Chlorophyll Content Of Lettuce Research Articles

The Effect of Exogenous Selenium Supplementation on the Nutritional Value and Shelf Life of Lettuce

Lettuce (Lactuca sativa) is rich in vitamins, minerals, and bioactive components, serving as an important source of selenium (Se) intake for humans. This study investigated the effects of Se treatment on lettuce using different concentrations of sodium selenite (Na2SeO3), focusing on biomass, physiological indicators, nutritional composition, and physiological changes during storage. Through correlation analysis of the transcriptome and Se species, the absorption and conversion mechanisms of Se in lettuce were revealed. The results showed that Se treatment initially increased the chlorophyll content in lettuce, followed by a decrease. Soluble sugar, soluble protein, total phenols, and anthocyanins increased at low Se concentrations but decreased at high concentrations. Flavonoid content decreased only at 1 mg/L Se, while other treatments were higher than the control group. GSH content and superoxide dismutase, catalase, and peroxidase activities initially increased and then decreased, while malondialdehyde (MDA) content first decreased and then increased. Five Se species, including Se (IV), Se (VI), selenocysteine (SeCys2), selenomethionine (SeMet), and methylselenocysteine (MeSeCys), were detected in lettuce leaves after Se treatment, with SeMet being the most abundant. During storage, Se-treated lettuce exhibited lower weight loss, a*, b*, browning index, and color difference (ΔE) values compared to the control group. CAT and POD activities and GSH content also followed a trend of initial increase followed by a decrease. Transcriptome data analysis revealed that genes such as MYB1, RPK1, PTR44, NTRC, WRKY7, and CSLD3 were associated with the stress response of Se-treated lettuce.

Estimation of Relative Chlorophyll Content in Lettuce (Lactuca sativa L.) Leaves under Cadmium Stress Using Visible—Near-Infrared Reflectance and Machine-Learning Models

Chlorophyll content is a crucial assessment parameter in the growth monitoring of lettuce, particularly in cases when it is affected by disease. Accurate estimation of chlorophyll content is beneficial for early detection and prevention of diseases and holds significant importance in practical production. To construct a model for estimating the chlorophyll content in lettuce leaves under cadmium stress, this study utilized lettuce as the experimental material. The visible–near-infrared reflectance spectra of lettuce leaves, as well as the relative chlorophyll content of the leaves, were detected and analyzed under different concentrations of cadmium stress. Subsequently, an inversion model for estimating the relative chlorophyll content in lettuce leaves was established. First, to determine the optimal spectral preprocessing method, eight techniques are utilized: Savitzky–Golay smoothing (SG), multiplicative scatter correction (MSC), standard normal variable transformation (SNV), mean normalization (MN), baseline offset (B), detrending (D), gap derivatives—first derivative (FD), and gap derivatives—second derivative (SD). These methods are used to preprocess the spectra and establish a partial least squares regression (PLSR) monitoring model. The optimal spectral preprocessing method is then selected. Next, the feature bands are extracted from the preprocessed spectral data using the correlation coefficient method. Finally, the selected feature bands will be combined with support vector regression (SVR) to establish a chlorophyll content estimation model using a training-to-testing set ratio of 4:1. The results showed that the PLSR model established after preprocessing with detrending (D) had the highest accuracy, with the coefficient of determination (Rv2) and root mean squared error (RMSEv) values of 0.87 and 1.16, respectively. The feature bands selected by the correlation coefficient method were used to establish SVR models for estimating the chlorophyll content of lettuce leaves under cadmium stress, with the highest accuracy being achieved by the genetic algorithm (GA)–SVR model. It can be seen that near-infrared spectroscopy technology provides a scientific basis for rapid, nondestructive, and accurate detection of lettuce diseases and stress.

Comprehensive effects of thiamethoxam from contaminated soil on lettuce growth and metabolism

The second-generation neonicotinoid thiamethoxam, is prevalent in soils because of its extensive application and persistence. However, the comprehensive effects of thiamethoxam residue in soils on cultivated plants are still poorly understood. This study examined variations of growth state, physiological parameters, antioxidant activity, and metabolites in lettuce after thiamethoxam exposure; the removal effects of different washing procedures were also investigated. The results indicated that thiamethoxam in soils significantly increased the fresh weight, seedling height and chlorophyll content in lettuce, and also altered its lipid, carbohydrate, nucleotide and amino acids composition based on untargeted metabolomics. KEGG pathway analysis uncovered a disruption of lipid pathways in lettuce exposed to both low and high concentrations of thiamethoxam treatments. In addition, the terminal residues of thiamethoxam in lettuce were below the corresponding maximum residue limits stipulated for China. The thiamethoxam removal rates achieved by common washing procedures in lettuce ranged from 26.9% to 42.6%. This study thus promotes the understanding of the potential food safety risk caused by residual thiamethoxam in soils.

