植物赤霉素生物合成关键基因GA3-oxidase的研究进展

在植物赤霉素合成途径中,GA3ox将无活性的GA12和GA53转变为有活性的GA4和GA1,进而实现了调控植物生长发育。GA生物合成及其信号传导途径相关基因的研究备受关注。本研究对高等植物体内GA3-oxidase基因的克隆、组织表达、调控表达、功能鉴定等方面的研究进行综述,并对进一步深入研究GA3ox的互作、抗逆性等方面进行了展望,揭示GA3-oxidase氧化酶信号网络系统及其作用机制。     

鲜切生菜气调包装保鲜条件优化

为研究气调包装对鲜切生菜保鲜效果的影响,筛选出最优的气调包装条件。生菜经过清洗、消毒、脱水、切割等一系列加工工艺流程后,用不同包装材料和不同气体比例对其进行气调包装,在4℃条件下冷藏,每隔1 天对生菜的失重率、Vc、叶绿素、微生物、电导率以及PPO、POD酶活性进行测定,筛选出适合生菜气调保鲜的最佳材料和最佳气体比例。结果表明：适宜的包装材料和O2和CO2气体比例组合有利于延长鲜切生菜的保鲜期,在4℃条件下,采用3% O2+ 10% CO2气体比例和BOPP/PE包装材料进行气调包装,可以维持鲜切生菜恰当的呼吸强度,有效抑制微生物的生长,降低了PPO、POD酶的活性、减少了Vc、叶绿素等营养物质的损失,使生菜的保鲜期由4~5 天延长至14 天。这在实际生产和流通中具有较强的应用价值。     

不同保鲜剂处理对切割生菜品质影响的研究

研究了5种保鲜剂（1mmol／L苯甲酸、0．5％氯化钙、1．0％过氧化氢、1．0％维生素C、1．0％柠檬酸）处理对新鲜切割生菜（10～15mm切割度）在3℃贮藏期间品质变化及贮藏效果的影响。结果表明,在3℃贮藏条件下,5种处理中,1mmol／L苯甲酸和0．5％氯化钙显著延缓切割生菜的叶绿素、总酸、VC以及可溶性固形物含量的下降,保持了较好感官品质,贮藏到第12天仍有商品价值;1,0％过氧化氢和1,0％VC处理对保持切割生菜的品质有一定的作用,但处理效果略次于苯甲酸和氯化钙,商品贮藏期仅为8天：1．0％柠檬酸的处理效果不明显,商品贮藏期仅为6天左右。     

棉花抗黄萎病生理与生化机制研究

本文概述了棉花抗黄萎病的特点与规律,指出棉花植株是通过自身组织结构的强化、植物抗毒素的合成以及微生物之间的互作三方面应对黄萎病菌的侵染。认为棉花植株主要通过促进木质素生成和增加积累量以强化组织结构。在棉花抗病反应中以植物抗毒素的合成为主要途径,包括萜类、酶类和激素类3类化学物质,其中酶类物质如几丁质酶已经在很多植物中被证明具有抗病作用,但是其具体作用途径仍不清楚。土壤中某些微生物也可以对黄萎病菌产生作用。重点讨论了在棉花抗黄萎病信号通路中重要分子磷酸激酶和磷酸酯酶在植株抗性防卫中起着级联调控开关的作用,在现有信号调控研究基础上其在抗病机制中可能的参与途径。对目前棉花抗黄萎病分子育种研究中存在的主要问题和可能的解决途径进行了探讨,展望了其发展的方向。     

断氮处理提高2种氮水平水培生菜品质的效应研究

为研究氮水平对断氮处理提高水培生菜营养品质效果的影响,以揭示氮营养条件影响断氮处理效果的机理,在玻璃温室中,以2种氮水平10,15 mmol/L水培紫叶生菜,并在生菜生长后期以KCl溶液进行5 d断氮处理。断氮处理前后,生菜生物量没有显著变化。生菜抗坏血酸、可溶性糖含量在断氮处理后都显著提高了,叶片和叶柄硝酸盐含量则显著降低。断氮处理前后,生菜地上部酚类物质相对含量受氮水平影响都不显著。断氮处理对生菜生物量影响不显著,但显著提高了生菜营养品质。氮水平显著影响了生菜抗坏血酸含量变化速率,氮水平降低,抗坏血酸增加速率显著提高。     

