Chromosome counts and male meiosis in two species of Pleurospermum Hoffm. (Apiaceae): additional comments on the cytogeographic pattern of the genus

Abstract

Pleurospermum Hoffm. (Apiaceae), a widely spread, heterogeneous genus of complex and controversial taxonomy, is poorly known for chromosome number and meiotic details from the Indian subcontinent. In the current study, we examined male meiosis, chromosome counts, and pollen fertility in two species, P. candollii and P. govanianum from alpine areas of north-west Indian Himalaya. Both the species exist at diploid level (P. candollii, n = 11 or 2n = 22, P. govanianum, n = 9 or 2n = 18) with two different basic chromosome numbers, x = 9 and 11. Meiotic course in the majority of pollen mother cells (PMCs) is normal; however, few meiocytes showed the occurrence of chromatin transfer among themselves which resulted into the formation of hypoploid and hyperploid PMCs. In addition, some PMCs depicted associated irregularities such as laggards, and chromatin bridges during meiosis-I and II. Microsporogenesis was also observed to be abnormal, and was characterized by the presence of micronuclei in the sporads. Owing to low frequency of meiotic irregularities, pollen fertility was not affected to greater extent; however, variable sized pollen grains were noticed in P. candollii. Analysis of previously published chromosome data revealed that there is no specific cytogeographic pattern formed for the genus on the basis of which we can construct any geographic segregation between the two basic numbers, x = 9 and 11. However, in a broader sense two overlapping zones seems to appear for the two basic numbers in the East, central and south Asia.

Keywords:

• Chromosome
• cytomixis
• pollen mother cells (PMCs)
• north-west Himalaya
• Chamba
• Lahaul-Spiti

Acknowledgements

The authors are very grateful to the Head of the Department of Botany, Punjabi University, Patiala and Dr Paramjit Singh, Director, Botanical Survey of India, Headquarters Kolkata and Joint Director, NRC, Dehradun, for necessary laboratory, Herbarium (PUN, BSD) and library facilities.