Arthur R. Davis

Nectar-carbohydrate production and composition vary in relation to nectary anatomy and location within individual flowers of several species of Brassicaceae

Abstract. Nectar-carbohydrate production and composition were investigated by high-performance liquid chromatography and enzymology in nine species from five tribes of the Brassicaceae. In six species (Arabidopsis thaliana (L.) Heynh., Brassica napus L., B. rapa L., Lobularia maritima (L.) Desv., Raphanus sativus L., Sinapis arvensis L.) that produced nectar from both lateral nectaries (associated with the short stamens) and median nectaries (outside the long stamens), on average 95% of the total nectar carbohydrate was collected from the lateral ones. Nectar from these glands possessed a higher glucose/fructose ratio (usually 1.0–1.2) than that from the median nectaries (0.2–0.9) within the same flower. Comparatively little sucrose was detected in any nectar samples except from Matthiola bicornus (Sibth. et Sm.) DC., which possessed lateral nectaries only and produced a sucrose-dominant exudate. The anatomy of the nectarial tissue in nectar-secreting flowers of six species, Hesperis matronalis L., L. maritima, M. bicornus, R. sativus, S. arvensis, and Sisymbrium loeselii L., was studied by light and scanning-electron microscopy. Phloem alone supplied the nectaries. However, in accordance with their overall nectar-carbohydrate production, the lateral glands received relatively rich quantities of phloem that penetrated far into the glandular tissue, whereas median glands were supplied with phloem that often barely innervated them. All nectarial tissue possessed modified stomata (with the exception of the median glands of S. loeselii, which did not produce nectar); further evidence was gathered to indicate that these structures do not regulate nectar flow by guard-cell movements. The numbers of modified stomata per gland showed no relation to nectar-carbohydrate production. Taken together, the data on nectar biochemistry and nectary anatomy indicate the existence of two distinct nectary types in those Brassicacean species that possess both lateral and median nectaries, regardless of whether nectarial tissue is united around the entire receptacle or not. It is proposed that the term “nectarium” be used to represent collectively the multiple nectaries that can be found in individual flowers.

Temporal changes in floral nectar production, reabsorption, and composition associated with dichogamy in annual caraway (Carum carvi; Apiaceae)

The dynamics of nectar production were studied in perfect florets of two varieties (Karzo, Moran) of annual caraway (Carum carvi L., Apiaceae). Florets were protandrous and strongly dichogamous, lasting 7-15 d but producing nectar from the stylopodia for 4-12 d, in an interrupted fashion. Nectar secretion began during a florets phase of stamen elongation and anther dehiscence. After reabsorption of uncollected nectar, at which point nectary surfaces were completely dry, the two styles elongated and a second bout of secretion commenced during the female phase, up to 5 d later, when a floret became receptive to pollination. During the male and female phases, respectively, 0.392 ± 0.064 μL and 1.083 ± 0.261 μL of nectar of similar solute concentration (844 mg/mL) was produced per ten florets. On a daily basis, florets yielded 1.5-fold more nectar in the female than during the male phase. First-time nectar removal throughout the female phase did not match the sum of nectar quantities from male and female phases combined, suggesting that under natural conditions, any uncollected male-phase nectar, once reabsorbed, is not made available to visitors of the same florets when in the female phase. Nectar-sugar composition differed between bouts of secretion; it was hexose-rich (59.6% fructose, 26.9% glucose, 13.6% sucrose) initially, but hexose-dominant (70.2, 26.8, 3.1) during the female phase. A 5.7-fold difference in mean nectar production per floret occurred among plants.

Laboratory Studies of Honeybee Larval Growth and Development as Affected by Systemic Insecticides at Adult-Sublethal Levels

SummaryThe effects of two systemic insecticides, carbofuran and dimethoate, at concentrations sublethal to adult worker honeybees (<1·25 μg/g food) on larval growth, pupation success and acetylcholinesterase (AChE) activity were investigated in worker larvae reared on royal jelly (RJ) in the laboratory. Larvae initially exposed to either insecticide at 5 μg/g RJ at a late age (e.g. 96 h) gained weight more slowly than control larvae and died relatively early. Insecticide concentrations of 1·25 μg/g rarely disrupted growth of larvae first exposed at 72–96 h of age. Concentrations sublethal to adults sometimes rcduced mature weights of larvae first exposed at an early age (44 h). Rcduced numbers of potentially viable pupae resulted when these larvae were exposed to carbofuran at 1·25 μg/g or dimethoate even at 0·313 μg/g. As activity of AChE in homogenstes of untreated larvae was highly variable, AChE activity does not appear to be as reliable a criterion for detecting insecticide poisoning of larvae as red...