番茄系统创伤信号因子研究进展

当植物受到机械损伤或害虫伤害时,植物体会在受伤部位产生创伤信号分子启动防御基因的系统表达.许多研究表明系统素(或其前体原系统素)在受伤部位激活茉莉酸的合成,使之达到系统反应的水平,应对外来伤害;茉莉酸或其衍生物是重要的系统伤信号分子,它诱导伤防御基因的系统表达.自从系统素和茉莉酸被认为是伤诱导防御基因表达的信号分子后,番茄成为研究植物系统伤信号很好的模式植物.本文介绍了番茄的茉莉酸合成突变体、茉莉酸感知突变体和系统素功能突变体,及它们之间相互作用,并推测了茉莉酸和系统素在系统创伤信号调节中的作用.     

虎榛子愈伤组织对土生空团菌菌丝生长的影响

新研究表明植物不能形成菌根的障碍是缺失一种植物形成菌根的信号物质,这种信号物质可以诱导菌根真菌菌丝的生长和分枝,为下一步研究植物与外生菌根真菌互作的生化机制和互作过程中的信号传导途径提供理论基础,建立虎榛子愈伤组织与其外生菌根菌的共培养体系,在纯培养条件下采用干重法,测定虎榛子愈伤组织、愈伤组织匀浆液和愈伤组织分泌物对两株土生空团菌[Cenococcum geophilum Fr. (Cg)]菌株生长的影响。结果表明,供试Cg菌株与宿主的愈伤组织共同培养可以明显地促进菌丝的萌发和生长,而愈伤组织匀浆液和愈伤组织分泌物也可促进菌丝体早期生长,其中共培养法培养促生作用最强,尤为突出,两菌株单菌落的生物量分别达到63.5 mg和45.2 mg。初步研究表明,虎榛子愈伤组织与菌根菌共培养可以明显促进菌丝生长,证明虎榛子愈伤组织细胞在生长的过程中会分泌一类生化物质对外生菌根真菌菌丝的生长有促进作用,但究竟有哪些物质在起作用,是进一步研究的内容。     

假禾谷镰孢侵染小麦后3种植物激素相关基因的差异表达分析

假禾谷镰孢(Fusarium pseudograminearum)是我国近年新发现的小麦病原真菌,本研究目的是揭示植物激素信号传导途径中相关基因表达对假禾谷镰孢侵染的响应。利用假禾谷镰孢野生菌株WZ2-8A侵染小麦品种周麦24,对接种后5 d和15 d样品进行转录组测序,分析差异表达基因,并对候选基因进行q RT-PCR验证。假禾谷镰孢侵染后,小麦幼苗生长受到明显抑制,根长、株高、根重和地上部分鲜重均显著降低。转录组分析结果表明,植物激素信号传导途径中有29个基因差异表达,涉及到生长素、细胞分裂素和脱落酸3种植物激素。在接种后5 d有11个差异表达基因,其中2个上调,9个下调;在接种后15 d共有25个差异表达基因,其中8个上调,17个下调。在生长素信号传导途径中,生长素输入载体AUX1差异表达,影响生长素的极性运输,从而影响小麦根部的细胞伸长。在细胞分裂素信号传导途径中,起正调控作用的B-ARR上调表达,推测其促进细胞分裂素的信号传导,从而抑制细胞分裂,与生长素协同作用,造成小麦的长势减弱。在脱落酸途径中,脱落酸受体PYR/PYL下调表达;起到负调控作用的PP2C相关基因均上调表达。脱落酸使植物对真菌和细菌的抗性起到负调控作用,其信号传导途径与茉莉酸/乙烯途径相互拮抗,脱落酸信号传导途径的阻遏可能会使茉莉酸/乙烯途径信号通路打开。q RT-PCR结果基本能够和转录组测序结果相拟合,说明在假禾谷镰孢侵染胁迫下,脱落酸的信号传导被抑制可能是中抗品种周麦24对假禾谷镰孢产生一定的抗性的生理基础。     

