Green Leaf Lettuce Research Articles

Microbiological Quality of Fresh Vegetables and Fruits Collected from Supermarkets in Istanbul, Turkey

Two hundred sixty one samples, collected from supermarkets in Istanbul, Turkey. All samples were analysed for aerobic mesophilic bacterial counts (AMC), aerobic psychrotrophic bacterial counts (APC), enumeration of yeasts and moulds (YM), coliforms, Escherichia coli and detection of Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, thermotolerant Campylobacter spp. AMC ranged from 2.95 to 3.75 log10 CFU/g. APC ranged from 0 to 3.55 log10 CFU/g. The highest counts of coliforms were found in carrot, spinach, green leaf lettuce, cos lettuce and iceberg lettuce. The highest counts of YM were found in tomato, spinach, green leaf lettuce, cos lettuce and iceberg lettuce. Green leaf lettuces, cos lettuces, iceberg lettuces, spinach and carrot were highly contaminated with aerobic mesophilic (3.6 log10 CFU/g), psychrotrophic microorganisms (3.4 log10 CFU/g), and showed a high incidence of E.coli (41.77% of samples). Of the samples analysed, 10 (3.83%) were Salmonella spp. positive and 17 (6.51%) were thermotolerant Campylobacter spp. positive. None of the samples was positive for Escherichia coli O157:H7 and Listeria monocytogenes. Fresh vegetables and fruits, sold in Istanbul, Turkey, are needed to control foodborne pathogens especially Salmonellosis and Campylobacteriosis.

완전제어형 식물공장에서 광원, 광질에 따른 엽채류 6종의 생육반응

This study was conducted to evaluate the growth response of economical six leafy vegetables that are crown daisy, pak-choi and four kinds of lettuce (Red leaf lettuce, Green leaf lettuce, Head lettuce, Romaine lettuce) by light treatment of LED in plant factory. The light treatments were composed of red, blue, red+farred, red+blue, red+blue+white LEDs, irradiation time ratio of the red and blue LED per minute (1 : 1, 2 : 1, 5 : 1, 10 : 1), and duty ratio of mixed light (100%, 99%, 97%). The following results were obtained in different LED light sources treatments: Shoot biomass and S/R ratio of romaine lettuce were the highest under mixed red+blue LEDs. S/R ratio of head lettuce was higher under mixed red+blue+white LEDs than red+blue LEDs. The others showed no difference in LED light treatment. Shoot biomass, total biomass and S/R ratio of green lettuce, head lettuce and pak-choi were highest in the higher red ratio (5: 1) on irradiation time of red: blue LED ratios. By the different duty ratio (red+blue and red+blue+white LEDs), Under the mixed light of red+blue, shoot and root biomass of crown daisy and romaine lettuce were high in duty ratio of 100% and 99%, and S/R ratio was highest in all the 6 kinds in duty ratio of 97%. All the 6 kinds showed a fine growth state in low duty ratio (97%). Green lettuce, romaine lettuce and pak-choi showed relatively high shoot biomass and total biomass in low duty ratio of 97% under the mixed light of red+blue+white. S/R ratio of romaine lettuce and head lettuce were highest in the duty ratio of 97% with red+blue+white LEDs. Thus, we can cultivate stably without reference to external factors, if we use appropriate light sources and light quality in closed-type plant factory.

Leaf Shape, Growth, and Antioxidant Phenolic Compounds of Two Lettuce Cultivars Grown under Various Combinations of Blue and Red Light-emitting Diodes