Analysis of Cadmium Contamination in Lettuce (Lactuca sativa L.) Using Visible-Near Infrared Reflectance Spectroscopy

In order to rapidly and accurately monitor cadmium contamination in lettuce and understand the growth conditions of lettuce under cadmium pollution, lettuce is used as the test material. Under different concentrations of cadmium stress and at different growth stages, relative chlorophyll content of lettuce leaves, the cadmium content in the leaves, and the visible-near infrared reflectance spectra are detected and analyzed. An inversion model of the cadmium content and relative chlorophyll content in the lettuce leaves is established. The results indicate that cadmium concentrations of 1 mg/kg and 5 mg/kg promote relative chlorophyll content, while concentrations of 10 mg/kg and 20 mg/kg inhibit relative chlorophyll content. The cadmium content in the leaves increases with increasing cadmium concentrations. Cadmium stress caused a “blue shift” in the red edge position only during the mature period, while the red valley position underwent a “blue shift” during the seedling and growth periods and a “red shift” during the mature period. The green peak position exhibited a “blue shift”. After model validation, it was found that the model constructed using the ratio of red edge area to yellow edge area and the normalized values of red edge area and yellow edge area effectively estimated the cadmium content in lettuce leaves. The model established using the normalized vegetation index of the red edge and the ratio of the peak green value to red shoulder amplitude can effectively estimate the relative chlorophyll content in lettuce leaves. This study demonstrates that the visible-near infrared spectroscopy technique holds great potential for monitoring cadmium contamination and estimating chlorophyll content in lettuce.

Correlation of the SPAD index with absolute leaf pigments in irrigated lettuce culture in the Northwest Paraná, Brazil

Photosynthesis is the most important biochemical process that takes place in plants and chlorophyll is the main pigment involved in it. Current destructive methods for determining chlorophyll content are accurate, but time-consuming and relatively expensive. The SPAD (Soil Plant Analysis Development) is a portable chlorophyll meter that provides an instant and nondestructive reading of the green color of leaves. As an important source of vitamins and antioxidants such as vitamins C, carotenoids and fiber content, lettuce (Lactuca sativa L.) plays a crucial role in human nutrition, being one of the most popular staple plant foods among the population. Considering the possibility of management based on the characteristics of photosynthetic pigments, the study aimed to relate the SPAD index values with the content of leaf pigments in lettuce. The study was conducted in the Northwest region of Paraná, Brazil. The experiment was carried out in a completely randomized design with 48 leaf samples being determined the SPAD index and the content of leaf pigments. The determination of the SPAD index was performed with the SPAD-502 equipment (Minota®) with three readings per sample. For the extraction of leaf pigments, chlorophyll (a; b), total chlorophyll (a + b) and carotenoids, acetone was used as an extractor and the reading was performed in a spectrophotometer. The SPAD index was correlated with the levels of chlorophyll a (0.93), chlorophyll b (0.89), total chlorophyll (0.93) and carotenoids (0.95) in lettuce leaves. Through the SPAD, the chlorophyll content in lettuce leaves can be determined in a representative way.

Development of smartphone-based imaging techniques for the estimation of chlorophyll content in lettuce leaves

Leaf color is a good indicator of plant’s health status. In this study, a new image acquisition technique was developed to estimate chlorophyll content of lettuce leaves. The images of lettuce leaves grown under artificial light were acquired using a smartphone. Leaves images was captured by directly attached the leaves to the camera lens with the aid of background illumination from SMD LED. Red, green, blue (RGB) color indices were extracted from leaves color images and some vegetation indices were also calculated. Then, the correlation between these indices and chlorophyll content obtained from SPAD502 chlorophyll meter were evaluated. Significant correlation was found between all the image indices and chlorophyll content with the R2 ranging from 0.63 to 0.85 except for G and B indices from RGB component. Highly significant correlation was found between vegetation indices (VI) and chlorophyll content (R2 = 0.85) with the lowest root mean square error (RMSE) of 8.07 g of chlorophyll/100 g fresh tissue. This demonstrated that the chlorophyll content of lettuce leaves can be successfully estimated using regular smartphone with added background light illumination from SMD LED.

