Pollen grains from two inbred lines, W22 and 824, and from a derivative of "Stock 6" (the high haploid line developed by E. H. Coe, Jr.) were cultured on a medium developed by Pfahler (Canad. J. Bot. 45:839, 1967) in petri dishes at 27 C. Three hours after inoculation all activity was stopped by flooding the surface of the medium with Farmer's solution; the pollen grains could then be observed under a dissecting microscope. The following data include the frequency of grains which germinated and the frequency of grains which developed more than one pollen tube:
These data show significant differences in the germination ability of pollen grains of the two inbred lines examined (824 and W22), which may reflect differences at the genotypic level. The derivative of "Stock 6" showed a percentage of pollen grain germination close to that of W22.
The differences in frequency of pollen grains showing two tubes may be of some significance. The highest value was found with the derivative of "Stock 6," the high haploid line. The heterofertilization frequency was also found to be high with Stock 6 (Sarkar, K. R., Diss. Abst. 27:1736, 1966; Coe, E. H. and K. R. Sarkar, J. Hered. 62:118, 1971). The present data, although preliminary, suggest that the abnormal germination of pollen grains with two tubes may have some correlation with the frequent induction of maternal haploids and with the high frequency of heterofertilization, perhaps as a consequence of an abnormal distribution of nuclei in double pollen tubes. Cytological examination of 96 grains with two pollen tubes from Stock 6 derivative material showed 76 cases with a 3:0 nuclei distribution (i.e., three nuclei in one pollen tube and none in the other) and 20 cases with a 2:1 distribution. One could suggest that the tubes having two nuclei might be capable of accomplishing an incomplete fertilization: the polar nuclei might receive a sperm nucleus, while the egg cell received none. The unfertilized egg could then either receive a sperm coming from another pollen tube (heterofertilization) or start development as a haploid.
N. Pogna and A. Marzetti
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