Insight into mechanisms of multiple stresses tolerance in a halophyte Aster tripolium subjected to salinity and heavy metal stress

The study aimed at comparing metabolic reactions of a halophyte Aster tripolium to abiotic stresses. Profiling of endogenous phytohormones, soluble carbohydrates and stress-related amino acids was conducted in plants exposed to moderate and high salinity (150 and 300 mM NaCl), and heavy metal salts CdCl2 or PbCl2 (100 and 200 pM). High NaCl and Pb doses inhibited growth of A. tripolium (Stress Tolerance Index STI) of 37% and 32-35%, respectively. The plants tolerated moderate salinity and Cd (STI = 91% and STI = 83-96%, respectively). Toxic metals accumulated mainly in the roots but Cd translocation to the shoots was also observed. The stressors did not affect total concentrations of the main growth promoting phytohormones but we observed enhanced deactivation of auxins and gibberellins, and reduced accumulation of jasmonate precursor. ABA content increased under stress except for moderate salinity. A common reaction was also activation of osmotic adjustment, however it was disparately manifested under salinity and metallic stress. The distinct responses to salinity and metallic stresses involved changes in carbohydrate profile and altered interplay between salicylic acid content and the pool of active gibberellins. The content of active jasmonates diversified A. tripolium reactions to salt excess and each of the heavy metals. This parameter was linked to the accumulation of ethylene precursor. The results of the study can be used to decipher potential co-tolerance mechanism of this halophyte species to multiple environmental stresses.