棉纤维发育响应高温胁迫的关键时间窗口

以温度弱敏感性棉花品种(科棉1号)和温度敏感性棉花品种(苏棉15)为材料,在人工气候室模拟自然温周期设置高温(34 ℃\[38/30 ℃\],HT)和对照(26 ℃\[30/22 ℃\],CK)2个温度处理,研究了花铃期不同时段进行高温胁迫后纤维发育重要相关物质的变化及其与纤维品质的关系.结果表明： 在花后不同时间开始高温胁迫持续处理5 d,苏棉15纤维长度、纤维比强度、马克隆值响应高温胁迫的关键时间窗口分别为花后0～18.3 d,花后10.9～26.1 d和花后10.5～34.0 d.因此,花后11～18 d左右是棉花综合纤维品质形成响应高温胁迫的关键时间窗口.在关键时间窗口对棉花进行高温处理5 d后,苏棉15纤维中的蔗糖含量相对常温条件下呈先降低后增加的变化趋势,胼胝质含量上升,纤维素含量下降4.2%,纤维长度变短(最大变幅为23.3%),纤维比强度上升(最大变幅为4.3%),马克隆值下降(最大变幅为10.5%)并偏离最适范围,纤维品质变差.科棉1号的上述纤维发育主要相关物质含量及纤维品质与苏棉15变化趋势一致、最敏感时间相近,仅变化幅度相对较小.     

不同温度敏感性棉花纤维发育相关酶活性变化对低温的响应

选用纤维比强度形成存在温度敏感性差异的两个棉花品种（科棉1号：温度弱敏感型品种,苏棉15：温度敏感型品种）为材料,于2006—2007年在江苏南京设置大田分期播种试验,使棉纤维发育处于不同的温度条件,研究低温对棉纤维发育相关酶（蔗糖酶、蔗糖合成酶、磷酸蔗糖合成酶、β-1,3-葡聚糖酶）活性及相应基因表达的影响.结果表明：由晚播造成的低温（棉纤维发育期日均最低温分别为21.1、20.5和18.1 ℃）影响了纤维发育相关酶的活性变化,从而影响了棉纤维素累积和纤维比强度的形成.低温提高了纤维中蔗糖酶和β-1,3-葡聚糖酶的活性,降低了蔗糖合成酶和磷酸蔗糖合成酶的活性.低温使Expansin、蔗糖合成酶基因的高表达时间延长,β-1,3-葡聚糖酶基因的表达峰值出现时间延迟,且表达量降低.两个棉花品种的纤维素合成相关酶对低温的响应存在差异,温度敏感型品种（苏棉15）的酶活性的变化幅度明显高于温度弱敏感型品种（科棉1号）, 可能是导致不同棉花品种纤维比强度形成存在温度敏感性差异的主要原因.     

Effects of different planting dates and low light on cotton fibre length formation

Declining temperature and low light often appear together to affect cotton (Gossypium hirsutum L.) growth and development. To investigate the interaction on fibre elongation, two cultivars were grown in fields in 2010 and 2011 and in pots in 2011 under three shading levels for three planting dates, and the differences of environmental conditions between different planting dates were primarily on temperature. Fibre length in the late planting date 25 May was the longest instead of the normal planting date. Late planting prolonged fibre elongation period and the effect of late planting on fibre length formation was greater than low light. In the normal planting date, shading increased fibre length through delaying the peak of β-1,3-glucanase gene expression and bringing the peak of β-1,3-glucan synthase gene expression forward, leading to a longer duration of plasmodesmata(PD) closure to increase fibre length, instead of changing sucrose contents or relate enzyme activities. However, in the late planting dates, the difference of the duration of PD closure between shading treatments was not obvious, but low light had a negative impact on sucrose contents, sucrose synthase (SuSy) and vacuolar invertase(VIN) activities during fibre rapid elongation period, leading to the decline of fibre length. Due to late planting and low light, the decreased extent of fibre length of Sumian 15 was larger than Kemian 1. Under the combined condition, Sumian 15 had a shorter gene expression of Expansin, and more sensitive sucrose content, VIN and SuSy activity during fibre rapid elongation period. This resulted in the length formation of Sumian 15 which was more sensitive than Kemian 1, when the cotton suffered the combined effects.     

