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The Nostoc‐Gunnera symbiosis: carbon fixation and translocation
Author(s) -
Söderbäck Erik,
Bergman Birgitta
Publication year - 1993
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1993.tb01795.x
Subject(s) - nostoc , carbon fixation , biology , rubisco , botany , photosynthesis , chloroplast , cyanobacteria , biochemistry , bacteria , genetics , gene
The in vitro specific activity of ribulose‐1,5‐bisphosphate carboxylase (Rubisco; EC 4. 1. 1. 39) and the dark and light in vivo CO 2 fixation activities were determined in the cyanobiont of Gunnera . Compared to the free‐living isolate Nostoc PCC 9231, the in vitro Rubisco activity was high, while the in vivo CO 2 fixation was very low. Light did not significantly influence CO 2 fixation if the cyanobiont was left in the sliced Gunnera tissues, while a small light stimulation was found for CO 2 fixation of the freshly‐isolated cyanobiont. The adjacent non‐infected Gunnera tissue showed a very low CO 2 fixation. A rapid translocation of fixed 14 CO 2 from leaves towards apical parts of the plant was apparent, in particular to the symbiotic tissue. The 14 C label appeared mainly in soluble form in this tissue and was rapidly catabolised as shown by 14 C chase experiments. Also, short‐term experiments revealed that maximum 14 C accumulation occurred in the symbiotic tissue showing the highest rates of nitrogen fixation (Söderbäck et al. 1990), about 10–15 mm from the plant apex. The data were taken to indicate that there is a modification in the photosynthetic light reaction of the cyanobiont and that the cyanobiont lives heterotrophically in the dark on photo‐synthate rapidly delivered from nearby leaves of the host plant.