Pathways of Amino Acid Degradation in Nilaparvata lugens (St?l) with Special Reference to Lysine-Ketoglutarate Reductase/Saccharopine Dehydrogenase (LKR/SDH)

Nilaparvata lugens harbors yeast-like symbionts (YLSs). In present paper, a genome-wide analysis found 115 genes from Ni. lugens and 90 genes from YLSs that were involved in the metabolic degradation of 20 proteinogenic amino acids. These 205 genes encoded for 77 enzymes. Accordingly, the degradation pathways for the 20 amino acids were manually constructed. It is postulated that Ni. lugens can independently degrade fourteen amino acids (threonine, alanine, glycine, serine, aspartate, asparagine, phenylalanine, tyrosine, glutamate, glutamine, proline, histidine, leucine and lysine). Ni. lugens and YLSs enzymes may work collaboratively to break down tryptophan, cysteine, arginine, isoleucine, methionine and valine. We cloned a lysine-ketoglutarate reductase/saccharopine dehydrogenase gene (Nllkr/sdh) that encoded a bifunctional enzyme catalyzing the first two steps of lysine catabolism. Nllkr/sdh is widely expressed in the first through fifth instar nymphs and adults, and is highly expressed in the fat body, ovary and gut in adults. Ingestion of dsNllkr/sdh by nymphs successfully knocked down the target gene, and caused nymphal/adult mortality, shortened nymphal development stage and reduced adult fresh weight. Moreover, Nllkr/sdh knockdown resulted in three defects: wings were shortened and thickened; cuticles were stretched and thinned; and old nymphal cuticles remained on the tips of legs and abdomen and were not completely shed. These data indicate that impaired lysine degradation negatively affects the survival and development of Ni. lugens.     

白背飞虱对不同抗虫性稻株糖类物质的利用

本文通过对白背飞虱Sogatella furcifeta Horvath在不同苗龄抗虫品种Rathu Hee nati(简称RHT)和感虫品种Taichung Native 1(简称TNl)稻株上的取食反应,对摄入食物中糖类的利用和体内葡糖苷酶的活性变化,以及对稻株含糖量的分析,初步探讨了白背飞虱对稻株糖类物质的利用。白背飞虱在抗虫、感虫品种上的取食均随稻株苗龄的增长而降低,沮不管品种的抗虫性如何,稻株内的总糖量却随稻株苗龄的增加而上升。高效液相色谱分析飞虱分泌的蜜露结果表明,在RHT上分泌的蜜露里,蔗糖和果糖的含量明显地低于在TNI上分泌的。由此推测白背飞虱从RHT稻株韧皮部中吸食的汁液较从TNI中的少,但利用率高。取食RHT后的白背飞虱,体内的葡糖苷酶活性明显地较取食TNl后的低,并与飞虱体重的变化呈正相关。在白背飞虱体内可能存在着两种独立的、可控制食物的摄入及摄入食物的消化和吸收的机制。     

Behavioral responses of the whitebacked planthopperSogatella furcifera (Homoptera: Delphacidae) on rice plants whose odors have been masked

In a two-choice test, moreS. furcifera females settled more often on exposed plants than on parafilm-masked ones, regardless of the susceptibility of rice varieties. This indicates that rice volatiles play an important role in the insect's short-range orientation to its host. The fact that more insects settled on exposed resistant Rathu Heenati (RHT) than to masked susceptible Taichung Native 1 (TN1) suggests that there must be certain common volatiles released by both varieties. Few females landed on masked plants of either RHT or TN1. This implies that the insect could not recognize at a distance that a plant was resistant or susceptible without olfactory stimuli.S. furcifera excreted less honeydew on masked plants than on exposed ones for both varieties and more on masked TN1 than on exposed RHT. The electronic monitoring of feeding behavior demonstrates that the insect made more frequent probes and had shorter phloem ingestion durations on exposed RHT than on exposed TN1 and on masked RHT than on masked TN1. Moreover, the insect had longer phloem ingestion durations on masked TN1 than on exposed RHT. These results suggest that volatile chemicals given off by resistant RHT plants have a negative effect on feeding.     

Amino acid metabolism during flight in tsetse flies.

