No abstract

Dark-grown Douglas-fir (Pseudotsuga menziesii [Mirb.J Franco) seedlings had approximately 30% of the major polypeptide of the light-harvesting chlorophyll a/b binding protein, 30% of cab mRNA, 54% of psbA mRNA, and 14% of total chlorophyll, in comparison with amounts in light-grown seedlings. Seedlings entrained under a 24-hour photoperiod of light and dark showed small diurnal fluctuations in cab and psbA mRNA levels and, when transferred to continuous conditions, no circadian rhythms in mRNA levels were apparent. These results suggest that regulation of cab gene expression in Douglas-fir differs from regulation in angiosperms, because in the latter, both light and circadian factors strongly influence the expression of cab genes.

ALOSI, M. C., and C. L. CALVIN. 1985. The ultrastructure of dwarf mistletoe (Arceuthobium spp.) sinker cells in the region of the host secondary vasculature. Can. J. Bot. 63: 889-898. Sinker cells showed ultrastructural similarities in three species of Arceuthobium on three different hosts despite differences in season of collection and fixation. All species had abundant osmiophilic lipid bodies, plastids with prolamellarlike bodies, mitochondria with large nucleoids, chromocentric nuclei, and peculiar saccules associated with plasmodesmatal fields. Xylem may not be continuous through sinkers. Apoplastic continuity between host and parasite is afforded by fused cellulosic cell walls. Pitlike wall thinnings and "half-plasmodesmata" are found between juxtaposed host and parasite cells. One-sided, imperforate sieve pores were noted between a sieve cell and a contiguous sinker cell. However, symplastic isolation of the host and parasite seems likely. Therefore, nutrients may be absorbed from the common host-parasite apoplast. Mobilization of nutrients out of the endophytic system to the aerial shoots is thought to be facilitated by differential starch storage in the parasite body. ALOSI, M. C., et C. L. CALVIN. 1985. The ultrastructure of dwarf mistletoe (Arceuthobium spp.) sinker cells in the region of the host secondary vasculature. Can. J. Bot. 63: 889-898.Les cellules de su~oirs de trois espkces du Arceuthobium sur trois h6tes diffkrents montrent des similaritks d'ultrastructure mCme si la saison d'kchantillonnage et la fixation sont diffkrentes. Chez toutes les espkces des corps lipidiques osmiophiles abondent, de mCme que des plastides avec des corps ressemblant a des prolamelles, des mitochondries avec de gros nuclko'ides, des noyaux chromocentriques et des saccules particuliers associks a des champs plasmodesmiques. Le xylkme peut ne pas Ctre continu a travers les su~oirs. La continuitk apoplastique entre I'h6te et le parasite est assurke par la fusion des parois cellulaires cellulosiques. Des amincissements pariktaux ressemblant a des ponctuations et des demi-plasmodesmes sont presents entre les cellules juxtaposees de I'h6te et du parasite. Des cribles unifaciaux imperforks ont ktk obsewks entre une cellule criblke et une cellule de su~oir contigue. Cependant, il semble probable qu'il y ait isolement symplastique de I'h6te et du parasite. Donc, les nutriments peuvent Ctre absorbks de I'apoplaste commun h6te-parasite. Nous croyons que la mobilisation de nutriments B l'extkrieur du systkme endophytique vers les pousses aCriennes est facilitke par le stockage differentiel d'amidon dans le corps du parasite.[Traduit par le journal]

Application. Development of DNA markers will provide abundant new genetic markers for forest tree improvement research. DNA markers will be most useful for estimating genetic diversity in breeding populations and for germplasm identification. Eventually, high-density maps may be used to identify quantitative trait loci and to practice marker-assisted selection.Abstract. DNA markers are rapidly being developed for forest trees. The most important markers are restriction fragment length polymorphisms (RFLPs), polymerase chain reaction-(PCR) based markers such as random amplified polymorphic DNA (RAPD), and fingerprinting markers. DNA markers can supplement isozyme markers for monitoring tree improvement activities such as; estimating genetic diversity in breeding populations, germplasm identification, verifying controlled crosses, and estimating seed orchard efficiencies. Because the number of DNA markers is potentially limitless, it should be possible to map individual quantitative trait loci (QTL) by linkage analysis with high-density maps. Finally, if such associations can be found, it may also be possible to design marker-assisted breeding strategies for forest trees.

In dark‐grown Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings, the steady‐state level of the major light‐harvesting chlorophyll a/b binding proteins mRNA (cab mRNA) was about 25% of the level that accumulated in light‐grown seedlings. A single, 5‐min irradiance with red light up‐regulated expression transiently, so that cab mRNAs accumulated to a Jevel approaching that determined for light‐grown seedlings. The response was reversible by far‐red light to the dark level, indicating that the up‐regulation was a phytochrome‐mediated response. Phytochrome action also up‐regulated genes that encode ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rbcS) in Douglas‐fir seedlings, but the maximal rbcS mRNA level that was attained after the red light treatment was several‐fold lower than the expression level deternined for light‐grown seedlings. Genes that produce ubiquitin and ubiquitin‐fusion transcripts were differentially expressed in dark‐ and light‐grown seedlings, but the genes did not appear to be phytochrome regulated.