Nitric oxide is downstream of auxin and is required for inducing adventitious root formation in herbaceous and woody plants.

LANTERI LUCIANA, PAGNUSSAT GABRIELA, LAXALT ANA MARÍA, LAMATTINA LORENZO.

Adventitious root formation of forest trees and horticultural plants - from genes to applications.

Research Signpost

Año: 2009; p. 31 - 50

The importance of adventitious root (AR) formation to successful in vivo and in vitro vegetative propagation and deployment of forest and horticultural crops has been recognized for centuries. The question of why some plant species readily form ARs and why some plant species do not has been the basis for much research because of its relevance to commercial application as well as improving our basic understanding of the regulation of plant developmental processes. At present, the process of AR formation is recognized to comprise of three phases: induction, initiation, and expression. We are only just beginning to understand the molecular mechanisms regulating these different phases of AR formation and their relationship to physiological and anatomical changes occurring during AR formation. The broad objective of this type of research approach has been to improve our ability to manipulate this important developmental event and develop new, more efficient procedures for propagating forest and horticultural crops. The objective of this book was to assemble up-to-date information on a broad spectrum of research themes related to the biology of AR formation. Several chapters in the first section of this book review current progress in understanding basic genetic and biochemical aspects of AR formation, while other chapters are more specific and focus on potential new directions for research on AR formation. The second section of this book includes chapters on specific applications of our current knowledge about AR formation. The significant role of auxins in AR formation has been recognized for almost a century and use of auxins is a common practice used by propagators to overcome rooting recalcitrance. However, in practice, application of auxins does not guarantee successful AR formation. Over the last few decades a combination of molecular, biochemical, and applied research has elucidated some of the reasons for variation in response to auxin treatments, including timing of application, temporal and spatial changes in endogenous concentrations, and interactions with other endogenous compounds. In this book, chapters 1, 6, and 11 summarize the molecular, biochemical, and histological evidence for the importance of varying concentrations of endogenous auxins during the different phases of AR formation and how cross-talk between hormones plays a pivotal role in regulating AR formation. Over the last two decades research on AR formation using model plants, such as Arabidopsis thaliana has elucidated several potential molecular mechanisms involved in the control of AR formation by a diverse array of biochemical and environmental signals. The intensive study of molecular bases for auxin role AR formation as well as messengers in the auxin-induced rooting of A. thaliana is summarized in chapters 1 and 2 of this book. Much recent research has been conducted using model plant species important in forestry and horticulture. In this book, the use of model woody plants for studying AR formation is described in the chapters 2, 4, 5 and 6. Additionally, chapter 12 summarizes current knowledge about the cellular, biochemical and molecular basis of AR formation in conifers, and the use of genomic tools and model plant species to discover new genes involved in AR formation. In plant propagation the physiological status of the donor plant, including age, canopy position, composition, and growth conditions greatly affect the ability to form ARs. Likewise, any handling and storage of plant materials and the propagation environment can influence rooting success. Applied research on AR formation has frequently focused on finding new root inducing compounds, developing optimal rates and methods for application of known root inducing compounds, determining biochemical markers to predict rooting potential, and understanding how abiotic and biotic factors in the production chain can influence AR formation. In this book the influence of stock plant qualities and propagation chain conditions on AR formation are discussed in chapters 9, 10 and 13. The deployment of gene modifications using of Agrobacterium rhizogenes rol genes to improve AR formation is presented in chapter 7 and the use of specific rooting adjuvants in chapter 8. Strategies for propagation of specific tree genera/species are presented in chapters 13, 14, 15, 16 and 17. Increased world-wide demand for forest products has intensified the need for efficient and rapid deployment of improved tree species in afforestation programs. Understanding the differential rooting response within a species and the ability to select for or manipulate this response has become a focus of several breeding programs for several forest tree species. This topic is covered in chapters 3 and 18. In addition to breeding programs, AR formation as a natural plant response in their native ecosystems has also recently received increased interest. A plant’s natural ability to form ARs has been interpreted by many researchers as response to stress. The formation of ARs can be an important adaptive mechanism of plants allowing for establishment and survival in several natural ecosystems. In this book the effect of burial on soil aeration in sandy coastal dune soils and the potential of AR formation as an adaptive trait for both flooding and burial tolerance are described in chapter 19. Twenty years ago, Davis et al. [Davis, T.D., Haissig, B.E., and N. Sankhla (eds). 1988. Adventitious root formation in cuttings. Advances in Plant Sciences Series, vol 2. Dioscorides Press, Portland, Oregon] presented a broad and indepth scope of information on AR formation. In the book Bruce Haissig wrote there is ‘hope for better enumeration and understanding of the causes and controls of rooting by cuttings, probably within this century and certainly by early in the next’. This prediction was made at the beginning of the explosion of molecular biology research and although there are still many open questions regarding the control of AR formation, molecular biology has significantly improved our knowledge. However, the translation of this knowledge into practical applications to improve AR formation has been much slower. This discrepancy between increasing knowledge versus applications may partly be due to differences in research approaches, the disciplines in which the scientists are professionally affiliated, and the journals in which they publish. Research reports concerning ARs span a broad range of disciplines and there is a growing amount of cross-over between applied and basic research related to AR formation. As editors, we fully enjoyed organizing and editing the chapters presented in this book and we greatly appreciate the hard work and enthusiasm of the authors for contributing their thoughts to this multi-disciplinary work. We also want to thank ESGEMO coordination and Academy of Finland (project 126488) for financial support. We all hope the ideas presented in this book will be useful to researchers, teachers, and propagators using practical aspects of AR formation in agriculture, horticulture, forestry, restoration, and ecology.