Photosynthesis and Oxygen Uptake Rate in Winter Rape Plants Treated with 5-Aminolevulinic Acid

Effects of 5-aminolevulinic acid (ALA) at 200 mg/L on photosynthesis, structural organization of photosynthetic apparatus, oxygen uptake rate by the leaf tissue, contents of key respiratory enzymes—cytochrome c-oxidase (COX) and alternative oxidase (AOX)—and COX activity in winter rape plants (Brassica napus L.) were studied. It was found that 4–7-day-old seedlings grown on ALA solution accumulated phenols and their derivatives anthocyanins; the composition of the latter compounds was the same as in the control seedlings. Photosynthesis was inhibited in the ALA-treated plants since their capability to form structural the components of the photosynthetic apparatus—pigment–protein complexes (PPC) of the photosystems I and II—was reduced. In these plants, oxygen uptake by the leaf tissue increased under dark conditions. Simultaneously, the activity of the terminal COX of the cytochrome part of the respiratory path also increased as did the activity of another terminal respiratory enzyme, AOX, which is usually activated under stress, including oxidative.