Karyotypic Analysis of Two Diploid Species of Crotalaria (Fabaceae, Papilionoideae) with Different Degrees of Floral and Foliar Specialization

Abstract

An enzymatic maceration and Giemsa staining method was used to compare the karyotypes of Crotalaria laburnifolia (trifoliate) and C. spectabilis (simple leaves) species belonging to distinct morphological sections and with different degrees of floral specialization. Both taxa share a 2n=16, asymmetric chromosome complement, and relatively similar karyotypic formulae. However, morphological differences in chromosome-SAT, chromosome sizes, and other related parameters stand out. Although the secondary constrictions (SC) and associated satellites are located on short arms of metacentric chromosomes, their position and size are different. In C. laburnifolia, the satellites were detected on the second chromosomal pair and not on the first, as is usual in Crotalaria, representing less than half of the short arm length. In contrast, in C. spectabilis, the satellites are located on the first pair and their size occupies most of the short arm. The role of SCs as nucleolus organizing regions (NORs) was corroborated in prometaphase cells, as they were frequently observed adjacent to or even embedded in a single large nucleolus. Furthermore, the possible relationship between floral specialization and leaf morphology is discussed concerning the chromosome sizes obtained. It is confirmed that the karyotypic characterization in Crotalaria is favorable and that chromosomal diversity provides valuable information on the organization and evolution of its karyotypes.