Masters Theses

Date of Award

12-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

Leslie G. Hickok

Committee Members

L.W. Jones, O.J. Schwarz

Abstract

Aluminum toxicity, associated with acid soil conditions, has received much attention in the recent literature because it can limit plant growth. Although much work has been done, more needs to be done to develop an understanding of the mechanisms of aluminum toxicity and aluminum tolerance. One research method is the development of single gene mutants that have altered response compared to the wild type when grown under aluminum-toxic conditions.

This study uses the fern Ceratopteris richardii to select and characterize mutants selected for aluminum tolerance. Mutations were induced in wild type spores with x-rays and screened for tolerance on medium containing Al-EDTA at pH 4.5. Thirty putative mutants were isolated and were available for this study. Of the six confirmed mutants, three (HαAT3, HαAT7, and HαAT29) were characterized.

The mutants were characterized morphologically. The mutants HαAT3 and HαAT29 were normal in the gametophyte stage. The mutant HαAT7 was morphologically normal in the gametophyte stage except it produced fewer rhizoids than the wild type at all levels of pH. This is not presumed to be the basis of tolerance, because the rhizoids would have to have aluminum specific uptake.

The relative tolerance levels of the mutants were determined by comparing their growth to the growth of the wild type on media that contained a range of Al-EDTA. Because of the complexity of the selection medium, testing was done to determine if the mutants were tolerant to aluminum and\or the individual components modified in the selection medium. The presence of additional sulfate in the selection medium was not considered significant in causing the response shown in the original screening. EDTA tolerance testing showed that the mutants HαAT3B and HαAT29 were EDTA tolerant. All three mutants had a lower pH optimum for growth than the wild type and were acid tolerant.

Genetic analyses were performed to determine the genetic basis of tolerance. Segregation analysis showed that tolerance in HαAT3 is due to a single nuclear gene. Tolerance in HαAT7 is probably controlled by a single nuclear gene, but epigenetic factors also play a large role in the extent of tolerance shown by the gametophytes and prevent the absolute determination of how many genes control tolerance. HαAT29 exhibited a complex mode of inheritance, but tolerance appeared to be under nuclear control. The number of genes controlling tolerance could not be determined from the tests performed.

Tests on sporophytes were performed in an attempt to characterize the parental response. A method that produced a response in the wild type was developed, but the mutants' responses were not fully determined.

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