Laboratory techniques of studying plant chromosomes

Abstract

Study of chromosomes helps in revealing the basic number, structure, and behavior of chromosome complement of a particular species which can then be compared with that of another species. The properties of chromosomes remain constant within a particular species and change only upon hybridization and/or evolution. As such, by studying the chromosomes, the parental lineage or evolutionary history can be elucidated. Also, we can find a relation between the chromosome complement and the phenotype of the species. On the basis of the properties of the chromosome complement, various taxonomic rearrangements have been made. Several of the plant species are polyploid, having a multiple set of basic chromosomes. The sterility and fertility of a species can be ascertained to the odd or even number of chromosome complement, respectively. The biggest challenge in chromosomal study is to obtain deeply stained, condensed chromosomes with well-defined primary and secondary constrictions. For this, every step is optimized according to the type of tissue and the type of species being studied. For this a variety of metallic and nonmetallic chemicals have been used in combination for fixation with varied time durations accompanied with different types of stains. Sometimes the use of mordants becomes necessary in order to enhance the staining properties. The traditional method of chromosome study by sectioning has largely become outdated and replaced by fast, easy, and low-cost squash and smear techniques. The meiotic chromosomes are studied through anther smear, whereas the somatic chromosomes are commonly studied through root tip squashing. Lately, chromosomal banding techniques have proved to be an additional tool in the hands of cytogeneticists for detailed chromosomal studies. In this chapter an attempt has been made to revisit the available procedures for studying plant chromosomes through squash and smear techniques and the fixatives and stains used therein in light of the available literature.