Rosmarinic acid ameliorates the negative effects of salinity in in vitro-regenerated potato explants ( Solanum tuberosum L.)

Salinity causes massive loss of economic crops due to the build-up of toxic salts in shoot. Rosmarinic acid (RA) has been known to prevent the inevitable damage to vital biological molecules under stress. There is an increasing interest, therefore, in the use of polyphenols in crop stress physiology studies. An in vitro regeneration protocol was established using explants of the potato cultivar White Desiree to assess tolerance to salinity at a morphological, cellular, and biochemical level. Additionally, we examined the potential ameliorative effects of RA on growth in salt-stressed potato explants. Based on our observations, we propose a model for the ameliorative effects of a caffeic acid conjugate of α-hydroxyhydrocaffeic acid. Explants of White Desiree showed differential responses to salt and RA supplementation. Salt-stressed and control explants grown in RA-supplemented media showed a pronounced expansion of leaf area, suggesting direct effects of RA on cell elongation in potato explants. Root elongation was less affected by salinity in comparison to shoot elongation. Moderate levels of RA resulted in stimulatory effects on growth. The microscopic examination of leaves and stems indicated the presence of unique trichomes at the early stages of explant growth under RA supplementation, which varied considerably in size, shape, and distribution in response to stress. Our data indicated that RA significantly decreased osmolyte content under stress. Salinity resulted in the biosynthesis of high levels of free proline, carbohydrates, and malondialdehyde (MDA). However, the lower contents of MDA in salt-stressed explants treated with RA indicate that RA possesses anti-lipid peroxidation properties. Our observations provide evidence for the stimulatory effects of RA on cellular growth and the protection of membranes from ion toxicity.