Relationship between the Quantum Efficiencies of Photosystems I and II in Pea Leaves

Abstract

The irradiance dependence of the efficiencies of photosystems I and 11 were measured for two pea (Pisum sativum [L.]) varieties grown under cold conditions and one pea variety grown under warm conditions. The efficiencies of both photosystems declined with increasing irradiance for all plants, and the quantum efficiency of photosystem I electron transport was closely correlated with the quantum efficiency of photosystem 11 electron transport. In contrast to the consistent pattern shown by efficiency of the photosystems, the redox state of photosystem 11 (as estimated from the photochemical quenching coefficient of chlorophyll fluorescence) exhibited relationships with both irradiance and the reduction of P-700 that varied with growth environment and genotype. This variability is considered in the context of the modulation of photosystem 11 quantum efficiency by both photochemical and nonphotochemical quenching of excitation energy.The well established organization of the electron transport system of higher plant thylakoids implies a close coordination of the activities of PSI and PSII in linear electron flow (13,28). Although considerable efforts have been applied for the characterization of the detailed structure and functions of PSI and PSII, remarkably little attention has been given to the potential regulatory mechanisms needed to coordinate PSI and PSII activities. In this paper we examine the relationships between PSI and PSII photochemical activities in leaves using noninvasive spectroscopic techniques.Under conditions of increasing irradiance, the quantum efficiencies of both PSI and PSII decline. Oxidized P-7002 (p- 700+) is as good a quencher of excitation energy present in PSI as is reduced P-700 (P-700°) (25), but whereas quenching by P-7000 results in electron transport from PSI, quenching by P-700+ results only in thermal deactivation of the excitation energy. Consequently, the quantum efficiency of PSI is given by the degree of reduction of the P-700 pool (i.e. the amount of P-7000 relative to the total amount of P-700). Measurements of the redox state of P-700 in vivo have shown that the quantum efficiency of PSI is linearly related to the quantum efficiency for CO2 fixation when photorespiration is suppressed (28). With increasing irradiance the P-700 pool becomes progressively oxidized (15,16,28), and hence the quantum efficiency of PSI falls. The situation for PSII is complicated by the multiplicity of ways that PSII quantum efficiency can be modified (5, 16). The resolution of Chl fluorescence in vivo (which is largely from PSII) in terms of photochemical (qQ) and nonphotochemical quenching (qNp) has been described by Bradbury and Baker (3) and Deitz et al. (8). With increasing irradiance, qQ declines and qNP increases (8) but not in a way that can be simply related to the decline of 4PsHj (the quantum efficiency for electron transport by PSII) (29). Recently, Genty et al. ( 11) (Fv/Fm) (2,6,19).'The sequential arrangement of photosystems II and I in noncyclic electron transport (...

Relationship between Photosynthetic Electron Transport and Stromal Enzyme Activity in Pea Leaves

“…tion. As 4l declines qQ also declines; in previous studies (5,6) this relationship has been found to be curvilinear, however, in this instance the degree of scatter makes it impossible to determine the detail of the relationship between 4l and qQ. At values of X, close to 1.0 an abrupt decline of both qQ and X,, is implied because even at the lowest irradiance employed (120 ,umol m-2 s') qQ and oil are lower than the values recorded for the dark adapted state.…”

“…Chl fluorescence and light-induced absorbance changes at 820 nm (AA820), due to P-700 oxidation or reduction, were measured within a leaf area of 1.25 cm2, defined by a circular mask as described previously (7,8 (6). The portion of the lamina that had been irradiated was immediately frozen and cut from the leaf using a solid brass cutter chilled to liquid nitrogen temperatures.…”

“…The r/, the redox state of PSII (qQ), the 0exc (that is the photochemical efficiency of open PSII centers), and the oi were calculated as described previously (4,6).…”

“…The relationship between the quantum efficiencies of PSI = NADP-malate dehydrogenase = quantum efficiency of PSI = quantum efficiency of PSII = quantum efficiency of photochemical quenching by oxidized reaction centres of PSII = product of X, and irradiance = product of X,, and irradiance = coefficient for the photochemical quenching of Chl a fluorescence = level of modulated Chi a fluorescence during a dark interval following a brief irradiation by far-red light to oxidize any QA = level of modulated Chl a fluorescence during a saturating pulse of irradiance = level of modulated Chl a fluorescence at steady state = fructose-1,6-bisphosphate = fructose-1,6-bisphosphatase = plastoquinone = the primary electron acceptor to PSII = ribulose-1,5-bisphosphate carboxylase and II, and the quantum efficiency of CO2 fixation has been described (5,6,28). These results have shown that there is a tight coupling between the quantum efficiencies of both photosystems, and that when photorespiration is suppressed there is a good correlation between the efficiency of either photosystem and the quantum yield of CO2 fixation.…”

From Endoplasmic Reticulum to Mitochondria: Absence of the Arabidopsis ATP Antiporter Endoplasmic Reticulum Adenylate Transporter1 Perturbs Photorespiration

“…For the determination of CO 2 compensation points, CO 2 concentrations varied from 40 to 400 ppm. The maximum quantum yield of PSII (F v /F m ) was quantified according to Harbinson et al (1989) before and after shifting the plants to ambient air for 1 week (Timm et al, 2011).…”