Effects of tourmaline catalyzed Fenton-like combined with bioremediation on the migration of PBDEs in soil-plant systems: Soil properties and physiological response of lettuce and selective uptake of PBDEs

A series of pollutants can be removed from soil using a Fenton-like oxidation and biological treatment. As a natural mineral, tourmaline has been used for as a material of Fenton-like reaction. In the present study, the risks of remediation technology tourmaline catalyzed Fenton-like reaction (TCFR) combined with Phanerochaete chrysosporium (TCFR + P) were assessed through measuring soil properties, physiological response of plant, and PBDEs migration from soil to plant. Batch pot experiments showed that the silicon contents, specific surface area and soil pore size of soil in TCFR and 5%TCFR + P groups increased obviously. TCFR and TCFR + P treatments promoted the lettuce growth compared to control. Moreover, chlorophyll content of lettuce in 2%TCFR + P and 5%TCFR + P group increased by 46.74% and 44.57% than that in the CK, respectively. The treatment of 2%TCFR decreased the total concentration of PBDEs in rhizosphere soil and non-rhizosphere soil by 52.0.2% and 64.17%, respectively, after 60 days compared to the soil of CK, and did not prompt the uptake of lower-brominated PBDEs by lettuce. TCFR and TCFR + P can alter the migration of BDE isomers from soil to plant, the ratio of BDE99/BDE100 in lettuce shoots decreased slightly. BDE-99/BDE-100 ratios in the shoots were lower than those in the roots, while BDE153/BDE154 ratios were higher than 1.0 and ratios in shoots were higher than those in roots. Therefore, our findings illustrated that the TCFR could be applied to remediate the agricultural soil, considering the appropriate doses of tourmaline.

Volatile organic compounds emitted from endophytic fungus Trichoderma asperellum T1 mediate antifungal activity, defense response and promote plant growth in lettuce (Lactuca sativa)

Abstract Trichoderma species are applied as biological control agents and biofertilizers to control plant diseases and enhance crop yields. The ability to inhibit pathogens, induce defense responses, and promote plant growth can result from the production of volatile organic compounds (VOCs). In this study, we evaluated the effects of VOCs from Trichoderma asperellum T1 on those multifaceted actions in lettuce. The VOCs released by T. asperellum T1 inhibited fungal growth of two leaf spot fungal pathogens, Corynespora cassiicola and Curvularia aeria. Lettuces responded to VOCs by increasing activities of the cell-wall degrading enzymes chitinase and β-1,3-glucanase to 1.26 U mL−1 and 4.45 U mL−1, respectively, above those in the control. Accumulation of cell-wall degrading enzymes in lettuce that had been treated with VOCs resulted in morphological changes to fungal cell-walls. Exposure to the VOCs emitted by T. asperellum T1 significantly increased numbers of leaves and roots, plant biomass and total chlorophyll content in lettuce. Furthermore, GC/MS analysis revealed that T. asperellum T1 emitted 22 volatile compounds, which are involved in antifungal activity, inducing defense responses, and promoting growth in lettuce.

Far-red radiation interacts with relative and absolute blue and red photon flux densities to regulate growth, morphology, and pigmentation of lettuce and basil seedlings

