Phytochrome And Photomorphogenesis

The discovery of the reversible red far-red control of plant growth and development and the subsequent in vivo identification and isolation of the photoreceptor pigment, phyto chrome, constitutes one of the great achievements in modern biology. It was primarily a group of investigators at the Plant Industry Station, Beltsville, Mary land, headed by the botanist H.A. BORTHWICK and the physical chemist S.B. HENDRICKS, who made the basic discoveries and developed a theoretical framework on which the current progress in the field of phytochrome is still largely based. While the earlier development of the phytochrome concept has been covered by a num ber of excellent articles by the original investigators [104,105,33,238] as well as by others who joined the field of phytochrome research later [72, 109, 219], a comprehensive and up-to-date treatment of photomorphogenesis is not available at present. Since it seems to be needed for teaching as well as for researchers I have tried to summarize the present state of the field, reviewing the historical aspects of the phytochrome story only insofar as they are required to understand the present situation. The emphasis of my treatment will be on developmental physiology ("photomorphogenesis") rather than on phytochrome per se.

It is perhaps not surprising that plants have evolved a mechanism to sense the light environment about them and to modify growth for optimal use of the available `life-giving' light. Green plants, and ultimately all forms of life, depend on the energy of sunlight fixed during photosynthesis. Unlike animals that use behaviour to find food, sedentary plants use physiology to optimize their growth and development for light absorption. By appreciating the quality, quantity, direction and duration of light, plants can control such complex processes as germination, growth and flowering. To perceive the light environment several receptor pigments have evolved, including the red/far-red reversible phytochrome and the blue/UV-absorbing photoreceptors (Part 1). The quantification of light (Part 2) and importance of instrumentation for photomorphogenesis research are introduced in Part 3. Isolation and characterization of phytochrome is a classic example of how photobiological techniques can predict the nature of an unknown photoreceptor. Current knowledge of the phytochrome photoreceptor family is given in Part 4 and that of blue/UV receptors in Part 5. Part 6 deals with the coaction of photoreceptors. The light environment and its perception is addressed in Part 7. Molecular and genetic approaches and the photoregulation of gene expression compose Part 8. Part 9 contains further selected topics: photomodulation of growth phototropism, photobiology of stomatal movements, photomovement, photocontrol of flavonoid biosynthesis, photobiology of fungi and photobiology of ferns. The 28 chapters written by leading experts from Europe, Israel, Japan and the USA, provide an advanced treatise on the exciting and rapidly developing field of plant photomorphogenesis.

With contributions by numerous experts

Plants as sessile organisms have evolved fascinating capacities to adapt to changes in their natural environment. Arguably, light is by far the most important and variable environmental factor. The quality, quantity, direction and duration of light is monitored by a series of photoreceptors covering spectral information from UVB to near infrared. The response of the plants to light is called photomorphogenesis and it is regulated by the concerted action of photoreceptors. The combined techniques of action spectroscopy and biochemistry allowed one of the important photoreceptors – phytochrome – to be identified in the middle of the last century. An enormous number of physiological studies published in the last century describe the properties of phytochrome and its function and also the physiology of blue and UV-B photoreceptors, unidentified at the time. This knowledge was summarized in the advanced textbook “Photomorphogenesis in Plants” (Kendrick and Kronenberg, eds., 1986, 1994). With the advent of molecular biology, genetics and new molecular, cellular techniques, our knowledge in the field of photomorphogenesis has dramatically increased over the last 15 years.

Phytochrome detection and isolation; The properties of phytochrome; Phytochrome controlled responses; Mode of action of phytochrome; Some practical exercises.

This book explores the ways in which plants detect, interpret and respond to the natural light environment.