Since white pollen is not functional, it offers the possibility of screening for mutations to functional capability (from c2 whp to C2 or Whp, for example) in populations of pollen grains. Experiments directed to this purpose are in progress. In addition to reconstruction experiments involving mixtures of pollen, described in an accompanying article, an in situ reconstruction was initiated with c2-m1. Progenies were derived from crosses of c2-m1 with c2 whp, anticipating that c2-m1 with homozygous whp would have mostly white pollen but that a low frequency of yellow pollen would come from C2 sectors in the anthers. However, c2-m1 c2 whp whp plants invariably produce uniform yellow pollen, which has functional capability. Presumably the yellow pollen results from functioning of c2-m1 at a low level. We have further observed that aleurone and plant tissues in c2-m1 have a light pale background with colored sectors, but that this background is colorless to the eye in c2-m1 whp constitutions. A substantial level of function is apparently necessary to produce a threshold level of anthocyanins, but a lower level is sufficient for yellow pollen and for functional capability.

A mass screening approach, with potentially high efficiency, might be to screen tassels of c2 whp bz plants under UV for yellow-fluorescent anthers, which are so brilliant that they should stand out in the field at some distance from the UV source. Mutations to C2 or Whp in such plants would be yellow-fluorescent. Since we have also noted that progenies with C2-Idf can segregate for white pollen, the expression of C2-Idf may permit enrichment screening for mutations of this allele also.

E. H. Coe, Jr. and Stephen A. Modena

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