Impact of blanching and packaging atmosphere on the formation of aroma compounds during long-term frozen storage of leek (Allium ampeloprasum Var. Bulga) slices.

The content of aroma compounds and the catalytic activity of lipoxygenase (LOX), alliinase, hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) were analyzed in unblanched and blanched 15-mm leek slices packed in atmospheric air (21% O2) or 100% nitrogen (0% O2) three times during 12 months of frozen storage (12 M). The total amount of sulfur compounds and the total amount of aldehydes were greatly influenced by storage time, atmosphere, and blanching [concentration of sulfur compounds in fresh unblanched (UNB) slices = 1.35 mg/L, fresh blanched (B) slices = 1.09 mg/L, UNB 21% O2 12 M = 0.656 mg/L, UNB 0% O2 12 M = 2.11 mg/L, B 21% O2 12 M = 1.14 mg/L, B 0% O2 12 M = 1.59 mg/L]. B 0% O2 was closest to the original ratio between sulfur compounds and aldehydes after 12 months. The activities of HPL and alliinase were totally lost after 12 months, and ADH showed minimal activity, whereas LOX (UNB 0% O2) showed approximately 25% of the original activity. LOX was the most and HPL the least heat labile enzyme investigated.     

Impact of blanching and packaging atmosphere on the formation of aroma compounds during long-term frozen storage of leek (Allium ampeloprasum Var. Bulga) slices.

The content of aroma compounds and the catalytic activity of lipoxygenase (LOX), alliinase, hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) were analyzed in unblanched and blanched 15-mm leek slices packed in atmospheric air (21% O2) or 100% nitrogen (0% O2) three times during 12 months of frozen storage (12 M). The total amount of sulfur compounds and the total amount of aldehydes were greatly influenced by storage time, atmosphere, and blanching [concentration of sulfur compounds in fresh unblanched (UNB) slices = 1.35 mg/L, fresh blanched (B) slices = 1.09 mg/L, UNB 21% O2 12 M = 0.656 mg/L, UNB 0% O2 12 M = 2.11 mg/L, B 21% O2 12 M = 1.14 mg/L, B 0% O2 12 M = 1.59 mg/L]. B 0% O2 was closest to the original ratio between sulfur compounds and aldehydes after 12 months. The activities of HPL and alliinase were totally lost after 12 months, and ADH showed minimal activity, whereas LOX (UNB 0% O2) showed approximately 25% of the original activity. LOX was the most and HPL the least heat labile enzyme investigated.     

Formation of aroma compounds and lipoxygenase (EC 1.13.11.12) activity in unblanched leek (Allium ampeloprasum Var. Bulga) slices during long-term frozen storage

The content of aroma compounds (dynamic headspace) and catalytic activity of lipoxygenase (LOX) (EC. 1.13.11.12) were analyzed in 15 mm unblanched leek slices seven times during 12 months of frozen storage. The aroma profile changed from consisting of almost only sulfur compounds such as dipropyl disulfide [concentration in fresh leek (FL) = 0.197 mg/L, concentration after 12 months of frozen storage (12M) = 0.0409 mg/L] and propyl (E)-propenyl disulfide (FL = 0.0437 mg/L, 12M = 0.00452 mg/L) in the fresh leeks to being dominated by numerous saturated and unsaturated aldehydes, such as hexanal (FL = 1.53 mg/L, 12M = 3.63 mg/L), (E,E)-2,4-nonadienal (FL = 0.000 mg/L, 12M = 0.0647 mg/L), and (E,E)-2,4-decadienal (FL = 0.129 mg/L, 12M = 0.594 mg/L) at the end of the storage period. The catalytic activity of LOX diminished throughout frozen storage, but approximately 25% of the original activity was present after 12 months of storage.     