Light-emitting diodes (LEDs) of short wavelength ranges are being developed as light sources in closed-type plant production systems. Among the various wavelengths, red and blue lights are known to be effective for enhancing plant photosynthesis. In this study, we determined the effects of blue and red LED ratios on leaf shape, plant growth, and the accumulation of antioxidant phenolic compounds of a red leaf lettuce (Lactuca sativa L. ‘Sunmang’) and a green leaf lettuce (Lactuca sativa L. ‘Grand Rapid TBR’). Lettuce seedlings grown under normal growth conditions (20 °C, fluorescent lamp + high-pressure sodium lamp 177 ± 5 μmol·m−2·s−1, 12-hour photoperiod) for 18 days were transferred into growth chambers that were set at 20 °C and equipped with various combinations of blue (456 nm) and red (655 nm) LEDs [blue:red = 0:100 (0 B), 13:87 (13 B), 26:74 (26 B), 35:65 (35 B), 47:53 (47 B) or 59:41 (59 B)] under the same light intensity and photoperiod (171 ± 7 μmol·m−2·s−1, 12-hour photoperiod). Leaf width, leaf length, leaf area, fresh and dry weights of shoots and roots, chlorophyll content (SPAD value), total phenolic concentration, total flavonoid concentration, and antioxidant capacity were measured at 2 and 4 weeks after the onset of LED treatment. The leaf shape indices (leaf length/leaf width) of the two lettuce cultivars subjected to blue LEDs treatment were similar to the control, regardless of the blue-to-red ratio during the entire growth stage. However, 0 B (100% red LED) induced a significantly higher leaf shape index, which represents elongated leaf shape, compared with the other treatments. Increasing blue LED levels negatively affected lettuce growth. Most growth characteristics (such as the fresh and dry weights of shoots and leaf area) were highest under 0 B for both cultivars compared with all other LED treatments. For red and green leaf lettuce cultivar plants, shoot fresh weight under 0 B was 4.3 and 4.1 times higher compared with that under 59 B after 4 weeks of LED treatment, respectively. In contrast, the accumulation of chlorophyll, phenolics (including flavonoids), and antioxidants in both red and green leaf lettuce showed an opposite trend compared with that observed for growth. The SPAD value (chlorophyll content), total phenolic concentration, total flavonoid concentration, and antioxidant capacity of lettuces grown under high ratios of blue LED (such as 59 B, 47 B, and 35 B) were significantly higher compared with 0 B or control conditions. Thus, this study indicates that the ratio of blue to red LEDs is important for the morphology, growth, and phenolic compounds with antioxidant properties in the two lettuce cultivars tested.

Lettuce production and antioxidant capacity are differentially modified by salt stress and light intensity under ambient and elevated CO2

As a consequence of the increasing importance of vegetables in the human diet, there is an interest in enhancing both the productivity and quality of vegetables. A number of factors, including plant genotype and environmental growing conditions, can impact the production and quality of vegetables. The objective of this study was to determine whether elevated CO2, salinity, or high light treatments assayed individually, or salinity or high light in combination with elevated CO2, increased biomass production and antioxidant capacity in two lettuce cultivars. Elevated CO2 and its combination with salinity or high light increased biomass production in both cultivars, while high light treatment alone increased production in green-leaf lettuce but not in red-leaf lettuce. On the other hand, elevated CO2 and its combination with salinity or high light increased the antioxidant capacity of both cultivars, while high light treatment alone increased the antioxidant capacity of red-leaf lettuce, but not of green-leaf lettuce.

