Multiplex PCR System Optimization with Potato SSR Markers

Potato variety Kexin18 was used as testing materials in this research to study the influence on main components in multiplex PCR system, different primer ratios and annealing temperatures in SSR marker...     

Effect of low-nitrogen stress on photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with different low-nitrogen tolerances

Nitrogen(N) is a critical element for plant growth and productivity that influences photosynthesis and chlorophyll fluorescence. We investigated the effect of low-N stress on leaf photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with difference in tolerance to low N levels. The low-N tolerant cultivar ZH311 and low-N sensitive cultivar XY508 were used as the test materials. A field experiment(with three N levels: N0, 0 kg ha–1; N1, 150 kg ha–1; N2, 300 kg ha–1) in Jiyanyang, Sichuan Province, China, and a hydroponic experiment(with two N levels: CK, 4 mmol L–1; LN, 0.04 mmol L–1) in Chengdu, Sichuan Province, China were conducted. Low-N stress significantly decreased chlorophyll content and rapid light response curves of the maximum fluorescence under light(Fm′), fluorescence instable state(Fs), non-photochemical quenching(qN), the maximum efficiency of PSII photochemistry under dark-adaption(Fv/Fm), potential activity of PSII(Fv/Fo), and actual photochemical efficiency of PSII(ΦPSII) of leaves. Further, it increased the chlorophyll(Chl) a/Chl b values and so on. The light compensation point of ZH311 decreased, while that of XY508 increased. The degree of variation of these indices in low-N tolerant cultivars was lower than that in low-N sensitive cultivars, especially at the seedling stage. Maize could increase Chl a/Chl b, apparent quantum yield and light saturation point to adapt to N stress. Compared to low-N sensitive cultivars, low-N tolerant cultivars maintained a higher net photosynthetic rate and electron transport rate to maintain stronger PSII activity, which further promoted the ability to harvest and transfer light. This might be a photosynthetic mechanism by which low-N tolerant cultivar adapt to low-N stress.     

Physiological and Biochemical Changes of IrlVHA-c gene Transgenic Tobacco Seedlings and Self-crossed Progeny Under NaHCO3 Stress

In order to study the alkali resistivity of VHA-c in Iris lacteal. (IrlVHA-c), the transgenic tobacco seedlings harboring IrlVHA-c gene from Iris lactea (T0), the self-crossed progeny (T1), and the non-transgenic lines of tobacco seedlings were grown in Hoagland nutrient solutions supplemented with 0, 100, 200, 300, 400 mmol·L-1 NaHCO3 . The MDA content, CAT, POD and SOD activity, electrical conductivity, chlorophyll content, soluble sugar content, proline content and polyphenol oxidase activity of the seedlings were determined. The results showed that the transgenic lines of tobacco maintained a high activity up to 200 mmol·L-1 NaHCO3 , and activity was slightly lower at 300 mmol·L-1 NaHCO3 . When the concentration of NaHCO3 was as high as 400 mmol·L-1 the seedlings were badly hurt. In addition, the activity of T0 and T1 transgentic tobacoo was maintained more or less. While the non-transgenic lines of tobacco could maintain viably up to 100 mmol·L-1 NaHCO3 , and they could not survive at 400 mmol·L-1 NaHCO3 . The conclusion was drawn that the alkali resistance of the tobacoo transformed IrlVHA-c was noticeably improved.     

Interactive effects of elevated carbon dioxide and nitrogen availability on fruit quality of cucumber (Cucumis sativus L.)

Elevated CO_2 and high N promote the yield of vegetables interactively, whilst their interactive effects on fruit quality of cucumber(Cucumis sativus L.) are unclear. We studied the effects of three CO_2 concentrations(400 μmol mol–1(ambient), 625 μmol mol–1(moderate) and 1 200 μmol mol–1(high)) and nitrate levels(2 mmol L~(–1)(low), 7 mmol L~(–1)(moderate) and 14 mmol L~(–1)(high)) on fruit quality of cucumber in open top chambers. Compared with ambient CO_2, high CO_2 increased the concentrations of fructose and glucose in fruits and maintained the titratable acidity, resulting in the greater ratio of sugar to acid in moderate N, whilst it had no significant effects on these parameters in high N. Moderate and high CO_2 had no significant effect on starch concentration and decreased dietary fiber concentration by 13 and 18%, nitrate by 31 and 84% and crude protein by 19 and 20% averagely, without interactions with N levels. The decreases in amino acids under high CO_2 were similar, ranging from 10–18%, except for tyrosine(50%). High CO_2 also increased the concentrations of P, K, Ca and Mg but decreased the concentrations of Fe and Zn in low N, whilst high CO_2 maintained the concentrations of P, K, Ca, Mg, Fe, Mn, Cu and Zn in moderate and high N. In conclusion, high CO_2 and moderate N availability can be the best combination for improving the fruit quality of cucumber. The fruit enlargement, carbon transformation and N assimilation are probably the main processes affecting fruit quality under CO_2 enrichment.     

