Senescence processes in plants. Annual Plant Reviews, Volume 26.

Abstract

This is a timely book that addresses many of the recent advances in the plant senescence field. Senescence is an important developmental step in the life cycle of a plant or a plant organ and the process can have a considerable influence on agriculture. Leaf senescence is induced as part of plant development but can also be prematurely induced as a result of environmental changes or harvesting. Premature senescence leads to reduced yield and quality of crops and this is likely to be of increasing concern in times of climate change and parallel population growth. Therefore, it might be expected that more research should be focussed on this important topic in the future as increased understanding of the senescence trait will lead to the development of crops with improved yield, stress tolerance and shelf life. The majority of this book addresses the events that occur during leaf senescence. Chapter 1 describes some plant and animal senescence terminology including mitotic senescence and a potential role for telomeres, but the rest of the book mainly addresses one aspect of senescence, the post-mitotic senescence that occurs in fully developed organs. Leaf senescence involves a highly controlled process of degradation and mobilization. The internal structures are dismantled, macromolecules are broken down and nutrients are mobilized from the leaf for use in growing parts of the plant or to be stored in developing seed. To maintain cell viability until maximum nutrient mobilization has occurred, the dismantling process must be highly regulated and there are several chapters that describe this process in detail. The most well characterized and understood senescence-related degradation process is that which targets chlorophyll and this is described clearly in Chapter 2. This chapter also addresses the age-old question of why leaves go red in the autumn. Membrane degradation (Chapter 3) and nutrient mobilization (Chapter 5) are also well covered, with a useful chapter on the importance of the control of oxidative stress in senescing tissues, sandwiched in between. Chapter 6 gives a clear description of all the different environmental stresses that can affect senescence and includes the effects of oxidative stress and pathogens. Senescence is an active process that has been shown to involve de novo synthesis of many genes and proteins. Many of the recent advances in our knowledge of plant senescence are due to extensive use of the model plant Arabidopsis thaliana. Genomic resources such as the entire DNA sequence, complete microarrays and resources for functional analysis and identification of mutated genes have made arabidopsis invaluable for identification and characterization of genes that have a role in leaf senescence. Many of the chapters in this book reflect this bias. Chapter 10 (‘Molecular regulation of leaf senescence’), Chapter 7 (‘Developmental and hormonal control’) and Chapter 9 (‘Genomics and proteomics of leaf senescence’) are focused on arabidopsis data and there is quite a lot of repetition between these chapters. This is probably inevitable due to the lack of current knowledge on senescence in other plants and the fairly limited literature on the subject. The arabidopsis bias is relieved somewhat by the chapter on QTL analysis of senescence (Chapter 8), which describes current understanding on natural variation in crop species such as rice and sorghum. Also, there is a detailed chapter on flower senescence and a brief description of the current knowledge of the control of fruit ripening, both of which show some similarities to certain aspects of leaf senescence. The final chapter of the book ‘Genetic manipulation of senescence’ focuses on the use of the cytokinin biosynthesis gene (IPT) that was shown over a decade ago to be an efficient if crude mechanism for the artificial control of senescence in many crop species. It is disappointing that this still appears to be the most effective method for manipulating senescence, and this should be a challenge to senescence researchers everywhere to discover and develop more subtle approaches. In summary, this book provides an excellent, up-to-date and very detailed description of our current knowledge on plant senescence and would be a valuable text for any students or other researchers interested in developing projects in this area.