Water temperature for hydrocooling field cucumbers in relation to chilling injury during storage

The objective of this study was to test the hypothesis that water temperatures less than the lowest recommended storage temperature (10°C) for cucumbers could be used for hydrocooling without inducing chilling injury or negatively affecting storage life. Field cucumbers were hydrocooled with water at 1.5, 3.5, 6, 8 or 10.5°C until the internal cucumber temperature reached 12°C, or hydrocooled with water at 1.5°C until the internal cucumber temperature reached 1.7, 8 or 12°C. Cucumber temperature at harvest was ≈20°C and the storage temperature was 12°C. Little or no visual symptoms of chilling injury were observed after 10–12 days of storage. However, chlorophyll fluorescence measurements indicated some chilling stress at the membrane level in cucumbers hydrocooled with water at temperatures below 6°C and in cucumbers hydrocooled with water at 1.5°C until the internal product temperature was 1.7°C, as indicated by lower F_v/F_m values. Approximately one third of the cucumbers from all hydrocooling treatments developed rot. There were no significant differences in % marketable cucumbers or in % mass loss after 10 or 12 days of storage. These results suggest that cucumbers could be hydrocooled using water at temperatures below the recommended storage temperature of 10°C. However, it is not recommended to use water below 6°C or to cool the cucumbers below this temperature, due to increased risk of chilling injury as indicated by the chlorophyll fluorescence measurements.     

<Emphasis Type="Italic">In vivo</Emphasis> Acclimatization Responses of <Emphasis Type="Italic">Platycodon grandiflorum</Emphasis> For. Duplex to Different Soil Types and Environmental Factors

This study aimed to evaluate the effects of soil types and environmental factors for optimum conditions of seedlings growth of the Platycodon grandiflorum for establishing the in vivo acclimatization system of regenerated plants derived from the in vitro culture. P. grandflorum seedlings were transferred to the in vivo condition and acclimatized under different soil types, light intensities, and various temperatures. Changes caused by environmental factors and soil types in plant growth viz. plant height, leaf width, leaf length, stem diameter, number of leaves, branches and nodes were recorded in this study. Among the nine types of soil, the best growth performances were obtained from the soil type SVP (Soil mixed with horticultural bed soil, vermiculite, and perlite @ 2:1:1). Seedlings of P. grandiflorum showed the best growth at higher levels of light intensity (60 μmol·m^-2·s^-1). In contrast, P. grandiflorum seedlings showed the best growth response at a moderate level of temperature (25°C). Collectively, the present study provides a better understanding of the responses of growth characteristics in P. grandiflorum seedlings exposed to various soil types, light intensities, and temperatures.     

Direct plant development from microspore-derived embryos of winter oilseed rape Brassica napus L. ssp. oleifera (DC.) Metzger

The influence of temperature/photoperiod treatment and gibberellic acid concentration (0, 0.1 or 1.0 mg/l) on direct conversion of microspore-derived embryos (MDEs) to plantlets of winter oilseed rape was investigated. Physiologically mature, 21-day-old MDEs were transferred to a solid B5 medium supplemented with gibberellic acid, and cultured at 24 ^°C, 4 ^°C or 1 ^°C for 14 days, and then at 24 ^°C for the next 21 days. Low temperature was linked with short photoperiod (8 h light/16 h dark), and high temperature was linked with long photoperiod (16 h light/8 h dark). The highest embryo conversion rate was at 1 ^°C with over 70%, compared to<20% at 4 ^°C. Two-way analysis of variance confirmed the significance of the effect of temperature/photoperiod treatment. By contrast, gibberellic acid concentration had no significant effect on stimulation of shoot development from apical meristems of MDEs. Roots developed from apical root meristems of MDEs very easily. The best obtained conversion rate of MDEs induced with cold treatment at1 ^°C for 14 days was 86.5%. Observations on morphological development of MDEs showed clear differences in reaction at various temperature/photoperiod treatments. This revised version was published online in August 2006 with corrections to the Cover Date.     

