Comparison of root xylem structure and hydraulic conductivity of triticale (X Triticosecale Wittmack) genotypes under salt stress

Abstract

To compare the root xylem and hydraulic conductivity of triticale genotypes (Sanabad, Juanillo, and ET-84-5) an experiment was carried out at two concentrations of NaCl (0 and 100 mM), hydroponically. When seedlings had a root length of 25-30 mm, they were transferred to a modified half-strength Hoagland nutrient solution in growth chamber. Then, xylem anatomy, root surface area, hydraulic conductivity, growth rate, and water loss in 14 to 18 days old plants were measured. The xylem anatomy was considered on free-hand cross-sections that were made from 5-10 mm root tips. Root surface area was determined by measuring the length and the radius of the main axis of seminal, adventitious and lateral roots of the 18 days old plants. Under salt, the length of seminal and adventitious roots decreased significantly and ranged from 53±4 to 29±5 mm and 11±1 to 9±2 mm, respectively. In all genotypes, salinity more negatively affected the diameter of central and peripheral metaxylem vessels compared to the number of vessels. The stellar cells in all genotypes were less lignified in adventitious roots and the mature xylem vessels of seminal roots of ET-84-5 and Sanabad had the most lignified walls. In all genotypes, the central metaxylem of seminal roots was less lignified compared to the peripheral metaxylem. Under salinity, the casparian bands could be detected more in the seminal roots as U-shape especially in ET-84-5 and Sanabad. The surface area of seminal root differed among the genotypes from 1.67×10-3 m2 in Juanillo to 1.04×10-3 m2 in Sanabad under salt stress. Juanillo with highest surface area and lowest thickness of lignified cell wall had the highest seminal root hydraulic conductivity (5.32×10-9 m s-1 MPa-1). It could be concluded that at the early growth stages of the triticale genotypes, the root structures of the Juanillo appeared to be more efficient for water uptake via seminal and adventitious roots and this might be attributed to less lignified cell wall of root cell.