The Relation between Photophosphorylation and Delayed Light Emission in Chloroplasts

Abstract

One millisecond delayed light emission has been studied in isolated coupled lettuce (Lactuca sativa var. romaine) chloroplasts. Delayed light emission was increased upon addition of ferricyanide or 2,3, 5,6-tetramethyl-p-phenylene diamine. In the presence of ferricyanide, the magnitude of the signal was increased by the addition of ADP (in the absence of orthophosphate), ATP, DIO-9, or phlorizin. The signal was also increased by the addition of NaCI and by the addition of NH4Cl in the presence of a high NaCl concentration. The signal of delayed light emission was decreased by the addition of gramicidin, valinomycin, and by the addition of NH4Cl in the presence of a low NaCl concentration.Phosphorylation, whether started by addition of ADP or by addition of glucose plus hexokinase plus ATP, caused a significant decrease in delayed light emission. It was concluded that the magnitude of delayed light emission reflects the size of the proton motive force across the thylakoid membrane. Calibration of delayed light emission by creating KCI gradients indicated that the value for the electrochemical potential gradient for H+ in the presence of ferricyanide was at least 155 millivolts decreasing to 134 millivolts after the onset of phosphorylation.Goedheer (8) has suggested that DLE' in photosynthetic organisms results from back reactions of electrons and holes in acceptor and donor pools of photosystem II or bacterial reaction centers in a reversal of the light reactions. On the basis of studies involving the effect of uncouplers and phosphorylating agents on DLE in chloroplasts, Mayne (17) suggested that the high energy state of phosphorylation is an additional source of energy for DLE, in direct equilibrium with the photochemical act. Subsequently, Fleischmann (7) suggested that during the photoact charge separation across the thylakoid membrane would provide a store of energy in the form of electrical potential. This so-called membrane potential provides a source of energy in the dark for DLE by presumably lowering the activa- tion energy for the recombination process. According to a more detailed model (6), the free energy difference between donor and acceptor pools is dependent (in addition to the concentration of Z+ and Q-) both on the proton concentration difference (ApH) and the electrostatic potential difference (AE) across the thylakoid membrane. Since according to the chemiosmotic hypothesis, AE and ApH comprise the driving force for ATP formation (19), DLE should indeed be closely related to photophosphorylation. In the present work, we have further studied this relationship using coupled phosphorylating lettuce chloroplasts. In addition, following the method of Barber (4, 5), the magnitude of the minimal value of the p.m.f. was estimated during electron flow and when electron flow was coupled to phosphorylation. MATERIALS AND METHODSChloroplasts were isolated from lettuce leaves Lactuica satii'a var. romaine. One hundred grams of leaves were homogenized for 15 sec in a Waring Blendor in 130 ml of...

The influence of cations and methylamine on structure and function of thylakoid membranes from barley chloroplasts

“…Many other phenomena in isolated chloroplasts are affected by cations. These include besides changes in structure (7,15,16,21,31,39,46), chloroplast lamellar volume (13,14,20,38,41,51) and light scattering properties (7,15,16,20,26,27,31,34,41,50) changes in chlorophyll absorption (15), fluorescence (9,11,12,15,16,19,24,26,27,(30)(31)(32)(33)(34)(35)50) and delayed light emission (4, 16,29,36). The 515-nm absorption change (13,16), the fluorescence of probes Abbreviations: BSA -bovine serum albumin, DCMU -3 (3,4-dichlorophenyl)-l,l-dimethyl urea, DBMIB -3-methyl-6-isopropyl-p-benzoquinone partitioned into chloroplast membrane lipids (16,31,…”

Biophysics of photosynthesis

“…Since under normal conditions an electrochemical potential gradient of protons is created during illumination then it is not surprising that the intensity of delayed light emission can reflect this light-induced gradient. I n fact, the sensitivity of the emission to the light-induced electrochemical potential gradient is only observed during the first few milliseconds of the decay and as expected is sensitive to the ability of the system to make ATP (Neumann et al 1973). Many other factors can affect the intensity of delayed light emission at any time including the rate of removal of the precursors Zf and Qand the fluorescence yield of the chlorophylls from which the emission occurs (see Amesz and van Gorkom 1978).…”

Estimation of the activation energy for millisecond delayed fluorescence from uncoupled chloroplasts

“…It has become clear from the work of Mayne [2,3] and subsequent workers [4,5] that the high-energy state of phosphorylation acts on this back reaction. This effect is most readily observed in the 1 msec region of the decay.…”

“…The mechanism that leads to delayed fluorescence from oxygen-evolving photosynthetic systems is thought to involve a back reaction between the reduced primary electron acceptor Q-and primary electron donor Z ÷ of photosystem two [ 1]. It has become clear from the work of Mayne [2,3] and subsequent workers [4,5] that the high-energy state of phosphorylation acts on this back reaction. This effect is most readily observed in the 1 msec region of the decay.…”