Cellular Regulatory Mechanisms. Cold Spring Harbor Symposia on Quantitative Biology.Review by: J. A. PatemanNew Phytologist, Vol. 62, No. 1 (Mar., 1963), pp. 109-110Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2429712 .

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Reviews lO9 this early stage of a graphic representation emphasizing changes in cell volume and number during apical growth.

The next ten chapters are concerned with shoot meristems; the first two of these treat orientation of divisions in apices with terminal cells and in multicellular apices respectively, here the good line drawings do much to help the account. Chapter 4 should prove of particular value to the student anxious to understand the development of leaves, for the ontogeny, growth and vascularization of these organs are clearly described. The concluding section of this chapter is devoted to the complex problem of the evidence from surgical experiments on apices to which subject a return is made in Chapter 8 on the determination of sites of leaves. The prob- lems of interpretation in these experiments are unsolved at the present time. The structural detail of apical cells revealed by the electron microscope has presumably been regarded as beyond the scope of this book, although brief reference is made to these studies in the last chapter. This would seem to present a possible fresh approach to this work, in particular an attempt to establish the structure and extent of intercellular protoplasmic connections in the different regions being severed would be of interest.

It is perhaps inevitable that Chapter 5 concerning the differentiation and origin of the procambium should prove in some measure difficult; this stems in part, as Dr. Clowes points out, from the fact that there isno absolutely reliable way of distinguishing procambium, so that different authors have used the term in different ways. The suggestion made of retaining Kaplan's (Restmeristem) or residual meristem for the situation where there may be a complete cylinder of procambium-like cells present near the apex would seem to be a good one, resolving ambiguity.

Whilst it is not the author's avowed intention in Chapter 6 to 'sink the French school' in the matter of theories of the shoot apex, his incisive resume has what would seem to be the very desirable effect of correcting the tendency amongst these workers to elaboration of theory (and attendant terminology) upon what is by comparison slender histological and cytological evidence.

From this chapter onwards, the reader is made increasingly aware of the progress of experi- mental analysis of apical growth and organization. It is for this reason that the second half of the book makes particularly interesting reading; culture and manipulation being easier, more information is available concerning root apical meristems and this is thoroughly and critically surveyed. The final chapter on differentiation in root apices well illustrates the rapidly increasing scope of physiological and biochemical studies on meristems.

Two interesting facets of the problem discus?ed in this chapter are the distribution and significance of polyploidy in different regions of the root and the origins of pattern in differentia- tion. These matters are clearly presented with appropriate emphasis on outstanding difficulties. It is this high standard of both lucid and critical exposition throughout the text which serves to make this a most informative and stimulating monograph. The photographs are of good quality and well supplement the text.

H. W. WOOLHOUSE

Cellular Regulatory Mechanisms. Cold Spring Harbor Symposia on Quantitative Biology, vol. 26. Pp. xv+4o8 with 417 figures and 12 plates. New York: Biological Labora- tory, Cold Spring Harbor. I962. Price: Institutions and booksellers, $12.00; individuals, $8.oo. Postage extra.

As a result of the last I5-20 years' work in biochemistry and genetics it is now taken almost as axiomatic that the information determining the amino-acid sequence of proteins is carried in the DNA of genes. There are a number of papers in this volume which deal with the role of DNA in protein synthesis. This work has the aim of establishing the relationship between the genetic sites of mutation and the resultant changes in specific proteins. In spite of progress in this field, much of which is reported in this volume, it is not yet possible to demonstrate experi- mentally the collinearity of amino-acid sequence in a protein and nucleotide sequence in the genetic material. But at least the work to date is consistent with the hypothesis. The part played by RNA in the mechanism of protein synthesis is the subject of a number of contributions. The recent significant advance in this field is the demonstration of messenger RNA as the agent responsible for the information transfer from DNA to the ribosomes, which are the site of protein

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110 Reviews synthesis. The experimental evidence for the existence and nature of 'messenger' is lucidly presented by a number of the leading workers in the field.

The majority of the papers given at the symposium were concerned with the regulation of enzyme synthesis and activity. It is now clear enzymes may be controlled in the cell in at least two main ways: through the regulation of enzyme synthesis and/or the regulation of enzyme activity. The rate of synthesis of a specific enzyme may depend on the concentration of a repressing substance which is usually an end-product of the pathway in which the enzyme is involved. It is only in the last few years that it has been clearly realized that repression and not induction is the basic mechanism controlling enzyme synthesis in those systems which have been intensively studied. The work on arginine synthesis and galactose metabolism in Escherichia coli has been largely responsible for this advance and current work on these and similar systems is well covered by a number of eminent contributors. The repression of enzyme activity, often by the end-product of the metabolic pathway involved, is also now well established as a mechanism of enzyme regulation in a number of systems. The investigation of 'feedback inhibition' both by end-products and other substances is the subject of a number of papers. Some of this work suggests that repression of enzyme synthesis and activity are not mutually exclusive control mechanisms, but complementary in their essential function of preventing oversynthesis by the cell in particular environmental conditions. It seems probable that repression of enzyme activity can provide a quicker and finer response to changing environmental conditions than can be achieved by repression of enzyme synthesis and thus prevent the synthesis of unessential metabolites.

Recent work on enzyme formation and activity in animal systems has shown that such sub- stances as the steroid hormones and DPN and TPN may have considerable effects on enzyme proteins. These effects include activation, inactivation and stabilization of enzymes. Also in the case of glutamic dehydrogenase from mammalian cells, these agents can produce a reversible dissociation of the glutamic dehydrogenase molecule into sub-units. These sub-units have lost glutamic dehydrogenase activity, but gained a new substrate affinity for alanine and can function as alanine dehydrogenase. This kind of information, together with work on adaptation and induction of enzymes in animal cells, suggests the possibility of studying a fundamental chemical mechanism of differentiation via the regulation of enzymes in cells.

The symposium opened with a paper by B. D. Davis dealing broadly with biosynthetic control mechanisms and their possible biological and evolutionary significance. It concluded with J. Monod and F. Jacob surveying the topics covered by the symposium and the field of cellular regulatory mechanisms, with particular reference to differentiation in higher animals. It is sufficient to say that these two stimulating contributions in themselves warrant a place for this volume on any biologist's bookshelf.

There is little doubt that the developments of the last few years in the study of biological control mechanisms reported and summarized in this volume represent the start of a new era in biology. It cannot be too highly recommended.

J. A. PATEMAN

Proceedings of the Summer School of Botany held June 2-I5, I960, at Darjeeling. Edited by P. MAHESHWARI, B. M. JOHRI and I. K. VASIL. 9 x 6 in. Pp. Vi+522 with 250 figures and 5 plates. New Delhi: Ministry of Scientific Research and Cultural Affairs, Government of India. I962. Price Rs 25.00.

This is an account of the proceedings of the second Scientific Summer School held in India and it is hoped and expected that others will be held regularly and that there may be one in the Life Sciences perhaps every second year. Professor Humayun Kabir, the Minister of Scientific Research and Cultural Affairs, was responsible for the idea and the plan to hold these meetings, and his deputy, Dr. M. M. Das, was present when the Chief Minister for West Bengal, Dr. B. C. Roy, opened the proceedings. In his foreword to the volume Professor Kabir makes it clear not only with what importance this kind of stimulation and encouragement of the sciences is viewed in official quarters but also that the discussion on teaching and research with which the proceedings finished will be given the active attention of the Government.

The papers read and discussed covered almost the whole field of botanical studies - from

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