PubMed · 11979614
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
N Apter, M Partinen. 1999. [Delayed sleep phase insomnia].. https://pubmed.ncbi.nlm.nih.gov/11979614/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
We investigated seed dormancy and germination in Ficus lundellii Standl. (Moraceae), a native species of Mexico's Los Tuxtlas tropical rain forest. In an 8-h photoperiod at an alternating diurnal (16/8 h) temperature of 20/30 degrees C, germination was essentially complete (96%) within 28 days, whereas in darkness, all seeds remained dormant. Neither potassium nitrate (0.05-0.2%) applied continuously nor gibberellic acid applied either continuously (10-200 ppm) or as a 24 hour pretreatment (2000 ppm) induced germination in the dark. Germination in the light was not reduced by a 24-h hydrochloric acid (0.1-1%) pretreatment, but it was reduced both by a 24-h pretreatment with either H(2)O(2) (0.1-5 M) or 5% HCl, or by more than 5 days of storage at 40 degrees C (4.5% seed water content). In a study with a 2-dimensional temperature gradient plate, seeds germinated fully and rapidly in the light at a constant temperature of 30 degrees C, and fully but less rapidly in the light at alternating temperatures with low amplitudes (< 12 degrees C) about the optimal constant temperature. The base, optimal and ceiling temperatures for rate of germination were estimated as 13.8, 30.1 and 41.1 degrees C, respectively. In all temperature regimes, light was essential for the germination of F. lundellii seeds.
Growth of young sporophytes of the brown algae Laminaria digitata, L. saccharina and L. solidungula from Spitsbergen were measured in the laboratory after being exposed for 21 days to either photosynthetically active radiation (PAR = P) or to full light spectrum (PAR + UV-A + UV-B = PAB) using of cutoff glass filters. The plants were grown at 8+/-2 degrees C and 16 h light : 8 h dark cycles with 6 h additional ultraviolet radiation (UVR) exposure in the middle of the light period. Growth was measured every 10 min using growth chambers with online video measuring technique. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll (Chl) a content and DNA damage were measured in treated thalli at the end of the experiment. In all species, growth rates were significantly higher in sporophytes exposed to P alone compared to sporophytes exposed to PAB. Tissue DNA damage is dependent on thallus thickness and absorption spectra characteristics of pigments and UV-absorbing compounds. In sporophytes exposed to UVR, energy demands for repair of DNA damage and synthesis of UV-absorbing compounds for protection effectively diverts photosynthate at the expense of growth. Photosynthetic pigment was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. The general growth pattern in sporophytes exposed to P alone showed an increasing growth rate from the onset of light (0500-0900 hours) to a peak at the middle of the light phase (0900-1500 hours), a decline towards the end of the light phase (1500-2100 hours) and a minimum "low" growth in the dark (2100-0500 hours) relative to growth during the entire light phase. Under PAB, different growth patterns were observed such as growth compensation at night in L. digitata, delayed growth recovery in L. saccharina and minimal but continuous growth in L. solidungula. Growth as an integrative parameter of all physiological processes showed that the effect of UVR is correlated to the depth distribution of these species.
Explore the source record for details and available documents.