No abstract

[Manuscript received 21 October 1971] AbBtractHaploid callus and plants were cultured from the anthers of diploid A. thaliana. This depends on removing anthers during late prophase of meiosis, selecting a genotype favouring callus formation from dividing sporocytes on a high auxin-low kinetin concentration, fully defined medium, then inducing differentiation by transfer to a low auxin-high kinetin concentration, fully defined medium, with a light-dark cycle. Attempts to produce embryoids directly from' anthers were unsuccessful. The view that our approach may have Ii. more general application is discussed in relation to the work of others and our culture of haploid callus and plantlets from tomato (LycoperBicon eBculentum) and haploid callus from barley (Hordeum vulgare).

The morphology of Cl. kluyveri is compared with that of CI. acetobutylicum. The multilayered cell wall of both organisms differ in the number of layers and total thickness. The plasma membrane of Cl. acetobutylicum is asymmetric in electron density and can be separated from the rest of the cell by plasmolysis. Tubular or vesicular structures are observed between the wall and the plasma membrane. In contrast, the plasma membrane of Cl. kluyveri is more symmetrical, with no structures between the cell wall and the plasma membrane.Intracytoplasmic membrane systems present in Cl. acetobutylicum are morphologically similar to the mesosomes of Gram-positive aerobes. The intracytoplasmic membrane systems' of ct. kluyveri are characteristically rough in appearance, and differ in general morphology from systems usually described as mesosomes. Roughness is attributed to membrane-bound ribosomes, these being smaller than those of Escherichia coli.Polygonal structures containing moderately electron-dense material (possibly DNA) were observed in C/. kluyveri. Cl. acetobutylicum possesses membrane-bounded inclusions containing electron-dense particles similar in dimensions to E. coli ribosomes. Rows of electron-dense bands were also observed.It is suggested that the polygonal structures and rough membranes of Cl. kluyveri are components of a system for the functional expression of genetic information.

A diploid callus line of Z. mays has been established on fully defined media, taking advantage of the callus-forming potential of squashed embryos. This method is general, and thereby not restrictive to one strain or mutant cell line. Methods for the differentiation of roots, shoot primordia, and ovule-bearing horns by transfer of callus to defined media with various hormonal constituents are discussed. The callus cell line has retained its growth characteristics and ploidy level for 12 months.Botanical, genetical, and physiological studies of Zea mays have contributed substantially towards an understanding of the biology of higher plants. Further progress, especially at a molecular level, would be assisted by the availability of cell lines in tissue culture. Straus and LaRue (1954) established an endosperm callus culture, but we understand that this is now lost and that subsequent attempts by other workers failed to show the same success (A. Schwartz, personal communication). We now present a method which has proven successful for the induction of diploid callus of several varieties of Z. mays. The differentiation of plant structures from callus was only attempted with Z. mays variety B-48.Seeds were surface-sterilized by washing with ethanol (100%) and sterile distilled water (each for 10 s), repeating the procedure three times. The seeds were then placed onto autoclaved, water-soaked Whatman filter paper in sterile Petri dishes. After 48 hr at 27°C in the dark, a swelling in the embryo area of the seeds was noticed. This indicated active growth of the embryo which was about to break through the seed coat. Embryos were removed aseptically and macerated with forceps and a scalpel blade, thereby removing any existing structural organization. The resulting "cell paste" (about 20 mg) was placed onto sterile, fully defined growth medium containing mineral salts (Gamborg and Eveleigh 1968; Gresshoff and Doy 1 972a, 1972b) vitamins,t trace elements, iron-chelate (Gresshoff and Doy 1 972a, 1 972b), Difco agar (0· 8 %), glucose (2 %), and growth hormones (growth medium 1, Table 1). The cultures were incubated at 27°C in the dark. Within 2 weeks the cell mass * Manuscript