2.3. Ploidy determination
For determining the ploidy of regenerates, 2 cm segments of fully developed leaves were collected and analysed using flow cytometry (the fluorescence intensity is proportional to the nuclear DNA content). All of the plants that successfully passed acclimatisation
to greenhouse conditions were analysed. Samples were prepared according to Petersen et al. (2002) and analysed using a Partec PA flow cytometer. Collected data were used to calculate the polyploidisation rates (the percentage of the detected polyploids in
the samples analysed).To investigate methods of determining ploidy aside from flow
cytometry, plants with known ploidy were examined in the second growing season for stomatal length and width, pollen grain diameter and spikelet length. Both untreated plants of known ploidy and the colchicine-generated polyploids (first colchicine generation – C0) were grown under greenhouse conditions and were in similar developmental stages. For determination of the length and width of the stoma, the leaf segments were hand-scraped with a razor blade, leaving only the abaxial region of the epidermis. After washing once, the epidermal segments were mounted on a microscope
slide with a drop of distilled water, covered with a cover slip and examined under a light microscope with the help of an ocularmicrometer. The size of 240 stomata (2 ploidy level×8 plants×3 leaves×5 stomata) was measured for each genotype. For determination
of pollen grain diameter, the anthers were mounted in a 2% acetocarmine solution and examined under a light microscope with the help of an ocular-micrometer. A total of 480 pollen grain diameters (2 ploidy levels×3 plants×1 inflorescence×8 anthers×10 pollen grains) were measured for each genotype. The spikelet lengths, defined as the length of the lower glume (without the distance of an awn), were estimated under a stereoscopic microscope using an ocular scale on spikelets dissected from the middle part of inflorescences collected in late autumn.Atotal of 480 spikelet lengths (2 ploidy levels×8 plants×3 inflorescences×10 spikelets) were measured for each genotype.