Changes in the main osmotica during the development of Kandelia candel hypocotyls and after mature hypocotyls were transplanted in solutions with different salinities

Abstract.

No direct correlation was found between salt tolerance and vivipary. Ion (Mg²⁺, Ca²⁺, Na⁺, K⁺ and Cl^–) concentrations on a dry weight basis (mg/g) and on a milli-molar basis per mass of water in fresh tissue (mM) were followed during the development of Kandelia candel hypocotyls and after mature hypocotyls were transplanted under different treatments (salinities of 0, 15 and 30‰). During hypocotyl development, ion concentrations on a dry weight basis declined especially for Mg²⁺ and Ca²⁺. The decrease could not be explained by the decrease in water content. However, the concentrations on a milli-molar basis did not decrease, but increased slightly at a later stage. Mass balance studies showed that the hypocotyl development was a salt accumulation process, especially for Na⁺, K⁺ and Cl^–. Mangrove propagules adapt themselves to hyposaline environments by accumulating salt, especially before leaving their parent plants. Substrate salinity showed no modification of trends in Ca²⁺ and Mg²⁺ after transplantation, increasing rapidly in the beginning, then remaining at a high level and declining rapidly when roots formed. There were no significant differences in Mg²⁺ and Ca²⁺ concentration among treatments. The significance of salt level changes during hypocotyl development to salt tolerance remains to be clarified. After hypocotyl transplantation, concentrations of Na⁺, K⁺ and Cl^– increased gradually after insignificantly early changes. However, once roots formed, K⁺, Na⁺ and Cl^– concentrations increased rapidly under 15‰ and 30‰ salinity treatments, and declined or remained constant when salinity was zero. If corrected for water content, it was found that when roots formed there was a leakage of ions in K. candel hypocotyl during the zero salinity treatment. There was a faster ion uptake at salinities of 15‰ and 30‰. This showed that once the root system is formed, exchange with the environment becomes more rapid.