Structure and function of the large pronotal horn of the sand‐living anthicid beetle Mecynotarsus tenuipes

Large insect horns function as antipredator armaments, digging implements and intraspecific combat weapons. The sand‐living anthicid beetle Mecynotarsus tenuipes possesses a large horn on the pronotum. Allometric relationships between body size and horn size did not show either a slope of more than 1 or sexual dimorphism, suggesting another function of the horn other than sexual selection via combat. Behavioral observation of individuals using a microvideo camera indicated that the horn is used to dig and move forward in loose sand. Only the horned M. tenuipes could dig into sand, in contrast to the hornless anthicid beetles Stricticollis valgipes and Clavicollis fugiens, which could not dig. When moving in sand, M. tenuipes joins its pronotal horn and head to form a conical shape, with which it pierces into the sand. Then, it opens its horn and head outward to create a space in the sand for forward motion. Although it can dig deeply into sand by repeating these behaviors sequentially, digging speed tends to slow with depth, probably because the weight of the substrate increases.     

Diurnal and seasonal variations in stomatal conductance of rice at elevated atmospheric CO2 under fully open‐air conditions

Understanding of leaf stomatal responses to the atmospheric CO₂ concentration, [CO₂], is essential for accurate prediction of plant water use under future climates. However, limited information is available for the diurnal and seasonal changes in stomatal conductance (g_s) under elevated [CO₂]. We examined the factors responsible for variations in g_s under elevated [CO₂] with three rice cultivars grown in an open‐field environment under flooded conditions during two growing seasons (a total of 2140 individual measurements). Conductance of all cultivars was generally higher in the morning and around noon than in the afternoon, and elevated [CO₂] decreased g_s by up to 64% over the 2 years (significantly on 26 out of 38 measurement days), with a mean g_s decrease of 23%. We plotted the g_s variations against three parameters from the Ball‐Berry model and two revised versions of the model, and all parameters explained the g_s variations well at each [CO₂] in the morning and around noon (R² > 0.68), but could not explain these variations in the afternoon (R² < 0.33). The present results provide an important basis for modelling future water use in rice production.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on growth, morphology and physiology of rice root at three levels of nitrogen fertilization

Over time, the relative effects of elevated [CO₂] on the aboveground photosynthesis, growth and development of rice (Oryza sativa L.) are likely to be changed with increasing duration of CO₂ exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO₂] on seasonal changes in root growth, morphology and physiology of rice, a free‐air CO₂ enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002–2003. A japonica cultivar with large panicle was exposed to two [CO₂] (ambient [CO₂], 370 μmol mol⁻¹; elevated [CO₂], 570 μmol mol⁻¹) at three levels of nitrogen (N): low (LN, 15 g N m⁻²), medium (MN, 25 g N m⁻²) and high N (HN, 35 g N m⁻²). Elevated [CO₂] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25–71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO₂] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO₂] during MGP and LGP, the decline being larger during MGP than LGP. The CO₂‐induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO₂‐induced increases in shoot growth of rice are similarly associated with increased root growth.     

Presence of two glycolytic gene clusters in a severe pathogenic line of Candidatus Phytoplasma asteris

Phytoplasmas are plant-pathogenic bacteria that are associated with numerous plant diseases. We have previously reported the complete genomic sequence of Candidatus Phytoplasma asteris, OY strain, OY-M line, which causes mild symptoms. The phytoplasma genome lacks several important metabolic genes, implying that the consumption of metabolites by phytoplasmas in plants may cause disease symptoms. Here we show that the approximately 30-kb region including the glycolytic genes was tandemly duplicated in the genome of OY-W phytoplasma, which causes severe symptoms. Almost duplicated genes became pseudogenes by frameshift and stop-codon mutations, probably because of their functional redundancy. However, five kinds of genes, including two glycolytic genes, remained full-length ORFs, suggesting that it is advantageous for the phytoplasma to retain these genes in its lifestyle. In particular, 6-phosphofructokinase is known as a rate-limiting enzyme of glycolysis, implying that the different number of glycolytic genes between OY-W and OY-M may influence their respective glycolysis activities. We previously reported that the phytoplasma population of OY-W was higher than that of OY-M in their infected plants. Taking this result into account, the higher consumption of the carbon source may affect the growth rate of phytoplasmas and also may directly or indirectly cause more severe symptoms.     