Seed set, pollen morphology and pollen surface composition response to heat stress in field pea

Pea (Pisum sativum L.) is a major legume crop grown in a semi-arid climate in Western Canada, where heat stress affects pollination, seed set and yield. Seed set and pod growth characteristics, along with in vitro percentage pollen germination, pollen tube growth and pollen surface composition, were measured in two pea cultivars (CDC Golden and CDC Sage) subjected to five maximum temperature regimes ranging from 24 to 36 °C. Heat stress reduced percentage pollen germination, pollen tube length, pod length, seed number per pod, and the seed-ovule ratio. Percentage pollen germination of CDC Sage was greater than CDC Golden at 36 °C. No visible morphological differences in pollen grains or the pollen surface were observed between the heat and control-treated pea. However, pollen wall (intine) thickness increased due to heat stress. Mid-infrared attenuated total reflectance (MIR-ATR) spectra revealed that the chemical composition (lipid, proteins and carbohydrates) of each cultivars pollen grains responded differently to heat stress. The lipid region of the pollen coat and exine of CDC Sage was more stable compared with CDC Golden at 36 °C. Secondary derivatives of ATR spectra indicated the presence of two lipid types, with different amounts present in pollen grains from each cultivar.

Regular dorsal dimples on Varroa destructor - Damage symptoms or developmental origin?*

Adult females (n = 518) of Varroa destructor from Apis mellifera prepupae were examined by scanning electron microscopy without prior fluid fixation, dehydration and critical-point drying. Fifty-five (10.6%) mites had one (8.1%) or two (2.5%) diagonal dimples positioned symmetrically on the idiosoma’s dorsum. Where one such regular dorsal dimple existed per mite body, it occurred on the left or right side, equally. Mites with at least one regular dorsal dimple were 3.4% longer, but neither idiosomal width nor elliptical area differed significantly from mites lacking dimples. Dimple length was normally distributed in the population, and averaged 462 ± 9.2 μm (s.e.; n = 68 dimples). Internally, each regular dorsal dimple aligns with a series of obliquely-situated, dorso-ventral muscles in the opisthosoma. It is concluded that regular dorsal dimples are faults originating during mite ontogeny and should be considered separately from damage to Varroa destructor inflicted by honeybees or predatory arthropods.ZusammenfassungUm vom Normalen abweichende Merkmale am Körper von Varroa destructor zutreffend auf durch Honigbienen oder andere Arthropoden hervorgerufene Verletzungen zurückführen zu können, ist es wichtig, diese von durch Unregelmässigkeiten in der Entwicklung von V. destructor hervorgerufene Symptome unterscheiden zu können. Von Mai bis Juli 2005 wurden adulte Weibchen (n = 518) von V. destructor aus Zellen mit Vorpuppen von Apis mellifera (zumeist Arbeiterinnenzellen) eingefroren oder in Laborversuchen in Gruppen von 10 in Petrischalen über bis zu 132 Stunden bis zu ihrem Tod gehalten (Kontrollen), oder Ameisen ausgesetzt (entweder mit Kontakt oder dem Geruch allein). Natürlicherweise in Luft getrocknete Milben wurden mit Rasterelektronenmikroskopie (SEM) untersucht, ohne die üblichen Prozeduren wie Flüssigkeitsfixierung, Entwässerung mit Lösungsmitteln oder einer Kritische Punkt Trocknung. SEM der Rückenseite des Idiosoma (Abb. 1) zeigten, dass 55 (10,6 %) der Milben eine (8,1 %) oder zwei (2,5 %) diagonale Grübchen in symmetrischen Positionen aufwiesen (Abb. 2–10; Tab. I). Nur bei Grübchen von beträchtlicher Tiefe war auch auf der Bauchseite der Milben eine Einsenkung an der Verbindung der metapodialen Platten und der Genitalplatten vorhanden, die mit der Position der dorsalen Einsenkungen korrespondierte.Für diese Einsenkungen, die in der Literatur als von den Mandibeln oder Beintritten der Bienen hervorgerufene Verletzungen angesehen werden, wird empfohlen, sie zukünftig als “reguläre dorsale Grübchen” zu bezeichnen. Diese regulären dorsalen Grübchen variierten in Tiefe und Ausdehnung (Abb. 2 und 3), sogar innerhalb der gleichen Milbe (Abb. 10). Die maximale Länge der regulären dorsalen Grübchen lag im Durchschnitt bei 462 ± 9,2 μm (Standardfehler; n = 68) Grübchen und war normalverteilt (Abb. 11). Bei Milben mit nur einem regulären dorsalen Grübchen hatten 20 das Grübchen auf der linken Seite (Abb. 3, 5 und 7), und 22 hatten sie auf der rechten Seite (Abb. 6, 8; Tab. I). Bei 55 Milben mit regulären dorsalen Grübchen entsprach das Verhältnis von 20 Milben mit einem Grübchen nur auf der linken Seite und 22 mit einem Grübchen nur auf der rechten Seite sowie 13 Milben mit Grübchen auf beiden Seiten in einem Anpassungstest einem Verhältnis von 2:2:1 (χ2df2 = 0,273; P > 0,85). Milben mit zumindest einem regulären dorsalen Grübchen waren im Schnitt bis zu 3,4 % länger, allerdings unterschied sich weder die Breite des Idiosomas noch die elliptische Fläche signifikant von der von Milben ohne Grübchen (Tab. II). Im Inneren der Milben liegt jedes der regulären dorsalen Grübchen in einer Linie mit einer Reihe von schräggerichteten an Rücken und Bauchseite befestigten Muskeln an jeder Seite des Mitteldarms der Milben (Abb. 12). Ein Versagen bei der Umwandlung der weiblichen Deutonymphe zu einem ausgewachsenen Tier von dem Doppelten der früheren Breite das Idiosoma vor der endgültigen Sklerotisierung voll Aufzublähen führt offensichtlich zur beständigen Ausbildung der dorsalen Vertiefungen in einer mit diesen Muskeln des Opistosomas übereinstimmenden Ausrichtung. Es wird geschlossen, dass die regulären dorsalen Grübchen Entwicklungsstörungen darstellen, die während der Ontogenie der Milben entstehen und von den durch Arthropoden verursachten Verletzungen von V. destructor getrennt gesehen werden müssen. Weitere Untersuchungen sind nötig, um die Ereignisse bei der Ausbildung der Grübchen sowie irgendwelche Konsequenzen für die Milben weiter zu klären.

