Inhibitory Effect Of High Temperature Research Articles

Enhanced high-temperature particle capture through an electrostatic precipitator with assistant electrodes

High-temperature electrostatic precipitators (ESPs) are a potentially effective technology for purifying high-temperature gases. In this study, a comprehensive numerical model was developed to investigate the electric field and particle migration characteristics of an ESP at temperatures ranging from 400 to 600 °C. Moreover, an optimized ESP with assistant electrodes for improved high-temperature particle capture was proposed. The electric field, flow field and particle capture characteristics of the two types of ESPs were compared to demonstrate the superiority of the optimized ESP. Results indicated that high temperatures had a negative impact on ESP performance. As the temperature increased, the operating voltage of the ESP decreased, leading to decreases in both the electric field strength and space charge density. The effective migration velocity of the particles also decreased with increasing temperature, and the inhibitory effect of high temperature on particle capture increased with increasing particle size. The optimized ESP with assistant electrodes exhibited more favorable electric field and flow field characteristics for particle capture compared to those of the conventional ESP. The optimized ESP exhibited higher electric field strength, which increased the electric field force on the particles and promoted particle capture. Meanwhile, the space charge density of the optimized ESP was lower, effectively inhibiting the occurrence of back corona. Moreover, the optimized ESP enhanced the ionic wind downstream of the discharge electrode, thereby promoting particle migration towards the collection electrode. Consequently, the ESP with assistant electrodes effectively improved the collection efficiency.

Combined effects of high irradiance and temperature on the photosynthetic and antioxidant responses of Thalassia hemprichii and Halophila ovalis

Abstract During midday low tides, tropical intertidal seagrasses are challenged by high irradiance and high temperature. This study assessed photosynthetic and oxidative stress responses of Thalassia hemprichii and Halophila ovalis exposed to 150 and 1000 μmol photons m−2 s−1 and 30 and 40 °C for 3 h. High temperature (40 °C) significantly decreased the maximum quantum yield of both seagrasses and this heat-induced photoinhibition was exacerbated by high irradiance (1000 μmol photons m−2 s−1). High irradiance also aggravated the effects of high temperature on the effective quantum yield of T. hemprichii. Non-photochemical quenching (NPQ) of T. hemprichii was induced by both stressors with no additive effects. In contrast, NPQ of H. ovalis was induced under high irradiance at 30 °C but was inhibited at 40 °C. Nevertheless, antioxidant enzyme activity and reactive oxygen species content did not differ among treatments in either seagrass. Monitoring chloroplast distribution in H. ovalis revealed a partial inhibitory effect of high temperature on chloroplast avoidance movement under high irradiance. Our results suggest that warming events may cause detrimental impacts on shallow water seagrasses. Halophila ovalis may be more vulnerable than T. hemprichii as its photoprotection, i.e. NPQ and chloroplast avoidance movement, was hindered at high temperature.

Responses of radial growth of Pinus sylvestris var. mongolica and Larix gmelinii to climate change

In the context of global warming, the increases of temperature may affect tree growth and thus disturb ecosystem balance. In this study, we explored the main limiting factors for radial growth of Pinus sylvestris var. mongolica and Larix gmelinii in the Mohe area of Greater Khingan Mountains by using growth-climate response function analysis and moving correlation analysis, as well as the interspecific difference of the responses of radial growth to rapid warming. The results showed that the radial growth of P. sylvestris var. mongolica and L. gmelinii was affected by both temperature and precipitation. P. sylvestris var. mongolica was more sensitive to climate change than L. gmelinii, and its sensitivity to climate factors was more stable than L. gmelinii. The radial growth of P. sylvestris var. mongolica was significantly positively correlated with the monthly mean temperature and the monthly mean minimum temperature of the growing season, while that of L. gmelinii was significantly positively correlated with the monthly mean temperature and the monthly mean maximum temperature of winter. Precipitation in winter promoted the growth of P. sylvestris var. mongolica, whereas precipitation in the late growing season of the previous year inhibited the radial growth of L. gmelinii. After the rapid warming in 1990, the limiting effect of precipitation on P. sylvestris var. mongolica changed from negative to significantly positive, with the inhibition effect of high temperature being greater than the promotion effect. The inhibitory effect of high temperature on L. gmelinii was enhanced, and the limiting effect of precipitation on L. gmelinii was also enhanced after heating up. The growth rate decreased significantly, with obvious difference being observed in the correlations between the growth rate of two species with temperature and precipitation. Our results could provide scientific basis for forest ecosystem management and protection in Greater Khingan Mountains.

