RHIZOBIAL COMMUNICATION WITH RICE ROOTS - INDUCTION OF PHENOTYPIC CHANGES, MODE OF INVASION AND EXTENT OF COLONIZATION

Citation
Pm. Reddy et al., RHIZOBIAL COMMUNICATION WITH RICE ROOTS - INDUCTION OF PHENOTYPIC CHANGES, MODE OF INVASION AND EXTENT OF COLONIZATION, Plant and soil, 194(1-2), 1997, pp. 81-98
Citations number
70
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Agriculture Soil Science","Plant Sciences",Agriculture
Journal title
ISSN journal
0032-079X
Volume
194
Issue
1-2
Year of publication
1997
Pages
81 - 98
Database
ISI
SICI code
0032-079X(1997)194:1-2<81:RCWRR->2.0.ZU;2-3
Abstract
Legume-rhizobial interactions culminate in the formation of structures known as nodules. In this specialized niche, rhizobia are insulated f rom microbial competition and fix nitrogen which becomes directly avai lable to the legume plant. It has been a long-standing goal in the fie ld of biological nitrogen fixation to extend the nitrogen-fixing symbi osis to non-nodulated cereal plants, such as rice. To achieve this goa l, extensive knowledge of the legume-rhizobia symbioses should help in formulating strategies for developing potential rice-rhizobia symbios es or endophytic interactions. As a first step to assess opportunities for developing a rice-rhizobia symbiosis, we evaluated certain aspect s of rice-rhizobia associations to determine the extent of predisposit ion of rice roots for forming an intimate association with rhizobia. O ur studies indicate that: a. Rice root exudates do not activate the ex pression of nodulation genes such as nodY of Bradyrhizobium japonicum USDA110, nodA of R. leguminosarum by. trifolii, or nodSU of Rhizobium. sp. NGR234; b. Neither viable wild-type rhizobia, nor purified chitol ipooligosaccharide (CLOS) Nod factors elicit root hair deformation or true nodule formation in rice; c. Rhizobia-produced indole-3-acetic ac id, but neither trans-zeatin nor CLOS Nod factors, seem to promote the formation of thick, short lateral roots in rice; d. Rhizobia develop neither the symbiont-specific pattern of root hair attachment nor exte nsive cellulose microfibril production on the rice root epidermis; e. A primary mode of rhizobial invasion of rice roots is through cracks i n the epidermis and fissures created during emergence of lateral roots ; f. This infection process is nod-gene independent, nonspecific, and does not involve the formation of infection threads; g. Endophytic col onization observed so far is restricted to intercellular spaces or wit hin host cells undergoing lysis. h. The cortical sclerenchymatous laye r containing tightly packed, thick wailed fibers appears to be a signi ficant barrier that restricts rhizobial invasion into deeper layers of the root cortex. Therefore, we conclude that the molecular and cell b iology of the Rhizobium-rice association differs in many respects from the biology underlying the development of root nodules in the Rhizobi um-legume symbiosis.