Interspecific Genome Size (2C DNA) Variation in Some Ornamental and Medicinal Plants: Is It a Phenomenon of Partial Sequence Amplification or Loss?

The flow cytometry technique has currently been employed in various fields of research, especially in measuring the 2C DNA of plants. The technique is also used in modern biosystematics, speciation, evolutionary studies and in molecular breeding. A large number of tissue culture raised ornamental and medicinal plants’ DNAs are currently made and compared with field grown plants. Various factors influence the quality of active nuclei isolation, which determines the success of accurate DNA estimation. The importance of extraction buffer, reference standards, fluorochrome dyes, and the process of gating is highlighted in order to understand various steps of flow cytometry in measuring DNA. An array of compounds act as inhibitors to disrupt fluorochrome binding to DNA, causing errors in estimating nuclear DNA content; these compounds with their families are presented and summarized. Micropropagation using shoot tips and nodal stems produces true-to type plants, while callus regenerated plants show somaclonal variations – a process showing altered DNA. The role of flow cytometry in investigating the genetic homogeneity of tissue cultured plant population is therefore reviewed. The 2C DNA and genome size of a few medicinal and ornamental plants such as Catharanthus, Allium, Rawolfia, Gladiolus, Caladium, Zephyranthes from authors’ laboratory were measured and described. The intra-specific and inter-specific genome size and chromosome number variation with reference to gene duplication and DNA sequence loss are discussed. The present chapter, in general, discusses the applications of flow cytometry in field and tissue culture grown ornamentals and medicinal plants.