The influence of two naturally occurring factors, from the leaves of Ricinus communis, on the fluorescence induction of higher plant chloroplasts and intact algae.

Changes in fluorescence induction, brought about by incubation of chloroplasts (Zea mays) in an aqueous extract of Ricinus leaf, have been divided, on the basis of speed of manifestation, into two categories: "fast" changes and "slow" changes (i.e. those observed after 5 min and 1(1/2) hr of incubation, respectively). The former, which include a large increase in the magnitude of the fast component of variable fluorescence and a retardation of decay from maximum to minimum levels of fluorescence, have been ascribed to inhibition of electron transport at a site beyond that of 3-(p-chlorophenyl)-1,1-dimethylurea (CMU)-i.e., towards system I; these changes result from the action of a fraction of the extract consisting of molecules of small size. The latter changes, which include a marked attenuation of the variable part of fluorescence induction, have been associated with system II and may arise from inhibition of electron flow between water and Q or from decrease in number of functional reaction centers; these changes result from the activity of a proteinaceous fraction of the extract, that simultaneously converts the low temperature steady-state emission spectrum of the chloroplasts into a one-banded one, with maximum at 698 nm.