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Genetic studies of the red mangrove Rhizophora mangle L.
Abstract
The frequency of red mangrove trees, Rhizophora mangle L., that were monohybrid heterozygotes for chlorophyll deficient alleles was determined for populations along the southwest coast of Puerto Rico. Segregation ratios for these trees were also calculated. Although nuclear, the different mutant homozygous genotypes had profound effects on chloroplast development and ultrastructure. In comparison to R. Mangle populations in Florida and San Salvador Island, Puerto Rican mangroves were more outcrossed (28.8% vs. 4.8%) and had lower per generation per genome mutation rates for chlorophyll-deficient mutations ($\rm 2.1\times10\sp{-3}\ vs.\ 5.8\times10\sp{-3}).$ The homozygous albino offspring from 11 different red mangrove trees (Rhizophora mangle) heterozygous for albinism were pigment fingerprinted by high-performance liquid chromatography/diode-array spectroscopy (HPLC/DAS). The majority of albino genotypes were deficient in suites of chlorophylls, xanthophylls and carotenes. A total of 5 different chemical phenotypes was distinguished. In red mangroves, genetic load due to homozygosity for chlorophyll-deficiency follows the mutation load model of Muller (1950), i.e. small load contributions are made by many different loci. The average load contribution is $1.3\times10\sp{-4}$ homozygous albino offspring per locus. Red mangrove (Rhizophora mangle) has shoot apices with a tunica-corpus organization; consequently somatic mutations are often manifested as complete or partial periclinal chimeras. Trees with branch systems exhibiting such chimeras for chlorophyll-deficiency are rare in natural populations. Less than 0.1% of red mangroves in Puerto Rico exhibit such chimeras. The detailed analysis of one such chimera (R35) revealed a number of unique characteristics. The mutant exhibited cytoplasmic inheritance, a pattern consistent with a plastid genome mutation. Based upon ultrastructural analysis of the guard cells and histological patterns in the apices and leaves, the mutant is in the LI histogen of the shoot apex (outer tunica). The LI in red mangrove gives rise to a protoderm that can divide periclinally. This results in sporogenous tissues and mesophyll cells along the leaf margins that are LI derived.
Subject Area
Genetics|Botany
Recommended Citation
Lowenfeld, Robin C, "Genetic studies of the red mangrove Rhizophora mangle L." (1996). Doctoral Dissertations Available from Proquest. AAI9619418.
https://scholarworks.umass.edu/dissertations/AAI9619418