Field-acclimated Gossypium hirsutum cultivars exhibit genotypic and seasonal differences in photosystem II thermostability

Previous investigations have demonstrated that photosystem II (PSII) thermostability acclimates to prior exposure to heat and drought, but contrasting results have been reported for cotton (Gossypium hirsutum). We hypothesized that PSII thermotolerance in G. hirsutum would acclimate to environmental conditions during the growing season and that there would be differences in PSII thermotolerance between commercially-available U.S. cultivars. To this end, three cotton cultivars were grown under dryland conditions in Tifton Georgia, and two under irrigated conditions in Marianna Arkansas. At Tifton, measurements included PSII thermotolerance (T₁₅, the temperature causing a 15% decline in maximum quantum yield), leaf temperatures, air temperatures, midday (1200 to 1400 h) leaf water potentials (Ψ_MD), leaf-air vapor pressure deficit (VPD), actual quantum yield (Φ_PSII) and electron transport rate through PSII (ETR) on three sample dates. At Marianna, T₁₅ was measured on two sample dates. Optimal air and leaf temperatures were observed on all sample dates in Tifton, but PSII thermotolerance increased with water deficit conditions (Ψ_MD = −3.1 MPa), and ETR was either unaffected or increased under water-stress. Additionally, T₁₅ for PHY 499 was ∼5 °C higher than for the other cultivars examined (DP 0912 and DP 1050). The Marianna site experienced more extreme high temperature conditions (20–30 days T_max ≥ 35 °C), and showed an increase in T₁₅ with higher average T_max. When average T₁₅ values for each location and sample date were plotted versus average daily T_max, strong, positive relationships (r² from .954 to .714) were observed between T_max and T₁₅. For all locations T₁₅ was substantially higher than actual field temperature conditions. We conclude that PSII thermostability in G. hirsutum acclimates to pre-existing environmental conditions; PSII is extremely tolerant to high temperature and water-deficit stress; and differences in PSII thermotolerance exist between commercially-available cultivars.     

Seasonal acclimatization to the hot summer over 60 days in the Republic of Korea suppresses sweating sensitivity during passive heating

The main objective of this study was to determine the central mechanisms involved in suppression of thermal sweating after seasonal acclimatization (SA) during passive heating (immersing the legs in 43 °C hot water for 30 min). Testing was performed in July (before-SA) and August (after-SA) [25.2±2.2 °C, 73.9±10.3% relative humidity (RH), Cheonan (Chungnam,126° 52′N, 33.38′E), in the Republic of Korea. All experiments were carried out in an automated climatic chamber (25.0±0.5 °C and RH 60.0±3.00%). Twelve healthy men (height, 174.6±5.40 cm; weight, 65.4±5.71 kg; age, 22.7±2.90 yr) participated. The local sweat onset time was delayed in the after-SA compared to that in the before-SA (p<0.001). The local sweat rate and whole body sweat loss volume decreased in the after-SA compared to those in the before-SA (p<0.001). In addition, evaporative loss volume decreased significantly in the after-SA compared to that in the before-SA [chest, upper-back, thigh and forearm (p<0.001)]. Changes in tympanic temperature and mean body temperature were significantly lower (p<0.05) and the basal metabolic rate decreased significantly in the after-SA compared to those in the before-SA (p<0.001). These results suggest that maintenance of a lower body temperature and basal metabolic rate can occur and blunt the central sudomotor mechanisms following seasonal acclimatization, which suppresses sweating sensitivity.     

Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils

For Gossypium hirsutum pollination, germination, and pollen tube growth must occur in a highly concerted fashion on the day of flowering for fertilization to occur. Because reproductive success could be influenced by the photosynthetic activity of major source leaves, we hypothesized that increased temperatures under field conditions would limit fertilization by inhibiting diurnal pollen tube growth through the style and decreasing subtending leaf photosynthesis. To address this hypothesis, G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures while at the same developmental stage (node 8 above the cotyledons). Collection and measurement were conducted at 06:00, 09:00, 12:00, 15:00, and 18:00 h on August 4 (34.6 °C maximum air temperature) and 14, 2009 (29.9 °C maximum air temperature). Microclimate measurements included photosynthetically active radiation, relative humidity, and air temperature. Pistil measurements included pistil surface temperature, pollen germination, pollen tube growth through the style, fertilization efficiency, fertilized ovule number, and total number of ovules per ovary. Subtending leaf measurements included leaf temperature, photosynthesis, and stomatal conductance. Under high temperatures the first measurable pollen tube growth through the style was observed earlier in the day (12:00 h) than under cooler conditions (15:00 h). Also, high temperature resulted in slower pollen tube growth through the style (2.05 mm h⁻¹) relative to cooler conditions (3.35 mm h⁻¹), but there were no differences in fertilization efficiency, number of fertilized ovules, or ovule number. There was no effect of sampling date on diurnal photosynthetic patterns, where the maximum photosynthetic rate was observed at 12:00 h on both dates. It is concluded that, of the measured physiological and reproductive processes, pollen tube growth rate showed the greatest sensitivity to high temperature under field conditions.     

