The Genetic Manipulation of Plants

H o w g e n e t i c a l l y m o d i f i e d p l a n t

This preview shows page 36 - 39 out of 153 pages.

H O W G E N E T I C A L L Y M O D I F I E D P L A N T S A R E P R O D U C E D 3 9
Image of page 36

Subscribe to view the full document.

(i) occurs naturally in the species concerned; and (ii) moves sporadically between genome sites; (c) an organism that: (i) results from the fusion of two animal cells; and (ii) is unable to form a viable whole animal; (d) an organism that results from protoplast fusion involving only non-pathogenic bacteria or non-pathogenic yeast; (e) a plant formed by (i) embryo rescue; or (ii) in vitro fertilization; or (iii) zygote implantation; or (iv) protoplast fusion between sexually compatible species. It would seem that a plant formed following protoplast fusion between sexually incompatible species will be treated as a genetically modified organism. Because sexual incompatibility provides a reason for attempting this kind of somatic hybridisation, a significant number of genetically modified plants can be expected to arise in this fashion. Rearrangement of the genome during tissue culture, a phenome- non termed ‘somaclonal variation’, has been excluded under (a) above, and left in the province of the conventional plant breeder. Once it was widely believed that all cells resulting from mitotic divisions in tissue culture were genetically identical to the original cells, so that all new plantlets differentiating in culture represented one clone. But this assumption was incorrect. The term ‘somaclonal variation’ was devised by Larkin and Scowcroft 34,35 to account for the heritable variation that they observed in plants derived from tissue culture. Evidently, the process of tissue culture itself causes some rearrangement within the nuclear genome, often allowing the placement of ‘silent’ genes under different promoters so that they are then expressed. Somaclonal variation has been particularly useful for revealing her- itable resistance to various fungal toxins, permitting resistance to pathogens to be expressed in subsequent progeny. Occasionally a virus-resistant strain results. Disease-resistant varieties of sugar cane, maize, rice, canola, lucerne and tomato have all been produced. 36 This simple procedure is an inexpensive way of generating new plant vari- eties, and has been widely adopted in India and China. In practice, the newer techniques of genetic recombination should not be considered in isolation from conventional measures for plant breeding, despite the frequent assumption that the latest techniques stand alone and can deliver marvellous new plant varieties by themselves. Monsanto’s claim quoted at the head of this chapter is breathtaking in 4 0 S E E D S O F C O N C E R N
Image of page 37
its arrogance, but typical of the ‘revolutionary’ view of biotechnology that displays a complete misunderstanding of the context in which genetic engineering has to operate. On the contrary, ‘biotechnology alone is unlikely to create useful varieties unless it is combined with a number of procedures used in conventional breeding’. 37 As noted earlier, these supporting procedures include embryogenesis in tissue
Image of page 38

Subscribe to view the full document.

Image of page 39

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern