Ecophysiological characteristics of seed germination of the relict plant Metasequoia glyptostroboides

Abstract

Metasequoia glyptostroboides, known as a “living fossil” that was once widely distributed in the Northern Hemisphere, is now only found in a few restricted places in China. Many researches have been done on this species, but few on its seeds. Seed, as a key phase of spermatophyte life cycle, is important for regeneration and dispersal. Seed germination, which can be considered the initiation of the spermatophyte life cycle, is easily affected by environment. We studied the effects of temperature and light on ecophysiological characteristics of seed germination of M. glyptostroboides. Seed samples were collected from Lichuan City, Hubei Province, and stored at -20℃ before the experiment. A temperature gradient from 10℃ to 35℃ was used to study the effect of temperature on seed germination. Germination percentage, vigor index, and activities of dehydrogenase and antioxidant enzymes were used as a measure of seed vigor and stress resistance. The results indicated that temperature had a strong effect on seed vigor and activities of antioxidant enzymes. The germination rate, vigor index, and activities of dehydrogenase and antioxidant enzymes of M. glyptostroboides seeds were higher when temperature ranged from 19℃ to 28℃, whereas seed vigor declined greatly when the temperature was above 32℃ or below 19℃, and little germination was observed below 10℃. Our results imply that a temperature ranging from 19℃ to 28℃ is suitable for seed germination, with an optimum of 24℃. Seed germination was greatly inhibited by light (65 μmol·m -2 ·s -1 , 12 h/d), which implied that the germination of M. glyptostroboides seeds requires dark conditions. The seeds were of poor quality with the percentage of empty seed over 90%. The unsuitable temperature in the original habitat of M. glyptostroboides, together with the poor seed quality might be important factors limiting the regeneration of the species, and this might explain the lack of seedlings and saplings in M. glyptostroboides populations.