High light might alleviate inhibitory effects of high temperature on growth and physiological parameters of Ulva prolifera

In order to explore the effects of high temperature (HT) and light on the physiological and biochemical aspects of macroalga Ulva prolifera, we cultured this species under two temperatures (20°C: low temperature, LT; 30°C: HT) and two light intensities (80 μmol m−2 s−1: low light, LL; 400 μmol m−2 s−1: high light, HL) for 5 days. It was found that (a) compared to 20°C, the chlorophyll a (Chl a) content was increased at 30°C under LL conditions, the relative growth rate (RGR) was significantly decreased at 30°C; (b) compared to LL treatment, HL significantly increased RGR but significantly decreased Chl a content; (c) LL-grown U. prolifera at 30°C showed the highest photosynthetic oxygen evolution rate; however, there were no significant effects of temperature and light on the relative electron transport rate; (d) superoxide dismutase activity was significantly decreased by HL, but no significant effects of temperature were observed; and (e) compared to LL, HL significantly increased the soluble sugar content at 20°C, but significantly reduced at 30°C. These results showed that the inhibitory effects of HT can be offset by HL intensity.

Elucidation of the factors affecting poor flowering in litchi (Litchi chinensisSonn.) and measures to overcome

It is a major concern of litchi growers in many locations that yields are often irregular and frequently below the trees bearing capacity. Poor litchi flowering is a worldwide problem, especially in regions where the weather during the induction period is too worm. Induction of flowering in litchi requires an average minimum temperature of approximately 10-14°C for 4-12 weeks, depending on the cultivars. Variation in time of panicle emergence, panicle development, and anthesis among the cultivars in relation to seasonal progressions in temperature affect the fruit set. Experimental evidence suggest that temperature above 15°C increased vegetative growth and reduced or eliminated flowering. However, the temperature above which flowering fails is still not clear, nor is the time that the plants needs to grow at lower temperature for successful flower induction. It has also been suggested that not only is low temperature needed for induction, but also water stress throughout the autumn and winter. Six weeks autumnal water stress was reported to cause a significant increase in flowering of 'Mauritus' and 'Floridian' litchi in Israel. Gibberellins inhibits flowering in litchi and counteracts the flower-inducing influence of low temperature, while treatments such as cincturing, root pruning and application of growth retardants reverse the inhibitory effects of high temperature. It is believed that the conversion of vegetative bud to panicle in litchi is dependent on changes in content of endogenous growth substances. This paper discussed the various factors influencing the flowering in litchi and available technology to overcome.

Survival and development of the forensically important blow fly, Calliphora varifrons (Diptera: Calliphoridae) at constant temperatures.

The influence of temperature on the development of the forensically important blow fly, Calliphora varifrons Malloch 1932 (Diptera: Calliphoridae), was investigated at seven constant temperatures ranging from 12 to 30°C. C. varifrons completed development between 12 and 27°C. At 30°C larvae formed pupae but did not successfully emerge. Temperature significantly influenced development time, mortality, maximum larval length, and adult body size. Development time (larviposition to adult emergence) ranged from 16.65±0.17days at 27°C to 49.93±0.26days at 12°C. Development rate was essentially linear throughout the 12-27°C temperature range. Linear estimates of lower developmental threshold and thermal requirement (K) for development of C. varifrons were 4.20°C and 368.46±26.38K. At 30°C, a slight inhibitory effect of high temperature on third instar development rate was observed followed by a rapid decline when subsequent development and survival ceased. Nonlinear estimates of lower developmental threshold for third instar development were comparatively higher (6.29°C). Nonlinear estimates of optimal developmental temperature and upper lethal developmental threshold were 25.94 and 32.13°C respectively. Mortality was high at both temperature extremes (12 and 27°C) and lowest between 18 and 24°C. Maximum larval length was inversely related to temperature. Adult body size was significantly smaller at 12°C, peaked at 18°C, and declined as temperatures increased. The species-specific development data presented are the first available for C. varifrons for use by forensic practitioners for estimation of minimum time since death.

