The rate constant of photoinhibition, measured in lincomycin-treated leaves, is directly proportional to light intensity.

Abstract

Pumpkin leaves grown under high light (500-700 ,umol of photons m-2 s'1) were illuminated under photon flux densities ranging from 6.5 to 1500 ,umol-m-2-s'1 in the presence of lincomycin, an inhibitor of chloroplast protein synthesis. The illumination at all light intensities caused photoinhibition, measured as a decrease in the ratio of variable to maximum fluorescence. Loss of photosystem II (PSII) electron transfer activity correlated with the decrease in the fluorescence ratio. The rate constant of photoinhibition, determined from first-order fits, was directly proportional to photon flux density at all light intensities studied. photon flux density (4). However, these experiments were done under high, photoinhibitory light, and it therefore remained unclear if photoinhibition is somehow related to the photon flux exceeding the flux that can be safely dissipated through photosynthesis (5-7). On the contrary, the first-order nature of photoinhibition suggests that each photon absorbed by PSII causes photoinhibition with the same probability. In the present paper, we describe results that prove the latter.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 2213Reciprocity between the amount of light and the duration of illumination was demonstrated for photoinhibition of isolated chloroplasts by Jones and Kok (8). Very recently, Park et al. (9) published data demonstrating that the law of reciprocity holds for photoinhibition of intact leaves too. The present study confirms most of their results, but we conclude that photoinhibition is a one-photon phenomenon instead of a photon counter-type poisoning process (9).The degradation and synthesis of the Dl protein are rapid under both high and low light if compared to other thylakoid proteins (10), and several hypotheses have been put forward to explain the reasons for the fast turnover. The high-lightdependent and normal turnover of the DI protein have often been treated separately because photoinhibition has been considered to be limited to light levels above the saturation of photosynthesis and because it has been assumed that photoinhibitory damage does not occur at low light. It was even suggested that the Dl protein turns over for reasons not at all related to light-induced damage to PSII (11). The rapid resynthesis of the Dl protein usually makes it impossible to detect the light-dependent loss of the Dl protein if the synthesis is not blocked during the experiment. Furthermore, since the Dl protein is degraded after but not simultaneously with photoinhibition of the reaction center, the dependence of the rate of degradation on light is far from linear (3). It must also be noted that because neither photoinhibition nor degradation of the Dl protein occurs with zero-order kinetics, fixed-time assays have no relevance with respect to the kinetics. The complexity of the kinetics has promoted the s...

Effects of light intensity and quality on phycobiliprotein accumulation in the cyanobacterium Nostoc sphaeroides Kützing

“…Chlorophyll a (Chla) and protein contents were also the highest with the same light intensity. The low contents recorded at high light intensity might be due to PBP degradation, which was previously reported (Nomsawai et al 1999), or by a photoinhibition phenomenon (Tyystjärvi and Aro 1996).…”

“…The cause for this observation is unknown. However, it may be speculated that under these conditions, respiratory metabolism could be greater than photosynthesis, leading to cell death, or that these effects are due to photoinhibition (Tyystjärvi and Aro 1996). This is why 30 lmol m -2 s -1 intensity was selected for the light quality assays.…”

Systematic Analysis of the Relation of Electron Transport and ATP Synthesis to the Photodamage and Repair of Photosystem II in Synechocystis

“…The initial rate of photodamage was proportional to light intensity, as has been observed also in the leaves of higher plants and in Synechocystis cells that had been treated with lincomycin (Tyystjärvi and Aro, 1996;Lee et al, 2001;Allakhverdiev and Murata, 2004).…”

Photoprotective Non-photochemical Quenching Does Not Prevent Kleptoplasts From Net Photoinactivation

“…Photoprotection mechanisms are essential for balancing the absorption and use of light to fuel photosynthesis and the dissipation of absorbed light that is harmful (Chow and Aro, 2005). Excessive light intensities generate reactive oxygen species (ROS) that mainly target and cause damage to the central transmembrane D1 protein of Photosystem II (PSII) (Tyystjärvi and Aro, 1996), which is crucial for PSII function. Thus, photoprotection mechanisms operate to minimize D1 photodamage and ensure an optimal photosynthesis under the given light intensity.…”