Mode of action of herbicides

Mode of action of herbicides

PESTIC’IDE BIOCHEMISTRY AND PHYSIOLOGY 4, 245-247 Book Reviews Protein RI. Boyd, $29.50. Deficiency Charles and Pesticide Toxicity. C. Thomas, ...

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4, 245-247

Book Reviews Protein RI. Boyd, $29.50.

Deficiency Charles

and Pesticide Toxicity. C. Thomas, Springfield,

Eldon 1972.

the degree of augmentation varied from almost nothing to over two thousand times for different compounds. Tests lasting 100 days showed DDT to be one of the safest pesticides in protein deficiency and captan to be one of the most toxic. Certainly few will yuarrel with Dr. Boyd’s conclusion that when marked augmentation of toxicity has been demonstrated in tests on laboratory animals, clinical toxicity trials in man should follow for confirmation or rejection of the conclusion in animals. The reader can find what he wishes, ranging from an overall summary little longer than this review to numerous clear halftones of tissue sections and detailed descriptions, graphs, and tables. The excellent index makes any detail accessible. The treatment is essentially descriptive; little attention is given to mode of action. To be sure, the contribution of protein deficiency to inhibition of drugmetabolism and the contribution of some poisons to anorexia and inanition are mentioned. However, the relative importance of these factors or the possible existence of other factors in increasing the susceptibility of protein-deficient rats to pesticides is touched on light,ly. It is not astonishing that the susceptibility of a rat to a poison is increased if he is already half dead from dietary imbalance. What is intriguing is the tremendous difference in the degree of increase associated with different compounds. Anyone who would continue the task that Dr. Boyd so recently laid down might do well to consider in its broadest sense what he had to say about nutrition as a cause of increased susceptibility rabher than confining the search to microsomal enzymes of the liver.

This book, apparently like everything the late Dr. Eldon Boyd did, is thorough. It summarizes investigations he and his colleagues made of the effect of dietary protein deficiency on the toxicity of 12 insect,icides, 3 herbicides, and 1 fungicide in rats. The studies started less than 10 yr ago, mainly as a result of questions raised by Dr. Frank Lu of t,he World Health Organization concerning the safety of pesticides in developing countries where t,he diet is normally low in protein. After some preliminary work, it was decided to make further studies in rats previously maintained for 4 wk after weaning on diets containing an optimal concentrat,ion of protein, one-third the optimal rate, about one-ninth t,he optimal rate, and no protein. Of these 4 diets, the opt,imal contains 27% protein derived from casein. A diet containing 9a/c casein allows weanling rats to grow at only about one-third the normal rate, but they survive more than 4 mo, the longest duration of any of the studies. A diet containing 3% to 3.5% protein from casein permits no growth, and rats dependent on it begin to die after 3 mo. When fed no protein, weanling rats slowly lose weight, and die during the second month of feeding. The book begins with a chapter on the calculation of toxic doses of chemical agents. This is a summary of some of the high points of “Predictive Toxicometrics,” another valuable book by Dr. Boyd published only a year earlier. There follows a detailed chapter on the effects of partial and complete starvation in rats and a brief chapter on kwashiorkor in human infants. The introductory section is completed by three chapters dealing with the effect in wear&g rats of protein-free diets, of a protein deficient diet permitting 110 growth, and of a diet containing a third the optimal protein, respectively. The body of the book consists of 16 chapters dealing with the effects of protein deficiency-and in some instances reduced food intake-on the toxicity of 16 pesticides. The book concludes with two summary chapters, dealing with the comparative toxicity associat,ed with a single dose and repeat,ed doses, respectively. Briefly, it was found that protein deficiency increased the susceptibilit,y of rat,s to pesticides, but

WAYL.IND J. HAYES, JR. Center in I’oxicology Department of Biochemistry Vanderbilt University Nashville, Tennessee 37232

Mode and A. $12.95.

