Contribution of NaCl excretion to salt resistance of Aeluropus littoralis (Willd) Parl

Aeluropus littoralis is a perennial halophyte, native to coastal zones. Although it is usually exposed to high saline, this plant grows normally without toxicity symptoms. In order to assess leaf salt excretion, different growth parameters, Na+, K+, Ca2+, Mg2+ and Cl− concentrations, as well as excreted ions were examined in plants grown for 2 months in the presence of various salinity levels (0–800 mM NaCl). In addition, salt crystals, salt glands and other leaf epidermal structures were investigated. Results showed that total plant growth decreased linearly with increase to medium salinity. This reduction concerns mainly shoot growth. In addition, this species was able to maintain its shoot water content at nearly 50% of the control even when subjected to 800 mM NaCl. Root water content seemed to be unaffected by salt. Sodium and chloride ion contents in shoots and in roots increased with salinity concentrations, in contrast to our observation for potassium. However, calcium and magnesium contents were not greatly affected by salinity. Excreted salts in A. littoralis leaves were in favor of sodium and chloride, but against potassium, calcium and magnesium which were retained in plants. Sodium and chloride were excreted from special salt glands, which were scattered on the both leaf surfaces. In addition to salt glands, papillae were the most frequent epidermal structure found on A. littoralis leaves, and are likely involved in A. littoralis salt resistance.