Experiments carried out using teneral Glossina pallidipes indicate that flight can continue for at least 4 to 7 min after the thoracic proline reserves have fallen to low levels, suggesting that some other energy source is available. Earlier work suggests that alanine formed during flight is transported from the thorax to the abdomen where proline is resynthesized. Injection experiments using ¹⁴C alanine confirm that the transport mechanism does occur, that it is enhanced by flight, and that alanine is more rapidly incorporated into glutamate and proline in the abdomen than in the thorax. An analysis of published work shows that there is evidence for the involvement of residual blood meal amino acids even in the early stages of flight and supports the suggestion that they are of importance in prolonging flight. A decline in amino nitrogen during the early stages of flight is consistent with the action of glutamate dehydrogenase at this time. The poor flight durations in teneral flies may be due both to the low proline levels and to the absence of the residual blood meal. Very high energy consumptions are noted and appear to be related to the abnormally large musculature necessary for the fly's haematophagous and viviparous habits.     

Sublethal effects of buprofezin on development,reproduction, and chitin synthase 1 gene (SfCHS1) expression in the white-backed planthopper,Sogatella furcifera (Hemiptera: Delphacidae)

The white-backed planthopper, Sogatella furcifera (Horváth) (Hemiptera: Delphacidae), is a major rice pest in some Asia-Pacific countries. Buprofezin is an insect growth regulator with relatively low mammalian toxicity but high efficacy to many rice pests. In this study, we estimated the toxicity of buprofezin against 3rd-instar nymphs of S. furcifera using the rice-stem dipping method. The results showed that the LC₅₀ of buprofezin to 3rd-instar nymphs were 0.89?mg/L. When 3rd-instar nymphs were exposed to the LC₁₀ and LC₂₅ (0.10 and 0.28?mg/L) of buprofezin, the duration of juvenile development was significantly prolonged in the F₀ and F₁ generations. The fecundity (eggs per female) of the F₁ females was reduced by 5.29% and 12.34%, respectively, in addition to the survival rate, emergence rate, copulation rate, and hatchability were decreased by treatment with buprofezin at LC₁₀ and LC₂₅, compared with the control group. The relative fitness of S. furcifera in LC₁₀ and LC₂₅ treatments was reduced by 47% and 63%, respectively. Furthermore, real-time quantitative PCR analyses revealed increased the expressions of SfCHS1 and its two variants following the exposure of nymphs to buprofezin. Increased these genes mRNA levels associated with reduced chitin biosynthesis may result from the inhibition of chitin synthase activity, and thereby leading to a higher mortality of S. furcifera. Overall, sublethal concentrations of buprofezin suppressed the population growth of S. furcifera.     

Catalytic properties of enzymes from Erwinia carotovora involved in transamination of phenylpyruvate

K _m for L-phenylalanine, L-glutamic acid, L-aspartic acid, and the corresponding keto acids were calculated, as well as V _max was measured for the following pairs of substrates: L-phenylalanine-2-ketoglutarate, L-phenylalanine-oxaloacetate, L-glutamic acid-phenylpyruvate, and L-aspartic acid-phenylpyruvate for aminotransferases PAT1, PAT2, and PAT3 from Erwinia carotovora catalyzing transamination of phenylpyruvate. The ping-pong bi-bi mechanism was shown for the studied aminotransferases. The substrate inhibition (K _s) of PAT3 with 2-ketoglutarate and oxaloacetate was 10.23 ± 3.20 and 3.73 ± 1.99 mM, respectively. It was shown that L-β-(N-benzylamino)alanine was a competitive inhibitor with respect to L-phenylalanine for PAT1 (K _i = 0.32 ± 0.07 mM, K _m = 0.45 ± 0.1 mM, V _max = 11. 6 ± 0.4 U/mg) at 25 mM concentration of 2-ketoglutarate in the reaction medium. L-β-(N-methylamino)alanine is a noncompetitive inhibitor with respect to L-phenylalanine for PAT3 (K _I = 138.4 ± 95.4 mM, K _m = 13.7 ±3.9 mM, V _max = 18.6 ± 4.1 U/mg) at 2 mM concentration of 2-ketoglutarate in the reaction medium. L-stereo isomers of nonprotein analogues of aromatic amino acids were studied as substrates for PAT1, PAT2, and PAT3. L-β-(2-Br-phenyl)alanine, L-β-(4-Br-phenyl)alanine, L-β-(2-F-phenyl)alanine, and L-(2-F)tryptophan were good substrates for all three aminotransferases; L-α-methyl-β-(2-Br-phenyl)alanine and L-O-benzyltyrosine were substrates only for PAT3; L-β-(4-F-phenyl)alanine was a substrate for PAT1 and PAT3. Thus, these analogues of aromatic amino acids can be stereoselectively synthesized using the studied aminotransferases in the presence of the corresponding keto acids.     