Allelopathic effect of sugar beet (Beta vulgaris) and eucalyptus (Eucalyptus camaldulensis) on seed germination and growth of Portulaca oleracea

Two experiments, a Petri dish assay and a pot experiment were carried out to evaluate possible allelopathic effects of water extracts (0, 10 and 20 g L^?1) of sugar beet (Beta vulgaris) and eucalyptus (Eucalyptus camaldulensis) on germination and growth of purslane (Portulaca oleracea). Results showed that germination percentage of purslane seeds was not inhibited by concentration of water extract of test plants. However, seed vigour and seedling growth strongly influenced by aqueous extracts of test plants. Maximum inhibitions on seedling growth were recorded when using the highest concentration of the aqueous extract (20 g L^?1). It was apparent that sugar beet had a greater inhibitory effect than eucalyptus. Shoot length of purslane seedlings significantly decreased at 10 and 20 g L^?1 aqueous extract concentration of sugar beet by 65.5 and 92.1% respectively compare to control, while eucalyptus decreased seedling shoot length of target weed at 10 and 20 g L^?1 extract concentration by 29.8% and 52.9% respectively. Root length was more affected than shoot so that low aqueous extract concentration (10 g L^?1) of sugar beet and eucalyptus decreased root length of target weed by 79.8% and 46% respectively. Foliar sprays with both 10 and 20 g L^?1 of test plants extracts significantly decrease leaf area, leaves, stem and root dry weight of Portulaca oleracea. Maximum leaf area (1010 cm²) was obtained from the untreated plants (0% extract), while the lowest value (166.6 cm²) occurred with 20 g L^?1 water extract of sugar beet. High aqueous extract concentration (20 g L^?1) of sugar beet decreased leaves, stem and root dry weight of purslane plants by 96%, 86.7% and 91.9% respectively.     

The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce (Lactuca sativa L.)

High nitrate(NO_3~- ) in vegetables, especially in leaf vegetables poses threaten to human health. Selenium(Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies. Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses. However, the influence of exogenous Se on NO_3~- accumulation in hydroponic vegetables is still not clear. In the present study, hydroponic lettuce plants were subjected to six different concentrations(0, 0.1, 0.5, 5, 10 and 50 μmol L–1) of Se as Na2 Se O3. The effects of Se on NO_3~- content, plant growth, and photosynthetic capacity of lettuce(Lactuca sativa L.) were investigated. The results showed that exogenous Se positively decreased NO_3~- content and this effect was concentration-dependent. The lowest NO_3~- content was obtained under 0.5 μmol L–1 Se treatment. The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate(Pn), stomatal conductance(Cs) and the transpiration efficiency(Tr) of lettuce. The transportation and assimilation of NO_3~- and activities of nitrogen metabolism enzymes in lettuce were also analysed. The NO_3~- efflux in the lettuce roots was markedly increased, but the efflux of NO_3~- from the root to the shoot was decreased after treated with exogenous Se. Moreover, Se application stimulated NO_3~- assimilation by enhancing nitrate reductase(NR), nitrite reductase(Ni R), glutamine synthetase(GS) and glutamate synthase enzyme(GOGAT) activities. These results provide direct evidence that exogenous Se shows positive function on decreasing NO_3~- accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce. We suggested that 0.5 μmol L–1 Se can be used to reduce NO_3~- content and increase hydroponic lettuce yield.     

Field identification of morphological and physiological traits in two special mutants with strong tolerance and high sensitivity to drought stress in upland rice(Oryza sativa L.)

