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Ariningsun P. Cinantya, Fure-Chyi Chen and Yao-Chien Alex Chang

fluorescence (Fv/Fm) was then calculated, where Fv = Fm – Fo. The chlorophyll fluorescence was measured with a photosynthesis yield analyzer (MINIPAM; Heinz Walz, Effeltrich, Germany). Chlorophyll fluorescence was measured from 0800 hr to 1030 hr . The leaf

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Nazir Mir, Michael Wendorf, Rufino Perez and Randolph M. Beaudry

The relationship between chlorophyll fluorescence of `Cortland', `Redchief Delicious', and `Empire' apple (Malus ×domestica Borkh.) fruit and the development of superficial scald was studied during 120 days of refrigerated air (RA) storage at 0 °C and during 7 days of poststorage holding at 22 °C. Minimal fluorescence (Fo), maximal fluorescence (Fm), photochemical efficiency (Fv/Fm, where Fv=Fm=Fo) and coefficient of photochemical fluorescence quenching (qp) were measured. During storage, while Fv/Fm and Fm declined in `Cortland' and `Redchief Delicious' fruit over time, these two measures of chlorophyll fluorescence remained stable in `Empire' fruit. Of the three cultivars, only `Empire' is resistant to and did not develop superficial scald. A decline in Fv/Fm preceded scald development in `Cortland' and `Redchief Delicious' fruit. After 30 days of storage, qp began to decrease in fruit from all three cultivars. Prestorage diphenylamine (DPA) application had no effect on Fv/Fm, Fo, and Fm and only marginally improved maintenance of qp, but completely prevented the development of superficial scald. Poststorage holding at 22 °C accelerated the rate of change in most fluorescence measurements. The decline in the Fv/Fm ratio and/or qp with storage time may be in response to senescence-related factors that also enhance scald susceptibility, however, Fv/Fm does not appear to be directly related to superficial scald susceptibility per se.

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Sarah E. Bruce, D. Bradley Rowe and James A. Flore

Chlorophyll fluorescence over the course of stem cutting propagation was examined in 10 cultivars of Taxus ×media (Taxus baccata L. × T. cuspidata Sieb. & Zucc.), including `Brownii', `Dark Green Pyramidalis', `Dark Green Spreader', `Densiformis', `Densiformis Gem', `Hicksii', `L.C. Bobbink', `Runyan', `Tauntoni', and `Wardii'. The fluorescence value measured was the ratio of variable over maximum chlorophyll fluorescence (Fv/Fm). This value reflects the maximum dark-adapted photochemical efficiency of photosystem II (PSII) reaction centers involved in photosynthesis and is an indirect measure of plant stress. The objective of this study was to examine Fv/Fm as a method for stock plant selection and for monitoring rooting progress of various cultivars. Fv/Fm varied significantly (P ≤ 0.05) among cultivars, initially and over time. However, there was significant overlap among some cultivars. The Fv/Fm decreased dramatically during cold storage, but usually returned to original levels after several weeks in the propagation beds. This appeared to be a reflection of the reduction of water stress as the cuttings formed roots. Initial stock plant Fv/Fm was not correlated (P ≤ 0.05) with rooting percentage, root number, root dry weight, or root length, indicating that Fv/Fm is not a reliable indicator of stock plant rooting potential. Visual assessment is just as reliable.

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Terri Starman and Leonardo Lombardini

A study was conducted to characterize the morphological and physiological responses of four herbaceous perennial species subjected to two subsequent drought cycles. Lantana camara L. `New Gold' (lantana), Lobelia cardinalis L. (cardinal flower), Salvia farinacea Benth. `Henry Duelberg' (mealy sage), and Scaevola aemula R. Br. `New Wonder' (fan flower) were subjected to two consecutive 10-day drought cycles. Growth response, leaf gas exchange, and chlorophyll fluorescence were measured during the experiment. The morphology of L. cardinalis and L. camara was not affected by drought, while S. farinacea had reductions in plant height and leaf area and S. aemula had reductions in dry weight. Overall, plant growth and development continued even when substrate water content was reduced to 0.13 mm3·mm-3, which indicated a level of substrate water below container capacity was sufficient for greenhouse production of these species. The drought treatments had little effect on the photochemical efficiency (Fv/Fm) of Photosystem II. An increase in minimal fluorescence (Fo) was observed in S. aemula on the last day of the second cycle. Drought treatment caused increased leaf-level water use efficiency (WUE) at the end of the first cycle in L. cardinalis and S. aemula, but not in L. camara and S. farinacea. Plants of L. camara, S. farinacea, and S. aemula that had received drought during both cycles became more water use efficient by the end of the second cycle, but L. cardinalis did not.

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Zhongjie Ji, James J. Camberato, Cankui Zhang and Yiwei Jiang

, leaf water content (LWC), leaf photochemical efficiency (Fv/Fm), and leaf Na + and K + concentration were measured. Height was recorded from the soil surface to the top of the highest leaf blade. Fresh weight was determined by weighing all leaves, and

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Steven J. McArtney, John D. Obermiller and Consuelo Arellano

reaction centers are open. Changes in Fv/Fm were used to study the recovery process after the addition of root-absorbed PSII inhibitors to the nutrient solution of sugar beets growing in hydroponic culture ( Abbaspoor et al., 2006 ). The objectives of the

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Sorkel Kadir, Michael Von Weihe and Kassim Al-Khatib

The photosystem II reaction center is the most sensitive reaction center in photosynthesis to heat stress ( Wen et al., 2005 ). Heat stress decreases photosynthetic electron transport activity and variable fluorescence and maximum fluorescence (Fv/Fm

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Shu-Ting Fan, Der-Ming Yeh and Tsu-Tsuen Wang

) ( DeEll et al., 1999 ). Chlorophyll fluorescence is an intriguing tool that can assess photosynthetic performance and monitor plant response to the environmental stress ( Adams and Demmig-Adams, 2004 ). The Fv/Fm (potential photochemical efficiency of PS

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Jessica D. Lubell and Jacob A. Griffith Gardner

Analyzer (PEA); Hansatech Instruments, Norfolk, England] for four randomly selected plants per species per shade level. For each plant, three Fv/Fm measurements were taken using different leaves of similar age, and these values were averaged for each plant

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Yu Cui, Jinsheng Wang, Xingchun Wang and Yiwei Jiang

( DaCosta and Huang, 2006 ; Jiang et al., 2009 ; Merewitz et al., 2010 ; Yu et al., 2013 ; Zhou et al., 2013 ). Some drought responses used for assessing plant stress tolerance include, but are not limited to, reduced growth, photosynthesis, LWC, Fv/Fm