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371.
Net primary production (NPP) is an important function of plant communities which has not often been examined seasonally in a forested ecosystem. The major objective of the study was to measure above-ground NPP seasonally and relate it to phenological activity on a hardwood forest watershed at Coweeta Hydrologic Laboratory, North Carolina. NPP was estimated as the increase in biomass, estimated from regression equations on diameter. Diameter increases were measured by vernier tree bands. Phenological observations were made on bud break, leaf emergence, flowering, mature fruit, leaf senescence, and leaf fall. The species studied intensively were Acer rubrum, Quercus prinus, Carya glabra, Cornus florida, and Liriodendron tulipifera. Liriodendron was found to be the most productive species per individual, but Quercus prinus was the most productive per unit ground area. The total watershed estimate of aboveground NPP was 8,754 kg ha-1 yr-1 and included 47.9% leaves, 33.2% wood, 7.8% bark, 4.8% reproductive tissues, 4.2% loss to consumers, and 2.1% twigs. Increases in leaf biomass were most rapid in the spring, but woody tissue production peaked in June and continued through August. Since leaf production peaked in the spring, the plants' photosynthetic machinery was activated early in the growing season to support woody tissue production, which followed the period of rapid leaf growth, and reproductive activity. Flowering occurred during the leaf expansion period except for Acer rubrum, which flowered before leaf emergence. Fruit maturation occurred during late summer to early fall, when there were no additional biomass increases. Acer rubrum was an exception as its fruit matured during the period of leaf expansion. 相似文献
372.
Sexing of preimplantation mouse embryos by measurement of X-linked gene dosage in a single blastomere 总被引:5,自引:0,他引:5
Single blastomeres were isolated from zona-free 8-cell mouse embryos and assayed for X-linked hypoxanthine phosphoribosyl transferase (HPRT) activity and autosome-linked adenine phosphoribosyl transferase (APRT) activity. At this stage of development both X chromosomes are active in female embryos. Hence, a bimodal distribution of HPRT: APRT ratios, corresponding to male (XY) and female (XX) biopsied samples, was observed due to the 2-fold difference in gene dosage for HPRT activity. Batches of putative male and female embryos identified in this way were transferred to pseudopregnant recipient females. Development of the seven-eighths embryos was equivalent to that of control zona-free intact embryos. Sex determination by measurement of X-linked gene dosage was accurate and rapid enough to allow transfer of embryos of known sex without the need for cryopreservation. 相似文献
373.
374.
375.
Expression of injected HPRT minigene DNA in mouse embryos and its inhibition by antisense DNA 总被引:1,自引:0,他引:1
We have used a highly sensitive biochemical microassay to monitor the expression of a cloned minigene for hypoxanthine phosphoribosyl transferase (HPRT, EC.2.4.2.8) in preimplantation mouse embryos. The mouse HPRT promoter and the mouse metallothionein promoter (MT-I) function equally well in embryos at the 2-cell stage whereas the viral SV40 promoter does not allow HPRT expression. Induced HPRT activity from the MT-I HPRT minigene construct occurs in cleavage embryos cultured in the presence of cadmium. In contrast, negation of enzyme expression from the injected minigene DNA is mediated by simultaneous injection of HPRT antisense DNA. 相似文献
376.
Variation in epigenetic inheritance 总被引:7,自引:0,他引:7
M Monk 《Trends in genetics : TIG》1990,6(4):110-114
Changing patterns of DNA methylation may underlie differential gene expression in development. Additional sources of variation in allelic methylation may be introduced by parental differences as well as by gamete of origin. 相似文献
377.
Lynn R. Fraser Susan Monk Bridget Wardley-Smith Shara Cohen Michael J. Halsey 《Molecular reproduction and development》1986,13(2):143-149
Male mice of the TO strain were exposed to 50 ATA helium (0.5 ATA oxygen) over 5 weeks and then assessed for fertility both in vitro and in vivo. Significantly lower values for acrosome loss and fertilization of zona intact eggs in vitro were obtained with spermatozoa from the pressure-treated males. These results, coupled with the significant decrease in incidence and degree of polyspermy in zona-free eggs, indicated that fewer competent cells were present after preincubation under capacitating conditions. Fewer motile cells were observed in most samples, along with a reduction in the incidence of hyperactivated motility in some. Testis weight was also significantly lower. Results of fertilization in vivo, after mating with untreated females, showed a consistent trend toward subfertility, with a lower pregnancy rate and a smaller litter size. These differences did not reach significance, however, unlike those obtained in earlier in vivo experiments with males of the BALB/c strain. The discrepancy between in vitro and in vivo results with TO males probably represents differences between unselected and selected sperm populations, while that observed in vivo between the two strains probably reflects the superior reproductive capacity of the TO strain. 相似文献
378.
Zhi Hong Hua Jin Anne-Catherine Fitchette Yang Xia Andrew M. Monk Lo?c Faye Jianming Li 《The Plant cell》2009,21(12):3792-3802
Asn-linked glycans, or the glycan code, carry crucial information for protein folding, transport, sorting, and degradation. The biochemical pathway for generating such a code is highly conserved in eukaryotic organisms and consists of ordered assembly of a lipid-linked tetradeccasaccharide. Most of our current knowledge on glycan biosynthesis was obtained from studies of yeast asparagine-linked glycosylation (alg) mutants. By contrast, little is known about biosynthesis and biological functions of N-glycans in plants. Here, we show that loss-of-function mutations in the Arabidopsis thaliana homolog of the yeast ALG12 result in transfer of incompletely assembled glycans to polypeptides. This metabolic defect significantly compromises the endoplasmic reticulum–associated degradation of bri1-9 and bri1-5, two defective transmembrane receptors for brassinosteroids. Consequently, overaccumulated bri1-9 or bri1-5 proteins saturate the quality control systems that retain the two mutated receptors in the endoplasmic reticulum and can thus leak out of the folding compartment, resulting in phenotypic suppression of the two bri1 mutants. Our results strongly suggest that the complete assembly of the lipid-linked glycans is essential for successful quality control of defective glycoproteins in Arabidopsis. 相似文献
379.
M Monk 《BioEssays : news and reviews in molecular, cellular and developmental biology》1988,8(6):184-189
The access to human pre-implantation embryos that is afforded by procedures now developed for the treatment of infertility presents the possibility of very early prenatal diagnosis, before implantation in the uterus, of certain genetic diseases. Only the normal embryos would be replaced in the mother for initiation of implantation and pregnancy. Early experiments on a mouse model for Lesch-Nyhan syndrome (HPRT-deficiency) show that pre-implantation diagnosis of genetic disease is feasible. 相似文献
380.