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Paul H. Li

The common bean (Phaseolus vulgaris L.) is a heat-sensitive plant species in which excessive abscission of reproductive organs occurs during hot weather. This results in yield reductions, and, in extreme heat stress, plants produce few or no pods. We evaluated 74 bean genotypes in terms of leaf heat tolerance (HT) and leaf heat acclimation potential (HAP), as expressed by heat killing time (HKT), the time in minutes needed to cause a 50% electrolyte leakage from leaf tissue heated at 50°C Leaf HT is defined as the leaf HKT of plants without prior conditioning at 37°C day/night temperature and leaf HAP as the change in leaf HT following exposure of the plant to 37°C day/night for 24-h. Among 74 bean genotypes examined leaf HT ranged from 5 to 30 min HKT, whereas leaf HAP ranged from 35 to 130 min HKT. Positive significant correlations were observed between leaf HAP and post-stress performance in photosynthetic activities, plant dry weight, pod set, pod weight and yield among bean genotypes. Correlations, however, were not significant between leaf HT and post-stress performance.

A relationship between heat resistance, consisting of the combination of HT and HAP, and heat injury is proposed. Interpretation of the differential amounts of heat injury among genotypes having different HAP, is discussed. We view leaf HT and leaf HAP as two distinguishable phenomena. We suggest that in breeding programs HAP may be the more important of the two, and should he evaluated as a selection criterion for improving crop performance in high temperature environments.

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Zhanguo Xin and Paul H. Li

Exogenous proline and ABA can induce chilling tolerance. Whether there is any relationship between the proline and ABA in inducing chilling tolerance is not known. We attempted to elucidate their interrelationship by comparing the time course of proline and ABA induced chilling tolerance and of the uptake of proline and ABA in the cultured cells of maize (Zea mays L. Black Mexican Sweet). The uptake of proline was increasing continually during a 24 h culture at 28°C. However, the proline induced chilling tolerance became significant after 6 h treatment and reached maximum after 12 h. When cells were transferred to a ABA-containing medium the uptake of ABA in the cells reached almost plateau in 2 h period. The ABA induced chilling tolerance was insignificant at 6 h, became significant at 12 h, and reached maximum at 24 h. Although the rate of ABA induced chilling tolerance was slower than the rate of proline induced chilling tolerance, there was no any increase in endogenous free proline in the ABA treated cells. Statistical analysis indicates that there is no interrelationship between proline and ABA in the induction of chilling tolerance in maize. ABA induces specific proteins which may play essential role(s) in the development of chilling tolerance. None of these proteins was observed in proline treated cells. We concluded that the induction mechanisms of chilling tolerance between proline and ABA are independent in maize.

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Jing-fen Chen, Paul H. Li, and David W. Davis

Exposure of young pepper plants to chilling temperatures delays the development of terminal flower buds to flowering during post-stress growth. Degree of adverse influence depends on chilling intensity, exposure duration and varietal sensitivity. `Ma Belle' pepper plants were grown in a greenhouse (GH) during winter months on the St. Paul campus, No supplemental lighting was provided. When plants were at the 2- to 3-leaf stage, they were foliar sprayed with mefluidide (Technical grade) at 0, 5, 10 and 15 ppm. One day after treatment, some plants were transferred from GH to a cold room (3° ∼4°C day/night) with 12-h photoperiod. Treatad plants remaining in the GH served as the control. Plants were chilled for 1, 2, 4 and 6 days and then brought back to the GH for post-stress growth and development observation. Treated and untreated plants grown in the GH showed no difference in days to flowering, and reached 50% flowering at about 62 days after treatment. When untreated plants were chilled for 1,2,4 and 6 days, they showed a delay of 8, 18, 30 and 34 days, respectively, to flowering, If not killed, as compared to the control The long delay to flowering was due to the injury of the terminal flower buds. After 4 and 6 days of chilling, most terminal flower buds were killed. However, when plants were treated with mefluidide and subsequently chilled days to flowering were significantly shortened. A difference of 10-12 days was observed between chilled untreated plants and chilled treated plants. Concentrations of 5 to 15 ppm were equally effective in protection against chilling.

