RESPONSE OF IN-VITRO CULTURES OF NICOTIANA-TABACUM L. TO COPPER STRESS AND SELECTION OF PLANTS FROM CU-TOLERANT CALLUS

In Nicotiana tabacum L. var. EEL W3 copper (Cu) at concentrations high er than 50 mu M significantly inhibited callus growth and shoot regene ration. After 5-6 months of culture only a few morphogenic callus line s survived in the presence of 100 mu M Cu. These calluses showed the c apacity to grow and regenerate shoots through successive subcultures o n medium containing 100 mu M CU. The 100 mu M Cu-tolerant shoots, in c omparison to regenerated control shoots, formed roots only when cultur ed in the presence of 100 mu M CU. From five independent Cu-tolerant c allus lines in a culture period of 4-5 months more than 50 plants (def ined 'tolerant') able to grow in presence of 100 mu M Cu were obtained . These plants showed normal xylem tissue formation while control rege nerated plants growing in normal Cu MS content (0.1 mu M) had few xyle m elements in the central cylinder. No difference as far chlorophyll c ontent and chloroplast structure was found among Cu-tolerant and contr ol plants. In Cu-tolerant plants, dry matter production was higher tha n in controls, particularly in roots.