Biocontrol ofEscherichia coliO157

The effect of a bacteriophage cocktail (EcoShield™) that is specific against Escherichia coli O157:H7 was evaluated against a nalidixic acid-resistant enterohemorrhagic E. coli O157:H7 RM4407 (EHEC) strain on leafy greens stored under either (1) ambient air or (2) modified atmosphere (MA; 5% O2/35% CO2/60% N2). Pieces (~2 × 2 cm2) of leafy greens (lettuce and spinach) inoculated with 4.5 log CFU/cm2 EHEC were sprayed with EcoShield™ (6.5 log PFU/cm2). Samples were stored at 4 or 10°C for up to 15 d. On spinach, the level of EHEC declined by 2.38 and 2.49 log CFU/cm2 at 4 and 10°C, respectively, 30 min after phage application (p ≤ 0.05). EcoShield™ was also effective in reducing EHEC on the surface of green leaf lettuce stored at 4°C by 2.49 and 3.28 log units in 30 min and 2 h, respectively (p ≤ 0.05). At 4°C under atmospheric air, the phage cocktail significantly (p ≤ 0.05) lowered the EHEC counts in one day by 1.19, 3.21 and 3.25 log CFU/cm2 on spinach, green leaf and romaine lettuce, respectively compared with control (no bacteriophage) treatments. When stored under MA at 4°C, phages reduced (p ≤ 0.05) EHEC populations by 2.18, 3.50 and 3.13 log CFU/cm2, on spinach, green leaf and romaine lettuce. At 10°C, EHEC reductions under atmospheric air storage were 1.99, 3.90 and 3.99 log CFU/cm2 (p ≤ 0.05), while population reductions under MA were 3.08, 3.89 and 4.34 logs on spinach, green leaf and romaine lettuce, respectively, compared with controls (p ≤ 0.05). The results of this study showed that bacteriophages were effective in reducing the levels of E. coli O157:H7 on fresh leafy produce, and that the reduction was further improved when produce was stored under the MA conditions.

Predicting perchlorate uptake in greenhouse lettuce from perchlorate, nitrate, and chloride irrigation water concentrations.

Perchlorate (ClO) has been detected in edible leafy vegetables irrigated with Colorado River water. The primary concern has been the ClO concentration in lettuce ( L. var. L.). There has been a limited number of studies on ClO uptake, but the interactive effect of other anions on ClO uptake is not known in detail. We conducted a greenhouse ClO uptake experiment using two types of lettuce (iceberg and butterhead) to investigate the interaction of uptake of ClO, Cl, and NO on ClO uptake under controlled conditions. We examined three concentrations of ClO, 40, 220, and 400 nmol/L; Cl at 2.5, 13.75, and 25 mmol/L; and NO at 2, 11, and 20 mmol/L. Perchlorate was taken up the most in lettuce when ClO was the greatest and NO and Cl were lowest in concentration in the irrigation water. More ClO was detected in leafy material than in root tissue. In general, the outer leaves of iceberg and butterhead lettuce contained more ClO than did the inner leaves. The results indicate that selective ClO uptake occurs for green leaf lettuce. A predictive model was developed to describe the ClO concentration in lettuce as related to the Cl, NO, and ClO concentration in the irrigation water. Research results can be utilized to elucidate the effect of salts on the accumulation and uptake of ClO by edible leafy vegetables.

단색 발광다이오드에서 자란 축면상추 두 품종의 엽형, 생장 및 기능성 물질

Abstract. As an artificial light source, light-emitting diode (LED) with a short wavelength range can be used in closed-type plant production systems. Among various wavelength ranges in visible light, individual light spectra induce distinguishing influences on plant growth and development. In this study, we determined the effects of monochromatic LEDs on leaf shape index, growth and the accumulation of phytochemicals in a red leaf lettuce ( Lactuca sativa L. ‘Sunmang’) and a green leaf lettuce ( Lactuca sativa L. ‘Grand rapid TBR’). Lettuce seedlings grown under normal grow ing conditions (20 ℃, fluorescent lamp + high pressure sodium lamp, 130 ± 5 µmol ･m -2 ･s -1 , 12 hours photoperiod) for 18 days were transferred into incubators at 20 ℃ equipped with various monochromatic LEDs (blue LED, 456 nm; green LED, 518 nm; red LED, 654 nm; white LED, 456 nm + 558 nm) under the same light intensity and photoperiod (130 ± 7 µmol ･m -2 ･s -1 , 12 hours photoperiod). Leaf leng th, leaf width, leaf area, fresh and dry weights of shoots and roots, shoot/root ratio, SPAD value, total phenolic concentration, antioxidant capacity, and the expression of a key gene involved in the biosynthesis of phenolic compounds, phenylalanine ammonia-lyase (PAL), were measured at 9 and 23 days after transplanting. The leaf shape indexes of both lettuce cultivars subjected to blue or white LEDs were similar with those of control during whole growth stage. However, red and green LEDs induced significantly higher leaf shape index than the other treatments. The green LED had a negative impact on the lettuce growth. Most of growth characteristics such as fresh and dry weights of shoots and leaf area were the highest in both cultivars subjected to red LED treatment. In case of red leaf lettuce plants, shoot fresh weight under red LED was 3.8 times higher than that under green LED at 23 days after transplanting. In contrast, the accumulation of chlorophyll, phenolics including antioxidants in lettuce plants showed an opposite trend compared with growth. SPAD value, total phenolic concentration, and antioxidant capacity of lettuce grown under blue LED were significantly higher than those under other LED treatments. In addition, PA L gene was remarkably activated by blue LED at 9 days after transplanting. Thus , this study suggested that the light quality using LEDs is a crucial factor for morphology, growth, and phytochemicals of two lettuce cultivars.