Formation of volatile compounds in model experiments with crude leek (Allium ampeloprasum Var. Lancelot) enzyme extract and linoleic acid or linolenic acid

Three continuous assays are described for lipoxygenase (LOX), hydroperoxide lyase (HPL) and alcohol dehydrogenase (ADH) in leek tissue. The catalytic activity of LOX showed significant difference (significance level 5%) between linolenic acid (9.43 x 10(-)(4) katals per kg protein) and linoleic acid (2.53 x 10(-)(4) katals per kg protein), and the pH-optimum of LOX was 4.5-5.5 against linoleic acid. The catalytic activity of HPL was statistically the same for 9-(S)-hydroperoxy-(10E,12Z)-octadecadienoic acid (1.01 x 10(-)(2) katals per kg protein) and 13-(S)-hydroperoxy-(9Z,11E)-octadecadienoic acid (7.69 x 10(-)(3) katals per kg protein). ADH showed a catalytic activity of 5.01 x 10(-)(4) katals/kg of protein toward hexanal. Model experiments with crude enzyme extract from leek mixed with linoleic acid or linolenic acid demonstrated differences in the amount of produced aroma compounds. Linoleic acid resulted in significantly most hexanal, heptanal, (E)-2-heptenal, (E)-2-octenal, (E,E)-2,4-decadienal, pentanol, and hexanol, whereas linolenic acid resulted in significantly most (E)-2-pentenal, (E)-2-hexenal, (E,Z)-2,4-heptadienal, (E,E)-2,4-heptadienal, and butanol. Leek LOX produced only the 13-hydroperoxide of linoleic acid and linolenic acid.     

Response of Tifway 2 bermudagrass to fresh or composted broiler litter containing boric acid‐treated paper bedding

Abstract

Recycled paper treated with boric acid (BA) is gaining acceptance as bedding in broiler production houses. Applying this litter, or compost made from this litter, to turf raises an issue of boron (B) toxicity. There is also the question of nitrogen (N) availability from composts made from borated paper and broiler manure. The objective of this study was to determine if broiler house litter containing recycled BA‐treated paper poses a toxicity hazard to bermudagrass turf (Cynodon dactylon L. pers x C. Transvaalensis, Burtt‐Davis) when applied at agronomic N rates. The effects of five N sources at rates equivalent to 224, 448, and 896 kg N/ha in a factorial arrangement plus an unfertilized control and a high nitrogen‐phosphorus‐potassium (NPK) treatment with B at 22 kg B/ha on bermudagrass were determined in pot culture during the summer of 1992. The five NPKB sources were (M1) compost made from broiler manure, BA‐treated paper and yard refuse; (M2) fresh broiler manure with BA paper bedding; (M3) fresh broiler manure with pine shavings bedding; (M4) inorganic NPK; and (M5) inorganic NPK and BA. The soil was Cecil sandy clay loam subsoil. Top growth was harvested four times at 4 cm height with tops, roots, and stubble harvested at the fifth and final harvest. Composted litter was higher in water content and lower in NPK and B than fresh litter. As a result, over four times the mass had to be applied to achieve the desired N inputs. Boron concentrations in M1 on a dry matter basis were 290, M2=390, M3=52 mg B/kg, respectively. The NPK gave highest yields and compost (M1) gave the lowest yields. Yield response of fresh manure + BA paper was not different from fresh manure + pine shavings. Nitrogen recovery in plant growth from composts was very low. Nitrogen recovery in compost residue at the soil surface was very high. Nitrogen recoveries for BA paper litter and pine shavings litter were similar. No visual symptoms of B toxicity were observed, although a 16% yield reduction occurred at 22.4 kg B/ha at the 896 kg N/ha rate from NPK. Boron recovery in plant growth was negligible, but considerable B remained in the residue at the soil surface. Yield response efficiency was M1=2.5, M2=4.8, M3=5.3, NPK=15.5, NPKB=14.3 mg DM/mg N, respectively. Plant top N recovery response efficiency in mg N recovered/mg N per pot was 0.07, 0.15, 0.165, 0.63, and 0.58 for M1, M2, M3, NPK, and NPKB, respectively. Adding stubble, roots, and residue to total N recovery resulted in the following recoveries: M1=0.97, M2=0.25, M3=0.35, NPK=0.73, NPKB=0.68 mg N/ mg N applied. The risk of B toxicity to Tifway 2 bermudagrass from compost or manure containing BA‐treated paper is minimal if N rates are in the agronomic utilization range.     

