BOTANY VOLUME 2 - PLANT PHYSIOLOGY - 2007

PHYSIOLOGY

While Morphology deals with The Structure of an Organism—ranging from the molecular architecture of characteristic cellular elements to the macroscopic appearance of a living being—the task of physiology (Greek physis, nature; logos, discourse) is not only to describe life manifestations, meaning the origin and functioning of these structures, but also to explain their causal relationships. At the same time, it is not enough merely to consider their functional design, i.e., their utility in interacting with the environment. Rather, the goal of physiology is to provide a logical and comprehensive explanation of biological processes in accordance with established Physical and Chemical laws. This requires the application of physical and chemical Methods, and increasingly, computational and informatics methods as well. In doing so, one must proceed from the premise of the purposeful design and function of both the individual parts and the organism as a whole, because, as a rule, only advantageous traits—that is, traits with positive selective value—could be phylogenetically preserved. Admittedly, the question of whether this ultimate goal—solving the riddle of Life in the form of a fully causally explained physicochemical system—will ever be achieved remains open. Practicing physiologists tend to doubt this, though not for matters of principle,

but rather in view of the sheer complexity of even relatively simple organisms.

The boundary between morphology and physiology is beginning to blur, at least in the field of molecular biology. Molecular biology can be described as a discipline where the causal link between form and function becomes comprehensible at THE MOLECULAR LEVEL, down to the atomic scale. Thus, for example, the DNA base sequence determines not only the molecular structure of all RNA molecules involved in Protein Synthesis, but also the Amino Acid Sequence of Proteins and, consequently, their molecular architecture and ultimately their function.

Plant physiology can be logically subdivided into five sub-disciplines: METABOLISM physiology, developmental physiology (including Cell physiology), movement and irritability physiology, allelophysiology, and ecophysiology.

Plant metabolism physiology (see Chapter 6) examines the chemical and physical processes of matter and energy exchange that must take place for an organism to sustain its physical and energetic distinction from the inanimate environment, engage in the exchange of matter and energy with it, and maintain a metabolic dynamic

equilibrium far removed from thermodynamic equilibrium. The Subject Matter of metabolism physiology is therefore the physical and Chemical foundations of Life processes.

Developmental physiology (see Chapter 7) deals with the phenomena of growth, differentiation, and reproduction. Its goal is to provide causal solutions to the problems of form that are described and compared in morphology. Ultimately, it is crucial to understand the molecular processes by which genetically encoded information is translated into Structure and function and passed on to offspring (inherited). Admittedly, The Study of heredity (genetics) now constitutes a distinct biological science.

In addition to metabolism and development, every living organism is characterized by its interaction with its environment—that is, its ability to perceive stimuli and respond to them in a purposeful manner. Stimuli may be of a physical or chemical nature and originate from either the inanimate (abiotic) or living (biotic) environment. Plant responses to abiotic and occasionally biotic stimuli frequently serve to orient the organism, or its individual Organs, Cells, or even cell Organelles, in space. These reactions are the subject of movement physiology (see Chapter 8). Furthermore, plants interact in diverse ways with other organisms in their environment, whether competitors, parasites, pathogens, herbivores, or symbionts. The Molecular Basis of these biotic interactions has often only recently begun to be understood. This rapidly expanding field of research is addressed under the heading of allelophysiology (Greek allelos, mutual) (see Chapter 9).

This general and molecular physiology is complemented by ecological physiology (see Chap. 13). Here, the plant organism is examined in its entirety and position within a complex environment consisting of abiotic and biotic factors.

The subfields into which physiology has been divided for clarity do overlap, albeit in various ways. For instance, all Plant Movements (barring passive movements of dead organs) are accompanied by metabolism, while irritability—that is, the perception and Processing of environmental signals—also plays a crucial role in the physiology of metabolism and development.

Acknowledgements

The rapid, at times swift progress of knowledge in plant physiology has in some areas fostered new concepts and thus led to a restructuring of the material compared to the 34th edition. An effort was made, on the one hand, to integrate the material as smoothly as possible with the proven framework of previous editions, and on the other hand, to make it more accessible to students without abandoning THE CONCEPT OF a textbook that also serves as a reference work and—as far as space permits—comprehensively covers the field as a whole. Given the sheer breadth of the material, some omissions were inevitable, and some readers may find this regrettable. The author is deeply grateful for all constructive suggestions for further improving the text and for pointing out any errors that managed to slip through proofreading (e-mail: elmar.weiler@ruhr-uni-bochum.de).

My heartfelt thanks go to everyone who patiently answered questions, provided illustrative material, or critically reviewed portions of the text during its preparation. I am especially grateful to the students Holger Bierhoff, Oliver Felber, Caroline Fichtner, Stephan Klasen, Daniela Müller, Katharina Nünning, and Daniela Schlüsener, who reviewed the entire text for clarity from a learner's perspective and offered numerous

suggestions for improvement. I thank Claudia Oeking for meticulously reading the “Physiology of Metabolism and Development” and for her numerous valuable editorial suggestions, and Widmar Tanner for his expert advice on the chapter “Water Relations”.

Having the opportunity to write in the tradition of the Strasbourg Institute is a privilege for which I am most grateful, above all to my academic mentors who introduced me to plant physiology in all its breadth: most notably Meinhart H. Zenk (Halle), Hubert Ziegler (Munich), and Nicolaus Amrhein (Zürich).

Special thanks are due to Klaus Hagemann, who redrew and masterfully crafted nearly all of the figures.

At my explicit request, the physiological section has not been adapted to the rules of the so-called new German orthography.

Class="right">Bochum, February 2002

Elmar W. Weiler