植物激发子及其信号传导之研究进展

植物诱导抗病性是当前科学研究的热点,是研究病源物和植物互作关系的关键。植物激发子在植物诱导抗病性中发挥着重要的作用,它是一类能诱导寄主植物产生防卫反应的特殊化合物,在与受体分子结合后,通过一定的信号传导途径激发植物产生防卫反应。综述了近年来激发子在植物诱导抗病性中的研究进展,包括激发子的种类,受体类型以及激发子引起的信号传导,并对激发子研究存在的问题及应用前景进行了展望。     

生菜WOX基因家族的鉴定与分析

WOX转录因子是植物特异性转录因子。已有研究表明,WOX家族成员在植物生长发育和非生物胁迫响应中起着重要作用,但在生菜(Lactuca sativa L.)中,WOX基因家族的生物学功能研究还很少。本研究在生菜中鉴定到14个可能的LsaWOX基因,分析了他们的基因结构、蛋白保守基序、三级结构、染色体定位和顺式作用元件等,并将其划分为三个主要分支(如远古支系,中间支系和WUS支系)。本研究对生菜中WOX家族成员进行了鉴定和初步分析,为进一步研究生菜中WOX基因家族的生物学功能提供理论依据。     

鲜切青笋加工工艺

以鲜切青笋为原料,分别采用单因素试验与正交试验方法确定不同护色剂的最佳浓度.试验结果表明,鲜切青笋经4%柠檬酸,5%抗坏血酸,0.07%苯甲酸钠混合溶液处理10min,再利用真空包装进行贮藏,可使鲜切青笋颜色保持鲜绿,贮藏期长达7～10天.     

Baby-leaf and multi-leaf of green and red lettuces are suitable raw materials for the fresh-cut industry

Consumer demand for softer leaves with variation in taste, shape and colours has encouraged the development of new lettuce products of baby-sized leaves. The objective of this study was the comparison of whole-head lettuce, as the most common raw material for fresh-cut, with baby-leaf and multi-leaf as the newest baby-sized lettuce leaves. Lettuces (Lactuca sativa L.) of the types Green Leaf, Red Leaf and Lollo Rosso were cultivated in the same field with different plant densities, under commercial conditions. Although baby-leaf was subjected to far less wound damage than the shredded lettuce from the whole-head, leaf age could play an important role in increasing respiration rate and determining postharvest quality. After 9-11 d of storage, minimally processed products from the three types of raw material showed good visual quality without differences among them. However, over the 12-d storage period, quality decreased to the limit of marketability mainly due to browning of the cut edge surface of the fresh-cut product from whole-heads and decay due to the soft tissue in the case of baby-leaves. Additionally, with the processing of whole-heads, the increase in cut-damage surfaces and availability of cell nutrients provided conditions that favoured the growth of lactic acid bacteria (LAB) and total coliforms compared to uncut surfaces of baby-sized leaves. The ratio between the oxidized and reduced forms of ascorbate (DHA/AA) increased 2-4 times after 9-11 d of storage. Furthermore, baby-sized leaves had higher phenolic contents than the shredded product from the whole-head which probably contributed to reaching a shelf-life of 11 d. In conclusion, the new green and red baby-sized leaves both at immature and mature stages provided high quality lettuce for the fresh-cut market, meeting specific requirements regarding visual quality, microbial load and high content of phytochemicals.     