温室盆栽茶梅光合特性研究

【目的】研究温室盆栽茶梅的光合特性,为温室茶梅的栽培提供理论依据。【方法】以4年生盆栽茶梅为试验材料,采用美国CI-301PS型便携式光合仪,对其光合特性及其相关生理生态因子指标进行测定,并通过统计分析,探索影响光合作用的主导因子。【结果】（1）茶梅叶片光合速率日变化呈双峰曲线型,有明显“午休”现象。光合作用的饱和点为221μmol·/m2·s,补偿点为13.9μmol·/m2·s。叶温27.5℃时光合速率最大,超过时逐步下降。（2）气孔导度、胞间CO2浓度、蒸腾速率、环境CO2浓度、光合有效辐射、叶温均与净光合速率呈显著相关,其中气孔导度是影响光合作用的主导生理因子,有效辐射为影响光合作用的主导生态因子。（3）胞间CO2浓度、蒸腾速率分别与大气CO2浓度、光合有效辐射之间呈极显著正相关。【结论】茶梅叶片光合速率日变化呈双峰曲线型,有明显“午休”现象;气孔导度是影响光合作用的主导生理因子,有效辐射为影响光合作用的主导生态因子。     

Chilling Tolerance in Hybrid Maize Induced by Seed Priming with Salicylic Acid

The optimum temperature for maize germination is between 25 and 28 °C. Poor and erratic germination at suboptimal temperature is the most important hindrance in its early sowing. This study was conducted to induce chilling tolerance in hybrid maize (Zea mays L.) by seed priming with salicylic acid (SA) and to unravel the background biochemical basis. For seed priming, maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 ppm (mg l^?1) aerated solutions of SA for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Performance of maize seedlings was hampered under chilling stress. But seed priming with SA improved the seedling emergence, root and shoot length, seedling fresh and dry weights, and leaf and root score considerably compared with control both at optimal and chilling temperatures. However, priming in 50 mg l^?1 SA solution was more effective, followed by priming in 100 mg l^?1 SA solution. Seed priming with SA improved the chilling tolerance in hybrid maize mainly by the activation of antioxidants (including catalase, superoxide dismutase and ascorbate peroxidase). Moreover, maintenance of high tissue water contents and reduced membrane permeability also contributed towards chilling tolerance.     

Exploring the Role of Calcium to Improve Chilling Tolerance in Hybrid Maize

Abiotic stresses, including chilling, impede the plant growth and development mainly by oxidative damage. In this study, seed priming with CaCl₂ was employed to reduce the damage caused by chilling stress in hybrid maize. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l⁻¹ (ppm) aerated solution of CaCl₂ for 24 h and dried. Treated and untreated seeds were sown at 27 °C (optimal temperature) and 15 °C (chilling stress) under controlled conditions. Seed priming with CaCl₂ significantly reduced the chilling damage and improved the germination rate, root and shoot length, and seedling fresh and dry weights. Activities of antioxidants, including catalase, superoxide dismutase and ascorbate peroxidase, were also improved. Soluble sugars and α-amylase concentrations determined as general metabolic indicators of stress were also increased by seed priming with CaCl₂. Priming also improved the performance of maize at optimal temperature. Maintenance of tissue water contents, reduction in membrane leakage and increase in antioxidant activities, and carbohydrate metabolism seemed to induce chilling tolerance by CaCl₂. Seed priming with 100 mg l⁻¹ CaCl₂ was the optimal concentration in improving the performance of hybrid maize both under optimal and stress conditions.     

QTL mapping of seedling traits in cucumber using recombinant inbred lines

Seedling traits are important for development, flower bud differentiation, fruit production and fruit quality of cucumber (Cucumis sativus L.). In this study, 160 recombinant inbred lines (RILs), derived from crossing wild cucumber inbred line PI 183967 (C. sativus var. hardwickii) with ‘931’ northern China cultivated cucumber inbred line 931, were employed to identify quantitative trait loci (QTLs) of cotyledon length (Cl), cotyledon width (Cw), hypocotyl length (Hl), first true leaf length (Fll), first true leaf width (Flw), aboveground fresh biomass (Afb) and aboveground dry biomass (Adb) at seedling stage. A genetic map including 307 SSR markers was developed which spanned 993.3 cM, with an average genetic distance of 3.23 cM between adjacent markers. 36 QTLs associated with the seven traits were detected on chromosomes 1, 2, 3, 5 and 6 in four environments (spring and autumn of 2012 and 2013), explaining 6.1 to 23.6% of the observed phenotypic variations. Among the 36 QTLs, 21 were responsible for more than 10% of observed phenotypic variations. We obtained 2, 2, 1 and 3 QTL loci for the traits of Fll, Flw, Afw and Adw, respectively. In addition, genes in the genetic region spanned by SSR15321‐SSR07711 on chr. 5 may contribute to Flw, Afw and Adw.     

