Diaspore diversity in the anemochorousGouanieae (Rhamnaceae)

Fruits and seeds of four anemochorous taxa ofRhamnaceae-Gouanieae were studied by SEM. Flight performance of diaspores of three genera was analyzed. Diverging postfloral morphogeneses lead to different fruit and diaspore types: (1) a solid schizocarp dehiscing into three 2-winged mericarps (Gouania, Crumenaria), (2) an inflated schizocarp dehiscing into three inflated mericarps (Reissekia), and (3) a hollow septicide capsule which releases three winged hemimericarps (Alvimiantha). The latter convey significantly heavier seeds thanGouania andReissekia at comparable fall rates. The generic status ofAlvimiantha is confirmed. The Neotropics are pointed out as being a site of strong adaptive radiation for the tribeGouanieae.     

Natural hybridization in the genus Colletia (Rhamnaceae)

Natural hybridization in the genus Colletia (Rhamnaceae). Natural hybridization between two Chilean species of Colletia is assumed on the basis of morphological evidence. The characters of both species, C. hystrix Clos and C. ulicina Gill. & Hook., and those of their putative hybrids are described. The morphological intermediacy of the assumed hybrids is tested through Wells' distance diagram.     

Phytochemical variation inCondalia microphylla (Rhamnaceae)

Seed oil composition (sterol esters and sterols) and seed protein profiles ofCondalia microphylla were investigated. The chemical differences observed may be attributed to genotypic changes and could support the existence of infraspecific taxa.     

Reproductive biology of the Andean-disjunct genusRetanilla (Rhamnaceae)

Various aspects of the reproductive biology of the Andean-disjunct genusRetanilla (DC.) Brongn. were studied in populations ofR. trinervia andR. ephedra located in central Chile and ofR. patagonica in southern Argentina. Flowering extends from -austral- winter (early spring inR. patagonica) to early summer. The small, white, entomophilous flowers are incompletely protandrous and last four to five days. A weak pleasant odor along with nectar and pollen attract thirty-seven diurnal insect species, ten of which are probable pollinators: these include the honey bee, eight species of solitary bees pertaining toAnthophoridae (1 sp.),Colletidae (3 spp.) andHalictidae (4 spp.), and a nemestrinid fly. Although flower morphology and individual flower phenology do not fully prevent self-pollination (and geitonogamy can easily take place), the level of autogamy is low. Therefore, some self-incompatibility mechanism seems operative inRetanilla. Fruit set of open-pollinated flowers is extremely low, with a maximal value of c. 3% inR. patagonica. In this species, ripe fruits contain on average 1.37 viable seeds. Predispersal (maternal) reproductive success (percent ovules becoming viable seeds) is 2.3%. For medium to full-sized individuals this corresponds to c. 4600 potential offspring per year. As presently known,Retanilla is a reproductively uniform group, in which the Andean disjunction seems to have exerted no particular impact, which is consistent with the view that pollination generalization exerts some stabilizing influence on floral morphology and other reproductive traits.Retanilla expresses a basic rhamnacean set of traits (including protandry and self-incompatibility) showing also high pollen production and secondary pollen presentation. The latter two traits seem characteristic of theRetanilla-Trevoa clade, suggesting that a trend to increased male effort and, perhaps, dependence upon polleneating has evolved within the tribe Colletieae.     

Pollen morphology of the genus Paliurus (Rhamnaceae)

The pollen morphology of the genus Paliurus and the 5 species it comprises is described. Consistent with the general morphological pattern of the family Rhamnaceae, the pollen grains of Paliurus are uniformly isopolar, radially symmetrical, 3-(zono)-colporate and angulaperturate. Despite this general infrageneric uniformity, certain differences and trends can be recognized with respect to pollen size, shape, and tectum architecture.     

Floral biology of Ziziphus mauritiana (Rhamnaceae)

Floral development of the synchronous dichogamous species Ziziphus mauritiana, as followed by light and scanning electron microscopy (SEM), was divided into 11 stages using a series of landmark events. Main cellular events happen synchronously in the female and the male structures, such as meiosis in micro- and macrosporocyte cells, tetrad microspore formation and appearance of the functional megaspore cell, and onset of embryo sac differentiation coinciding with mitosis in the microspores. The last stage was characterized by anthesis and continued development of the flower, beginning with anther dehiscence (male phase) and proceeding to the female phase, which was characterized by style elongation. Flowers exhibit synchronous protandrous dichogamy; anthesis takes place in the morning (group A, e.g., clone Q-29) and afternoon (group B, e.g., clone B5/4). Stigma receptivity started after the male phase and occurred synchronously and complementarily with pollen dispersal in the two clones. Pollen viability and production were similar in the two clones, but the pollen diameter of Q-29 was significantly larger than that of B5/4. This study provides the basis for understanding the biological mechanisms regulating floral development, thus expanding the prospects for Z. mauritiana breeding programs and for further molecular and genetic studies of this species.     