Although outside the photosynthetic photon flux density (PPFD) waveband (400–700 nm), far-red (FR; 700–800 nm) radiation regulates photomorphogenesis and photochemistry, thereby meriting consideration in sole-source plant-lighting applications. We investigated how FR radiation interacted with the ratio of blue (B; 400–500 nm) to red (R; 600–700 nm) radiation (B:R) (experiment I) and PPFD (experiment II) to regulate seedling growth under sole-source lighting. We postulated that adding FR radiation to B + R radiation would increase leaf expansion and thus radiation capture to promote whole-plant photosynthesis, but that FR effects would depend on B:R and PPFD. In experiment I, lettuce (Lactuca sativa) ‘Rex’ and ‘Cherokee’ and basil (Ocimum basilicum) ‘Genovese’ were continuously irradiated by 180 μmol m–2 s–1 of B and/or R radiation [B30R150 (low B:R), B90R90 (high B:R), R180, or B180, where subscripts indicate respective photon flux densities in μmol m–2 s–1] with or without 30 μmol m–2 s–1 of FR radiation. Twelve and 16 days after seed sow for lettuce and basil, respectively, the addition of FR radiation increased leaf length and shoot weight of all crops with more pronounced impacts under high B:R than low B:R. It also increased root dry weight of basil and lettuce ‘Cherokee’. Adding FR to B + R radiation reduced specific chlorophyll content in lettuce by 10–20%, but not in basil. Red pigmentation of lettuce ‘Cherokee’ increased with increasing B:R but decreased with the inclusion of FR radiation. In experiment II, we grew lettuce ‘Rex’ (for 8 days) and ‘Rouxai’ (for 10 days) under B90R90 (low PPFD) or B180R180 (high PPFD) at the same B:R with or without FR radiation at 30 or 75 μmol m–2 s–1. Additional FR radiation increased lettuce shoot weight and extension growth but reduced relative specific chlorophyll content under both PPFDs, although FR effects were attenuated under the high PPFD. Shoot dry weight, relative specific chlorophyll content, and red foliage pigmentation increased with PPFD. We conclude that FR enrichment improves photosynthetic radiation capture and thus promotes crop growth under sole-source lighting, and that its effects are especially pronounced under high B:R and a low PPFD.

Synthesis of biochar from sugarcane filter-cake and its impacts on physiological performance of lettuce (Lettuce sativa) grown on cadmium contaminated soil

Soil contamination with cadmium has become major concern all over the world because of its adverse impacts on ecosystem health and agricultural land. Soil amendment with biochar may have varied effects on physical and chemical properties of soil. The objective of the study was to explore the impact of sugarcane filter-cake biochar on physiological performance and growth of lettuce in an aged soil. Four different doses (0, 1.5%, 3%, and 5%) of biochar were used in the soil and conditioned for 1 month. After this, lettuce seedlings were grown in the soil. The results showed that the biochar treatment improved the fresh and dry biomass of leaves and roots as well as plant height while diminished the bioavailability of cadmium from the soil. As compared to control, biochar significantly enhanced the chlorophyll content in lettuce leaves. Due to the biochar amendment, the oxidative stress decreased in lettuce shoots over the control. As compared to control, concentration of cadmium in lettuce significantly decreased after the application of biochar. It was concluded that biochar could mitigate the toxicity of cadmium in lettuce by altering the biochemical and physiological processes in cadmium contaminated soil.

Effect of Polyolefin Film and Light Transition Film on the Growth of Lettuce

In this study, effects of polyolefin(PO) film and light transition film on the growth of lettuce were investigated compared with ethylene-vinylacetate (EVA, antifogging, no drops and longevity type) film covering. Results showed that the temperature and humidity in greenhouse covered with PO film and light transition film were significantly increased. The average temperature in the greenhouse was 4 oC higher than outdoor temperature. The average illumination intensity in the greenhouse covered with PO film was 293.22 umol m-2 s-1, light transmittance was 80.37%, the average illumination intensity in the greenhouse covered with EVA film was 193.04 umol m-2 s-1, light transmittance was 52.91%. Compared with the common film, light transmittance of the PO film was significantly increased. Light transition film increased the chlorophyll content of lettuce by changing the element of the sunlight and increased production of vegetables. PO film and light transition film display a good application prospective in the production of vegetables.

Effects of Biogas byproducts “three-dimensional” Fertilization on Yield and Quality of Lettuce

Effect of three-dimension fertilizing mode (3-DFM) using CO2 and liquid/solid fractions of the digesate from anaerobic digester was investigated in quality and yield of lettuce. CO2, solid fraction of digestate (SFD), and liquid fraction of digestate (LFD) were used as fertilizer for gaseous fertilizer, the base fertilizer, and foliar fertilizer, respectively. The result showed that the 3-DFM was appropriate for lettuce. Lettuce’s plant height, width and number of leaves growth amount were 29.25 cm, 22.38 cm, and 16.2 cm, which were 26.8%, 16.5%, and 18.4% higher than the control, respectively. The overall yield of lettuce was 30.78% more than that of the control. The soluble sugar content and the chlorophyll content in lettuce was the highest, which were 29.4% and 11.4% higher than the control. Under the CO2 and SFD condition, the content of vitamin C in lettuce, the content of free amino acid, crude protein and crude fiber contents of lettuce were the highest. The experimental study can provide an effective way to improve yield and quality of lettuce and utilize biogas plants wastes.