Nitrogen-regulated effects of free-air CO2 enrichment on methane emissions from paddy rice fields

Using the free‐air CO₂ enrichment (FACE) techniques, we carried out a 3‐year mono‐factorial experiment in temperate paddy rice fields of Japan (1998–2000) and a 3‐year multifactorial experiment in subtropical paddy rice fields in the Yangtze River delta in China (2001–2003), to investigate the methane (CH₄) emissions in response to an elevated atmospheric CO₂ concentration (200±40 mmol mol^?1 higher than that in the ambient atmosphere). No significant effect of the elevated CO₂ upon seasonal accumulative CH₄ emissions was observed in the first rice season, but significant stimulatory effects (CH₄ increase ranging from 38% to 188%, with a mean of 88%) were observed in the second and third rice seasons in the fields with or without organic matter addition. The stimulatory effects of the elevated CO₂ upon seasonal accumulative CH₄ emissions were negatively correlated with the addition rates of decomposable organic carbon (P<0.05), but positively with the rates of nitrogen fertilizers applied in either the current rice season (P<0.05) or the whole year (P<0.01). Six mechanisms were proposed to explain collectively the observations. Soil nitrogen availability was identified as an important regulator. The effect of soil nitrogen availability on the observed relation between elevated CO₂ and CH₄ emission can be explained by (a) modifying the C/N ratio of the plant residues formed in the previous growing season(s); (b) changing the inhibitory effect of high C/N ratio on plant residue decomposition in the current growing season; and (c) altering the stimulatory effects of CO₂ enrichment upon plant growth, as well as nitrogen uptake in the current growing season. This study implies that the concurrent enrichment of reactive nitrogen in the global ecosystems may accelerate the increase of atmospheric methane by initiating a stimulatory effect of the ongoing dramatic atmospheric CO₂ enrichment upon methane emissions from nitrogen‐poor paddy rice ecosystems and further amplifying the existing stimulatory effect in nitrogen‐rich paddy rice ecosystems.     

Multiple oviposition by Apoderus balteatus (Coleoptera, Attelabidae) is associated with larger leaves

ABSTRACT.

• 1 The female weevil of Apoderus balteatus Roelofs cuts the leaf near its base in order to make a leaf-roll‘cradle', in which one, two or three eggs are laid. Cuts are always located about 5 mm from the leaf base, independent of leaf size.
• 2 Larger leaves are made into larger cradles.
• 3 Weevils tend to lay more eggs in large cradles.
• 4 Eggs are laid through different holes and separated by leaf layers in the cradle. Cannibalism by larvae will be prevented by this isolated oviposition.
• 5 Multiple oviposition of this weevil allows larger leaves to be used by multiple larvae. It facilitates more efficient use of larger leaves and economizes on female effort in cradle formation.

     

Ubiquitous distribution of fluorescent protein in muscles of four species and two subspecies of eel (genus <Emphasis Type="Italic">Anguilla</Emphasis>)

In this study, the localization of fluorescent protein (FP) was characterized in the muscles of four species and two subspecies of eels Anguilla anguilla, A. australis, A. bicolor bicolor (b.), A. bicolor pacifica (p.) and A. mossambica in addition to the previously reported A. japonica. The open reading frame of each eel FP was 417 bp encoding 139 amino acid residues. The deduced amino acid sequences among the four species and two subspecies exhibited 91.4–100% identity, and belonged to the fatty-acid-binding protein (FABP) family. The gene structure of eel FPs in A. japonica, A. anguilla, A. australis, A. bicolor b., A. bicolor p. and A. mossambica have four exons and three introns, and were common to that of FABP family. The apo eel FPs expressed by Escherichia coli with recombinant eel FP genes were analysed for the fluorescent properties in the presence of bilirubin. The excitation and emission spectra of holo eel FPs had the maximum wavelengths of 490–496 and 527–530 nm, respectively. The holo eel FPs indicated that the fluorescent intensities were stronger in A. japonica and A. bicolor than in A. mossambica, A. australis and A. anguilla. The comparison of amino acid sequences revealed two common substitutions in A. mossambica, A. australis and A. anguilla with weak fluorescent intensity.