Reproductive biology of Colletia spinosissima (Rhamnaceae) in Argentina

 We studied the reproductive behavior of Colletia spinosissima Gmel. at six sites in two regions of Argentina during the 1998–2000 flowering seasons. Flowering takes place in winter. The flowers are homogamous, fragrant, and entomophilous. There was evidence of self-incompatibility and cross-incompatibility between nearby partners. Fruit set of open-pollinated flowers (13.3%) seemed pollen-limited, since low fecundity was consistently associated with small stigmatic pollen loads and with low numbers of successful pollen tubes, and fecundity increased with abundance of efficient pollinators. Reproductive success (percent ovules becoming viable seeds) was 3.6. It is hypothesized that homogamy was established in Colletia because in an impoverished pollination environment – such as the one likely prevailing when this lineage evolved – achieving pollen export and receipt in a single pollinator visit has selective advantages. A large stigma and an extragynoecial compitum would compensate for the homogamy-driven, increased pollen-stigma interference. Received March 8, 2001 Accepted July 19, 2001     

Presence of sporangia of Frankia in the rhizosphere of Discaria (Rhamnaceae)

Discaria trinervis and Discaria americana are native actinorhizal plants in Argentina. Discaria seedlings growing in N-free liquid culture, inoculated with dry soils, developed Frankia colonies in the rhizosphere. The occurrence of hyphae, vesicles and sporangia characteristic of Frankia are described in these colonies. The presence of sporangia of Frankia has previously neither been reported in the genus Discaria, nor in the other genera of the tribe Colletieae inside root nodules or outside roots. The infective capacity of the colonies has been demonstrated.     

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba, Z. mauritiana and Z. spina-christi, with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z. mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba, probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba, the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.     

Leaf domatia in the section Alaternus (Miller) DC. of the genus Rhamnus (Rhamnaceae)

MARTINEZ-SOLIS, I., IRANZO, J., ESTRELLES, E. & IBARS, A. M., 1993. Leaf domatia in the section Alaternus (Miller) D C, of the genus Rhamnus (Rhamnaceae). Anatomical and morphological study of leaves from three species of Rhamnus {R. alaternus, R. myrtifolius and R. ludovici-salvatoris) which comprise the section Alaternus (Miller) DC. from the Iberian Peninsula and Balearic Islands, have revealed the presence of domatia, which are macroscopic infundibuliform structures. Although not all the leaves of one single plant showed domatia, all the individuals of each species examined presented these structures.     

Exudate flavonoids of eight species of Ceanothus (Rhamnaceae)

Leaf glands of Ceanothus species excrete a lipophilic material that contains a variety of flavonoids. Most of these are aglycones, but some glycosides were also observed. Seven out of eight species exhibit flavonols, whereas flavones are excreted by only one species. Four species produce flavanones and dihydroflavonols; one excretes a remarkable quantity of flavonol glycosides. The exudate flavonoids thus form different patterns that might be characteristic for different Ceanothus species.     

The microflora of soak water during natural fermentation of coarsely ground chickpea (Cicer arietinum) seeds

K. KATSABOXAKIS AND K. MALLIDIS. 1996. The microflora of soak water was studied during natural fermentation of coarsely ground chickpea seeds at 32°, 37° and 42°C. The soak water was slightly salted with NaCl 0.5% (w/v) and its proportion to sample was 10 : 1 (v/w). A gas-producing Clostridium species isolated from Reinforced Clostridium Agar (RCA) plates incubated anaerobically, was found to dominate this fermentation system particularly at the higher temperatures. Gram-negative bacteria and yeasts were not found. Bacillus species were isolated from Plate Count Agar (PCA) plates and Lactobacillus, Corynebacterium, Micrococcus and Pediococcus spp. from RCA plates were incubated aerobically. Butyric was the main acid produced at 37° and 42°C and CO₂ with hydrogen were identified as main fermentation gases.     

Heavy browsing affects the hydraulic capacity of Ceanothus rigidus (Rhamnaceae)

Defoliation by herbivores can reduce carbon assimilation, change plant water relations, and even shift the biotic structure of plant communities. In this study, we took advantage of a long-term deer exclosure experiment to examine the consequences of persistent deer herbivory on plant water relations and the xylem structure–function relationships in Ceanothus rigidus, a maritime chaparral shrub in coastal California. Browsed plants had thicker stems with many intertwined short distal twigs, and significantly higher sapwood-to-leaf area ratios than their non-browsed counterparts. Leaf area-specific hydraulic conductivity was similar in both browsed and non-browsed plants, but xylem area-specific conductivity was significantly lower in the browsed plants. Vessel diameters were equivalent in both plant groups, but the number of vessels on a transverse area basis was nearly 40 % lower in the browsed plants, accounting for their lower transport efficiency. Mid-day in situ water potentials and losses of hydraulic conductivity due to embolism were similar in both groups of plants but stomatal conductance was higher in the browsed shrubs in the early part of the growing season. We discuss our findings in the context of whole-plant ecophysiology, and explore the consequences of herbivory on hormonal signals, wood anatomy, and xylem function.     

Antibacterial and cytotoxic activities of extracts from (Tunisian)Rhamnus alaternus (Rhamnaceae)

The petroleum ether, chloroformic, ethyl acetate, methanolic, Total Oligomers Flavonoids (TOF) enriched extracts, water extract as well as its fractions A₁, A₂, A₃ obtained from aerial parts ofRhamnus alaternus, a Tunisian-Mediterranean medicinal species, were investigated for the contents of phenolic compounds, cytotoxic activity against the K562 human chronic myelogenous leukaemia cell line and L1210 leukaemia murine cells and for antibacterial activity against Gram positive and Gram negative bacterial reference strains. A pronounced cytotoxic effect on both the cell lines was shown in the TOF, ethyl acetate, methanolic, aqueous extracts and A₂ fraction, with respectively IC₅₀ values 75, 232, 298, 606 and 571 μg/ml on K562 cells and 198, 176, 767, 560 and 614 μg/ml on L1210 cell line. Significant activity against bacterial reference strains:Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Salmonella enteritidis andSalmonella typhimurium was shown with ethyl acetate, TOF extracts and A2 fraction. The antimicrobial and cytotoxic activities showed byR. alatemus depended on the chemical composition of the tested extracts.