Effectiveness of arbuscular mycorrhizal fungi (AMF) for inducing the accumulation of major carotenoids, chlorophylls and tocopherol in green and red leaf lettuces.

Previous studies demonstrated that arbuscular mycorrhizal fungi (AMF) can induce the accumulation of carotenoids, phenolics, anthocyanins and some mineral nutrients in leaves of lettuce (Lactuca sativa L.) thus enhancing its nutritional quality. Our objectives were to know which carotenoids were the most accumulated in leaves of mycorrhizal lettuces and to assess the effect of AMF on tocopherols' levels in leaves of lettuce plants. AMF always enhanced growth and, in most cases, increased the levels of all major carotenoids, chlorophylls and tocopherols in green and red leaf lettuces. Since these molecules are also important nutraceuticals, mycorrhization emerges as reliable technique to enhance the nutritional value of edible vegetables. These results are compared with other methods developed to improve nutritional quality.

Digital Image Analysis to Supplement Direct Measures of Lettuce Biomass

Plant growth and biomass assessments are required in production and research. Such assessments are followed by major decisions (e.g., harvest timing) that channel resources and influence outcomes. In research, resources required to assess crop status affect other aspects of experimentation and, therefore, discovery. Destructive harvests are important because they influence treatment selection, replicate number and size, and the opportunity for true repeated measures. This work sought to establish the limits to which image acquisition and analysis may replace standard, destructive measures of fresh lettuce biomass. Outdoor, high tunnel, and greenhouse plantings of three cultivars of red and green leaf lettuce (Lactuca sativa) were direct-seeded in raised beds and plastic trays in spring, summer, and fall seasons in 2009–10 in Wooster, OH. Overhead images (624 in total) were captured at specific time points after seeding using handheld and tripod-mounted commercial digital cameras. Fresh weight and leaf area of destructive plant samples within the digital images were also collected. Images were analyzed using user-defined settings in WinCAM software (Regent Instruments, Quebec, QC, Canada). A reference grid captured within each image allowed for the calculation of crop canopy cover (percent of two-dimensional image area covered by leaves). Calculations of canopy cover require differentiating leaves and rooting medium by color. The rooting medium was dark in color, and differentiating red leaves against this background was less reliable than differentiating green leaves from background. Nevertheless, in samples collected in the greenhouse 7 to 16 days after sowing (DAS), significant correlations (r) of 0.85 to 0.96 (P < 0.05) were observed between measures of canopy cover calculated by image analysis software and leaf area obtained with a leaf area meter on harvested plant material. In outdoor and high tunnel plots 16 to 30 DAS, correlation coefficients between direct measures of plant biomass and WinCAM estimates of canopy cover were 0.71 to 0.95 (P < 0.0001). We conclude that digital image analysis may be useful in real-time, nondestructive assessments of early stage leaf lettuce canopy development, particularly when the leaf area index (LAI) is less than one and settings are dominated by green leaves.

