Variations in Seed Size Within Populations of Silene dioica (L.) Clairv. in Relation to Habitat

The sizes of seeds in populations of Silene dioica were comparedincluding observations on variation within and between plantsin a population growing wild in south-east England. The meanseed weights of different populations from Europe displayedvariations, which contrasted with rather stable means foundin a population sampled in 4 different years, or compared whengrowing under natural conditions or in cultivation. Variationsfrom plant to plant within a population, between populationswithin a particular area, and between different capsules fromthe same plant were similar in range and distribution to thedifferences found between populations. Seed size did not appearto be correlated with season of maturity, level of dormancy,or position on the flower truss, but significant differenceswere found in mean seed weights from different individual plants. The results are discussed in relation to the natural distributionof the species, and its role as an opportunist species inhabitingthe edges of deciduous woodlands. Silene dioica (L.) Clairv., red campion, seed size     

The parallel expression of metal tolerance in pollen and sporophytes of Silene dioica (L.) Clairv., S. alba (mill.) krause and Mimulus guttatus DC

Summary The purpose of this paper was to determine if heavy metal tolerance was expressed in pollen and if its expression was correlated with the tolerance of the pollen source. Clones of Silene dioica, tolerant to zinc, closely related but nontolerant S. alba and clones of Mimulus guttatus tolerant and sensitive to copper were grown in the greenhouse in either standard potting soil or nutrient culture. Pollen was collected shortly after dehiscence, hydrated, and tested over a broad range of metal concentrations. The tolerance of the pollen source was determined by comparing root growth in solutions with and without heavy metals. In both Silene species and M. guttatus, the tolerance of the parental clone was expressed in its pollen. Pollen from tolerant individuals was able to germinate and grow at concentrations of metals which markedly inhibited pollen from nontolerants.     

Characterization of the Germination Responses to Temperature of Lettuce (Lactuca sativa L.) Achenes

Germination tests were done on 23 cultivars of lettuce (Lactucasativa L.) comprising a variety of different morphological formsselected for cultivation at various seasons. Significant differences at the upper limit of temperature tolerancewere found between different cultivars: maximum temperaturesfor 50 per cent germination ranged from 23 to 32 °C, andsusceptibility to the induction of secondary dormancy by hightemperatures varied widely from one cultivar to another. Nocorrelations were established between germination responsesand heading type, achene colour or growing season The germination responses of all cultivars at temperatures fromjust above 0 to 20 °C were closely similar and results froma large number of experiments were used to produce a standardgermination reference curve foti culvars of L. sativa. Departfuresrom this curve were found to arise predominantly from variationsin seed quality or test conditions rather than from the genotypeof the cultivar. Detailed comparisons of germination at all possible combinationsof alternate and constant day/night temperatures are presentedfor two cultivars. One with relatively high tolerance to high-temperatureinducedinhibition, the other with low tolerance. The results are discussed in relation to the original distributionof the species as a wild plant and its history of cultivationby man. Lactuca sativa L., Lettuce, achene germination, temperature response     

Temperature conditions control embryo growth and seed germination of Corydalis solida (L.) Clairv., a temperate forest spring geophyte

Spring is often the most suitable period for seedling establishment of temperate woodland species. Different physiological mechanisms resulting in spring emergence have evolved in seeds of such plants. The aim of this study was to determine the requirements for breaking dormancy and for seed germination of the European perennial spring geophyte Corydalis solida (Fumariaceae). Ripe seeds of C. solida contain an underdeveloped embryo, consisting of no more than a clump of cells. As a consequence, the embryo has to differentiate and grow to a critical length before germination can occur. In nature, seeds are dispersed in spring, while growth of the embryo starts in the autumn and continues in winter. Germination starts in late winter, immediately after embryo growth is completed, resulting in seedling emergence in the following spring. Experiments in controlled conditions showed that temperature is the main factor controlling dormancy and germination. Incubation at autumn temperatures (15/6 °C; 20/10 °C) for at least 8 weeks is required to initiate embryo growth, while a transfer to 5 °C is needed for completion of embryo growth and germination. Growth of the embryo of C. solida occurs at different temperatures over an extended period, a feature typical of temperate forest herbs. Our results indicate that the dormancy mechanism in seeds of C. solida is very similar to mechanisms in other Corydalis species studied thus far, suggesting that stasis in the dormancy trait has occurred.     

