HISTOLOGICAL AND CYTOCHEMICAL STUDIES ON FIVE GENETIC MALE-STERILE LINES OF BARLEY (HORDEUM VULGARE)

Abstract

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.

Male Sterility in Barley

“…In these three mutants the tapetal cells, unlike those in male fertile anthers, do not start degenerating after the tetrad stage but stay firm, enlarge considerably and encroach upon the sporangial lumen. Similar tapetal hypertrophy followed mierospore degeneration occurs in some other male sterile mutants of barley (KAUL and SINGH 1966, RoATH and HOCKETT 1970, MIAN et al 1974 and rye (CEBRAT and ZADECKA 1978). On the other hand, unlike in msg2o, msg7a, msg7b and msg27, the ms genes in msgi4, msg24, msg32 and msg33 impair growth and maturation of the microspores only and not the tapetum.…”

“…The tapetal development and disintegration in these four barley mutants are similar to that of the male fertile anthers. Similar specific action of ms genes on microspores only and not on tapetum and other anther wall layers is also (normal) The events until free mierospore stage in male steriles are similar to male fertiles except in ms2c in which tapetal and PMC degeneration initiates after meiosis I. known in some other male sterile mutants of barley (KAUL and SINGH 1966, 1968, ROATH and HOCKETT 1970, MIAN et al 1974) and maize (ALBERTSEN and PHILLIPS 1981). Whereas in many of these barley and maize mutants, the ws gene action and expression are variable and diffuse, in the presently investigated barley mutants, ms genes expression is specific, stable and strong in all the male sterile genotypes except in that variations occur in the degree and time of degeneration.…”

Cyto-histological studies on anther and pollen development in alloplasmic rye.

“…However, the precise role of tapetum on male sterility is still controversial, specially in the cause-effect relationships between tapetal alterations and microsporogenesis abortion. So, although in many papers tapetal alterations preceding pollen abortion have been described, Mian et al (1974) on analyzing the effect of several barley male sterilizing genes on the basis of DNA and histone turnover, pointed out that the genic effect can first manifest at micro spore or first at tapetum; but always both tapetum and microspore showed altera tions. Other authors, as Fukasawa (1956) in wheat on ovata cytoplasm and Toku masu (1976) in Pelargonium, have not found aberrant behaviour of tapetum in male sterile lines.…”

“…Thus, the precocious degeneration of tapetum or its delayed dis appearance in relation to its normal evolution may be the cause of pollen abortion (Chaugan and Shing 1966, Jouve 1973, Rai and Stoskopf 1974, Mian et al 1974.…”

Implications of cytoplasmic male-sterility systems for development and deployment of pest resistant hybrids in cereals.

“…Asparagine and glutamine are important vehicles of nitrogen transport in higher plants, and their accumulation influences pollen development and physiology. Reduced nucleic acid content has also been reported in male-sterile anthers of sorghum [5,6] and barley [7]. Nucleic acid content increases in male-fertile wheat anthers, and decreases in T-type CMS anthers after the tetrad stage, and in Taign CMS system after the sporogenous cell stage [8].…”