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; Taiz and Zeiger, 2010 ). In pecan trees, inadequate N levels in soils can compromise nut development and quality ( Heerema, 2013 ; Heerema et al., 2014 ). Pecan leaf greenness and P n activity are affected by leaf tissue concentrations of N and

Open Access

Common swedish ivy plants when exposed to nitrogen (N) stress display typical nitrogen deficiency symptoms such as reddening of stems and petioles and yellowing of leaves. When N levels are restored, leaves of swedish ivy plants will re-green without leaf loss. An experiment was conducted to determine how proteins change when leaves were re-greened after N deficiency. Cuttings of Plectranthus australis were rooted under mist and allowed to yellow. Plants were then potted up and fertilized with one of two treatments: complete nutrients with N at 150 ppm or complete nutrients with 0.8 ppm N. The experimental design was a randomized complete-block design with six blocks. Each block had the two N treatments and six plants per treatment. After 3–4 weeks, all plants in the 150-ppm N treatment had re-greened and leaf samples for protein analysis were taken. Plants in four of the six blocks were then switched to the other treatment. After leaves had re-greened once again, leaf samples were taken and the experiment was terminated. Two-dimensional polyacrylamide gel electrophoresis was used to compare the treatments. No obvious differences in protein absence or presence were noted. However, Rubisco appeared to be differentially expressed between the two treatments. 2-D gel analysis with subsequent Western blots showed that for most of the leaf samples, the large subunit of Rubisco (56kD) was quantitatively about 1.3 times more concentrated in the N-deficient plants and possibly modified. The small subunit (12kD) was not reliably detectable. Additional protein results for repeated leaf re-greening and the role Rubsico may play in leaf re-greening will be discussed.

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objectives of lettuce breeders working in these environments. Being a cool-season crop, lettuce is vulnerable to global warming. In this study, we evaluated green and red leaf lettuce germplasm collections for their tolerance to high temperatures to find heat

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Abstract

One of the more subtle plant responses to ozone may be a reduction in chlorophyll content of leaf tissue (3). Existing chlorophyll may degrade (premature senescence) or chlorophyll synthesis may decline. This reduction of chlorophyll may impair photo-synthetic processes, leading to a reduction in carbon fixation. Reduced chlorophyll concentration may be reversible over time following ozone exposure. A nondestructive method of repeatedly measuring the greenness of a leaf can assess initial response and recovery of a leaf from ozone exposure. The unitless numbers generated by a portable chlorophyll meter (SPAD-501, Minolta Corp.) correlate with actual chlorophyll concentration determined by traditional extraction methods (1). The unitless readings may themselves constitute a useful response variable, without conversion using a standard curve. This instrument is potentially very useful for making rapid, repeated, in situ measurements of the same leaf over time, and is therefore suited to studying plant recovery from ozone exposure. The chlorophyll meter may also be useful for measuring leaf greenness prior to environmental stress. These values may be used as a covariate to adjust the post-treatment observations, potentially reducing the variability of the data and increasing the precision of data analysis (2). The SPAD-501 portable chlorophyll meter was used to determine greenness of intact leaves before and following exposure of Tiny Tim’ and ‘New Yorker’ tomato (Lycopersicon esculentum L.) plants to ozone. The usefulness of these SPAD-501 readings as a covariate in analysis of covariance (2) was evaluated.

Open Access

Abstract

Traditional quantification of leaf chlorophyll requires destructive sampling of leaves and tedious extraction in 80% acetone (1,2), whereas N, N-dimethylformamide (DMF) is an alternative solvent that does not require tissue grinding (3). Minolta has recently marketed a portable meter (SPAD-501) for a rapid and nondestructive estimate of leaf greenness. Earlier results indicate a weak but significant correlation (r 2 = 0.48) between SPAD readings and leaf chlorophyll extracted in acetone from data pooled from 22 species (5). The purpose of this study was to address three questions: a) is there a species-specific relationship between the SPAD readings and extractable chlorophyll; b) is the relationship of SPAD readings stronger when chlorophyll is expressed on a leaf area-or fresh-weight basis; and c) what is the consistency between two individual SPAD-501 instruments?

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. The use of resistant cultivars does reduce chemical usage, which benefits growers, consumers, and the environment. However, lettuce cultivars with a high level of resistance to leafminers are not currently available. We describe two green leaf, one red

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increasing consumption and production of leaf lettuce, there is a need for public germplasm that facilitates the research and development of new cultivars and germplasm. In this article, we describe two green leaf breeding lines with resistance to corky root

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leafminers are not currently available. In this article, we describe a green leaf lettuce breeding line with combined resistance to leafminers and LMV, which is adapted to the major lettuce production areas of the central coast of California. Origin The

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Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, `Moonlight' (dark green) and `Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality by 58% (`Moonlight') and 77% (`Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in `Moonlight' relative to `Limerick' under UV-B stress and during recovery. `Moonlight' contained greater levels of chlorophyll (1.5 to1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than `Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.

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Broadleaf’ has been selected to exhibit high levels of resistance to a bacterial leaf blight disease caused by Pseudomonas cannabina pv. alisalensis ( Pca ). Leafy-green mustards are one type of Brassica “leafy greens” among several other important

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