Green Leaf Lettuce Breeding Lines with Resistance to Corky Root, 06-831 and 06-833

Corky root of lettuce (Lactuca sativa L.) has been found in major lettuce-producing regions of the world, including North America, Western Europe, Australia, and New Zealand. Roots of infected plants develop yellow to brown lesions that later become longitudinal corky ridges. Yield losses from reduced head size can reach 30% to 70% in severely infested fields in California and Florida (van Bruggen, 1997). The pathogen most commonly isolated from diseased roots is the bacterium Sphingomonas suberifaciens (Yabuuchi et al., 1999), formerly Rhizomonas suberifaciens, although several other bacterial species have also been isolated (van Bruggen, 1997). The incidence of corky root can be reduced by soil fumigation (O’Brien and van Bruggen, 1990) and by using lettuce transplants instead of directseeding (van Bruggen and Rubatzky, 1992). However, these practices may not be economically feasible for the Salinas Valley, CA, the major lettuce production area in the United States (Patterson et al., 1986). The use of cultivars resistant to S. suberifaciens has been an important management strategy for corky root. The resistance to corky root is controlled by a recessive allele (cor) at a single locus (Brown and Michelmore,1988), which has been deployed in most resistant lettuce cultivars. Although corky root resistance has been transferred into many crisphead lettuce cultivars, there are few leaf lettuce varieties with the resistance, especially for publicly released cultivars. With increasing consumption and production of leaf lettuce, there is a need for public germplasm that facilitates the research and development of new cultivars and germplasm. In this article, we describe two green leaf breeding lines with resistance to corky root and adaptation to the major lettuce production areas of the central coast of California. Origin

Comparison between Hydroponically and Conventionally and Organically Grown Lettuces for Taste, Odor, Visual Quality and Texture: A Pilot Study

Hydroponic production of vegetables is becoming more common. In this study hydroponic lettuce, grown by a local distributor, and conventionally and organically field-grown lettuce, purchased at local retail stores were compared by descriptive analysis for taste, odor, visual quality and texture. Five lettuce varieties were compared; Romaine, Green Leaf, Red Leaf, Butter, and Common lettuce. A twenty-three member sensory panel randomly rated the lettuce using a 5 point scale or a 3 point scale for taste, odor, visual quality and texture. Analysis of variance (ANOVA) was performed for each lettuce variety with comparison between those hydroponically, organically or conventionally grown. Overall, panel members equally like the different lettuce samples. The results showed that for each of the five varieties of let-tuces, all lettuces were perceived to be equal in their sensory evaluation for locally grown hydroponic lettuce or pur-chased from local grocery outlets as organically or conventionally grown.

Whole-leaf wash improves chlorine efficacy for microbial reduction and prevents pathogen cross-contamination during fresh-cut lettuce processing.

Currently, most fresh-cut processing facilities in the United States use chlorinated water or other sanitizer solutions for microbial reduction after lettuce is cut. Freshly cut lettuce releases significant amounts of organic matter that negatively impacts the effectiveness of chlorine or other sanitizers for microbial reduction. The objective of this study is to evaluate whether a sanitizer wash before cutting improves microbial reduction efficacy compared to a traditional postcutting sanitizer wash. Romaine lettuce leaves were quantitatively inoculated with E. coli O157:H7 strains and washed in chlorinated water before or after cutting, and E. coli O157:H7 cells that survived the washing process were enumerated to determine the effectiveness of microbial reduction for the 2 cutting and washing sequences. Whole-leaf washing in chlorinated water improved pathogen reduction by approximately 1 log unit over traditional cut-leaf sanitization. Similar improvement in the reduction of background microflora was also observed. Inoculated "Lollo Rossa" red lettuce leaves were mixed with noninoculated Green-Leaf lettuce leaves to evaluate pathogen cross-contamination during processing. High level (96.7% subsamples, average MPN 0.6 log CFU/g) of cross-contamination of noninoculated green leaves by inoculated red leaves was observed when mixed lettuce leaves were cut prior to washing in chlorinated water. In contrast, cross-contamination of noninoculated green leaves was significantly reduced (3.3% of subsamples, average MPN <or=-0.3 log CFU/g) when the mixed leaves were washed in chlorinated water before cutting. This result suggests that whole-leaf sanitizing washes could be a practical strategy for enhancing the efficacy of chlorine washes for pathogen reduction and cross-contamination prevention.