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Agnes A. Flores-Nimedez, Paul H. Li, and Charles C. Shin

GLK-8903, an experimental product whose main ingredient is produced by hydrogenation of a primary alcohol extracted from plants, showed significant potential in protecting bean (Phaseolus vulgaris L.) plants from chilling injury. The GLK-8903 protection mechanism was assessed by examining several physiological and biochemical responses. The decline in leaf water potential and the increase in osmotic potential caused by chilling exposure to 4C (day/night) were minimized by the application of GLK-8903. Chilling causes an increase in electrolyte leakage, an indication of chilling injury of the plasma membrane. Increased electrolyte leakage was reduced significantly in the GLK-8903-treated plants during chilling. This minimized leakage may be due to less damage of the plasma membrane. Plasmolysis and deplasmolysis studies of the epidermal cells suggest that GLK-8903 is able to reduce the plasma membrane perturbation in the chilling environment, as evident by: 1) the lower permeability coefficient to urea at 4C, and 2) the swelling of protoplasts in the cells of untreated tissues after chilling exposure with no swelling of the protoplast being observed in the GLK-8903-treated cells. Malondialdehyde (MDA), a product of lipid peroxidation, increased more in untreated controls than in treated plants exposed to 4C. Plasma membrane ATPase activity decreased less in GLK-8903-treated plants than in untreated controls after 3 days at 4C. The mechanism of GLK-8903-alleviated chilling injury is discussed.

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Jing-fen Chen, Paul H. Li, and David W. Davis

Exposure of young pepper plants to chilling temperatures delays the development of terminal flower buds to flowering during post-stress growth. Degree of adverse influence depends on chilling intensity, exposure duration and varietal sensitivity. `Ma Belle' pepper plants were grown in a greenhouse (GH) during winter months on the St. Paul campus, No supplemental lighting was provided. When plants were at the 2- to 3-leaf stage, they were foliar sprayed with mefluidide (Technical grade) at 0, 5, 10 and 15 ppm. One day after treatment, some plants were transferred from GH to a cold room (3° ∼4°C day/night) with 12-h photoperiod. Treatad plants remaining in the GH served as the control. Plants were chilled for 1, 2, 4 and 6 days and then brought back to the GH for post-stress growth and development observation. Treated and untreated plants grown in the GH showed no difference in days to flowering, and reached 50% flowering at about 62 days after treatment. When untreated plants were chilled for 1,2,4 and 6 days, they showed a delay of 8, 18, 30 and 34 days, respectively, to flowering, If not killed, as compared to the control The long delay to flowering was due to the injury of the terminal flower buds. After 4 and 6 days of chilling, most terminal flower buds were killed. However, when plants were treated with mefluidide and subsequently chilled days to flowering were significantly shortened. A difference of 10-12 days was observed between chilled untreated plants and chilled treated plants. Concentrations of 5 to 15 ppm were equally effective in protection against chilling.

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Cheng-lie Zhang, Paul H. Li, and Charles C. Shin

Twenty-day-old `Bush Blue Lake 47' common bean plants grown in a growth chamber at 25 days/22C night and a 12-hour photoperiod regime were foliar sprayed with 0.5% GLK-8903 including 0.05% Tween-20. After 24 hours of treatment, plants were chilled in a cold room (4C day/night, 12 hours of light). After 3 days of chilling, leaves of untreated controls were injured, as visually characterized by leaf wilting, whereas leaves of the GLK-8903-treated plants still retained turgor. During chilling, the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) decreased. GLK-8903 treatment had no effect on SOD and POD activities; however, the CAT activity was reduced significantly after GLK-8903 treatment either at 25 or at 4C. During chilling, the content of malondialdehyde, a decomposition product of phospholipid peroxidation, increased in treated plants and untreated controls, with increased content significantly lower in the former compared with the latter. The GLK-8903 per se and total lipid extracted from GLK-8903-treated plants were able to reduce the linoleic acid oxidation in vitro. The mechanism by which GLK-8903 alleviates chilling injury in bean plants is discussed.

