Populations of photoinactivated photosystem II reaction centers characterized by chlorophyllafluorescence lifetimein vivo

Abstract

O xygenic photosynthetic organisms grow under an everchanging sunlight environment. Fluctuations of solar energy input can be accommodated by a tradeoff between energy utilization in photosynthetic carbon assimilation and energy dissipation by various photoprotective mechanisms that modulate absorption and dissipation of excess light energy (1-3). Despite the complex suite of strategies for photoprotection, however, photooxidative damage inevitably occurs to photosystem (PS) II, in which P680 ϩ (a special Chl in the PSII reaction center), the strongest biological oxidant, is generated to split water to molecular oxygen, protons, and electrons (4). The consequent loss of PSII photochemical efficiency measured under low light, termed photoinhibition or photoinactivation (5), depends inter alia on the number of absorbed photons during the light exposure (6-8). That is, PSII photoinactivation can occur with a light-dosage-dependent probability under any light environment in nature, ranging from limiting to saturating irradiances. Over a sunny day, the entire population of PSII in a leaf may undergo photoinactivation.Yet, effects of photoinactivation on PSII efficiency are not always obvious; they are noticeable only when the rate of inactivation exceeds the capacity for rapid and efficient repair of nonfunctional PSII reaction centers by de novo synthesis of D1 protein (psbA gene product in PSII reaction center) (9). The operation of the PSII repair cycle involves coordinated regulation of degradation and synthesis of D1 protein (10). When the supply of newly synthesized D1 protein is insufficient, such as under high light and͞or low temperature, the degradation process also slows down (11,12), resulting in the accumulation of nonfunctional PSII reaction centers in stacked grana domains of the thylakoid membranes of higher plants (13). These nonfunctional PSII centers, capable of light absorption but not of photosynthetic electron transfer, reduce the PSII quantum efficiency of leaves or leaf segments.An important implication of PSII photoinactivation is that nonfunctional PSII centers, still embracing pigment molecules, can exacerbate photooxidative damage to the thylakoid membranes unless light energy absorbed by the pigments is dissipated safely. Thus, it has been hypothesized that photoinactivated PSII complexes are able to efficiently dissipate excitation energy harmlessly (14), and further, may contribute to photoprotection of their functional neighbors by acting as sinks for excitation energy (13,15).Experimental results consistent with this hypothesis have emerged from recent studies using leaves of Capsicum annuum L (16, 17). In leaves of C. annuum in the presence of lincomycin (an inhibitor of chloroplast-encoded protein synthesis), the functional fraction of PSII ( f ), determined from the oxygen yield per single-turnover flash or from chlorophyll (Chl) a fluorescence, decreased monoexponentially from 1.0 (ϭ the original level) to Ϸ0.3 under illumination (16). However, the decrease in f thereafter proceed...

The lack of LHCII proteins modulates excitation energy partitioning and PSII charge recombination in Chlorina F2 mutant of barley

“…It has been shown that some of these PSII centers are inactive in electron transport and may function as an additional antenna to the fraction of active PSII centers (Terao and Katoh, 1996). Recently, Matsubara and Chow (2004) have suggested that un-active (or photoinhibited) centers of PSII can receive energy from neighboring functional PSII reaction centers and subsequently dissipates this energy nonphotochemically via non-radiative charge recombination between Q A -and P680 + . We suggest that such a mechanism would provide effective photoprotection of the remaining functional PSII units, although the possibility for reaction center quenching in active PSII centers can not be ruled out.…”

From ecophysiology to phenomics: some implications of photoprotection and shade–sun acclimation in situ for dynamics of thylakoids in vitro

“…The second is the photoprotective capacity associated with these photoinactivated PSII reaction centres and regulation of the D1 repair cycle [62]. Matsubara & Chow [63] demonstrated that these inactive centres are highly dissipative. This component of NPQ PI , with its particularly slow relaxation in the dark, seems to persist for one to two weeks in avocado leaves.…”

Remote Sensing of Coral Bleaching Using Temperature and Light: Progress towards an Operational Algorithm

“…Whilst there are photoacclimatory mechanisms that involve photochemical quenching, only photoacclimation involving an upregulation of non-photochemical quenching, such as the accumulation of inactive PSII (a population of PSII that engage solely in mitigating excess excitation energy via heat dissipation), will reduce F v /F m [51]. The rate of inactive PSII accumulation and the consequent reduction in F v /F m is proportional to the light absorbed in excess by the photosynthetic membranes of the algae [52]. According to this physiological background, two main parameters need to be generated to quantify photodamage: the first describes the amount of excess solar energy absorbed by a symbiont that significantly contributes to increased rates of PSII photoinactivation, called Excess Excitation Energy (EEE, mol quanta m −2 day −1 ); and the second is the amount of photodamage accumulated (i.e., inactive PSII).…”