06-857, a Green Leaf Lettuce Breeding Line with Resistance to Leafminer and Lettuce Mosaic Virus

This paper describes a green leaf lettuce breeding line with combined resistance to leafminers (Liriomyza langei [L. huidobrensis]) and Lettuce mosaic virus (LMV), which is adapted to the major lettuce production areas of the central coast of California, USA. The breeding line 06-857 was derived from a cross between crisphead cultivar 'Salinas 88' that has mo-1e (mo12) alleles, and red leaf cultivar 'Lolla Rossa' that showed low leafminer sting density in previous screening experiments.

Effects of different sanitizing treatments on biofilms and attachment of Escherichia coli and Listeria monocytogenes on green leaf lettuce

The effects of ozone (2 mg/L), chlorine (100 mg/L) and organic acid (0.25 g/100 g citric acid plus 0.50 g/100 g ascorbic acid) treatments at 10 °C for 2 min on the removal of Escherichia coli and Listeria monocytogenes cells embedded inside biofilms on the surface of lettuce leaves were studied. None of the sanitizing treatments were found effective in removing the bacterial biofilms. Initiation of biofilms was observed after 24 h of incubation. Bacterial cells appeared as individual cells, rather than clusters after 6 h incubation, thus 99.9% reductions in both E. coli and L. monocytogenes counts were achieved with all the three treatments. However, after 48 h incubation, none of the treatments resulted in higher than 90% reduction in microbial counts. Biofilm formation was demonstrated for the 48 h incubated samples with SEM images.

Understanding E. coli internalization in lettuce leaves for optimization of irradiation treatment

Irradiation penetrates food tissues and effectively reduces the number of food microorganisms in fresh produce, but the efficacy of the process against internalized bacteria is unknown. The objective of this study was to understand the mechanisms of pathogen colonization of plants relative to lettuce leaf structures so that radiation treatment of fresh leafy vegetables can be optimized. Leaves of iceberg, Boston, green leaf, and red leaf lettuces were cut into pieces, submerged in a cocktail mixture of two isolates of Escherichia coli (Rifampicin resistant), and subjected to a vacuum perfusion process to force the bacterial cells into the intercellular spaces in the leaves. Sixty bags containing 20 g of lettuce each were tested. The inoculated leaves were gamma irradiated (Lanthanum-140, 0.16 kGy/h) at 0.25–1.0-kGy (surface dose values), with increments of 0.25 kGy at 15 °C. Microbial analysis was performed right after irradiation, including non-irradiated leaf pieces (controls). A dose uniformity ratio (max/min dose) of 2.8 was set to confirm the effect of non-uniform dose distribution. Calculated D 10-values varied between 48 and 62% based on the dose distribution from the entrance dose. However, despite the subtle differences in composition and structure among the four lettuce varieties, the D 10-values were not significantly different. Irradiation up to 1.0-kGy resulted in 3–4-log reduction of internalized E. coli on the lettuce leaves. The SEM images suggest that the contamination sites of pathogens in leafy vegetables are mainly localized on crevices and into the stomata. This study shows that irradiation effectively reduces viable E. coli cells internalized in lettuce, and decontamination is not influenced by lettuce variety. Ionizing irradiation effectively reduced the population of internalized pathogen in a dose-dependent manner and could be used as an effective killing step to mitigate the risk of foodborne disease outbreaks.

