[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[SANET-MG] transgenic crops with high or low lignin

September 18, 2005

Prof. Joe Cummins

“Transgenic crops with high or low lignin”

The plant cell is protected by a cell wall that has a structure analogous to reinforced concrete. The cellulose fibrils play the role of steel reinforcing rods, while concrete is represented by lignin. Lignin determines the rigidity, strength and resistance of a plant structure. High lignin levels are undesirable in forage crops because they make the forage less digestible thus reducing the quality of fodder such as maize fodder. Crops with high lignin also decompose more slowly in the soil leading to a buildup of undigested plant material in the soil. Genetically modified (GM) crops with low lignin content are more digestible but those crops are prone to disease and lodging. The following discussion will consider the high lignin problem encountered as a pleiotropic effect ( effect of a single gene on several different traits) from modification of maize with a gene for insect resistance from Bacillus thuringiensis (Bt) cry 1Ab toxin and contrast that effect with genetic modification to reduce lignin content in trees and crops.

In 2001 Saxena and Stotsky (1) reported that maize modified with the Bt cry1Ab toxin contained higher (33 to 97%) than isolines that had not been modified. In 2005 Poerschman et al (2) reported that Bt maize Cry1Ab modification led to elevated lignin levels in stems but somewhat less differences in leaves. Flores et al (3) reported that maize, rice, tobacco, canola, cotton or potato plants modified with Bt cry 1AB toxin, cry 3A or cry1Ac all decompose less in soil than comparable non Bt lines. The main hindrance to prompt decomposition in soil . was the elevated lignin level in those crops.

The results clearly show that crops modified with Bt toxins cannot be considered substantially equivalent to their unmodified counterparts. Substantial equivalence is an assumption that GM crops are equivalent to their non-GM counterparts. A conference sponsored by the Austrian Federal Environment Agency defined substantial equivalence (4)“The concept of Substantial Equivalence was introduced into the discussion of safety evaluation of food from genetically modified organisms for the first time in 1993.. Subsequently, the concept was agreed in many countries as a basis for safety evaluation of novel food. Substantial Equivalence in this regard means that a genetically modified plant or food derived therefrom is equivalent to their conventional counterparts. Substantial Equivalence is determined by comparing plant compounds as well as agronomic and morphologic properties. In case of significant differences further testing will be decided on a case-by-case basis. Thus, the concept of Substantial Equivalence represents an important part of safety evaluation of food produced from genetically modified organisms.” Indeed, Substantial Equivalence was the cornerstone for approval of the Bt crops. Clearly, the evidence that Bt crops are plagued with elevated lignin that effects digestibility of food and feed derived from the crops shows that the crops are not Substantially Equivalent to unmodified food and feed products and on that basis approvals for the Bt crops should be revoked.

Last year the Institute for Science and Society pointed out the significant defects in crops and trees genetically modified to contain low lignin levels(5). The problems included mainly poor resistance to disease, lodging due to stem weakness or breakage of branches in wind .Low lignin will certainly enhance rapid decay of plant leaves, roots and stems enhancing carbon dioxide loss from the soil. This year Pedersen et al (6) reviewed the impact of reduced lignin on plant fitness. In general crop yields were reduced by crops with reduced lignin. Lodging of crops and long term survival of perennials were observed. However, reducing lignin in some lines or populations did not reduce fitness. The authors suggested that lignin could be reduced without detrimental side effects provided that appropriate cultivars or populations could be located. However, in most instances the low lignin phenotype was detrimental to a crop.

The biotechnology industry seems blissfully unaware of its inability to get things right. Powerful public relations efforts have concealed fundamental defects in the crops , feed or foods produced using genetic engineering. The lignin example shows the problems related to prematurely releasing GM crops that are not yet ready for the environment and food supply.


  1. Saxena,D. and Stotsky,G. Bt corn has a higher lignin content than
     non-Bt corn American Journal of Botany 2001, 88,1704-6

2.Poerschmann J, Gathmann A, Augustin J, Langer U and Gorecki T. Molecular composition of leaves and stems of genetically modified bt and near-isogenic non-bt maize--characterization of lignin patterns. J Environ Qual. 2005 Aug 9;34(5):1508-18

3. Flores,S,Saxena,D. and Stotsky,G. Transgenic Bt plants decompose less in soil than non-Bt plants Soil Biology and Biochemistry 2005, 37,1073-82

4. Federal Environment Agency-Austria Evaluating Substantial Equivalence Conference Papers Vo.32 Vienna 2002 http://www.umweltbundesamt.at/fileadmin/site/publikationen/CP032.pdf

5. Cummins,J. Low lignin GM trees and forage crops 2004 Science in Society 23,38-9

6. Pedersen,J,Vogel,K. and Funnell,D. Impact of reduced lignin on plant fitness Crop.Sci. 2005,45,812-9

To unsubscribe from SANET-MG:
1- Visit http://lists.sare.org/archives/sanet-mg.html to unsubscribe or;
2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message.

Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html
For more information on grants and other resources available through the SARE program, please visit http://www.sare.org.