Kinetin applications alleviate salt stress and improve the antioxidant composition of leaf extracts in Salvia officinalis

A pot experiment was carried out under glasshouse conditions with common sage (Salvia officinalis L.) to investigate the interactive effects of salt stress and kinetin on growth attributes and the abundance of pigments, ions, phenolic diterpenes and α-tocopherol in leaf extracts of this species. The plants were subjected to the following four treatments: (i) control (nutrient solution), (ii) control + 10 μM kinetin, (iii) salt stress (nutrient solution + 100 mM NaCl), and (iv) salt stress + 10 μM kinetin. Kinetin was applied as a foliar fertilizer. Salt stress reduced water contents, photosynthetic activity and pigment contents of sage leaves. In addition, it increased Na+ contents, and reduced those of Ca2+ and K+ in leaves. Salt stress reduced carnosic acid and 12-O-methyl carnosic acid contents in leaves, while it did not affect carnosol and α-tocopherol contents. Foliar applications of kinetin seemed to counterbalance or alleviate the stress symptoms induced by salinity, improving ion and pigment contents, while leaf phenolic diterpene (mainly carnosol) and α-tocopherol contents also increased in both control and NaCl-treated plants; still this effect was much more obvious in salt-treated plants. A similar effect was also obtained when plants were sprayed with KNO3 or Ca(NO3)2, thus suggesting that kinetin effects were at least partly due to an improvement of ion homeostasis. Kinetin applications resulted in increased transcript levels of the isoprenoid and tocopherol biosynthetic genes, DXPRI and VTE2 and VTE4 in control plants, but not in NaCl-treated plants. We conclude that kinetin can alleviate the negative impact of salt on sage plants cultivated under arid environments with salinity problems.