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Greg Litus and James Klett

During Summer 2005, green ash (Fraxinus pennsylvanica `Patmore') trees planted at the Colorado State University Agricultural Research Development and Education Center in 1996 were exposed to simulated drought by restricting irrigation for 33 to 41 days. During this period, predawn leaf water potentials in drought-stressed trees progressively dropped to a low of –2.04 MPa, while the control plot was maintained with full irrigation such that predawn leaf water potentials did not fall below –0.5 MPa. On 24 Aug. 2005, 31 days into this drought cycle, mid-day leaf water potentials and stomatal conductance were measured at –3.0 MPa and 22.63 mmol·m-2·s-1, respectively. Measurements in control trees collected at about the same time were –2.0 MPa and 169 mmol·m-2·s-1. The dramatic reduction in stomatal conductance in the drought-stressed trees began at about 10:30 a.m. and continued into the evening. Once irrigation was resumed, drought stressed trees rebounded from depressed predawn leaf water potentials and mid-day leaf water potentials and stomatal conductance and reached levels similar to control trees in 2 to 5 days. Stem flow gauges indicate that, during this period, fully hydrated control trees used about 250 liters/day.

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Krishna Nemali and Marc W. van Iersel

mechanisms that help bedding plants cope with drought stress. Bedding plants comprise an important sector of the U.S. greenhouse industry with sales estimated at ≈$1.86 billion in 2015 ( U.S. Department of Agriculture, 2015 ). Drought conditions can be more

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Yajun Chen, Jingjin Yu and Bingru Huang

Drought stress is one of the most detrimental abiotic stresses for plant growth. Water deficit in plants leads to stomatal closure and reduces photosynthesis resulting from restricted CO 2 diffusion through leaf stomata (stomatal limitation) and

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Yu Liu, Miao He, Fengli Dong, Yingjie Cai, Wenjie Gao, Yunwei Zhou, He Huang and Silan Dai

tobacco ( Tang et al., 2012 ). The Rosa RhNAC3 transcription factor is involved in response to drought stress in rose ( Rosa hybrida ) and participates in the stress response through an ABA-dependent regulatory pathway ( Jiang et al., 2014 ). BraNAC

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Kelly T. Morgan, Smita Barkataky, Davie Kadyampakeni, Robert Ebel and Fritz Roka

. To evaluate the effect of short- and long-term water drought stress on mechanical harvesting, a 3-year field study was conducted to test the hypothesis that no significant injury by mechanical harvesting occurs to healthy, well-watered citrus trees

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Emily B. Merewitz, Thomas Gianfagna and Bingru Huang

Drought is a detrimental abiotic stress for plant growth, including perennial turfgrass species. A typical drought stress symptom in turfgrass is a decline in turf quality (TQ) resulting from leaf senescence, slow shoot and root growth, and leaf

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Joel L. Shuman, Ron Mittler and Vladimir Shulaev

Drought and heat stress have been extensively studied in plants, but little is known about how the combination of drought and heat impact their physiology and metabolism. The metabolite profile of Arabidopsis subjected to heat, drought, and the combination of heat and drought were analyzed by gas-chromatography-mass spectrometry (GC-MS). Fatty acid retention time standards and the internal standard (IS) ribitol (adonitol) were added to each leaf sample and the polar phase was extracted, methoximated, and derivatized (trimethylsilylated) prior to analysis by GC-MS (Trace DSQ with Combi-PAL autosampler). Compounds were identified based upon retention time (relative to fatty acid standards) and comparison with reference spectra in our custom mass spectral library. Semi-quantitation of compound peak area was done relative to the internal standard. Plants subjected to both heat and drought stress accumulated sucrose and other sugars/sugar alchohols such as maltose, gulose, mannitol. The amino acid proline (Pro) was found in drought-stressed plants, but not found in drought- and heat-stressed plants. Proline has been reported to function as an osmoprotectant in cold-, salt-, and drought-stressed plants, but could be toxic to drought- and heat-stressed plants. We found that growth of heat-stressed Arabidopsis seedlings is inhibited by Pro, but not in drought- and heat-stressed seedlings. These results also indicate that sucrose replaces proline as the major osmoprotectant in heat- and drought-stressed plants. Plants subjected to combined heat and drought also exhibited enhanced respiration, suppressed photosynthesis, and distinct transcriptome expression.

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Ralf Uptmoor, Mildred Osei-Kwarteng, Susanne Gürtler and Hartmut Stützel

) population under well-watered and drought stress conditions individually for each DH line of the population, the detection of QTL on the parameters of the model followed by a model parameterization based on QTL effects, the evaluation of the model using

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Robert C. Ebel

Apple leaves were shown to increase 6 volatile compounds in response to drought stress severe enough to promote senescence. Apple trees were allowed to dry to -2.0 MPa and -2.7 MPa, levels that were previously shown to reduce fruit growth by 50% and 70%, respectively. The 6 volatile compounds measured included hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexen-l-ol, hexyl acetate, and (Z)-3-hexenyl acetate. Hexanal, (E)-2-hexenal, and 1-hexanol have been previously shown to be byproducts of lipoxygenase (LOX) activity. There is considerable information in the literature implicating LOX as a key enzyme involved in senescence, whether induced by pathogenic infection, insect feeding, or in ripening climacteric fruit and vegetables. It is reasonable to propose that LOX is also involved in promotion of senescence induced by drought stress.

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Bingru Huang and Hongwen Gao

Drought is among the most limiting factors for turfgrass growth. Understanding genetic variations and physiological mechanisms in turfgrass drought resistance would facilitate breeding and management programs to improve drought resistance. The experiment was designed to investigate shoot physiological responses of six tall fescue (Festuca arundinacea Schreb.) cultivars representing several generations of turfgrass improvement to drought stress. Grasses were grown in well-watered or drying (nonirrigated) soil for 35 days in the greenhouse. Net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), relative water content (RWC), and photochemical efficiency (Fv/Fm) declined during drought progression in all cultivars, but the time and the severity of reductions varied with cultivar and physiological factors. The values of Pn, RWC, gs, and Tr decreased significantly for `Rebel Jr', `Bonsai', and `Phoenix' when soil water content declined to 20% after 9 days of treatment (DOT) and for `Houndog V', `Kentucky-31', and `Falcon II' when soil water content dropped to 10% at 15 DOT. A significant decrease in Fv/Fm was not observed in drought-stressed plants until 21 DOT for `Rebel Jr', `Bonsai', and `Phoenix' and 28 DOT for `Houndog V', `Kentucky-31', and `Falcon II'. The decline in Pn resulted mainly from internal water deficit and stomatal closure under mild drought-stress conditions. After a prolonged period of drought stress (35 DOT), `Falcon II', `Houndog V', and `Kentucky-31' maintained higher Pn than did `Rebel Jr', `Bonsai', and `Phoenix', which could be attributed to their higher Fv/Fm. This study demonstrated variation in drought resistance among tall fescue cultivars, which was related to their differential responses in photosynthetic capacity and water relations.