Combined effects of temperature and salinity on critical thermal minima of pacific white shrimp Litopenaeus vannamei (Crustacea: Penaeidae)

Critical thermal minima (CTMin) were determined for the Pacific white shrimp Litopenaeus vannamei juveniles from four different acclimation temperatures (15, 20, 25, and 30 °C) and salinities (10‰, 20‰, 30‰, and 40‰). The lowest and highest CTMin of shrimp ranged between 7.2 °C at 15 °C/30‰ and 11.44 °C at 30 °C/20‰ at the cooling rate of 1 °C h⁻¹. Acclimation temperature and salinity, as well as the interaction of both parameters, had significant effects on the CTMin values of L. vannamei (P<0.01). Yet, the results showed a much more profound effect of temperature on low thermal tolerance of juveniles. Only 40‰ salinity had an influence on the CTMin values (P<0.01). As the acclimation temperature was lowered from 30 to 15 °C thermal tolerance of the shrimp significantly increased by 3.25–4.14 °C. The acclimation response ratio (ARR) of the Pacific white shrimp exposed to different combinations of salinity and temperature ranged between 0.25 and 0.27. When this species is farmed in sub-tropical regions, its pond water temperature in the over-wintering facilities (regardless of the water salinity level) must never fall below 12 °C throughout the cold season to prevent mortalities.     

High temperature limits in vivo pollen tube growth rates by altering diurnal carbohydrate balance in field-grown Gossypium hirsutum pistils

It has recently been reported that high temperature slows in vivo pollen tube growth rates in Gossypium hirsutum pistils under field conditions. Although numerous physical and biochemical pollen-pistil interactions are necessary for in vivo pollen tube growth to occur, studies investigating the influence of heat-induced changes in pistil biochemistry on in vivo pollen tube growth rates are lacking. We hypothesized that high temperature would alter diurnal pistil biochemistry and that pollen tube growth rates would be dependent upon the soluble carbohydrate content of the pistil during pollen tube growth. G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures but at the same developmental stage. Diurnal pistil measurements included carbohydrate balance, glutathione reductase (GR; EC 1.8.1.7), soluble protein, superoxide dismutase (SOD; EC 1.15.1.1), NADPH oxidase (NOX; EC 1.6.3.1), adenosine triphosphate (ATP), and water-soluble calcium. Soluble carbohydrate levels in cotton pistils were as much as 67.5% lower under high temperature conditions (34.6 °C maximum air temperature; August 4, 2009) than under cooler conditions (29.9 °C maximum air temperature; August 14, 2009). Regression analysis revealed that pollen tube growth rates were highly correlated with the soluble carbohydrate content of the pistil during pollen tube growth (r² = 0.932). Higher ambient temperature conditions on August 4 increased GR activity in the pistil only during periods not associated with in vivo pollen tube growth; pistil protein content declined earlier in the day under high temperatures; SOD and NOX were unaffected by either sample date or time of day; pistil ATP and water soluble calcium were unaffected by the warmer temperatures. We conclude that moderate heat stress significantly alters diurnal carbohydrate balance in the pistil and suggest that pollen tube growth rate through the style may be limited by soluble carbohydrate supply in the pistil.     

Multigenerational analysis of temperature and salinity variability affects on metabolic rate,generation time,and acute thermal and salinity tolerance in Daphnia pulex

