Bioengineering of crop plants and resistant biotype evolution in insects: Counteracting coevolution

The use, as opposed to the procurement, of transgenic crop plants is discussed in this paper. Transgenic crop plants must not be used until appropriate strategies for their use have been designed and not before crop plants with a variety of insect defenses have been developed. The use of a crop plant with a single defense will pose as strong a selection pressure as the use of a single synthetic insecticide, since insect herbivores are able to evolve effective counter-defenses. The defenses of insects in natural plant-insect associations and with regard to synthetic insecticides are described to demonstrate that there is nothing unique about insecticide resistance. It is the inevitable alternative to local extinction in response to a persistent and predictable selection pressure. Plants counteract insect defensive evolution by keeping the selection pressure as variable as possible. This leads to the conclusion that the best use of biotechnology in crop protection is to reintroduce chemical diversity into crop plants.     

Chemical defense,mycorrhizal colonization and growth responses in <Emphasis Type="Italic">Plantago lanceolata</Emphasis> L.

Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and belowground mutualism with arbuscular mycorrhizal fungi (AMF) in Plantago lanceolata L., using plant genotypes from lines selected for low and high constitutive levels of the iridoid glycosides (IG) aucubin and catalpol. As selection was based on IG concentrations in leaves, we first examined whether IG concentrations covaried in roots. Root and leaf IG concentrations were strongly positively correlated among genotypes, indicating genetic interdependence of leaf and root defense. We then found that root AMF arbuscule colonization was negatively correlated with root aucubin concentration. This negative correlation was observed both in plants grown with monocultures of Glomus intraradices and in plants colonized from whole-field soil inoculum. Overall, AMF did not affect total biomass of plants; an enhancement of initial shoot biomass was offset by a lower root biomass and reduced regrowth after defoliation. Although the precise effects of AMF on plant biomass varied among genotypes, plants with high IG levels and low AMF arbuscule colonization in roots did not produce less biomass than plants with low IG and high AMF arbuscule colonization. Therefore, although an apparent trade-off was observed between high root chemical defense and AMF arbuscule colonization, this did not negatively affect the growth responses of the plants to AMF. Interestingly, AMF induced an increase in root aucubin concentration in the high root IG genotype of P. lanceolata. We conclude that AMF does not necessarily stimulate plant growth, that direct plant defense by secondary metabolites does not necessarily reduce potential benefits from AMF, and that AMF can enhance concentrations of root chemical defenses, but that these responses are plant genotype-dependent.     

植物化感物质对种子萌发的影响

所有的化感物质都对一些植物的种子萌发产生影响.本文介绍了植物化感作用和化感物质的定义,化感物质的释放方式和种类,然后重点综述了化感物质影响种子萌发的作用机理、内外因素和生态学意义.化感物质通过影响细胞膜透性、细胞分裂生长和分化、呼吸作用、蛋白质合成、基因表达、激素合成和平衡,最终影响种子萌发.化感物质对种子萌发的影响与化感物质的种类、浓度、受体植物种类和环境条件等有关.     

外源毒素对林地土壤养分的影响

杉木 (Ｃｕｎｎｉｎｇｈａｍｉａｌａｎｃｅｏｌａｔａ)人工林连栽导致地力退化是一个不争的事实[5] 。近年来许多研究表明 ,杉木连栽后的地力退化与植物化感作用有关[8,12 ,15,16] 。香草醛、对羟基苯甲酸是土壤中毒物质 ,早在 2 0世纪 6 0年代周崇莲等人在研究杉木连栽土壤氧化代谢能力时发现三耕土中香草醛的氧化代谢能力比头耕土高 ,为头耕土的 143% ,这证明三耕土中含有较多的土壤中毒物质[3 ] 。马越强等人的研究表明酚醛类化感物质会影响杉木种子发芽、幼苗生长和光合效率[1] ,Ｈｕａｎｇ等[12 ] 发现杉木根系水浸液中含有香草醛和对…     

Screening of Grassland Plants for Restoration after Spotted Knapweed Invasion

Invasions of North American grasslands by Spotted knapweed (Centaurea maculosa Lam.) are mediated in part by Spotted knapweed root exudation of (±)‐catechin, a potent phytotoxin. Residual soil (±)‐catechin may interfere with reestablishment of native grassland species even after Spotted knapweed populations are controlled. Grassland species that are resistant to (±)‐catechin may be more successful for restoration of areas infested by Spotted knapweed. We evaluated the (±)‐catechin resistance of 23 grassland species by measuring the effects of seven (±)‐catechin concentrations (0–4.0 mg/mL) on seed germination, seedling root and shoot elongation, and seedling mortality. (±)‐Catechin treatments were chosen to reflect the range of observed Spotted knapweed field soil (±)‐catechin concentrations. Inhibition of root elongation was the strongest and most common effect of (±)‐catechin treatment. High (±)‐catechin concentrations reduced mean root lengths of 5 of the species by more than 75% and another 10 species by more than 55%. Experimentally derived concentrations needed to reduce root length by 50% (EC50), an indicator of (±)‐catechin resistance, ranged from 0.43 mg/mL ± 0.30 SE to greater than 4.0 mg/mL among species. Eight species with EC50s greater than 3.0 mg/mL were identified as resistant to (±)‐catechin and are likely suitable for revegetation of Spotted knapweed–infested areas. (±)‐Catechin resistance was positively correlated with mean seed mass, suggesting that seed carbohydrate reserves may allow seedlings to detoxify (±)‐catechin, develop barriers to (±)‐catechin exposure, or sustain a positive growth rate, despite (±)‐catechin‐induced cell death. Future efforts to identify allelochemical‐resistant grassland species should focus on large‐seeded species.     

