BOOK R E V f E W S

MODIFICATION OF THE INFORMATION CONTENT OF PLANT CELLS. Proceedings of the second John Innes Symposiun~. Edited by R. Markham., D~ Daviesj D.A~ Hopwood aL~d R~ Home. 1975. North-Holland/Ame- rican E l s e v i e r , 350 pages~ 24.50 U . S . d o l l a r s ,

The s p e c t a c u l a r a c h i e v e m e n t s w i th E s c h e r { c h [ a co l t and the tet~dency to- w a r d a n i m a l c h a u v i n i s m have p u s h e d p l a n t b i o l o g y i~to the b a c k g r o u n d ~ In a w o r l d r i d d e n wi th the twin c r i s e s o[ o v e r - p o p u l a t i o n and e n e r g y s h o r t a g e , the on ly r e a s s u r i n g o r g a n i s m s a r e g r e e n p l a n t s . The g r e e n p l a n t ' s a b i l i t y to t r a n s f o r m l igh t e n e r g y into c h e m i c a l e n e r g y of food m o l e c u l e s is the b a s i s of a l l h e t e r o t r o p h i c f o r m s of l i fe . it: would be n~ost d e s i r a b l e [f p l an t s cou ld he g e n e t i c a l l y m o d i f i e d f o r h i g h e r p h o t o s y n t h e t i c r a t e s , a b i l i t y to s y n t h e s i z e n u t r i t i o n a l l y - i m p o r t a n t c o m p o u n d s , and f o r r e s i s t a n c e to p e s t s and p a t h o g e n s . The John Innes I n s t i t u t e in N o r w i c h , Eng land , o r g a n i z e d a S y t n p o s i u m in J u l y 1974 on ' T h e M o d i f i c a t i o n of the I n f o r m a t i o n C o n t e n t of P l a n t C e l l s ' . T h i s book is a P r o c e e d i n g s of that S y m p o s i u m and p r o v i d e s a u t h o r i t a t i v e a c c o u n t s of e x p e r i m e n t a l a p p r o a c h e s t o w a r d s e x t e n d i n g the gene} ic v a r i a b i l i t y in p l a n t s .

The t w e n t y p a p e r s a r e c l a s s i f i e d u n d e r the f o l l o w i n g s e c t i o n s : g e n o m e a m p l i f i c a t i o n , t r a n s f o r m a t i o n , p r o t o p l a s t s ~ v i r o i d s a n d p l a n t - m t c r o b e l u t e r - a c t i o n s . A l e c t u r e by P r o f e s s o r p o n t e c o r v o , " A l t e r n a t i v e s to s e x : g e n e t i c s by m e a n s of s o m a t i c c e i l s " , d e l i v e r e d to h o n o r the m e m o r y of W i l l i a m Bate.- son, is i n c l u d e d a s the open ing a r t i c l e . It is a s u c c i n c t a c c o u n t of the d e v e - l o p m e n t of the s u b j e c t . One is r e m i n d e d that the now f a s h i o n a b l e f i e ld of ' s o m a t i c c e l l g e n e t i c s ' had i ts o r i g i n in the mo ld , A s p e r g i l l u s n idn lans , w h e r e i n p a r a s e x u a l t t y was d i s c o v e r e d . M e t h o d s i d e n t i c a l [n p r i n c i p l e to those d e v e l o p e d f o r A s p e r g i l l u s by P r o f e s s o r P o n t e c o r v o a r e now r o u t i n e l y u s e d f o r h u m a n g e n e t i c a n a l y s i s by m e a n s of s o r n a t i c c e l l h y b r i d s . M o s t w o r k e r s use the A s p e r g i l h s m e t h o d o l o g y " w i t h o u t b e i n g a w a r e w h e r e t h e y got it f r o m " ~ P r o f e s s o r P o n t e c o r v o d r i v e s h o m e the po in t that " w h i l e in the c a s e of auG. r e a l s s o m a t i c c e i l f u s i o n is, f o r t u n a t e l y , otl ly an a n a l y t i c a l tool , in the c a s e of p l a n t s - w i t h t h e i r t o t [ o p o t e n t l a l i t y of s o m a t i c c e l l s , - it ~s a l s o a s y n t h e t i c tool wi th f a n t a s t i c p o s s i b i l i t i e s " . Indeed , the " m o m e n t o u s e x p e r i m e n t " in p a r a s e x u a l h y b r i d i z a t i o n - t h e p r o d u c t i o n of c o m p l e t e h y b r i d o r g a n i s m f r o m f u s i o n of c e l l s of two s p e c i e s - ha s b e e n p o s s i b l e o n l y w i t h p l a n t s . T h i s was done by C a r l s o n and h i s c o l l e a g u e s in 197Z in U . S . A .

