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Stephen S. Deschamps and Shinsuke Agehara

in March. To speed up establishment and increase early yields, Florida strawberry growers have recently begun to advance transplanting dates from mid October to late September. As a result, plants are exposed to even greater heat stress conditions

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Yan Xu and Bingru Huang

transport. Cool-season turfgrass species such as Agrostis stolonifera are sensitive to heat stress and experience a series of physiological injuries when exposed to temperatures above 30 °C. Leaf senescence was observed after 20 d at 30 °C and only 8 d at

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Wenjie Ma, Wen Liang, and Bing Zhao

As plants are sessile organisms that cannot avoid heat, they often encounter harsh heat stress ( Wang et al., 2018 ). Heat stress can impose different metabolic and physical challenges on almost all aspects of plant development, growth, reproduction

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Renée L. Eriksen, Laban K. Rutto, James E. Dombrowski, and John A. Henning

node below the youngest, fully unfurled leaf because young and mature senescing tissues have different sensitivities to heat stress ( Karim et al., 1999 ; Marias et al., 2017 ). Dark-adapted F o and F V /F M measurements were performed after 10 h of

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Sylvie Jenni, David de Koeyer, and George Emery

(20.2 °C and 125 mm rainfall in 2001 and 20.7 °C and 123 mm rainfall in 2002), the lettuce heads harvested within 50 and 51 d experienced 15 d (2001) and 19 d (2002) of heat stress above 28 °C. In the first planting of 2001, the susceptible parent had

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Katsumi Suzuki, Tadashi Tsukaguchi, Hiroyuki Takeda, and Yoshinobu Egawa

Pod yield of `Kentucky Wonder' green bean (Phaseolus vulgaris L.) decreased at high temperatures due to a reduction of pod set. A highly positive correlation was observed between pod set and pollen stainability in flowers that were affected by heat stress about 10 days before anthesis. Pollen stainability was decreased by heat stress applied 8 to 11 days before flowering under controlled environment conditions. When mean air temperature during this period exceeded 28 °C, pollen stainability decreased under field conditions. Low pollen stainability indicated sensitivity to high temperatures about 10 days before flowering. A heat-tolerant cultivar showed higher pollen stainability than did heat-sensitive cultivars under high temperatures. These results demonstrated that heat tolerance at an early reproductive stage could be evaluated by analyzing pollen stainability using flowers developed under high temperatures.

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Elizabeth Vierling

When plants experience high temperature stress, they respond by synthesizing a discrete set of proteins called heat shock proteins (HSPs). This response is not unique to plants, but is observed in all other eukaryotes. It is now known that the HSPs are evolutionarily conserved proteins, and furthermore, that HSPs function not only during stress, but also during normal growth and development. My laboratory has characterized several of the major groups of HSPs in higher plants. We have cloned genes encoding plant HSP70 proteins and low molecular weight (LMW) HSPs (17-23 kDa). Using this information we have investigated the expression of HSPs both in the field, and under laboratory conditions which mimic field situations. We have determined the temperature limits for expression of HSPs in vegetative tissues, and have also found that HSPs are frequently produced in plant reproductive structures, even in the absence of stress. As a first step toward understanding HSP function, we have characterized the intracellular localization of HSPs. Results show that there are unique HSPs in the cytoplasm, chloroplast and endomembrane system. These ubiquitous proteins appear to play essential roles in many cellular processes.

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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

Mature green `Sunbeam' tomato fruit (Lycopersicon esculentum Mill.) were treated in water for 1 hr at 27 (ambient), 39, 42, 45, or 48°C, and then either ripened at 20°C (nonchilled) or stored at 2°C (chilled) for 14 days before ripening at 20°C. The most-effective heat treatment was 42°C, which reduced decay 67% in chilled fruit and 53% in nonchilled fruit. Heat treatment had no effect on time required to ripen the fruit. Red-ripe tomatoes had higher respiration rates and evolved more ethylene following nonchilling storage, but heat treatment had no effect on respiration or ethylene evolution. Red color development was enhanced by heat treatment, and inhibited by chilling. At red ripe, fruit were firmer as a result of storage at the chilling temperature, while heat treatment had no effect on firmness. Heat-treated fruit were preferred in terms of taste and texture over nontreated fruit in informal taste tests, with the exception of the 45°C treatment. With increasing temperature of heat treatment, there was increased electrolyte leakage following chilling storage. Of the 15 flavor volatiles analyzed, the levels of five were decreased with increasing temperature of heat treatment. Storage at the chilling temperature reduced the levels of six flavor volatiles. Prestorage heat treatments can reduce decay with only minimal adverse effects on tomato fruit quality.

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Ritu Dhir, Richard L. Harkess, and Guihong Bi

Ivy geranium ( Pelargonium peltatum L.) is an important floriculture crop but it does not tolerate the high temperatures of southeastern U.S. summers. Under heat stress, the newly developing leaves of ivy geranium are partially or completely white

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Abbas Lafta, Thomas Turini, German V. Sandoya, and Beiquan Mou

and the environment ( Jenni and Yan, 2009 ). Tipburn is one of the physiological disorders associated with heat stress and the symptom appears as brown necrosis around the margin of the affected leaves. This disorder is also believed to be associated