The two mutants idr1-1 and 297-28, which were obtained from the radiation mutation of HD297 and IAPAR9, were used as experimental materials in this study for a 2-year(2012 and 2013) experiment about field drought resistance identification in Beijing, China. Key agronomic traits and water-related physiological indexes were observed and measured, including the leaf anti-dead level(LADL), days to heading, plant height, setting percentage, aboveground biomass, leaf water potential(LWP), net photosynthetic rate(Pn) and transpiration rate. The results showed that the mutant idr1-1 that was under drought stress(DS) conditions for 2 years had the highest LADL grades(1.3 and 2.0) among all the materials, and they were 2–3 grades stronger than the wild-type IAPAR9 with an average that was 21.4% higher for the setting percentage than the wild type. Compared with the IAPAR9 for the 2-year average delay in the days to heading and the reduction rates in the plant height, setting percentage, and aboveground biomass under DS compared with the well-watered(WW) treatment, idr1-1 showed 3.2% less delay and 19.1, 16.4, and 6.1% less reduction, respectively. The idr1-1 in the LWP always exhibited the highest performance among all the materials. The Pn of idr1-1 under severe and mild DS comparing with that under WW was slightly decreased and even slightly increased, respectively, leading to an average reduction rate of only 0.92%, which was 26.93% less than that of IAPAR9. Under the severe DS, idr1-1 still showed the highest value of 16.88 μmol CO2 m–2 s–1 among all the materials and was significantly higher than that of IAPAR9(11.66 μmol CO2 m–2 s–1). Furthermore, only idr1-1 had the increased and the highest transpiration rate values(7.6 and 6.04 mmol H2 O m–2 s–1) under both mild and severe DS compared with the values under WW, when the transpiration rate of all the other materials significantly decreased. By contrast, the 297-28 in terms of the LADL grade under DS was the lowest(7.0), and it was four grades weaker than its wildtype HD297 and even one grade weaker than the drought-sensitive paddy rice SN265. For the 2-year average reduction rates in aboveground biomass and plant heights under DS compared with those under the WW, 297-28 was 31.6 and 31.8% higher than HD297, respectively. Meanwhile, 297-28 showed the worst performance for the LWP, Pn, and transpiration rate. These results suggest that idr1-1 might be a superior drought tolerant mutant of upland rice found in China. It has a strong ability to maintain and even enhance leaf transpiration while maintaining a high plant water potential under DS, thus supporting a high Pn and alleviating the delay in agronomic trait development and yield loss effectively. 297-28 is a much more highly drought-sensitive mutant that is even more sensitive than paddy rice varieties. The two mutants could be used as drought tolerance controls for rice germplasm identification and the drought resistant mechanism studies in the future. idr1-1 is also suitable for breeding drought-tolerant and lodging-resistant high-yield rice varieties.     

Evaluating the efficacy of an attenuated Streptococcus equi ssp. zooepidemicus vaccine produced by multi-gene deletion in pathogenicity island SeseCisland_4

Streptococcus equi ssp. zooepidemicus(SEZ) is a pathogen associated with a wild range of animal species. Frequent outbreaks have occurred in recent years in pigs, horses, goats and dogs which is liable to infect humans. There is a lack of efficient vaccines against this disease and the occurrence of antibiotic resistance may render drug therapies ineffective. In this study, gene deletion mutant(ΔSEZ) in pathogenicity islands SeseCisland_4 was constructed. The mutant ΔSEZ had a 52-fold decrease in 50% lethal dose(LD_(50)) and had less capacity to adhere epithelial cells. Importantly, immunization of mice with attenuated vaccine ΔSEZ at the dose of 10~2 colony-forming units(CFU) mL~(–1) elicited a significant humoral antibody response, with an antibody titer of 1:12 800. Therefore, 10~2 CFU mL~(–1) might be used as the appropriate immune dose for the attenuated vaccine ΔSEZ, which provided mice with efficient protection against virulent SEZ. In addition, the hyperimmune sera against 10~2 CFU m L–1 attenuated vaccine ΔSEZ could confer significant protection against virulent SEZ infection in the passive immunization experiment and exhibited efficient bactericidal activity in the whole blood assay. Meanwhile, no viable bacteria was detected in blood when mice were immunized with ΔSEZ at the dose of 10~2 CFU mL~(–1) via hypodermic injection. Thereafter, the mutant ΔSEZ at the dose of 10~2 CFU mL~(–1) could confer significant protection in mice and had less negative effects on host, which could be an effective attenuated vaccine candidate for the prevention of SEZ.     

