Biosynthesis of digalactosyldiacylglycerol in plastids from 16:3 and 18:3 plants

Intact chloroplasts isolated from leaves of eight species of 16:3 and 18:3 plants and chromoplasts isolated from Narcissus pseudonarcissus L. flowers synthesize galactose-labeled mono-, di-, and trigalactosyldiacylglycerol (MGDG, DGDG, and TGDG) when incubated with UDP-[6-³H]galactose. In all plastids, galactolipid synthesis, and especially synthesis of DGDG and TGDG, is reduced by treatment of the organelles with the nonpenetrating protease thermolysin. Envelope membranes isolated from thermolysin-treated chloroplasts of Spinacia oleracea L. (16:3 plant) and Pisum sativum L. (18:3 plant) or membranes isolated from thermolysin-treated chromoplasts are strongly reduced in galactolipid:galactolipid galactosyltransferase activity, but not with regard to UDP-Gal:diacylglycerol galactosyltransferase. For the intact plastids, this indicates that thermolysin treatment specifically blocks DGDG (and TGDG) synthesis, whereas MGDG synthesis is not affected. Neither in chloroplast nor in chromoplast membranes is DGDG synthesis stimulated by UDP-Gal. DGDG synthesis in S. oleracea chloroplasts is not stimulated by nucleoside 5′-diphospho digalactosides. Therefore, galactolipid:galactolipid galactosyltransferase is so far the only detectable enzyme synthesizing DGDG. These results conclusively suggest that the latter enzyme is located in the outer envelope membrane of different types of plastids and has a general function in DGDG synthesis, both in 16:3 and 18:3 plants.     

Ichnology and sedimentology of the early Permian deep-water deposits from the Lercara-Roccapalumba area (Western Sicily,Italy)

Summary Diverse and abundant trace fossils of the deep-waterNereites ichnofacies have been found in well-dated Early Permian deep-water turbidites (Lercara Formation) of western Sicily (Italy). Conodonts indicate a latest Artinskian to Cathedralian (late Early Permian) age. Microfossils (pelagic conodonts, albaillellid Radiolaria, paleopsychrospheric ostracods, foraminiferal associations dominated byBathysiphon), trace fossils (deep-bathyal to abyssalNereites ichnofacies) and sedimentologic data collectively indicate a deep-water environment for the Early Permian turbidites of the Lercara Formation. The dominance ofAgrichnium and of thePaleodictyon subichnogeneraSquamodictyon andMegadictyon suggests that this icnofauna is closely related in ichnotaxonomic composition to other late Paleozoic deep-water ichnofaunas. The occurrence ofAcanthorhaphe. Dendrotichnium andHelicoraphe, to date only reported from Cretaceous or Tertiary flysch deposits, suggests that the entire ichnofauna corresponds well to previously documented Silurian-Tertiary flysch ichnofaunas. Eight new ichnospecies and a new ichnosubgenus,Megadictyon, are described.     

Apios americana,a fly-pollinated papilionaceous flower?

In the flowers ofApios americana the vexillum remains ± in its bud position. In this way, a dark cavity is formed displaying a bright window at its base. Insect visitors are attracted to the hidden inflorescences by scent. In their attempt to reach the window they trigger an explosive release of stigma and pollen. Stigmatic fluid glues pollen to the visitor. All characters of the flower fit well into the myiophilous syndrome and thus flies are expected to be the proper pollinators.Apios americana seems to be the only myiophilous exception within the predominantly melittophilousFabaceae.     

Functional cis-element sequence requirements for suppression of gene expression by the TNPA protein of the Zea mays transposon En/Spm

TNPA, one of the two transposition proteins encoded by the En/Spm transposable elements of Zea mays, suppresses the expression of genes that contain an appropriate cis element. Suppression can be monitored in tobacco protoplasts in a transient expression assay as follows. The plant promoter-driven expression of the Escherichia coli-glucuronidase (GUS)-encoding gene, uidA, is repressed in the presence of TNPA if the GUS gene contains a functional cis element in the untranslated RNA leader sequence. Earlier, we found that the minimal cis element is composed of two 12 by sequences in a tail-to-tail inverted orientation. Each 12 by sequence is sufficient to bind TNPA in vitro and can be thought of as a half-site in the cis element. Here, we investigated the sequence requirements of the minimal cis element. Our observations support our expectations that a functional cis element must provide a template to which two TNPA molecules can bind in the correct orientation. Sequences within the half-sites can be altered as long as the eight bases that make up the consensus binding sites are not changed. However, we found the following unexpected sequence specificities. Firstly, some changes to the consensus binding sequence can be tolerated in one half-site, as long as the other site matches the consensus. Secondly, although the region between the half-sites can vary in sequence and in length between two and four bases, a thymidine residue is not tolerated directly 5′ preceding the second half-site. Since many variants of the cis element sequence remain functional, the suppressor response element provides a flexible tool for artificially manipulating the expression of genes.