Xanthophyll cycle conversion

Changes in xanthophyll cycle conversion and energy dissipation over the course of sunny days under environmental conditions favorable for growth have now been examined in many different plant species, and in all cases pronounced diurnal changes were... 

Figures 2 and 3 show diurnal changes in xanthophyll cycle conversion and PS II characteristics for understory leaves experiencing intermittent sunflecks. Growing on the deeply shaded floor of a multilayered subtropical rainforest, leaves of the very shade-tolerant species Alocasia brisbanensis experienced only two sunflecks of low intensity during the whole day (Fig. 2). In contrast, the vine Stephania japonica which can be found in sites ranging from full sun to deep shade was characterized in an understory site where it experienced multiple, high-intensity sunflecks over the course of the day (Fig. 3). Despite these profound differences in sunfleck...

One of the few available studies considering both xanthophyll cycle conversions and PS II composition and function—as the two processes that have been implicated in the phenomenon of photoinhibition (Osmond, 1994 Adams et al., 1995a Anderson et al., 1997)—is the study by Ottander et al. (1995) of seasonal transitions in the field in Scots pine (pinus silvestris). Scots pine ceases growth during the winter season and downregulates overall photosynthetic... 

In concordance with the diel dynamics in Fv/Fm, active xanthophyll cycling was observed over the day (Fig. 2A, B). The ratio of diatoxan-thin (dt) to diadinoxanthin (dd) was closely linked to irradiance, with maximum conversion of dd into dt recorded during maximum irradiance. Whereas the total pool of dd + dt was highest in iron-limited cells (Table 1), the dt/dd ratio was significantly higher in iron-replete cells 0.9 versus 0.15 for Fe-limited cells (Fig. 2). 

Fig. 2.25 Enzymatic conversion in xanthophyll cycling in (a) higher plants, green algae (chlorophytes) and brown algae (phaeophytes), (b) most other algae (e.g. diatoms, dinoflagellates, chrysophytes and haptophytes see Table 3.6).

Niyogi KK, Grossman and Bjbrkman O (1998) Arabidopsis mutants define a central role for the xanthophyll cycle in the regulation of photosynthetic energy conversion. Plant Cell 10 1121-1134... 

C. Sun/Shade Acclimation, PS II Composition, and Functional Relevance of Xanthophyll Cycle Pool Size and Conversion State... 

Fig. 6. Fractional carotenoid composition (expressed relative to foliar chlorophyll content top panel) and (bottom panel) the midday conversion state of the xanthophyll cycle (fractionally expressed relative to foliar chlorophyll content) as well as the allocation of excitation energy absorbed by PS II to photochemistry (P) and dissipation (D) in leaves of Smilax australis growing in a deeply shaded (midday PFD=30 miol photons m" s ) or a fully exposed (midday PFD = 1500 /imol photons m" s" ) habitat in Australia during June of 1994. Data from Adams et al. (1999).

Fig. 8. Degree of conversion of the xanthophyll cycle to Z+A (top panel), relative to either total chlorophyll content or total xanthophyll cycle content, as well as (bottom panels) the level of energy dissipation activity quantified from the nonphotochemical quenching of and the efficiency of open PS II units following illumination with a high PFD of between 1800 and 2050 /tmol photons m" s" for 10 to 15 min. Data are means ( SE) of means from 7 species growing in deep shade (solid bars) and 18 species growing in full sunlight (open bars) in Boulder, Colorado. Data from Demmig-Adams (1998),...

Farber A, Young AJ, Ruban AV, Horton P and Jahns P (1997) Dynamics of xanthophyll-cycle activity in different antenna subcomplexes in the photosynthetic membranes of higher plants. The relationship between zeaxanthin conversion and nonphotochemical fluorescence quenching. Plant Physiol 115 1609-1618... 

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