Cytoplasmic male sterility in barley: Evidence for the involvement of cytokinins in fertility restoration

Abstract

The hypothesis of the association between an increase in cytokinin activity and restoration of anther fertility in mmi cytoplasm was tested. The following barley lines with Hordeum vulgare cv. Adorra nuclear gene background were studied: Adorra cytoplasm without nuclear restorer gene (fertile), Adorra cytoplasm homozygous for nuclear Rfmla gene (fertile), msml cytoplasm without restorer gene (male sterile), miml cytoplasm homozygous for nuclear Rfmia gene (fertile). Ethanolic extracts of root exudate were fractionated and bioassayed for cytokinins. Both the biological activity and the total quantity of cytokinins appeared lowest in the unrestored male sterile line. The total biological activities ofcytokinins in the three fertile lines were similar, but the quantities in the restorer gene carriers appeared lower. On the other hand, the restorer gene carriers, independent of the cytoplasm, showed 8-9 times more of a bound cytokinin. Because the bound form is evidently underestimated by the bioassay, the increase in the bound cytokinin fraction may mean even a higher total content in the Rfmla gene carriers than in Adorra without the gene. The bound cytokinin may be translocated more readily to distal organs (e.g., the anthers) compared with unbound cytokinins. Because cytokinins are associated with various ecophysiological processes, the rise in a particular form may explain the heterogeneous distribution ofthe restorer gene in wild barley populations in different regions of Israel.The msml and msm2 maternal male sterilities in barley were derived from two strains of the wild progenitor of barley originating from Israel (1, 2). The original strain carrying msml is homozygous for a dominant restorer gene designated as Rfmla (3). This msml-Rfmla system with the genetic background of a domesticated barley cultivar is considered in this article.Some genotypes of wild (4) and domesticated barley (5) are capable of partial restoration of male fertility. In partially restored msml plants, fertile anthers appear at the lowest florets ofthe spikes (5), which probably means that the agent for partial fertility is an acropetally translocated substance or substances. In previous studies (6, 7) a number of physiological features of unrestored male sterile plants could be explained as responses to decreased cytokinin level. Such features were increased chlorophyll a/b ratio, decreased carotenoid content, increased xanthophyll/,B carotene ratio, higher susceptibility to induced leaf senescence, anther protein instability, low amino nitrogen pool in the anthers, and increased rate of germinal root elongation of the seedlings. Respectively, the restored plants had features indicating normal or increased levels of cytokinins. Based on these observations, the hypothesis was proposed (i) that the carrier of the restorer gene has either a higher total cytokinin content or else greater amounts of one or more cytokinin types than has the noncarrier; (ii) because the Rfmia gene is dominant, it was probable that this gene would ...

Transgenic Studies on the Involvement of Cytokinin and Gibberellin in Male Development

“…Anthers of several male-sterile mutants including the sl-2 (stamenless-2) mutant of tomato (Lycopersicon esculentum; Sawhney and Shukla, 1994) and a genic male-sterile line of rapeseed (Brassica napus; Shukla and Sawhney, 1993) have lower endogenous cytokinin levels. Cytokinins have also been shown to reverse cytoplasmic male sterility in barley (Hordeum vulgare;Ahokas, 1982). In the female plants of dioecious species such as hemp (Cannabis sativa) and spinach (Spinacia oleracea), and the gynoecious line of cucumber (Cucumis sativus), the formation of male flowers is promoted by exogenous applications of GAs (Mitchell and Wittwer, 1962;Pike and Peterson, 1969;Mohan Ram and Jaiswal, 1972; Khrianin, 1978a, 1978b).…”

Positive Selection for Male-Sterile Mutants of Arabidopsis Lacking Adenine Phosphoribosyl Transferase Activity

“…In some sections the tetrads of the mutant appear to be slightly altered, but it is not clear whether this is an indication that microsporogenesis is affected initially at the tetrad stage. It is often difficult to determine precisely when pollen development becomes aberrant in a male-sterile mutant (9 Several reports have suggested that cytokinins may have a role in pollen development (1,22). Indeed, it has been suggested that a nuclear restorer gene for cytoplasmic male sterility in barley acts by altering cytokinin metabolism (1).…”

“…It is often difficult to determine precisely when pollen development becomes aberrant in a male-sterile mutant (9 Several reports have suggested that cytokinins may have a role in pollen development (1,22). Indeed, it has been suggested that a nuclear restorer gene for cytoplasmic male sterility in barley acts by altering cytokinin metabolism (1). APRT has been implicated in the phosphoribosylation of cytokinin bases in vitro (4,7) and in vivo (10,19 The ability to select for loss of APRT activity should facilitate the use of the apt locus in a variety of different experiments in the molecular genetic analysis of Arabidopsis.…”

“…APRT catalyzes the synthesis of adenylic acid from adenine and 5-phosphoribosyl-pyrophosphate. Mutants deficient in APRT activity have been isolated in several bacterial and mammalian species by selecting for resistance to 2-fluo- 12 [1] adenine phosphoribosyltransferase, [2] hypoxanthine/guanine phosphoribosyltransferase, [3] adenosine nucleotidase, [4] adenine aminohydrolase, [5] inosine phosphotransferase and inosine kinase, [6] 5'-nucleosidase, [7] xanthine oxidoreductase, [8] guanine aminohydrolase, [9] adenylosuccinate synthetase, [10] IMP dehydrogenase, [11] GMP synthetase, [12] GMP reductase. Adapted from Barankiewicz and Paszkowski (3).…”

Map-based cloning of the fertility restoration locus Rfm1 in cultivated barley (Hordeum vulgare)

“…Recent years have seen the market introduction of hybrid cultivars for winter barley based on the msm1 sterile cytoplasm described by Ahokas (1979Ahokas ( , 1982Ahokas ( , 1983, following the pioneer work by Paul Bury and his team at New Farm Crops, Lincolnshire UK. The conversion of elite European winter barley material into male and female parental lines culminated into the commercialization of the first ever barley hybrid, named Colossus under the Hyvido trademark.…”