Hydroxamic acids affecting barley yellow dwarf virus transmission by the aphid Rhopalosiphum padi

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid (Hx) occurring in wheat, was shown to deter feeding by the aphid Rhopalosiphum padi (L.), and to reduce BYDV transmission to the plant. Dual choice tests with wheat leaves showed the preferential settlement of aphids on leaves with lower levels of DIMBOA. Electric monitoring of aphid feeding behaviour showed that in seedlings with higher DIMBOA levels fewer aphids reached the phloem and they needed longer times to contact a phloem vessel than in those with lower levels. When aphids carrying BYDV were allowed to feed on wheat cultivars with different DIMBOA levels, fewer plants were infected with BYDV in the higher DIMBOA cultivars than in the lower ones. Preliminary field experiments showed a tendency for wheat cultivars with higher Hx levels to be more tolerant to infection by BYDV than lower Hx level ones.     

稗草潜在化感物质的排查

针对已报道属于羟基肟酸(丁布)、酚酸和酞酸酯类的稗草潜在的化感物质,本文以水稻、稗草和莴苣为试验材料,对2,4-二叔丁基酚、对羟基扁桃酸2种酚酸以及3种酞酸酯类物质的化感活性进行了研究.采用高效液相色谱法( HPLC)研究了上述5种物质以及丁布在稗草组织、根区土壤和种子萌发液的含量.结果表明:在100μg·ml-1作用浓度下,对羟基扁桃酸对莴苣、水稻以及稗草的种子萌发和幼苗生长的综合抑制活性最弱,2,4-二叔丁基酚化感抑制活性相对最强.酞酸二甲酯、酞酸二异辛酯和2,4-二叔丁基酚这3种物质对稗草的抑制活性大干水稻.通过HPLC只在稗草苗期叶、根和种子萌发液中检测出对羟基扁桃酸,其含量分别为9.72 μg·g-1、7.29 μg·g-1和0.24 μg·ml-1,而其他生长期组织以及根区土壤中均未检出.所有样品均未检测出2,4-二叔丁基酚、丁布和3种酞酸酯类物质.对羟基扁桃酸的浓度-效应试验显示,接近实测浓度(20 μg·g-1)时其对3种受试植物没有显著的化感抑制效应.本研究表明,对羟基扁桃酸不是稗草中主要的化感物质;通过HPLC-标准物质比对方法可以准确分析上述6种化合物,并证实了稗草不含有2,4-二叔丁基酚、丁布和酞酸酯类物质.     

Transformation of maize by 2,4-dihydroxy-7-methoxy-2H-1,4-benzo- xazin-3(4H)-one resistant Agrobacterium strains

One of the important factors responsible for recalcitrance of maize tissue towards Agrobacterium-mediated transformation is the presence of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), an inhibitory metabolite found in maize cells. DIMBOA-resistant strains of Agrobacterium tumefaciens were used to transfer genes coding for GUS (-glucuronidase) and NPTII (neomycine phosphotransferase II) in maize shoot apical meristems derived from 20 day-old seedlings and immature embryos. GUS expression was higher (21–34%) in the apical meristem and was dependent on the type of infecting strain and explant-age. The PCR analysis of selected tissues confirmed the presence of GUS gene in the transformed cells.     

Proteomic profile of aphids exposed to wheat with different contents of benzoxazinoids

Benzoxazinoids are key defence chemicals in cereals that are known to affect several aspects of aphid biology. However, little is known about how they affect aphid physiology. In the present study, we report changes in the whole‐body proteomic profiles of a 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA)‐susceptible genotype of the grain aphid Sitobion avenae (F.) after being exposed to wheat cultivars containing contrasting levels of DIMBOA. The proteome is analyzed after 14 days (short term) and 28 days (long term) of rearing on these cultivars. Seventy‐two proteins are differentially regulated among the treatments and 49 are identified. Exposure to high‐DIMBOA plants results in a higher number of proteins regulated long term. DIMBOA exposure in S. avenae initially generates greater cellular activities, mostly involving cytoskeleton function and possibly related to detoxification. This function appears to be unimportant at long term and is eventually replaced by effects on metabolism function and homeostasis. Taken together, the results of the present study show that the responses of aphids to the secondary plant compounds, such as DIMBOA, exhibit a temporal dynamic in the proteome, possibly helping aphids to overcome the effect of these toxic compounds.     

Effects of DIMBOA levels in wheat on the susceptibility of the grain aphid (Sitobion avenue) to deltamethrin

The effects of DIMBOA in cultivars of wheat on aphid antibiosis and tolerance to the insecticide deltamethrin were investigated for the aphid Sitobion auenae. Over 48 hours the mean relative growth rate differed significantly between nymphs of S. auenae reared on wheat cultivars containing different levels of DIMBOA. Nymphs on the resistant cv. Altar showed a significantly greater susceptibility to deltamethrin, with nearly a three-fold increase in the relative toxicity of deltamethrin, compared with the susceptible cv. Dollarbird. The LC₅₀, adjusted for weight, was reduced by 91% for nymphs reared on the high DIMBOA cultivar. The potential for the enhancement of predation under a reduced pesticide régime is discussed in relation to this research.     

