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Anterior limb bud cells cultured in microdissociation environment develop ZPA signaling capacity that is transient and decreases with decrease in the culture time. Fibroblast growth factor-2 (FGF2) regulates the signaling capacity of anterior limb bud cells. Deletion of apical ectodermal ridge also results in the conversion of bud cells to ZPA signaling cells with FGF2 maintaining the positional properties of the cells.

Patterns occurring with proximal-distal (PrDi) and anterior-posterior (AP) axes of limb buds are correlated to the domain expression of genes occurring at 5' end of the HoxD complex. The positional information during limb development is specified by the HoxD gene products. Limb development requires an apical ectodermal ridge which influences the mesodermal cells at the distal end of the limb bud.

Local treatment of fibroblast growth factor-2 (FGF-2) on amputated stage 25 chick limb bud stimulates the regeneration of digit-like structures. Location of the heparan sulfate conjugated beads, loaded with FGF-2, on the limb stump is related to the regenerative response. Without the use of FGF-2, regeneration is not possible in the chick limb after amputation.

There is increasing urgency to develop and deploy sustainable sources of energy to reduce our global dependency on finite, high-carbon fossil fuels. Lignocellulosic feedstocks, used in power and liquid fuel generation, are valuable sources of non-food plant biomass. They are cultivated with minimal inputs on marginal or degraded lands to prevent competition with arable agriculture and offer significant potential for sustainable intensification (the improvement of yield without the necessity for additional inputs) through advanced molecular breeding. This article explores progress made in next generation sequencing, advanced genotyping, association genetics, and genetic modification in second generation bioenergy production. Using poplar as an exemplar where most progress has been made, a suite of target traits is also identified giving insight into possible routes for crop improvement and deployment in the immediate future. [ABSTRACT FROM AUTHOR]

Abstract: Vegetation plays a key role in both the global carbon and water cycles. Therefore, the representation of leaf-level fluxes of carbon and water in process-based land-surface schemes is central to accurately predicting these surface exchanges on a larger scale. Leaf-level models of photosynthesis used in such schemes are commonly based on the equations of , which were founded on the assumption that differences in the drawdown of CO2 from sub-stomatal cavities (c i ) to the site of carboxylation inside chloroplasts (c c ) were negligible. Recent research, however, indicates an important role for this additional internal pathway of CO2 transfer (g i ) in photosynthesis. This work therefore combined fieldwork and modelling to assess the impact of g i on estimation of key photosynthetic parameters, and on the accuracy of simulated photosynthesis (A net ) and stomatal conductance (g s ) in a coupled model of leaf-level A net and g s embedded in a land-surface scheme. It was shown that, in a fast growing poplar genotype (Populus nigra), the photosynthetic parameter V max was sensitive to g i . Determination of V max under the assumption of finite g i led to estimates of V max in well-watered trees that were, on average, 52% higher than values calculated on a c i basis. Drought induced declines in all key photosynthetic parameters measured were observed (V max , J max and g i ), in addition to a two-fold increase in photosynthetic biochemical capacity upon re-watering. Reasons for this and the implications for land-surface modelling are discussed. It was shown that inclusion of a constant (non-water stressed) internal conductance to CO2 in a coupled model of leaf-level A net and g s did not improve the accuracy of these simulated fluxes. It was concluded that, for application within a land-surface scheme, currently, accurate calibration of V max potentially has a greater impact on simulated A net and g s than the inclusion of additional, fine-scale leaf-level processes such as g i . [Copyright &y& Elsevier]

Relatively little is known about the transcriptional response or genetic control of response and adaptation of trees to tropospheric ozone exposure. Such understanding is needed as up to 50% of forests, globally, may be subjected to phytotoxic concentrations of ozone. The physiological, transcriptional and genetic response to ozone was examined in Populus trichocarpa and P. deltoides, which show extreme sensitivity and tolerance to ozone, respectively. Using an inbred F2 mapping population derived from these two species, we mapped quantitative trait loci (QTL) for traits associated with ozone response, examined segregation of the transcriptional response to ozone and co-located genes showing divergent responses between tolerant and sensitive genotypes with QTL. QTL were identified linking detrimental effects of ozone with leaf and biomass traits and differential responses were found for key genes involved in ethylene production and response. [Copyright &y& Elsevier]