不同处理对鲜切莴苣褐变及贮藏品质的影响

以莴苣为研究材料,以10 g/L L-抗坏血酸、5 g/L柠檬酸、0.2 g/L水杨酸和0.2 g/L阿魏酸处理鲜切莴苣,去离子水浸泡为对照组,通过测定褐变度、总酚、类黄酮、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性及苯丙氨酸解氨酶(PAL)活性,探讨不同抗褐变剂对鲜切莴苣褐变的影响。结果表明,4种抗褐变剂处理均能够有效抑制酶促褐变有关酶活性的升高,减少多酚物质的含量,降低褐变度,有效地保证了鲜切莴苣的贮藏品质,其中0.2 g/L阿魏酸处理的效果最好。     

Sensory quality,bioactive constituents and microbiological quality of green and red fresh-cut lettuces (Lactuca sativa L.) are influenced by soil and soilless agricultural production systems

Quality characteristics and shelf-life of fresh-cut lettuce cultivated in soil, as the traditional production system, and soilless, as an innovative production system, were investigated. Three lettuce genotypes, lollo rosso and red oak leaf as red-leafed genotypes, and butterhead as a green-leafed genotype, were studied. Lettuces from both production systems were grown in the same open field and at the same time in the winter season. A longer growing period was needed, to obtain the same maturity stage, in the soil than in the soilless (102 and 63 d after planting, respectively). After harvest, the visual quality of the fresh-cut produce from red-leafed lettuce cultivated in soilless was better than those in soil. In the case of green-leafed genotype, the soilless system gave a lower visual quality of the fresh-cut product. Lollo rosso cultivated in the soilless system had a higher content of phytochemicals, including vitamin C and individual and total phenolics, than that cultivated in soil. At the end of storage, fresh-cut lollo rosso and red oak leaf grown in the soilless system showed significantly higher content of vitamin C than those in soil. This high content of antioxidants was linked to a better maintenance of visual quality and the control of browning when compared with the fresh-cut product from lettuces cultivated in soil. The soilless system was more effective in controlling microbial contamination as lettuce cultivated in the soilless system had a lower initial microbial load and slower microbial growth during storage. At the end of shelf-life, differences in microbial counts between soil and soilless lettuce were 3 and 1.5 log units higher for lactic acid bacteria and total coliforms, respectively, in soil. This study shows that higher quality and microbiologically safer raw product can be provided by the soilless system as a new growing system although it depends on the genotype and the season.     

Preharvest and postharvest factors related to off-odours of fresh-cut iceberg lettuce

The influence of different preharvest and postharvest factors affecting off-odour development of fresh-cut iceberg lettuce in low-O₂ modified atmospheres (MA) was investigated. Fresh-cut iceberg lettuce developed undesirable off-odours under low O₂ and elevated CO₂ atmospheres. A strong relationship between CO₂ concentration and off-odour development was observed. Significant differences in off-odour development existed among different cultivars in two harvests in consecutive years. The influence of maturity stage was evaluated, comparing fresh-cut product from immature and over-mature heads with commercial ones. Higher CO₂ concentrations and higher accumulation of ethanol and acetaldehyde were detected in the headspace of MA-packed lettuce from immature heads. Differences in respiration rate of the fresh-cut product from heads cultivated during the winter–spring seasons were around 30%. Respiration rate of fresh-cut iceberg lettuce increased when medium temperature during cultivation increased. Changes in the product weight generated different CO₂ levels which correlated with the production of ethanol and acetaldehyde and other off-odour metabolites related with the lipoxygenase (LOX) pathway such as hexanal, 1-hexanol, and cis-3-hexen-1-ol. Volatile compounds such as cis-3-hexen-1-ol, β-elemene, ethyl acetate and dimethyl sulphide increased their content more than 10 times compared with other volatiles. Moreover, differences in the initial flushed gas-mixture with or without CO₂ showed higher CO₂ concentrations and the development of stronger off-odours when samples were flushed with an enriched CO₂ gas-mixture. In summary, visual quality of fresh-cut iceberg lettuce is important but so are odour and flavour. MAP currently used for fresh-cut lettuce may need some modification to inhibit off-odours and achieve better aroma and flavour qualities for preserving “freshness” of the cut product. Screening for cultivars with low browning potential and fermentation, harvested at optimum maturity stage and with an adequate package design are recommended.     