Retention of Quality and Nutritional Value of 13 Fresh‐Cut Vegetables Treated with Low‐Dose Radiation

Improving the microbial safety while maintaining quality of fresh fruits and vegetables will increase consumer confidence in fresh produce. This study was conducted to investigate the effects of irradiation at 1 kGy, a dose that potentially inactivates E. coli O157:H7 by 5 logs, on the quality of 13 common fresh-cut vegetables: iceberg, romaine, green and red leaf lettuce, spinach, tomato, cilantro, parsley, green onion, carrot, broccoli, red cabbage, and celery. The results showed that the appearance of irradiated samples was similar to the nonirradiated ones except that irradiated carrots, celery, cilantro, and green onions had higher appearance scores than corresponding nonirradiated vegetables. There was no difference in the instrumental texture between irradiated samples and nonirradiated ones. The aroma of several irradiated vegetables was significantly better than controls after 14-d storage, because these control samples decayed or senesced. The 1 kGy irradiation did not affect vitamin C content of most vegetables; however, irradiated green and red leaf lettuce had 24% to 53% lower vitamin C contents than the controls. Our results suggest that most fresh-cut fruits and vegetables tested can tolerate up to 1 kGy irradiation without significant losses in any of the quality attributes.

Optimization of ozone treatment of fresh-cut green leaf lettuce

The optimization of ozone treatment for fresh-cut green leaf lettuce was studied to determine the effects of ozone concentration (0.5–4.5 ppm) and exposure time (0.5–3.5 min) on Listeria monocytogenes counts and the overall visual quality of lettuce. Prior to the optimization study, the effect of temperature on the efficacy of ozone treatment was evaluated in the range of 10–26 °C. No significant effect of temperature on the efficacy of ozone treatment was observed. The quality and safety of lettuce samples treated at the determined optimum ozonation condition (2 ppm) were compared with the chlorinated water (100 ppm), organic acid (0.25 g/100 g citric acid plus 0.50 g/100 g ascorbic acid), and water treatments applied at 10 °C for 2 min. Samples were stored at 4 °C for 12 days. Analysis include aerobic mesophilic count, Enterobactericeae, psychrotrophic bacteria, vitamin C, β-carotene, and sensory quality. Ozone treatment was found to be better than the chlorine and organic acid treatments in maintaining the sensory quality.

Effects of common soil anions and pH on the uptake and accumulation of perchlorate in lettuce

A mechanistic understanding of perchlorate ( $$ {\text{ClO}}^{ - }_{4} $$ ) entry into plants is important for establishing the human health risk associated with consumption of contaminated produce and for assessing the effectiveness of $$ {\text{ClO}}^{ - }_{4} $$ phytoremediation. To determine whether common soil anions affect $$ {\text{ClO}}^{ - }_{4} $$ uptake and accumulation in higher plants, a series of competition experiments using lettuce (Lactuca sativa L.) were conducted between $$ {\text{ClO}}^{ - }_{4} $$ (50 nM) and $$ {\text{NO}}^{ - }_{3} $$ (4–12 mM), $$ {\text{SO}}^{{2 - }}_{4} $$ (1–10 mM), or Cl− (5–15 mM) in hydroponic solution. The effects of $$ {\text{HCO}}^{ - }_{3} $$ (0–5 mM) and pH (5.5–7.5) on $$ {\text{ClO}}^{ - }_{4} $$ uptake were also examined. Increasing $$ {\text{NO}}^{ - }_{3} $$ in solution significantly reduced the amount of $$ {\text{ClO}}^{ - }_{4} $$ taken up by green leaf, butter head, and crisphead lettuces. Sulfate and Cl− had no significant effects on $$ {\text{ClO}}^{ - }_{4} $$ uptake in lettuce over the concentrations tested. Increasing pH significantly reduced the amount of $$ {\text{ClO}}^{ - }_{4} $$ taken up by crisphead and green leaf lettuces, whereas increasing $$ {\text{HCO}}^{ - }_{3} $$ significantly reduced $$ {\text{ClO}}^{ - }_{4} $$ uptake in butter head lettuce. The inhibition by $$ {\text{NO}}^{ - }_{3} $$ across all lettuce genotypes suggests that $$ {\text{ClO}}^{ - }_{4} $$ may share an ion carrier with $$ {\text{NO}}^{ - }_{3} $$ , and the decrease in uptake with increasing pH or $$ {\text{HCO}}^{ - }_{3} $$ provides macroscopic evidence for $$ {{\text{ClO}}^{ - }_{4} } \mathord{\left/ {\vphantom {{{\text{ClO}}^{ - }_{4} } {{\text{H}}^{ + } }}} \right. \kern-\nulldelimiterspace} {{\text{H}}^{ + } } $$ cotransport across the plasma membrane.

