ABSORPTION OF HCO3- BY ROOTS AND ITS EFFECT ON CARBON METABOLISM OF TOMATO

Six-week old seedlings of tomato (Lycopersicon esculentum) were placed in growth chambers, hypocotyl and the root system (in the lower part of the chamber) being precisely separated from the stem (the upper part of the chamber). The composition of the medium was modified by enriching it with KHCO3 (converted to the value of about 0.1% CO2 concentration) or additionally with C-14. The total radioactivity associated with roots, shoots, and leaves after 72 h chase period was determined. About 61% of the total radioactivity were found in root and 39% in shoots and leaves. Differences in the concentration of HCO-3 in the medium significantly modified the concentration of malic acid (MA) in the tissues. An increase in KHCO3 concentration in the medium to the level equivalent to about 0.1% CO2 raised the level of MA by about 854%, 150%, and 134% in root, shoot, and leaf, respectively, in relation to the control (without KHCO3). The occurrence of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) was found in longitudinal-sections of roots, using immunofluorescent technique method. The obtained results confirm a significant role of absorption of CO2 forms dissolved in the medium, by roots and also of the massive transport of carbon compounds from roots to shoot and leaves. The results also suggest that this kind of root absorption might play an important role as an alternative source of CO2 besides the photosynthetic carboxylation of CO2 from atmospheric air.