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Dean A. Kopsell and Carl E. Sams

.01) after exposure to the blue LED treatment. The blue LED treatment did not impact concentrations of LUT, ZEA, or NEO in the broccoli microgreen tissues. Concentrations of total xanthophyll cycle pigments (ZEA + ANT + VIO) increased 28.3% ( P ≤ 0

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Brandon Smith* and Lailiang Cheng

One-year-old `Concord' grapevines (Vitis labrusca L.) were fertigated twice weekly for 11 weeks with a complete nutrient solution containing 1, 10, 20, 50 or 100 μmol iron (Fe) from ferric ethylenediamine di (o-hydroxyphenylacetic) acid (Fe-EDDHA). Leaf total Fe content did not increase in response to Fe supply, however both “active” Fe (extracted with 2, 2'-dipyridyl) and chlorophyll (Chl) content increased as applied Fe increased. At the lowest active Fe level, leaf absorptance and maximum PSII efficiency (Fv/Fm) were slightly decreased, and non-photochemical quenching was significantly greater. PSII quantum efficiency decreased curvilinearly as active Fe content decreased. On a Chl basis, the xanthophyll cycle pool size, lutein, and beta-carotene increased curvilinearly as active Fe decreased, and neoxanthin increased at the lowest Fe level. Activities of antioxidant enzymes superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase followed a similar trend and increased under Fe deficiency, when expressed on a Chl basis. Antioxidant metabolites also increased in response to Fe limitation. On a Chl basis, ascorbate (AsA), dehydroascorbate (DAsA), reduced glutathione (GSH) and oxidized glutathione (GSSG) content was greater at the lowest active Fe levels. We did not find a difference in the ratio of AsA to DAsA or GSH to GSSG. In conclusion, both photoprotective mechanisms, xanthophyll cyle-dependent thermal dissipation and the ascorbate-glutatione antioxidant system, are enhanced in response to iron deficiency to cope with excess absorbed light.

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Dean A. Kopsell, James T. Brosnan, Gregory R. Armel, and J. Scott McElroy

oxidative damage can occur or by active non-photochemical quenching (NPQ) of excess light energy ( Demmig-Adams et al., 1996 ; Frank and Cogdell, 1996 ). The xanthophyll cycle (or the violaxanthin de-epoxidase cycle) is the primary cycle attributed to

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Shuyang Zhen and Marc W. van Iersel

content and activity ( Björkman, 1981 ; Seemann, 1989 ), xanthophyll cycle pigment pool size (involved in heat dissipation of the absorbed light) ( Demmig-Adams and Adams, 1992 ; Logan et al., 1998 ), and maximum photosynthetic capacity ( Oguchi et al

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Dean A. Kopsell, Carl E. Sams, T. Casey Barickman, and Robert C. Morrow

blue wavelengths (455 to 470 nm) significantly increased sprouting broccoli ( Brassica oleacea var. italica ) microgreen shoot tissue β-carotene, violaxanthin, total xanthophyll cycle pigments, glucoraphanin, epiprogoitrin, aliphatic glucosinolates

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Ryan N. Contreras, John M. Ruter, James S. Owen Jr., and Andy Hoegh

plays a role ( Han and Mukai, 1999 ; Ida, 1981 ). Plants have several mechanisms to cope with excess light during periods of low temperature when Calvin cycle activity is limiting, including reduction of chlorophyll, pH-dependent xanthophyll cycle

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Dean A. Kopsell, Carl E. Sams, and Robert C. Morrow

photodamage ( Christie, 2007 ; Fraikin et al., 2013 ). The xanthophyll cycle pigments (zeaxanthin, antheraxanthin, violaxanthin) in plants are vital for energy dissipation of excess absorbed radiant light energy. Under high-light stress, violaxanthin is

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Zhenghai Zhang, Hai Sun, Cai Shao, Huixia Lei, Jiaqi Qian, Yinyin Ruan, and Yayu Zhang

protect itself against damage by excess illumination ( Bizarre et al., 2019 ; Klughammer and Schreiber, 2008 ). Y(NPQ) is linked to the xanthophyll cycle, which involves nonphotochemical quenching of excess light energy in PS II ( Jahns and Holzwarth

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Marjorie Reyes-Diaz, Miren Alberdi, and Maria de la Luz Mora

Barker, D.H. 1998 Seasonal changes in xanthophyll cycle-dependent energy dissipation in Yucca glauca Nuttall Plant Cell Environ. 21 501 511 Adams W.W. III Zarter, C.R. Ebbert, V. Demmig

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Marc W. van Iersel, Geoffrey Weaver, Michael T. Martin, Rhuanito S. Ferrarezi, Erico Mattos, and Mark Haidekker

.0001). The decrease in Φ PSII was negatively correlated with the increase in NPQ ( r = −0.73, P < 0.0001). This increase in NPQ was likely due to the upregulation of the xanthophyll cycle: lumen acidification triggers the de-epoxidation of violaxanthin to