| Pistillody of the hybrids studied manifests itself in the transformation of stamens into
pistils and involves one, two or all the three stamens. Depending on this the floret
becomes two-, three- or four-pistilled while the number of stamens reduces to two, one or
is missing altogether. A pistil can be formed on a stamen at the apex of the anther, in the
middle or basal part of it or even in the filament. The stamen thus resembles a female
floret in appearance. Among polygynous florets, transitional forms are found which carry the traits both of stamens and pistils. Stamens with hardly noticeable pubescence at the terminal part as well as well-defined stigmas with characteristic hairs were observed among them. In some stamens the transformation into pistils involved one half of the anther while the other remained unchanged. There was a numerous group of stamens whose basal part turned into the ovary. Finally, there was another group of stamens which completely turned into pistils where the stigma and ovaries were differentiated. Transitional forms from male to female sex are of interest cytoembryologically. For the sake of convinience, we shall dwell on the results of studying florets with a single pistil and three stamens, then on pistilloid florets with two, three and four pistils. During the study of permanent preparations made by standard cytological methods, normally developed ovules were found in the ovaries of florets with three stamens and a single pistil. The ovules had outer and inner integuments, a nucellus with an embryo sac containing the egg-apparatus of two synergids, and an egg cell (Fig. 1). Polar nuclei in the embryo sacs were normally positioned under the egg cell, and ten to twelve antipodal cells either in the chalazal area or at one of the lateral sides. The ovaries with the ovules containing normally structured embryo sacs were considered fertile, capable of forming grain as a whole. However, there were embryo sacs with changed antipodal cells compared to fertile plants. The changes occured in the cytoplasm, nucleus and nucleolus of the antipodal cells. ln most cases the cytoplasm was more vacuolized compared to the normal state. Large vacuoli were formed as a result of fusion of smaller ones. Clumps of chromatin appeared in the nuclei which did not resemble chromosomes in form. The nucleoli differed in size and form. They were much larger not round as usual, but rod-like elongated and not vacuolated. Since such changes in the antipodal cells were found in the embryo sacs of CMS plants and were not observed normally, they may be related to the manifestation of the cytoplasmic factor responsible for pollen sterility. In florets with one pisitil of interest is also the fact that some ovules were underdeveloped: the mother-cells of the macrospores in them were not differentiated, i.e. the cells whose development results in the long run in the formation of the embryo sacs. Studies of polygynous florets show that one pistil, the central (we term it the main pistil) in all pistilloid florets is normal, a pubescent stigma is clearly seen in its upper part and the ovary in the lower part. Investigations revealed that the ovules were formed in the ovaries (Fig.2). However, the ovules cease the development. The outer coats do not develop, the mother cells of the macrospores and embryo sacs do not differentiate. The ovules of the main pistils should be considered sterile. It should be noted that the ovaries were fixed in the period of expected maturity of the embryo sacs. |
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