Photosynthetic independence of initial light-caused increase in extractable nitrate reductase activity from maize seedlings

Comparisons of the effects of light on extractable nitrate reductase(EC 1.6.6.1 [EC] ) activity in Zea mays L. seedlings with and withoutnormally developing photosynthetic systems were made. Generally,plants lacking chlorophyll, due to either chemical treatment(fluridone) or genetic lesion (a chlorophyll and a carotenoidmutant), had as high or higher nitrate reductase (NR) activitiesas normally greening plants during the first 12 to 24 hr ofcontinuous white light (W) induction. This trend was especiallypronounced in mesocotyl tissues. In apical tissues (includingleaf, coleoptile and apical meristem) NR activity continuedto increase in normally greening plants between 24 and 48 hrwhile activities of achlorophyllous plants decreased markedly.These decreases could not be explained by a toxic accumulationof nitrite. Continuous far-red light (FR), which causes pronouncedphotomorphogenic development without significant greening, inducedabout one-half as much NR in the mesocotyls as did continuouswhite light. In apical tissues the effects of W and FR weresimilar throughout a 72 hr time course. Although trends weresimilar, the effects of light (W and FR) on nitrate concentrationwere kinetically different from effects on NR activity. Theseresults indicate that photosynthetic pigments are only secondarilyinvolved in NR induction. (Received June 12, 1979; )     

Actin filaments elongate from their membrane-associated ends

In limulus sperm an actin filament bundle 55 mum in length extends from the acrosomal vacuole membrane through a canal in the nucleus and then coils in a regular fashion around the base of the nucleus. The bundle expands systematically from 15 filaments near the acrosomal vacuole to 85 filaments at the basal end. Thin sections of sperm fixed during stages in spermatid maturation reveal that the filament bundle begins to assemble on dense material attached to the acrosomal vacuole membrane. In micrographs fo these early stages in maturation, short bundles are seen extending posteriorly from the dense material. The significance is that these short, developing bundles have about 85 filaments, suggesting that the 85-filament end of the bundle is assembled first. By using filament bundles isolated and incubated in vitro with G actin from muscle, we can determine the end “preferred” for addition of actin monomers during polymerization. The end that would be associated with the acrosomal vacuole membrane, a membrane destined to be continuous with the plasma membrane, is preferred about 10 times over the other, thicker end. Decoration of the newly polymerized portions of the filament bundle with subfragment 1 of myosin reveals that the arrowheads point away from the acrosomal vacuole membrane, as is true of other actin filament bundles attached to membranes. From these observations we conclude that the bundle is nucleated from the dense material associated with the acrosomal vacuole and that monomers are added to the membrane-associated end. As monomers are added at the dense material, the thick first-made end of the filament bundle is pushed down through the nucleus where, upon reaching the base of the nucleus, it coils up. Tapering is brought about by the capping of the peripheral filaments in the bundle.     

EFFECTS OF LIGHT ON GROWTH,RuBPCase ACTIVITY AND CHEMICAL COMPOSITION OF ULVA SPECIES (CHLOROPHYTA)1

The effects of light on growth, RuBPCase activity, and chemical composition of Ulva curvata (Kütz.) De Toni and U.Lactuca L. were examined at a range of temperatures and N-supply levels. Groeth of Ulva speices becomes more light-dependent with increasing temperature and N. The effect of light on RuBPcase is N-dependent, with a positive correlation under N-sufficient and a negative correlation under N-limited conditions. Light effects on pigment levels and ratios may be independent of effects on growth rate. These interactions uncouple growth rate from RuBPCase and pigments, and thus from tissue%N. The limits of variability of the growth-%N relationship can be described by a parabola. Under relative light or temperature-limitation, %N is negatively, growth increase with increasing %N. Tight coupling of seaweed wrowth and chemical composition may therefor be relatively rare in natural waters where growth can be simultaneously limited by light, temperature, and N.     

Identification of interstitial cells of Cajal in the digestive tract of turkeys (Meleagris gallopavo)

