Calcium is an ubiquitous, crucial second messenger, that plays an essential and versatile role in cellular signaling. It has been shown to act as an intracellular regulator in many aspects of plant growth, development and stress responses. Many distinct signals induce spatial and temporal Ca2+ spikes as well as the frequency and amplitude of Ca2+ oscillations.

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.

Nitric oxide (NO) is a free radical that has been extensively studied as a substance causing air pollution and the product of metabolism of certain groups of bacteria. Ways to download it, metabolism and harmful effects on plants are well established. It turned out , however, that not only the plants respond to changes in the NO concentration in the environment, but they are in a position to produce it .

Cyclic adenosine 3’:5’-monophosphate and cyclic guanosine 3’:5’-monophosphate, common- ly know as cAMP and cGMP, are key second messengers in living organisms ranging from bacteria to Homo sapiens. Cyclic AMP and cyclic GMP are produced from ATP and GTP by the action of adenylyl cyclase and guanylyl cylase and are hydrolyzed to AMP and GMP by the cyclic nucleotide phosphodie- sterase. The natural occurrence of cyclic nucleotides in higher plants is now established, as is the presence of enzymes involved in their metabolism.

Nucleotides are among the most important compounds in all living organisms. They partici- pate in many biochemical processes in cells. They are precursors for nucleic acid synthesis, an energy source and precursors for components of primary and secondary metabolic products. Therefore, the metabolism of nucleotides are crucial for the growth and development of all organisms.