D. BOULTER and B. PARTHIER At the time of the former edition of the
Encyclopedia of Plant Physiology, approximately 25 years ago, no
complete plant protein amino acid sequences or nucleic acid sequences
had been determined. Although the structure of DNA and its function as
the genetic material had just been reported, little detail was known of
the mechanism of its action, and D. G. CATCHSIDE was to write in the
first chapter of the first volume of the Encyclopedia: "There is a
consider- able body of evidence that the gene acts as a unit of
physiological action through the control of individual enzymes". No
cell-free transcription and pro- tein-synthesizing systems were
available and the whole range of powerful meth- ods of recombinant DNA
technology was still to be developed. Today for the first time with
plant systems, it is possible not only to describe their molecular
biology but also to manipulate it, i. e., to move from a description to
a technological phase. The properties of living systems are inscribed by
those of the proteins and nucleic acids which they synthesize. Proteins,
due to their very large size, occur as macromolecules in colloidal
solution or associated in supra-molecular colloi- dal form. The
colloidal state confers low thermal conductivity, low diffusion
coefficients and high viscosity, properties which buffer a biological
system from the effects of a changing environment. Biological systems
not only have great stability, but also the capacity to reproduce.