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| Global change and temperate forest responseSignaling and regulatory mechanisms in stress defense |
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Jaakko Kangasjärvi
Institute of Biotechnology, University of Helsinki
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The growth, distribution, and productivity as well as product quality of plants is greatly influenced by the environmental stresses and other external stimuli to which they are continuously exposed. As sessile organisms, plants have developed various sophisticated ways to adapt in accordance with environmental demands by altering their metabolism, growth and development. Effective responses to both external and internal stimuli will ensure optimal growth and survival in an environment where productivity and product quality are adversely affected by biotic stresses, such as diseases and herbivores (wounding), and abiotic stresses, such as cold, heat and air pollutants. Plants must have effective means of defending themselves against invading pathogens and adapting to changes in their environment.
The main features of such defense measures involve early recognition and perception of the developing stress, and subsequent activation of induced adaptive and defensive responses leading to both local and systemic resistance. Reactive oxygen species (ROS) that are formed in plant cells by several stresses may be one of the factors that contribute to, and regulate plant stress sensitivity/tolerance. Strong evidence has accumulated that ROS play an important role in the signaling resulting in induction of plant defense responses.
The recognition of a stress is followed by involvement of a small number of signal transduction pathways mediated by at least salicylic acid (SA), ethylene and jasmonic acid (JA). JA, SA, and ethylene also seem to control and potentiate each other's activities, indicating that cross talk between these pathways may be very common in defense gene regulation. Several abiotic or biotic stresses are experienced by plants much in the same way. Therefore, it seems obvious that the signal transduction pathways involved are, at least partially, identical and combinations of signal molecules might direct the activation of certain defense responses. Synergistic or inhibitory cross-talk between these regulators may help the plant to prioritize the activation of a particular signal pathway over another and fine-tune its defense by upregulating different sets of overlapping genes against different aggressors. The studies on signal transduction will further lead to detailed understanding of several of the key signal transduction cascades involved in stress adaptation in plants. The hormonal networks responsible for the regulation of cell death as a result of oxidative attack will be presented as an example of interaction between multiple regulatory cascades.
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