PARTICIPATION OF SECOND MESSENGERS IN PLANT RESPONSES TO ABIOTIC STRESS

It is known that environmental stresses can have devastating effects on plants and represent the most limiting factors for productivity. Apart from biotic stress caused by plant pathogens, there are a number of abiotic stresses such as extremes in temperature, drought, salinity, heavy metals, radiation and mechanical wounding which have detrimental effects on plant growth and development. Certain plant species have developed various mechanisms to defence or adapt to such stress conditions. Mechanisms of signal perception and subsequent responses to stress are complex and consist of cascades of multiple reactions. For a couple of years these signaling cascades and metabolic responses are of great interest to plant biologists. A better understanding of plant stress responses can lead to improved plant breeding strategies resulting in better plant growth and increased crop yields under disadvantageous conditions. However, as we learn more about the signaling pathways leading to these responses, it is becoming clear that they constitute a network that is interconnected at many levels. Stress signal is first perceived by the receptors, then transduced downstream resulting in the activation of various stress responsive genes, transport across membrane and cytoskeleton reorganization. During the last couple of decades a number of second messengers such as calcium ions, cyclic nucleotides, polyphosphoinositides, that are altered in response to abiotic stressors, have been identified. They act on downstream effectors (decoding elements) that ultimately initiate a multitude of cellular responses. Primary targets of second messengers are calcium-dependent protein kinase, calmodulin, calmodulin-like proteins, SOS proteins in case of Ca2+, cyclic nucleotide gated cation channels for cNMP and calcium channels and various enzymes for phosphoinositides. The knowledge concerning the role of above proteins in stress is far from comprehensive. The usage of mutants, introduction of transgenes that reverse the effect of gene knock-out, blocking of genes by antisens mRNA or point mutations aim in better understanding the mechanisms of adaptation to stress. In this review, we summarize recent progress in abiotic stress studies concerning the participation of second messengers and their effectors in plant adaptation to various abiotic stress factors.