Flow Cytometric Determination of Relative Nuclear DNA Contents in Bicellulate and Tricellulate Pollen

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Abstract
Nuclear DNA content in mature pollen was measured with a flow cytometer Pollen of Lilium longiflorum, Dendranthema grandiflora (syn Chrysanthemum monfolium) and Zea mays was chopped and stained with the DNA fluorochrome DAPI DNA levels, expressed as arbitrary C values, were compared with those of nuclei isolated from leaf or root material of the same plants In mature tricellulate pollen the generative cell is divided after second pollen mitosis into two sperm cells Tricellulate pollen from maize and chrysanthemum gave rise to one large 1C peak and, only in the case of chrysanthemum, a much smaller one at the 2C level These results suggest that the haploid nuclei of the vegetative as well as both sperm cells in tricellulate pollen are arrested in the G1 stage of nuclear division The small 2C peak in the case of chrysanthemum probably arose from a fraction of pollen with the sporophytic chromosome number (2n pollen) In contrast to this, mature bicellulate lily pollen gave rise to two identical peaks at the 1C and the 2C level From this result it was concluded that in bicellulate pollen, the 1C peak is caused by the signal of the haploid vegetative nucleus arrested in the G1 stage of nuclear division, whereas the 2C peak originates from the haploid generative nucleus which has already undergone DNA synthesis and is arrested in G2