Outcrossing and coexistence of genetically modified with (genetically) unmodified crops: a case study of the situation in the Netherlands.
Wiel, C.C.M. van de; Lotz, L.A.P. - \ 2006
NJAS Wageningen Journal of Life Sciences 54 (2006)1. - ISSN 1573-5214 - p. 17 - 35.
genetische modificatie - kruisingen - genetische verontreiniging - landbouwbeleid - biologische landbouw - genenstroom - isolatie - maïs - koolzaad - suikerbieten - aardappelen - genetic engineering - crosses - genetic contamination - agricultural policy - organic farming - gene flow - isolation - maize - rape - sugarbeet - potatoes - brassica-napus l. - raphanus-raphanistrum l. - potato solanum-tuberosum - tolerant rapeseed crops - zea-mays-l - oilseed rape - transgenic potatoes - wild radish - modified organisms
With the introduction of genetically modified (GM) crops the EU has demanded that individual member states enact measures to prevent inadvertent admixture ¿ through outcrossing ¿ of genetically modified organisms (GMOs) with products from conventional and organic farming. A literature review on outcrossing was prepared for the Coexistence Committee installed in the Netherlands in 2004. For sugar beet and potato, isolation distances do not appear to be of overriding importance, as true seeds are not part of the harvested product. The only route for admixture is through persistence of GM hybrid volunteers, and these should already be subject to strict control in good agricultural practice. Data on maize indicate that a distance larger than 25 m is needed to keep admixture below the EU labelling threshold of 0.9%, and larger than 250 m to remain below the 0.1% threshold as favoured by organic farming organizations. Oilseed rape is more complex because apart from pollen flow also persistence of volunteers in and outside arable fields, and hybridization with wild relatives play a role. At the present state of knowledge, isolation distances of 100¿200 m and rotation intervals of 6¿8 years might be warranted for the 0.9% threshold. It is as yet not clear whether a threshold of 0.1% is achievable in practice. The conclusions are compared with the measures recommended by the Dutch Coexistence Committee.
Differential longevities in desiccated anhydrobiotic plant systems
Hoekstra, F.A. - \ 2005
Integrative and Comparative Biology 45 (2005)5. - ISSN 1540-7063 - p. 725 - 733.
electron-paramagnetic-resonance - fatty-acid composition - zea-mays-l - molecular mobility - arabidopsis-thaliana - trinucleate pollen - storage behavior - sugar glasses - seed - respiration
Desiccation tolerance is a wide-spread phenomenon in the plant kingdom, particularly in small propagules lacking own root or rhizome system, such as seeds, pollen, spores of spore plants, and whole moss plants, but rare in whole, vascular plants. Longevities in the desiccated state vary from a few days in some pollen and spore types to many decades in some seeds and moss spores, green vegetative tissues being intermediate in that respect. Therefore, small size of a propagule does not appear to be a factor limiting life span. The formation of a glassy state in the cytoplasm upon water loss considerably increases viscosity and slows deteriorative chemical reactions. Intermolecular hydrogen bonding strength and length in the glassy cytoplasm have been suggested to play a role in desiccation tolerance and longevity. To further explore this, a comparative Fourier transform IR study among dried anhydrobiotic plant propagules belonging to different phyla was conducted. This study indicated that strong hydrogen bonding does not correlate with long life span, but rather depends on the composition of the glass forming compounds. By contrast, a large number of double bonds in the acyl chains of the polar lipids correlated with short life span. This result suggests that deteriorative processes in membranes rather than in the glassy cytoplasm determine the rate of aging of dried anhydrobiotic propagules. This would agree with the view that lipids form the only fluid or semi-fluid phase in the dried propagules, which renders them comparatively susceptible to free radical attack.
|Associative Nitrogen Fixation and Root Exudation - What is Theoretically Possible in the Rhizosphere?
Jones, D.L. ; Farrar, J. ; Giller, K.E. - \ 2003
Symbiosis 35 (2003)1-3. - ISSN 0334-5114 - p. 19 - 38.
zea-mays-l - organic-compounds - re-sorption - carbon-flow - amino-acids - wheat roots - soil - transporters - malate - plants
Root exudation is a key driver of many rhizosphere processes including nitrogen fixation by diazotrophic bacteria residing in the soil. We critically review our knowledge of rhizosphere carbon flow and determine the extent to which rhizodeposition could fuel associative N2 fixation by soil microorganisms. We conclude that most estimates of rhizosphere C flow are fundamentally flawed due to the use of inappropriate methodology combined with a poor mechanistic understanding of root C flow. Using a mathematical model, we predicted that rhizodeposition could under optimal conditions support the fixation of between 0.2 to 4 kg N ha-1 year-1 which is in good agreement with experimentally derived values for natural ecosystems (0.05 to 5 kg N ha-1 y-1). Our model indicated that fixation was highly dependent upon the number of potential N2 fixers in the rhizosphere relative to the total microbial population. If N2 fixer populations could be enhanced, we predict that fixation rates may reach up to 20 kg N ha-1 y-1 given highly optimal conditions which again agree with experimentally derived results. We conclude that whilst the potential for rhizodeposition-driven N2 fixation in the soil is small in comparison to inorganic and symbiotic-N2 fixation inputs, it may be of importance in N-limited ecosystems.