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[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
5. Cummins,J. Low lignin GM trees and forage crops 2004 Science in
6. Pedersen,J,Vogel,K. and Funnell,D. Impact of reduced lignin on plant
fitness Crop.Sci. 2005,45,812-9
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