Heterotrophic whole plant tissues show more C-13 enrichment than their carbon sources

An inhibitor of carotene synthesis was applied to produce chlorophyll-free heterotrophic leaves on some branches of photoautotrophic tomato (Lycopersicon esculentum) plants and to produce fully heterotrophic in vitro cultured tobacco (Nicotiana tabacum) plants. The delta(13)C values of heterotrophic leaves were 1-3 parts per thousand less negative than those of the adjacent, simultaneously produced photoautotrophic leaves that would have provided the source of organic carbon for growth of tomato plants. The delta(13)C values of heterotrophic tobacco plants were > 2 parts per thousand less negative than the sucrose or any other assimilable carbon compound in the organic growth media in which they were grown. These results indicate that isotope effects associated with the use of translocated organic carbon for growth can cause an enrichment in C-13 of whole tissue. Furthermore, mass balance considerations indicate that the enrichment does not simply reflect the delta(13)C value of the organic substrate for growth. Copyright (C) 1996 Elsevier Science Ltd