Physical methods for the transformation of plant cells.

Transfer and expression of foreign genes in adult plants and their progeny has been achieved by acceleration of DNA-coated particles or microinjection techniques. Cultured cells or embryoids served as targets for the introduction of marker genes that were stably expressed in the nucleus or the chloroplast. Cloned genes from the maize anthocyanin pathway were regulated in a tissue-specific manner when transferred into maize by particle acceleration. In spite of these successes, stable transformation efficiency was low due to uneven particle distribution and cell death after bombardment. Transferred genes did not always segregate in a Mendelian fashion in the succeeding generation, and additional efforts of embryo rescue or shoot grafts were needed to obtain viable progeny from original transformants. New technical advances such as the helium-driven particle gun may improve transformation rates in the future, but some problems of cell manipulation remain.