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What is SenNet?

SenNet is a network of the leading European laboratories engaged in research on plant senescence. It was established in 2003 in response to an initiative from Dolores Abarca and Paul Dijkwel. The partners in SenNet use a very wide range of techniques to study common senescence-related processes. They have agreed that synergism existing between the partners will provide a much greater fundamental and holistic understanding than would be possible if laboratories continue to work in isolation from one another.

Why is plant senescence important for people?

The senescence of plants can be defined as a developmentally regulated, highly controlled process that leads ultimately to the death of the plant or plant tissue. A significant proportion of all fresh plant products for food or feed are lost, or suffer from reduced quality, due to plant senescence. For example, environmental stress leading to premature senescence can result in loss of yield and reduced nutritional quality whilst crops bred to stay green longer have improved yield and stress resistance. Failing to harvest crops at an appropriate stage leads to loss of quantity and/or quality as the crop matures or over ripens. Once harvested, degradative processes continue unless appropriate handling and storage regimes are employed and even then deterioration is only minimised, not stopped completely. Often the deterioration may not be apparent to the casual observer when fresh produce is purchased and it is only when the process is at an advanced stage that the symptoms of poor handling, incorrect storage and inappropriate transport become apparent. Conversely for some non-food plant products, it is desirable to promote post-harvest senescence, as in the example of flax retting.

Why is senescence important for plants?

In some cases it is the whole plant that senesces, usually after flowering, in a highly coordinated manner. In other species single organs, for example leaves, senesce in an ordered fashion, often when mutual shading results in lowered photosynthetic effort. In both cases considerable translocation of metabolites occurs from the senescing organ to other developing tissues; in the former example to the developing seeds or fruits and in the latter to other, younger, leaves. Senescence is an active process controlled by novel gene expression. Increasing our understanding of the triggers that cause the plant or organ to senesce and the genes that control the processes of cellular breakdown and the re-translocation of nutrients has extensive environmental and commercial implications.

What are the benefits of senescence research?

By studying the control of the degradative processes that occur during senescence it will be possible to:
• Identify genes that encode products that accelerate or delay senescence
• Identify and quantify metabolites associated with senescence and the degradation of fresh produce and other plant commodities

Data collected so far suggest that many different factors can cause the onset of senescence and there are many different signalling pathways involved. For example programmed cell death involves specific genes which have homologues in many species, including animals. In other tissues the catabolism of cellular components leads to the degradation of essential macromolecules. Despite these apparent differences the activation of some genes appears to be common to several, apparently, dissimilar routes to death. Increased understanding of the genes involved, through expression profiling, and the metabolic consequences of their action is essential if plant breeding and the commercial handling of fresh produce is to lead to a better quality product for the consumer.

What are the practical objectives of SenNet?

1. Senescence database
The network has identified as a priority the collation of senescence data into a dedicated bioinformatic database to facilitate the comparison of genomic and metabolomic information from a wide range of species and tissues which can then be applied to:
• Establish the set of core senescence components common to a wide range of economically-important plant species
• Improve and monitor conventional breeding techniques to ensure new varieties possess more desirable genetic traits
• Identify genes that would be immediate candidates for manipulation by targetted mutagenesis (e.g. transposon tagging) and by transgenesis if/when this technology becomes viable in the European market
• Modify harvest, transport or storage regimes to delay deterioration of fresh produce
• Design diagnostic tests to rapidly assess the stage of senescence of fresh produce and/or predict its longevity

2. Training
Training is required in the methodologies available to study plant senescence, to meet the future needs of European Agroindustries for knowledgeable staff able to develop new handling, storage and transport regimes for fresh plant-based foodstuffs. Controlling and exploiting post-harvest changes is also essential for new uses of plants, e.g. conversion of crop residues into biofuels. At the present time there are serious shortages of such trained staff. Moreover, the trained researchers will become invaluable for continued basic investigations into plant senescence as well as related areas of biological and biomedical research.