Inhibitory Effect of High Temperature- and High Pressure-Treated Red Ginseng on Exercise-Induced Oxidative Stress in ICR Mouse

As previously reported, high temperature- and high pressure-treated red ginseng (HRG) contain higher contents of phenolic compounds and protect C2C12 muscle cells and 3T3-L1 adipocytes against oxidative stress. This study investigated the effect of HRG on oxidative stress using a mouse model. Our results show that the levels of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase, hepatic malondialdehyde in the HRG group were significantly lower than those of the exercise groups supplemented with commercial red ginseng (CRG) or not supplemented. The muscular glycogen level, glucose-6-phosphate dehydrogenase and lactate dehydrogenase activities of the HGR group were higher than that of the CGR group. Furthermore, the HRG treatment group displayed upregulated mRNA expression of Cu/Zn-SOD and muscle regulatory factor 4. These results indicate that HRG may protect oxidative stress induced by exercise as well as improve exercise performance capacity.

Global VGIIa isolates are of comparable virulence to the major fatal Cryptococcus gattii Vancouver Island outbreak genotype

The ongoing cryptococcosis outbreak on Vancouver Island, BC, Canada, is caused by two VGII sub-genotypes of the primary pathogen, Cryptococcus gattii: VGIIa isolates predominate, whereas VGIIb isolates are rare. Although higher virulence of the VGIIa genotype has been proposed, an unresolved key question is whether VGIIa isolates from other regions are also more virulent than VGIIb isolates. We report the relationship between genotype and virulence for a global collection of C. gattii VGIIa and VGIIb isolates (from Australia, Argentina, Brazil, Canada, Thailand and the USA). In vitro and in vivo virulence studies were conducted. At 37°C, growth [at 18 h: 0.2 optical density (OD) difference, p 0.026; at 36 h: 0.6 OD difference, p 0.036) and mean melanin production (OD = 0.25 vs. OD = 0.15, p 0.059] of VGIIa isolates was greater than that of VGIIb isolates. The inhibitory effect of high temperature on melanin production of VGIIa isolates was less than that of VGIIb isolates (OD = 0.36 vs. OD = 0.69; p 0.001). Capsule production at 37°C of VGIIa isolates was less than that of VGIIb isolates. All VGIIa isolates were fertile, whereas only 17% of VGIIb isolates were fertile (p <0.001). In vivo virulence studies using the BALB/c mice nasal inhalation model revealed that VGIIa isolates were more virulent than VGIIb isolates (p <0.001) independent of their clinical (p 0.003) or environmental origin (p <0.001). This study established a clear association between genotype and virulence of the primary fungal pathogen, C. gattii.

Physiological responses to temperature and haeme synthesis modifiers in earthworm Lumbricus terrestris (Annelida: Oligochaeta)

Earthworms (Lumbricus terrestris) acclimated at 2° and 6°C above their average habitat temperature (10°C) had respectively 15 and 40% higher rate of respiration than those at habitat temperature. At 14°C, the rate of respiration and blood hemoglobin (Hb) concentration both increased by ∼60 and 50%, respectively, of the values at habitat temperature. At higher temperatures the rate of respiration and Hb synthesis started decreasing. At 20-23°C, the respiration and Hb concentration decreased respectively by about 85% and 35% of that at 14°C. Decrease in blood Hb concentration at higher temperatures appeared to be due to the lowering of the activity of blood enzyme δ-aminolaevulinic acid dehydratase (ALAD). Exposure of 20-23°C-acclimated pale worms to ALAD inhibitor (lead), lowered the already compromised rate of respiration and blood Hb concentration; while exposure to hexachlorobenzene (HCB, inducer of haeme synthesis) and ferric chloride (enhancer of haeme synthesis) did not overcome the inhibitory effect of high temperature on Hb synthesis. At 20-23°C the affinity of Hb for oxygen also decreased as indicated by the lowering of oxy-Hb (HbO) concentration in blood. The lowering of concentration of blood Hb and its affinity for oxygen may lower the amount of oxygen delivered to cells, which may limit the level of aerobic metabolism (glycolysis, oxidative phosphorylation), as indicated by an increase in blood glucose concentration and a decrease in in vitro activities of mitochondrial electron transport system components (ETS) namely NADH-cytochrome c reductase, succinate dehydrogenase, cytochrome c oxidase, and ATPases. Although the oxygen concentration in air, at sea level, does not decrease significantly from 6° to 20-23°C (lack of hypoxia), lowering of both Hb and HbO concentrations by high temperature may cause significant hypoxemia. The latter may lead to inhibition of the activity of muscle mitochondrial respiratory enzymes (ETS). The resulting inhibition of ATP synthesis and hydrolysis may cause deficit of energy needed for peristalsis/fictive locomotion of body and heart muscles (as indicated by a decrease in heart rate) to facilitate diffusion and transport of gases. The upper critical temperature (20-23°C) also slows down the heart rate and causes hyperosmotic stress (hypovolemia). Thus, a rise in soil temperature above 18°C, which inhibits Hb synthesis, Hb oxygenation, and mitochondrial ETS activity, and slows down the heart rate and causes hyperosmotic stress, can make this and higher temperatures lethal to populations of these earthworms, especially in the presence of metabolic inhibitors and respiratory poisons.

