Absorption of HCO₃^‐ by roots and its effect on carbon metabolism of tomato

Abstract

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 ¹⁴C. 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 HCOâ 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.