0 1974 by Academic of reproduction in my

Press, Inc. form reserved.

of Herbicides. Wiley-Interscience,


There is a wealth of useful and up-to-date tion in this book. The science of chemical 245

Copyright All rights

of Action S. Crafts,

M. Ashton New York. informaweed con-



trol is developing so rapidly that to cover the subject in a single volume is no easy task, yet in this book no less than 150 commercially available products, classified into 14 chemical types, receive at,tention. The first part of the book is concerned with the principles underlying the mode of action of herbicides, there being separate chapters dealing wit.1~ such aspects as Selectivity, Morphological Responses, Absorption and Translocation, Molecular Fate in the Plant and Biochemical Responses. Then follows an important chapter in which the authors present a well balanced account of the relevant aspects and factors which might operate in mode of action. At t,he end of each chapter is a useful list of references which, it is good to report, give adequate coverage of foreign as well as American publications. Other useful features of the book are the two tables at the end, one giving trade names of the different herbicides and their manufacturers, and the ot,her providing some useful physical and toxicological properties of the more important herbicides. The book is well arranged and very readable. The figures, charts, formulae and diagrams are clearly presented and the index enables any required information to be obtained easily. The volume is recommended to students, research and extension workers and, indeed, all those who have interests in the control of weeds with chemicals. k L. WAIN Agricultural Rtscarch Council Plant Growth Substance and Systemic Fungicide Unit Wyc College, Univcisity of London Wyc, Ashford, Kent United Kingdonl

Enzyme Inhibitors as Substrates. and Elsa Reiner, Frontiers in Biology North Holland-American Elsevier, New York, 1973. $22.50.

W. N. Aldridge Series, Vol. 26, Amsterdam-

This is in many ways an excellent book, but with some clearly discernible drawbacks. The title is more general than the contents. Those who are interested in the question of enzyme inhibitors which are also substrates for the corresponding enzymes will find that the coverage is too restricted. Most of the book deals with “B-esterases” i.e., all the esterases which can be inhibited by organophosphates; but in fact the cholinesterases get the giant’s share of the attention. One chapter is dedicated to the “A-esterases”, defined as “enzymes which hydrolyze rapidly inhibitors which acylate B-esterases” ; hut which turn out to be the phosphotriesterases only. The chapter is brief (13 p.) and certainly does not “review the present state of knowledge about the esterases,” for it omits a great deal of the literature


on the subject. A more general objection is that non-esteratic enzymes can also have inhibitors which act as substrates, and these cases are not treated at all. An effective treatment is given by the late J. L. Webb in Vol. II of “Enzyme and Metabolic Inhibitors,” in the chapter on “Analogs of Enzyme Reaction Components.” The other undesirable feature of the title is t,hal those who work with organophosphates and carbamates as inhibitors of the cholinesterases, may miss the significance of this book, which is directed very much at them. It is unfortunate that the authors tend to play down the differences between acetylcholinesterases from different sources. For example, some unusual properties of housefly acetylcholinesterase are neglected. It is of unusual interest that this enzyme in vitro does not undergo spontaneous reactivation after phosphorylation ; and yet reactivation can be induced hy oximes, and spontaneous reactivation occurs In Go. And an extensive @-page) Table of “aging” rates of dialkylphosphorylated enzymes omits housefly data, in which an unexpected dependence on the alkyl group has been shown. Nor is mention made of the fact that acetylation is rat,elimiting in the hydrolysis of acetylcholine by housefly enzyme, whereas deacetylation is rate-limiting in that from vertebrates. Iaozymes or multiple molecular forms are nowhere mentioned. Allosteric effects are discussed in detail to account for inhibition by some unusual phosphates and carbamates, and to a lesser extent in describing the bizarre effects of aziridiniums. But one would have liked more extensive discussion of these along with the well-documented allosleric activating and effects of tetraethylammonium gallamine. Within the limitations indicated above, the book is however an extraordinarily fine one. The thesis of the close analogy between the acetylation by acetylcholine, the phosphorylation by organophosphates and the carbamylation by carbamates is well sustained through the text, and it is made the core of a very persuasive presentation. The kinetic aspects receive the most attention, and this complicated subject is dealt with extremely well. The great virtue of the text is that it does not attempt to provide the kind of total coverage found in an annual review, but it does stress a critical appraisal of the literature and a lucid demonstration of the way which it relates to the themes of the book. An example is the replotting (in Fig. 8.3) of the data (plotted in a somewhat different way by this reviewer 8 yr ago) in a way which makes the point much more effectively than did the original. The designation of their constants is, however, somewhat confusing. They replace the well-known ki for the apparent second-order reaction E + PX