Effect of two types of stress (heat shock/high temperature and malnutrition/serum deprivation) on porcine ovarian cell functions and their response to hormones

The aim of the present study was to understand the interrelationships between stress, hormones and basic ovarian functions in the ovary. For this purpose, we compared the expression of markers of proliferation (PCNA, cyclin B1), of apoptosis (Bax, caspase-3) and secretory activity (release of progesterone, P(4), and insulin-like growth factor, IGF-I) in whole ovarian follicles and granulosa cells cultured in conditions of normal temperature (37.5 degrees C) and feeding (with serum), high temperature (41.5 degrees C, with serum) and malnutrition (37.5 degrees C, without serum), with and without hormones [IGF-I, leptin and follicle-stimulating hormone (FSH)]. The expression of proliferation and apoptosis markers was evaluated by SDS PAGE-western blotting whereas radioimmunoassay (RIA) measured the release of hormones. High temperature dramatically induced a reduction in both proliferation and apoptosis markers in both ovarian follicles and granulosa cells and induced a significant increase in P(4) and IGF-I release by ovarian granulosa cells but not in P(4) secretion by ovarian follicles. Serum deprivation increased accumulation of cyclin B1 but not other markers of proliferation (PCNA) and apoptosis (Bax, caspase-3) or P(4) release in ovarian follicles. On the contrary, it inhibited the expression of apoptotic marker (Bax), release of both P(4) and IGF-I but it did not affect proliferation marker (PCNA) in granulosa cells. Adding IGF-I, leptin and FSH affected proliferation, apoptosis and secretory activity of ovarian cell functions but also prevented an inhibitory effect of high temperature on the expression of Bax and PCNA and an inhibitory action of serum deprivation on PCNA in ovarian follicles. Furthermore, treatment with these hormones prevented an inhibitory action of thermal stress on Bax, PCNA, P(4) and IGF-I in ovarian granulosa cells. The present observations (1) confirm the involvement of hormones (IGF-I, leptin and FSH) in the control of proliferation, apoptosis and secretory activity of ovarian cells, (2) demonstrate for the first time that heat stress/increased temperature can induce a reduction in ovarian cell proliferation and apoptosis and an oversecretion of ovarian hormones, (3) show that malnutrition/serum deprivation can reduce both apoptosis and secretory activity of ovarian cells, (4) demonstrate the differences in the response of granulosa and other ovarian follicular cells to stresses, and (5) are the first demonstration that hormones (IGF-I, leptin and FSH) could be used for preventing the effect of stresses on ovarian cell functions.

Fusicoccin counteracts inhibitory effects of high temperature on auxin-induced growth and proton extrusion in maize coleoptile segments

Plant growth and development are tightly regulated by both plant growth substances and environmental factors such as temperature. Taking into account the above, it was reasonable to point out that indole-3-acetic acid (IAA), the most abundant type of auxin in plants, could be involved in temperature-dependent growth of plant cells. We have recently shown that growth of maize coleoptile segments in the presence of auxin (IAA) and fusicoccin (FC) shows the maximum value in the range 30-35˚C and 35-40˚C, respectively. Furthermore, simultaneous measurements of growth and external medium pH indicated that FC at stressful temperatures was not only much more active in the stimulation of growth, but was also more effective in acidifying the external medium than IAA. The aim of this addendum is to determine interrelations between the action of IAA and FC (applied together with IAA) on growth and medium pH of maize coleoptile segments incubated at high temperature (40˚C), which was optimal for FC but not for IAA. Addendum to: Karcz W, Burdach Z. Effect of temperature on growth, proton extrusion and membrane potential in maize (Zea mays L.) coleoptile segments. Plant Growth Regul 2007; 52:141-50.