Effects of sodium benzoate on growth and physiological characteristics of wheat seedlings under compound heavy metal stress

In this study, we investigated the effect of exogenous sodium benzoate on wheat seedlings(Yangmai 16) grown under heavy metal stress. The results showed that 2.4 mmol kg~(–1) of heavy metals significantly inhibited growth and delayed emergence of wheat seedlings. Under compound heavy metal stress, application of 2–4 g L~(–1) sodium benzoate significantly increased(P0.01) chlorophyll content and chlorophyll fluorescence parameters F_v/F_m and F_v/F_o of wheat, compared to the control(water treatment). Further analysis showed that application of 2–4 g L~(–1) sodium benzoate alleviated osmotic stress by promoting the accumulation of osmolytes such as soluble proteins and free proline, increased the activity of superoxide dismutase(SOD) and reduced malondialdehyde content(MDA). In contrast, higher concentrations of sodium benzoate solution(6 g L~(–1)) inhibited the growth of wheat seedlings and even caused damage to seedlings. Correlation analysis showed that when the sodium benzoate concentration was in the range of 1.97–3.12 g L~(–1)(2016) and 1.58–3.27 g L~(–1)(2017), values of chlorophyll and its components, root activity, SOD activity, soluble protein, and free proline content were the highest. When the sodium benzoate concentration was raised to 2.59 g L~(–1)(2016) or 3.02 g L~(–1)(2017), MDA content was the lowest. Ultimately, exogenous sodium benzoate(2–4 g L~(–1)) facilitates root development and improves the root activity of wheat seedlings grown under compound heavy metals stress, thereby effectively alleviating the damage of compound heavy metal stress in wheat seedlings.     

Interactive Effect of GA3, N and P Ameliorate Growth,Seed and Fibre Yield by Enhancing Photosynthetic Capacity and Carbonic Anhydrase Activity of Linseed: A Dual Purpose Crop

Linseed (Linum usitatissimum L.) is an important dual-purpose, industrial crop. Its seeds are used for the extraction of oil and stem for fibres. However, the production of linseed is not going parallel with the increasing demand of its products. The present work was carried out with an aim to find out whether exogenous application of gibberellic acid (GA₃) with or without graded levels of nitrogen (N) and phosphorus (P) could improve the performance of three linseed genotypes Parvati, Shekhar and Shubhra together with minimizing the costly fertilizer input and losses. Four combinations of N and P, viz., 0 mg N+0 mg P kg^?1 soil (N₀P₀), N_13.4P_4.46, N_26.8P_8.94 and N_40.2P_13.4 were constituted. Half dose of each combination was applied basally at the time of sowing and remaining half dose was given at 40 d after sowing (DAS) as foliar spray along with 10^?6 mol L^?1 GA₃. Prior to sowing, the seeds of each linseed genotype were grouped in to two, one group of seeds was soaked in 0 mol L^?1 GA₃ (control) and the other group was soaked in 10^?6 M GA₃ solution, each for 8 hours. Treatments were comprised of (i) 0 mol L^?1 GA₃+N₀P₀ (T₀, control), (ii) 10^?6 mol L^?1 GA₃ + N₁₃₄P₄₄₆ (T₁), (iii) 10^?6 mol L^?1 GA₃+N_26.8P_8.94 (T₂) and (iv) 10^?6 mol L^?1 GA₃+N_40.2P_13.4 (T₃). The crop performance was assessed in terms of growth, physiological and biochemical parameters at 60 and 75 DAS and yield attributes at harvest (175 DAS). The results showed a parallel increase in most of the parameters with increasing levels of N and P. However, application of 10^?6 mol L^?1 GA₃ in association with N_26.8P_8.94 proved best, it enhanced seed yield, oil yield and fibre yield by 83.3, 97.3 and 78.7%, respectively accompanied with increase in net photosynthetic rate, carbonic anhydrase activity and dry matter accumulation. Among the genotypes tested, Shubhra performed best, while Parvati the least for most of the parameters studied. Thus, combined application of 10^?6 mol L^?1 GA₃ plus N_26.8P_8.94 proved best and can be recommended to exploit the linseed as a dual-purpose crop for good yield of seed and fibre.     

Comparison of phenolic profiles and antioxidant activities in skins and pulps of eleven grape cultivars(Vitis vinifera L.)