As one reads through the pages, the terrn 'tot[opotency' assun'tes a dif- ferent m e a n i n g ~ A~ S i e g e l frot-n U . S . A . ( "Gene a m p l i f i c a t i o n in p l a n t s " ) r e - p o r t s the f i n d i n g of m o r e c h l o r o p l a s t DNA in the l e a f c e i l s tha t in roo t c e i l s a,~d c o n s i d e r s it l i k e l y that m u c h of c e l l ' s c h l o r o p l a s t DNA n~ay be in the nucleus rather than in plastids. In U. Ko, J.Ingle and JoNo Tin,his ("A role for differential replication of DNA in deveIopITmnt") concur that the genome does not necessarily remain constant during development. For example, during fruit development certain portions of the genoese may be amplified~

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Thus it appears that genome amplification may be a normal process of dif- ferentiation in plants although there is as yet no evidence for a n~ass[ve an~pl[f[cat[on of the type observed for ribosomal genes in amphibian oocytes. Can stable genetic changes be induced in plants? C.A, Cull[s froL~n John Innes Institute repol'ts on varieties of flax where mechanisms appear to exist for a differential a~Ylplif[cation of various portions of the genoL~ne in response to environmental factors.

Among the other cont1'ibut[ons, that of Professor Ledoux and his asso~ c[ates from Belgium ("DNA mediated genetic correction of th[am[neless Arabidops[s thal[ana") deserves special mention, not least because this is the only paper for \vh[eh the introductory remarks of the cha[rnnan of the session is included. Professor Ledotux has claimed snccess for just the sort of thing one expects in genetic engineering. ThiaL~n[neless mutants of the plants, Arabidops[s thaliana, are corrected for this deficiency by t~'eat[ng seeds only with that bacterial DNA which contained gene for its synthesis. The correction is hereditary. This experhT1ent on genetic transformation by exogenous application of heterologous DNA has generated much controversy concerning the l~echanism of uptake, conservation, integration and replica- tion of foreign DNA. However, as Professor Herbert Stern observed in his introductory remarks, "practical success is not necessarily tied to thoret[cal insight and there may be a considerable lag between the achieve~nens and the explanaI:[on".

Th'e subsequent papers disclose the numerous experimental possibilities on genetic modifications with plant tissue and cell cultures. Hary Smith's group from England ("Studies on the uptake and expression of.foreign genetic material by. higher plant cells") have studied t1"ansforrnatlon of sycamore cells by a lac transducing phage. As a result, the cells acquire the ability to utilize lactose. It may be recalled that the term 'transgenos[s' was coined by C.H. Doy and his colleagues in Australia for similar experiments where the donor and the recipient cells are widely separated by evolution and the mechanism of gene transfer and maintenance are obscure.

At the moment experiments on genetic modification seem most popular with the protoplasts because the problem of introducing foreign DNA into plant cells is simplified and also because they are used in somatic hybridization. Techniques for the isolation of protoplasts have been induced to regenerate conqplete plants. J.W. Watts and his colleagues in England ("Plant protoplasts in transformation studies: some practical considerations") are using proto- plasts for deter[Ylin[ng the conditions necessary for introducing nucleic acid into cells. A polycation seems essential and the condition of the plant mate- r[al fron~ which protoplasts are prepared is critical. In Germany, I.Potrykus has been attel~npt[ng to transplant nuclei and chloroplasts into isolated proto- plasts and this approach appears pro[-n[s[ng. .Evel" since protoplasts were isolated and cultured by Professor Cocking in U.K., researchers l~ave been in search of agents or cheL~nicals which would induce effective fusion of plant

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protoplasts (such as the inactivated Sendai virus for fusion of human cells). It is therefore significant that Oluf Gamborg's group in Canada ("Plant proto- plasts in genetic modifications a~id production of intergeneric hybrids") have found that polyethylene glycol agglutinates protoplasts of different species, for e.g., Soyabean-barley, pea-carrot, soyabean-rapeseed. That a "break- through" in so~lqatic hybridizgtion of plants has occurred is confirmed by experiments conducted in Professor Melchers' laboratory in Tublngen. Somatic hybrid plants were produced by the fusion of mesophyll pr0toplasts from chlorophyll deficient, light-sensitive parents. As a result of comple- n%entation they had a nor1<nal chlorophyll content and were light-insensitive.

