Except for the preliminary work of McClintock (1929) on pollen karyotyping in the first microspore division, no further attempt has been made in this regard. The present study was undertaken to standardize an efficient and easy method of pollen karyotyping in maize. A simple smear-cum-squash technique with 2% acetocarmine staining has been established for maize pollen using mature anthers of two inbreds, PKMS and MSIDR. Appropriate sized mature anthers were dissected in 2% acetocarmine and then were stored in 2% acetocarmine stain for 4-5 days. Then these anthers were squashed in a drop of fresh stain on the slide. Alternate warming, cooling and tapping of a coverglass placed on the material was done repeatedly for obtaining better spread of chromosomes and bursting of pollen grains. Overstaining followed by destaining with 45% glacial acetic acid resulted in good preparations. Another protocol of fixation of mature tassels in 3:1 alcohol-acetic acid mixture followed by overstaining and destaining of pollen also gave a high degree of success. The first microspore division was the appropriate phase for identifying individual chromosomes of the haploid complement.
Clearly delineated heterochromatic bands and knobs were visible during early prophase of the 1st microspore division. Gradually the bands, due to chromosomal condensation, lose their individual identity, while the knobs continue to maintain identity up to late prophase. The total length, relative length and arm ratio of individual chromosomes was found to be constant along with fixed position of heterochromatic knobs and bands. The karyotype of pollen chromosomes gives us a clear and better understanding of the genome being contributed to the next generation.
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