Grain development and endoreduplication in maize and the impact of heat stress |
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Authors: | T G G Bringezu T F Sharbel and W E Weber |
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Institution: | (1) Plant Breeding, Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Betty-Heimann-Str. 5, 06120 Halle/Saale, Germany;(2) Apomixis Research Group, Department of Cytogenetics and Genome Analysis, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany; |
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Abstract: | The post-anthesis development of growing maize kernels is strongly affected by heat stress. The maize cultivar “Spezi” was
used to quantify this effect in kernels from 14 days after flowering until maturity. Day/night temperature of control plants
was 25/20°C. Stress of 40/25°C was given for seven days or continuously up to maturity. Kernels were analysed weekly for dry
matter and extractable DNA. In addition the ploidy levels and the DNA content in intact cell nuclei were determined by flow
cytometry. The dry matter reduction started immediately after heat treatment and reached, at maturity, 40% for temporary heat
stress and 60% for permanent heat stress. The reduction of extractable DNA started later and was not as extensive. Endopolyploidy
was found in all kernel tissues, namely embryo, endosperm and pericarp. In endosperm, 3C nuclei reached their maximum number
at approximately 14–17 days, and cells with higher ploidy levels between 21 and 26 days after flowering. Later on 6C nuclei
were dominant. The DNA content in intact cells of the endosperm reached a maximum 21 days after flowering. This maximum was
lower for heat stress variants and decreased more rapidly. Heat stress can vary from year to year under field conditions.
Since heat stress changes the ratio between embryo and endosperm DNA in the direction of a higher portion of embryo DNA at
maturity, this has an influence on the measured content of GM DNA from GM pollen transfer into conventional maize fields. |
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