Abstract: The quantitative and qualitative estimation of aboveground biomass production is essential for short-rotation forestry. Indirect methods of biomass estimation have been developed based on the establishment of regressions between biomass components and tree dimensions as well as canopy architecture. The difficulty encountered with this method is to know whether, and to what degree, the obtained equations can be used under contrasting environmental conditions and for different genetic backgrounds. In the present study, allometric equations were developed linking tree dry weight (stem, branch and aboveground tree dry weight) with stem circumference, stem height and number of sylleptic branches for five 2-year-old intra- as well as interspecific poplar (Populus) families growing at three contrasting sites in Europe, i.e. Northern Italy, Central France and Southern UK. The multiple regression method was used to find the most precise biomass equation which represents the genetic variation for each family at each site, independently, as well as a common equation involving all families and sites. The two F1 P. deltoides × P. trichocarpa families and the F1 P. alba × P. alba family were the most productive families irrespective of site. However, different patterns in biomass accumulation were observed between these crosses. The F1 P. alba × P. alba family accumulated significantly more biomass in branches than in the stem as compared to both other families. In most cases, different transformations of the dependent variables were needed to improve the linear equations. Stem circumference was superior in predicting tree dry weight, but stem height and number of sylleptic branches were often needed to optimize the equations dependent on family and site. A standardized equation combining the five families and the three sites explained more than 95% of the observed variation for tree dry weight. However, there was a significant family effect, and at the UK site, a severe rust attack could have affected the relationships among the three predictors resulting in a significantly different equation for this site. When the UK site was excluded from the model, no overall site effect was observed. Thus, a single equation might be applied at family level regardless of the environmental conditions when stand density, age and plantation management are comparable. [Copyright &y& Elsevier]

Trees are effective in the capture of particles from urban air to the extent that they can significantly improve urban air quality. As a result of their aerodynamic properties conifers, with their smaller leaves and more complex shoot structures, have been shown to capture larger amounts of particle matter than broadleaved trees. This study focuses on the effects of particle size on the deposition velocity of particles (Vg) to five urban tree species (coniferous and broadleaved) measured at two field sites, one urban and polluted and a second more rural. The larger uptake to conifers is confirmed, and for broadleaves and conifers Vg values are shown to be greater for ultra-fine particles (Dp<1.0 μm) than for fine and coarse particles. This is important since finer particles are more likely to be deposited deep in the alveoli of the human lung causing adverse health effects. The finer particle fraction is also shown to be transported further from the emission source; in this study a busy urban road. In further sets of data the aqueous soluble and insoluble fractions of the ultra-fines were separated, indicating that aqueous insoluble particles made up only a small proportion of the ultra-fines. Much of the ultra-fine fraction is present as aerosol. Chemical analysis of the aqueous soluble fractions of coarse, fine and ultra-fine particles showed the importance of nitrates, chloride and phosphates in all three size categories at the polluted and more rural location. [Copyright &y& Elsevier]

Irrigation, the practice of artificially supplementing the water available to crops, accounts for 70% of global freshwater abstractions. Since water supply is increasingly under threat from climate change, implementing novel deficit irrigation techniques - the practice of applying less than the optimum amount of water required by the crop- is a pressing priority for future horticulture. Several studies show that deficit irrigation not only saves water, but may also improve crop quality, for example in fruit trees, wine grapes and culinary herbs such as mint. Here we synthesise current knowledge and practice on irrigation in herb crop production, since dietary trends in recent decades have shown a rise in popularity of fresh produce including culinary herbs, but there has been little progress in developing irrigation techniques and scheduling in such crops. We find strong evidence that water deficit can improve crop quality for several leafy herb crops. This includes increase in essential oils, aroma and quality, alongside increases in the plant metabolites that contribute to antioxidant potential. Despite these positive findings, this review also highlights a gap in understanding the application of deficit irrigation technologies to commercial herb crop systems and suggests further innovation and research is required in this area of precision horticulture. [ABSTRACT FROM AUTHOR]