钼对苹果砧木平邑甜茶幼苗硝态氮吸收、转化及分配的影响

【目的】氮肥利用率低是制约果树产业可持续发展的重要因素之一。过量施用氮肥以及不当的农业措施造成当前多数苹果果园发生不同程度的土壤酸化,而钼在酸性土壤中有效含量的降低会影响氮素吸收利用效率。本试验旨在探索能提高氮肥吸收利用效率的适宜钼用量,了解钼对苹果砧木平邑甜茶(Malus hupehensis Rehd.)幼苗硝态氮吸收、转化和分配利用特性的影响,为苹果生产中钼肥与氮肥的合理施用提供科学数据。【方法】以平邑甜茶幼苗为试验材料,采用全硝态氮霍格兰营养液进行培养。试验设置5个供钼水平:营养液不含钼(CK);营养液含0.25μmol/L钼酸(M1);营养液含0.5μmol/L钼酸(M2);营养液含1.5μmol/L钼酸(M3);叶片喷0.04%钼酸,营养液不含钼(M4)。运用15N同位素示踪技术,研究不同供钼水平对幼苗15N吸收量、全氮量、分配率和利用率的影响,同时测定钼对不同时期幼苗叶片和根系硝酸还原酶活性的影响。【结果】供钼处理幼苗的根系活力不同程度地高于不施钼处理(对照),其中营养液含0.5μmol/L钼酸的处理(M2)效果最佳。培养8 d内M2处理的平邑甜茶幼苗的根系硝酸还原酶活性一直高于其他处理,且与对照差异显著;培养4 d时各种处理的叶片硝酸还原酶活性上升至最高值,随后下降,8 d后又出现上升和下降的趋势,但上升幅度明显小于培养4 d。M1、M2、M3和M4处理的植株总干重分别比CK提高3.88%、21.12%、12.38%和19.90%。与对照相比,0.5μmol/L钼酸处理幼苗的15N吸收量增加的比例最大,全氮量表现出相同的趋势。供钼处理的氮肥利用率均明显高于对照,其中以0.5μmol/L钼酸处理的效果最显著,利用率为13.97%,比对照高48.92%。施钼处理对幼苗的15N分配率有一定的影响,0.5μmol/L钼酸处理(M2)和叶片喷施0.04%钼酸处理(M4)的茎和叶片的15N分配率明显高于对照,对照根系中15N分配率最高。0.5μmol/L钼酸处理叶片、茎和根的Ndff均达到最高,分别为对照同一部位的1.59倍、1.56倍和1.33倍。以上结果表明适量供钼可促进幼苗对肥料15N的吸收征调利用。【结论】供钼可以提高苹果砧木平邑甜茶幼苗的生物量、根系活力、15N吸收量、全氮量和15N利用率,其中经过0.5μmol/L钼酸处理(M2),其对平邑甜茶幼苗生长及硝态氮吸收、转化和分配利用的影响最显著。     

