Growth performance of Cakile maritima Scop and Brassica tournefortii Gouan in relation to the regulation of some sodium-inducible genes at salt affected lands in the Nile Delta coast

Understanding the mechanisms by which salt-tolerant species maintain growth under saline conditions is crucial for developing effective strategies to improve crop salt tolerance. Comparative studies of species with varying salt tolerance levels, particularly under natural environmental conditions, can reveal valuable adaptive mechanisms. Cakile maritima and Brassica tournefortii are halophytic species capable of thriving in saline habitats. Based on electrical conductivity measurements, individuals of both species were collected from sites characterized by low salinity (LS) and high salinity (HS). The growth of C. maritima was significantly enhanced at the HS site compared to the LS site, whereas B. tournefortii exhibited reduced growth under high salinity. Analysis of Rubisco protein content per unit leaf fresh weight revealed a significant decrease in C. maritima at the HS site relative to the LS site, suggesting nitrogen remobilization from Rubisco to support new biomass synthesis. In contrast, B. tournefortii accumulated Rubisco protein at the HS site, which may be associated with reduced photosynthetic assimilation and consequent growth inhibition. Both species accumulated sodium ions (Na⁺) in their leaves at the HS site; however, their strategies to cope with excess Na⁺ differed. Regulation of sodium-inducible genes in C. maritima suggests a controlled expression pattern that facilitates tolerance to elevated Na⁺ levels. Conversely, B. tournefortii appears to mitigate salt stress by upregulating sodium extrusion genes, actively removing excess Na⁺ to the external environment. Efficient utilization of Na⁺ likely contributes to osmotic adjustment and enhanced growth in C. maritima, whereas excessive Na⁺ accumulation in B. tournefortii may exert toxic effects, leading to growth inhibition.