FLORAL STRUCTURE AND DYNAMICS OF NECTAR PRODUCTION IN ECHINACEA PALLIDA VAR. ANGUSTIFOLIA (ASTERACEAE)

The reproductive structure of the disk florets of Echinacea pallida var. angustifolia (Asteraceae) in relation to insect pollination was investigated using light, fluorescence, and scanning electron microscopy. The study of this self‐incompatible species emphasized pollen production, pollen‐stigma interactions, transmitting tissue, and vasculature within the style. Nectary structure and nectar production dynamics were also examined. Produced in the fused anther tubes, the trinucleate pollen with yellow pollenkitt was plentiful per floret, yielding a pollen:ovule ratio of 24,130. Encircling the style base at the ovary summit, the floral nectary possessed modified stomata whose pores, as well as nonstomatal gaps in the epidermis, provided apoplastic pathways for nectar escape and reabsorption. Phloem alone supplied the gland interior, the sieve element–companion cell complexes reaching up to the nectary epidermis. Nectar was hexose dominant, its volume and nectar‐sugar quantity per floret peaking on the afternoon of the first day of anthesis until the morning of the second day. Nectar production only occurred in half of the florets for 3 d, rarely for 5 d. Potential honey production from fields of this species was estimated at 2.1–11.9 kg/ha.

Minor pollinator-prey conflict in the carnivorous plant, Drosera anglica

We studied the physical and temporal isolation of two arthropod guilds interacting with Drosera anglica Huds., a terrestrial carnivorous plant. Flowers are separated from basal trap leaves by a leafless stalk. Since arthropods are potentially employed both as prey and pollinators, we asked whether separation of traps from flowers reduces the frequency with which flower visitors are captured by the leaves. Plants captured prey throughout the season, with peak trapping activity occurring before flowering began. The diverse prey spectrum included at least 109 species in 94 genera in 26 of 37 identified families representing 11 arthropod orders. The most common prey were adult flies of Nematocera, particularly Ceratopogonidae (50%) and Chironomidae (42%). The following taxa were periodically abundant: Acarina, Diptera–Cecidomyiidae, Chloropidae, Sciaridae, Hemiptera nymphs and Thysanoptera–Thripidae. Flies (Diptera) were chief flower visitors (95%), dominated by Syrphidae (66%), Bombyliidae and Muscidae (10% each), Calliphoridae (7%), Tachinidae and Dolichopodidae (3% each). Additionally, visitors were a bee (Hymenoptera–Halictidae) and thrips (Thysanoptera–Thripidae). Four families were common to both guilds: Diptera–Dolichopodidae, Muscidae, Tachinidae; and Thysanoptera–Thripidae. However, direct comparisons of identified taxa within these families showed that overlap between flower visitors and prey occurred for Thrips sp. larvae alone, which comprised only 3% of all flower visitors and 0.5% of prey. Drosera anglica exploits distinct guilds of insects for pollinators and prey.

