Estudio cromosómico en tres especies de Karwinskia (Rhamnaceae) endémicas de México

Abstract

MERISTEMATIC ROOT CELLS FROM GERMINATING SEEDS OF 5-10 INDIVIDUALS OF EACH OF THE FOLLOWING SPECIES: KARWINSKIA MOLLIS (GUADALCAZAR, SAN LUIS POTOSI). K. TEHUACANA (ATOYATEMPAN, PUEBLA) AND K. UMBELLATA (AHUETZINGO, MORELOS) WERE CYTOGENETICALLY ANALIZED. THE CHROMOSOME NUMBER OF 2N=24 WAS CONSTANT IN THE THREE SPECIES WITH A BASIC NUMBER OF X=12; TOTAL DIPLOID CHROMOSOME LENGTH AND CHROMOSOME INTERVAL WERE ALSO OBTAINED. THE CHROMOSOME COMPLEMENTS WERE CHARACTERIZED BY VERY SMALL CHROMOSOMES (0.68-1.28 MM), PREDOMINATING THOSE WITH MEDIAN AND SUBMEDIAN CENTROMERES. THE SMALLEST CHROMOSOME PAIR OF EACH SPECIES PRESENTED A SECONDARY CONSTRICTION, ASSOCIATED TO A MARKED SATELLITE PORTION. THE COMPARISON OF THESE DATA WITH THOSE PREVIOUSLY REPORTED FOR K HUMBOLDTIANA SUGGESTS THAT CHROMOSOMAL CHANGES PROBABLY HAVE HAD A SCARCE INFLUENCE IN SPECIATION EVENTS OF KARWINSKIA: HOWEVER, THE DIFFERENCES IN SIZE OF THE CHROMOSOME COMPLEMENTS ARE CONSIDERED AS A POSSIBLE EXPLANATION FOR THE PRESENT DISTRIBUTION OF THESE SPECIES.