The intricacies of plant growth and development present a fascinating intellectual challenge, and yet our understanding of the subject has increased relatively slowly, despite the application of many different experimental approaches. Now, however, the introduction of molecular methods, coupled with genetic transformation technology, has provided a change in pace, and fundamental advances are occurring rapidly. This volume, the second in our Plant Biotechnology series, shows how we are beginning to understand the molecular basis of plant growth and development, and are thus moving from the descriptive to the predictive stage. The ability, discussed in chapter one, to generate a fivefold change in plant height by overexpression of a single gene for the photoreceptor phytochrome heralds not only a new phase in plant photobiology but also highlights the close relationship between fundamental knowledge and commercial application. Other chapters review progress in our understanding of the molecular basis of hormone action and processes such as tuber development, seed protein synthesis and deposition, fruit ripening, and self-recognition during pollination. The successful uses of antisense genes to alter the colour and pattern of flowers and to change the enzymic composition of ripening fruit are also discussed, together with identification and down regulation of a gene involved in ethylene synthesis by antisense technology. Opportunities are considered for altering the composition and quality of harvested plant organs and for using plants to synthesise novel products.