To optimise trade-offs provided by future changes in grassland use intensity, spatially and temporally explicit estimates of respective grassland productivities are required at the systems level. Here, we benchmark the potential national availability of grassland biomass, identify optimal strategies for its management, and investigate the relative importance of intensification over reversion (prioritising productivity versus environmental ecosystem services). Process-conservative meta-models for different grasslands were used to calculate the baseline dry matter yields (DMY; 1961–1990) at 1 km 2 resolution for the whole UK. The effects of climate change, rising atmospheric [CO 2 ] and technological progress on baseline DMYs were used to estimate future grassland productivities (up to 2050) for low and medium CO 2 emission scenarios of UKCP09. UK benchmark productivities of 12.5, 8.7 and 2.8 t/ha on temporary, permanent and rough-grazing grassland, respectively, accounted for productivity gains by 2010. By 2050, productivities under medium emission scenario are predicted to increase to 15.5 and 9.8 t/ha on temporary and permanent grassland, respectively, but not on rough grassland. Based on surveyed grassland distributions for Great Britain in 2010 the annual availability of grassland biomass is likely to rise from 64 to 72 million tonnes by 2050. Assuming optimal N application could close existing productivity gaps of ca. 40% a range of management options could deliver additional 21 ∗ 10 6 tonnes of biomass available for bioenergy. Scenarios of changes in grassland use intensity demonstrated considerable scope for maintaining or further increasing grassland production and sparing some grassland for the provision of environmental ecosystem services. [ABSTRACT FROM AUTHOR]

We examined the response of hybrid poplar to elevated CO2in contrasting growth environments: controlled environment chamber (CE), open-top chamber (OTC) and poplar free air CO2 enrichment (POPFACE) in order to compare short versus long-term effects andto determine whether generalisations in response are possible for this fast growing tree. Leaf growth, which for poplar is an important determinant of stemwood productivity was followed in all environments,as were the determinants of leaf growth//cell expansion and cell production. Elevated CO2 (550/700 Mumol mol-1, depending on environment) resulted in an increase in final leaf size forPopulus trichocarpax Populus deltoides (Populusx interamericana) andP. deltoidesx Populus nigra (Populusx euramericana), irrespective ofwhether plants were exposed during a short-term CE glasshouse study (90 days), a long-term OTC experiment (3 years) or during the first year of a POPFACE experiment. An exception was observed in the closed canopy POPFACE experiment, where final leaf size remained unaltered by CO2. Increased leaf extension rate was observed in elevated CO2 in all experiments, at some point during leaf development, as determined by leaf length. Again the exception were the POPFACE experiment, where effects were not statistically significant. Leaf production and specific leaf area (SLA) were increased and decreased, respectively, on five out of six occasions, although both were only statistically significant on two occasions and interestingly forSLA never in the FACE experiment. Although both cell expansion and cell production were sensitive to CO2 concentration, effects appeared highly dependent on growth environment and genotype. However, increased leaf cell expansion in elevated CO2 was often associated with changes in the biophysical properties of the cell wall, usually increased cell wall plasticity. This research has shown that en [ABSTRACT FROM AUTHOR]