Effects of Temperature and Photoperiod on Vegetative and Reproductive Growth of Groundnut (Arachis hypogaea L.)*

Effects of temperature × photoperiod interaction on vegetative and reproductive growth were examined in three selected groundnut genotypes by growing them in controlled-environment growth chambers with three temperature regimes (22/18, 26/22, and 30/26°C, day/night) under long (12 h, long day), and short (9 h, short day) photoperiods. The effect of photoperiod on the total dry-matter production (TDM) was significant with the genotypes producing 32–72% greater dry matter under LD than SD. Temperature × genotype interaction effects were significant, with the dry-matter production being greatest at 26/22°C and least at 30/26°C and 22/18°C in two of the three genotypes. Leaf area (LA) was greater under LD than SD at all temperature regimes. LA accounted for 76% of the variation in shoot + root dry weight (R²= 0.76, P < 0.01). A lack of relationship between LA and pod weight or pod numbers suggested that the pod development is controlled by factors other than carbon assimilation. The temperature × photoperiod interaction was significant for root growth, with the root weight being maximal and photoperiod effects being minimal at 22/18°C, while at 26/22°C, root weight declined and photoperiod effects became prominent. Low temperature (22/18°C) affected the reproductive development by reducing the proportion of reproductive nodes in total (vegetative + reproductive) nodes. The conversion of pegs into pods, as indicated by pod to peg ratio (PPR), was lower in LD than in SD conditions. Results suggested that the PPR could be used as an indicator of genotypic sensitivity to photoperiod in groundnut.     

Glycinebetaine Improves Chilling Tolerance in Hybrid Maize

Plant growth and development is hampered by various environmental stresses including chilling. We investigated the possibility of improving chilling tolerance in hybrid maize by glycinebetaine (GB) seed treatments. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l^?1 (p.p.m.) aerated solution of GB for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Germination and seedling growth was significantly hindered under chilling stress. Moreover, chilling stress significantly reduced the starch metabolism and relative water contents (RWC), and increased the membrane electrolyte leakage. However, activities of antioxidants (catalase, superoxide dismutase and ascorbate peroxidase) were increased under stress conditions. Seed treatments with GB improved the germination rate, root and shoot length, seedling fresh and dry weights, leaf and root scores, RWC, soluble sugars, α‐amylase activity and antioxidants significantly compared with untreated seeds under optimal and stress conditions. Induction of chilling tolerance was attributed to maintenance of high tissue water contents, reduced membrane electrolyte leakage, and higher antioxidant activities and carbohydrate metabolism. Seed treatment with 100 mg l^?1 GB was the best treatment for improving the performance of hybrid maize under normal and stress conditions compared with control and other levels used.     

Leaf appearance of annual clovers responds to photoperiod at emergence

Leaf appearance rate and time to canopy expansion of four annual clover species (arrowleaf, balansa, gland and Persian) were quantified in field and controlled environment studies. Crops sown in autumn, which experienced shortening daylengths at emergence, had a slower rate of leaf production and consequently took a longer time to initiate branching, than spring-sown crops. When autumn-sown ‘Bolta’ balansa clover emerged on the shortest day in winter (21 June), the rate of leaf appearance was lengthened by 4 °C d/leaf/h. When the same species emerged after the shortest day, into an increasing photoperiod, the phyllochron was shortened by 5 °C d/leaf/h. This influence of photoperiod on the phyllochron consequently altered the time to axillary leaf production (branching). Throughout all sowing dates, phyllochron was the fastest for ‘Prima’ gland (33–91 °C d/leaf) and slowest for ‘Cefalu’ arrowleaf (53–116 °C d/leaf) clovers. ‘Bolta’ balansa was 44–82 °C d/leaf and ‘Mihi’ Persian 61–93 °C d/leaf. The response of phyllochron to photoperiod suggests these annual clovers should be sown in late summer or early autumn to initiate axillary leaf production as soon as possible to ensure maximize dry matter for early spring.     

Dynamics of dissolved silicium and nitrogen-nutrients at low temperature in the Ems-dollard estuary

With salinity and natural fluorescence as conservative tracers to discriminate between fresh water contributions from two different fresh water sources (the river Ems and the river Westerwoldse Aa), deviations from conservative behaviour for silicate, ammonia and nitrate during winter conditions (4–6°C) are reported and discussed. For silicate a net removal from overlying water during transport through the estuary of 15% was found. Nitrification in overlying water (260 μmol·m⁻³·h⁻¹) was the only important process in nitrogen cycling; sediment-water exchange was of no importance during this period.     

