EFFECT OF LINOLENATE ON PHOTOSYNTHESIS BY INTACT SPINACH CHLOROPLASTS Conditions for the inhibition of orthophosphate uptake

Linolenate has been shown [I] to inhibit photosynthesis in intact spinach chloroplasts by inhibiting the influx of orthophosphate and the efflux of 3-phosphoglyceraldehyde. The inhibitory effect of linolenate was shown to depend on the level of the internal pool of metabolites [2] as a result of experiments which on the one hand used chloroplasts from preilluminated leaves or chloroplasts which were artificially loaded with 3-phosphoglyceric acid (‘high pool’ chloroplasts) and on the other hand chloroplasts from darkened leaves (‘low pool’ chloroplasts). This suggested that the inhibition of photosynthesis by linolenate is due to an inhibition of the ‘phosphate translocator’ which is located in the envelope and mediates the exchange of orthophosphate and internal phosphorylated metabolites [3,4]. This investigation is an attempt to elucidate the mechanism by which linolenate inhibits the function of the ‘phosphate translocator’, in particular with respect to the uptake of orthophosphate.