Growth and Anthocyanins of Lettuce Grown under Red or Blue Light-emitting Diodes with Distinct Peak Wavelength

Growth and anthocyanins of lettuce (Lactuca sativa L., ‘Mid-season’) grown under LED lamps with blue light in the range of 430-470 nm or with red light in the range of 630-670 nm were analyzed in this study. Cool-white fluorescent light was used as the control. Photosynthetic photon flux, photoperiod, air temperature, relative humidity, and CO2 concentration in a closed plant production system were 201 ± 2 μmol・m -2 ・s -1 , 16/8 hours (day/night), 22/18°C, 70%, and 400 μmol・mol -1 , respectively. At 21 days after light quality treatment, growth characteristics and anthocyanins content of lettuce as affected by the peak wavelength of blue or red LED were significantly different. Among peak wavelengths treated in this stusy, R1 treatment (peak wavelength 634 nm) and R6 treatment (peak wavelength 659 nm) were effective for increasing leaf width, leaf area, shoot fresh weight, and photosynthetic rate of lettuce. B5 treatment (peak wavelength 450 nm) and B4 treatment (peak wavelength 446 nm) increased the anthocyanins concentration and chlorophyll content in lettuce leaves, respectively. Anthocyanins in lettuce leaves increased linearly with decreasing hue value of leaf color and with increasing SPAD value of lettuce leaves. From these results, it was concluded that the red LED with peak wavelengths of 634 nm and 659 nm and the blue LED with peak wavelengths of 450 nm can be used as potential light spectra for increasing the yield and anthocyanins accumulation of leafy vegetable. Additional key words: artificial lighting source, chlorophyll content, leaf color, photosynthetic rate, phytochemicals, plant factory *Corresponding author: yhkim@jbnu.ac.kr ※ Received 16 September 2013; Revised 9 December 2013; Accepted 5 February 2014. 본 연구는 농촌진흥청 공동연구사업(과제번호: PJ907043) 의 지원에 의해 이루어진 것임. C 2014 Korean Society for Horticultural Science 서 언 발광다이오드(light-emitting diodes, LED)는 소형으로서, 높은 신뢰성과 응답성을 지니고 있으며, 전력소모가 낮고, 수명이 길며, 광합성속도에 영향을 미치는 펄스 조사가 가 능한 점 등의 장점을 지니고 있다(Barta et al., 1992; Kim, 1999; Tennessen et al., 1995). 때문에 LED를 식물조직배양 (Eun et al., 2000), 과채류의 보광재배(An et al., 2011; Brown et al., 1995; Lee et al., 2012), 접목묘의 활착(Kim and Park, 2003), 식물공장 또는 폐쇄형 식물 생산시스템의 인공광원 (Johkan et al., 2010)으로 활용하기 위한 연구가 활발하게 이루어지고 있다.

Effect of Polyolefine Greenhouse Covering Film on Growth of Lettuce and Cucumber in Cool Season Cultivation

This study evaluated the effect of polyolefine greenhouse covering film on growth of lettuce and cucumber. The growth of lettuce and cucumber plants under conventional film (polyethylene plus ethylenevinyl acetate, PE + EVA) and polyolefine (PO) film were evaluated in a greenhouse. The physical qualities of PO film, such as tensile strength and tear strength, were stronger than conventional PE + EVA film. PO film showed 4% higher transmission performance in photosynthetic active radiation (PAR) than PE + EVA film. The average day and night temperature in greenhouse under PO film were 1.5oC and 0.8oC higher but there was no significant difference in relative humidity compared with conventional film. Chlorophyll content of lettuce and cucumber plants grown under PO film were higher than conventional film. Growth characteristics; plant height, leaf area, fresh weight and dry weight of cucumber was shown better for PO film. The yields of cucumber and lettuce was increased 14.0% and 13.6% respectively, when the crops were grown under PO covering film greenhouse.