Biosynthesis of trans-2-hexenal in response to wounding in strawberry fruit

Wounded strawberry fruit produces a diverse group of volatile compounds including aldehydes, alcohols, and esters derived from the lipoxygenase (LOX) and hydroperoxide lyase (HPL) pathways. Because the wound volatiles may play an important role in plant-fungal interaction, the goal of this study was to develop a greater understanding about the biosynthesis of the major wound volatile, trans-2-hexenal (t-2-H), produced by strawberry fruit upon wounding. To that end, composition and quantity of total and free fatty acids of control and wounded strawberry fruit were analyzed. In addition, activities of the key enzymes, LOX and HPL, and production of C6 aldehydes were determined. Intact strawberry fruit did not produce detectable t-2-H which is derived from alpha-linolenic acid (18:3). However, in response to wounding by bruising, strawberry fruit emitted t-2-H and its precursor cis-3-hexenal (c-3-H). The level of total lipid 18:3 in the fruit increased 2-fold in response to wounding, whereas free 18:3 declined slightly ( approximately 30%). At 10 min following wounding, fruit exhibited a 25% increase in LOX activity, which leads to the production of 13-hydroperoxyoctadecatrienoic acid (13-HPOT) from 18:3. The activity of HPL, which catalyzes formation of cis-3-hexenal from 13-HPOT, increased 2-fold by 10 min after wounding. Thus, during a 15 min period after wounding, free 18:3 substrate availability and the activity of two key enzymes, LOX and HPL, changed in a manner consistent with increased c-3-H and t-2-H biosynthesis.     

水体氮浓度对狐尾藻和金鱼藻片段萌发及生长的影响

为了厘清水体氮浓度对沉水植物片段萌发及生长的影响,通过模拟控制试验,设计了水体总氮浓度分别为0 (CK)、 0.5 mg/L (N1)、 2 mg/L (N2)、 8 mg/L (N3)和12 mg/L (N4）共5个处理,研究了水体不同氮浓度条件下狐尾藻 (Myriophyllum spicatum) 和金鱼藻 (Ceratophyllum demersum)片段(3节)萌芽数、 萌发位置、 芽长和生物量的差异。结果表明, 水体氮浓度对不同沉水植物片段萌发的影响存在差异,较高的水体氮浓度不利于狐尾藻片断萌发,而对金鱼藻片段却有一定程度的促进;氮浓度处理促进了狐尾藻顶端优势,却抑制了金鱼藻的顶端优势。狐尾藻以0.5 mg/L处理的芽长较长,生物量以2 mg/L处理最大;而金鱼藻以8 mg/L处理芽长最长,生物量以2 mg/L处理最大。由此可见,不同沉水植物对水体氮适应性存在差异,水体氮浓度较低时,沉水植物断枝可以进行萌发和生长, 而当氮浓度超过2 mg/L时,对沉水植物断枝萌发及生长反而有抑制作用;金鱼藻片段比狐尾藻对水体氮浓度的耐受性强。     

Thermal inactivation kinetics of recombinant proteins of the lipoxygenase pathway related to the synthesis of virgin olive oil volatile compounds

The aim of this work was to characterize the thermal inactivation parameters of recombinant proteins related to the biosynthesis of virgin olive oil (VOO) volatile compounds through the lipoxygenase (LOX) pathway. Three purified LOX isoforms (Oep2LOX1, Oep1LOX2, and Oep2LOX2) and a hydroperoxide lyase (HPL) protein (OepHPL) were studied. According to their thermal inactivation parameters, recombinant Oep1LOX2 and Oep2LOX2 could be identified as the two LOX isoforms active in olive fruit crude preparations responsible for the synthesis of 13-hydroperoxides, the main substrates for the synthesis of VOO volatile compounds. Recombinant Oep2LOX1 displayed a low thermal stability, which suggests a weak actuation during the oil extraction process considering the current thermal conditions of this industrial process. In addition, recombinant OepHPL could be identified as the HPL activity in crude preparations. The thermal stability was the highest among the recombinant proteins studied, which suggests that HPL activity is not a limiting factor for the synthesis of VOO volatile compounds.     

