PHOTOCHEMICAL ACTIVITY OF ISOLATED CHLOROPLASTS IN RELATION TO THEIR SOURCE AND PREVIOUS HISTORY

Abstract

A survey of the major subdivisions of the plant kingdom revealed photochemical activity in chloroplasts and chloroplast fragments isolated from unicellular and filamentous green algae, liverworts, horsetails, herbaceous monocotyledons, and dicotyledons. Active chloroplasts were not obtained from mosses, ferns, gymnosperms, and woody angiosperms. Among 80 species and varieties tested in Hill solution by the titration method, 45 showed photochemical activity quotients above 100, 19 had quotients above 500, and six (millet, flax, spinach, lamb's-quarters, Swiss chard, and lettuce) showed quotients above 1000. Photochemical activity varied greatly within both genera and species. The majority of the chloroplast suspensions produced acid in darkness when mixed with ferricyanide – ferric oxalate solution. Natural inhibitors of photochemical activity were found in the cell sap and cytoplasm of several species.Chloroplast activity quotients in ferricyanide – ferric oxalate and quinone solutions increased with leaf maturation, and declined with senescence. Chloroplasts isolated from very young green leaves of active species were photochemically inactive. The activity of the chloroplasts was relatively insensitive to the supply of essential mineral nutrients and water as well as to growth temperature. Chloroplasts isolated from leaves showing pronounced symptoms of nitrogen, iron, copper, manganese, or magnesium deficiency had low activity quotients, but remained photochemically active until the leaves were about to die. The observed responses to previous illumination and darkness did not support the hypothesis that a labile photosynthetic intermediate, stored in the chloroplasts, is required for oxygen production after isolation.Chloroplast activity was stabilized for weeks by snap-freezing suspensions containing 0.5 M sucrose and storing at or below −40 °C. Lyophilization did not prevent storage deterioration at higher temperatures.