Activation of Antioxidant System by KCl Improves the Chilling Tolerance in Hybrid Maize

As maize is a chilling-sensitive crop, low temperatures during the early stages of development can be injurious to crop growth and development. Prime mechanism behind chilling-induced damage is oxidative stress. This study was undertaken to improve the chilling tolerance in hybrid maize by seed priming with KCl. For priming, seeds of the maize hybrid Hycorn 8288 were soaked in 50, 100 and 150 mg l⁻¹ aerated solution of KCl for 24 h and then re-dried close to original weight. Primed and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Seed priming improved the performance of maize under both normal and stress conditions. It was found that the chilling tolerance in maize is well associated with the enhanced capacity of the anti-oxidative system. Priming with KCl significantly improved the chilling tolerance mainly by the activation of antioxidants including catalase, superoxide dismutase and ascorbate peroxidase enzymes. KCl treatments also improved the germination rate and time, root and shoot length, and fresh and dry weights of seedlings compared with control. Soluble sugars and α-amylase activity determined as general metabolic indicators of stress were also improved by seed priming with KCl. Other possible bases of chilling tolerance in maize included maintenance of high tissue water contents, reduced electrolyte leakage and carbohydrate metabolism. Seed treatment with 100 mg l⁻¹ KCl was the best treatment to improve the performance of hybrid maize both under normal and chilling stress conditions.     

氯钾离子共体诱导后黄瓜叶片内酶活性的变化

分别用浓度为0．2％,0．5％,1．0％,1．5％,2．0％的氯钾离子共体液,在黄瓜幼苗子叶期(子叶充分展开)和第一真叶期(第一真叶横宽5cm)进行2次诱导。然后对其第一真叶的POD,PPO,PAL活性进行测定。结果表明：不同浓度氯钾离子共体液处理后,POD,PPO,PAL活性均有不同程度的变化,变化趋势均为随时间的增加先升高、后降低,诱导后10d左右达到最大值,且极显著高于对照。试验还筛选出导致POD,PPO,PAL活性变化最大的氯钾离子共体液的浓度范围为0．5％～1．0％。     

Effects of Soil Moisture on Gas Exchange, Partitioning of Fed 14CO2 and Stable Carbon Isotope Composition (δ13C) of Leymus chinensis Under Two Different Diurnal Temperature Variations

In a pot experiment under controlled condition, Leymus chinensis was grown at five soil water contents and two diurnal temperature variation levels. The leaf relative water content of L. chinensis decreased under soil drought conditions, and increased at high diurnal temperature variation (30/20 °C). Severe and very severe soil drought remarkably reduced photosynthetic rate, stomatal conductance, transpiration rate and water use efficiency (WUE), especially at the low temperature variation. Severe drought mainly increased the specific radioactivity of ¹⁴C of sheaths, roots and rhizomes, but significantly decreased that of fed leaves and the not fully expanded leaves. Root percentage of total radioactivity remaining in the whole plant increased from 15 % at 30/25 °C to 28 % at 30/20 °C. Leaf carbon stable isotope composition (δ¹³C) increased with soil drought, ranged from ?26 ‰ of the well‐watered to ?24 ‰ of severe drought treatments. High diurnal temperature variation improved leaf water status, and increased partitioning of carbon to root and δ¹³C values, especially under severe soil drought conditions. In conclusion, higher diurnal temperature variation enhanced the resistance of the plant to drought.     

Methods for evaluation of soybean chilling tolerance at the reproductive stage under artificial climatic conditions

Several evaluation methods for soybean chilling tolerance at the reproductive stage were examined under artificial climatic conditions. Comparisons were made on plants in control and treated plots using three cultivars differing in the level of chilling tolerance. In all methods, plants were grown at 22/17°C (day/night) until first flowering, and then transferred to growth chambers at 24/17°C for control and 15/15°C for chilling treatment, respectively. A method, in which plants were grown at 20/16°C after 4 weeks of the different temperature treatments, proved comparable to the conventional one, in which chilling tolerance at the flowering stage is evaluated using natural and artificial conditions. Another method, in which the plants in chilling treatment plots were grown at 15°C until maturity, also proved usable to evaluate genotypic differences in chilling tolerance independently of maturity time.     

