Kinetic Relationship between Energy-Dependent Fluorescence Quenching, Light Scattering, Chlorophyll Luminescence and Proton Pumping in Intact Leaves

A measur ing system was designed fo r s imul taneous record ing o f modu la ted ch lo rophy l l f luorescence and l ight scatter ing changes. The k inet ic re la t ionsh ip was invest igated between l ightinduced changes in non-pho tochemica l f luorescence quenching, as de te rmined by the saturat ion pulse method , and in l ight scatter ing, as measured via the apparent absorbance change at 543 nm. V e r y s imi lar , but no t ident ical k inet ics were observed, re f lec t ing a close nonl inear re lat ionship between these two indicators o f t hy l ako id membrane energ izat ion. Fluorescence was found more sensitive at low levels o f energ izat ion, wh i le scatter ing con t inued ind ica t ing fu r ther increases in energizat ion when quenching a l ready was saturated. A general re la t ionsh ip between quenching and scattering is demonst ra ted wh i ch holds i r respect ive o f whether energizat ion is var ied dur ing induct ion or via changes in l ight in tens i ty o r C 0 2 concent ra t ion. I n the l igh t -o f f responses, on ly par t of f luorescence quenching was f o u n d to relax w i t h the same kinet ics as scattering. I t is suggested that at h igh levels o f energ izat ion s lowly reversible membrane changes may be induced wh ich have the po tent ia l o f non-pho tochemica l quench ing at a l ow level of energizat ion, and wh ich are not accompanied by scatter ing changes. Ne i ther quench ing nor scatter ing changes displayed kinet ics suf f ic ient ly fast to be taken as a d i rect expression o f in terna l thy lako id acidif icat ion in intact leaves. Th is conclus ion is d rawn f r o m comparat ive measurements o f p ro ton -up take , as ref lected by C0 2 so lub i l i za t i on upon l igh t induced s t roma a lka l iza t ion , and o f ch lo rophy l l luminescence. B o t h , the in i t ia l C 0 2 g u l p and the pH-dependen t luminescence rise were found to clearly precede the deve lopment o f energy-dependent quenching.