Investigation of chloroplast DNA heteroplasmy in Medicago sativa L. using cultured tissue.

Medicago sativa L. cv Regen S is heteroplasmic for chloroplast DNA (cpDNA). Previous analyses of regenerated plants have shown a predominance of one of the cpDNAs which we have designated type A (the other we have designated type B). Studies of the replication of the two cpDNAs in tissue culture were carried out using leaflet expiants with defined cpDNA types and a distinguishing probe. The explants obtained showed a bias toward type A cpDNA during tissue culture. The data suggest that chloroplasts with different DNAs in a common nuclear background can multiply at different rates.