To improve the transformation efficiency of wheat (Triticum aestivum L.) mediated by Agrobacterium tumefaciens, we explored the possibility of employing the basal portion of wheat seedling (shoot apical meristem) as the explants. Three genotypes of wheat were transformed by A. tumefaciens carrying β-1, 3-glucanase gene. After vernalization, the seeds to be transformed were germinated. When these seedlings grew up to 2～5cm, their coleop tile and half of the cotyledon were cut out, and the basal portions were infected by A. tumefaciens. A total 27 To transgenic plants were obtained, and the average transfor mation efficiency was as high as 9.82%. Evident segrega tion occurred in some of the T1 plants, as was indicated by PCR and Southern blotting analysis. Investigation of the T2 plants revealed that some transformed plants had higher resistance to powdery mildew than the controls. Northern blotting revealed that β-1, 3-glucanase gene was normally expressed in the T2 plants, which showed an increased resistance to powdery mildew. The results above indicate that the exogenous gene has been successfully integrated into the genome of wheat, transmitted and expressed in the transgenic progeny. From all the results above, it can be concluded that Agrobacterium-inoculum to the basal por-tion of wheat seedling is a highly efficient and dependable transformation method. It can be developed into a practi-cable method for transfer of target gene to wheat.

We report the production and characterization of somatic hybrids between Triticum aestivum L. and Agropyron elongatum (Host) Nevishi (the synonym is Thinopyrum ponticum). Asymmetric protoplast fusion was performed between Agropyron elongatum protoplasts irradiated with a low UV dose and protoplasts of wheat taken from nonregenerable suspension cultures. More than 40 green plantlets were obtained from 15 regenerated clones and one of them produced seeds. The phenotypes of the hybrid plants and seeds were intermediate between wheat and Agropyron elongatum. All of the regenerated calli and plants were verified as intergeneric hybrids on the basis of morphological observation and analysis of isozyme, cytological, 5SrDNA spacer sequences and random amplified polymorphic DNA (RAPD). RFLP analysis of the mitochondrial genome revealed evidence of random segregation and recombination of mtDNA.

Intergeneric somatic hybridization between wheat (cv Jinan 177) protoplasts that have 24 28 chromosomes and Hapnaldi villosa protoplasts con-taining 11 14 chromosomes was carried out by the polyethylene glycol (PEG) method A high frequency of hybrid calli and plants were obtained frpin the fusion products, as revealed by cytological and biochemical techniques and by PCR analysis of 5S rDNA spacer sequences GISH (genomic in situ hvbridization) anal-ysis confirmed the presence of chromosomes frpin both parents in the hybrid clones and the COlBitlon occur-rence of translocations between them The RFLP analysis of the organellar DNA using mitochondrion-and chloroplast-specific probes revealed that mito-chondria frpin both parents existed in the cells of hybrid calli and their recombination. whereas chloro-plasts segregated and recombined randomly The gross momhology of hybrid plants resembled that of wheat, but the gross morphologv of their ovaries and anthers were intermediate between those of the two parents The relationship between hybrid plant regeneration and the balance of genetic materials in hybrid clones is discussed.

Wheat productivity is severely affected by soil salinity mainly due to Na+ toxicity to plant cells. To improve the yield performance of wheat in saline soils, we have generated transgenic wheat expressing a vacuolar Na+/H+ antiporter gene AtNHX1 from Arabidopsis thaliana, to enhance the plant capacity of reducing cytosolic Na+ by sequestering Na+ in the vacuole. The AtNHX1 transgenic wheat lines exhibited improved biomass production at the vegetative growth stage and germination rates in severe saline conditions. A field trial revealed that the transgenic wheat lines produced higher grain yields and heavier and larger grains in the field of saline soils with the electrical conductivity values of soil saturation extracts (ECe) of 10.6 and 13.7dSm−1. The transgenic lines accumulated a lower level of Na+ and a higher level of K+ in the leaves than non-transgenic plants under saline conditions (100 and 150mM NaCl). These results indicate that the salt tolerance of wheat and grain yield in saline soils can be improved by enhancing the level of the vacuolar Na+/H+ antiporter.

The vast majority of angiosperms are (or were once) polyploid, and as hexaploid bread wheat has undergone two ploidy events separated by approximately 0.5 million years, it represents an elegant model to study gene silencing over time in polyploids. Using an SSCP platform, we have analysed patterns of transcriptional silencing (frequency, genome identity and organ specificity) within 236 single-copy genes, each mapping to one locus on one of the three homoeologous chromosomes within groups 1, 2, 3 and 7 of wheat. In about 27% of unigenes expressed in leaf, and about 26% of those in root, one (rarely two) members of a gene set (homoeoalleles) were not present in the cDNA template. Organ-specific regulation is commonplace, with many homoeoalleles transcribed in leaf but not root (and vice versa). There was little indication of extensive bias towards selective silencing of a particular genome copy. Expression of some of the silenced homoeoalleles was restored in certain aneuploid lines and varieties, and these displayed a significant degree of genetic variation for the silencing of a given homoeoallele. We propose that a substantial proportion of this phenomenon is effected by an epigenetic mechanism, and suggest that this form of genetic variation may be a significant player in the determination of phenotypic diversity in breeding populations.