Climate change, sea level rise, and human freshwater demands are predicted to result in elevated temperature and salinity variability in upper estuarine ecosystems. Increasing levels of environmental stresses are known to induce the cellular stress response (CSR). Energy for the CSR may be provided by an elevated overall metabolic rate. However, if metabolic rate is constant or lower under elevated stress, energy for the CSR is taken from other physiological processes, such as growth or reproduction. This study investigated the examined energetic responses to the combination of temperature and salinity variability during a multigenerational exposure of partheogenetically reproducing Daphnia pulex. We raised D. pulex in an orthogonal combination of daily fluctuations in temperature (15, 15–25, 15–30 °C) and salinity (0, 0–2, 0–5). Initially metabolic rates were lower under all variable temperature and variable salinity treatments. By the 6th generation there was little metabolic variation among low and intermediate temperature and salinity treatments, but metabolic suppression persisted at the most extreme salinity. When grown in the control condition for the 6th generation, metabolic suppression was only observed in D. pulex from the most extreme condition (15–30 °C, 0–5 salinity). Generation time was influenced by acclimation temperature but not salinity and was quickest in specimens reared at 15–25 °C, likely due to Q₁₀ effects at temperatures closer to the optima for D. pulex, and slowest in specimens reared at 15–30 °C, which may have reflected elevated CSR. Acute tolerance to temperature (LT₅₀) and salinity (LC₅₀) were both highest in D. pulex acclimated to 15–30 °C and salinity 0. LT₅₀ and LC₅₀ increased with increasing salinity in specimens raised at 15 °C and 15–25 °C, but decreased with increasing salinity in specimens raised at 15–30 °C. Thus, increasing temperature confers cross-tolerance to salinity stress, but the directionality of synergistic effects of temperature and salinity depend on the degree of environmental variability. Overall, the results of our study suggest that temperature is a stronger determinant of metabolism, growth, and tolerance thresholds, and assessment of the ecological impacts of environmental change requires explicit information regarding the degree of environmental variability.     

Diapause and prolonged development in the embryo and their ecological significance in two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata

The seasonal timing mechanism of egg hatching was examined in two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata, with different but overlapping geographical distributions. These species lay eggs in summer, and nymphs hatch in the summer of the following year after egg durations of 10-12 months. When eggs were maintained at 25 °C from oviposition, both the species entered embryonic diapause within 60 days irrespective of photoperiod, but at different developmental stages between the two species. The optimal temperature for diapause development was approximately 15 °C in both the species. The development rate for postdiapause morphogenesis increased linearly with temperature in the range of 20-27.5 °C in C. facialis, and of 15-25 °C in G. nigrofuscata. The lower development threshold and the sum of effective temperatures were computed as 14.3 °C and 715.3 day-degrees in C. facialis and 12.1 °C and 566.6 day-degrees in G. nigrofuscata, respectively. The hatching dates predicted by these large thermal constants accorded with the hatching dates observed in the field, i.e., late June and mid-July in G. nigrofuscata and C. facialis, respectively. Therefore, the high thermal requirements for postdiapause development compel the cicadas to hatch in summer.     

Heat tolerance, behavioural temperature selection and temperature-dependent respiration in larval Octopus huttoni

This study reports temperature effects on paralarvae from a benthic octopus species, Octopus huttoni, found throughout New Zealand and temperate Australia. We quantified the thermal tolerance, thermal preference and temperature-dependent respiration rates in 1-5 days old paralarvae. Thermal stress (1 °C increase h⁻¹) and thermal selection (∼10-24 °C vertical gradient) experiments were conducted with paralarvae reared for 4 days at 16 °C. In addition, measurement of oxygen consumption at 10, 15, 20 and 25 °C was made for paralarvae aged 1, 4 and 5 days using microrespirometry. Onset of spasms, rigour (CT_max) and mortality (upper lethal limit) occurred for 50% of experimental animals at, respectively, 26.0±0.2 °C, 27.8±0.2 °C and 31.4±0.1 °C. The upper, 23.1±0.2 °C, and lower, 15.0±1.7 °C, temperatures actively avoided by paralarvae correspond with the temperature range over which normal behaviours were observed in the thermal stress experiments. Over the temperature range of 10 °C-25 °C, respiration rates, standardized for an individual larva, increased with age, from 54.0 to 165.2 nmol larvae⁻¹ h⁻¹ in one-day old larvae to 40.1-99.4 nmol h⁻¹ at five days. Older larvae showed a lesser response to increased temperature: the effect of increasing temperature from 20 to 25 °C (Q₁₀) on 5 days old larvae (Q₁₀=1.35) was lower when compared with the 1 day old larvae (Q₁₀=1.68). The lower Q₁₀ in older larvae may reflect age-related changes in metabolic processes or a greater scope of older larvae to respond to thermal stress such as by reducing activity. Collectively, our data indicate that temperatures >25 °C may be a critical temperature. Further studies on the population-level variation in thermal tolerance in this species are warranted to predict how continued increases in ocean temperature will limit O. huttoni at early larval stages across the range of this species.     

