Flower orientation enhances pollen transfer in bilaterally symmetrical flowers

Zygomorphic flowers are usually more complex than actinomorphic flowers and are more likely to be visited by specialized pollinators. Complex zygomorphic flowers tend to be oriented horizontally. It is hypothesized that a horizontal flower orientation ensures effective pollen transfer by facilitating pollinator recognition (the recognition-facilitation hypothesis) and/or pollinator landing (the landing-control hypothesis). To examine these two hypotheses, we altered the angle of Commelina communis flowers and examined the efficiency of pollen transfer, as well as the behavior of their visitors. We exposed unmanipulated (horizontal-), upward-, and downward-facing flowers to syrphid flies (mostly Episyrphus balteatus), which are natural visitors to C. communis. The frequency of pollinator approaches and landings, as well as the amount of pollen deposited by E. balteatus, decreased for the downward-facing flowers, supporting both hypotheses. The upward-facing flowers received the same numbers of approaches and landings as the unmanipulated flowers, but experienced more illegitimate landings. In addition, the visitors failed to touch the stigmas or anthers on the upward-facing flowers, leading to reduced pollen export and receipt, and supporting the landing-control hypothesis. Collectively, our data suggested that the horizontal orientation of zygomorphic flowers enhances pollen transfer by both facilitating pollinator recognition and controlling pollinator landing position. These findings suggest that zygomorphic flowers which deviate from a horizontal orientation may have lower fitness because of decreased pollen transfer.     

c-di-GMP Enhances Protective Innate Immunity in a Murine Model of Pertussis

Innate immunity represents the first line of defense against invading pathogens in the respiratory tract. Innate immune cells such as monocytes, macrophages, dendritic cells, NK cells, and granulocytes contain specific pathogen-recognition molecules which induce the production of cytokines and subsequently activate the adaptive immune response. c-di-GMP is a ubiquitous second messenger that stimulates innate immunity and regulates biofilm formation, motility and virulence in a diverse range of bacterial species with potent immunomodulatory properties. In the present study, c-di-GMP was used to enhance the innate immune response against pertussis, a respiratory infection mainly caused by Bordetella pertussis. Intranasal treatment with c-di-GMP resulted in the induction of robust innate immune responses to infection with B. pertussis characterized by enhanced recruitment of neutrophils, macrophages, natural killer cells and dendritic cells. The immune responses were associated with an earlier and more vigorous expression of Th1-type cytokines, as well as an increase in the induction of nitric oxide in the lungs of treated animals, resulting in significant reduction of bacterial numbers in the lungs of infected mice. These results demonstrate that c-di-GMP is a potent innate immune stimulatory molecule that can be used to enhance protection against bacterial respiratory infections. In addition, our data suggest that priming of the innate immune system by c-di-GMP could further skew the immune response towards a Th1 type phenotype during subsequent infection. Thus, our data suggest that c-di-GMP might be useful as an adjuvant for the next generation of acellular pertussis vaccine to mount a more protective Th1 phenotype immune response, and also in other systems where a Th1 type immune response is required.     

Use of carbon-13 and carbon-14 natural abundances for stream food web studies

We review the use of stable carbon isotope ratios (δ¹³C) and radiocarbon natural abundances (Δ¹⁴C) for stream food web studies. The δ¹³C value of primary producers (e.g., periphytic algae, hereafter periphyton) in streams is controlled by isotopic fractionation during photosynthesis and variable δ¹³C of dissolved CO₂. When periphyton δ¹³C differs from that of terrestrial primary producers, the relative contribution of autochthony and allochthony to stream food webs can be calculated. Moreover, the variation in periphyton δ¹³C can reveal how much stream consumers rely on local resources because each stream habitat (e.g., riffle vs. pool, open vs. shaded) usually has a distinctive δ¹³C. However, periphyton δ¹³C often overlaps with that of terrestrial organic matter. On the other hand, periphyton Δ¹⁴C is less variable than δ¹³C among habitats, and reflects the Δ¹⁴C of dissolved CO₂, which could be a mixture of “aged” (Δ¹⁴C < 0 ‰) and “modern” (Δ¹⁴C > 0 ‰) carbon. This is because the Δ¹⁴C is corrected by its δ¹³C value for the isotopic fractionation during photosynthesis. Recent studies and our data indicate that many stream food webs are supported by “aged” carbon derived from the watershed via autochthonous production. The combined use of δ¹³C and Δ¹⁴C allows robust estimation of the carbon transfer pathway in a stream food web at multiple spatial scales ranging from the stream habitat level (e.g., riffle and pool) to watershed level (autochthony and allochthony). Furthermore, the Δ¹⁴C of stream food webs will expand our understanding about the time frame of carbon cycles in the watersheds.     

Determination of Copper Content in o-Diphenol Oxidase by Neutron Activation Analysis

A polyphenol oxidase (o-diphenol oxidase) [o-diphenol: O₂ oxidoreductase E. C. 1.10. 3.1] from sweet potato named component II_b was highly purified. The copper content of this enzyme was measured by neutron activation analysis. Samples were analyzed with or without chemical separation after neutron irradiation. The copper content of the enzyme was determined to be 0.27%, and the minimum molecular weight of this enzyme was caluculated to be 23,500.     

Changes in phenylalanine ammonia-lyase activity in Satsuraa mandarin fruit during ontogeny

PAL activity in young fruits of Citrus unshiu was initiallyvery high. It decreased gradually as the fruit grew and afterthe "June drop", declined markedly. PAL behavior appears tobe closely related to the tissue differentiation of fruit. Proteincontent of the fruit showed a pattern of change similar to thatof PAL activity. Also, the amount of hesperidine was high inimmature fruit. Accumulation of hesperidine per fruit was greatlyenhanced as growth of the fruit progressed, but after PAL activityhad almost disappeared, the accumulation ceased. ¹Present address: Kozo Keikaku Engineering Incorporation, Nakano,Tokyo, Japan. (Received March 16, 1973; )     

Microtubule-dependent microtubule nucleation based on recruitment of gamma-tubulin in higher plants

Despite the absence of a conspicuous microtubule-organizing centre, microtubules in plant cells at interphase are present in the cell cortex as a well oriented array. A recent report suggests that microtubule nucleation sites for the array are capable of associating with and dissociating from the cortex. Here, we show that nucleation requires extant cortical microtubules, onto which cytosolic gamma-tubulin is recruited. In both living cells and the cell-free system, microtubules are nucleated as branches on the extant cortical microtubules. The branch points contain gamma-tubulin, which is abundant in the cytoplasm, and microtubule nucleation in the cell-free system is prevented by inhibiting gamma-tubulin function with a specific antibody. When isolated plasma membrane with microtubules is exposed to purified neuro-tubulin, no microtubules are nucleated. However, when the membrane is exposed to a cytosolic extract, gamma-tubulin binds microtubules on the membrane, and after a subsequent incubation in neuro-tubulin, microtubules are nucleated on the pre-existing microtubules. We propose that a cytoplasmic gamma-tubulin complex shuttles between the cytoplasm and the side of a cortical microtubule, and has nucleation activity only when bound to the microtubule.