The effects of salt stress on physio-biochemical traits, total phenolic and mucilage content of <i>Plantago ovata</i> Forsk under <i>in vitro</i> conditions

Plantago ovata Forsk (psyllium) is an important source of mucilage which is an ingredient in certain drugs and foodstuffs. The calli of 14 genotypes of psyllium were cultured on MS (Murashige and Skoog, 1962) medium containing 0, 100, and 200 mM NaCl, for four weeks, and the effects of salt stress on the following callus traits were evaluated: growth rate (CGR), relative growth rate (RGR), relative water content (RWC), Na+ concentration, K+ concentration, K+/Na+ ratio, proline content, total phenolic compounds (TPC), and mucilage content. A reducing trend was observed in GR, RGR, RWC and K+/ Na+ of the callus cultured in the medium with 100 mM NaCl, comparing to NaCl-free medium, while an increasing trend was observed in Na+ content, proline content, and TPC under the same conditions. Mucilage content of callus was found to increase in the medium containing 100 mM NaCl (0.13 g g-1 DW) but decreased afterwards at 200 mM NaCl (0.117 g g-1 DW), albeit with significant variations among genotypes. The results showed that among evaluated genotypes, Isfahan-1 was the most salt tolerant genotype at cellular level. In addition, the highest mucilage content was obtained in Khor-Biabanak genotype when the calli grown at 100 mM NaCl. It was postulated that mucilage content likely to be associated with salt tolerance and could be exploited to counteract the negative osmotic potential in callus affected by salt stress in P. ovata