**3. Conclusions**

*Cell Growth*

germination percentage at 100 ppm. The treatment of freshly harvested and 1 year old seeds of soybean (*Glycine max*) with, 1 ppm 6-BAP increased the germination percentage from 50 to 85% in freshly harvested seeds and to 75% in the older seeds [48]. The effect of kinetin and 6-BAP on the seed germination of *Vicia faba* were studied, [49] found an increase in its germination percentage at the concentration of 100 ppm kinetin. While [50] found that, the highest germination percentage for faba bean (*Vicia faba* L.) was achieved at the concentration of 100 ppm 6-BAP. Also [37, 51] reported that the storage has an adverse effect on the hormone within the seeds of *Acacia saligna*, *Acacia Cyclopes*, *Acacia nilotica* and *Acacia albida*, which contained the lowest value of GA3, IAA and the highest content of phenols.

Plant hormones can also alleviate abiotic stress such as drought, extreme temperatures, and salinity [52, 53]. The action of these hormones in response to situations of stress can be developed through synergistic or antagonistic activities [54]. Also, [55] concluded that the plant growth regulators like ABA, JA, and ethylene are involved in the regulation of the plant response to abiotic stress. Cytokinins are also able to enhance seed germination by the alleviation of stresses such as salinity, drought, heavy metals and oxidative stress [56–59]. Ref. [60] found that GA3 plays an important role in the growth and metabolism of microalgae *Chlorella vulgaris* exposed to heavy metal stress and its adaptation ability to a low-level polluted aquatic environment. Meanwhile, gibberellin leads to enhancement for *Zea mays* seedling growth and establishment under saline soil conditions by improving nutrient levels and membrane permeability [61]. Also, hormonal interactions between plant and rhizosphere bacteria can affect plant tolerance to stress. As such, the plant and bacteria can be genetically modified so that they can perform more optimally

The decreased cytokinin and gibberellic acid (GA3) and increased abscisic acid contents are often observed responding in plants subjected to environmental stresses [63, 64]. Exogenous application of plant growth regulators [such as cytokinin or antioxidants (ascorbic acid) [65], Moringa (*Moringa oleifera*) leaves extract [66, 67], humic acid (HA) [68], or seaweed extract (SE) [69] could be an alternative strategy to ameliorate, minimizing or alleviating the adverse effects of abiotic stress factors on plant growth which led to promoting plant growth and development metabolism in plants. Several studies also indicated that results on wheat [70]; and on spinach [71]. Ref. [72] reported that the foliar application of Moringa (*Moringa oleifera*) leaves extract MLE is proved to be the most effective PGR in reducing plant

Also, bio-fertilization has beneficial microorganisms that increasing plant hormones, which led to enhances yield, plant growth and nutrient uptake under various environmental conditions such as salinity [73–76], drought and low fertility supply [77–79], especially that some endomycorrhizal fungi (Arbuscular mycorrhizal fungi) have been proven to improve drought stress; they colonize bio-trophically the root cortex and develop an extra-metrical mycelium that helps the plants to acquire mineral nutrients from the soil particularly those, which are immobile. They can under drought conditions stimulate growth-regulating substances, increase photosynthesis, improve osmotic adjustment, optimize hormonal balance

Numerous studies have found also, that it can be alleviation of salt stress on peanut [81]; on pumpkin plants [82]; on *Moringa peregrina* plants [83] by using foliar application of nano-fertilizers. Also, [84] reported that nano Zn-Fe oxide plays a significant role importance in alleviating salt stress, oxidative damages on plant cells by activation of certain antioxidant enzymes. In addition, [85] reported that the application of nano-oxide and bio-fertilizer reduced the negative effects of

under a range of conditions, including stress [62].

(*Lagerstroemia indica* L. seedlings) exposure to salinity stress.

and enhance water uptake [80].

salinity due to its contributed to produce hormones.

**4**

This chapter was indicated by many studies that the plant hormones, including IAA, cytokinins, ethylene, gibberellins, and brassinosteroids, can positively affect seed germination and seedling growth, for many plants as mentioned previously in the chapter, under favorable conditions. While ABA has an adverse on affect seed germination and the growth.

Also, this chapter sheds the light on the important role of soil bacteria in the production of plant hormones or as an alternative in the case of the low rate of plant hormones in the plant, which led to hence seed germination, growth, and hence crop production.

In addition, this chapter provided many studies that prove that the plant hormones very important to overcome dormancy or growth under stress condition. Also, shed the lights on the importance of the exogenous application of plant growth regulators (cytokinin or antioxidants, Moringa leaves extract, humic acid, or seaweed extract, bio- or nano fertilizers) for enhancing the productivity of plant hormones which led to increased cell growth.

Finally, it can be stated that the plant hormones are essential for cell growth, whether under normal conditions or under stress conditions.