Mapping QTL, epistasis and genotype × environment interaction of antioxidant activity, chlorophyll content and head formation in domesticated lettuce (Lactuca sativa).

Fruits and vegetables are rich sources of antioxidants in human diets and their intake is associated with chronic disease prevention. Lettuce (Lactuca sativa L.) is a common vegetable in diets worldwide, but its nutritional content is relatively low. To elucidate the genetic basis of antioxidant content in lettuce, we measured the oxygen radical absorbance capacity (ORAC) and chlorophyll (Chl) content as a proxy of β-carotene in an F(8) recombinant inbred line (RIL) in multiple production cycles at two different production sites. Plants were phenotyped at the open-leaf stage to measure genetic potential (GP) or at market maturity (MM) to measure the influence of head architecture ('head' or 'open'). Main effect quantitative trait loci (QTL) were identified at MM (three Chl and one ORAC QTL) and GP (two ORAC QTL). No main effect QTL for Chl was detected at GP, but epistatic interaction was identified in one pair of marker intervals for each trait at GP. Interactions with environment were also detected for both main and epistatic effects (two for main effect, and one for epistatic effect). Main effect QTL for plant architecture and nutritional traits at MM colocated to a single genomic region. Chlorophyll contents and ORAC values at MM were significantly higher and Chl a to Chl b ratios were lower in 'open' types compared to 'head' types. The nutritional traits assessed for GP showed a significant association with plant architecture suggesting pleiotropic effects or closely linked genes. Taken together, the antioxidant and chlorophyll content of lettuce is controlled by complex mechanisms and participating alleles change depending on growth stage and production environment.

Carotenoids of lettuce (Lactuca sativa L.) grown on soil enriched with spent coffee grounds.

The impact of spent coffee grounds on carotenoid and chlorophyll content in lettuce (Lactuca sativa L. var. capitata) was evaluated. A greenhouse pot experiment was conducted with spent coffee amounts ranging from 0% to 20% (v/v). All evaluated pigments increased proportionally to spent coffee amounts. Lutein and β-carotene levels increased up to 90% and 72%, respectively, while chlorophylls increased up to 61%. Biomass was also improved in the presence of 2.5% to 10% spent coffee, decreasing for higher amounts. Nevertheless, all plants were characterized by lower organic nitrogen content than the control ones, inversely to the spent coffee amounts, pointing to possible induced stress. Collected data suggests that plants nutritional features, with regards to these bioactive compounds, can be improved by the presence of low amounts of spent coffee grounds (up to 10%). This observation is particularly important because soil amendment with spent coffee grounds is becoming increasingly common within domestic agriculture. Still, further studies on the detailed influence of spent coffee bioactive compounds are mandatory, particularly regarding caffeine.

English

The effect of selected plant growth promoting rhizobacteria (PGPR) on growth,chlorophyll content, nutrient uptake and yield of lettuce under salt stress was investigated. The study was conducted in pot experiments. Seeds were coated with suspensions of Bacillus subtilis, Bacillus atrophaeus, Bacillus spharicus,Staphylococcus kloosii and Kocuria erythromyxa, which were isolated from highly salty soils. Pots were irrigated with NaCl solutions of 0, 50 or 100 mM. Salinity negatively affected growth and chlorophyll content of lettuce; however, PGPR treatments positively affected growth parameters such as head weight, head height, root diameter and chlorophyll content compared to non-treated plants that were challenged with salt stress. Leaf number was affected by neither salt nor PGPR treatments. Nutrient contents of the leaves of lettuce plants were significantly affected by salt stress and PGPR treatments. All nutrient element contents investigated were significantly decreased except for Na and Cl under salt stress. PGPR under salinity conditions usually increased plant nutrient element contents of the leaves. It can be concluded from the study that treatment with PGPR can ameliorate the deleterious effects of salt stress on nutrition and on the growth parameters of lettuce plants under salinity conditions. Key words: Plant growth promoting rhizobacteria, plant nutrient, salinity stress, lettuce.

Postharvest changes in water status and chlorophyll content of lettuce (Lactuca sativa L.) and their relationship with overall visual quality.