Effects of high temperature on the hemocyte cell cycle in silkworm larvae

To understand the inhibitory effects of high temperature on insect growth at the cellular level, we investigated the influence of high temperature on the proliferation and division of larval hemocytes in the silkworm, Bombyx mori. Although the total number of hemocytes in the larval body increased enormously over time at 26°C, no increase was observed at 38°C. The number of mitotic hemocytes in circulation increased between days 1 and 2 of the fourth larval stage at 26°C, whereas fewer hemocytes were observed at 38°C. Laser scanning cytometry revealed that the DNA content of hemocytes collected from the fourth-stadium larvae was predominantly 2C, 4C, and 8C, and the proportion of each type of hemocyte changed dynamically with development during the fourth instar. Specifically, the proportion of hemocytes with a higher DNA content increased gradually during the feeding phase then decreased during the molting phase at 26°C; in contrast, no decrease was observed at 38°C. The heat-induced accumulation of 8C hemocytes was mainly detected in granulocytes and plasmatocytes. These data suggest that high temperatures induce a G2 arrest in larval hemocytes.

Compensatory effects of elevated CO&lt;sub&gt;2&lt;/sub&gt; concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

We determined the interactive effects of irradiance, elevated CO2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 µmol m-2 s-1), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO2 concentrations (C a), AC and EC (350 and 750 µmol mol-1, respectively). Rates of net photosynthesis (P N) and transpiration (E) and stomatal conductance (g s ) were measured, along with water use efficiency (WUE) and ratio of internal and external CO2 concentrations (C i/C a). P N revealed an interactive effect between PAR and C a. As PAR increased so did P N under both C a regimes. The g s showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 µmol m-2 s- 1 PAR under EC. The C i /C a was influenced independently by temperature and C a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on P N and WUE.

Ethylene evolution and endo-beta-mannanase activity during lettuce seed germination at high temperature

High temperatures during lettuce seed imbibition can delay or completely inhibit germination and the endosperm layer appears to restrict the radicle protrusion. The role of endo-beta-mannanase during lettuce seed germination at 35°C and the influence of ethylene in endo-beta-mannanase regulation were investigated. Seeds of 'Dark Green Boston' (DGB) and 'Everglades' (EVE) were germinated in water, or 10 mmol L-1 of 1-aminocyclopropane-1-carboxylic acid (ACC), or 10 mmol L-1 of aminoethoxyvinylglycine (AVG), or 20 mmol L-1 of silver thiosulphate (STS). Seeds were also primed in polyethylene glycol (PEG), or PEG + ACC, PEG + AVG, or PEG + STS. Untreated seeds germinated 100% at 20°C. At 35°C, EVE seeds germinated 100%, whereas DGB seeds germinated only 33%. Seed priming or adding ACC during incubation increased germination at 35°C. Higher ethylene evolution was detected in EVE than in DGB during germination at 35°C. AVG did not inhibit seed germination of DGB at 35°C, but STS did. Higher endo-beta-mannanase activity was observed in EVE compared with DGB seeds. Providing ACC either during priming or during germination increased endo-beta-mannanase activity, whereas AVG and STS led to decreased or no activity. Ethylene may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-beta-mannanase, possibly leading to weakening of the endosperm.

