II.25. Histological and cytochemical studies on five genetic male-sterile lines of barley (Hordeum vulgare L.).
H. R. Mian, J. Kuspira, G. W. R. Walker and N. Muntjewerff, Department of Genetics, University of Alberta, Edmonton, Alberta, Canada.
Developmental studies were carried out on anthers of male-steriles and their normal sibs for msg 5, msg 9, msg 10, msg 14 and msg 18, using the original lines supplied by Hockett. Male-sterile and male-fertile sibs of each line were compared at six stages, from the archesporial stage to the 'mononucleate pollen' stage a) for differences in histological and cellular morphology b) for microphotometric differences in DNA and histone turnover in tapetal and sporogenous cells.
The action of all five msg genes is almost entirely restricted to the sporogenous and tapetal tissues of the anther. Histologically the development of these two tissues is similar to that of the normal anthers up to the completion of meiosis which is completely normal. Subsequently their behaviour becomes distinctly deviant.
In msg 5, 9, 14, and 18 the microspores begin to deteriorate soon after meiosis and are almost completely deformed at a period corresponding to that just before the microspore division in normal anthers. In msg 10 deleterious effects on the microspores first appear midway between the end of meiosis and the beginning of microspore karyokinesis.
The tapetum remains nondegenerative and persistent in msg 5, 10, and 14 but suddenly collapses after the free microspore stage in msg 9. In msg 18 it shows an unusually early effect during the meiotic period consisting of a failure in the last nuclear division (karyokinesis) of tapetum which results in an early collapse of this tissue.
Nuclear DNA and histone in sterile sporogenous and tapetal tissues as measured by microspectrophotometry increases at the normal rate during the premeiotic S phase. However, in the sporogenous tissues, the subsequent DNA and histone synthesis that normally culminates in microspore mitosis is distinctly lacking. Thus in all male-steriles, except those of msg 10, the microspore nuclei show an actual loss in these two macromolecules and in msg 10 there is an initial rise only for a short period, followed by a dramatic drop.
The tapetal tissue shows variable behaviour which seems to be specific for each male-sterile line with respect to the DNA-histone changes in sporogenous and tapetal tissues throughout anther development.
The behaviour of sporogenous and tapetal tissues thus lend support to the hypothesis that there is transport of substances, critical to development, between the sporogenous tissue and tapetum. The effects on DNA-histone turnover, first in the sporogenous tissue and then in the tapetum, suggest that the action of msg 5 and 9 is initiated within the microspores when they are still invested in the callose wall. On the other hand a reverse sequence indicates that the action is initiated in tapetal tissue in msg 10 and 14.
The effect in msg 18 is due to a direct consequence of defective tapetal functioning.
All male-steriles after the completion of meiosis, specifically at the free microspore stages, depict a drastic reduction in the nucleolar volume and hence in rRNA synthesis of microspores. This is accompanied by a high frequency of binucleolate microspore nuclei.