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The action of the genes msg5, msg9, msg10, msg14, and msg18 in barley (Hordeum vulgare L.) is almost entirely restricted to the sporogenous and tapetal tissues of the anther. No histological effects are found before the completion of meiosis except in msg18. Subsequently their behavior becomes distinctly deviant. In msg5, 9, 14 and 18 soon after a normal meiosis the microspores begin to deteriorate and are almost completely deformed at a period corresponding to that just before microspore division in normal anthers. In msg10 deleterious effects on microspores first appear midway between the end of meiosis and the beginning of microspore karyokinesis.The tapetum remains nondegenerate and persistent in msg5, 10 and 14 but suddenly collapses after the free microspore stage in msg9. In msg18 it shows an early effect during the meiotic period, when failure in the last tapetal nuclear division (karyokinesis) results in an early collapse of this tissue.Nuclear DNA and histone in male-sterile sporogenous and tapetal tissues as measured by microspectrophotometry increase at the normal rate during the premeiotic S phase. However, in the sporogenous tissues, the subsequent DNA and histone syntheses that normally culminate in microspore mitosis are distinctly lacking. Thus in all male-steriles except msg10, the microspore nuclei show an actual loss in these two macromolecules and in msg10 there is an initial rise only for a short period, followed by a dramatic drop.Nuclear DNA and histone in tapetal tissues subsequently show variable behavior, which seems to be specific for each male-sterile line.The behavior of sporogenous and tapetal tissues thus lends support to the hypothesis that there is transport of substances, critical to development, between the porogenous tissue and tapetum. The effects on DNA-histone turnover, first in the sporogenous tissue and then in the tapetum, suggest that the action of msg5 and 9 is initiated within the microspores when they are still invested in a callose wall. On the other hand, in msg10 and 14 a reverse sequence indicates that the action is initiated in tapetal tissues. The effect in msg18 is a direct consequence of defective tapetal functioning.All male-steriles at the free microspore stage show drastic reductions in nucleolar volume (and hence in rRNA synthesis) accompanied by a high frequency of binucleolate microspore nuclei.

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