No abstract

In Arabidopsis, the regulation network of the seed maturation program controls the induction of seed dormancy. Wheat EST sequences showing homology with the master regulators of seed maturation, LEAFY COTYLEDON1 (LEC1), LEC2 and FUSCA3 (FUS3), were searched from databases and designated respectively as TaL1L (LEC1-LIKE), TaL2L (LEC2-LIKE), and TaFUS3. TaL1LA, TaL2LA and TaFUS3 mainly expressed in seeds or embryos, with the expression limited to the early stages of seed development. Results show that tissue-specific and developmental-stage-dependent expressions are similar to those of seed maturation regulators in Arabidopsis. In wheat cultivars, the expression level of TaL1LA is correlated significantly with the germination index (GI) of whole seeds at 40 days after pollination (DAP) (r = –0.83**). Expression levels of TaFUS3 and TaL2LA are significantly correlated respectively with GIs at 40 DAP and 50 DAP, except for dormant cultivars. No correlation was found between the expression level of TaVP1, orthologue of ABA INSENSITIVE3 (ABI3), and seed dormancy. DELAY OF GERMINATION1 (DOG1) was identified as a quantitative trait locus (QTL) for the regulation of seed dormancy in Arabidopsis. Its promoter has RY motif, which is a target sequence of LEC2. Significant correlation was found between the expression of TaDOG1 and seed dormancy except for dormant cultivars. These results indicate that TaL1LA, TaL2LA, and TaFUS3 are wheat orthologues of seed maturation regulators. The expressions of these genes affect the level of seed dormancy. Furthermore, the pathways, which involve seed maturation regulators and TaDOG1, are important for regulating seed dormancy in wheat.

Maize transcription factors for the genes of anthocyanin synthesis pathway, C1/B-peru, were delivered into developing wheat coleoptiles by a particle bombardment method. Anthocyanin pigments were induced as discrete red spots and their number reached about 60 spots per coleoptile, compared to about 20 diffused blue GUS spots, which were induced by the GusA gene transferred concomitantly. Coleoptiles of seedlings collected 36 h after germination were most suitable tissue for the expression of delivered foreign genes. One to five µg of plasmid DNA for coating gold particles was sufficient for induction of anthocyanin and GUS, indicating that the transferred gene was expressed efficiently in coleoptile cells. Helium gas pressure (900, 1100, 1300 or 1500 pounds per square inch) and distances (10, 15, or 20 cm) between the stopping screen and coleoptile did not affect significantly the efficiency of gene transfer. Seedlings arranged in a circle with a 1-cm radius on a MS medium plate were targeted well by gold particles. The results showed that the wheat coleoptile was a good target tissue for transient assay of wheat genes and that C1/B-peru can be used as a reporter gene.

Callus growth and shoot regeneration were examined in cultures of immature barley embryos incubated under various combinations of a week under a 16-h photoperiod and a week under continuous darkness. Incubation in darkness for four weeks, during which calli were formed, enhanced shoot regeneration in 'K-3' and 'Kanto Nijo-5', but inhibited it in 'Lenins'. 'K-3' and 'Kanto Nijo-5', incubated in darkness during the first two weeks of callus induction, followed by two weeks of a 16-h photoperiod (D2L2), showed a higher percentage of shoot regeneration than those incubated for two weeks with a 16-h photoperiod followed by two weeks of darkness (L2D2). Nevertheless, when the light conditions, D2L2 and L2D2, were combined into the same periods of a 16-h photoperiod and continuous darkness, except for the order, light conditions affected shoot regeneration differently. The early stage of callus induction seems to be sensitive to light. The expression ratios of the auxin-responsive gene (AUX/IAA) to the cytokinin-responsive gene (WPK4) were increased in continuous darkness in 'K-3' and 'Kanto Nijo-5'. The effects of light qualities (white, red, farred, and blue) on callus growth and shoot regeneration were also examined. Blue light inhibited shoot regeneration, as did white light, in 'K-3' and 'Kanto Nijo-5', and far-red light in 'Kanto Nijo-5'. Light probably controls shoot regeneration from calli by modifying cytokinin levels and/or response; blue light signals act in photo-inhibition of shoot regeneration in immature barley embryo culture.