The composition and amounts of dust or particulate matter (PM) vary greatly in the atmosphere and particulates can have major adverse impacts on human health. Since PM 10 deposition to foliage can improve air quality, there have been a number of studies of PM 10 amounts on the surface of urban vegetation. Much less is known about PM in agricultural areas, although PM 10 can be harmful to vegetation and, for food crops, have the potential to be ingested. Here we have quantified PM across the agricultural landscape of California, measuring the amounts present on the foliage of 18 crops at 21 locations. The amounts of particulates present varied (0.17–6.9 gm-2) and PM loads on leaves in the south and east of the area were higher than those in the northern and westerly locations. Our findings suggest that the amounts of particulates on the surface of agricultural crops can be high; exceeding the usual range of values for urban areas. Our data indicate that agricultural crops grown in regions like California and the Mediterranean where summer rainfall is largely absent and drip rather than spray irrigation is used are more vulnerable to PM accumulation and to any adverse effects resulting from these deposits. Microscopic analysis of PM 10 on foliage showed that in these agricultural areas wind-blown soil particles make up 74.2% of the PM 10 present; this is thus a very significant source. A small number of microplastic particles (2.2%) were also identified on foliage. We suggest that PM and microplastics could impact food and forage quality and that more work is needed to examine PM deposition to crops and their range of impacts. [Display omitted] • Little is known on particulate matter deposition and impacts in agriculture. • Particulates (PM 10) can be harmful to vegetation and to human health if ingested. • Particulates amount on crops can be high; exceeding the usual range in urban areas. • In agriculture soil & microplastics make up 74.2 and 2.2 % of leaf surface dust. • Dust effects food & forage quality; more work is needed on deposition & impacts. [ABSTRACT FROM AUTHOR]

Abstract: There is momentum, globally, to increase the use of plant biomass for the production of heat, power and liquid transport fuels. This review assesses the evidence base for potential impacts of large-scale bioenergy crop deployment principally within the UK context, but with wider implications for Europe, the USA and elsewhere. We focus on second generation, dedicated lignocellulosic crops, but where appropriate draw comparison with current first-generation oil and starch crops, often primarily grown for food. For lignocellulosic crops, positive effects on soil properties, biodiversity, energy balance, greenhouse gas (GHG) mitigation, carbon footprint and visual impact are likely, when growth is compared to arable crops. Compared to replacement of set-aside and permanent unimproved grassland, benefits are less apparent. For hydrology, strict guidelines on catchment management must be enforced to ensure detrimental effects do not occur to hydrological resources. The threat of climate change suggests that action will be required to ensure new genotypes are available with high water use efficiency and that catchment-scale management is in place to secure these resources in future. In general, for environmental impacts, less is known about the consequences of large-scale deployment of the C4 grass Miscanthus, compared to short rotation coppice (SRC) willow and poplar, including effects on biodiversity and hydrology and this requires further research. Detailed consideration of GHG mitigation and energy balance for both crop growth and utilization suggest that perennial crops are favoured over annual crops, where energy balances may be poor. Similarly, crops for heat and power generation, especially combined heat and power (CHP), are favoured over the production of liquid biofuels. However, it is recognized that in contrast to heat and power, few alternatives exist for liquid transportation fuels at present and research to improve the efficiency and energy balance of liquid transport fuel production from lignocellulosic sources is a high current priority. Although SRC, and to a lesser extent energy grasses such as Miscanthus, may offer significant benefits for the environment, this potential will only be realized if landscape-scale issues are effectively managed and the whole chain of crop growth and utilization is placed within a regulatory framework where sustainability is a central driver. Land resource in the UK and throughout Europe will limit the contribution that crops can make to biofuel and other renewable targets, providing a strong driver to consider sustainability in a global context. [Copyright &y& Elsevier]

Short-rotation coppice Salix genotypes of differing biomass yields were studied over two growing seasons with the long-term aim of identifying traits definitive of high yield for the breeding of elite energy crops. In the first season, basic leaf and stem traits were measured in six Salix genotypes, to identify morphological characteristics associated with high biomass yields. Thereafter, S. viminalis L. ‘L78183’ (low yield) and the hybrid genotype S. schwerinii E. Wolf× S. viminalis L. ‘Tora’ (high yield) were compared. Maximum stem heights and stem diameters increased with biomass yield. ‘Tora’ produced more sylleptic branches on the leading stems than ‘L78183’. Leaf traits differed significantly between the two genotypes: individual leaf area and cell number per leaf was greater in ‘Tora’, whereas cell area was greater in ‘L78183’, suggesting that final leaf areas were attained in ‘Tora’ through the production of many, small cells, and in ‘L78183’ through fewer, large cells. Leaf extension rates were higher in ‘Tora’ than ‘L78183’. This result was mirrored for leaf production rate. Leaf area index, examined at two coppice stages, was higher in ‘L78183’ (values of 2.06 and 1.67) than in ‘Tora’ (maximum value 1.43) which had a very open canopy. Furthermore, A/Ci analysis revealed the low-yielding genotype as the most photosynthetically efficient at the individual leaf level whereas light response curves suggest that ‘Tora’ utilised light more efficiently. The results presented in this study suggest that leaf extension rate, final leaf size and cell number per leaf may be indicative of yield, and may be useful as selection criteria for potentially high-yielding hybrids for biomass use. [Copyright &y& Elsevier]