The purpose of this study was to evaluate water status, chlorophyll content (C), and overall visual quality (OVQ) of fresh butter lettuce (Lactuca sativa var. Lores) as well as these indexes' evolution during storage and their relationships, if any. Whole lettuce plants were stored at optimal postharvest conditions (0 to 2 degrees C and 97% to 99% relative humidity). Measured parameters during each sampling day were relative water content (RWC), water content (WC), free water (FW), bound water (BW), free water to total water ratio (FW/TW), C, and OVQ. All parameters were evaluated in the external, middle, and internal zones of lettuce heads. The external zone had higher initial values of RWC, WC, and FW than the internal zone. The external zone yielded the highest FW/TW ratio (85%), indicating that external leaves had more water available to be used in degradation reactions and were more perishable, with the lowest shelf life if compared with the other lettuce zones. During storage, water status index evolution differed from zone to zone. An increase in BW and a decrease in FW were detected in all lettuce zones. RWC turned out to be a more sensitive measurement than WC. Yet RWC showed no significant correlation with any index. The OVQ parameter correlates with FW directly, or indirectly through FW/TW in all lettuce zones; therefore, FW is an objective and quantitative measurement, which impacts on the visual quality of butter lettuce. The decrease in chlorophyll content observed in the external leaves strongly correlated with the decrease in OVQ.

Plant growth inhibitors isolated from sugarcane ( Saccharum officinarum) straw

Several compounds related with plant defense and pharmacological activities have been isolated from sugarcane. Straw phytotoxins and their possible mechanisms of growth inhibition are largely unknown. A bioassay-guided fractionation of the phytotoxic constituents leachated from a sugarcane straw led to the isolation of trans-ferulic (trans-FA), cis-ferulic (cis-FA), vanillic (VA) and syringic (SA) acids. The straw leachates and their identified constituents significantly inhibited root growth of lettuce and four weeds. VA was more phytotoxic to root elongation than FA and SA. The identified phenolic compounds significantly increased leakage of root cell constituents, inhibited dehydrogenase activity and reduced chlorophyll content in lettuce. VA and FA inhibited mitotic index while SA increased cell division. Additive (VA-FA and FA-SA) and synergistic (VA-SA) interactions on root growth were observed at the response level of EC(25). Although the isolated compounds differed in their relative phytotoxic activities, the observed physiological responses suggest that they have a common mode of action. HPLC analysis indicated that sugarcane straw can potentially release 1.43 (ratio 2:1, trans:cis), 1.14 and 0.14mmolkg(-1) (straw dry weight) of FA, VA and SA, respectively. As phenolic acids are often found spatially concentrated in the top soil layers under plant straws, further studies are needed to establish the impact of these compounds in natural settings.

Artemisinin, a Constituent of Annual Wormwood (Artemisia annua), is a Selective Phytotoxin

Artemisinin (qinghaosu), a sesquiterpenoid lactone peroxide constituent of annual wormwood (Artemisia annuaL. # ARTAN) that is used as an antimalarial drug, was tested for phytotoxic properties. It inhibited germination of lettuce (Lactuca sativaL.) and annual wormwood, and growth of roots and shoots of lettuce, redroot pigweed (Amaranthus retroflexusL. # AMARE), pitted morningglory (Ipomoea lacunosaL. # IPOLA), annual wormwood, and common purslane (Portulaca oleraceaL. # POROL) was inhibited at 33 μM. No effects of 33 μM artemisinin were detected on growth of velvetleaf (Abutilon theophrastiMedik. # ABUTH) and grain sorghum [Sorghum bicolor(L.) Moench.]. Chlorophyll content was not affected in lettuce, and chlorosis was not observed in any species tested. The probable biosynthetic precursors of artemisinin, arteannuin B and qinghao acid, had no effect on growth or chlorophyll content of lettuce; however, they inhibited lettuce seed germination. Artemisinin and cinmethylin {exo-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo [2.2.1] heptane} were equally effective in reducing growth of lettuce; however, cinmethylin had no effect on germination. Respiration of lettuce roots or cotyledons was not inhibited by artemisinin. Artemisinin only marginally increased the mitotic index of lettuce root tips at 33 μM. At the ultrastructural level, however, chromosomes were less condensed during mitosis in artemisinin-treated than control meristematic cells. The growth-inhibiting ability of artemisinin could not be reduced by feeding the plants with hydrolyzed protein or treatment with putrescine. Artemisinin is a selective phytotoxin that reduces growth by a mechanism other than mitotic disruption or inhibition of protein synthesis.