Growth and Dormancy in Lunularia cruciata (L.) Dum.: I. RESUMPTION OF GROWTH AND ITS CONTINUATION

Lunularia cruciata may become dormant at three stages in itslife history: mature thallus, gemma, and spore. The resumptionof growth and its continuation in various conditions have beenstudied in thalli and gemmae. Air-dry, mature thalli of theIsrael strain, planted on a suitable medium, produce adventitiousbranches ventrally from the region immediately posterior tothe existing meristem, which itself fails to resume growth.When dormant gemmae are taken from the gemma-cup, however, theexisting apical cells and meristems simply recommence growing,so that the new growth is continuous with the old. Except inthe case of mature thalli aroused from dormancy, apical dominanceis pronounced, and branching occurs only by bifurcation. Thisdominance can be broken by applying sucrose solution to thegrowing tips—possibly a plasmolytic effect. The growth in area of freshly planted gemmae accelerates forabout 25 days before its relative rate slows to any great extent.During the first half of this period, growth is due exclusivelyto the expansion of existing cells, but subsequently cell numbersincrease rapidly from the 8–10,000 present in the dormantgemma. Cell numbers were estimated by using a modified macerationtechnique, in which chelation followed prolonged fixation. Lunularia grows successfully at quite low light intensities.Of the mineral nutrient deficienccs investigated, lack of Plimits growth most severely, although N-deficiency also restrictsit to a very low level. Gemma-cup production appears to be unaffected by light intensity,at least within levels permitting growth. There is, however,a large temperature effect, cup production decreasing markedlyabove 12° C.     

Resistance to desiccation and distribution patterns in the land snail Sphincterochila

The land snail Sphincterochila is represented in Israel by five species that replace one another along a climatic gradient that ranges from the Mediterranean areas receiving up to 1000 mm down to arid areas receiving only 70 mm of rain per year.
The resistance to three weeks of desiccation was studied in all five species. Total water loss was lowest in the desert-dwelling species S. zonata and highest in the Mediterranean S. aharonii and the desert-dwelling S. prophetarum , while the steppe-dwelling S. cariosa and S. fimbriata were intermediate. Sphincterochila zonata had a significantly thicker epiphragm, the lowest area specific water vapour conductance, the quickest response to desiccation (secretion of epiphragm), and a favourable surface-to-volume ratio compared to all other species. The Mediterranean-type water economy of S. prophetarum , despite its desert distribution, is related to its being an under-rock-dweller while S. zonata , which has the best adaptions to desiccating conditions, thrives in exposed areas. It is concluded that the differences in resistance to desiccation among the five species of one genus correspond to the gross distribution patterns and reflect the abiotic regime and the microhabitat of each species.     

Effects of Chloroquine on the Feeding Mechanism of the Intraerythrocytic Human Malarial Parasite Plasmodium falciparum1

Ultrastructural investigations of P. falciparum cultivated in vitro in human erythrocytes revealed new features of the feeding mechanism of the parasite. Mature trophozoites and schizonts take up a portion of the host cytosol by endocytosis which is restricted to cytostomes and which involves the invagination of both parasitophorous and parasite membranes. The resulting endocytic vesicles, surrounded by two concentric membranes, migrate towards the central food vacuole membrane. The external membrane of the endocytic vesicles apposes that of the food vacuole, leading to the internalization of vesicles bounded by a single membrane into the vacuolar space where they are rapidly degraded. We conclude from this sequence of events that endocytic vesicles fuse with the food vacuole. Treatment of infected cells with therapeutic concentrations of chloroquine inhibited the last step of the feeding process, i.e. vacuolar degradation. This was manifested by the accumulation within the vacuolar space of intact vesicles bounded by single membranes. The implications of these findings for the antimalarial activity of chloroquine are discussed.     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: II. THE RESPONSE TO DAYLENGTH AND TEMPERATURE

In the Israel strain of Lunularia under investigation long-daytreatment induces dormancy while short-day breaks it. Daylengthis perceived by all parts of the thallus, and even by younggemmae while in the cup of the mother thallus. Since light-breaktreatment is equivalent to long-day the effect is truly photoperiodic,but the critical daylength is not well defined. Temperatureinteracts strongly with photoperiod. High temperature (24°C.) combined with continuous light rapidly induces dormancy(c. 6 days). Fewer short days are required to restart growth,and the number (3–4) is unaltered by the duration of thecontinuous light treatment preceding it. Rinsing experimentssuggest that at least some of the inhibitory factor producedin long photoperiods can be leached from the plant. Dormancy-inducingtreatment quantitatively confers the capacity to resist drought(dormant plants survive air-drying, while actively growing thalliare killed in 80 per cent. R.H.). The photoperiodic effects on growth and dormancy are discussedand an inhibitor hypothesis is suggested to explain the responsesfound.     

Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya'aqov, Israel: ecology, longevity and fecundity

Ashkenazi, S., Klass, K., Mienis, H.K., Spiro, B. & Abel, R. 2010: Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya'aqov, Israel: ecology, longevity and fecundity. Lethaia, Vol. 43, pp. 116–127.
A unique fossil assemblage of the extinct freshwater viviparids Viviparus apameae galileae and Bellamya sp. with intact embryos enabled the assessment of population ecology parameters applied so far only to recent living populations. The assemblage, from the Early Middle Pleistocene site of Gesher Benot Ya'aqov, occurs in the sedimentary sequence above the Matuyama Brunhes Boundary (MB boundary) at 0.78 Ma. This fossil assemblage is related to a shoreline habitat that was affected by desiccation during a sudden drop in water level. In both species, the youngest females with embryos had five or more whorls, with heights of >24.8 and >16.1 mm in Viviparus and Bellamya respectively. Comparison of shell height and width, aperture height and width and the ratio of shell height/width indicated that females are significantly longer and larger than the shells without embryos. Longevity was estimated as at least 9 years for Viviparus and 8 years for Bellamya and lifetime fecundity of female viviparids was estimated based on longevity and reproductive period. The high number of reproducing females and high number of embryos indicate favourable habitat and climate conditions for both Viviparidae. The fossil Viviparidae from GBY have the characteristics of organisms that are K-selected by natural selection forces. □ Fecundity , fossil embryos , longevity , molluscs , Pleistocene , reproductive output , sexual dimorphism , viviparids.