Salinity Stress Alters Root Morphology and Root Hair Traits in Brassica napus

Abstract

Plant roots show morphological plasticity and play a substantial role in tolerance to various edaphic stresses. The aim of this study was to explore salinity-induced morphogenic responses of root traits and root hairs of two rapeseed varieties, BARI Sarisha-8 and Binasarisha-5, at the reproductive stage and perceive the effects on their reproductive growth. The experiment was conducted in a hydroponic culture. Two treatments, 0 mM NaCl as control and 100 mM NaCl, were imposed 55 d after germination. Plants exposed to 100 mM NaCl for seven days displayed greater damage in the leaves, flowers, and siliquae compared to control. Length of root hairs on first-order and third-order lateral roots, density of root hairs on first-order lateral roots, and length of third-order lateral roots were significantly greater by 91%, 22%, 29%, and 48%, respectively, in the treated condition compared to the control. An increase in estimated root surface area by 20% under salt stress conditions indicated that the spontaneous responses of plants to uptake more water and nutrients allowed a plant to cope with stressful conditions. The results of this study suggest that any future stress breeding programs should consider plasticity of root traits intensively.

Keywords: Brassica napus; reproductive growth; root hair; salinity.

Figure 1

A typical root system architecture of Brassica napus. Root hairs appear on the main axis and all types of lateral roots.

Figure 2

Leaf injury scoring for salinity stress.

Figure 3

Measurement of root hair traits under microscope (a) first-order lateral root of Binasarisha-5 in control conditions, and (b) first-order lateral root of BARI sarisha-8 in 100 mM NaCl treated conditions.

Figure 4

Effect of salinity on the reproductive organs at 7 d after treatment. (a) Inflorescence under control conditions; (b) inflorescence under 100 mM NaCl; (c) siliquae at control conditions; and (d) siliquae under 100 mM NaCl.

Figure 5

Injury scoring of two rapeseed genotypes, under control and 100 mM NaCl treated conditions at the reproductive stage, in a heat map created using conditional formatting in Microsoft Excel (Supplementary Datasheet 1). DAT, days after treatment. Each data point is the median value of five independent observations. Green, yellow, and red colors represent no, moderate, and severe injury levels.

Figure 6

(A) Density of second-order lateral roots, (B) length of root hairs originating on first-order lateral roots, (C) diameter of root hairs originating on first-order lateral roots, and (D) length of root hairs originating on third-order lateral roots of two rapeseed varieties under 0 mM and 100 mM NaCl treatments. Vertical bars indicate standard error of mean of four replicates against each variable. Different letters indicate significant differences among the genotype × treatment interactions.

Figure 7

Estimated root surface area of two rapeseed varieties under 0 mM and 100 mM NaCl treatments. Vertical bars indicate standard error of mean of four replicates against each variable. Different letters indicate significant differences among the genotype × treatment interactions.

Figure 8

Biplot of root and root hair traits. BARI-8.C = BARI Sarisha-8 under Control, BARI-8.T = BARI Sarisha-8 under Treated condition, BINA-5.C = Binasarisha-5 Control, BINA-5.T = Binasarisha-5 under Treated condition, FRd = Diameter of first-order lateral roots, SRD = Density of second-order lateral roots, TRL = Length of third-order lateral roots, TRd = Diameter of third-order lateral roots, TRD = Density of third-order lateral roots, RHLf = Length of root hairs on first-order lateral roots, RHdf = Diameter of root hairs on first-order lateral roots, RHDf = Density of root hairs on first-order lateral roots, RHLt = Length of root hairs on third-order lateral roots, and RHdt = Diameter of root hairs on third-order lateral roots.