**2.5 Photosynthesis**

Salinity hinders the photosynthesis process by limiting plants' stomatal and/or non-stomatal activities to some extent [66]. Salt stress affects stomatal conductance (g*s*) initially due to disrupted water relations and then later because of local abscisic acid (ABA) production [67]. Salinization caused some stomatal closure, although photosynthetic losses were predominantly non-stomatal in nature. According to several investigations done with various oilseed *Brassica* cultivars, the duration and doses of salt stress have a substantial impact on plant photosynthetic properties (**Table 3**). Salt stress also has a deleterious effect on photosynthesis because it reduces photosynthetic pigments, and causes considerable changes in photochemistry [5]. The study


#### **Table 3.**

*Impact of salinity stress on photosynthesis and associated parameters of oilseed Brassica sp.*

performed by Mahmud et al. [65] found that salt stress (100 and 150 mM of NaCl) adversely affected the levels of photosynthetic pigments in *B*. *napus* plants.

Salt stress has an impact on cell organelles, such as the chloroplast, where most of the photosynthetic activities, such as photosystem I (PS I) and PS II, take place [75]. It reduced the density of active reaction centers and the structural performance of PSII photochemistry, owing to damage on the receptor side of PSII [17]. According to an experiment by El-Badri et al. [54] with five different *B. napus* cultivars, Yangyou 9 and Zhongshuang 11 responded differently under 150 mM NaCl regarding photosynthetic pigments, such as Chl *a,* Chl *b*, and carotenoids (Car). Under salt stress, Chl *a* content was decreased by 36% in Yangyou 9 cultivar and 39% in Zhongshuang 11 cultivar, whereas Chl *b* content was reduced by 39% and 40% in Yangyou 9 and Zhongshuang 11 cultivar, respectively. Also, total Chl was reduced by 38 and 39% in Yangyou 9 and Zhongshuang 11, respectively, under the same dose of salinity. Moreover, Car content in Yangyou 9 and Zhongshuang 11 was decreased by 41% and 35%, respectively, under stress.