It is clear that we now possess the technology for culturing higher plant cells under defined conditions. Is it feasible to apply the selective systems of Iznicrobial genetics to cultured cells of higher plant cells and achieve altered responses to pathogens, or to selectively increase the level of nutritionally h<nportant components? In a paper ("Higher plant cells as experimental orga- n~s11~s"), R.S. Chaleff and P.S. Carlson derhonstrate an approach to these proble~zns. Tobacco cells were selected fron~ a n%utagenized haploid cell

population for their ability to grow in a mediul~ containing an inhlb[tory con- centration of a toxin, 1~nethionine sulfoximine, an analogue of methionine, produced by a bacterial pathogen. Toxin-resistant l~nutant cells were rege- nerated into mature plants by tissue culture methods which proved resistant to infection by the pathogen, and the.mutant contained elevated intracellular levels of free l~nethionine - an essential amino acid.

The last two sections in the book pertain to genetic information transfer from viroids or bacteria ~nto plant cells, as a result of which the phetfotype of affected cells is transformed. T.O. Diener in U.S.A. has recently dis- covered a class of subviral pathogens termed 'viroids' which consist solely of a low molecular weight infectious RNA. They are the smallest known agents of infectious disease. The discovery of vi~oids is significant as they may be involved in instances where viral aetiology of an infectious disease has been assumed, but where no causative agent has ever been isolated. There are also four contributions on the crown-gall tul-l]ol" (a plant "cancer") which enlphasize the fact that the chemical identify of the tumor-inducing- principle has still not been found. Live bacteria are necessary for crown- gall initiation; no system has been developed in which isolated bacterial con%ponents reproducibly induce crown-gall tumors, perhaps the latest clue, the correlation between plasL~nid-containing bacterial strains and tumori- genec[ty will lead to an answer.

After reading the collection of papers, the impression was gained that genetic engineering of plants would be accon~pl[shed quietly, if it has not al- ready happened.

Rarne sh Mahe shwari Department of Biochemistry Indian Institute of Science, Bangalore 560 OlZ, India

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M O L E C U L A R STUDIES IN VIRAL N E O P L A S I S : A c o l l e c t i o ~ of p a p e r s p r e s e n t e d a t Twen ty -FLf th A n n u a l Sy~npostm~ o~ ~ u n d a ~ a e n t a l Can.cer Re- search, 1972. Published for the University of Texas M.D. A~dersor~ HospLtal

and Turnout Institute at Houston, Houston,, Texas~ The Wtl][ams& Wilk[ns Co,~ Baltimore, 1974, 608 p., $ Z4.

This collection of 37 papers derives from presenLat[ons made at the Twenty-Fifth Annual Symposh~m oa FuL~darnental Cancer Research held in Houston, Texas, h~ March of 1972. h~ keepLng with the hLgh sl-andards set by the organizers of this aL~nual event, Lh[s collection or' co~xLrLbudons main- tains thaL trad[tLorz. Of partLcular Lmportance is The Bertner Foundation Memorial Lecture given by Dr. Howard Terni~l and enLi.tled "Fro:T~ Prov[.ruses to Proto-vLruses. RNA-Directed DNA SynLhesis by RNA Tumor Viruses and Cells". 7"hLs lucid contribution describes the events leading up to the di.seo- very of reverse transcr[pease and development of the protovtrus hypothesLs. The other papc~'rs are arra~iged under such categorLes as "iZropert[es of Onco- gen[c Viruses 'r, rfTu~nor Virus Geuet[cs", "Enzyn~es of I~NA Tun~or ~f[ruses", "B[ochemlcal Events in Tumor V[~'us Replication", "The h~eeractzon of Tun~or V~ruses with Their Host Cells", and "The Search for Huraa~ Tumor Viruses",

Included h~ the volume are the Hvely d[scussious thai: tookplace after each sessi_on. This book ts highly recommended to all viral oncolog[st.s, r~o{ o~ly because the authors represent most of the leadh~g laboratories tn the field, but also because they describe some of LheLr best work.

The only criticism the referee has to make about the book is {hat although the subject [s very timely, the book suffers from a deftcietacy of current Ln- formation. In thLs rapLdly expandLng field th-neiLness of publ[cadon would appear to be imperative. Only certaLn aspects os this fascinating new frontier of biological knowledge have been covered tn the book and many of the recendy available data must be sought elsewhere. However, the references to other l~terature and indexing are both thorough and accurate. Although multi- authored, the volume ts internally constseent and the authors have succeeded in presenting thetr views in a seLmulaeh~g and h~teresdng ~nanner.

T. Rarnakr[ shnaL~ Microbiology and Cell Btology Laboratory Indian Institute o]~ Science, Bangalore 560 01Z, India