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Hussein Al-Amier, Robert Lussier, Ming Coler, Margaret Stoltzman, and Lyle Craker

The stress level in a plant may be directly associated with the intensity of the Kautsky effect (the sudden increase in fluorescence emission by chlorophyll following a dark adaptation). The decrease in photosynthetic efficiency, linked with the rate of photochemistry of plants under stress, provides a definitive signature (graphical pattern) that can be quantified and monitored, even for plants that have no visible stress symptoms. Using a prototype GrowScanner®, signature differences in plants under nitrogen and water stress, as compared with plants not under stress, could be detected and measured. Returning stressed plants to a nonstressed condition returned the stress signatures to that of control plants not under stress. Development of the technology may provide a relatively quick, presymptomatic methodology for detecting plant stress without sacrificing plant tissue.

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Ning Li and Larry S. Daley

The goal of our project is to develop a non-invasive means to monitor the physiological status of plants. Spectral image acquisition is a powerful analytical approach for determining chemically distinct species in heterogeneous materials. It was found by Callis and Brukner that the combination of a continuously tunable monochromatic light with a thermoelectric-cooled CCD detector offered the best approach. In the in vivo spectra of leaf, researches has been focused on interpreting the visible spectra in terms of the profile of various types of chlorophyll-protein complexes and relating these to selected aspects of plant pathology and physiology. A computer interfaced imaging spectrometer employing a CCD detector was constructed. It can record the transmitted spectra of up to 31,680 positions for each sample. The instrument was used to study in vivo spectra of sugar cane and barley leaves. The light harvesting complex proteins were then `interpreted from the spectra and were shown graphically. Excellent results were also obtained when we measured the relative respiration rate of plant roots. A pH sensitive dye Resazurin was used to show the pH changes around a soybean root. The spectral images changing as a function of time were recorded and the relative respiration rate of any position of the root could be determined.

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Jiwan P. Palta

In recent years evidence has been presented that implicates the role of free (cytosolic) Ca2+ as a major metabolic and developmental controller in plants. Calcium concentrations in the cytoplasm are kept very low under normal conditions (10-6 to 10-8 M). Small changes in the absolute amount of calcium can create a 10- to 100-fold change in the Ca2+ concentration without upsetting the ionic balance of the ceil. This feature makes Ca2+ an excellent candidate as a second messenger. Thus, a stress induced change in the cytosolic Ca2+ could bring a cellular/plant response to stress. This response is thought to be mediated through activation of Ca2+ and/or Ca2+-calmodulin-dependent protein kinases which in turn mediate the activity of various enzymes via phosphorylation. Recent evidences from the impact of salinity, low temperature, high temperature, and biotic stresses support such a role of calcium. Data on the association between stress-induced injury and perturbation of membrane/cytosolic calcium are available. In addition, evidences for the role of calcium in acclimation to stress have been reported. These studies suggest that manipulation of cellular Ca2+ may be one of the approaches we have on hand to bridge the gap between science and technology.

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Kristian Borch, Kathleen B. Evensen, and Jonathan Lynch

Impatiens (Impatiens × hybrida `Impulse Orange'), and marigold (Tagetes × hybrida `Janie Tangerine') plants grown under low phosphorus were more resistant to drought stress than plants grown with a conventional, high-P fertilization program. Low concentrations of P were supplied using alumina-buffered P incorporated into the peat media. Alumina was charged with two levels of P, giving two levels of P-desorption. The alumina-buffered P amendment amounted to 2% by volume of the medium. Control plants (high-P treatment) were fertilized with a nutrient solution containing a P concentration of 1.5 mm. Phosphorous leaching was reduced by 96% to 99.4% in the low-P treatments compared with controls. Low-P plants showed no signs of P deficiency or aluminum toxicity. Impatiens plant diameter was significantly reduced by low-P fertilization, and leaf area was reduced by low P in both species. In marigold plants, roots were confined to a small volume beneath the drip tube in high-P plants, while in low-P plants they were well distributed through the medium. Impatiens roots showed no obvious differences in root distribution. Plants at the marketing stage were exposed to drought. The low-P plants of both species wilted more slowly and recovered more quickly when irrigated than the high-P controls. The reduced leaf area on the low-P plants may account for the improvement in drought tolerance.

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D. Michael Glenn

Kaolin-based particle films have use in reducing insect, heat, photosynthetically active radiation (PAR), and ultraviolet radiation stress in plants resulting from the reflective nature of the particles. Particle films with a residue density of 1 to 4 g·m−2 have been evaluated in a range of crops and agricultural environments. The particle film is a general insect repellant resulting from the change in the plant’s leaf/fruit texture but also because it changes the reflected light signature of the plant causing insect avoidance for many pests. The alteration of reflected light is the result of the ability of the particle film to reflect infrared (IR), PAR, and ultraviolet radiation. Reflection of IR can reduce canopy temperature as much as 5 °C, which will reduce potential transpiration. The reduction of PAR by the film at the leaf level is compensated in varying degrees by diffusion of PAR into the interior of the canopy. Whole canopy photosynthesis can be increased by the combined particle film effects of reduced canopy temperature and increased diffusion of PAR into the interior of the canopy. In apple, reducing fruit surface temperature, PAR, and ultraviolet is an effective means of reducing sunburn damage. The use of a reflective particle film is effective in mitigating environmental stress and has significant economic benefits in agricultural crops.

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G. Bagatto, T.J. Zmijowskyj, and J.D. Shorthouse

Mineral nutrient levels in tissues of the domestic shrub rose (Rosa rugosa Thunb.) were examined following gall induction by the cynipid wasp Diplolepis spinosa (Ashmead). Higher levels of Cu, Zn, Fe, Mn, and Ni were found in the galls, leaves protuding from the galls, and stems to which galls are attached than were found in normal stems and leaves, indicating that cynipid galls alter the nutritional status of their hosts. Cynipid galls must be removed or controlled because the stress they cause will increase the vulnerability of roses to attack by other pestiferous insects.

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Daniel K. MacKinnon, Dale Shaner, Scott Nissen, and Phil Westra

A study was conducted with a wettable powder formulation of 1-methylcyclopropene (1-MCP) to determine the effects of surfactants, spray volume, nozzle type, and rain fastness on the efficacy of 1-MCP to protect tomato plants from the epinastic effects of ethephon. 1-MCP at 25 and 50 g·ha−1 protected tomato plants from 250 and 500 g·ha−1 of ethephon. Of the three best surfactants tested, two (Dyne-Amic and Silwet L-77) contained silicone and one (Herbimax) an emulsified petroleum oil. The efficacy of 1-MCP increased with an increase in spray volume from 150 L·ha−1 to 400 L·ha−1, suggesting that an increase in leaf coverage leads to greater protection and that the translocation of 1-MCP is limited within tomato plants. There was no significant effect of spray nozzle type on 1-MCP activity. 1-MCP appeared to be rainfast within 15 min after application.

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Fred T. Davies Jr., Chunajiu He, Amanda Chau, Kevin M. Heinz, and Andrew D. Cartmill

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.

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C.L. Haynes, O. M. Lindstrom, and M. A. Dirr