Reactive oxygen species (ROS) are excited or partially reduced forms of atmospheric oxygen, which are continuously produced during aerobic metabolism like many physiochemical processes operating throughout seed life. Previously, it was believed that ROS are merely cytotoxic molecules, however, now it has been established that they perform numerous beneficial functions in plants including many critical roles in seed physiology. ROS facilitate seed germination via cell wall loosening, endosperm weakening, signaling, and decreasing abscisic acid (ABA) levels. Most of the existing knowledge about ROS homeostasis and functions is based on the seeds of common plants or model ones. There is little information about the role of ROS in the germination process of halophyte seeds. There are several definitions for halophytic plants, however, we believed “halophytes are plants that can grow in very saline environment and complete their life cycle by adopting various phenological, morphological and physiological mechanisms at canopy, plant, organelle and molecular scales”. Furthermore, mechanisms underlying ROS functions such as downstream targets, cross-talk with other molecules, and alternative routes are still obscure. The primary objective of this review is to decipher the mechanisms of ROS homeostasis in halophytes and dry seeds, as well as ROS flux in germinating seeds of halophytes.

Halophytes adapt to salinity using different biochemical response mechanisms. Temporal measurements of biochemical parameters over a period of exposure to salinity may clarify the patterns and kinetics of stress responses in halophytes. This study aimed to evaluate short-term temporal changes in shoot biomass and several biochemical variables, including the contents of photosynthetic pigments, ions (Na⁺, K⁺, Ca²⁺, and Mg²⁺), osmolytes (proline and glycine betaine), oxidative stress markers (H₂O₂ and malondialdehyde), and antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) activities of three halophytic Salicornia species (S. persica, S. europaea, and S. bigelovii) in response to non-saline, moderate (300 mM NaCl), and high (500 mM NaCl) salinity treatments at three sampling times. Salicornia plants showed maximum shoot biomass under moderate salinity conditions. The results indicated that high Na⁺ accumulation in the shoots, coupled with the relative retention of K⁺ and Ca²⁺ under salt stress conditions, contributed significantly to ionic and osmotic balance and salinity tolerance in the tested Salicornia species. Glycine betaine accumulation, both constitutive and salt-induced, also seems to play a crucial role in osmotic adjustment in Salicornia plants subjected to salinity treatments. Salicornia species possess an efficient antioxidant enzyme system that largely relies on the ascorbate peroxidase and peroxidase activities to partly counteract salt-induced oxidative stress. The results also revealed that S. persica exhibited higher salinity tolerance than S. europaea and S. bigelovii, as shown by better plant growth under moderate and high salinity. This higher tolerance was associated with higher peroxidase activities and increased glycine betaine and proline accumulation in S. persica. Taking all the data together, this study allowed the identification of the biochemical mechanisms contributing significantly to salinity tolerance of Salicornia through the maintenance of ion and osmotic homeostasis and protection against oxidative stress.

A comprehensive body of scientific evidence indicates that rhizobial bacteria and melatonin enhance salt tolerance of crop plants. The overall goal of this research was to evaluate the ability of Rhizobium leguminoserum bv phaseoli to suppress salinity stress impacts in common bean treated with melatonin. Treatments included bacterial inoculations (inoculated (RI) and non-inoculated (NI)), different salinity levels (non-saline (NS), 4 (S1) and 8 (S2) dS m⁻¹ of NaCl) and priming (dry (PD), melatonin (PM100) and hydro (PH) priming) with six replications in growing media containing sterile sand and perlite (1:1). The results showed that the bacterial strain had the ability to produce indole acetic acid (IAA), ACC deaminase and siderophore. Plants exposed to salinity stress indicated a significant decline in growth, yield, yield components, nitrogen fixation and selective transport (ST), while showed a significant increase in sodium uptake. However, the combination of PM100 and RI treatments by improving growth, photosynthesis rate and nitrogen fixation positively influenced plant performance in saline conditions. The combined treatment declined the negative impacts of salinity by improving the potassium translocation, potassium to sodium ratio in the shoot and root and ST. In conclusion, the combination of melatonin and ACC deaminase producing rhizobium mitigated the negative effects of salinity. This result is attributed to the increased ST and decreased sodium uptake, which significantly reduced the accumulation of sodium ions in shoot.

Salinity tolerance is presumed to be improved in the intercropping system, however, there has been inadequate evidence to scientifically prove this. In the current study, the effect of salinity was examined on forage yield and quality of sorghum and kochia in an intercropping system with different planting ratios in a two-year field trial at Shiraz University. The treatments included three salinity levels of irrigation water; 2 (non-saline as a control), 7 and 14 dS m⁻¹ in main plots and planting ratios; sole sorghum (SS), ⅔ sorghum-⅓ kochia (S₂K₁), ½ sorghum-½ kochia (SK), ⅓ sorghum-⅔ kochia (S₁K₂) and sole kochia in subplots. The results showed that salt stress decreased forage yield of both plants, especially of sorghum. Salt stress at 14 dS m⁻¹ reduced fresh and dry weights by 44.9% and 62.4% in sorghum, and 38.7% and 23.3% in kochia, respectively. Salinity also reduced forage quality assessed in terms of crude protein, ash, neutral detergent fiber (NDF), acid detergent fiber (ADF), and total digestible nutrients (TDN). The optimum intercropping systems did not change forage yield, but it increased forage quality via reducing ash, ADF and NDF. The optimum planting ratio was S₂K₁ for both sorghum and kochia, while the SK ratio was suitable for kochia only. Under non-saline conditions, the sole crop cultivation was a better system, while under saline conditions intercropping with a low density of another plant led to higher dry and fresh weights, as well as lower ash, ADF and NDF for each plant. Since kochia performed as a dominant plant, sorghum growth was considerably suppressed under the high density of kochia (i.e., S₁K₂), especially at 14 dS m⁻¹ salinity level, which might have been due to high salt tolerance of kochia. Based on the findings of the current study, it could be inferred that in regions with limited freshwater, optimum planting ratio (SK in general for both plants) in an intercropping system could improve the quality of forage with no significant reduction in forage quantity.