Endogenous hormone levels during direct somatic embryogenesis in Medicago falcata

Endogenous indole-3-acetic acid, abscisic acid and cytokinins (zeatin, zeatin riboside, N-isopentenyladenine and N-isopentenyladenosine) were evaluated in initial explants (leaves) of in vitro propagated plants of alfalfa ( Medicago falcata L.) lines varying in embryogenic capacity and during the somatic embryogenesis process. Fast embryo-genic induction was correlated with high IAA and low ABA levels in the initial explants. No significant differences were observed in the cytokinin contents. Our results suggest that a certain hormone balance is necessary to allow the expression of the embryogenic potential. The consistent stages of the direct somatic embryogenesis are also characterized by changes in hormonal levels.     

Nodule ultrastructure and initial growth of Anadenanthera peregrina (L.) Speg. var. falcata (Benth.) altschul plants infected with rhizobia

The anatomy and ultrastructure of root nodules of Anadenanthera peregrina var. falcata (Leguminosae-Mimosoideae) were analysed, as was plant growth. To ensure that nodules developed, seedlings were inoculated with a mixture of six strains of rhizobia. Nodules were produced that differed in appearance-and probably also effectiveness-but their structure was similar and they showed characteristics typical of indeterminate nodules, such as persistent meristematic tissue and a gradient of cells at different stages of development. Many starch grains were present in inner cortex cells and interstitial cells of infected tissue. Infected cells were densely packed with bacteroids, which contained many poly-beta-hydroxybutyrate granules. The high incidence of these granules, together with high levels of starch accumulation in interstitial cells, suggested low N2-fixation efficiency of the rhizobia isolates used for inoculation. In the symbiosomes of early-senescent infected cells, reticulum-like structures, small vesicles and a fibrillar material were observed; these may be related to bacteroid degradation. In the cytoplasm of late-senescent infected cells, many vesicles and membrane-like structures were observed, probably associated with membrane degradation of bacteroids and peribacteroids. The total biomass of plants inoculated with rhizobia was low and their xylopodia and shoots had low levels of N compared with noninoculated plants fertilized with ammonium nitrate. However, inoculated plants did not show N-deficiency symptoms and grew better than non-inoculated plants without N fertilization. These growth results, together with ultrastructural observations of nodules, suggest that nitrogen fixation of rhizobia isolates associated with Anadenanthera peregrina var. falcata roots is poor.     

Reproductive Biology of Erythrina falcata (Fabaceae: Papilionoideae)1

Reproductive phenology, floral biology, degree of self‐incompatibility, and floral visitors of Erythrina falcata were studied in an Argentinean population. Flowering occurs during the dry season from late August to late October. Flower lifetime is 5–6 d. Phylogenetic studies indicate that E. falcata, together with E. fusca and E. crista‐galli, are included in a basal clade within Erythrina. Its phylogenetic position, floral morphology, and nectar characteristics suggest a hummingbird–passerine mixed pollination system. The flowers are nontubular, and the vexillum (the upper petal of the corolla) covers the other remaining floral parts until displaced by a visiting passerine (Icterus cayanensis) or a hummingbird (Amazilia chionogaster). Both birds act as pollen vectors. Bees were observed as occasional pollinators. Nectar production begins at anther dehiscence and coincides with maximum stigmatic receptivity. The base of the keel forms a secondary nectar reservoir. Controlled pollinations showed that this species is self‐incompatible, although a few fruits develop from selfing. Pollen:ovule ratio (43,200:7) is as expected for a xenogamous plant. Only 1 percent of the flowers set seeds under natural conditions. Possible explanations for the low reproductive success are discussed.     

镰形棘豆的一个新变型——白花镰形棘豆

描述了豆科棘豆属镰形棘豆(Oxytropis falcata Bunge)的一个新变型:白花镰形棘豆(Oxytropis falcataBunge form.atbiflora Y.H.Wu).原变型的花冠为蓝紫色或紫红色,而新变型花冠为白色.     

Isolation and characterization of microsatellite loci in the western pearlshell mussel, Margaritifera falcata (Gould)

Ten microsatellite loci were isolated from the western pearlshell, Margaritifera falcata (Gould, 1850) and characterized in populations from Washington and Montana, USA. We also assessed eight microsatellite loci developed in M. margaritifera, two of which showed utility. Both of our test populations showed significant heterozygote deficiencies at most loci, consistent with a hermaphroditic life history. Populations differed markedly with respect to allelic richness, allele frequencies and numbers of identical multilocus genotypes. This panel of loci should prove useful in describing gene flow and genetic diversity patterns among M. falcata populations, information that should aid future conservation efforts.     

