Effects of temperature and light on growth and development of embryos of Fucus edentatus and F. distichus ssp. distichus

Abstract

Growth and development of embryos, starting from zygotes, of Fucus edentatus De la Pyl. and F. distichus L. ssp. distichus (nomenclature is that used by McLachlan et al. 1971) were investigated under a variety of temperatures combined with various light conditions; both species appeared to respond in a similar manner. Growth was more rapid with increase in temperature up to 15°; at 20° embryos developed abnormally under prolonged incubation. Light (cool-white fluorescent lamps) saturation for growth occurred at about 3000 μW/cm² at 15°, and no inhibition was noted up to 12 000 μW/cm². In darkness or under light-deficient conditions, the primary rhizoid became relatively long but apical hairs were suppressed or reduced, and additionally in darkness there was little increase in the size of the thallus over that of the original zygote. Below 15° growth and development were limited by temperature. At 15° and a photoperiod exceeding 16 h or at 20° and a photoperiod exceeding 12 h aberrant morphological development of the embryo occurred. Incubation on a 6-, 36-, or 48-h day at 15° did not result in abnormal development where the light:dark (L:D) ratio was kept at 2:1. Under 36- and 48-h days growth was slower, indicating an inefficient use of light during the long light periods. The laboratory results suggest that distribution of this species in nature is largely controlled by factors acting on the embryo and that these responses may be different from those of the mature plant.