Microbial growth in fresh-cut lettuce increases when wound-induced phenolic accumulation is suppressed

Wounding lettuce (Lactuca sativa L. Longifolia) leaf mid-rib tissue initiates physiological responses that include increased synthesis and accumulation of phenolic compounds. Chlorogenic acid is the predominant wound-induced phenolic compound that accumulates in excised lettuce leaf tissue held at 10 °C for 2 days. The growth of five bacterial isolates associated with lettuce decay (Erwinia carotovora, Erwinia chrisanthemi, Pseudomonas putida, Pseudomonas fluorescens, or Pseudomonas syringae) on TSA (tryptic soy agar) media was not markedly reduced by concentrations of chlorogenic acid identical to those found in wounded lettuce. Growth of E. carotovora and P. fluorescens was stimulated when prepared with TSA media containing homogenized non-wounded lettuce mid-rib tissue, while the increase was much less when the media was prepared with 5 mm thick mid-rib tissue segments that were held for 2 days at 10 °C after excision. Inhibiting the wound-induced increase in phenolic content with a 1-hexanol or heat-shock treatment allowed E. carotovora to grow on media prepared with excised tissue that had been held at 10 °C for 2 days at significantly higher rates than on media prepared with non-treated excised tissue. Hexanol is thought to interfere with the synthesis and/or propagation of the wound signal, so delaying its application to excised mid-rib tissue reduces its effectiveness. Delaying application of the inhibitor for 4 h, allowed increased accumulation of wound-induced phenolic compounds in 2 day old lettuce tissue that resulted in a concomitant reduction in the growth of E. carotovora on media prepared with this tissue. Neither the hexanol nor the heat-shock treatment themselves made the excised lettuce tissue a better substrate for microbial growth. It appears that treatments that suppress wound-induced increases in antimicrobial phenolic compounds reduce the ability of excised lettuce tissue to suppress the growth of bacteria associated with lettuce decay by limiting the production and accumulation of these antimicrobial compounds. A critical distinction is made between whether a treatment renders the tissue more susceptible to microbial growth, or whether a treatment prevents the wound-induced increase in disease resistance that limits microbial growth. If all treatments that reduce tissue browning by interfering with the wound-induced accumulation of phenolic compounds also inadvertently make the tissue more susceptible to microbial growth, then research should be directed to prevent the production of brown pigments from the wound-induced accumulated phenolic compounds, rather than devising treatments that reduce their accumulation.     

Aromatic- and di-carboxylates inhibit wound-induced phenolic accumulation in excised lettuce (Lactuca sativa L.) leaf tissue

Excision of de-bladed 5-mm mid-rib segments from Romaine lettuce leaf tissue induced a five-fold rise in phenolic concentration when held at 10 °C for 48 h. Immersion in aqueous solutions of various di-carboxylates and aromatic carboxylates for 1 h reduced this wound-induced increase. The decrease was linear for di-carboxylates with increasing length from 3 to 14 carbons, with the phenolic concentration becoming less than the control for compounds with more than 6 carbons. Aromatic carboxylates with a hydroxyl at the 2 position and another at an even position produced an average reduction of 46%, while aromatic carboxylates with no hydroxyl groups, groups at odd positions, or adjacent groups produced an average 12% reduction. The decrease in wound-induced phenolic accumulation produced by 10 mM solutions of aromatic- and di-carboxylates was linearly correlated (R² = 0.91) with the rate of carbon dioxide production, indicating possible tissue damage. This possibility was supported by the fact that most effective concentrations were highly correlated with increased ion leakage, another measure of tissue damage. While delaying the application of inhibitors of wound signal synthesis (e.g., n-alcohols) decreases their effectiveness, delaying the 1 h immersion in aromatic and di-carboxylate solutions for 4 h did not significantly reduce their effectiveness. Like mono-carboxylates, aromatic and di-carboxylates do not appear to be interfering with the synthesis or propagation of a wound signal, but appear to be inhibiting phenolic synthesis and/or accumulation at some subsequent step in the wound response.     

