Aluminum toxicity studies in rice (Oryza sativa L.) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5t34sn245

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  • A nutrient solution technique developed for wheat was used to determine tolerance of rice cultivars to aluminum (Al) toxicity. Pre-germinated rice seed was placed on top of a screen and allowed to grow on the Al-free solution for 72-96 hours or until the primary root was 2-3 cms long. Seedlings were then transferred to the Al containing solution. After 96 hours the primary root length was measured and seedlings were transferred back to the Al-free solution. Forty-eight hours after removal from the Al treatment, the primary root was again measured and the rate of recovery (difference between the two measurements) was taken as a criteria for Al toxicity. Aluminum concentration, nutrient composition, pH, and temperature of the nutrient solutions, as well as time of exposure to the Al treatment were rigidly controlled. Solutions were also aerated. Monolaya and Bluebonnet 50 were found to be tolerant to Al toxicity when exposed to either 20 or 25 ppm Al for 96 hours in a one-tenth strength nutrient solution at pH 4 and 25 °C±1. Cultivars such as Colombia 1, CICA 4, IR 5, IR 8 and IR 665-23-3-1 were sensitive. All the cultivars were sensitive at 30 ppm Al when grown under the same conditions. The sensitivity of plants to Al toxicity also appeared to be influenced by environmental factors. Root tip samples were taken at various times during and after the Al treatment. Microscopic examination revealed no differences in the root anatomy of sensitive and tolerant cultivars when grown in the absence of Al. The boundary between the root cap and root apex was the first area penetrated by aluminum, and from there, Al possibly penetrated into the meristematic cells of the vascular cylinder. Aluminum also penetrated the epidermis and cortex. Cell desintegration and desorganization were noticed as a result of the Al treatment. Lateral roots were initiated in the pericycle at or near the root tip in sensitive cultivars after only 48 hours of Al treatment. This was not observed to happen in tolerant cultivars. This lateral root development could have resulted from Al destroying the apical dominance of the primary root meristem. Acetocarmine root squashes showed that mitotic activity declined rapidly; particularly in sensitive cultivars. Furthermore, tolerant cultivars differed significantly from sensitive types in number of mitotic figures present during and after the Al treatment. Nevertheless, no abnormalities were observed in the mitotic process. That is, no one particular stage of mitosis was impeded by Al, but the whole process was inhibited. After removal from the Al treatment, mitotic activity increased quickly in tolerant cultivars but remained at a very low level in sensitive types. Crosses between cultivars representing different levels of tolerance were made to learn the mode of inheritance of tolerance to Al toxicity. Twenty parts per million of Al were used to screen the parents, F₁'s and selected segregating populations. Results indicated that this kind of tolerance is recessive and simply inherited. Furthermore, two major genes appeared to condition this trait. Genes for Al tolerance in Monolaya and Bluebonnet 50 appeared to be allelic. These genes seemed to have various degrees of expression, and/or incomplete penetrance. Following the recommended procedures for gene symbolization in rice, the two gene pairs for Al tolerance in Monolaya and Bluebonnet 50 are designated alu 1. alu 1, alu 2 alu 2.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-10-24T17:34:33Z (GMT) No. of bitstreams: 1 Martinez-RacinesCesar1977.pdf: 1361333 bytes, checksum: ed9f1ab752e564097387c3470748535e (MD5)
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