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

From Mendel’s discovery on pea to today’s plant genetics and breeding

In 2015, we celebrated the 150th anniversary of the presentation of the seminal work of Gregor Johann Mendel. While Darwin’s theory of evolution was based on differential survival and differential reproductive success, Mendel’s theory of heredity relies on equality and stability throughout all stages of the life cycle. Darwin’s concepts were continuous variation and “soft” heredity; Mendel espoused discontinuous variation and “hard” heredity. Thus, the combination of Mendelian genetics with Darwin’s theory of natural selection was the process that resulted in the modern synthesis of evolutionary biology. Although biology, genetics, and genomics have been revolutionized in recent years, modern genetics will forever rely on simple principles founded on pea breeding using seven single gene characters. Purposeful use of mutants to study gene function is one of the essential tools of modern genetics. Today, over 100 plant species genomes have been sequenced. Mapping populations and their use in segregation of molecular markers and marker–trait association to map and isolate genes, were developed on the basis of Mendel's work. Genome-wide or genomic selection is a recent approach for the development of improved breeding lines. The analysis of complex traits has been enhanced by high-throughput phenotyping and developments in statistical and modeling methods for the analysis of phenotypic data. Introgression of novel alleles from landraces and wild relatives widens genetic diversity and improves traits; transgenic methodologies allow for the introduction of novel genes from diverse sources, and gene editing approaches offer possibilities to manipulate gene in a precise manner

Kuhn’s “wrong turning” and legacy today

Alexander Bird indicates that the significance of Thomas Kuhn in the history of philosophy of science is somehow paradoxical. On the one hand, Kuhn was one of the most influential and important philosophers of science in the second half of the twentieth century. On the other hand, nowadays there is little distinctively Kuhn’s legacy in the sense that most of Kuhn’s work has no longer any philosophical significance. Bird argues that the explanation of the paradox of Kuhn’s legacy is that Kuhn took a direction opposite to that of the mainstream of the philosophy of science in his later academic career. This paper aims to provide a new way to understand and develop Kuhn’s legacy by revisiting the development of Kuhn’s philosophy of science in 1970s and proposing a new account of exemplar. Firstly, I propose my diagnosis of Kuhn’s “wrong turning” by identifying Kuhn’s two novel contributions: the introduction of paradigm and the proposal of the incommensurability thesis. Secondly, I argue that Kuhn made a conceptual/terminological turn from paradigm to theory, which undermined Kuhn’s novel contributions. Thirdly, I propose a new articulation of exemplar and propose an exemplar-based approach to analysing the history of science. Finally, I show how the exemplar-based approach can be applied to analyse the history of science by my case study of the early development of genetics