Effect of NaCl on proline and glycinebetaine metabolism in Kosteletzkya pentacarpos exposed to Cd and Zn toxicities

Abstract

Proline and glycinebetaine are osmolytes playing a role in resistance to salt and water stress but their involvement in plant adaptation to heavy metals remain unclear. Young plants of the halophyte Kosteletzkya pentacarpos were grown in nutrient solution in the presence of Cd (20 or 40 μM) or Zn (200 or 400 μM), or a combination of both heavy metals and in the presence or absence of NaCl 50 mM for 48 h. Osmolytes concentrations, enzyme activities involved in their metabolism and expression of corresponding genes were determined in roots and leaves. Cadmium but not zinc increased proline and glycinebetaine in the leaves. Salinity reduced proline content in Cd-treated plants but increased it in plants exposed to Cd + Zn. Proline was produced through both glutamate and ornithine pathways while proline dehydrogenase was inhibited in response to heavy metals. Correlation between enzyme activities and corresponding gene expression was significant in the leaves but not in the roots. Gene coding for proline transport (KvProT) was upregulated in response to heavy metals. Low NaCl dose (50 mM) afford protection to heavy metal stress in K. pentacarpos and its effect on osmolyte synthesis depends on considered metal and plant organ.