Interstitial cells of Cajal (ICCs) were identified in the digestive tract of turkeys by electron microscopy. ICCs have been implicated as sources of pacemaking slow wave potentials that initiate peristalsis in the stomach and intestines in mammals. The gastroduodenal contraction cycle in turkeys, however, is uniquely coordinated by a neurogenic pacemaker in the isthmus area between the glandular stomach and the gizzard, and this controls the coordinated phasic contractions of the muscles of the gizzard, duodenum and glandular stomach. Thus, it becomes important to look for the presence and distribution of ICCs in the avian digestive tract, especially in the gizzard and duodenum. This investigation has identified that cells are present which contain the typical characteristics of ICCs including: numerous mitochondria, caveolae, thin processes, basement membrane, filaments, rough ER, Golgi, and occasional gap junctions. They were mostly located in the region of the myenteric plexus between the longitudinal and circular muscle layers and occasionally within the longitudinal muscle layer. They were frequently near nerve axon bundles and were usually surrounded by collagen, elastin fibers, and occasional fibroblasts or blood vessels. ICCs were easily found in the ileum, but were also present in the duodenum, cecum, and rectum. None were found in the serosal region of the thick muscle of the gizzard. The presence of ICCs in the turkey duodenum, which like the gizzard is under neurogenic control, suggests that ICCs may play a role(s) in addition to initiating peristalsis.     

Mechanisms of excreta formation and elimination in turkeys and ostriches

Undigested feed and precipitated uric acid are excreted together in domestic turkeys, whereas in ostriches, liquid urine then discrete fecal boli are excreted in rapid succession. Gross anatomy and physiology of the cloacal structures of these two species also differ, providing an explanation for the differences in their waste products.     

Redox Chemistry in Laccase-Catalyzed Oxidation of N-Hydroxy Compounds

1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an “outer-sphere” type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation.     

Cellular Localization of Protoporphyrinogen-Oxidizing Activities of Etiolated Barley (Hordeum vulgare L.) Leaves (Relationship to Mechanism of Action of Protoporphyrinogen Oxidase-Inhibiting Herbicides)

Barley (Hordeum vulgare L.) that had been malted for 5 d developed only a small amount of bound (inactive) limit dextrinase, and very little free (active) enzyme was detected. Continuation of malting for up to 10 d only slightly increased the amount of both bound and free forms. Grain grown under conditions of ample moisture (wet grown) for 5 d produced a much higher amount of bound enzyme but a similarly low amount of free enzyme compared to malting conditions. After 10 d of growth there was a decrease in the amount of bound enzyme and a large increase in the amount of free enzyme, such that almost all of the enzyme was present in the free form. A more detailed study of limit dextrinase development in wet-grown grains revealed that a bound form was rapidly produced soon after germination. Five to 6 d after germination the amount of bound enzyme decreased rapidly and a very low amount was found in grains 9 d after germination. Meanwhile, a free form appeared slightly later and its initial rate of development was slow. At about 5 d after germination, precisely when the bound enzyme began to decrease, the free form increased rapidly, so that by 9 d after germination nearly all the enzyme was in the free form. The release of bound limit dextrinase in vitro occurred by proteolytic modification through the action of cysteine proteinases that were kept active or activated by the presence of reduced thiols in the extraction medium. The presence of cysteine proteinases was confirmed by inhibition studies using the inhibitors iodoacetamide, N-ethylmaleimide, antipain, and leupeptin. In addition, most of the bound form of limit dextrinase was soluble in 0.2 M sodium acetate buffer (pH 5.0) following extraction at 30[deg]C for 16 h and centrifugation at 3000g.     

Conservation of alternative splicing and genomic organization of the myosin alkali light-chain (Mlc1) gene among Drosophila species

The Mlc1 gene of Drosophila melanogaster encodes two MLC1 isoforms via developmentally regulated alternative pre-mRNA splicing. In larval muscle and tubular and abdominal muscles of adults, all of the six exons are included in the spliced mRNA, whereas, in the fibrillar indirect flight muscle of adult, exon 5 is excluded from the mRNA. We show that this tissue-specific pattern of alternative splicing of the Mlc1 pre-mRNA is conserved in D. simulans, D. pseudoobscura, and D. virilis. Isolation and sequencing of the Mlc1 genes from these three other Drosophila species have revealed that the overall organization of the genes is identical and that the genes have maintained a very high level of sequence identity within the coding region. Pairwise amino acid identities are 94%-99%, and there are no charge changes among the proteins. Total nucleotide divergence within the coding region of the four genes supports the accepted genealogy of these species, but the data indicate a significantly higher rate of amino acid replacement in the branch leading to D. pseudoobscura. A comparison of nucleotide substitutions in the coding portions of exon 5 and exon 6, which encode the alternative carboxyl termini of the two MLC1 isoforms, suggests that exon 5 is subject to greater evolutionary constraints than is exon 6. In addition to the coding sequences, there is significant sequence conservation within the 5' and 3' noncoding DNA and two of the introns, including one that flanks exon 5. These regions are candidates for cis- regulatory elements. Our results suggest that evolutionary constraints are acting on both the coding and noncoding sequences of the Mlc1 gene to maintain proper expression and function of the two MLC1 polypeptides.