thalloid type of body structure. This means that their body is not differentiated into roots, stem and leaves. Yeast is unicellular fungi and rests all other fungi are multicellular. Hyphae are thread-like elongated structures that are present in the body of fungi. The fungi grow in warm and humid places. They are cosmopolitan in nature, which means that they are present everywhere be it air, water, soil and even on the body of plants and animals. The nature of their hyphae is aseptate and multinucleate. This type of hyphae is called coenocytic hyphae. But, in the majority of the fungi, their hyphae are separate in nature. There are pores present in the septum and hence it is not continuous in nature. The simple pore is present in ascomycetes but in basidiomycetes, dolipore septum is present. Chitin and fungal cellulose are present in the cell wall of fungi. It is basically made up of acetylglucosamine that is a polysaccharide that contains nitrogenous compounds.
Some fungi have cell walls that are made up of cellulose. Oil and glycogen are the reserved food materials. Unicisternal Golgi bodies are present in them. Mitosis takes place in them and in this mitosis, the spindle fibres are formed intracellularly. The fungi have a heterotrophic mode of nutrition with a presence of the digestive tract. They also show the saprophytic, parasitic and symbiotic mode of nutrition. Two types of phases are present that are vegetative and reproductive phases. The mycorrhizal fungi examples are commonly all basidiomycetes and one of them is Boletus. The fungi help the plants by increasing the surface area for the absorption of minerals. They also help in increasing the supply of nitrogen and phosphorus to the plant.
Gymnosperms are the other important part of the mycorrhizal association. These plants are associated with the fungi and they provide shelter and nourishment to the fungi. The gymnosperms have medium-sized trees along with herbs and shrubs. The male and female gametophytes in the gymnosperms do not have a free-living existence. In their life cycle, a diploid sporophytic phase is present. Proper differentiation of roots, stems and leaves is present in the gymnosperms. The stems of the gymnosperms can be branched and unbranched in nature. The leaves present in the gymnosperms can be of a simple type and compound type. Pinnate leaves are also present in the gymnosperms. Vascular tissues such as Xylem and Phloem are also present in these gymnosperms.
They are heterosporous. This means that the size of their gametes is different. The male gametophyte is smaller in nature whereas the female gametophyte is larger than the male gametophyte. In Gymnosperms the male and the female organs can be present in the same tree and sometimes on different trees as well. The pollen grains of these gymnosperms are carried out by air current. These pollens reach the opening of the ovules that are present on the megasporophylls. A zygote is formed after the process of fertilization. Zamia is the smallest gymnosperm and Sequoia is the largest gymnosperm.
Types of Mycorrhiza
The mycorrhiza is a structure that is formed for a symbiotic association of fungi and gymnosperms. The fungus in this is associated with the roots of higher plants. They are generally the gymnosperms and angiosperms and this structure together is known as mycorrhiza. The roots of the mycorrhiza are different in their shape from the normal roots. These roots have a woolly covering on them. Root cap and root hairs are also absent on them. A fungus can form an association with many numbers of plants and in the same way, many plants can form an association with the fungus. Based on the location, the mycorrhiza is of two types that are ectomycorrhizal and endomycorrhiza. In ectomycorrhiza, the fungal part is external in nature. It forms a woolly covering on the external surface of the roots and thus helps in forming a network of mycelium. This network is formed in the intercellular spaces of the cortex. Basidiomycetes and zygomycetes are the majority of the fungal partners. In the endomycorrhiza, the hyphae are present in the tissues of the roots. It then spreads intracellularly and also intercellularly. The cell wall is broken by the fungus and it enters the cortex region. It is known as a symbiotic relationship because both partners are benefited from it. The fungal part is dependent on the cortical cells of the root for nourishment and shelter. The fungal parts help in absorbing the nitrogen, minerals, phosphorus and water from the soil. Pine trees will show stunted growth if fungi are not associated with their roots.
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