Cytokinesis in onion roots: Inhibition by vanadate and caffeine

Summary The effect of vanadate ions on plant cytokinesis has been studied inAllium cepa root meristematic cells. Vanadate induces binucleate cells by inhibiting cell plate formation. Moreover, vanadate and caffeine have additive effects in the induction of binucleate cells.     

Genetic and photoperiodic control of an avian reproductive cycle

European blackcaps,Sylvia atricapilla, with one breeding season per year, have a single-peaked annual testes cycle. However, African conspecifics from the Cape Verde Islands with two breeding seasons per annum demonstrate a two-peaked cycle. Both population-specific cycles reflect differences in the respective endogenous circannual rhythms. Experimental hybridization of birds of the two populations resulted in an intermediate pattern of testes cycle, thus demonstrating that there are genetic components for some temporal aspects in an avian reproductive cycle. Another characteristic of the African birds, their extremely rapid juvenile development and early sexual maturity (at an age of 5–6 months) proved largely to be a photoperiodic (short-day) effect in birds hatched in autumn. The same effect could also be induced in European conspecifics exposed to correspondingly short day-lengths.     

Effect of photoperiod and all-female grouping on the estrous cycle of the bandicoot rat,Bandicota bengalensis

Summary Female bandicoot rats showing irregular cycles in 12L12D, were exposed to light-darkness cycles of 1L23D, 4L20D and 8L16D. Significant regularization of the estrous cycle was observed in 8L16D with most of the rats exhibiting a regular 3-day cycle and the regularity was further enhanced by all-female grouping (4/cage).     

Inhibition of virus multiplication and alteration of cyclic AMP level in cell cultures by flavonoids

Summary The inhibitory effect of four flavonoid compounds on virus multiplication and their influence on the intracellular cyclic AMP (cAMP) level were studied in cell cultures. Quercetin and quercitrin reduced the yields ofHuman (alpha) herpesvirus 1 (HSV-1) andSuid (alpha) herpesvirus 1 (pseudorabies virus), but hesperidin and rutin had no effect. Further, quercetin and quercitrin elevated the intracellular level of cAMP, whereas hesperidin and rutin did not alter the cAMP level. Both antiviral activity and cAMP-enhancing effect were dependent on the concentrations of the flavonoids, and these effects turned out to be parallel.This study suggests that a relation exists between the antiviral effect and the cAMP-enhancing activity of flavonoids.     

The presence and function of melatonin and structurally related indoleamines in a dinoflagellate,and a hypothesis on the evolutionary significance of these tryptophan metabolites in unicellulars

The bioluminescent dinoflagellateGonyaulax polyedra contains various indoleamines, in particular, melatonin and 5-methoxytryptamine, as well as enzymes of their biosynthetic pathway. Melatonin exhibits a high-amplitude circadian rhythm characterized by a dramatic increase shortly after the onset of darkness. The maximum of melatonin is followed by a peak of 5-methoxytryptamine. These 5-methoxylated indoleamines seem to be involved in the mediation of the information darkness.G. polyedra shows a short-day response, which consists in the formation of asexual cysts. Light break experiments demonstrate the photoperiodic nature of this reaction. Cells become sensitive to short days only upon exposure to a lowered temperature (<16°C). Melatonin mimics the short-day effect, but only at decreased temperature. 5-Methoxytryptamine is even a better inducer of cyst formation, acting also at 20°C and in any lighting schedule, including LL. Cyst induction is associated with stimulation of bioluminescence and cytoplasmic acidification. A model on the intracellular pathway of photoperiodic information transduction assumes increased deacetylation of melatonin under cyst-inducing conditions, binding of 5-methoxytryptamine to the membrane of an acidic vacuole, proton transfer to the cytoplasm, and decreased intracellular pH as the stimulus for encystment. Melatonin shows the property of a scavenger of superoxide anions. This reaction, which is efficiently catalyzed by hemin, leads to the formation of a substituted kynuramine (AFMK). Destruction of melatonin by light-induced superoxide anions in the presence of cellular hemin may represent a property which, during evolution, has made this molecule suitable as an indicator of darkness. On the other hand, AFMK, which is formed under illumination, might have become a mediator of the information light. Photoperiodism inGonyaulax shows surprising parallels to that in mammals, but allows the analysis of this phenomenon at an entirely cellular level.     

Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly

Summary Monarch butterflies sequester cardenolides from their larval host plants in the milkweed genusAsclepias for use in defense against predation. Of 108Asclepias species in North America, monarchs are known to feed as larvae on 27. Research on 11 of these has shown that monarchs sequester cardenolides most effectively, to an asymptote of approximately 350 g/0.1 g dry butterfly, from plants with intermediate cardenolide contents rather than from those with very high or very low cardenolide contents. SinceAsclepias host plant species are distributed widely in space and time across the continent, monarchs exploit them by migration between breeding and overwintering areas. After overwintering in central Mexico, spring migrants east of the Rocky Mountains exploit three predominantAsclepias species in the southern USA that have moderately high cardenolide contents. Monarchs sequester cardenolides very effectively from these species. First generation butterflies are thus well protected against predators and continue the migration north. Across the northern USA and southern Canada most summer breeding occurs on a fourthAsclepias species and in autumn most of these monarchs migrate back to Mexican overwintering sites. The ecological implications of this cycle of cardenolide sequestration for the evolution of monarch migration are discussed.