采后褪黑素处理对鲜切花椰菜保鲜品质及货架期的影响

为研究采后外源性褪黑素处理对鲜切花椰菜货架期间品质及生理的影响,试验以"雪白"花椰菜为材料,拟从中筛选出有效的使用浓度,进而从生理、细胞和基因表达水平解析褪黑素对鲜切花椰菜保鲜品质的调节作用,以期为探索鲜切花椰菜保鲜和衰老调控的有效途径提供科学依据。采用0.05、0.10、0.50 mmol/L褪黑素溶液浸泡鲜切花椰菜样本15 min,分析货架期间（0、4、8、12、16 d）样本的失重率、硬度、1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl, DPPH）值、总酚含量、抗坏血酸含量、色泽、总硫代葡萄糖苷含量、内源性褪黑素含量、多聚半乳糖醛酸酶（polygalacturonase, PG）和脂氧合酶（lipoxygenases, LOX）活性及基因表达水平、细胞超微结构的变化。结果表明：0.10 mmol/L褪黑素处理明显延缓（P<0.05）了失重率、硬度、色泽和总硫代葡萄糖苷含量的下降,提升（P<0.05）了样本中内源性褪黑素的含量。同时,0.10 mmol/L褪黑素处理最有利于提高总酚含量和抗氧化能力,延缓抗坏血酸的降低。此外,0.10 mmol/L可抑制细胞结构的损伤,降低PG和LOX的基因表达,延缓PG和LOX的活性。由此可知,对鲜切花椰菜进行外源褪黑素处理可能是延长其采后寿命和提高品质的有效技术。     

Thermal stability of lipoxygenase and hydroperoxide lyase from olive fruit and repercussion on olive oil aroma biosynthesis

Thermal stabilities of main enzymes involved in the biosynthesis of virgin olive oil (VOO) aroma through the lipoxygenase (LOX) pathway were studied in crude enzymatic preparations. Kinetic parameters of thermal inactivation for LOX were determined graphically and were shown to be compatible with the presence of two LOX isoenzymes (LOXlab and LOXres) having different thermal stabilities and displaying relative activities of 88 and 12% each. Data on hydroperoxide lyase (HPL) suggest the existence of just one HPL isoform. Thermal stabilities of LOX and HPL enzymatic activities in crude preparations seem to explain the observed decrease of volatile contents in VOO aroma as a consequence of heat treatments of olive fruit. Moreover, differences in thermal stability of LOXlab and LOXres would justify the distinct pattern of reduction of C6 and C5 compound contents observed in the aroma of these oils.     

臭氧处理和低温保藏对黄鱼保鲜效果

探讨臭氧水及低温保藏对黄鱼的保鲜效果。分别使用098、312和468mg/L 3种浓度的臭氧水对冰鲜黄鱼进行处理,浸泡时间分别为5、10和15min,低温4℃下贮藏至10d。结果表明,臭氧浓度越高、浸泡时间越长,杀菌及保鲜效果越好。使用浓度为468mg/L的臭氧水浸泡处理黄鱼15min后杀菌效果最好,其TVB-N值第6天为2353mg/100g,结合感官指标,黄鱼保鲜期比对照延长2d。试验结果表明,臭氧水可有效用于黄鱼的保鲜。     

低温贮藏对美味猕猴桃布鲁诺果实主要挥发性物质和脂肪酸代谢的影响

为探讨贮藏温度对美味猕猴桃果实风味品质的影响,将猕猴桃布鲁诺果实贮藏于常温(20±0.5℃)、低温(1±0.5℃)下,采用气相色谱-质谱联用(GC-MS)测定猕猴桃果实常温和低温贮藏后主要挥发性成分的种类和含量变化;同时,分析果实挥发性成分合成的脂肪酸代谢途径底物(亚麻酸、亚油酸)含量、关键酶活性及其基因表达量的变化。结果表明,与常温相比,低温贮藏降低了猕猴桃果实中酯类物质的种类和相对含量,保持较高醛酮类物质种类和相对含量;常温贮藏下猕猴桃果实风味物质随贮藏时间变化明显,而低温则能够较好维持猕猴桃果实的特征风味。与常温贮藏相比,低温贮藏抑制了脂肪酸代谢中脂氧合酶(LOX)、脂氢过氧化物裂解酶(HPL)、乙醇脱氢酶(ADH)以及醇酰基转移酶(AAT)等关键酶活性及其基因的表达,降低了果实亚油酸和亚麻酸的分解,通过脂肪酸代谢途径合成的酯类物质也因此有所降低。本研究为低温贮藏调控猕猴桃果实风味物质合成及维持猕猴桃果实特征风味提供了理论依据。     