Effect of temperature on development, growth and reproduction in the marine copepod Pseudocalanus newmani at satiating food condition

Post-embryonic development time, somatic growth, egg production rate, survival and sex ratio for the marine calanoid copepod Pseudocalanus newmani from the Pacific coast off southwestern Hokkaido were determined at five temperatures (3, 6, 10, 15 and 20°C) when a mixed algal diet was provided at satiating food condition (0.36 μg C ml -1 ) in the laboratory. At temperatures between 3 and 15°C, the development time from hatching to adult female increased exponentially with decreasing temperature, being 23.3, 33.1, 46.7 and 74.6 days at 15, 10, 6 and 3°C, respectively. Males developed into adults 2-5 days earlier than did the females. At the highest temperature of 20°C, both embryonic and post-embryonic development and egg production of P newmani were suppressed. This inhibitory effect of high temperature is consistent with the vertical distribution range and seasonal abundance cycle of this copepod in the field; it tends to avoid the warm surface layer (>15°C) and scarcely appears in the water column during summer and autumn. Body size of P newmani was not affected by temperature until C1, but increased with decreasing temperature after C2. The weight-specific growth rate (SGR) increased linearly with temperature (T) until 15°C, which is expressed as SGR = 0. 0095T + 0.0462 (r = 0.996). This growth pattern may also indicate high-temperature stress to this copepod, the general pattern of copepod growth being exponential. The weight-specific egg production rate (SER) also increased with temperature (SER = 0. 02T + 0.014, r = 0.99), below 15°C. The proportion of male offspring of P newmani that grew to adulthood was nearly 50% at 3 and 6°C, but decreased with increasing temperature at 10-15°C. This unequal sex ratio may be due to sex change during juvenile development under temperature control. These results suggest that temperature plays an important role in life history traits of P newmani through not only temperature- dependent growth and reproduction, but also through high-temperature inhibition and temperature- controlled sex ratio under sufficient food supply.

Ethylene and lettuce seed germination

Ethylene can stimulate seed germination and overcome dormancy in many species. For instance, the inhibitory effect of high temperature on lettuce seed germination can be overcome by exogenous ethylene. Involvement of ethylene in seed germination is a widely accepted fact, but the mechanistic details are poorly understood. A critical factor in ethylene studies is the response of seed germination properties to various ethylene inhibitors. Lettuce seed has been used as a model to study the role of ethylene in seed germination at high temperature. The role of ethylene in germination is not known but either ethylene evolution or addition of 1-aminocyclopropane-1-carboxilic acid (ACC) have been associated with increased activity of endo-beta-mannanase, a cell-wall enzyme that weakens the endosperm and allows lettuce seed to germinate at high temperature. This review describes some results on seed germination studies in response to ethylene and its possible role in promoting germination at high temperature.

Expression of penicillin G acylase from the cloned pac gene of Escherichia coli ATCC11105. Effects of pacR and temperature.

The structural gene pac in Eschericia coli ATCC11105 encodes penicillin G acylase (PGA). Within the pac gene, there is a regulatory gene pacR, which is transcribed in the opposite direction. Site-directed mutagenesis was performed at base 1045 of pac by replacing a T with a C. This substitution did not alter the amino-acid sequence of PGA, but changed the translation start codon of pacR from AUG to GUG. The expression of the mutant pacR decreased dramatically and the lacZ transcriptional fusion analysis showed that GUG was an extremely poor initiation codon for pacR. The pacR mutation caused PGA expression to be constitutive rather than inductive in two strains (E. coli A56, DH10B). The pac inducer phenylacetic acid (PAA) gave significant induction of PGA production at a concentration of 0.2% in wild type, but PAA at this concentration inhibited both cell growth and PGA production in the pacR mutated strains. The temperature-dependent expression character of pac is preserved in the pacR translation-initiation mutant and the optimum temperature of PGA production was 22 degrees C in both wild type and mutant. At a higher temperature of 37 degrees C, the PGA precursor polypeptide could not be matured into subunits and formed inclusion bodies, as revealed by western blot analysis. Our investigations confirmed the hypothesis of pacR-mediated PAA induction for PGA expression and clarified the inhibitory effect of high temperature upon the post-translational processing of the PGA precursor polypeptide.