Adaptation to shade of the light-harvesting apparatus in Silene dioica

Abstract. The physiological characteristics and photo-system composition of the photosynthetic apparatus of Silene dioica , a woodland plant, grown in sun and natural shade are examined. As expected, shade leaves exhibited lower chlorophyll a/b ratios, light saturated rates of CO₂ assimilation (A_sat), dark respiration (R_d,) and light compensation points ( Г ), with both sun and shade leaves having similar absorptances and quantum yields of CO₂ assimilation (φ). Shade leaves were able to utilize far-red light for electron transport and carbon assimilation and reach the compensation point. Sun leaves in far-red light had a rate of carbon assimilation equivalent to their dark respiration rate. Chlorophyll fluorescence kinetics from leaves at 77 K together with analyses of thylakoid contents of photosystems (PS) I and II and the light-harvesting cholorphyll a/b protein complex associated with PSII (LHCII) demonstrated that the antenna size of PSII was similar in thylakoids of sun and shade leaves, but shade leaves contained ca. 20% more PSII and ca. 12% less PSI complexes. The increased PSII/PSI ratio in shade leaves accounted for their ability to achieve the compensation point in far-red light. An important feature of photosynethic shade adaptation in S. dioica is an increase in the PSII/PSI ratio and not an increase in the antenna size of PSII. The adaptive response of sun leaves when placed in a shade environment was rapid and had a half-time of ca. 18h.     

DNA diversity in sex-linked and autosomal genes of the plant species Silene latifolia and Silene dioica

The relatively recent origin of sex chromosomes in the plant genus Silene provides an opportunity to study the early stages of sex chromosome evolution and, potentially, to test between the different population genetic processes likely to operate in nonrecombining chromosomes such as Y chromosomes. We previously reported much lower nucleotide polymorphism in a Y-linked gene (SlY1) of the plant Silene latifolia than in the homologous X-linked gene (SlX1). Here, we report a more extensive study of nucleotide diversity in these sex-linked genes, including a larger S. latifolia sample and a sample from the closely related species Silene dioica, and we also study the diversity of an autosomal gene, CCLS37.1. We demonstrate that nucleotide diversity in the Y-linked genes of both S. latifolia and S. dioica is very low compared with that of the X-linked gene. However, the autosomal gene also has low DNA polymorphism, which may be due to a selective sweep. We use a single individual of the related hermaphrodite species Silene conica, as an outgroup to show that the low SlY1 diversity is not due to a lower mutation rate than that for the X-linked gene. We also investigate several other possibilities for the low SlY1 diversity, including differential gene flow between the two species for Y-linked, X-linked, and autosomal genes. The frequency spectrum of nucleotide polymorphism on the Y chromosome deviates significantly from that expected under a selective-sweep model. However, we detect population subdivision in both S. latifolia and S. dioica, so it is not simple to test for selective sweeps. We also discuss the possibility that Y-linked diversity is reduced due to highly variable male reproductive success, and we conclude that this explanation is unlikely.     

Changes in Germination Responses of Silene secundiflora in Relation to the Climate of its Habitat

Silene secundiflora is a Mediterranean species restricted in range to the southern coasts of Spain and the Balearic Islands. Germination tests were made in incubators and on thermo-gradient bars to evaluate changes in temperature-responses at intervals after seed harvest. Results were compared to average temperatures occurring in the region and interpreted in relation to the climatic characteristics of the area. Germination of freshly harvested seed was restricted to a narrow temperature band between ca. 7 and 16°C. After-ripening during the first four months resulted in a progressive widening of the temperature band favouring germination, but this remained below average summer temperatures. Exposure of imbibed seed to high temperatures (31°C) reduced the subsequent temperature maximum for germination by about 4°C, but did not induce a fully effective secondary dormancy. The results appeared to be well correlated with a situation in which germination normally occurs in September at the start of the winter growing season.     

