Mitigation of Salt Stress-Induced Inhibition of Plantago crassifolia Reproductive Development by Supplemental Calcium or Magnesium

In Plantago crassifolia, a moderate halophyte characteristic of borders of salt marshes in the Mediterranean region, reproductivedevelopment is more sensitive to high soil salinity than vegetative growth. To investigate the possible role of calcium and magnesiumsalts in the responses of this species to salt stress, adult plants were submitted over a 2-month period to treatments with 300 mMNaCl-a concentration which affects, but does not completely inhibit seed formation in P. crassifolia-either alone or combined with lowconcentrations of CaCl2 (10 mM) or MgCl2 (20 mM). The NaCl treatment did not affect plant vegetative growth and had a stimulatingeffect on flowering. Yet almost half the spikes produced had aborted seeds, and the effect on seed number and quality-estimated bytheir mean weight and germination capacity-was obviously deleterious. Addition of calcium or magnesium chloride during the saltstresstreatment completely counteracted the negative effect of NaCl on the ‘reproductive success’ of the plants: the number, weightand germination frequency of the seeds were similar to that in the control, non-stressed plants. These results indicate that both divalentcations can suppress or mitigate the deleterious effects of salt stress. While this protective role is well established in the case of calcium,we provide here the first experimental evidence of a similar function for magnesium.