Inhibition of nitrification in forest soil by monoterpenes

Nitrate production was detected in untreated soil of a Norway spruce (Picea abies L.) stand only after clear-cutting the stand. The aim of this study was to determine whether allelochemical inhibition of nitrification by monoterpenes played any role in inhibiting nitrification in the stand. Therefore, soils from a clear-cut plot and from a forest plot were studied. In the field, monoterpenes (mostly - and -pinenes), measured by soil microair diffusive samplers, were intensively produced in the forest plot, but not in the clear-cut plot. In the laboratory, soil samples taken from the forest plot produced only small amounts of monoterpenes, indicating that monoterpenes were mainly produced by the roots and not to great extent by the soil microbial population. The effect of a mixture of monoterpenes (seven major monoterpenes detected in the field) on net nitrification, net N mineralization and denitrification activities of soil from the clear cut plot, and on carbon mineralization of soils from both the forest and clear-cut plots, was studied in the laboratory. In both aerobic incubation experiments and in soil suspensions with excess NH4-N, nitrification was inhibited by exposure to the vapours of monoterpenes at similar concentrations at which they had been detected in forest plot. This indicates direct inhibition of nitrification by monoterpenes. Exposure to monoterpenes did not affect denitrification. However, it increased respiration activity of both soils. This could also indicate indirect inhibition of nitrification by monoterpenes, due to immobilization of mineral N. Thus it seems that monoterpenes could play a role in inhibiting nitrification in the forest soil.     

外源NO缓解紫茎泽兰提取物对黄瓜根边缘细胞的化感胁迫

以津优35号黄瓜为材料,采用根尖悬空气培养的方法,研究了紫茎泽兰提取物对黄瓜根边缘细胞的化感胁迫,以及外源NO缓解化感胁迫的效应.结果表明: 1000 mg·L^-1紫茎泽兰提取物对黄瓜根尖有明显的伤害作用,根尖组织结构被破坏,根尖表层细胞脱落,细胞排列混乱且疏松;这些伤害能够被外源NO有效缓解.与对照相比,紫茎泽兰提取物处理黄瓜幼苗根尖根边缘细胞(RBC)的数量和细胞活率被显著抑制,分别降低54.5%和97.2%,细胞凋亡率升高12.3倍,RBC的黏胶层厚度增加31.4%,根边缘细胞根冠果胶甲基酯酶(PME)活性显著增加.与紫茎泽兰提取物处理相比,提取物胁迫下添加外源NO处理的RBC数量和细胞活率分别增加72.4%和146.0%,细胞凋亡率和RBC黏胶层厚度分别降低30.7%和15.0%,PME活性在处理72 h时降低了14.3%.紫茎泽兰提取物对黄瓜RBC产生细胞毒性,诱导细胞发生凋亡和死亡,破坏RBC对根尖的保护,提取物进一步对根尖产生胁迫伤害,破坏根尖的组织结构.外源NO可以在一定程度上缓解提取物对黄瓜根尖及RBC的化感胁迫伤害.     

Allelochemical induced stress: Effects of l-canavanine on the pathogenicity of Bacillus thuringiensis in Manduca sexta

Increased susceptibility of Manduca sexta to commercial formulations of the microbial insecticide, Bacillus thuringiensis, as evidenced by lower LD₅₀ and LT₅₀ values, was observed when M. sexta were reared on an artificial diet supplemented with a sublethal concentration (2.5 mm) of l-canavanine. At several dosages of B. thuringiensis, which were administered either by diet contamination or by per os forced feeding, a greater than 70% reduction (P < 0.05) occurred in the LT₅₀ response with canavanine-treated larvae. The LD₅₀ values also were lowered by canavanine treatment. This constitutes the first report of a plant allelochemical enhancing the effect of B. thuringiensis in vivo. It is suggested that canavanine enhances the effect of B. thuringiensis on gut permeability and active transport.     

绞股蓝提取液对蛋白核小球藻的化感效应及影响机理研究

以中草药植物绞股蓝[Gynostemma pentaphyllum(Thunb.) Makino]为化感供体材料,研究其不同浓度的提取液(0、5、10、25、50 g/L)对蛋白核小球藻(Chlorella pyrenoidesa)生长及生理生化特征的化感效应。结果表明:(1)绞股蓝提取液对蛋白核小球藻生长均具有抑制作用,其抑制作用随提取液质量浓度增大和培养时间延长均呈增强趋势,且25 g/L绞股蓝提取液培养15 d时的抑制率达到最大(79.41%)。(2)各浓度绞股蓝处理组蛋白核小球藻细胞内的叶绿素a含量均低于对照组,且随着提取液浓度升高以及处理时间延长叶绿素a含量较对照的降低量越多,表明蛋白核小球藻光合作用受到的影响也越大。(3)绞股蓝处理组蛋白核小球藻细胞的膜透性(吸光度OD_(264))显著高于对照,且膜透性随着提取液浓度增大而增强;高浓度提取液处理下,藻细胞内部的可溶性蛋白质(OD_(280))及核酸(OD_(260))含量均显著高于对照,且随着处理时间延长,细胞膜透性增大,细胞内部的可溶性蛋白质及核酸向胞外渗透增多。研究发现,绞股蓝提取液能够抑制蛋白核小球藻生长,并随着提取液质量浓度增大而增强;绞股蓝提取液能促进藻细胞叶绿素分解、增加细胞膜透性,引起可溶性蛋白质和核酸向胞外渗透量升高,导致藻细胞结构受损,代谢功能紊乱,从而达到化感抑制作用。