>Magister Scientiae - MSc / In agriculture crop productivity is greatly affected by stresses such as salinity, drought, temperature and honnonal changes of crop plants and responses to these stresses. Studies have shown that a natriuretic peptide based regulatory system responsible for water and ion homeostasis in animals has a hctcrologous equivalent in plants. Plant natriuretic peptide immunoreactants (irPNPs) have been reported to be involved in K+, Na+ and er ions fluxes in plants. Previously, an Arabidopsis thaliana transcript (AtPNP-A) encoding an irPNP (AtPNP-A) has been identified and isolated (Ludidi et al., 2002). The AtPNP-A a novel protein and part of its physiological role is presented here.