II.1 Male sterile mutants of barley. III. Additional inaperturate mutants.
H. Ahokas. Department of Genetics, University of Helsinki, P. Rautatiekatu 13, SF-00100 Helsinki 10, Finland. "R"
The male steriles msg8ch (Male sterile stock No. 56), and msg16co (Male sterile stock No. 65) produce inaperturate or poreless undeveloped pollen grains. The quality of their pollen is variable as revealed by the different stainings (Roath & Hockett 1971) The mutant msg6cf was previously shown to be inaperturate (Ahokas 1975a, 1975b). Two of the uninduced or spontaneous mutants found by the present author are inaperturate. They are now assigned by the symbols msg,,dm and msg,,dn (Hockett, pers. comm.). Some genetic data of the new mutants are given in Table 1. Neither of them was found to be allelic to msg6cf: The fertile : sterile ratio of the first generation of the cross, the new mutant x the heterozygote Msg6cf/msg6cf, was for msg,,dm 37 : 0, and for msg,,dn 32 : 0. Both the mutants are of the normal female fertility. In the routine crosses, msg,,dm and msg,,dn displayed a seed set of 69% and 65%, respectively.
Table 1 Ratios of fertile to sterile plants in F2 and selfing behavior of sterile plants.
The pollen grains of the male steriles were studied with the Fast Blue B salt staining method (FBB), which is specific for the sporopollenin containing structures (Ahokas 1975b, 1976) The unsectioned pollen grains can be mounted by applying to cover slip a droplet of warm 1% gelatin. The pollen grains or dissected anthers are mixed in the gelatin solution which is dried to form a film in a current of air at 37°C.
The aperture site of the msg8ch pollen grains can usually be demonstrated with FBB staining. The anthers, which open at anthesis, mostly bear undeveloped pollen grains with a stainable ring of the apertural annulus without any actual pore (Fig. 2). The less advanced anthers have pollen grains with apertures much more reduced or the site is indistinguishable (Fig. 3). The exine staining with FBB is darker than that of a non-mutant.
Both the mutants msg16co and msg,,dm produced completely inaperturate pollen grains which differ from each other by the appearance and the FBB staining of the exine and bv the quality of the pollen grains. While the exine relief and staining in msg,,dm is normal, the staining of the msg16co exine is of the darker reddish tinge typical of the immature pollen. The exine of msg16co is variably thinner, not distinctly two-layered, and bears less spinules than that of a non-mutant. The pollen shower is sometimes lacking in the mutant msg16co (Roath & Hockett 1971, and observations under Finnish conditions), while msg,,dm has a normal anther behavior both in field and greenhouse.
The apertural site of the msg,,dn pollen grain is variable by its developmental stage and stainability (Fig. 4, 5). A low percentage of adequately porate pollen must be produced, since selfing is possible (Table 1). A narrow, unstainable pore is present in some of the pollen grains. The apertures of msg,,dn are similar to or a little more advanced than those of msg6cf (Fig. 1) when examined with the differential interference microscope or with FBB staining. The pollen shower is normal.
Figures 1-6. Apertures of barley pollen grains stained with FBB. The staining of the exine was largely eliminated with printing the photographs. 1. The male sterile msg6cf. 2 & 3. The male sterile msg8ch. 2 is of a dehiscing anther. There is no actual pore, but the space inside the ring is covered by the exine. 3 is a typical example of a less advanced, undehiscing anther. 4 & 5. The male sterile msg,,dn. That in Fig. 4 has a fairly large pore, which is not circle-shaped. 5 shows a much less advanced aperture. 6. The aperture of a fertile plant of cv. Betzes for control. - Scale (10 "mu"/m), common to all the figures.
Especially the mutants msg,,dm, msg6cf, and msg,,dn can be classified as actual pollen steriles. This type of male sterility might not provide the best facility for hybrid seed production, The stigmas of the pollen steriles become occupied by their own inert pollen grains to a varying degree. That may decrease the probability of catching foreign pollen.
Though the tests for allelism are incomplete, it can be concluded that several genes contribute to the apertural formation of barley.
References:
Ahokas, H. 1975a. Male sterile mutants of barley. I. Inaperturate pollen of the msg6cf mutants. Ann. Bot. Fennici 12:17-21.
Ahokas, H. 1975b. Male sterile mutants of barley. II. Cytochemistry of nonmutant and msg6cf microspores and pollen. Hereditas 81:33-45.
Ahokas, H. 1976. Evidence of a pollen esterase capable of hydrolyzing sporopollenin. Experientia 32: 175-177.
Hockett, E.A. Personal communication dated December 9, 1975.
Roath, W.W. & Hockett, E.A. 1971: Genetic male sterility in barley. III. Pollen and anther characteristics. Crop Sci. 11:200-203.
