SummaryA novel endosperm-specific gene named Esr (embryo _surrounding region) has been isolated by differential display between early developmental stages of maize endosperms and embryos. It is expressed in a restricted region of the endosperm, surrounding the entire embryo at early stages (4 to 7 days after pollination, DAP) and everdecreasing parts of the suspensor at subsequent stages. The expression starts at 4 DAP and is maintained until at least 28 DAP. A minimum of three Esr genes are present in the maize genome and at least two of them map to the short arm of chromosome 1 at position 56. The Esr genes contain no introns and show no significant nucleotide or amino acid sequence homologies to sequences in the databases. The open reading frames encode basic proteins of 14 kDa with presumptive signal peptides at their Ntermini followed by a hypervariable and a conserved region. The gene product may play a role in the nutrition of the developing embryo or in the establishment of a physical barrier between embryo and endosperm.

SummaryIn cereal seeds, the aleurone layer and the embryo share several characteristics, including synthesis and accumulation of lipid bodies, desiccation tolerance and dormancy. A number of Balem transcripts present in both the barley deurone layer and the embryo have been cloned by differential screening of a cDNA library from aleurone layers of immature barley grains. The Balem clones constitute two subgroups, one for which the transcripts are detectable in aleurone layers and embryos of developing seeds only (B23D and Bl5C), and another for which transcripts are present also in germinating embryos and in maternal tissues (B12D, B14E and 831 E). Sequence analysis identified 8230 and B15C as the barley homologues of the 18 kDa oleosin of maize embryos (72% amino acid identity) and the dormancy-associated transcript pBS128 from Bromus secalinus (95% identity), respectively. In sifu hybridization experiments demonstrate that in the embryo, the B23D transcript is mainly present in the scutellum, whereas the B15C transcript is predominantly present in shoot and root apices. Using anther-derived embryos and embryogenic cell suspensions, it is demonstrated that the B23D and B15C transcripts can be used as molecular markers for somatic embryogenesis. The functions of the transcripts in the second Balem subgroup remain unknown. Further studies on the Balem transcripts may shed light on the molecular basis for the extensive similarities between the embryo and the aleurone layer of the endosperm in the grass family.

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The maize ( Zea mays L.) endosperm consists of an epidermal like layer of isodiametric aleurone cells surrounding a central body of starchy endosperm cells. In disorgal1 ( dil1) and disorgal2 ( dil2) mutants the control of the mitotic division plane is relaxed or missing, resulting in mature grains with disorganized aleurone layers. In addition to orientation of the division plane, both the shape and size of the aleurone cells are affected, and often more than one layer of aleurone cells is present. Homozygous dil1 and dil2 grains are shrunken due to reduced accumulation of starchy endosperm and premature developmental arrest of the embryo, and mature mutant grains germinate at a very low rate and fail to develop into plants. However, homozygous mutant plants can be obtained through embryo rescue, revealing that both mutants have an irregular leaf epidermis as well as roots with a strongly reduced number of root hairs and aberrant root hair morphology. Our results suggest the presence of common regulatory mechanisms for the control of cell division orientation in the aleurone and plant epidermis.

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In a study of androgenesis in 90 Norwegian genotypes of perennial ryegrass (Lolium perenne L.), heritabilities ranged from h b (2) =0.46 to 0.80. Very high or completely positive genotypic correlations were found between most characters of androgenetic response (e.g. embryo-like structures per 100 anthers, plants per 100 embryo-like structures, albino plants per 100 anthers, green plants per 100 anthers). Three genotypes, 2 Norwegian (7-5 and 9-5) and 1 Danish (245), which had significantly different androgenetic responses were selected to study the genetic control of the processes. Genotypes 7-5 and 9-5 were highly embryogenie, 7-5 and 245 were relatively high producers of green plants, while 9-5 was unable to produce green plants. The six possible reciprocal crosses between these three genotypes were made, and 10 or 11 F1 plants from each cross were used for anther culture experiments. The cross 7-5 x 245 showed average superiority over both parents for total plant regeneration and green plant production, results not previously reported. The phenotypic correlations estimated among progenies from the crosses ranged from r=-0.99(***) to 0.81(***). These considerable changes, relative to the results of the screening experiment, are most likely the result of changed allele frequencies caused by the strong selection of parents in these crosses, and a relatively simple genetical control. This is also inferred from the large transgressive segregation observed.

Genotypes of Lolium perenne L. with different androgenetic responses were used to test effects of induction medium composition. The media tested were potato II (pII), 190-2, and modified Linsmaier and Skoog media, LS-1, LS-2, and LS-3. The effect of different gelling agents, activated charcoal in a 'double layer' design, and casein hydrolysate were also studied. From 36,696 anthers, 25,906 embryo-like structures, 1,959 albino and 173 green plants were generated. Significant differences were found between media, genotypes and medium-genotype interactions studied. All three media commonly used, pII, 190-2, and LS-3, were equivalent in production of green plants. Cold pretreatment of the anthers (4°C) significantly increased the number of embryo-like structures, the number and proportion of albino plants produced, but not the production of green plants.

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