Tissue cultures ofTriticum aestivum L. (wheat) initiated from young inflorescences and immature embryos possessed the potential for regeneration of whole plants. Both a friable and a compact type of callus were produced on Murashige and Skoog's medium with 2 mg/l 2,4-dichlorophenoxyacetic acid. The friable callus contained meristematic centers in which the peripheral cells ceased dividing, elongated, and could be easily separated. Roots were frequently formed in this type of callus. The compact, yellowish, and nodular callus arose from the epithelial and sub-epithelial cells of the embryo scutellum, and the rachis and glumes of the young inflorescence. Such callus had a smooth surface and characteristic chlorophyllous areas. Plants were regenerated only from the compact callus. The first sign of differentiation in the compact callus was the formation of a cleft or notch on the smooth surface, followed by the appearance of trichomes and the direct development of leafy structures which were not associated initially with any shoot meristems. Multiple shoots subsequently arose at the bases of the leafy structures, which are considered modifications of the scutellum, a definitive part of the cereal embryo. Accordingly, we suggest that while typical bipolar embryos are generally not formed, plant regeneration nevertheless takes place through embryogenesis and the precocious germination of the embryoids. Plants regenerated from immature embryo and inflorescence cultures were grown to maturity in soil, and were shown to have the normal chromosome number of 2n=6x=42.

Plant regeneration from cultured immature embryos and inflorescences ofTriticum aestivum L. (wheat): Evidence for somatic embryogenesis

Efficient tissue culture and regeneration methods were established using immature wheat embryos as expiants. Genotype differences in culturability were evident, and from the ten accessions most amenable to culture, a total of 2,846 plants were regenerated. Extensive somaclonal variation for morphological and biochemical traits was observed among 142 regenerants of a Mexican breeding line, ‘Yaqui 50E’, and their progeny. Variant characters included height, awns, tiller number, grain colour, heading date, waxiness, glume colour, gliadin proteins and α-amylase regulation. The variant characters were heritable through two seed generations and included traits under both simple and quantitative genetic control. Segregation data suggested that mutations both from dominance to recessiveness, and from recessiveness to dominance, had occurred. Most mutations in the primary regenerants were in the heterozygous state but some were true-breeding and presumed to be homozygous. Chromosome loss or addition did not account for the variation and none of the variant phenotypes was observed in over 400 plants from the parental seed source. The distinctive parental gliadin pattern was maintained in the somaclones thus excluding seed contamination or cross-pollination as a source of the variation.

Heritable somaclonal variation in wheat

Immature embryos and inflorescences of wheat (Triticum aestivum) were cultured on agar media. The presence of the auxin 2,4-D induced the formation of multiple shoots in a proportion of cultures. In some cases the shoots developed from organized, embryoid-like structures. The morphogenetic capacities of 25 different cultivars of spring and winter wheat were compared, and clear differences were found between genotypes. Shoots were cultured separately, and the resulting plants grown to maturity in the glasshouse. Over a thousand plants were regenerated in this way, and phenotypic variation was observed amongst the regenerants.

Plant Regeneration from Cultured Immature Embryos and Inflorescences of 25 Cultivars of Wheat (Triticum aestivum)

Embryogenic callus was induced on segments of young leaves of sugarcane (Saccharum officinarum L) cultured on Murashige and Skoog's medium supplemented with 05–30 mg/2,4-D, 5% coconut milk and 3–8% sucrose The fourth and fifth leaves, especially their midrib and sheath regions within 5 cm from the leaf base, were most suitable for the induction of embryogenic callus Many embryoids (= somatic embryos) were formed when the callus was transferred to low 2,4-D media (025–05 mg/l), or was allowed to remain on the high 2,4-D medium for a prolonged period Plantlets obtained from the germination of embryoids were transferred to soil and grown to maturity

Somatic embryogenesis in sugarcane (Saccharum officinarum L.) I. The morphology and physiology of callus formation and the ontogeny of somatic embryos

A method for reproducibly initiating tissue cultures from immature sorghum inflorescences is described. The cultures are maintained through the proliferation of embryo-like structures and shoot primordia, which under appropriate conditions grow further to form plants. Evidence is presented that these structures develop from a tissue similar to that found in the scutellum of immature embryos, which arises from superficial cells of the inflorescence expiants. Possible applications of such a system are discussed.

Embryogenesis from cultured immature inflorescences of Sorghum bicolor

Callus cultures of wheat (Triticum aestivum L.) were established by incubation of segments from root tips, shoots of seedlings, and from rachis with B5 and T media. 2,4,5-Tri-chlorophenoxyacetic acid, Benazolin, and Banvel D (Dicamba) were found to be appropriate growth regulators for initiation and maintenance of wheat callus cultures. Cytokinins inhibited callus growth. This effect was less pronounced with zeatin than with kinetin and benzyladenine. Supplementation of media with cytokinins, however, increased the number of roots formed in the callus. Shoots and complete plants were regenerated from rachis and shoot callus.

D. Dudits

Papers

Study of callus growth and organ formation in wheat (Triticum aestivum) tissue cultures