A Nectar Reward: Is More Better?1

Characters involved in pollinator attraction are likely maintained by selection. Plants that invest more in floral displays and/or rewards are expected to attract more pollinators than those that do not. A large number of plants, however, are severely pollen-limited yet either produce small rewards or none at all. The orchid, Comparettia falcata, is a pollinator-dependent, self-compatible epiphyte distributed throughout the Greater Antilles, Central and South America. In Puerto Rico where it is pollinated by the hummingbird Chlorostilbon maugaeus, C. falcata presents a smaller nectar reward than most other plants pollinated by the same species. To determine whether or not selection would favor the production of higher nectar levels, we enhanced the quantity of nectar offered by flowers in a Puerto Rican population for two flowering seasons. We monitored visitation frequencies, pollen movement, and reproductive success at three sites with different canopy coverages. Daily censuses of hummingbirds provided estimates of relative pollinator abundance. A multiway contingency test employing Wal?s statistic showed no overall differences in reproductive success between plants with enhanced rewards and unmanipulated controls. Site differences, however, were clear. Plants of the mid- and high-light sites had greater success than those of the low-light site, and the differences were usually at least two-fold. There was a significant site-treatment interaction in reproductive success that could be attributed to the overall trend whereby controls of both mid- and high-light sites did better than the nectar-enhanced plants. Most of the observed pollinations (85%) with stained pollinia resulted in self-pollinations that did not differ among treatments. Seed crops from self- and cross-pollinations revealed no differences in the number of viable seeds. Because we found little evidence of selection for increasing nectar reward via inbreeding depression or male and female reproductive success, and previous studies have indicated that meager natural levels of reward are better than none at all, we suspect that reward production in C. falcata may be driven by a combination of pollination-limitation and resource constraints.     

Rapid and efficient transformation of diploid Medicago truncatula and Medicago sativa ssp. falcata lines improved in somatic embryogenesis

We describe a simple and efficient protocol for regeneration-transformation of two diploid Medicago lines: the annual M. truncatula R108-1(c3) and the perennial M. sativa ssp. falcata (L.) Arcangeli PI.564263 selected previously as highly embryogenic genotypes. Here, embryo regeneration of R108-1 to complete plants was further improved by three successive in vitro regeneration cycles resulting in the line R108-1(c3). Agrobacterium tumefaciens-mediated transformation of leaf explants was carried out with promoter-gus constructs of two early nodulins (MsEnod12A and MsEnod12B) and one late nodulin (Srglb3). The transgenic plants thus produced on all explants within 3–4 months remained diploid and were fertile. This protocol appears to be the most efficient and fastest reported so far for leguminous plants. Received: 18 March 1997 / Revision received: 25 June 1997 / Accepted: 15 July 1997     

Measurement of light gradients and spectral regime in plant tissue with a fiber optic probe

A method is described in which light gradients and spectral regime can be measured within plant tissue using fiber optics. A fiber optic probe was made by modifying a single optical fiber (200 μm diameter) so that it had a light harvesting end that was a truncated tip 20–70 μm in diameter. The probe was a directional sensor with a half-band acceptance angle of 17–20°. Light measurements were made as the fiber optic probe was driven through plant tissue by a motorized micromanipulator, and the light that entered the fiber tip was piped to a spectroradiometer. By irradiating green leaf tissue of the succulent Crassula falcata L. with collimated light and inserting the probe from different directions, it was possible to measure light quality and quantity at different depths. Collimated light was scattered completely by the initial 1.0 mm of leaf tissue, which also greatly attenuated all light except the green and far-red. Light scatter contributed significantly to light quantity and had a pronounced spectral structure. Immediately beneath the irradiated surface the amount of light at 550 nm was 1.2 times that of the incident light. The light gradient declined rapidly to 0.5 times incident light at 1.4 mm depth. In contrast, the amount of light at 750 nm increased during the initial 0.5 mm to 2.9 times incident light and then declined linearly to 0.5 times incident light at the dark side of the leaf (4.5 mm). The implications of the magnitude of the contribution of light scatter to the light gradient is also discussed.     

Host-hemiparasite transfer of the C-glucosyl xanthone mangiferin between Mangifera indica and Dendrophthoe falcata

Abstract

To test the hypothesis that higher antioxidant potential of hemiparasitic plants is due to sequestration of phenolic compounds from the host plants, samples of Dendrophthoe falcata, a hemiparasite collected from different hosts, were investigated for total phenolics, total flavonoids and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activity. The hosts significantly influenced the phenolic content of the hemiparasite. However, similar influence was not detected on radical scavenging activity and no correlation was found in the phenolics and free radical scavenging activities. Further investigation on transfer of constituents revealed that D. falcata sample obtained from a host, Mangifera indica, contained mangiferin, a C-glucosyl xanthone, and some unidentified flavonoids as confirmed by HPTLC flavonoid patterns. The data indicated that the hosts significantly affected total phenolics and total flavonoids in a hemiparasite. This is the first report of transfer of mangiferin from M. indica to a hemiparasite. The present report points towards the need of further investigations on the possible role of transferred phenolics either as mediators of host defense, host defense compounds utilized as cues of identification of the host by the hemiparasite or compounds taken up by the parasites to support their defense against rejection by the hosts.