24 research outputs found
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Oxidative discolouration in whole-head and cut lettuce: biochemical and environmental influences on a complex phenotype and potential breeding strategies to improve shelf-life
Lettuce discolouration is a key post-harvest trait. The major enzyme controlling oxidative discolouration
has long been considered to be polyphenol oxidase (PPO) however, levels of PPO and subsequent development of discolouration symptoms have not always correlated. The predominance of a latent state of the enzyme in plant tissues combined with substrate activation and contemporaneous suicide inactivation
mechanisms are considered as potential explanations for
this phenomenon. Leaf tissue physical properties have
been associated with subsequent discolouration and
these may be influenced by variation in nutrient
availability, especially excess nitrogen and head maturity at harvest. Mild calcium and irrigation stress has
also been associated with a reduction in subsequent
discolouration, although excess irrigation has been
linked to increased discolouration potentially through
leaf physical properties. These environmental factors,
including high temperature and UV light intensities,
often have impacts on levels of phenolic compounds
linking the environmental responses to the biochemistry
of the PPO pathway. Breeding strategies targeting the
PALand PPOpathway biochemistry and environmental
response genes are discussed as a more cost-effective
method of mitigating oxidative discolouration then
either modified atmosphere packaging or post-harvest
treatments, although current understanding of the
biochemistry means that such programs are likely to
be limited in nature and it is likely that they will need to be deployed alongside other methods for the foreseeable future
Density and Urban Sprawl
Along with its economic reform, China has experienced a rapid urbanization. This study mapped urban land expansion in China using high-resolution Landsat Thematic Mapper and Enhanced Thematic Mapper data of 1989/1990, 1995/1996 and 1999/2000 and analyzed ...
Is the Pandemic Causing a Return to Urban Sprawl?
Urban sprawl is a catch-all term and a scapegoat for everything that is bad about urban growth today, such as congestion, blight, monotony, and ecological destruction. In recent decades, sprawl might have attenuated as America experienced a period of urban revival even as technology made working from home (WFH) and shopping from home possible nearly anywhere. The onset of the COVID-19 pandemic has accelerated the adoption of infrastructures and forced firms to rethink the necessity of workplaces. Retailers have accelerated the pace of online sales and home deliveries by years if not decades. These and other advances have decoupled people from their workplaces, shopping and other activities usually associated with density. Indeed, the sudden spurning of urban density attributable to the pandemic raises fundamental questions for the future of cities. While the pandemic has accelerated trends in people moving out of denser neighborhoods in metropolitan areas in favor of smaller metros, suburban, and exurban locations, the major shift in net migration is from a drop in people moving into central cities. This paper contextualizes pandemic era migration literature with prior studies of urban sprawl to derive a useful framework for planners, developers, and decision-makers to better understand how cities expand and to predict the lasting impacts that COVID-19 will leave on U.S. cities
Is the Pandemic Causing a Return to Urban Sprawl?
Urban sprawl is a catch-all term and a scapegoat for everything that is bad about urban growth today, such as congestion, blight, monotony, and ecological destruction. In recent decades, sprawl might have attenuated as America experienced a period of urban revival even as technology made working from home (WFH) and shopping from home possible nearly anywhere. The onset of the COVID-19 pandemic has accelerated the adoption of infrastructures and forced firms to rethink the necessity of workplaces. Retailers have accelerated the pace of online sales and home deliveries by years if not decades. These and other advances have decoupled people from their workplaces, shopping and other activities usually associated with density. Indeed, the sudden spurning of urban density attributable to the pandemic raises fundamental questions for the future of cities. While the pandemic has accelerated trends in people moving out of denser neighborhoods in metropolitan areas in favor of smaller metros, suburban, and exurban locations, the major shift in net migration is from a drop in people moving into central cities. This paper contextualizes pandemic era migration literature with prior studies of urban sprawl to derive a useful framework for planners, developers, and decision-makers to better understand how cities expand and to predict the lasting impacts that COVID-19 will leave on U.S. cities