UNUSUAL ‘TUBULAR CLUSTERS’ IN THE PLASTIDS OF A DUCKWEED (LEMNA PAUCICOSTATA) MUTANT INCAPABLE OF PHOTOSYNTHESIS AND AMMONIUM ION UPTAKE

Light‐grown plants of the wild type 6746 strain and the mutant strain 1073 of Lemna paucicostata were compared. It was confirmed that this photosynthetically defective mutant is dependent on supply of sucrose for its growth. Moreover it was found that it is unable to take up NH₄⁺ in the absence of added sucrose; addition of a‐oxoglutarate did not allow ammonium ion uptake. In the mutant, mitochondria are unusually long and distorted and in its chloroplasts the grana contain many more thylakoid membranes than in the wild‐type chloroplasts of the same age. Moreover, at all ages, the presence of specific new structures known as ‘tubular clusters’ can be detected; tubular clusters differ from prolamellar bodies found in etioplasts. In addition, both strains produced in young fronds, upon standing in darkness for 28 h, prolamella bodies with typical crystalline structure. A possible connection between the tubular clusters and physiological aberrations of the mutant is discussed.