Accumulation of salicylic acid,jasmonic acid and phytoalexins in rice, <Emphasis Type="Italic">Oryza sativa</Emphasis>, infested by the white-backed planthopper, <Emphasis Type="Italic">Sogatella furcifera</Emphasis> (Hemiptera: Delphacidae)

In order to clarify the mechanism of induced resistance to blast disease in rice, Oryza sativa, that had been previously infested by the white-backed planthopper, Sogatella furcifera Horváth, we first investigated the accumulation of salicylic acid (SA) and jasmonic acid (JA) in rice plants infested by the planthopper. The results confirmed that infestation of S. furcifera strongly stimulates the production of SA and JA in rice. These results indicate that both salicylate- and jasmonate-mediated pathways (SA and JA pathways), which are involved in the general defense system in plants, were activated in rice infested by S. furcifera. Further results confirmed that S. furcifera infestation induces accumulation of a major rice diterpenoid phytoalexin, momilactone A, and a flavonoid phytoalexin, sakuranetin, which are well known as antimicrobial chemicals, particularly in blast disease caused by the blast fungus, Magnaporthe oryzae B. Couch. All these results strongly suggest the following hypothetical mechanism of induced-resistance to M. oryzae in rice infested by S. furcifera. First, S. furcifera releases some elicitor-active compounds, which might be produced in the salivary glands, into the rice plant during feeding. Next, the defense signal systems, SA- and JA-mediated pathways, are activated by the elicitor. Finally, phytoalexins are induced in rice as antimicrobial compounds mainly through activation of the JA-mediated pathway.     

Determination of the site of pheromone emission in the virgin females Culicoides nubeculosus Meigen (Diptera: Ceratopogonidae)

The zone of emission of the sex pheromone from the body of Culicoides nubeculosus was investigated. The amount of pheromone emitted was evaluated by counting the number of matings between males and females exposed to a flow of air coming from a chamber containing virgin females. The number of matings is higher than that recorded when the air flow comes from an empty chamber (control). Three parts of the body were examined: head, thorax and abdomen. Each part was studied by neutralizing the effect of the others. The head was neutralized by decapitation and the females continued to emit pheromone. The head is, therefore, not indispensible for pheromone emission. The roles of the thorax and abdomen were studied by coating these with paraffin wax. When the thorax is coated, pheromone emission continues, but when the abdomen is coated, it stops. It appears that the abdomen alone is responsible for emission of the sex pheromone.     

Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants

A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.     

Elicitor(s) in Sogatella furcifera (Horváth) Causing the Japanese Rice Plant (Oryza sativa L.) to Induce the Ovicidal Substance,Benzyl Benzoate

We elucidate the mechanism for inducing the production of ovicidal benzyl benzoate by Japonica rice varieties to kill eggs of the whitebacked planthopper, Sogatella furcifera (Horváth), lying in the rice plant. Even when subjected to physical damage by a needle or damage with water, the rice plant produced no benzyl benzoate. However, significant benzyl benzoate was produced when the plant was damaged with a methanol extract or homogenate of S. furcifera. The extract of the male did not induce the production of benzyl benzoate, but that of the female did. We concluded from these results that benzyl benzoate was induced by some elicitor(s) in the female of S. furcifera.     

Effects of the susceptibility of rice varieties to Sogatella furcifera on nymphal development and reproduction of Microvelia horvathi through a food chain

The effects of four rice varieties highly susceptible （ Xiang-Zao-Xian31 and Jia-Yu 164 ）, moderately susceptible （ Wei-You402 ）, and resistant （ Zhu-Liang-You02 ） to the whitebacked planthopper Sogatellafurcifera on the nymphal development, reproduc- tion and survival of Microvelia horoathi were investigated through a food chain using SogateUafurcifera as herbivore prey. Significant longer nymphal developmental time were observed in the 1 st, 4th, 5th instar and whole nymphal stage of M. horvathi raised on S. furcifera fed ZLY02 and WY402 than those of the other two varieties. M. horvathi raised on S. furcifera fed resistant ZLY02 showed a significant lower survival of whole nymphal stage than those fed other three susceptible varieties. Moreover, M. horvathi raised on S. furcifera fed resistant ZLY02 had shorter female longevity and lower lifetime fecundity than those of on susceptible XZX3l. Our results suggest that the S. furcifera- resistant rice variety ZLY02 had a negative effect on the growth and development of the predator M. horvathi through a food chain.     