Eleven grape cultivars were analysed to explore the variety differences of fresh grape phenolic profiles. The results showed that free phenolics were predominant in grape skins and pulps, and showed the higher antioxidant activities than bound. In 11 cultivars, Muscat Kyoho extracts had the highest total phenolic content in skins(10.525 mg GAE g~(–1) FW) and pulps(1.134 mg GAE g~(–1) FW), and exhibited the highest DPPH radical scavening capacity(EC_(50)=11.7 μg mL~(–1)) and oxygen radical absorbance capacity(ORAC) value(190.57 μmol TE g~(–1) FW) of free phenolic in skin. In addition, the most abundant phenolics in grape skins were found to be flavonoids such as kaempferol in Kyoho skin(541.2 μg g~(–1) FW), rutin, catechin and epicatechin in Muscat Kyoho skin(262.3, 86.3 and 70.0 μg g~(–1) FW, respectively). Furthermore, the principal component analysis showed a strong difference of phenolic profiles with the cultivars, existing forms and distributions. Pearson correlation coefficient analysis showed a significant linear correlation between total phenolic content and antioxidant activity(P0.05). Therefore, both skins and pulps were rich sources of bioactive phenolic compounds, and Muscat Kyoho was the ideal source among all samples.     

Study on Mutant Induction of Gladiolus by in vitro Culture of Petals

Petals of Gladiolus 'Rose Supreme' were used to establish regeneration system. Developmental characteristics of petals were observed. A total of 94 plantlets of petal somaclonal line were marked in Mj ...     

Effects of pentoxifylline, platelet activating factor and prostaglandin F 2-alpha on Giant Panda (Ailuropoda melanoleuca) post-thawed sperm in vitro fertilizing capability

Is it possible that Giant Panda (Ailuropoda melanoleuca) post-thawed sperm fertilization is improved with pentoxifylline (PF), platelet activated factor (PAF) and prostaglandin F 2-alpha (PGF_2α)? In our study Giant Panda post-thawed sperm was incubated in Ham’s F-10 medium with different concentration of PF, PAF and PGF_2α under 37°C. The effects of PF, PAF and PGF_2α on Giant Panda post-thawed sperm fertility were evaluated through sperm motility, survival time, sperm membrane integrity, acrosome state and heterospecific egg penetration. The results were that PF, PAF and PGF_2α all can affect Giant Panda post-thawed sperm in vitro fertilizing capability. In the experiment: 1 mg·mL^?1 PF was most suitable for improving Giant Panda post-thawed sperm in vitro fertilizing capability. In the 1 mg·mL^?1 PF group, sperm survival time was (15.33±4.73) h, the heterospecific egg penetration was 51.44% after incubating for 4 hours, the heterospecific egg penetration was 7.49% after incubating for 6 hours. The results of the 1 mg·mL^?1 PF group were significantly higher than those of the control group (P<0.01). The results were also higher than those of the other treatment groups; Treated Giant Panda post-thawed sperm with 50 ng·mL^?1 PAF had a better effect than 100 ng·mL^?1 PAF, but the sperm fertilizing capability was damaged when incubation time exceeded 2 hours; 50 ng·mL^?1 PGF_2α had no significant effect on Giant Panda postthawed sperm, but when the PGF_2α treated concentration was increased, sperm in vitro fertilizing capability decreased because of the damaged motility and declined acrosomal reaction rate. The conclusions suggest that it is possible to improve post-thawed Giant Panda sperm fertility with 1 mg·mL^?1 PF.     

Sodium dehydroacetate treatment prolongs the shelf-life of ‘Kyoho’ grape by regulating oxidative stress and DNA methylation

In this study, we tested the ability of sodium dehydroacetate (SD) to extend the shelf-life of ‘Kyoho’ grape. Among the different concentrations of SD tested (0, 0.01, 0.1 and 1.0 mmol L^–1), 0.01 mmol L^–1 SD was the most effective in prolonging the shelf-life of ‘Kyoho’ grape. Compared with the control, the weight loss rate, browning index and hydrogen peroxide (H₂O₂) and malonaldehyde contents were significantly lower in the 0.01 mmol L^–1 SD treatment, whereas the healthy berry rate, berry firmness, total soluble solids (TSS) content, ascorbic acid content and superoxide dismutase (SOD) activity were significantly higher. In addition, an analysis of ‘Kyoho’ grape DNA using methylation sensitive amplification polymorphism (MSAP) markers showed that the average DNA methylation level was significantly higher in the 0.01 mmol L^–1 SD treatment than in the control. Together, these results indicate that 0.01 mmol L^–1 SD could be used to extend the shelf-life of ‘Kyoho’ grape. Moreover, a strong connection between reactive oxygen species (ROS) metabolism and DNA methylation change during storage was revealed.     