Pathways to decarbonisation are commonly explored by government and industry through the use of energy system models. However, such models rarely consider where new energy infrastructure might be located. This is problematic as the spatial context of new renewable energy infrastructure will determine, in part, the environmental, social, and technical impacts of the energy transition. This paper presents the ADVENT-NEV model which brings together innovations in energy and natural capital modelling to identify the optimal locations of multiple renewable energy technologies at a national scale and high spatial resolution. Using Great Britain as a case study, the results show how the spatial distribution of renewable energy technologies changes when a natural capital approach is taken. In particular, the least-cost locations for onshore wind farms and bioenergy crops are highly influenced by the value of carbon sequestration, or emissions associated with their land use change. Siting using a natural capital approach produced appreciable ecosystem service benefits, such that the overall welfare gain to society was estimated at nearly £25 B. Overall, this paper demonstrates that understanding the geospatial context of the energy transition is essential to identifying which renewable energy pathways are consistent with decarbonisation and environmental objectives. [Display omitted] [ABSTRACT FROM AUTHOR]

• Delivering fresh, safe, high quality and long shelf life lettuce is a key challenge. • Poor shelf life leads to major crop waste, largely overlooked in breeding programmes. • Research has identified genetic variation for post-harvest quality. • We outline multiomic datasets, genetic and genomic resources for lettuce breeding. Societal awareness of healthy eating is increasing alongside the market for processed bagged salads, which remain as one of the strongest growing food sectors internationally, including most recently from indoor growing systems. Lettuce represents a significant proportion of this ready-to-eat salad market. However, such products typically have a short shelf life, with decay of post-harvest quality occurring through complex biochemical and physiological changes in leaves and resulting in spoilage, food waste and risks to health. We review the functional and quantitative genetic understanding of lettuce post-harvest quality, revealing that few findings have translated into improved cultivar development. We identify (i) phytonutrient status (for enhanced antioxidant and vitamin status, aroma and flavour) (ii) leaf biophysical, cell wall and water relations traits (for longer shelf life) (iii) leaf surface traits (for enhanced food safety and reduced spoilage) and (iv) chlorophyll, other pigments and developmental senescence traits (for appearance and colour), as key targets for future post-harvest breeding. Lettuce is well-placed for rapid future exploitation to address postharvest quality traits with extensive genomic resources including the recent release of the lettuce genome and the development of innovative breeding technologies. Although technologies such as CRISPR/Cas genome editing are paving the way for accelerated crop improvement, other equally important resources available for lettuce include extensive germplasm collections, bi-parental mapping and wide populations with genotyping for genomic selection strategies and extensive multiomic datasets for candidate gene discovery. We discuss current progress towards post-harvest quality breeding for lettuce and how such resources may be utilised for future crop improvement. [ABSTRACT FROM AUTHOR]

