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

to a decrease in chlorophyll and carotenoid production caused by the inactivity of phytoene desaturase. The lack of tocopherols also contributes to plant death through a decrease in buffering capacity to reactive oxygen species ( Matringe et al., 2005

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Corrie Cotton and Gregory E. Welbaum

Maturity at harvest determines seed viability and vigor. However, separating seeds from different stages of development can be difficult using existing seed sorting technologies. New technology non-destructively sorts seeds based on their chlorophyll fluorescence (CF), so seeds with the same dry weight but with different physiological maturates can be separated. We determined whether chlorophyll content of muskmelon (Cucumis melo L. cv. Top Mark) seeds changes during development and whether those changes were related to viability and vigor. Seed viability and vigor were determined using an Association of Official Seed Analysts wet paper towel germination test. `Top Mark' seeds from nine stages of development were run through the SeedMaster Analyzer (Satake USA Inc., Houston, Texas), which calculated the chlorophyll content of each seed. The CF signal was fed into a computer to obtain a frequency histogram. Forty, 45, and 55 days after anthesis (DAA) seeds had germination percentages of 96%, 98%, and 100%, respectively, the highest in the study. Fifty-five DAA had greater seed vigor and viability and contained the lowest CF values; 207 on the 1000-value scale. The less-mature seeds contained higher chlorophyll content and had the lowest seed vigor and viability. Seed vigor and chlorophyll content were negatively correlated in this study. All seeds with high CF values had low vigor, but not all seeds with low CF values have high vigor. Seed aging during storage can reduce viability and vigor independent of chlorophyll content. Based on chlorophyll content, the SeedMaster Analyzer can non-destructively remove immature, low-vigor seeds that have the same physical characteristics and weight as more mature seeds. Chlorophyll fluorescence technology may allow the seed industry to further improve seed quality and maximize vigor.

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Ellen T. Paparozzi, Jazbaat K. Chahal, Petre Dobrev, Elizabeth A. Claassen, Walter W. Stroup, and Radomira Vankova

., 2009 ; Kiba et al., 2011 ). As cytokinins, often referred to as the leaf regreening hormone, also exhibit positive effects on chlorophyll concentration in leaves we decided to compare the dynamics of the response to N deficiency and subsequent N

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Dámaris L. Ojeda-Barrios, Eloísa Perea-Portillo, O. Adriana Hernández-Rodríguez, Graciela Ávila-Quezada, Javier Abadía, and Leonardo Lombardini

include reductions in leaf chlorophyll concentrations and photosynthesis ( Hu and Sparks, 1991 ), impairments in the development of reproductive structures ( Hu and Sparks, 1990 ), decreased carbonic anhydrase activity in leaves ( Snir, 1983 ), and changes

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Schuyler D. Seeley, Hossein Damavandy, J. LaMar Anderson, Richard Renquist, and Nancy W. Callan

Abbreviations: CL, chlorophyll; CO, Colorado; GR, growth regulator; LR, leaf retention; MT, Montana; PF, leaf detachment pull force; UT, Utah; XN, xanthophyll. 1 Current address: 2355 Weymouth Lane, Crofton, MD 21114. This report is based, in part

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Jinpeng Xing, Yan Xu, Jiang Tian, Thomas Gianfagna, and Bingru Huang

of leaves as chlorophyll and other cellular components (e.g., proteins and nucleic acids) are degraded during natural or stress-induced leaf aging. Cytokinins (CK) have been well known for delaying leaf senescence, and in some cases, reversing this

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Ian R. Rodriguez and Grady L. Miller

Because high rates of nitrogen fertility are necessary for producing high-quality turfgrasses, quick, reliable methods of determining the N status of turfgrasses would be valuable management tools. The objective of this study was to evaluate the capacity of a hand-held chlorophyll meter (SPAD-502) to provide a relative index of chlorophyll concentrations, N concentrations, and visual quality in St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze]. Two experiments were conducted in a greenhouse in 1998 to evaluate the utility of SPAD readings. Established pots of `Floratam' were subjected to weekly foliar Fe treatments at Fe rates of 0 and 0.17 kg·ha–1 for 4 weeks. Six weekly nitrogen fertilizer treatments were applied in the form of ammonium sulfate at N rates of 0, 5.75, 11.5, 17.25, and 23 kg·ha–1 for 4 weeks. Greenhouse SPAD readings were not affected by Fe treatment, but N treatments resulted in differences in SPAD readings, visual quality, and chlorophyll concentrations. The readings were positively correlated with chlorophyll concentrations (r 2 = 0.79), visual ratings (r 2 = 0.74), and total Kjeldahl nitrogen (TKN) (r 2 = 0.71). Readings taken from field-grown `Floratam', `Floratine', and `Floralawn' St. Augustinegrass were poorly correlated (r 2 < 0.63) with chlorophyll concentrations and TKN. Unless future techniques improve dependability of the SPAD meter under field conditions for measuring chlorophyll and N concentration of a stand of turfgrass, the usefulness of such readings for the management of St. Augustinegrass seems limited.

Open access

Qinglu Ying, Chase Jones-Baumgardt, Youbin Zheng, and Gale Bozzo

with their corresponding mature plants ( Xiao et al., 2012 ). Phytochemicals that are present in microgreens, specifically in those of the Brassicaceae family, include ascorbate (i.e., vitamin C), chlorophylls, carotenoids, phenolics, and anthocyanins

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Jack Olson and Matthew Clark

chlorophyll (Chl) a / b and carotenoid pigments. This type of variegation is called pigment-related variegation, originally described by Hara (1957 ) in his findings of four general mechanism for variegation from his studies on 55 variegated plant species

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R. Andrew Schofield, Jennifer R. DeEll, and Dennis P. Murr

Chlorophyll fluorescence responds to a range of environmental stresses that affect horticultural crops. This technique has been used successfully to evaluate the quality of commodities after exposure to a number of postharvest stresses such as chilling, heat, and atmospheric stress. As well, chlorophyll fluorescence measurements have been incorporated as the main characteristics in shelf-life prediction models. Our objective was to evaluate the use of chlorophyll fluorescence measurements at harvest to predict the shelf-life of `Iceberg' lettuce. It was hypothesized that storage potential is influenced by the degree of stress induced by field conditions and that different cultivars, although grown under the same conditions, experience varying degrees of stress that can be detected by fluorescence measurements at harvest, even in the absence of visual differences in quality. The utility of fluorescence measurements was limited by inconsistencies in the development of the heads, such as maturity and leaf formation, and by variation among different areas of the same leaf. Fluorescence data from a homogeneous group of heads revealed that the variation associated with different areas of the same leaf was larger than that associated with measurements from different heads. Also, fluorescence readings from one leaf differed from those taken from any non-adjacent leaves. These sources of variation, along with strong cultivar-dependant differences in the fluorescence signal, were quite large, and hence, any trends in fluorescence measurements related to storage potential were not observed. Therefore, chlorophyll fluorescence at harvest does not appear to be a good predictor of lettuce storability.