Ovarian development status and population characteristics of Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål): implications for pest forecasting

Migratory behaviour in insects correlates with reproductive development in females, and migration often occurs during the pre‐reproductive stage of adults. The relationship between ovarian development and population status of the white‐backed planthopper Sogatella furcifera (Horváth) and the brown planthopper Nilaparvata lugens (Stål) was evaluated. Females of both species were captured in rice fields and light traps and then dissected in double‐season rice‐farming regions of southern China. The ovarian development of S. furcifera and N. lugens was divided into five levels, following previous studies. The population statuses of both species were examined based on the ovarian development of female adults caught in rice paddies. The ovarian development in N. lugens females caught in light traps mostly ranged from level I to level II, whereas that in S. furcifera females caught in light traps mostly ranged from level I to level III. During peak immigration, ovarian development in N. lugens females was mainly at level II, whereas that in S. furcifera females was mainly at level II and sporadically at level III. During peak emigration, both S. furcifera and N. lugens showed level I ovarian development. The temporal dynamics of ovarian development in light trap catches revealed that (i) significant emigration and partial immigration periods occur in S. furcifera, with ovarian development mainly at level I and sporadically from level II to level III and (ii) numerous immigrants of N. lugens were detected during sedentary and local breeding periods. The temporal dynamics of ovarian development provides more information than does the paddy population. Thus, this study proposes another method for pest forecasting, which is more precise and efficient than conventional forecasting methods such as light trap catching and monitoring population dynamics in rice fields.     

Glycosylation regulates specific induction of rice immune responses by Acidovorax avenae flagellin

Plants have a sensitive system that detects various pathogen-derived molecules to protect against infection. Flagellin, a main component of the bacterial flagellum, from the rice avirulent N1141 strain of the Gram-negative phytopathogenic bacterium Acidovorax avenae induces plant immune responses including H₂O₂ generation, whereas flagellin from the rice virulent K1 strain of A. avenae does not induce these immune responses. To clarify the molecular mechanism that leads to these differing responses between the K1 and N1141 flagellins, recombinant K1 and N1141 flagellins were generated using an Escherichia coli expression system. When cultured rice cells were treated with recombinant K1 or N1141 flagellin, both flagellins equally induced H₂O₂ generation, suggesting that post-translational modifications of the flagellins are involved in the specific induction of immune responses. Mass spectrometry analyses using glycosyltransferase-deficient mutants showed that 1,600- and 2,150-Da glycans were present on the flagellins from N1141 and K1, respectively. A deglycosylated K1 flagellin induced immune responses in the same manner as N1141 flagellin. Site-directed mutagenesis revealed that glycans were attached to four amino acid residues (Ser¹⁷⁸, Ser¹⁸³, Ser²¹², and Thr³⁵¹) in K1 flagellin. Among mutant K1 flagellins in which each glycan-attached amino acid residue was changed to alanine, S178A and S183A, K1 flagellin induced a strong immune response in cultured rice cells, indicating that the glycans at Ser¹⁷⁸ and Ser¹⁸³ in K1 flagellin prevent epitope recognition in rice.     

Sulphur deficiency inhibits nitrogen assimilation and recycling in barley plants

Sulphur (S) is incorporated into diverse primary and secondary metabolites that play important roles in proper growth and development of plants. In cereals, a fraction of the nitrogen (N) accumulated in developing grains is guaranteed by amino acid remobilization from vegetative tissues, a contribution that becomes critical when soil nutrients are deficient. Glutamine synthetase (GS) and amino acid transporters (AAT) are key components involved in N assimilation and recycling. The aim of the present study was to evaluate the effect of S availability on the expressions of HvGS and several selected HvAAT genes in barley plants and on the phloem exudation rate of amino acids. To this end, two independent experiments were designed to impose low S availability conditions to barley plants. Low S availability caused a decrease in the phloem exudation rate of amino acids as well as in the gene expression of all the HvGS genes and five of the six HvAAT genes analyzed. The strong correlation found between the phloem amino acid exudation rate and HvGS1-1, HvGS1-2, HvAAP7, and HvProT1 gene expression may indicate the participation of these genes in the regulation of amino acid remobilization through the phloem.     