Drying characteristics,functional properties and in vitro digestion of purple potato slices dried by different methods

The drying characteristics, physico-chemical and functional properties, as well as starch digestibility, of purple potato slices dried using different methods (such as, vacuum freeze-drying, VFD; hot-air drying, HAD; air-impingement jet drying, AIJD; and far-infrared assisted heat-pump drying, FIHPD) were investigated. Drying rate was the highest (3.0 g 100 g^?1 min^?1) using AIJD, followed by FIHPD and HAD, and the rate of VFD was the lowest one (0.3 g 100 g^?1 min^?1). Drying data were fitted to 12 thin-layer drying models, with the Midilli model giving the best predictions. Moreover, AIJD showed higher diffusivity (5.5×10^?10 m² s^?1) and energy efficiency (55 J g^?1) than any other drying method used in this study. With reference to the samples dried by VFD, the starch granules of the samples obtained by HAD, FIHPD, and AIJD exhibited different extent of disruption, which significantly increased their water absorption capacity, swelling power, and in vitro digestibility, but decreased the peak viscosity. The sample resulting from AIJD had the greatest water absorption capacity (7.9 g g^?1) and solubility (21.6%), but the smallest syneresis rate (48%). Good correlation coefficients (R²>0.98) implied that the pseudo-first order kinetic model adequately described the rate and extent of starch digestion of dried potato flours. Samples from AIJD and FIHPD showed the highest digestibility percentages, reaching to 72.4 and 72.5%. Based on the drying rate, specific energy consumption, functional properties and digestibility, AIJD appeared to be quite effective and suitable to be transferred on the industry scale.     

不同磷浓度对土壤理化性质及防风生长和药材品质的影响

【目的】探讨不同磷浓度处理对土壤特性及防风Saposhnikovia divaricata生长状况、色原酮含量的影响,为防风人工栽培的技术策略制定以及防风对低磷胁迫响应机制的研究提供理论依据。【方法】以2年生防风为材料,设置营养液磷（NH₄H₂PO₄）浓度分别为1.0、0.1和0 （无磷） mmol/L,分别在30、60、90 d时测定土壤理化性质及防风生长特性和4种色原酮总含量,分析不同磷浓度处理防风各指标与4种色原酮总含量的关系。【结果】无磷处理下,2年生防风根粗、根生物量在整个处理期间均低于1.0 mmol·L^-1磷处理,根长在90 d时显著高于1.0和0.1 mmol·L^-1磷处理;土壤pH在60 d后表现为1.0 mmol·L^-1磷处理显著高于0.1 mmol·L^-1和无磷处理;土壤有机质含量在整个试验期表现为1.0和0.1 mmol·L^-1磷处理显著低于无磷处理;90 d时,无磷处理的土壤碱解氮含量显...     

Postharvest responses of hydroponically grown lettuce varieties to nitrogen application rate

Limited information is available on the influence of preharvest N application rates on postharvest quality of different lettuce genotypes. Two green leafy lettuce(Multigreen 1 and Multigreen 3) and red leafy lettuce(Multired 4) were grown in gravel film technique and fertigated with five different N application rates: 60, 90, 120, 150 and 180 mg L~(–1). The 120 mg L~(–1) N application is commercially recommended for lettuce. After harvest, lettuce samples were packed in a bioriented poly propylene packaging(5% O_2 and 5% CO_2) and held at 5°C and 85% RH for 3, 6, 9 and 12 days. The genotypes, preharvest N application rates and storage time affected the leaf colour coordinates, phenolic acids(dicaffeoyltataric acid, caffeoyl tartaric acid, 3-caffeoylquinic acid and 3,4-dihydroxycinnamic acid) and browning enzyme activities(phenylalanine ammonia-lyase(PAL), polyphenol oxidase(PPO) and peroxidase(POD)). Lower rates of N application at preharvest stage showed higher weight loss with the storage time increasing in Multigreen 3. In Multigreen 1, colour coordinate b* value decreased remarkably with N application rates from 60 to 120 mg L~(–1) due to the onset of browning during storage. While in Multigreen 3 and N application higher than 60 mg L~(–1) influenced the decrease in b* value. Browning occurred due to the increased activity of PAL enzyme and the availability of the substrates caftaric, chlorogenic, caffeic acids, PPO activity and production of browning pigments due to the activity of POD. Higher, N application rates(120 mg L~(–1)) influenced the browning mechanism and showed brownish red leaves in Multired 4 during storage. Higher ascorbic acid concentration played a role in reducing the onset of browning in the fresh cuts leaves of Mulitired 4 and Multigreen 3 fertilized with lower preharvest lower N application rates(120 mg L~(–1)). Preharvest N application at 90 mg L~(–1) retained the colour, ascorbic acid content and the phenolic acid components and extended the shelf life of Multired 4 lettuce up to 6 days.