There is increasing recognition that a whole systems approach is required to inform decisions on future energy options. Based on a qualitative and quantitative analysis of forty influential energy and ecosystem services scenario exercises, we consider how the benefits to society that are derived from the natural environment are integrated within current energy scenarios. The analysis demonstrates a set of common underlying themes across scenario exercises. These include the relative contribution of fossil sources of energy, rates of decarbonisation, the level of international cooperation and globalisation, rate of technological development and deployment, and societies focus on environmental sustainability. Across energy scenario exercises, ecosystem services consideration is primarily limited to climate regulation, food, water resources, and air quality. In contrast, ecosystem services scenarios consider energy systems in a highly aggregated narrative form, with impacts of energy options mediated primarily through climate and land use change. Emerging data and tools offer opportunities for closer integration of energy and ecosystem services scenarios. This can be achieved by incorporating into scenarios exercises both monetary and non-monetary values of ecosystem services, and increasing the spatial representation of both energy systems and ecosystem services. The importance of ecosystem services for human well-being is increasingly recognised in policy at local, national and international scales. Tighter integration of energy and ecosystem service scenarios exercises will allow policy makers to identify pathways consistent with international obligations relating to both anthropogenic climate change and the loss and degradation of biodiversity and ecosystem services. [ABSTRACT FROM AUTHOR]

This study presents a multi-objective optimisation model that is configured to account for a range of interrelated or conflicting questions with regard to the introduction of bioenergy systems. A spatial-temporal mixed integer linear programming model ETI-BVCM (Energy Technologies Institute – Bioenergy Value Chain Model) ( ETI, 2015b; Newton-Cross, 2015; Samsatli et al., 2015 ) was adopted and extended to incorporate resource-competing systems and effects on ecosystem services brought about by the land-use transitions in response to increasing bioenergy penetration over five decades. The extended model functionality allows exploration of the effects of constraining ecosystem services impacts on other system-wide performance measures such as cost or greenhouse gas emissions. The users can therefore constrain the overall model by metric indicators which quantify the changes of ecosystem services due to land use transitions. The model provides a decision-making tool for optimal design of bioenergy value chains supporting an economically and land-use efficient and environmentally sustainable UK energy system while still delivering multiple ecosystem services. [ABSTRACT FROM AUTHOR]

• Vertical farm (VF) cultivation increased fresh weight and leaf area. • Glucosinolate (GLS) content was highest for VF-grown watercress. • Previously unidentified 4-Phenylbutyl GLS was only found in VF-grown watercress. • Watercress is highly suited for cultivation in vertical farms. Watercress (Nasturtium officinale R. Br.) is a highly nutritious leafy crop with a rich health-related phytonutrient profile including secondary plant metabolites such as glucosinolates. This semi-aquatic crop is well-suited for indoor hydroponic cultivation and has a growing market for its distinctive peppery taste and health benefits. We describe crop trials in three contrasting environments and report the changes to plant morphology, yield, and nutritional profile under varying blue light treatments. Yield and glucosinolate quantity were significantly increased in a vertical farm system enriched in blue light, relative to field-grown crops. Additionally, PBITC, a glucosinolate not previously identified in field-grown watercress, was found in plants grown in a vertical farm. This work demonstrates the great potential of watercress in a new era of controlled environment agriculture to deliver improved health benefits to customers. [ABSTRACT FROM AUTHOR]

Abstract: The cultivation of bioenergy crops (BECs) represents a significant land-use change in agri-environments, but their deployment has raised important issues globally regarding possible impacts on biodiversity. Few studies however, have systematically examined the effect of commercial scale bioenergy plantations on biodiversity in agri-ecosystems. In this study we investigate how the abundance and diversity of two key components of farmland biodiversity (ground flora and winged invertebrates) varied between mature willow Short Rotation Coppice (SRC) and two alternative land-use options (arable crops and set-aside land). Although the abundance of winged invertebrates was similar across all land-uses, taxonomic composition varied markedly. Hymenoptera and large Hemiptera (>5 mm) were more abundant in willow SRC than in arable or set-aside. Similarly although plant species richness was greater in set-aside, our data show that willow SRC supports a different plant community to the other land-uses, being dominated by competitive perennial species such as Elytrigia repens and Urtica dioica. Our results suggest that under current management practices a mixed farming system incorporating willow SRC can benefit native farm-scale biodiversity. In particular the reduced disturbance in willow SRC allows the persistence of perennial plant species, potentially providing a stable refuge and food sources for invertebrates. In addition, increased Hymenoptera abundance in willow SRC could potentially have concomitant effects on ecosystem processes, as many members of this Order are important pollinators of crop plants or otherwise fulfil an important beneficial role as predators or parasites of crop pests. [ABSTRACT FROM AUTHOR]

