**6. Conclusion**

**5.4. Cu stress**

(Table 2).

**5.5. Zn stress**

**Effects on gene**

**Effects on protein**

consequence of Zn toxicity [142].

alleviated the Zn-induced oxidative stress.

**content** --- Increased Decreased protein

Among the pollutants of agricultural soils, Cu has become increasingly hazardous due to its involvement in fungicides, fertilizers, and pesticides [130]. In addition, Cu present in excess has been known to decrease root biomass and alter plant metabolism [131, 132]. Sharma and Bhardwaj [127] demonstrated decrease in growth parameters of *Brassica juncea* grown under Cu stress. The reduction in growth parameters due to the Cu stress occurred as a result of decreasing mitotic activity and cell elongation [133, 134]. Moreover, Chen et al. [130] suggested a different opinion. They concluded that Cu-induced inhibition in root growth of rice seedlings was due to the stiffening of the cell wall. Moreover, excess of Cu ion leads to the generation of

Effects of exogenous application of BRs were studied on *Raphanus sativus* seedlings under Cu stress. It was found that 24-epiBL promoted the shoot and root growth by overcoming the Cu toxicity [136]. The growth-promoting effects of BRs on seedlings under Cu stress may be linked to the general ability of BRs to promote cell elongation and cell cycle progression [137, 138] as well as the stimulation of genes encoding xyloglucanses and expansins [139]. BRs applications also increase antioxidant enzyme activities [140, 141]. Increasing all parameters as a result of BRs application improves plant tolerance against Cu stress, and finally plant development

Zn is an essential microelement, the second most abundant transition metal after iron (Fe), and has a role in many metabolic reactions in plants [35, 36]. However, high concentrations of Zn are toxic, induce structural disorders, and cause functional problems in plants. At organism level, Zn stress causes reduced rooting capacity, growth, and at cellular level alters mitotic activity [37, 38]. It induces oxidative stress by promoting ROS production as a result of indirect

Application of BRs on plants alleviates Zn stress via increasing protein content and antioxidant enzyme activities (Table 2). Çağ et al. [143] reported that EBL application effectively enhanced the protein content in *Brassica oleraceae* cotyledons. Sharma et al. [144] also reported that presowing treatments of HBL lowered the uptake of metal and enhanced the activities of antiox‐ idative enzymes and protein concentration of *B. juncea* seedlings under Zn stress. Moreover, Ramakrishna and Rao [145] also reported that the application of 24-epiBL significantly

**References** [114] [146] [30] [147] [141] [145]

**expression** --- --- --- --- --- ---

content ---

Showed varying results


harmful ROS via the formation of free radicals [135].

380 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

Roots are very important plant organs whose architecture is determined by endogenous and environmental conditions to adjust water and nutrient uptake from soil [148, 149]. BRs, one of the plant hormones, have both positive and negative effects on root growth related to hormone concentrations [150]. Experimental condition is one of the most important factors for analysing BRs effects on root development. The procedures using BRs to alleviate abiotic systems generally are easy, time saving, and one of the most reliable systems [53]. Therefore, BRs open up new approaches for plant tolerance against hazardous environmental conditions [151]. Morphological, biochemical, and molecular analyses have been performed to analyse the effects of BRs. However, detailed analyses should be performed to investigate the relationship between abiotic stresses and BRs, especially gene expression studies will provide knowledge about interaction at molecular level in plants [152]. We tried to cite as many papers as possible. Yet we apologize to authors whose works are gone unmentioned in this chapter.