Spore Germination of Ceratopteris thalictroides (L.) Brongn

Germination of the spores of Ceratopteris thalictroides wasexamined by light and scanning electron microscopy. Spores germinateby scission of the spore coat at the trilete markings. The initialcell divisions produce a proximal prothallial initial with rhizoidsthat are distal and lateral. This represents a reverse orientationof the more common situation in ferns. Evidence is presentedthat rhizoid initials divide with the most lateral of the daughtercells differentiating into a rhizoid. Rhizoids are long andunbranched. The uniseriate protonema is transient with bi-dimensionalgrowth established quite early. About a week following germination,the gametophyte is broad at the basal region and narrow at theanterior region. Further growth of cells in the basal regionis by elongation and the anterior region broadens to producean elongate-ovate gametophyte.     

Growth and longevity of Mytilus edulis (L.) from northeast Europe

The growth of mussels, Mytilus edulis (L.), was studied in most of the northeastern part of their distribution. The growth, longevity and maximal size of molluscs from 24 wild populations and one cultured population located in the White Sea and the southeast part of the Barents Sea were compared. The 25 studied populations were combined in six clusters. The maximal longevity and the size of the mussels varied between 7 and 18 years and 25.5 and 77.7 mm, respectively. The geographical location of the population within the studied region did not affect either maximal longevity or maximal size, or the growth rate of mussels. However, these parameters were influenced by local habitat conditions, primarily connected with the position within intertidal and subtidal zones. Animals inhabiting the intertidal zone were characterized by relatively low growth performance, a short life span and a small size. The longest life span was typical for deep subtidal mussels, whereas the highest growth rate was recorded in the cultured population and in the upper subtidal habitats. Growth patterns of Mytilus edulis in the subarctic White and the Arctic southeast Barents seas are similar to those reported from other parts of the area of distribution. Therefore, growth was mostly determined by local environmental factors, including those related to vertical zonation, rather than by latitude/longitude and related temperature effects.     

Genetic structure of hybrid zones between Silene latifolia and Silene dioica (Caryophyllaceae): evidence for introgressive hybridization

Natural hybrid zones provide a valuable tool to study introgressive hybridization, because they can contain a wide variety of genotypes that result from many generations of recombination. Here we used molecular markers and morphological variation to describe the structure of two natural hybrid zones between Silene latifolia and Silene dioica in the Swiss Alps. Populations in both hybrid zones consisted of few intermediate hybrids and were dominated by backcross hybrids. The latter were also found in the parental populations at the margins of the hybrid zones. Out of 209 amplified fragment length polymorphism (AFLP) markers scored in 390 individuals, only 7 (3.3%) were species specific. These results indicate that introgression between S. dioica and S. latifolia is extensive, and that hybrid zones act as bridges to gene flow between these two species. Analysis of linkage disequilibrium identified few populations in which hybridization is ongoing, whereas in most populations linkage disequilibrium has eroded. Where hybridization is ongoing, strong changes in species-specific marker frequencies and morphological traits were observed. Plastid introgression into the hybrid zone was found to be bidirectional, but only the S. latifolia plastid haplotype was found in a nuclear S. dioica background. This unidirectional plastid introgression from S. latifolia into S. dioica is most likely due to pollen-flow from S. dioica onto S. latifolia, and results in plastid capture. Comparisons between the molecular and the morphological hybrid indices revealed that morphology in this study system is useful for identifying hybrids, but not for detailed analysis of hybrid zone structure.     

Characterization of a proteinase inhibitor from Cajanus cajan (L.)

