Effects of shoot and root application of thiamin on salt-stressed sunflower plants

Abstract

Plants of sunflower (Helianthus annuus L. cv Giza2) were salt-stressed with a combination of NaCl and CaCl2 inconcentrations having different osmotic potentials (ψs from 0 to −1.0MPa) and were treated with 5 and 10mg L−1 of thiamin either sprayed on the shoot orapplied to the root. The membranes of leaf discs from salt-stressed plantsappeared to be less stable (more injured) under heat(51 °C) and drought (40% polyethylene glycol6000) stresses than control plants. Salinity slowed the rate of growth (lengthand dry mass production), lowered leaf relative water content (RWC) and leafandroot water potential (ψw), decreased the contents of chlorophyll (Chl),soluble sugars (SS) and the K+/Na+ ratio butenhanced total free amino acids (TAA), Na+,Ca2+and Cl− accumulation in the shoot and root system. Root orshoot application of thiamin reduced membrane injury by either heat ordehydration stress, lowered leaf ψw, improved uptake of K+,and increased leaf RWC, Chl, SS, TAA contents and dry mass production. Theeffects of salinity (ψs), thiamin (Thi.) and their interaction(ψs × Thi) on the parameters tested were significant.Salinity was dominant (as indicated by η2 values) in affectingthe contents of Ca2+, Cl−, TAA and membranestability to heat and leaf ψw. The role of thiamin was dominant forNa+, K+ and SS contents and the contribution ofinteraction was dominant for growth parameters, Chl. and root ψw.