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Jason J. Griffin, Thomas G. Ranney, and D. Mason Pharr

Tolerance to high solar irradiation is an important aspect of stress tolerance for landscape plants, particularly for species native to understory conditions. The objective of this study was to evaluate differential tolerance to high solar irradiation and underlying photosynthetic characteristics of diverse taxa of Illicium L. grown under full sun or 50% shade. Eleven commercially available taxa of Illicium were evaluated for light tolerance by measuring light-saturated photosynthetic capacity (Amax), dark-adapted quantum efficiency of photosystem II (Fv/Fm), and relative chlorophyll content using a SPAD chlorophyll meter. Comparisons of Amax indicated that three of the 11 taxa (I. anisatum L., I. parviflorum Michx. ex Vent., and I. parviflorum `Forest Green') maintained similar rates of light-saturated carbon assimilation when grown in either shade or full sun. All other taxa experienced a significant reduction in Amax when grown in full sun. Chlorophyll fluorescence analysis demonstrated that Fv/Fm was similar between sun and shade plants for the same three taxa that were able to maintain Amax. These taxa appeared to experience less photoinhibition than the others and maintained greater maximum photochemical efficiency of absorbed light. SPAD readings were not significantly reduced in these three taxa either, whereas most other taxa experienced a significant reduction. In fact, SPAD readings were significantly higher in I. parviflorum `Forest Green' when grown under full sun, which also maintained the highest Amax of all the taxa. These results suggest that there is considerable variation in light tolerance among these taxa, with I. parviflorum `Forest Green' demonstrating superior tolerance to high light among the plants compared. A more rigorous examination of I. parviflorum `Forest Green' (high light tolerance) and I. floridanum Ellis (low-light tolerance) demonstrated that I. parviflorum `Forest Green' had a considerably higher Amax, a higher light saturation point, greater potential photosynthetic capacity, reduced susceptibility to photoinhibition as indicated by superior PSII efficiency following light exposure, greater capacity for thermal de-excitation as indicated by a higher rate of nonphotochemical quenching (NPQ) under full sun, greater apparent electron transport rate (ETR) at mid-day, and higher concentrations of the free-radical scavenger myo-inositol. All of these factors contribute potentially to a greater capacity to use light energy for carbon fixation while minimizing photodamage.

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Dominique-André Demers, Sylvain Dubé, Serge Yelle, and André Gosselin

Growing tomato and pepper plants under continuous light causes negative effects such as leaf chlorosis and deformities, and decreased growth and yield. Such effects are more pronounced on tomato plants. Our general objectives are to identify the physiological process(es) responsible for these negative effects and to explain the difference in sensitivity of tomato and pepper plants to continuous light. The specific objective of this experiment was to determine the effects of continuous light and light spectral composition on photosynthesis and related processes of tomato and pepper plants. Tomato and pepper plants were place on 7 June 1994 in growth chambers under photoperiod treatments of 12 h [high-pressure sodium (HPS) lamps], 24 h (HPS lamps), and 24 h [metal halide (MH) lamps]. For all treatments, FPP was 350 μmol·m–2·s–1, temperatures were 21C (day) and 17C (night), and RH was 70%. Every 2 weeks (7 June until 2 Aug.), tomato and pepper leaf samples were harvested and frozen in liquid nitrogen for subsequent measurements of starch content (Robinson et al, 1988, Plant Physiol.), sucrose phosphate synthase activities (Dali et al., 1992, Plant Physiol.) and chlorophyll and carotenoid content (determination on HPLC). A system that measured gas exchange and chlorophyll fluorescence of fresh leaf samples was used to determine the photosynthetic rate and quantum yield of CO2 fixation and electron transport. Development of the negative effects of continuous light on plants was monitored. Light spectral composition of the two types of lamps was measured using a spectroradiometer. Results show that, under continuous light, pepper plants were less-efficient than tomato plants in using light for CO2 fixation, but were more efficient in dissipating the extra energy received. This may explain why pepper plants are less sensitive to continuous light than tomato plants. MH lamps caused more-severe chloroses on tomato leaves than HPS plants. We believe that the higher proportion of UV-light provided by MH lamps may be related to this effect. Detailed results will be presented.

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Jinhong Yuan, Man Xu, Wei Duan, Peige Fan, and Shaohua Li

, trapped excitons, transported electrons, and dissipated energy can also be indicated by the transient parameters ( Strasser and Tsimilli-Michael, 2001 ). The decrease in photosynthesis of plant leaves under water stress causes inefficient use of light

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Lijuan Xie, Deying Li, Wenjuan Fang, and Kirk Howatt

. Table 5. Quantum yield of photosynthesis system II–mediated electron transport of creeping bentgrass treated with mesotrione in 2007 and 2008 as affected by different rates, timings, and concentrations of urea ammonium nitrate. In conclusion, mesotrione

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Holger Weichert, Stefanie Peschel, Moritz Knoche, and Dieter Neumann

. After adding cocktail, radioactivity was quantified by liquid scintillation counting. Fluxes (J) were calculated from equilibrium flow rates as described above. The effect of pH on 55 Fe-transport was indexed by the change in J [ΔJ (ΔJ = J I − J II

Open access

Xinyi Chang, Junli Sun, Lianling Liu, Wang He, and Baolong Zhao

induced by salt stress. The results showed that salt stress caused damage to the photosynthetic apparatus of the PSII reaction center, causing decreases in the initial capture ability and photosynthetic electron transport rate of light energy, which

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Wayne A. Mackay, Brent Pemberton, Joseph Maxim, and Suresh D. Pillai

‘Rocky Mountain Lavender’ unrooted cuttings were obtained from Fischer USA (Boulder, CO) and transported in the original shipping container to the National Center for Electron Beam Research facilities at Texas A & M University in College Station, TX, for

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Guoting Liang, Junhui Liu, Jingmin Zhang, and Jing Guo

chloroplasts is dissipated through three reciprocally related pathways: photosynthetic electron transport, chlorophyll fluorescence, and heat dissipation ( Hendrickson et al., 2004 ). F V / F M reflects the ability of antenna pigments to absorb and convert

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Dawei Shi, Xiaodong Wei, Guoxiang Chen, and Yanli Xu

photosynthetic rates indicated that the ginkgo leaves at Day 266 (September) were mature, and the leaves after this time showed progressive stages of senescence. As shown in Figure 4 , the decrease in the PSII electron transport activity was larger than that of

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Julián Miralles-Crespo, Juan Antonio Martínez-López, José Antonio Franco-Leemhuis, and Sebastián Bañón-Arias

) . The éPSII was used for the calculation of the linear electron transport rate (ETR) according to Krall and Edwards (1992) : ETR = éPSII × PPFD × 0.84 × 0.5, where PPFD represents the PPF density incident on the leaf, 0.84 the assumed leaf