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO₃-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO₃-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH₄-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH₄-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.     

样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响

为研究样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响,分别选用3种保存温度(常温23℃/15 d、冷藏2℃/90 d、冷冻-18℃/360 d)、2种取样方式(虾仁取样、整虾取样),以新鲜沼虾样本为对照组,对比不同样本预处理方式对罗氏沼虾碳稳定同位素比值(δ¹³C)、氮稳定同位素比值(δ¹⁵N)、碳氮比(C/N)的影响。结果表明,不同保存温度和不同取样方式对罗氏沼虾δ¹³C、δ¹⁵N、C/N的影响明显。与对照组相比,常温保存条件下的δ¹⁵N偏移量最大(1.31‰~13.16‰,平均值为6.02‰),冷冻保存条件下的δ¹³C偏移量最大(2.34‰~2.84‰,平均值为2.57‰),室温保存条件下的C/N显著增加(P<0.05),冷藏和冷冻保存条件下的C/N显著减少(P<0.05)。不同取样方式对罗氏沼虾δ¹⁵N、δ¹³C的影响还取决于保存温度,在冷冻保存条件下,整虾取样的δ¹⁵N、δ¹³C显著高于虾仁取样,而在常温保存条件下,整虾取样的δ¹⁵N偏移量显著低于虾仁取样。因此,常温(23℃)和冷藏(2℃)条件不适合保存罗氏沼虾、冷冻(-18℃)保存罗氏沼虾的时间不宜超过60 d,建议新鲜沼虾采集后应立即干燥并开展碳和氮稳定同位素检测。本研究结果为水产品碳和氮稳定同位素比值检测的样本预处理方式提供了参考。     

适量稳定供钾促进苹果矮化砧M9T337幼苗生长和氮素吸收利用

  【目的】  钾在氮代谢中发挥重要作用,通过同位素示踪技术,研究供钾水平和稳定性对苹果矮化砧M9T337幼苗生长及氮素吸收利用的影响,以深化理解钾素水平对苹果氮素吸收利用的影响机制,为苹果生产上科学施钾提供理论依据。  【方法】  以苹果矮化砧M9T337幼苗为试验材料进行砂培试验,总处理周期为60天。以Hoagland营养液为基础,设置5个供钾处理,分别为持续低钾 (K 0.5 mmol/L,K1)、1～30天低钾 (0.5 mmol/L) 和31～60天高钾 (12 mmol/L,K2)、适量稳定供钾 (6 mmol/L,K3)、1～30天高钾 (12 mmol/L) 和31～60天低钾 (0.5 mmol/L,K4)、持续高钾 (12 mmol/L,K5)。每3天更换一次营养液,每次在营养液中加入0.01 g Ca(15NO₃)₂,共加入0.2 g。于处理后第31天和第60天取样,测定幼苗生长、根系性状以及氮素吸收利用分配状况。  【结果】  供试苹果砧木幼苗处理第60天,以适量稳定供钾处理K3的生物量最大,根系总长、总表面积最大,根系活力也显著高于其他处理。31～60天,K2处理地上部干重增幅最大 (174.8%),K4处理根系干重增幅最大 (176.3%),幼苗总生物量、根系长度、根系总表面积增量最大的处理为K3 (依次为12.99 g/株、1059 cm/株和1113 cm2/株)。第31天和第60天两次测定结果显示,幼苗根部NO₃–吸收速率均以K3处理最大,分别为29.63和36.19 pmol/(cm2·s);K1、K4处理幼苗根部NO₃–离子流在第31天时为内流,在第60天时变为外排。整个处理期内,硝酸还原酶 (NR) 活性均以K3处理最高;处理41～60天,K2处理幼苗NR活性显著升高,而K4处理则显著降低。15N示踪结果表明,K3处理下苹果砧木幼苗对氮素的吸收能力最强,植株总吸氮量、15N利用率和叶片15N分配率均显著高于其他处理;处理第60天15N吸收量表现为K3>K5>K2>K4>K1。  【结论】  持续的低钾、高钾以及变换性的高低钾处理会抑制苹果幼苗根系生长以及氮素向地上部运移,不利于氮素的吸收利用。而持续适宜稳定地供钾可以提高根系活力和硝酸还原酶活性,保持根系较高的NO₃–吸收速率,同时促进氮素由根系向叶片的运移,实现对氮素的高效吸收利用,从而促进苹果砧木幼苗的生长。     

