Thin cell layers: developmental building blocks in ornamental biotechnology

The capacity to control developmental and morphogenetic processes in vitro has always been the fascination and primary focus of many ornamental tissue culture studies. Thin cell layers or TCLs were first used to control the development of flowers, roots, shoots and somatic embryos in tobacco pedicels. Since those studies over 30 years ago, TCLs have been successfully used in the micropropagation of many ornamental plant species whose previous in vitro morphogenetic pathways were not clearly defined using conventional methods. TCL technology focuses on the size and origin of the explant, which, when appropriately chosen, serves as a fine-scale developmental block for regeneration and transformation. This review highlights the fundamentals of TCLs, and their application in ornamental plant micropropagation and transformation.