PRODUÇÃO DE ALFACE NO SISTEMA ORGÂNICO EM SUCESSÃO A AVEIA PRETA, SOBRE A PALHA, E DIFERENTES COBERTURAS DO SOLO

Objetivou-se avaliar o efeito da cobertura do solo com aveia preta e manutenção da palha sobre o terreno, bem como cobertura do solo com filme de polietileno preto, sobre o desenvolvimento, produção e teor de nitrogênio de alface cultivada no sistema orgânico. Definiram-se cinco manejos da cobertura do solo: sem cobertura, coberto com filme de polietileno preto, coberto com aveia deitada, coberto com aveia ceifada e coberto com aveia na sua forma natural, para o cultivo de três cultivares de alface. O experimento foi conduzido na Associação Brasileira de Agricultura Biodinâmica (ABD), Botucatu - SP, em delineamento experimental de blocos ao acaso, com quatro repetições, em análise estatística com parcelas subdivididas. Concluiu-se que, as coberturas do solo promoveram melhor desenvolvimento e maior produção de alface quando comparadas ao solo sem cobertura. Entre os manejos da cobertura do solo, o solo coberto com plástico preto promoveu a maior produção de alface, e entre os manejos da palha, a alface lisa apresentou maior produção no solo coberto com aveia deitada, a crespa nos solos cobertos com aveia deitada e aveia em pé, e a americana nos solos cobertos com aveia ceifada e aveia em pé.

Effects of Ascorbic Acid Applied by Two Hydrocooling Methods on Physical and Chemical Properties of Green Leaf Lettuce Stored at 5°C

ABSTRACT: The effect of ascorbic acid applied by 2 hydrocooling methods on chemical and physical properties of‘Waldmann's’dark green leaf lettuce (Lactuca sativa L.) during cold storage was evaluated. Lettuce was immersed (in 1% ascorbic acid or tap water) or sprayed (with 1% ascorbic acid or tap water) or left untreated (control). Treatment solutions for immersion or spraying were applied at 5°C for 2 min. Afterward, lettuce was packaged in moisture impermeable plastic bags and stored at 5°C for up to 21 d. Analytical assays included total ascorbate content, 2,2′-azinobis (3-ethylbenz-thiazoline-6-sulphonic acid) (ABTS˙+) Trolox equivalent antioxidant capacity, total phenolic content, relative water content and instrumental color. Lettuce was analyzed at 5 time intervals: before treatment application and at days 1, 7, 14, and 21 of storage time. Hydrocooling of leaf lettuce by immersion or spraying using 1% ascorbic acid solution increased total ascorbate content for up to 7 d, with an increase of more than 300% in total ascorbate content on day 1 compared with its initial value before treatments. However, the ABTS antioxidant capacity of leaf lettuce did not increase in ascorbic acid treated lettuce even though total ascorbate content increased. Ascorbic acid immersion was the only treatment that maintained the relative water content of leaf lettuce for 21 d. Further experimentation with the application of ascorbic acid during hydrocooling is needed to assess its usefulness as a processing treatment.