Photosystem II efficiency

Yang, C. F. 1996. Action of allelochemicals on algal growth and photosystem II efficiency. MS Thesis. Southwest Missouri State University,... 

Direct photodegradation of organic molecules by UV-B also takes place in exposed tissue affecting photosystem II efficiency (e.g. Krause et al., 1999). 

Adams WW III, Demmig-Adams B, Logan BA, Barker DH and Osmond CB (1999) Rapid changes in xanthophyll cycle-dependent energy dissipation and Photosystem II efficiency in two vines, Stephania japonica and Smilax australis, growing in the understory of an open Eucalyptus forest. Plant Cell Environ 22 125-136... 

Demmig-Adams B, Adams HI WW, Logan BA and Verhoevan AS (1995a) Xanthophyll cycle-dependent energy dissipation and flexible Photosystem II efficiency in plants acchmated to light stress. Aust J Plant Physiol 22 249-60... 

Abadia J, Morales F, and Abadia A. Photosystem II efficiency in low chlorophyll, iron deficient leaves. Plant and Soil 2000 215 183-192... 

Weis, E. Berry, J. A. (1987). Quantum efficiency of photosystem II in relation to energy -dependent quenching of chlorophyll fluorescence. Biochimica Bio-physica Acta, 894, 198-208. 

Principle Chlorophyll fluorescence is a sensitive and early indicator of damage to photosynthesis and to the physiology of the plant resulting from the effect of allelochemicals, which directly or indirectly affects the function of photosystem II (Bolhar-Nordenkemf et ah, 1989, Krause and Weiss 1991). This approach is convenient for a photosynthesis analysis in situ and in vivo and quick detection of otherwise invisible leaf damage. The photosynthetic plant efficiency was measured using the method of induced chlorophyll fluorescence kinetics of photosystem II [Fo, non-variable fluorescence Fm, maximum fluorescence Fv=Fm-Fo, variable fluorescence t /2, half the time required to reach maximum fluorescence from Fo to Fm and photosynthetic efficiency Fv/Fm]. 

These observations could be explained by the Z scheme if the absorption spectra of the antennas associated with photosystems I and II are different. Because the two photosystems must operate in series, light is used most efficiently when the flux of electrons through photosystem II is equal to that through photosystem I. If light of a particular wavelength excites one photosystem more frequently than the other, some of the light is wasted. 

Chl-coated semiconductor (n-type) electrodes have thus far been studied using ZnO, CdS, and Sn02, all of which act as efficient photoanodes for converting visible light. Such Chl-sensi-tized photoanodes could be regarded as in vitro models for the photosystem II (oxygen evolution) function in photosynthesis, p-type semiconductor electrodes have not been utilized successfully to produce cathodic Chl-sensitized photocurrents with satisfactory efficiencies. On the other hand, Chl-coated metal electrode systems seem to overcome this problem. 

EC50 values (and 95% confidence limits) for the effects of linuron on the efficiency of photosystem II in aquatic macrophytes... 

Fig. 4 Dynamics of in vivo chlorophyll fluorescence (Fo) and photosynthetic efficiency (Fv/Fm) of Phaeocystis globosa during viral infection as assessed by fluorometry. Open symbols represent uninfected cultures, while the filled symbols represent virally infected P. globosa. Maximum fluorescence (Fm) was obtained after addition of the photosystem II inhibitor DCMU (20 pM final concentration). Fv equals Fm-Fo. Data are expressed in relative units (r.u.)...

FIGURE 3.5 One of the postulated pathways for the 02 release step of the WOC. The naturally occurring WOC of photosystem II is able to efficiently photooxidize water in a sustainable manner using visible light according to the reaction 2 HzO —> 02 + 4 H+ + 4 e. SOURCE Presented by Charles Dismukes. 

Photosystem II of green plants is reasonably similar to the bacterial reaction center (Figure 19,12). The core of photosystem II is formed hy D1 and D2, a pair of similar 32-kd subunits that span the thylakoid membrane. These suhunits are homologous to the L and M chains of the bacterial reaction center. Unlike the bacterial system, photosystem II contains a large number of additional subunits that bind additional chlorophylls and increase the efficiency with which light energy is absorbed and transferred to the reaction center (Section 19.5). 

I. The electrons given up by photosystem I are replenished by photosystem II, which needs to absorb an equal number of photons. Hence, eight photons are needed to generate the required NADPH. The energy input of 8 moles of photons is 381 kcal. Thus, the overall efficiency of photosynthesis under standard conditions is at least 114/381, or 30%. 

Krause, G. H., Schmude, C., Garden, H., Koroleva, O. Y., Winter, K. 1999. Effects of solar ultraviolet radiation on the potential efficiency of photosystem II in leaves of tropical plants. Plant Physiol. 121 1349-1358. 

In the photosynthetic primary processes, electrons are pumped via two photosystems (photosystem I and II), where light induced charge separation takes place efficiently in association with uni-dlrectional electron transport. The oxidative water splitting reaction Is linked to photosystem II photosystem I is followed by... 

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