Sexual development and sex chromosomes in hop.

The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex-specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in 'cones'. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.

The genetic control of grain esterases in hexaploid wheat : 2. Homoeologous loci in related species.

A comparison of EST-5 grain esterase phenotypes from wheat-alien amphiploid, addition and substitution genotypes, resolved by flat-bed isoelectric focusing identified homoeologous Est-5 loci on chromosome 3H of Hordeum vulgare, 3H(ch) of H. chilense, 3S(b) of Aegilops bicornis, 3S(1) of Ae. sharonensis and Ae. longissima and 6R of Secale cereale and 6R(m) of S. montanum. The Est-5 genes in alien species provide evidence for chromosome homoeology with wheat.

Allelic variation at α-Amylase loci in hexaploid wheat.

A study of α-amylase isozyme patterns from gibberellin-induced endosperms from more than 200 wheat genotypes has revealed allelic variation at five of the six α-Amy-1 and α-Amy-2 structural loci. These differences will find application as genetic markers and in varietal identification. The α-Amy-B1 locus on chromosome 6B was most variable and displayed eight distinct allelic forms. The nature of the allelic phenotypes, observations of segregating populations and the number of in vivo translation products of mRNAs from the α-Amy-1 and α-Amy-2 loci indicated that the individual loci are multigenic, each consisting of tightly linked subunits which produce several different isoforms.

The chromosomal locations of leaf peroxidase genes in hexaploid wheat, rye and barley.

Eight leaf peroxidase isozymes were distinguished by IEF in 'Chinese Spring'. Two genes which control the production of three of these isozymes were located on chromosome arms 1BS and 1DS by nullisomic analysis. These loci probably form part of a homoeoallelic series and have been designated Per-B1 and Per-D1 respectively. Analysis of chromosome 1B short arm terminal deletion stocks indicated that the Per-B1 locus is located between the nucleolar organiser region and another isozyme marker, Hk-B1. Two variant leaf peroxidase phenotypes were distinguished in a small sample of hexaploid wheat varieties. Analysis of wheat-alien addition and substitution lines identified homoeologous loci in rye (Per-R1) and barley (Per-H1).

Characterization of anther differentiation in cytoplasmic male sterile maize using a specific isozyme system (esterase).

During anther development, characterized in maize plants with N cytoplasm, certain esterase isozymes in non-microspore cells decrease in amount with anther age and new isozymes appear in the developing microspores. In anthers from male sterile plants with cms T or cms C cytoplasm, neither of these changes in esterase patterns occurred. In anthers from plants with cms S cytoplasm, the decrease in the esterases of non-microsporogenous cells was observed but not the appearance of microspore esterases. In lines carrying cms S cytoplasm and nuclear restorer genes, esterase changes during anther development were as in normal fertile anthers. These results are discussed with respect to the phenomenon of cytoplasmic male sterility in the different maize genotypes.

The genetic control of grain esterases in hexaploid wheat : 1. Allelic variation.

Analysis of grain esterase isozymes in Chinese Spring aneuploid genotypes by IEF confirmed that genes on the long arms of chromosomes 3A, 3B and 3D (Est-5) control the production of 19 isozymes. Allelic variants have been found for the isozyme pattern controlled by each chromosome. Segregational data involving null alleles and complex phenotypic differences indicate that the wheat grain esterases are encoded by three compound and probably homoeoallelic loci, each capable of producing at least six different isozymes. In a sample of 138 hexaploid genotypes, seven alleles were distinguished.

The use of irradiated pollen for differential gene transfer in wheat (Triticum aestivum).

The use of irradiated pollen to bring about limited gene transfer in wheat has been investigated. Doses of X-rays of 2Kr, 3Kr and 5Kr were used to generate M1 progeny between maternal and paternal genotypes differing in quantitative and major gene characters. Cytological studies of M1 plants revealed hybrids with widespread aneuploidy and structural rearrangements in the paternal genome. These effects resulted in phenotypic variation between M1 progeny and complex multivalent formation at meiosis. All M1 plants at the 5Kr and 3Kr doses were sterile and all but 2 plants at the 2Kr dose.Studies of the two M2 families from these plants revealed disturbances in genotype frequencies for some of the marker loci with an excess of maternal homozygotes and a deficit of paternal homozygotes. This was also reflected in a more maternal appearance for quantitative characters. These results are interpreted as showing that irradiation damage to the paternal genome in M1 plants results in the differential transmission of maternal alleles.

The genetics of ß-amylase isozymes in wheat : 1. Allelic variation among hexaploid varieties and intrachromosomal gene locations.

Thirty-three ß-amylase isozymes were separated in 'Chinese Spring' by IEF and the structural genes encoding seventeen of these were located by nullisomic analysis. The locations of the previously reported ß-Amy-1 loci on chromosome arms 4Aß (ß-Amy-A1) and 4DL (ß-Amy-D1) were confirmed and another set, ß-Amy-2, was found on the group 5 chromosomes. A locus on 5AL (ß-Amy-A1) was identified by nullisomic analysis and another on chromosome 5B (ß-Amy-B2) was identified by analysis of inter-varietal chromosome substitution lines. The loci are complex, each coding for several isozymes, and allelic variation occurs at all four. Two alleles were identified at ß-Amy-A1, five at ß-Amy-D1, five at ß-Amy-A2 and two at ß-Amy-B2. Eleven different ß-AMY phenotypes were distinguished amongst the 46 wheat varieties screened. The ß-Amy-A2 locus was mapped by employing chromosome 5A recombinant lines and found to be closely linked and proximal to the awn inhibitor, B1, on the long arm. An attempt to map the ß-Amy-D1 locus on chromosome 4D showed the gene to be located in the distal region of the long arm.