Germination of mucilaginous seeds of Plantago albicans (Plantaginaceae): effects of temperature, light, pre-sowing treatments, osmotic stress and salinity

Plantago albicans L. (Plantaginaceae) is a perennial herbaceous plant widely distributed throughout the Mediterranean region. The germination requirements (under different controlled conditions of light and temperature, and after two pre-sowing treatments) and tolerance to osmotic stress (polyethylene glycol, PEG 6000) and salinity (NaCl) of P. albicans seeds were studied. Seeds were germinated under constant temperatures (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, 25 degrees C and 30 degrees C) and alternating temperature regimes of 20/10 degrees C and 25/15 degrees C with a 16h/8h light/dark photoperiod. The outer layer of seeds become mucilaginous when wetted and the presence of mucilage on seeds significantly increased germination percentages at all temperatures tested. P. albicans seeds were non-dormant and temperature significantly affected germination percentages and germination rate (germination velocity expressed as mean germination time, MGT). The final germination percentages ranged from 34% to 89% for intact seeds (seeds with mucilage) and from 9% to 62% for demucilaged seeds, depending on the temperature. Temperatures of 25 degrees C and 25/15 degrees C gave the highest germination percentages. Light did not affect seed germination at both temperature regimes assayed (25 degrees C and 25/15 degrees C). Germination percentages of seeds soaked for 24h in distilled water or in a gibberellic acid (GA(3)) solution were not significantly higher than that of untreated seeds. In general, both the final germination percentage and germination rate were reduced by increasing salinity and PEG concentration. Seeds germinated in up to 35% PEG and 300mmol center dot L-1 NaCl. Recovery of germination for seeds when transferred to distilled water after being in PEG or salinity treatments for 15 days was quite high, suggesting that P. albicans seeds are tolerant to osmotic and salt stresses.