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Rangjian Qiu, Taisheng Du, Shaozhong Kang, Renqiang Chen and Laosheng Wu

.S. Walter, C.H. Clarkson, D.T. 1988 Growth response of barley and tomato to nitrogen stress and its control by abscisic acid, water relations and photosynthesis Planta 173 352 366 Claussen, W. 2002 Growth, water use efficiency, and proline content of

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

Nitrogen response was compared in two Plectranthus species, Plectranthus parviflorus and Plectranthus ambiguus, which differ substantially in their phenotypic reaction to nitrogen limitation. The leaves of the former species gradually yellow during the nitrogen stress but are retained on the plant. This species copes with nitrogen deficiency also by gradual hydrolysis of starch grains. The latter species, P. ambiguus, responds by abscission of lower leaves. As plant hormones cytokinins are involved in nitrogen response as well as in regulation of the chlorophyll content, their dynamics were followed to explore the fast responses as well as the impact of nitrogen treatment. Both plant species responded to nitrogen deficiency/supplementation in similar ways, by downregulation and upregulation, respectively, of active cytokinins. However, the different phenotypic reactions imposed by nitrogen limitation were associated with specific regulation of cytokinin pool accompanying the stress response by the two species. The increase of the active cytokinins on nitrogen resupply was faster and stronger in the regreening species, P. parviflorus than in P. ambiguus. However, the P. ambiguus plants maintained higher basal levels of all cytokinin metabolites as well as chlorophyll content when compared with P. parviflorus. Nitrogen deficiency was associated in this species with accumulation of cis-zeatin-type cytokinins, which preceded abscission of lower and later on of middle leaves. The achieved results indicate that phenotypic variations in the response to nitrogen deficiency/supplementation are associated with significant quantitative and qualitative differences in the cytokinin pool.

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G.W. Stutte and C.A. Stutte

Computer analysis of airborne, broad-band, near-infrared (NIR, 710 to 1100 nm) video imagery of peach tree canopies was used to determine spatial variability of cumulative stress in two peach orchards. A significant quadratic correlation was found between leaf-N content and the normalized mean pixel intensity (MPI) of the digital imagery of NIR canopy reflectance. This correlation was used to establish MPI estimates of N-stressed trees in the orchard. The relationship was used to localize site-specific spatial variability in a commercial peach orchard. The underlying soil type was found to be closely associated with the spatial variability in NIR imagery in the commercial peach orchard. Assessing spatial variability in the orchard with NIR video permits early localization of potentially low productivity regions within an orchard.

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Joan R. Davenport and Nicholi Vorsa

Cranberry (Vaccinium macrocarpon Ait.) has the opportunity to partition resources into sexual and/or asexual (stolons) modes of reproduction. Nitrogen status has been shown to impact the degree of stoloniferous growth. To determine whether there is a genotypic response to varying nitrogen levels, six hybrid and four native cultivars were treated with three annual rates of nitrogen fertilizer (17, 34, or 67 kg·ha-1) for 4 years. Fruit yield was determined each year and asexual vegetative growth (stolons) weight was removed and measured in all but the first year of the experiment. Cultivars exhibited different patterns of yield and stolon weight response over the three nitrogen rates. Not all cultivars exhibited significant yield decreases at the high N levels. Vegetative growth (stolon weight) generally increased with increasing N, however, not all cultivars responded similarly over three N rates. Partitioning between yield and stolon production favored fruit yield at the lower N rates in three of the four native cultivars studied (`Cropper', `Early Black', and `Howes'). Yield over N rates was more stable for four of the six hybrid cultivars, which may be the result of greater heterozygosity in hybrids than natives, and/or genetic gain from one breeding and selection cycle, offering increased tolerance to nitrogen stress. This study indicates that genetic variation exists for yield, yield stability, and stolon production relative to nitrogen level, and that genetic gain in cranberry is possible for these traits. Future studies involving cranberry physiology and nutrition should consider the genotypes used.

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Yun-wen Wang, Bruce L. Dunn and Daryl B. Arnall

nitrogen stress in corn using remote sensing Agron. J. 98 579 587 Debaeke, P. Rouet, P. Justes, E. 2006 Relationship between the normalized SPAD index and the nitrogen nutrition index: Application to durum wheat J. Plant Nutr. 29 75 92 Dole, J.M. Wilkins, H

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Yiwei Jiang, Yaoshen Li, Gang Nie and Huifen Liu

( Lolium perenne ) to alterations in nitrogen supply Metabolomics 9 145 156 Gao, K. Chen, F. Yuan, L. Zhang, F. Mi, G. 2015 A comprehensive analysis of root morphological changes and nitrogen allocation in maize in response to low nitrogen stress Plant Cell

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James F. Cahill and Eric G. Lamb

and Keddie, unpublished data). We measured competitive response, the ability to withstand nitrogen stress, and the tolerance of herbivory by Trichoplusia ni in 47 lines of Arabidopsis, including both mutants and ecotypes. There were three major

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Sohrab Davarpanah, Ali Tehranifar, Gholamhossein Davarynejad, Mehdi Aran, Javier Abadía and Reza Khorassani

disruption of photosynthetic membranes, thus increasing sensitivity to high light levels, whereas anthocyanins act as a photoprotective pigments that may provide protection against light-induced oxidative damage ( Guidi et al., 1998 ). Nitrogen stress can

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Francisca López-Granados, M. Teresa Gómez-Casero, José M. Peña-Barragán, Montserrat Jurado-Expósito and Luis García-Torres

.B. Dutilleul, P. Goel, P.K. 2005a Discriminant analysis of hyperspectral data for assessing water and nitrogen stresses in corn Trans. Amer. Soc. Agr. Eng. 48 805 813 Karimi, Y. Prasher, S.O. McNaim, H

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M. Teresa Gómez-Casero, Francisca López-Granados, José M. Peña-Barragán, Montserrat Jurado-Expósito, Luis García-Torres and Ricardo Fernández-Escobar

for weed and nitrogen stress detection in corn Trans. Amer. Soc. Agr. Eng. 48 1261 1268 Karimi, Y. Prasher, S.O. Mcnaim, H. Bonnell, R.B. Dutilleul, P. Goel, P.K. 2005b