Suitability of aqueous chlorine dioxide versus sodium hypochlorite as an effective sanitizer for preserving quality of fresh-cut lettuce while avoiding by-product formation

Aqueous chlorine dioxide (ClO₂) has been postulated as an alternative to sodium hypochlorite (NaClO) for fresh-cut produce sanitization with the advantage of avoiding the risks associated with chlorination by-products. However, little is known about its influence on preserving quality and the potential formation of trihalomethanes (THMs) under typical processing conditions. The suitability of aqueous chlorine dioxide (3 mg L⁻¹) as an effective sanitizer of fresh-cut iceberg lettuce stored under active modified atmosphere packaging (MAP) at refrigerated conditions was determined and compared with sodium hypochlorite (100 mg L⁻¹). Fresh-cut lettuce washed with tap water was used as a control. The epiphytic microbiota were characterized by the evaluation of the major relevant microbial groups such as mesophiles, psychrophiles, Pseudomonas spp., Enterobacteriaceae, lactic acid bacteria, yeasts and moulds. Additionally, gas composition, sensory quality, vitamin C and individual and total phenolics were monitored after washing and during storage for 3 d at 4 °C followed by 7 d at 8 °C. In general, the natural microbiota of fresh-cut lettuce after washing and storage was equally affected by the different washing solutions, with the exception of yeasts which showed the highest growth after 10 d storage in samples washed with chlorine dioxide. None of the tested washings negatively affected sensory quality, which was acceptable after 10 d storage. Additionally, the content of bioactive compounds was not significantly affected either by washing solution or by storage time. The potential formation of THMs was evaluated by the analysis of lettuce washed in water with a chemical oxygen demand (COD) of 700 mg L⁻¹ treated for 30 min with sodium hypochlorite (100 mg L⁻¹) or chlorine dioxide (3.7 mg L⁻¹). Trihalomethane formation was only detected in the process water in which sodium hypochlorite was applied (217 ± 38 μg L⁻¹). However, THMs formation in fresh-cut lettuce was negligible despite the sanitation procedure. The formation of THMs was only detected in fresh-cut lettuce when sodium hypochlorite was used under very extreme conditions where lettuce was washed in water with a high level of organic matter (COD = 1800 mg L⁻¹), high sodium hypochlorite concentration (700 mg L⁻¹) and long contact time (60 min). Our data suggest that aqueous chlorine dioxide is as suitable as sodium hypochlorite for fresh-cut lettuce sanitation with the advantage of preventing the formation of THMs.     

Role of commercial sanitizers and washing systems on epiphytic microorganisms and sensory quality of fresh-cut escarole and lettuce

Increasing concerns about the possible formation of carcinogenic compounds and the emergence of new, more tolerant pathogens, have raised questions on the use of chlorine in fresh-cut produce. There is a growing need to investigate the efficacy of new commercial sanitizing and other alternative technologies. In the present study, the effectiveness of chlorine and other commercial sanitizer agents (Sanova, Sanoxol 20, Tsunami 100, Purac FCC 80, Citrox 14W and Catallix) was evaluated on epiphytic microorganisms and their influence on the sensory quality of fresh-cut escarole and lettuce. Different sanitizer concentrations (manufacturer's recommended dose and half of this dose) and application systems (submersion and spray) were also compared. The antimicrobial efficacy of the treatments was evaluated, initially after washing, and after 8 days of storage simulating a commercial shelf-life (3 days at 4 °C + 5 days at 8 °C). All the tested washing solutions were more effective in reducing the microbial load than water washes, particularly in fresh-cut escarole. However, the microbial load of fresh-cut escarole and lettuce after 8 days of storage was very similar for most of the treatments despite the different application systems and concentrations of the sanitizers. Clearly epiphytic microorganisms of fresh-cut escarole and lettuce were able to grow rapidly during storage under low temperature, reaching similar or higher values than the unwashed fresh-cut produce at the day of production. The overall visual quality of fresh-cut salad leaves was scored as good or very good (≥6) after 8 days of storage, except for the product washed with Purac. Thus, despite the high number of mesophilic bacteria present in the product, between 6 and 8 log cfu g⁻¹, it was not associated with a detrimental quality. Therefore, the determination of the initial epiphytic reductions of fresh-cut products after washing with different sanitizing agents provides little information about the microbial or sensory quality of the product at the time of consumption.