Near-isogenic lines for measuring phenotypic effects of DIMBOA-Glc methyltransferase activity in maize

Three O-methyltransferases (BX10a, b, c) catalyze the conversion of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc) to 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) in maize (Zea mays). Variation in benzoxazinoid accumulation and resistance to Rhopalosiphum maidis (corn leaf aphid) was attributed to a natural CACTA family transposon insertion that inactivates Bx10c. Whereas maize inbred line B73 has this transposon insertion, line CML277 does not. To characterize the phenotypic effects of DIMBOA-Glc methyltransferase activity, we created near-isogenic lines derived from B73 and CML277 that do or do not contain the transposon insertion. Bx10c inactivation causes high DIMBOA-Glc, low HDMBOA-Glc, and decreased aphid reproduction relative to near-isogenic lines that have a functional Bx10c gene. These results confirm the importance of this locus in maize aphid resistance. The availability of Bx10c near-isogenic lines will facilitate further research on the function of different benzoxazinoids and DIMBOA-Glc methyltransferase activity in maize defense against herbivores and pathogens.     

Physiological adaptation of the Asian corn borer Ostrinia furnacalis to chemical defenses of its host plant, maize

A number of gramineous plants such as maize contain cyclic hydroxamic acids (cHx) that are toxic to many herbivores. Among the Ostrinia species found in Japan, the Asian corn borer Ostrinia furnacalis is the only one that utilizes maize, a gramineous plant. We used O. furnacalis and two congeners, Ostrinia scapulalis and Ostrinia latipennis, to obtain insights into the physiological adaptation of O. furnacalis to cHx. When an artificial diet containing a low concentration (0.3 mg/g diet) of cHx was fed to the larvae of O. furnacalis and O. scapulalis, larval growth and survival were significantly less affected in O. furnacalis than O. scapulalis. An artificial diet containing a high level (0.7 mg/g diet) of cHx was found to severely retard the growth of both species, albeit to different degrees. In an assay in vitro, homogenate of the digestive tract of O. furnacalis larvae degraded cHx more rapidly than that of O. scapulalis or O. latipennis. The degradation was found to be enzymatic and dependent on a cofactor, UDP-glucose, suggesting that UDP-glucosyltransferase or other UDP-glucose-dependent enzymes were involved. This enzymatic adaptation probably has enabled O. furnacalis to utilize plants containing cHx.     

Biosynthesis of 1,4-benzoxazin-3-ones in Zea mays

¹⁴C- and ¹⁵N-anthranilic acid are incorporated into the 1,4-benzoxazin-3-ones in maize seedling leaves with low dilution of the isotope. o-Aminophenol and 3-hydroxyanthranilic acid are not incorporated and are probably not intermediates. The cyclic hydroxamic acid and lactam members of the 1,4-benzoxazin-3-one group of compounds are readily interconverted.     

冬小麦幼苗生长和化感物质对CO2和O3浓度升高的响应

利用开顶式气室(OTC), 采用盆栽试验研究了CO₂浓度为550 μL·L^-1、O₃浓度为60 μL·L^-1及CO₂浓度为550 μL·L^-1+O₃浓度为60 μL·L^-1对7个冬小麦品种幼苗生物量和化感物质丁布(DIMBOA)的影响.结果表明：在高CO₂浓度下,冬小麦幼苗地上生物量与丁布含量在品种间存在显著差异,品种碧蚂1号幼苗和根干质量比对照（CO₂浓度为370 μL·L^-1,O₃浓度为40 μL·L^-1）增加了36.8%和24.7%;丁布含量增幅为5.7%~184.6%.除碧蚂1号和陕139外,高浓度O₃导致冬小麦生物量降低,但使所有品种丁布含量显著增加,变幅为0.5~3倍.交互作用下所有品种根干质量降低,长武134地上部质量、根质量和丁布含量降幅最大,分别为82%、27.9%和35.5%;与长武134、远丰175和兰考217丁布含量降低相反,陕139丁布含量增加84.6%.聚类分析显示,不同处理和不同品种均显著影响丁布含量,陕139、兰考217和长武134在高CO₂和O₃浓度处理下聚为一类,而陕139在所有处理中丁布含量均表现为增加.表明化感物质丁布可以作为气候变化条件下,尤其是CO₂和O₃变化下抗性育种的特定指标.     

cis-Jasmone induces accumulation of defence compounds in wheat, Triticum aestivum

Liquid phase extraction (LPE) and vapor phase extraction (VPE) methodologies were used to evaluate the impact of the plant activator, cis-jasmone, on the secondary metabolism of wheat, Triticum aestivum, var. Solstice. LPE allowed the measurement of benzoxazinoids, i.e. 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), 2-hydroxy-7-methoxy-1,4-benzoxazin-3-one (HMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA), and phenolic acids such as trans-p-coumaric acid, syringic acid, p-hydroxybenzoic acid, vanillic acid and cis- and trans-ferulic acid. Using LPE, a significantly higher level of DIMBOA was found in aerial parts and roots of T. aestivum following treatment with cis-jasmone, when compared with untreated plants. Similar results were obtained for phenolic acids, such as trans-ferulic acid and vanillic acid in roots. Using VPE, it was possible to measure levels of 2-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (HBOA), benzoxazolin-2(3H)-one (BOA), ferulic acid, syringic acid and coumaric acid. The levels of HBOA in aerial parts and roots were significantly greater in cis-jasmone treated plants compared to untreated plants. cis-Jasmone is known to be a plant activator in terms of production of defence-related volatile semiochemicals that repel aphids and increase the foraging activity of aphid parasitoids. These results show, for the first time, that cis-jasmone also induces selective production of secondary metabolites that are capable of directly reducing development of pests, diseases and weeds.