*4.1. Plant Material and Experimental Design*

Seeds of maize (cultivar Gohar-19) were obtained from the Maize & Millets Research Institute, Yusafwala, Sahiwal, Pakistan, and the experiments were conducted at the Department of Botany, Government College University Faisalabad, Pakistan. The seeds were surface-sterilized using a 1% sodium hypochloride solution for 5 min. Surface-sterilized seeds were thoroughly washed with distilled water and air-dried for 12 h. These seeds were soaked in 0, 50, 100 and 150 μM of SA solution for 12 h. Plastic pots were filled with 1 kg of washed and air-dried sand at the botanical garden, Government College University Faisalabad, and a 100% field capacity was maintained in pots by adding boron-free water. The experiment was carried out in a completely randomized design (CRD) with three replicates. Ten seeds were sown in each pot. After 5 days of germination, 5 seedlings were selected based on their similarity in size and vigor. B stress was applied using Nable's solution containing boric acid (H3BO3) by maintaining pH at 5.7. The final B concentrations of 0, 15 and 30 mg Kg−<sup>1</sup> soil were maintained in each pot for one week. After one week of B stress application, the plants were harvested and stored in a freezer for further analysis.

#### *4.2. Morphological Parameters and Plant Biomass*

The root and shoot lengths were measured for individual plants using a meter scale. The root and shoot fresh and dry weight, after drying at 70 ◦C for 72 h, was calculated using the same weight balance.

#### *4.3. Physiological and Biochemical Analysis*

Different physio-biochemical analyses were carried out as described below.

#### 4.3.1. Photosynthetic Pigments

Contents of chlorophyll a, b and carotenoids were determined using a 0.5 g fresh leaf sample. The Arnon [67] method with minor modifications was used for the determination of photosynthetic pigments. The collected sample was ground in 15 mL of 85% acetone and centrifuged at 10,000× *g* for 15 min. The absorbance of the supernatant was measured at 480, 645 and 663 nm using a spectrophotometer (Hitachi U-2001, Tokyo, Japan).

#### 4.3.2. Anthocyanin Content

The anthocyanin content was measured as reported previously [68]. Fresh root and shoot samples (0.1 g each) were ground separately in 2 mL of 1% acidified methanol (1 mL HCL and 99 mL methanol), then the extract was heated up to 50 ◦C for one in a water bath. The anthocyanin content was then quantified using a spectrophotometer (Hitachi U-2001, Tokyo, Japan) at 535 nm.

#### 4.3.3. Ascorbic Acid Content

The protocol of Mukherjee and Choudhuri [68] was followed to determine the ascorbic acid content. Root and shoot fresh samples (0.1 g) were taken and ground in 5 mL of trichloroacetic acid (TCA) using a pestle and mortar. The extract was filtered, and 4 mL of the homogenate sample was allowed to react with 2 mL of 2% dinitrophenyl hydrazine in an acidified medium. One drop of 10% thiourea (prepared in 70% ethanol) was added and the mixture was then allowed to boil at 100 ◦C

for 15 min. The absorbance at 530 nm was recorded through UV-spectrophotometer (Hitachi U-2001, Tokyo, Japan) for calculating the ascorbic acid content.