Effect of sowing dates and vernalization on Betavulgaris L. cv. Univers C-leaf structure

This research was conducted to study the effect of three different sowing dates (15th October, 15th November and 15th December) and two vernalization treatments (5 °C and −20 °C) on leaf structure of Betavulgaris L. cv. Univers. The obtained data are summarized as follows:The maximum values of the most studied parameters; lower epidermis + spongy tissue thickness, midrib, mesophyll tissue, vascular bundle, collenchymatous tissue and number of xylem vessels per arm were found as a result of 15th October sowing date treatment compared with the two other sowing dates. Furthermore, effect of the cooling treatments varied according to the recorded character, sowing date and cooling degree. Most of the vernalization treatments at early sowing dates increased the mesophyll tissue, midrib, number of vascular bundles per transverse section, vascular bundle thickness and number of xylem arms per transverse section.The two studied cooling treatments at 15th October sowing date increased both stomatal index and average number of stomata: average number of epidermis cells compared with the control. Furthermore, 15th October under −20 °C treatment led to small epidermal cells and stomata formation, straight epidermal cell walls and closed stomata in comparison to the control.     

Effects of pre-treatments and temperature on seed viability and germination of Juniperus macrocarpa Sm.

The effects of collecting season, collection site, laboratory pre-treatments and temperatures on seed viability and germination of Juniperus macrocarpa were investigated. Ripe cones were collected in four Sardinian dune systems, in two seasons, from plant and soil. Warm (W) and cold (C) stratifications, two combinations of them (W + C, C + W), and no pre-treatment (0) were applied. Seeds were incubated in a range of constant (10–25 °C) and an alternating (25/10 °C) temperature regime. Seed viability was low (ca. 40%) and varied significantly according to the collecting season. Seed germination was also low (ca. 10%), the 0 and W were the most effective pre-treatments on stimulating germination. The best germination temperature, without any pre-treatment, was 15 °C (ca. 20%). J. macrocarpa seeds are dormant and the achieved results suggested that the presence of secondary dormancy is induced by cold stratification. Spring appeared to be the best season for seed collecting, whereas autumn was the best for sowing. These results give new findings for restoration activities on this species.     

Temperature and functional plasticity of L-type Ca channels in Drosophila

The question of optimization of ion channel function to surrounding temperatures in poikilothermic organisms remains largely uninvestigated. Here, we addressed it by studying the temperature-dependence of L-type Ca²⁺ channels (LTCCs) in Drosophila larval muscles in the context of their modulation by protein kinase A (PKA). LTCC currents were recorded between 4 and 30 °C. Different aspects of LTCC function reached maxima between 15 and 25 °C: conductance, tail current amplitude, inactivation rate, and the level of basal up-regulation by PKA (26% at 21 °C). Anomalous temperature-dependencies of LTCC conductance and kinetics were similar in control and in the presence of the PKA inhibitor H-89. Analysis of deactivation kinetics revealed excessive tail currents at lower temperatures (up to 15 °C), indicative of voltage-dependent facilitation of LTCCs. Tail current magnitude gradually decreased with temperature from a maximum at 15 °C until a nearly complete disappearance at 30 °C. Elimination of excessive tail currents at higher temperatures coincided with unusual slowing of inactivation, suggesting disruption of the facilitation by rising temperature, possibly through depletion of the pool of contributing channels. Overall, these results suggest the presence of a physiological plasticity optimum of LTCC function in the temperature range of normal Drosophila development.     

A comparison of low temperature tolerance traits between closely related aphids from the tropics, temperate zone, and Arctic

The survival of aphids exposed to low temperatures is strongly influenced by their ability to move within and between plants and to survive exposure to potentially lethal low temperatures. Little is known about the physiological and behavioural limitations on aphid movement at low temperatures or how they may relate to lethal temperature thresholds. These questions are addressed here through an analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a ubiquitous temperate zone pest, Myzus polaris, an arctic species, and Myzus ornatus, a sub-tropical species. Lower lethal temperatures (LLT₅₀) of aphids reared at 15 °C were similar for M. persicae and M. polaris (range: −12.7 to −13.9 °C), but significantly higher for M. ornatus (−6.6 °C). The temperature thresholds for activity and chill coma increased with rearing temperature (10, 15, 20, and 25 °C) for all clones. For M. polaris and M. ornatus the slopes of these relationships were approximately parallel; by contrast, for M. persicae the difference in slopes meant that the difference between the temperatures at which aphids cease walking and enter coma increased by approximately 0.5 °C per 1 °C increase in rearing temperature. The data suggest that all three species have the potential to increase population sizes and expand their ranges if low temperature limitation is relaxed.