Environmental Engineering Reference
In-Depth Information
FIGure 16.13 (see color insert)
Diagrammatic representation of genetic and environmental factors influ-
encing plant growth and development.
Introduction of genes for herbicide, insect, and rootworm resistance into maize has indirectly
led to increased biomass by controlling weeds that would otherwise compete for nutrients and
water, and maintaining healthy roots and leaves for continued nutrient absorption, and improved
photosynthesis, respectively.
Attempts at improving biomass by altering the expression of metabolic genes have given mixed
results. Transgenic expression of single genes has been reported to increase biomass in several
plant species (Smidansky et al. 2002, 2007; Biemelt et al. 2004; Lefebvre et al. 2005). These types
of results are often obtained with experimental lines and in highly controlled environments. Any
of these types of discoveries has yet to lead to a commercial product, in part perhaps because of
the inherent plasticity of the complex plant metabolism to maintain homeostasis despite transgenic
perturbations (Carrari et al. 2003). It is possible that the experimental line being used in a study
claiming the positive effect of a transgene on biomass is indeed deficient in the particular function
that the transgene enhances under the specific experimental conditions used. The positive effect of
a transgene on biomass observed in an experimental line disappeared when it was backcrossed into
agronomically elite genetic backgrounds (Meyer et al. 2007).
Grain sink in maize could potentially be made limiting by space-planting the hybrids adapted
to high planting density. Reduced shading allows plants to increase photosynthate production that
may exceed the amount needed to fill the available grains. Progressive farmers deliberately increase
planting density to the extent that the kernels at the ear tip do not fill, a phenotype referred to as
