Plant senescence is key to many aspects of growth and development. Senescence is developmentally regulated and is also induced prematurely by stress and thus, studies on senescence overlap with many other programs of plant research. There are also links with programmed cell death in plants.

“The efficiency of plant senescence has a considerable effect on crop yield and resistance to environmental stress.”

This review presents the current understanding of the mechanisms by which plants control senescence and describes the molecular approaches that are being used to analyze the process. It includes a summary of the biochemical events that occur during senescence and the tools that are available to identify and characterize the key regulatory genes and pathways.

This paper describes the progress being made in the analysis of senescence in the model plant species Arabidopsis, which was the first plant for which the full genome sequence was available. Extensive genomic tools are available in Arabidopsis and these are starting to be extremely useful in the elucidation of complex processes such as leaf senescence.

Leaf senescence is a very well-controlled process by which the plant reclaims the contents of the leaf for use in further plant growth or for storage in developing seeds. Therefore it is very different when compared with senescence in animals, which mainly involves age-related deterioration.

The efficiency of plant senescence has a considerable effect on crop yield and resistance to environmental stress. Understanding how senescence is regulated will enable crop improvements in the future with consequent benefits to both producers and consumers.

In 1990, I was in a position to initiate my own research program and, after much reading, I decided that the molecular analysis of plant senescence was a topic that was receiving very little attention in spite of the importance of this process to many agronomic traits.

Improvements in resources available in plant molecular biology, especially the development of Arabidopsis as a model species, has enabled the project to develop from the identification of individual regulatory genes to the analysis of the expression changes of the complete genome using microarray technology. Targeted mutants allow functional analysis of specific genes.

A major challenge in this research has been the fact that the control of senescence is highly complex and involves a number of interlinking signalling pathways that exhibit cross-talk with other stress response and metabolic pathways. This has made it very difficult to identify key senescence regulators and the identification of mutants showing altered senescence has not contributed much as yet to our understanding of how the process is controlled.

The functional analysis that we are carrying out on genes that control senescence is generating large data sets that will require an application of a different approach to analysis. Extensive bioinformatic analysis leading to a systems biology approach, to identify and focus on key controlling points within the interlinked signalling pathways, will be an essential next step to this analysis.

The timing and efficiency of senescence has an important role in determining the yield and pre-harvest quality of many cereal, forage, and horticultural crops. Post-harvest senescence and loss of nutrients in green vegetables are important economic problems causing substantial losses to producers as well as loss of quality and nutritional value to the consumer.

Therefore, the identification of key regulatory genes and pathways involved in the control of senescence will provide plant breeders with tools for the generation of crops with improved yield, stress-resistance, and also post-harvest quality.

We are currently investigating genetic variation in broccoli with the aim of identifying genetic loci linked to post-harvest yellowing and nutrient losses and carrying out comparative analysis with Arabidopsis leaf senescence.