Effect of nodule and pathogenic bacteria on levels of nitric oxide and cyclic adenosine monophosphate in pea roots at initial stages of interaction

Abstract

A significant role in the initial stages of rhizobial symbiosis formation in pea plants is performed by innate immunity. In this connection, the present study is focused on the concentration dynamics of two signalling molecules – nitric oxide (NO) and cyclic adenosine monophosphate (cAMP) – in the roots of etiolated seedlings of the Pisum sativum L. pea interacting with pathogenic (Pseudomonas syringae pv. Pisi) and nodule (Rhizobium leguminosarum bv. Viceae) bacteria. In time dynamics experiments, an endogenous rhythm of nitric oxide content changes in the root tissues of pea seedlings was characterised by an increase followed by a decrease in the level of nitric oxide and depending on exogenous biotic factors (symbiotic and pathogenic bacteria). Similar fluctuations were also observed when studying the dynamics of cyclic adenosine monophosphate concentration under the influence of the same biotic factors. The observed effects are assumed to be associated with certain exometabolites of Rhizobium leguminosarum bv. viceae (Nod-factors) and Pseudomonas syringae pv. pisi (cell wall exopolysaccharides) influencing the legume plant and activeting its innate immunity. Moreover, it is feasible that the different dynamics of changes in the studied components of the host plant signalling systems at the initial stages of interaction with symbiotic and pathogenic microorganisms have a variegated function: regulatory or protective in cases of symbiosis and pathogenesis, respectively. The observed change in the dynamics of the NO-synthase and adenylate cyclase signalling systems (NO and cAMP) components is assumed to be applied by the host plant as a “code” for transmitting a signal concerning the nature of the operating factor and the generation of corresponding reactions at the molecular level.