Light-Induced Changes in the Fluorescence Yield of Chlorophyll a In Vivo

Abstract

The fluorescence transient of Chlorella pyrenoidosa, excited by saturating blue light, has a base level O, hump I, dip D, peak P, and at 1.5 sec a quasi-steady level S (12). With 2 sec exciting exposures and 4 min dark periods, preillumination-1 (lambda >/= 690 nm, intensities 1-750 ergs/sec-cm(2) incident), replacing the dark periods, lowers I more effectively than preillumination-2 (650 nm </= lambda </= 680 nm) in both aerobic and anaerobic cells. Results indicate that the intersystem electron transport pool A as well as the primary electron acceptor of pigment system II Q (fluorescence quencher) is normally being reduced at I. Preillumination-1 lowers and delays P. Preillumination-2 (absorbed by both pigment systems) also lowers P, but delays P only at low intensity; at high intensity it hastens P. Preillumination-1 raises S while preillumination-2 lowers S. With 30 instead of 2 sec exciting light exposures, preillumination-1 causes a large S increase, and at low intensity a P increase. The S effects seem to be of a long-term nature (26-29) rather than rapid changes in the redox state of Q. As exciting light intensity increases, fluorescence yield at P increases three-fold maximally. The ratio of P (anaerobic) to O (aerobic) is 5.5. These high ratios restrict the Franck-Rosenberg model of photosynthesis (13), which is based on fluorescence yield doubling.

Photosynthetic responses of sun- and shade-grown barley leaves to high light: is the lower PSII connectivity in shade leaves associated with protection against excess of light?

“…The variable Chl fluorescence increase from I to P represents the measure of electron transport from Q B beyond PSI (Munday and Govindjee 1969 ; Schansker et al 2003 ). As is evident by the values of the probability with which the electron moves toward PSI end acceptors, ψ RE1o , the electron transport between PSII and PSI after HL treatment becomes less limited (Table 4 ), especially in shade leaves.…”

EFFECTS OF BICARBONATE ION ON CHLOROPHYLL a FLUORESCENCE TRANSIENTS AND DELAYED LIGHT EMISSION FROM MAIZE CHLOROPLASTS

“…Fluorescence-transient measurements were made as described by Munday and Govindjee (1969). The photomultiplier signal was fed through a Tektronix oscilloscope (type 501) and displayed on an Esterline Angus (model E 11015) or a Midwestern oscillograph recorder (model 801).…”

Nuclear, Virescent Mutants of Zea mays L. with High Levels of Chlorophyll (a/b) Light-Harvesting Complex during Thylakoid Assembly

“…1). This slow rise and subsequent decline have been attributed to the reduction and subsequent oxidation of PSII reaction centers (24). The fluorescence data indicated that PSII was not functional during early greening and that delayed PSII assembly could be the basis for the high fluorescence yield.…”