Regulation of Light Harvesting in Green Plants (Indication by Nonphotochemical Quenching of Chlorophyll Fluorescence)

Abstract

ce has become one of the most powerful methods for assessing photosynthetic performance in plant physiological experiments (Horton and Bowyer, 1990; Krause and Weis, 1991). This has resulted almost entirely from the development of methods to distinguish photochemical and nonphotochemical quenching of fluorescence. Moreover, it is now clear that the process of nonphotochemical quenching itself indicates important regulatory adjustments in the photosynthetic membrane in response to altered external and internal conditions (Demmig-Adams and Adams, 1992;Horton and Ruban, 1992). In particular, the dissipation of excess absorbed excitation that is monitored by the main component of nonphotochemical quenching is a process that is necessary if plants are to avoid photoinhibition and photodestruction under conditions of light stress.When light is absorbed by the Chl molecules in the thylakoid membrane, the excited state has several alternative and competing fates: a small proportion is emitted as fluorescence, but, under light-limiting conditions, the major pathway of de-excitation is through photosynthetic electron transfer. The effect of photochemical utilization of energy is to quench fluorescence, and it is well known that when photosynthetic electron flow is saturated the yield of fluorescence rises. This photochemical quenching has been termed qP and, using the light-doubling principle as applied with modulated fluorimetry, it is easy to calculate it in leaves, chloroplasts, and cells (Schreiber et al., 1986;Horton and Bowyer, 1990; van Kooten and Snel, 1990). However, qP does not account for all of the quenching observed. Indeed, in light saturating for electron transport, qP tends to zero, yet there can be large amounts of quenching. Such quenching is therefore called nonphotochemical quenching and refers to the difference between the initial, dark-adapted maximum level of fluorescence and that recorded after a period of illumination. This quenching can be calculated in a number of ways, leading to it being termed variously as qN (Schreiber et al., 1986; van Kooten and Snel, 1990), NPQ (Bilger and Bjorkman, 1994), or SV, (Gilmore andBjorkman, 1994); these all refer to the same biological process and in this article we will use the term qN.qN results from the nonphotochemical de-excitation of the singlet excited state of Chl associated with PSII. A number of processes occurring in the thylakoid membrane contribute to qN in vivo, but the major proportion arises from an increase in nonradiative decay as heat, the quenching processes being referred to as qE and qI (Horton and Bowyer, 1990; Krause and Weis, 1991). Both these are induced under conditions of light stress (i.e. at intensities above those that can be used completely in photosynthetic electron transport). They were distinguished initially in aqueous phase measurement (chloroplasts and protoplasts) by virtue of their sensitivity to DCMU and uncouplers. Thus, qE is dependent on the enereation of the thylakoid membrane or, more specifically, the thylakoid...

The Xanthophyll Cycle Modulates the Kinetics of Nonphotochemical Energy Dissipation in Isolated Light-Harvesting Complexes, Intact Chloroplasts, and Leaves of Spinach1

“…However, it is important to point out that in these plants quenching is less efficient (Briantais, 1994) and is expressed in terms of quenching efficiency with respect either to the de-epoxidation state of the xanthophyll pool (Gilmore et al, 1996b) or to ⌬pH (Schonknecht et al, 1996). Efficient quenching and its physiological regulation may therefore require a complete system containing all of the LHCII proteins, implying that the xanthophyll cycle and ⌬pH exert control over the organization of the whole PSII antenna, as depicted in Horton et al (1994). It should also be emphasized that the xanthophyll cycle carotenoids bound by the minor LHCII account for only approximately 30% of the PSII-associated pool, with the remainder associated with LHCIIb (Ruban et al, 1994b).…”

Biological weighting function for xanthophyll de‐epoxidation induced by ultraviolet radiation

“…Among these, the formation of de-epoxidated xanthophylls, correlated with the development of NPQ (Demmig-Adams 1990, Horton et al 1994), has been described as an effective protective mechanism under severe PAR (for review Müller et al 2001) and UVR exposure (Götz et al 1999). However, the role of UVR in the stimulation of the xanthophyll de-epoxidation is still unclear (Bischof et al 2002, Döhler and Haas 1995, Döhler and Hagmeier 1997, Goss et al 1999, Mewes and Richter 2002, Pfündel et al 1992, Zudaire and Roy 2001.…”

“…This decrease in pH within the thylakoid lumen is a signal of excessive irradiance and induces , H 2 O 2 and O 2 (Gilmore andYamamoto 1993, Niyogi et al 2001). NPQ also prevents the overreduction of the electron-transport chain and the overacidification of the lumen (Demmig-Adams 1990, Horton et al 1994, for review Mü ller et al 2001.…”

Antioxidatic and photochemical activity of photosynthetic apparatus of spring wheat at action of Рseudomonas syringae pv. аtrofaciens

“…Under these conditions, the induction coefficient (Ki), which correlated with the intensity of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (the main enzyme of the Calvin cycle), and usually indicated to effectiveness of the dark reactions of photosynthesis [3] -was at the control level, and on the 12th day of infecting, it decreased by 35% (Table 4), which indicated to a gradual suppression of the effectiveness of dark processes of photosynthesis with increasing exposure of the causative agent of basal bacteriosis, which deepened with time. However, the level of fluorescence depends on a number of molecularbiochemical processes, the activation of which, when adapted to light, leads to a decrease in the fluorescence signal level of chlorophyll (quenching fluorescence, qF) [5,12]. The photochemical side of it (photochemical extinction) depends on the oxidation-reducing state of the primary electron carrier -QA, whereas not photochemical -from the level of thermal dissipation of the excitation energy.…”