A protein proteinase inhibitor (PI) has been purified from pigeonpea Cajanus cajan (L.) PUSA 33 variety by acetic-acid precipitation, salt fractionation and chromatography on a DEAE-Cellulose column. The content of inhibitor was found to be 15 mg/20 g dry weight of pulse. The molecular weight of the inhibitor as determined by SDS-PAGE under reducing conditions was found to be about 14,000. It showed inhibitory activity toward proteolytic enzymes belonging to the serine protease group, namely trypsin and alpha-chymotrypsin. The inhibitory activity was stable over a wide range of pH and temperatures. Estimation of sulfhydryl groups yielded one free cysteine and at least two disulfide linkages. N-terminal sequence homology suggests that it belongs to the Kunitz inhibitor family. Structural analysis by circular dichroism shows that the inhibitor possesses a largely disordered structure.     

Identification and properties of UDP-glucose: Cyanidin-3-O-glucosyltransferase isolated from petals of the red campion (Silene dioica)

An enzyme catalyzing the transfer of the glucosyl moiety of UDP-glucose to the 3-hydroxyl group of cyanidin has been demonstrated in petal extracts of Silene dioica mutants with cyanidin-3-O-glucoside in the petals. This transferase activity was also present in young rosette leaves and calyces of these plants. The highest glucosyltransferase activity was found in petals of opening flowers of young plants. The enzyme was purified ninetyfold by PVP and Sephadex chromatography. The glucosyltransferase had a pH optimum of 7.5, had a “true K_m value” of 4.1×10^?4 m for UDP-glucose and 0.4×10^?4 m for cyanidin chloride, and was not stimulated by divalent metal ions. Both p-chloromercuribenzoate and HgCl₂ inhibited the enzyme activity. Pelargonidin chloride and delphinidin chloride at reduced rates also served as substrates. The enzyme did not catalyze the glucosylation of the 3-hydroxyl group of flavonols or the 5-hydroxyl group of anthocyanins. ADP-glucose could not serve as a glucosyl donor. The results of Sephadex G150 chromatography suggest that the glucosyltransferase can exist as dimer of about 125,000 daltons and as active monomers of 60,000 daltons. The genetic control of the glucosyltransferase activity is discussed.     

Characterization of the S-RNase promoters from sweet cherry (Prunus avium L.)

Genomic DNA fragments containing the S(3)-, S(4)-, and S(6)-RNase genes were isolated from the sweet cherry (Prunus avium L.) and sequenced. Comparison of the 5'-flanking sequences of these three S-RNases indicated that a highly conserved region (designated CR) existed just upstream from the putative TATA boxes. We postulate that CR contains cis-regulatory element(s) involved in pistil expression. To examine the activity of the isolated S-RNase promoters of sweet cherry in the pistil, we transiently introduced approximately 650-bp fragments of the S(4)- and S(6)-RNase promoters fused to beta-glucuronidase (GUS) gene into the pistil of the petunia using a particle bombardment technique. Histochemical analysis showed that the 5'-flanking region of each S-RNase was active in the pistil. This suggests that cis-regulatory element(s) for pistil-specific expression may exist(s) within the 650-bp region upstream from the TATA box in the sweet cherry S-RNase promoter.     

Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

Genetic Diversity in Natural Populations of Arabidopsis thaliana (L.) Heynh. from Karelia

The genetic structure of ten natural populations of Arabidopsis thaliana (L.) Heynh. at eight isozyme loci was studied. The populations were located in the northern part of the species range, 200 km from the north to the south along the Onega Lake coast in Karelia. Considerable genetic diversity (P _99% = 43.7, H _obs = 0.003) was revealed that is not typical of populations of self-pollinating plant species. A direct correlation between the proportion of polymorphic loci and geographical latitude was shown (r = 0.68; P < 0.05). It is suggested that a high polymorphism level in Karelian Arabidopsis thaliana (L.) populations increasing from the south to the north is due to extreme environmental conditions in the northern part of the species range. The distribution of genetic diversity within and between populations is typical of self-pollinating species: the larger part of the total diversity resides among populations (G _ST = 0.583).