402 Lettuce Seed Germination and Endo-mannanase Activity are Stimulated by Ethylene at High Temperature

Temperatures above 30 °C may delay or inhibit germination of most of commercial lettuce cultivars. Ethylene enhances lettuce seed germination at high temperatures. Enzyme-mediated degradation of endosperm cell walls appears to be a crucial factor for lettuce germination at high temperature. The galactomannan polysaccharides in lettuce endosperm cell wall are mobilized by endomannanase. The role of endo-mannanase during germination of lettuce seeds at high temperature (35 °C) and the possible role of etlene in enzyme regulation were investigated. Seeds of thermotolerant (`Everglades'-EVE) and thermosensitive (`Dark Green Boston'-DGB) lettuce genotypes were incubated at 20 and 35 °C in water, 10 mM of 1-aminocyclopropane-1-carboxylic acid (ACC), or 20 mM of silver thiosulphate (STS). Also, seeds were primed in an aerated solution of polyethylene glycol (PEG), or PEG+ACC, or PEG+STS. Untreated seeds germinated 100% at 20 °C. At 35 °C, EVE germinated 100%, whereas DGB germinated only 33%. Seed priming or adding ACC during imbibition increased germination of DGB to 100% at 35 °C. Adding STS during imbibition led to a decrease in germination at 35%C in EVE and completely inhibited germination of DGB. Priming with STS led to reduced germination at 35%C of both genotypes. EVE produced more ethylene than DGB during germination at high temperature. Providing ACC either during priming or during germination led to an increase in endo-mannanase activity, whereas STS inhibited mannanase activity. Higher endo-mannana activity was observed in EVE than DGB seeds. The results suggest that ethylene might overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds via weakening of endosperm due to increased endo-mannanase activity.

Ameliorative effect of polyamines on the high temperature inhibition of in vitro pollen germination in tomato ( Lycopersicon esculentum Mill.)

Effect of polyamines on in vitro pollen germination at high temperatures in tomato ( Lycopersicon esculentum Mill.) was investigated. Pollen germination and tube growth were significantly inhibited at 33°C and 35°C compared to those at 25°C. This inhibition was reversed by the addition of spermidine or spermine in the germination medium. Spermidine at 0.5 mM was slightly more effective than spermine at 0.05 mM. Spermidine at 0.05 and 0.5 mM and spermine at 0.05 mM slightly increased pollen germination rates at 25°C. Spermidine at 5 mM and spermine at 0.5 M were inhibitory to pollen germination, regardless of incubation temperatures. Spermidine also promoted germination of pollen grains incubated at 38°C for 1 and 3 h and then at 25°C for the rest of the 20 h incubation period. The effect was higher at 0.5 mM than at 0.05 mM. Treatment of spermidine to intact flowers 1 day before anthesis was also effective in ameliorating the high temperature inhibition of in vitro pollen germination on the polyamine-free medium. Here, the optimum concentration was 5 mM. These results demonstrate that polyamines can counteract the inhibitory effects of high temperature on pollen germination. They also suggest that the endogenous level of polyamines in germinating pollen grains is an important factor for the pollen germinability at high temperature.

Endo-β-mannanase Activity and Seed Germination of Thermosensitive Lettuce Genotype in Response to Temperature and Seed Priming

Under high temperatures (above 30 °C) in the greenhouse (transplant industry) or field, lettuce germination can be erratic or completely inhibited. Seed priming circumvents thermodormancy of lettuce seeds and allows germination at higher temperatures. Weakening of the endosperm layer of lettuce seeds is a prerequisite to radicle protrusion at high temperatures. Enzyme-mediated degradation of endosperm cell walls may be a crucial factor for lettuce seed germination at high temperatures. Softening of the endosperm could occur during seed priming and result in improved germination. A single-seed assay for endo-β-mannanase was used to follow the activity of this enzyme during priming in lettuce seeds. We also investigated the effects of seed priming on seed germination and mannanase activity at both inhibitory and non-inhibitory temperatures for seed germination in a thermosensitive lettuce cultivar Dark Green Boston. Seeds were primed for 3 days at 15 °C with constant light in aerated solutions of polyethylene glycol (PEG) at an osmotic potential of –1.2 MPa. Afterward, seeds were rinsed and redried at 10 °C and 45% RH for 3 days. Primed and nonprimed seeds germinated 100% at 20 °C. At 35 °C, primed seeds germinated 100%, whereas nonprimed seeds did not germinate. During priming, endo-β-mannanase activity increased between 24 and 72 h after the beginning of osmotic imbibition. Mannanase activity persisted in primed seeds, even following seed drying. Radicle protrusion did not occur under the priming conditions used in this study. Higher enzyme activity was observed in primed seeds compared with nonprimed seeds. The results suggest that priming overcomes the inhibitory effect of high temperature in thermosensitive lettuce seeds by weakening of endosperm due to increased endo-β-mannanase activity.