Abstract
Plants of sunflower (Helianthus annuus L. cv Giza 2) were salt-stressed with a combination of NaCl and CaCl2
in concentrations having different osmotic potentials (
s from 0 to −1.0 MPa) and were treated with 5 and 10
mg L−1 of thiamin either sprayed on the shoot or applied to the root. The membranes of leaf discs from saltstressed
plants appeared to be less stable (more injured) under heat (51 °C) and drought (40% polyethylene glycol
6000) stresses than control plants. Salinity slowed the rate of growth (length and dry mass production), lowered
leaf relative water content (RWC) and leaf and root water potential (
w), decreased the contents of chlorophyll
(Chl), soluble sugars (SS) and the K+/Na+ ratio but enhanced total free amino acids (TAA), Na+, Ca2+
and Cl− accumulation in the shoot and root system. Root or shoot application of thiamin reduced membrane
injury by either heat or dehydration stress, lowered leaf
w, improved uptake of K+, and increased leaf RWC,
Chl, SS, TAA contents and dry mass production. The effects of salinity (
s), thiamin (Thi.) and their interaction
(
s × Thi) on the parameters tested were significant. Salinity was dominant (as indicated by 2 values) in affecting
the contents of Ca2+, Cl−, TAA and membrane stability to heat and leaf
w. The role of thiamin was dominant
for Na+, K+ and SS contents and the contribution of interaction was dominant for growth parameters, Chl.
and root
w.