**1. Introduction**

Abrupt changes in climate along with the potential abiotic and biotic stresses are serious challenges for plant growth and production worldwide [1]. Environmental stresses negatively influence the

germination, growth and yield of the crop plants. The continuous yield losses caused by abiotic stresses are one of the important reasons for socioeconomic imbalance [2]. Drought reduces the yield of staple food crops throughout the world up to 70% [3], and the effects of drought and salt stress on plant growth mechanisms and patterns have been discussed [3,4]. In the last few decades, soil and water resources are being contaminated with toxic elements due to industrial revolution and urbanization together with the use of artificial fertilizers [5,6]. Increasing levels of these toxic elements are imposing harmful effects on plants, plant-dependent animals and ultimately human health [7].

Boron is an important micronutrient in many plants for their normal functioning [8]. It is also considered to be an essential element for vascular plants according to the defined criteria for essentiality. The indirect association of B with photosynthesis has been reported in crop plants—e.g., soybean [9]. However, the rate of emergence and productivity is also decreased in many plants, including tomato, maize, wheat, alfalfa and carrot under B toxicity [10]. The B toxicity significantly reduces the yield of crop plants in relatively dry areas of the world [11]. Some of the factors contributing to the elevating levels of B are the use of fertilizers, mining and irrigation [12,13]. The B-induced toxicity occurs more commonly in saline soil in semi-arid geographical zones [14]. The interplay between salt stress and B nutrition in plants has been described, with contrasting results showing antagonistic and synergistic relations even within the same plant species [15]. It has been observed that salinity increases B toxicity [16], but the interaction of salinity and B is not fully understood [17], making it an important area of research in plant physiology and ecotoxicology.

Oxidative stress may result from a deficiency or excess of B, which triggers the over-production of reactive oxygen species (ROS). The ROS and their derivatives are highly toxic agents and damage cellular membranes due to lipid peroxidation, causing protein denaturation and mutations in DNA [18]. Different nutrients such as silicon (Si) [19], zinc (Zn) [20,21], potassium (K) [22] and calcium (Ca) [23] can ameliorate B toxicity in different crop plants. The SA signal molecule [24] plays an important role in reducing the hazardous effects posed by biotic and abiotic stresses. Thus, SA has been used by many researchers to reduce the hazardous effects of different stresses such as osmotic stress [25], heat, saline and B toxicity in wheat [26].

Among the most important staple foods, maize holds an important position after wheat and rice [27]. Maize is well known for its high potential of extracting heavy metals from soil [28]. Despite this phytoextraction ability, maize is affected by various environmental stresses along with the high metal concentrations. The abiotic stress effects on maize growth and yield have been studied [29,30]. In the current study, the main objective was to assess the effects of high B toxicity under the remodeling effects of SA in terms of physio-biochemical improvements in the maize cultivar Gohar-19.

#### **2. Results**

For assessing the effects of SA on mitigating the effects of B toxicity, plants were supplied with 0, 50, 100 and 150 μM of SA. The B toxicity levels were 0, 15 and 30 mg kg−<sup>1</sup> soil. Roots transport B via passive diffusion or facilitate transport [30] in the plant body through transpiration streams and it is accumulated in older shoots without being translocated [31], therefore the study parameters include both the root and shoot data of maize cv. Gohar-19.

#### *2.1. Root and Shoot Length*

The B toxicity significantly reduced the root and shoot length of maize seedlings. High B concentrations in soil inhibit the root and shoot growth due to the decreased photosynthetic activity and net plant productivity. Elevating the B concentration in soil decreased the root and shoot length up to 21.77% and 25.25%, respectively, which are significant reductions (Table 1, Figure 1). The priming of seeds with SA reduced the B toxic effects and retained the root and shoot lengths. Plant seeds that were primed with various concentrations (0, 50, 100 and 150 μM) of SA improved the root and shoot lengths. Significant increases in the root and shoot lengths were observed at 100 μM SA (Figure 2, Table 1). A 23.8% increase in root length was observed with the application of 100 μM of SA in 30 mg kg−<sup>1</sup> of

B-treated plants, while a 26.7% decrease was observed in the shoot length of 30 mg kg−<sup>1</sup> B-treated plants as compared with the control. The SA application at 100 μM was found to be the best treatment and caused increases in the shoot length in 30 mg kg−<sup>1</sup> B-treated plants up to 31.8%.


**Table 1.** Effects of SA (0, 50, 100 and 150 μM) on the plant root and shoot length of maize cultivar Gohar-19 under different B toxicity levels (0, 15 and 30 mg kg<sup>−</sup>1).

LSD 5% = 0.44. Values in the same column with different letters in superscript differ significantly.

**Figure 1.** Score (**a**) and loading plot (**b**) of principal component analysis (PCA) on different attributes of maize cultivar Gohar-19 plants supplemented with and without SA while grown under B stress. Score plot represents the separation of treatments as T1: 0 mg B without SA; T2: 0 mg B with 50 μM SA; T3: 0 mg B with 100 μM SA; T4: 0 mg B with 150 μM SA; T5: 15 mg/kg B without SA; T6: 15 mg/kg B with 50 μM SA; T7: 15 mg/kg B with 100 μM SA; T8: 15 mg/kg B with 150 μM SA; T9: 30 mg/kg B without SA; T10: 30 mg/kg B with 50 μM SA; T11: 30 mg/kg B with 100 μM SA; T12: 30 mg/kg B with 150 μM SA. Attributes evaluated include R L = root length; Car = carotenoids; R Nit = root nitrate; R K = root potassium; R Ca = root calcium, Antho = anthocyanin; L ASA = leaf ascorbic acid.

**Figure 2.** Correlations (r values) among the different studied parameters of maize cultivar Gohar-19 grown under different B stress levels and fertigated with and without SA. R L = root length; S L = shoot length; RFW=root fresh weight; RDW = root dry weight; SFW = shoot fresh weight; SDW = shoot dry weight; Chl a = chlorophyll a; Chl b = chlorophyll b; Car = carotenoids; Antho = anthocyanin; L ASA = leaf ascorbic acid; L H2O2 = leaf hydrogen peroxide; L Pro = leaf proline; L GB = leaf glycine betaine; R K = root potassium; L K = leaf potassium; R Ca = root calcium; L Ca = leaf calcium; R Nit = root nitrate; L Nit = leaf nitrate.
