The influence of phosphorus nutrition on growth, chlorophyll formation and ¹⁴CO₂ fixation of chlorophyllous carrot callus cultures

Abstract

Freshly isolated carrot root sec. phloem explants were cultured in nutrient solution plus inositol, IAA and kinetin and a varied supply of inorganic phosphorus. 14CO2 fixation experiments with the greened cultures were carried out under steady state conditions at the age of 21 days in light and darkness for four minutes. The results show that photosynthetic CO2 fixation by the Calvin cycle is greatly reduced in phosphorus deficient cultures whereas CO2 fixation via PEPC is enhanced. Under phosphorus deficiency the export of primary photosynthetates from the chloroplasts seems to be suppressed while the radioactivity of the labelled insoluble fraction, which represents mainly chloroplastic starch after this short time of 14CO2 fixation, was increased. The results are discussed with respect to the influence of phosphorus nutrition on photosynthetic CO2 fixation and PEP carboxylation in carrot tissue cultures.