基于15N示踪法的双根大豆系统氮素吸收和分配特性研究

【目的】施氮可以促进大豆生长并提高产量,同时会抑制根瘤生长和固氮。因此研究大豆对不同形态氮素的吸收、分配及再分配特点,可以为解析大豆氮的转运特性及施氮对根瘤的系统性抑制提供参考。【方法】利用嫁接方法,制备具有两个根部和一个地上部的双根大豆植株,在砂培条件下分别以NO₃–和NH₄+为氮源设置两种试验处理。试验Ⅰ,一侧施50 mg/L的15NO₃– 或15NH₄+(A侧),另一侧不施氮 (B侧);试验Ⅱ,一侧施50 mg/L的15NO₃– 或15NH₄+(A侧),另一侧施同形态的50 mg/L的NO₃– 或NH₄+(B侧)。于始花期 (R1) 和始粒期 (R5) 取样两次,将植株分为A根、B根、A侧根瘤、B侧根瘤、茎、叶片、叶柄、荚等部位,用于测定15N丰度、干重和氮含量等指标。【结果】试验Ⅰ和试验Ⅱ结果发现,大豆A和B两侧根瘤的15N丰度均高于自然丰度 (0.365%),说明根瘤的生长发育过程中,所需要的氮不是全部来自自身固氮,还需要从根中吸取氮。与试验Ⅰ相比,试验Ⅱ的根瘤固氮率明显下降,表明大豆植株优先吸收利用肥料氮。NO₃–与NH₄+处理相比,各器官15N丰度均没有显著性差异,说明在50 mg/L的氮浓度下,NO₃–和NH₄+对大豆的氮营养没有显著差异。试验Ⅰ和试验Ⅱ均发现大豆B侧根及根瘤的15N丰度高于自然丰度 (0.365%),且小于施加的肥料氮的15N丰度 (3.63%),表明A侧根吸收的氮会经地上部转移到B侧的根及根瘤中,即根吸收的肥料氮会以一定的比例运输到地上部,随后会再次重新分配回根及根瘤中。本试验将双根大豆系统中地上部和B侧根及根瘤看成一个氮转移系统,利用15N丰度的差异,构建了R1～R5期地上部向根及根瘤转移氮量的计算方法。经计算发现,当施氮浓度为50 mg/L时,在始花期至始粒期,根来自地上部转移的氮占根部氮积累量的28.4%～40.8%,根瘤来自地上部转移的氮占其氮积累量的14.4%～17.2%。【结论】根瘤生长所需要的氮不是全部来源于自身固氮,有一部分来源于根系吸收的氮。在有肥料氮存在时,大豆植株优先吸收肥料氮。根系吸收的肥料氮以及根瘤固氮被运输到地上部后,会再次重新分配回根及根瘤中。在50 mg/L的氮浓度下,氮素形态 (NO₃–和NH₄+) 不会影响大豆植株对氮的吸收及分配。     

Prevention of oxidative rancidity in rice bran during storage.

