Callus formation from stem internodes of the apple rootstocks M.9, M.25, M.26, M.27 and the cherry rootstock Colt, and from pith of Nicotiana tabacum cv. Wisconsin 38 was initiated on 4 c~-naphthaleneacetic acid (NAA)-based media (2.0-10.0mgl-~). Transfer of callus to corresponding media lacking NAA allowed regeneration of shoots from callus of M.25, M. 27, Colt and tobacco but not of M.9 and M.26. With M.25 phloroglucinol (PG) depressed regeneration from 30 to 10% and no regeneration was observed in cultures grown in the presence of casein hydrolysate (CH) and glutathione (GSH).Organogenesis was also obtained from leaf discs of M.27 employing 6-benzylaminopurine (BAP) at 5.0mg1-1 and 2,4-dichlorophenoxy acetic acid (2,4-D) at 0.1 mg 1-~. The regenerated shoots have been multiplied and rooted.Organogenesis also occurred in M.26 from small (1-2mm), green, compact embryoid-like structures derived from stem and leaf surfaces of excised axiUary shoots. These structures differentiated into shoots at a low frequency (< 1%) on media containing BAP (1.0 mg 1 -~ ) and indole-3-butyric acid (IBA) (0.1 mg 1 -~ ) and could also be micropropagated by subsequent axillary shoot proliferation.

An in vitro regeneration technique using root callus has been combined with colchicine application to produce hexaploid plants from the sterile triploid cherry rootstock Colt. Colchicine (50 mg/l) was applied together with auxin (IBA) (3 mg/l) either before or after root primordium formation in single excised micropropagating shoots. In both cases shoots were regenerated in vitro from the putative hexaploid roots. Both methods produced hexaploid plants but more than 70% of the regenerated clones were still triploid. The hexaploid plants were distinguishable from the triploids on morphological as well as cytogenetic grounds. Quantitative characters such as leaf length/breadth ratio, stomatal length and density in the hexaploids were significantly different from both regenerated and non-regenerated triploids.

Cardiac myocyte cell culture from fourteen day old embryonic chicken heart was prepared. This cultured cell system was used to examine the regulation of troponin C (TnC) synthesis in cardiac muscle. To examine the regulation of TnC polypeptide synthesis, cardiac myocyte cells were pulse labelled with 35S-methionine at different days after plating. The synthesis of TnC was measured by determining the amount of radioactivity incorporated into the TnC polypeptide following separation by two dimensional gel electrophoresis. These measurements showed that TnC synthesis was maximum in 36 to 48 h old cultures and reached its lowest level in 4 day old cultures. This was in contrast to the synthesis of actin and tropomyosin. Synthesis of these polypeptides were lowest in 36 to 48 h old cultures and was maximum in 7 day old cultures. To examine whether the synthesis of TnC polypeptide paralleled the levels of TnC mRNA the sequences homologous to quail slow TnC cDNA clone were measured by hybridisation. The results showed that the decrease in the synthesis of troponin C polypeptide cannot be fully explained by the decrease in the steady state level of troponin C mRNA. The possibility of a role of translational control of troponin C mRNA in this process is discussed.