The light and temperature dependence of growth rate and elemental composition of Phaeocystis globosa scherffel and P. Pouchetii (HAR.) Lagerh. in batch cultures

The light and temperature dependence of growth, cellular elemental composition (C, N, P) and chlorophyll content during exponential growth and phosphate starvation of batch cultures of the temperate algal species Phaeocystis globosa were investigated. Temperature-dependent minimum generation time and cell phosphorus content were compared with those of the cold water species P. pouchetii. The variation in growth and cell carbon content was due to the different origin of seawater used for the culture media. Coastal, estuarine seawater enabled shorter doubling times than “offshore” and oceanic-influenced seawater. At nutrient-saturated growth, P. globosa was able to compete with diatoms only if high temperature (14°C) and high irradiances (180 μE·m⁻²·s⁻¹) predominated. P. pouchetti showed markedly shorter generation times than P. globosa did at temperatures below 10°C. At 6°C, the cell carbon content exceeded the value at 18°C by a factor of 1.7. High C/N atomic ratios of 6.9±0.7 and high C/Chl a ratios of ≥ 54.0 during exponential growth could not entirely be explained by the carbon content of the colony mucus. There was no significant light and temperature dependence of the : N : P ratio during exponential growth. At phosphate starvation (subsistence P quota of cells) this was so only at temperatures higher than 10°C. With their stored phosphorus quota P. globosa and P. pouchetii were capable of only two cell divisions. Hence, because of their limited ability to store phosphorus, the two Phaeocystis species cannot compete with planktonic diatoms for growth. The frequent change in nutrient concentrations (particularly of silicate and phosphate) in coastal and estuarine waters at summer temperatures and light conditions causes a rapid alternation of smaller blooms of P. globosa and diatoms.     

Photoperiod sensitivity gene controlling heading date in rice cultivars in the northernmost region of Japan

Rice is grown in diverse environments at latitudes ranging from 53^°N to 40^°S. In Japan, Hokkaido is the northernmost rice cultivation region(42–45^°N latitude). Only extremely early maturing (heading) varieties that have extremely low photoperiod sensitivity are adapted to this area. Heading date is the most important trait in adaptation to this particular environment. Also, the efficient manipulation of heading date is a crucial component of rice improvement. To determine the genetic basis for heading date among cultivars grown in Hokkaido, the heading behaviour was analyzed. Clear segregations were observed. To estimate the photoperiod sensitivity of the genes involved, the cultivars and F₁ plants from crosses between the cultivars were grown under different daylength conditions. The results indicated that the genes controlling heading date are photoperiod sensitive, suggesting they play important roles in the northernmost rice cultivation regions in Japan, to which only cultivars with extremely low photoperiod sensitivity are adapted. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of hot water treatments on chilling injury and expression of a new C-repeat binding factor (CBF) in ‘Hongyang’ kiwifruit during low temperature storage

Kiwifruit is cold-sensitive and very susceptible to chilling injury (CI) during low temperature storage. In this study, kiwifruit (Actinidia chinensis cv. Hongyang) were pre-treated by water dip for 10 min at 20 (control) or 35, 45, or 55 °C (heat pretreatments) and then stored at 0 °C for 90 days to investigate the effect of hot water treatments (HWT) on chilling injury tolerance. Results showed that 35 °C and 45 °C HWT alleviated but did not completely prevent chilling injury development. By contrast, 55 °C HWT increased symptoms of chilling injury. The 45 °C HWT was the most effective at reducing chilling injury index and incidence. Compared with the other HWT, fruit treated at 45 °C exhibited higher firmness and soluble solids content (SSC), and lower malondialdehyde (MDA) content, lipoxygenase (LOX) activity and ethylene production rate. C-repeat/dehydration-responsive element binding factors (CBFs) are key regulators in cold response. To investigate the molecular regulation of HWT on chilling tolerance of kiwifruit, a 637 bp CBF gene was identified and the relative expression of AcCBF was measured by RT-qPCR. In accordance with the effects of HWT on physiological parameters of chilling injury, AcCBF expression level was highest in the 45 °C HWT. These results indicate that HWT at 45 °C for 10 min prior to low temperature storage is effective for alleviating symptoms of chilling injury in ‘Hongyang’ kiwifruit.