The effect of microwave heat on lipoxygenase (LOX) activity in rice bran under various storage conditions was examined. Raw rice bran from the long-grain variety Lemont was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran samples were packed in zipper-top bags or vacuum packs and stored at room temperature (25 degrees C) or in the refrigerator (4-5 degrees C) for 16 weeks. Samples were analyzed for LOX activity at 4-week intervals. LOX activity did not significantly change from its initial value at week 0 for zipper-top and vacuum-packed samples while stored at 4-5 degrees C for 12 weeks, but decreased at week 16. Vacuum packing did not show a significant impact on LOX activity during 16 weeks of storage. Microwave-heated samples stored in the refrigerator did not show significant change in LOX activity for up to 12 weeks but showed a significant (p < 0. 05) decrease at 16 weeks. Results showed that oxidative rancidity of rice bran could be prevented by microwave heating the samples, packing in zipper-top bags, and storing at 4-5 degrees C for up to 16 weeks.     

不同基因型糯玉米氮素吸收利用效率的研究 II.氮素积累动态的基因型差异

为了解糯玉米氮素积累进程的变化规律,阐明不同生育时期氮素积累的基因型差异及其对产量形成的作用,分析了31个糯玉米品种在同一施氮水平下四叶期、拔节期、大口期(12叶期)、开花(吐丝)期、鲜穗采收期和成熟期的植株氮素积累量。结果表明,植株氮素含量随生育进程逐渐下降,植株氮素积累量随生育进程的增加呈不对称的S型曲线变化,可用Richards方程拟合。不同品种各生育时期的氮素含量和积累量均存在显著差异。鲜穗高产品种主要在大口至开花阶段增加了吸氮量;而鲜子粒及成熟子粒高产品种主要在大口至开花,其次在开花至鲜穗采收阶段增加了吸氮量。通径分析表明,氮素积累过程主要影响氮素积累总量的高低,而对氮素利用效率影响较小。氮素积累过程S型曲线的Richards方程特征参数品种间差异显著。最大积累速率大、活跃积累期长、快增期的积累速率大和持续时间长对提高品种的氮素吸收总量有利。属于高产、氮素吸收量大、氮素利用效率高的基因型有6个品种,其大口至开花及开花至鲜穗采收阶段的吸氮量平均值分别为1.136和0.554.g/plant,比其它品种分别高24.3%和37.8%;最大积累速率和快增期的积累速率分别为0.068和0.059.g/(d.plant),比其它品种分别高15.8%和15.9%。活跃积累期和快增期的持续时间平均值分别为63.4和29.5.d,比其它品种分别延长了1.9和0.9d。     

Effect of hexanal on the shelf life of fresh apple slices.

In this work the effects of hexanal, as a component of packaging atmosphere, on the shelf life of and evolution of naturally occurring microbial populations in fresh apple slices during storage at 4 and 15 degrees C were evaluated. Although hexanal had no bactericidal effects, in all conditions considered, this volatile molecule significantly extended the shelf life. In fact, the presence of hexanal in the storage atmosphere (at 4 degrees C) totally inhibited mesophilic bacteria and considerably prolonged the lag phase of psychrotrophic bacteria. Also, at 15 degrees C, hexanal strongly inhibited molds, yeasts, and mesophilic and psychrotrophic bacteria. Moreover, hexanal led to a yeast selection favoring species having a reduced spoilage potential due to their prevalent respiratory activity. When added to a modified atmosphere (70% N(2) and 30% CO(2)), this molecule was also very effective in preventing browning reactions for at least 16 days at 15 degrees C. No changes in hue angle values were observed in samples packaged in modified atmosphere with hexanal, even after 16 days of storage at 4 degrees C.