Abstract: Fast-growing poplar trees may in future be used as a source of renewable energy for heat, electricity and biofuels such as bioethanol. Water use in Populus x euramericana (clone I214), following long-term exposure to elevated CO2 in the POPFACE (poplar free-air carbon dioxide enrichment) experiment, is quantified here. Stomatal conductance was measured and, during two measurement campaigns made before and after coppicing, whole-tree water use was determined using heat-balance sap-flow gauges, first validated using eddy covariance measurements of latent heat flux. Water use was determined by the balance between leaf-level reductions in stomatal conductance and tree-level stimulations in transpiration. Reductions in stomatal conductance were found that varied between 16 and 39% relative to ambient air. Whole-tree sap flow was increased in plants growing under elevated CO2, on average, by 12 and 23%, respectively, in the first and in the second measurement campaigns. These results suggest that future CO2 concentrations may result in an increase in seasonal water use in fast-growing, short-rotation Populus plantations. [Copyright &y& Elsevier]

Abstract: Baby leaf salads are gaining in popularity over traditional whole head lettuce salads in response to consumer demand for greater variety and convenience in their diet. Baby lettuce leaves are mixed, washed and packaged as whole leaves, with a shelf-life of approximately 10 days post-processing. End of shelf-life, as determined by the consumer, is typified by bruising, water-logging and blackening of the leaves, but the biological events causing this phenotype have not been studied to date. We investigated the physiological and ultrastructural characteristics during postharvest shelf-life of two lettuce varieties with very different leaf morphologies. Membrane disruption was an important determinant of cell death in both varieties, although the timing and characteristics of breakdown was different in each with Lollo rossa showing signs of aging such as thylakoid disruption and plastoglobuli accumulation earlier than Cos. Membranes in Lollo rossa showed a later, but more distinct increase in permeability than in Cos, as indicated by electrolyte leakage and the presence of cytoplasmic fragments in the vacuole, but Cos membranes show distinct fractures towards the end of shelf-life. The tissue lost less than 25% fresh weight during shelf-life and there was little protein loss compared to developmentally aging leaves in an ambient environment. Biophysical measurements showed that breakstrength was significantly reduced in Lollo rossa, whereas irreversible leaf plasticity was significantly reduced in Cos leaves. The reversible elastic properties of both varieties changed throughout shelf-life. We compared the characteristics of shelf-life in both varieties of bagged lettuce leaves with other leafy salad crops and discuss the potential targets for future work to improve postharvest quality of baby leaf lettuce. [Copyright &y& Elsevier]

The ‘processability’ of baby salad leaves may be defined as the ability to withstand the postharvest washing and packing processes that are involved in the production of ready-to-eat bagged salads. The inability of baby salad leaves (species including Lactuca sativa L. and Spinacia oleracea L.) to withstand processing results in a reduction in crop shelf-life. Leaves from geographically diverse locations displayed strikingly different processability scores from visual inspection. We have shown that these ‘good’ and ‘poor’ quality leaves may be differentiated from assessments of the biophysical properties of the cell wall (% plasticity) and epidermal cell size. Artificial manipulation of processability in the glasshouse through the application of a mechanical stress or a high salt stress produced L. sativa cv. Ravita (a leaf type ‘lollo rosso’ lettuce) leaves covering a range of processability. Mechanical stress, applied as a daily dose of 100 paper strokes, increased lettuce leaf shelf-life by 33% and was associated with reduced % plasticity and smaller leaf epidermal cells. These traits are thus proposed to be of key importance in the description of processability, with the plant cell wall and plant cell wall gene expression implicated. The potential for future manipulation of these traits for the pre-packed salad market is considered. [Copyright &y& Elsevier]