Host-recognition kairomone from Sogatella furcifera for the parasitoid Anagrus nilaparvatae

A kairomone produced by the rice white-backed planthopper Sogatella furcifera (Horvath) for the mymarid egg parasitoid Anagrus nilaparvatae Pang et Wang was investigated. Eggs, female and male adults, nymphs, exuvia, honeydew, nymph-damaged plants and plants with S. furcifera eggs all elicited searching behavior in the parasitoid. Eggs, female adults and plants with eggs were the most attractive, while exuvia and honeydew evoked the weakest responses. The active compound(s) from S. furcifera female adults, nymphs and plants with eggs could be effectively extracted with methanol, acetone, n-hexane, ethyl ether and dichloromethane. Isolation of the active chemical(s) in three solvent extracts, the acetone and n-hexane extracts of S. furcifera female adults, and the acetone extract of S. furcifera nymphs, was accomplished by thin-layer chromatography. Only one fraction was active and had the same chemical properties in the three solvent extracts. Infra-red analysis of this fraction revealed a kind of ester with saturated and unsaturated fatty acids, which was previously found to be active in the same compound as the extracts from the nymphs and female adults of the rice brown planthopper, Nilaparvata lugens (Stål), and identified as palm oil. The results are discussed in relation to host location by A. nilaparvatae.     

Effect of organic rice farming on planthoppers 4. Reproduction of the white backed planthopper,Sogatella furcifera Horváth (Homoptera: Delphacidae)

The reproduction ofSogatella furcifera was investigated in a chemically fertilized rice field and an organically farmed field. In the latter, the density of immigrants was significantly higher, while the settling rate of female adults and the survival rate of immature stages of ensuing generations were lower. The number of eggs laid by a female of the invading and following generations was smaller, and the percentage of brachypterous females in the next generation was also lower. Consequently, the density of nymphs and adults in the ensuing generations decreased in the organically farmed field. For an experimental comparison, potted rice plants were cultivated using seedlings and soil from the chemically fertilized or the organically farmed fields. WhenSogatella furcifera was reared on these plants, both the reproductive rate and the appearance rate of brachypterous female adults were lower in the organic treatment. Egg hatchability was also lower in the organic treatment. This experiment suggested that a specific nutritional condition in rice plants suppressed the population ofS. furcifera in the organically farmed field.     

Nitrogen nutrition and metabolic interconversions of nitrogenous solutes in developing cowpea fruits

Budgets for import and utilization of ureide, amides, and a range of amino acids were constructed for the developing first-formed fruit of symbiotically dependent cowpea (Vigna unguiculata [L.] Walp. cv Vita 3). Data on fruit total N economy, and analyses of the xylem and phloem streams serving the fruit, were used to predict the input of various solutes while the compositions of the soluble and protein pools of pod, seed coat, and embryo were used to estimate the net consumption of compounds. Ureides and amides provided virtually all of the fruit's N requirements for net synthesis of amino compounds supplied inadequately from the parent plant. Xylem was the principal source of ureide to the pod, while phloem was the major source of amides to pod and seed. All fruit parts showed in vitro activity of urease (EC 3.5.1.5), allantoinase (EC 3.5.2.5), asparaginase (EC 3.5.11), ammonia-assimilating enzymes and aspartate and alanine aminotransferases (EC 2.61.1 and EC 2.6.1.1.2). Asparagine:pyruvate aminotransferase (EC 2.6.1.14) was recovered only from the pod. The pod was initially the major site for processing and incorporating N; later seed coats and finally embryos became predominant. Ureides were broken down mainly in the pod and seed coat. Amide metabolism occurred in all fruit organs, but principally in the embryo during much of seed growth. Seed coats released N to embryos mainly as histidine, arginine, glutamine, and asparagine, hardly at all as ureide. Amino compounds delivered in noticeably deficient amounts to the fruit were arginine, histidine, glycine, glutamate, and aspartate, while seeds received insufficient arginine, histidine, serine, glycine, and alanine. Quantitatively based schemes are proposed depicting the principal metabolic transformation accompanying N-flow between seed compartments during development.