Molecular phylogenetic relationships among four species of the mangrove tree genus Bruguiera (Rhizophoraceae), as revealed by chromosome and RAPD markers

Analysis of karyotype, nuclear DNA content and RAPD markers were performed in four species of Bruguiera (Rhizophoraceae) of Bhitarkanika mangrove forests, Orissa, India. Detailed karyotype analysis revealing 2n=34 in B. cylindrica and 2n=36 in B. gymnorrhiza was reported for the first time and 2n=34 in B. parviflora and B. sexangula was confirmed. On the basis of the common types of chromosomes present among Bruguiera, two distinct groups were found; one consists of B. cylindrica and B. parviflora and the other of B. gymnorrhiza and B. sexangula. The symmetrical karyotype with same chromosome types grouped B. cylindrica and B. parviflora together and presence of Type E chromosomes placed B. gymnorrhiza and B. sexangula in a separate group, suggesting their closer affinity in their respective group. Analysis of chromosome length, volume, INV and 4C DNA content confirmed this division. Nuclear DNA content was two-fold higher (~17.0 pg) in the second group than in the first (~8.0 pg). The amplification products generated through RAPD revealed 1-9 amplicons with size variations from 600 bp to 2 500 bp with 49.31% genetic similarity between B. gymnorrhiza and B. sexangula and 47.10% in between B. cylindrica and B. parviflora. The high copy number marker band (~ 1 100 bp) yielded in OPN-15 primer in B. parviflora the characteristic DNA marker, which was cloned and used as probes for assessment of genetic diversity, and demonstrated its close genetic affinity to B. cylindrica. B. gymnorrhiza and B. sexangula also produced similar marker bands of ~600 bp and ~2 200 bp in the same primer. All of the cytological, 4C DNA content and RAPD data confirmed the existence of two taxonomically distinct groups of Bruguiera: one consisting of B. cylindrica and B. parviflora and the other of B. gymnorrhiza and B. sexangula as placed earlier (1862) in the tribe Rhizophoreae by Bentham and Hooker, on the basis of the flowering habits of Bruguiera. Genetically, the B. sexangula and B. gymnorrhiza group was found to be very closely, rather than distantly, related to B. parviflora and B. cylindrica. Our results demonstrate that molecular markers together with cytological evidence provide an effective tool to access the existing interspecific genetic polymorphism in mangrove species, to solve the taxonomic problems and to design their conservation strategy. Rev. Biol. Trop. 55 (2): 437-448. Epub 2007 June, 29.

Estudiamos cuatro especies del mangle Bruguiera (Rhizophoraceae) en Orissa, India. Los cromosomas indican queB. cylindrica y B. parviflora son un grupo taxonómico, y que B. gymnorrhiza y B. sexangula son otro. Genéticamente, el par B. sexangula y B. gymnorrhiza está cercanamente emparentado con B. parviflora and B. cylindrica. Nuestros datos indican que el uso combinado de marcadores genéticos y evidencia citológica permiten discernir el polimorfismo genético interespecífico en los mangles, tanto para resolver problemas taxonómicos como para diseña estrategias eficaces de conservación.

Molecular phylogenetic relationships among four species of the mangrove tree genus Bruguiera (Rhizophoraceae), as revealed by chromosome and RAPD markers.

Analysis of karyotype, nuclear DNA content and RAPD markers were performed in four species of Bruguiera (Rhizophoraceae) of Bhitarkanika mangrove forests, Orissa, India. Detailed karyotype analysis revealing 2n=34 in B. cylindrica and 2n=36 in B. gymnorrhiza was reported for the first time and 2n=34 in B. parviflora and B. sexangula was confirmed. On the basis of the common types of chromosomes present among Bruguiera, two distinct groups were found; one consists of B. cylindrica and B. parviflora and the other of B. gymnorrhiza and B. sexangula. The symmetrical karyotype with same chromosome types grouped B. cylindrica and B. parviflora together and presence of Type E chromosomes placed B. gymnorrhiza and B. sexangula in a separate group, suggesting their closer affinity in their respective group. Analysis of chromosome length, volume, INV and 4C DNA content confirmed this division. Nuclear DNA content was two-fold higher (approximately 17.0 pg) in the second group than in the first (approximately 8.0 pg). The amplification products generated through RAPD revealed 1-9 amplicons with size variations from 600 bp to 2 500 bp with 49.31% genetic similarity between B. gymnorrhiza and B. sexangula and 47.10% in between B. cylindrica and B. parviflora. The high copy number marker band (approximately 1,100 bp) yielded in OPN-15 primer in B. parviflora the characteristic DNA marker, which was cloned and used as probes for assessment of genetic diversity, and demonstrated its close genetic affinity to B. cylindrica. B. gymnorrhiza and B. sexangula also produced similar marker bands of approximately 600 bp and approximately 2,200 bp in the same primer. All of the cytological, 4C DNA content and RAPD data confirmed the existence of two taxonomically distinct groups of Bruguiera: one consisting of B. cylindrica and B. parviflora and the other of B. gymnorrhiza and B. sexangula as placed earlier (1862) in the tribe Rhizophoreae by Bentham and Hooker, on the basis of the flowering habits ofBruguiera. Genetically, the B. sexangula and B. gymnorrhiza group was found to be very closely, rather than distantly, related to B. parviflora and B. cylindrica. Our results demonstrate that molecular markers together with cytological evidence provide an effective tool to access the existing interspecific genetic polymorphism in mangrove species, to solve the taxonomic problems and to design their conservation strategy.

Effect of a low dose of aluminum on mitotic and meiotic activity, 4C DNA content, and pollen sterility in rice, Oryza sativa L. cv. Lalat.

Aluminum toxicity in acidic soils poses a major threat to plant growth and development. The effects of a low dose of aluminum (50 microM, AlCl3) on various cytological parameters, including mitotic and meiotic chromosomal divisions, in situ nuclear DNA content, interphase nuclear volume (INV), and pollen fertility were compared in untreated (controls) and treated rice plants (Oryza sativa cv. Lalat). The results showed varied chromosomal abnormalities, including chromosome stickiness, laggards, sticky bridge, occurrence of micronuclei, as well as binucleate and multinucleated cells, as a result of aluminum treatment. Aluminum toxicity also inhibited to a small extent the growth of the rice cultivar Lalat. The mitotic and meiotic indexes, even after a prolonged period of recovery, were significantly low. The chromosomal anomalies in the meiotic cells persisted, and plants exhibited a high percentage of pollen sterility (approximately 64%). The nuclear DNA content declined markedly from 11.85 pg in the control to 6.30 pg in the treated plants. The INV also varied significantly between the untreated (controls) and the treated plants. The occurrences of different types of chromosomal aberrations, reduction in the amount of nuclear DNA, and persistence of the phytotoxic effects at the post-treatment stage suggest carcinogenic effects of aluminum on rice plants. The presence of aluminum in acidic soils might thus be extremely hazardous and might cause permanent cytotoxic disorder in rice plants.