Influence of elevated CO2 and ultraviolet-B radiation levels on floral nectar production: a nectary-morphological perspective

Abstract. Investigations of the effects of two global events – elevated CO2 levels and enhanced ultraviolet-B (UV-B) radiation – on floral nectar production are reviewed from twelve dicotyledonous families. Furthermore, to allow comparisons between nectary morphology and nectar production in treated plants of these fifteen species, new data on floral nectary structure are provided for Malcolmia maritima (L.) R. Br. (Brassicaceae) and Scabiosa columbaria L. (Dipsacaceae). All but the last taxon possessed mesenchymatic floral nectaries with surface stomata. Few clear relationships existed between nectary morphology and various physiological responses to CO2 or UV-B enrichment, indicating that species responded notwithstanding nectary structure itself. Overall, nectar-solute concentration was least affected by elevated CO2 or UV-B radiation; consequently, changes in nectar volume were responsible for differences in nectar-sugar production per flower. Three species of Fabaceae experienced no change in floral nectar production upon exposure to elevated CO2. To date, no study of enhanced UV-B radiation reported a consistent reduction in floral nectar production; three species of Brassicaceae responded differently, but various levels of ozone depletion were simulated. Experimentation with more taxa – including those possessing nectary types such as septal (gynopleural) nectaries (e.g. many monocotyledons) or aggregations of glandular trichomes – and expanding such physiological studies to species possessing extrafloral nectaries, are recommended.

Ontogeny of floral organs in flax (Linum usitatissimum; Linaceae)

PREMISE OF THE STUDY Flax (Linum usitatissimum) is an important crop worldwide; however, a detailed study on flower development of this species is lacking. Here we describe the pattern of initiation and a program of key developmental events in flax flower ontogeny. This study provides important fundamental information for future research in various aspects of flax biology and biotechnology. METHODS Floral buds and organs were measured throughout development and examined using scanning electron microscopy. KEY RESULTS Floral organs were initiated in the following sequence: sepals, stamens and petals, gynoecium, and nectaries. The five sepals originated in a helical pattern, followed evidently by simultaneous initiation of five stamens and five petals, the former opposite of the sepals and the latter alternate to them. The gynoecium, with five carpels, was produced from the remaining, central region of the floral apex. Stamens at early stages were dominated by anther growth but filaments elongated rapidly shortly before anthesis. Early gynoecium development occurred predominantly in the ovary, and ovule initiation began prior to enclosure of carpels. A characteristic feature was the twisted growth of styles, accompanied by the differentiation of papillate stigmas. Petal growth lagged behind that of other floral organs, but petals eventually grew rapidly to enclose the inner whorls after style elongation. Flask-shaped nectaries bearing stomata developed on the external surface of the filament bases. CONCLUSIONS This is the first detailed study on flax floral organ development and has established a key of 12 developmental stages, which should be useful to flax researchers.

Stomatal frequency, maturity and index on developing bracts of four abscisic acid mutants and wild-type plants of Arabidopsis thaliana

Abstract This study was conducted to determine any relationships between leaf surface features and endogenous levels of abscisic acid (ABA). General growth patterns and various parameters of stomatal location and development were investigated in bracts (cauline leaves) at the onset of flowering of three mutants (abi-1, abi-2, abi-3) of Arabidopsis thaliana (L.) Heynh. insensitive to ABA, one mutant (aba-1) deficient in ABA, and the wild-type (Landsberg) from which the mutants were derived. These ABA mutants have become useful models because they provide an alternative to exogenous application of ABA, thus effectively allowing the study of endogenous ABA activity on plant growth and development. Briefly, plants of the aba-1 mutant were slow growing and dwarf. Bracts were fewer and smaller in abi-1 and abi-2 than the wild-type and abi-3. Stomatal maturity (% stomata with externally visible pores) was higher on the adaxial than the abaxial bract surface for all plant types, and in all mutants than the wild-type. Stomatal maturity was positively correlated with bract age, but not bract area. Stomatal frequency (number of stomata per unit area) was higher on the abaxial bract surface than the adaxial for all plant types. Epidermal cells expanded more quickly on wild-type plants than on the ABA mutants. In aba-1, abi-1, and abi-2 mutants, epidermal cells were small such that stomatal frequency was higher than that of wild-type bracts. Stomatal index [stomatal frequency×100%/(stomatal frequency+epidermal cell frequency)] was remarkably similar among Landsberg and the four mutants as a result of a relatively constant ratio of epidermal:stomatal frequencies in all plant types. In general, differences among these stomatal parameters were smallest between the wild-type and abi-3. Stomatal features and epidermal-cell growth on bracts of A. thaliana differed between wild-type and mutant plants, yet were similar in three mutants having an insensitivity (abi-1, abi-2) to, or near absence (aba-1) of, endogenous ABA.