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Grace M. Pietsch, Paul H. Li, and Neil O. Anderson

Cold acclimation has been extensively studied in woody species such as Cornus sericea and Malu × domestica. These studies have shown that cold acclimation is initiated by short days and completed with the addition of a cold treatment. It is unknown whether herbaceous perennials respond in a similar manner to these environmental cues. Our research objective was to examine short day photoperiod effects on cold acclimation in herbaceous gaura populations collected at different latitudes. Gaura drummondii collected in Texas, and Gaura coccinea collected in Minnesota and Texas were clonally propagated, grown under a 16-hour long day photoperiod and 25/20 °C [day/night (D/N)] temperature for 8 weeks. Plants were then subjected to 0, 1, 2, 3, 4, or 5 weeks of 8-hour short days at 20/15 °C (D/N) temperatures. Cold acclimation was determined using electrolyte leakage (freezing stem pieces from –1 to –9 °C) and measuring electrical conductivity after treatment and tissue death. Mean separations showed two distinct statistical groupings of 0-2 weeks and 3–5 weeks of short days for Minnesota gaura, whereas Texas gaura overlapped for 0–5 weeks of short day treatments. It is unknown what environmental cue(s) initiate cold acclimation in Gaura native to southern latitudes such as Texas.

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Agnes A. Flores-Nimedez, Paul H. Li, and Charles C. Shin

Protection mechanism of a new compound, coded as GLK-8903, from chilling injury in bean plants was assessed by measuring several physiological parameters. The decline in leaf water potential caused by the chilling exposure to 4°C (day/night) was minimized when GLK-8903 was applied to the plants as compared to the non-treated control. Chilling causes an increase in electrolyte leakage, an indication of chilling injury that occurs at the site of plasma membrane. An increased electrolyte leakage was reduced in the GLK-8903-treated plants during chilling. Data from plasmolysis and deplasmolysis studies of epidermal cells suggest that GLK-8903 is able to stabilize the plasma membrane under stress condition by determining the permeability coefficients plasmometrically (1.96 cm s-1 × 10-4 for GLK-8903-treated plants vs. 4.00 for the controls 3 d at 4°C) with less decreased activity of the plasma membrane ATPase (9.36 μmol ATP.mg chl-1·h-1 for GLK-8903-treated plants vs. 5.04 for the controls 3 d at 4°C). GLK-8903 appears to have high application potential in protecting bean plants from chilling injury with improved yield.

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Ling-cheng Jian, Jiang-ming Deng, Ji-hong Li, and Paul H. Li

Seasonal alteration of the cytosolic and nuclear Ca2+ concentrations of spruce (Picea engelmannii Parry) and brome grass (Bromus inermis Leyss) was investigated by the antimonate precipitation cytochemical technique. Electron microscopic (EM) observations revealed that electron-dense Ca2+ antimonate deposits, an indication of Ca2+ localization, were seen mainly in the vacuole, the cell wall and the intercellular space in samples of both species, collected on 14 July 1997. Few deposits were found in the cytosol and nuclei, showing a low resting level during summer months. On 8 Aug. 1997 following a decrease in daylength of 1 hour and 12 minutes, Ca2+ accumulation was initiated in spruce with increased cytosolic and nuclear Ca2+ deposits, but not in brome grass. On 8 Sept. 1997, Ca2+ accumulation occurred in the cytosol of brome grass. This followed a drop in ambient temperature to 12 °C. Cytosolic and nuclear Ca2+ deposits continued to increase in spruce. Controlled experiments confirmed that it was the low temperature, not shortening daylength, that triggered Ca2+ accumulation in brome grass. High cytosolic and nuclear Ca2+ concentrations lasted about three months in spruce from early August to early November. However, the high cytosolic and nuclear Ca2+ concentrations in brome grass lasted only about 20 days from early September to the end of the month. During winter and spring, both species had low resting cytosolic and nuclear Ca2+ concentrations. The relationship between the duration of the high cytosolic and nuclear Ca2+ concentrations and the status of the developed dormancy/cold hardiness is discussed in light of current findings.

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Karl J. Sauter, David W. Davis, Paul H. Li, and I.S. Wallerstein

Yield in common bean, Phaseolus vulgaris L., can be significantly reduced by high temperature (I-IT) during bloom. Ethylene production from plant tissue increases as a consequence of various stresses, including heat stress. The inheritance of leaf ethylene evolution rate (EER) of HT-stressed (35/30C day/night) progenies from crosses among bean genotypes previously categorized as HT sensitive or tolerant, based on cell electrolyte leakage, was investigated. Evidence from generation means analysis of Fl, F2, and backcross progenies shows EER to be genetically controlled, with additive, dominance, and epistatic effects indicated for low EER. The range (0.62 to 2.52 μg-1·hr-1) of EER from field-grown lines and cultivars suggests the existence of considerable genetic variability. EER was associated (r = –0.70) with heat tolerance, as estimated by cell electrolyte; leakage.