Root Nodules Caused by Frankia Actinorhizal Symbiosis

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Actinorhizal Plants Frankia Induced Nodulation Root Nodules Caused by Frankia Actinorhizal Symbiosis Cross Inoculation Experiments Isolation and Characteristics of Frankia Cultural Characteristics of Frankia Taxonomy of Frankia Entry of Frankia to the Host Plant Structure of Actinorhizal Nodule

Root Nodules Caused by Frankia Actinorhizal Symbiosis

Root Nodules Caused by Frankia (Actinorhizal Symbiosis)
Apart from legumes nodulated by bacteria of the genus Rhizobium, roots of some plants belonging to diverse families are also nodulated by members of actinomycelates (tentatively classified in the genus Frankia) and fix considerable amounts of nitrogen. Alder trees (Alnus spp.) are known to recuperate soil nitrogen in temperate forest ecosystems.

This is a well-recognised fact all over the world in forest management. Under field conditions, nodules of Alnus and Casuarina occur in clusters attaining a diameter of 5 to 6cm somewhat resembling a tennis ball, often weighing up to 444 kg dry weight of nodules/ha.

Field estimates have shown that alder trees increase the nitrogen content of soil by about 61.5 to 157 kg N/ha/year and Casuarina trees release about 60 kg N/ha/year which indicate the importance of root nodule bearing non-leguminous plants in the overall nitrogen economy of soil.

Actinorhizal Root Nodules

Actinorhizal Root Nodules	Young Nodule Lobes, Degenerating Nodule Lobes

The term actinorhiza and actinorhizal plants is derived from 'actino' for the actinomycete Frankia named after its discoverer Frank in the 1880s and "rhiza' for the plant root bearing the nodules formed by symbiosis.

In developing countries, deforestation for fuel has rendered the land barren and continuous deforestation of the same land in overpopulated regions of such countries has resulted in soils which remain deficient in nitrogen, the most important element for the normal growth of plants.

One of the least expensive and non-polluting ways to replenish the lost soil nitrogen is reafforestation by planting self-supporting nitrogen-fixing trees.

In Pennsylvania, U.S.A., reafforestation of mine spoils have been done by planting nitrogen fixing red alder (Alnus rubra) inoculated with nodule forming Frankia. In New Quebec, Canada, alder plants (Alnus spp.) have been planted on a large scale to fill dam dykes. In Senegal, Egypt, and the coastal region of India and China nitrogen-fixing Casuarina spp. have been planted on a large scale to contain and stabilise sandy tracts which have made inroads to agricultural land.
There are 24 genera from 8 Angiosperm families which have been described to possess actinorhizal root nodules.

These genera with families mentioned in parentheses, from most primitive to most advanced orders,are Coriaria (Coriariaceae), Cerocarpus, Chamaebatia, Cowania, Dryas, Purshia, Rubus Rosaceae, Datisca (Dastiscaceae), Comptonia, Myrica (Myricaceae), Alnus (Betulaceae), Elaeagnus, Hippophae, Shepherdia (Elaeagnaceae), Coenothus, Colletia, Discaria, Kentrothamnus, Retamnilla, Talguenea, Trevoa (Rhamnaceae), Allocasuarina, Casunrina and Gymnostoma (Casuarinaceae). The genera Casuarina for tropical and sub-tropical regions and Alnus

(A. rubra., A. glutinosa, A. crispa, A. jorullensis, A. acuminata) for temperate regions stand out as excellent examples for the benefits they provide to the ecosystems by way of nitrogen inputs. They can adapt themselves to grow under most diverse.

environmental conditions and geographical zones. Casuarina species (C. equisetifolia. C. cunninghamiana, C. littoralis, C. stricta, C. junghuniana, C. glauca and C. torulosa) provide substantial fuel and building materials in tropical countries while alders provide the most utilised hard wood as well as bark for paper industries in temperate regions. The microsymbiont in actinorhizal root nodules is an actinomycete and has been collectively designated as Frankia.

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Nitrogen Fixation and Assimilation Field Experiments on the Benefit of Frankia Inoculation Mycorrhizae and Actinorhizal Plants Proteoid Roots Genetics of Frankia Rhizobium Induced Root Nodulation of Parasponia Leaf Nodules Gymnosperm Nodules

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