Abaxial and Adaxial Stomatal Density, Stomatal Conductances and Water Status of Bean Primary Leaves as Affected by Paclobutrazol

The plant growth retardant, paclobutrazol at 8.5 or 17.0 μM concentrations effectively inhibited the stem elongation and primary leaf expansion of bean seedlings. Although the retardant reduced the relative water content in well-watered plants, the water and pressure potentials remained high in the primary leaves. K⁺, Na⁺, Mg²⁺ and Ca²⁺ contents in the primary leaves of the paclobutrazol-treated plants were not significantly different from those in the control. The stomatal density increased on both surfaces but the length of guard cells was not reduced significantly on the adaxial epidermes of the paclobutrazol-treated primary leaves. The inhibitory effect of paclobutrazol on the abaxial stomatal conductances became more pronounced with time during the light period but the adaxial surfaces displayed similar or slightly higher conductances than those of the control. The transpiration rate on a unit area basis did not change significantly or increased in the treated leaves thus the reduced water loss of paclobutrazol-treated plants was due to the reduced leaf area. Stomatal conductances of the adaxial surfaces responded more intensively to exogenous abscisic acid and the total leaf conductance decreased faster with increasing ABA concentration in the control than in the paclobutrazol-treated leaves. Paclobutrazol, an effective inhibitor of phytosterol biosynthesis, not only amplified the stomatal differentiation but increased the differences between the adaxial and abaxial stomatal conductances of the primary leaves.     

Is proline involved in stomata regulation of Commelina communis plants recovering from salinity stress?

Plants of Commelina communis L. were grown in culture solution to which NaCl was added for 48 h. The solutions were then replaced with normal medium, so that the plants could recover from the stress. The water potential increased almost to that of the controls during 4 h of recovery, but stomatal resistance stayed high. Cytokinin treatment of leaf discs failed to enhance recovery of stomatal aperture, although it enhanced stomatal recovery of identically treated epidermal tissue. Proline levels in leaves correlated well with stomatal resistance. Incubation of epidermal tissue in D-proline inhibited stomatal opening. NaCl and benzyladenine interacted with the effect of proline, and the effect of abscisic acid and was additive to that of proline.     

The Relation between Photosynthesis and Stomatal Resistance of Each Leaf Surface in Cotton Leaves

The relation between photosynthesis and stomatal resistance of each leaf surface in cotton leaves (Gossypium hirsutum) was studied during ageing and with increase in light intensity. During ageing of leaves the stomatal resistance of the upper surface increases before that of the lower surface. This observation would suggest that the stomata of the upper leaf surface commence to age before those of the lower leaf surface. The earlier commencement of the increase in upper stomatal resistance results in the decline in photosynthesis at an early stage of ageing being negatively correlated with the upper stomatal resistance and not related to the lower stomatal resistance. The results indicate that in this initial phase of ageing the decrease in photosynthesis and increase in stomatal resistance of the upper surface are not causally related but occur simultaneously. At a more advanced stage of ageing the lower stomatal resistance also increases and then the decline in photosynthesis becomes related to the increase in stomatal resistance of both leaf surfaces. When illumination of leaves is increased stepwise, the resultant increase in photosynthesis is related to the reduction in stomatal resistance of each leaf surface. At low light intensities the stomatal resistance of the lower surface is low while that of the upper surface is relatively high. The difference between them decreases with increase in light intensity. This would indicate that the upper stomata require a higher light intensity to open than the lower stomata. The stormatal resistance of the two leaf surfaces is not related to the stomatal frequencey.     

脯氨酸对不结球白菜（Brassica chinensis）镉积累的影响

采用溶液培养的方法,研究了过量Cd对不结球白菜（Brassica chinensis）幼苗内源脯氨酸含量的影响及外源脯氨酸在不结球白菜Cd积累中的作用。100μmol？L-1 Cd处理明显增加不结球白菜叶片脯氨酸（Pro）的含量,并且随着Cd胁迫时间的延长,其含量也显著上升。100μmol？L-1 Cd处理明显降低脯氨酸脱氢酶（PDH）活性,而增加δ1-吡咯啉-5-羧酸合成酶（P5CS）的活性。1~5 mmol？L-1外源Pro处理显著降低不结球白菜幼苗地上部Cd含量,对根系Cd含量无显著影响,但外源Pro处理并不能缓解过量Cd对不结球白菜幼苗生物量的抑制作用。外源Pro处理下,不结球白菜叶片中Pro含量与其地上部干重呈显著的负相关关系。     

Effects of cycloheximide on abscisic Acid biosynthesis and stomatal aperture in bean leaves

Cycloheximide was shown to block abscisic acid (ABA) biosynthesis in nonstressed as well as in stressed Phaseolus vulgaris leaves. Leaf wilting caused by cycloheximide resulted from increased stomatal opening as judged by a decreased stomatal diffusion resistance. The inhibition of ABA biosynthesis by cycloheximide was at least partially responsible for the increase in stomatal opening as suggested by the cooccurrence of inhibition of ABA biosynthesis and increased stomatal opening, and the partial reversal of stomatal opening in cycloheximide-treated leaves by exogenous ABA. Dark treatment failed to close stomatal in cycloheximide-treated leaves, suggesting that stomatal closure in response to darkness may normally be mediated by ABA.     

外源脯氨酸对高温胁迫下黄瓜幼苗叶片AsA-GSH循环和光合荧光特性的影响

以抗热性较弱的黄瓜品种‘新泰密刺'为试材,在人工气候箱内采用营养液栽培法,研究了外源脯氨酸(Pro)预处理对高温胁迫下黄瓜幼苗叶片抗坏血酸-谷胱甘肽循环和光合荧光特性的影响.结果显示:(1)与清水处理相比,高温胁迫4 h和8 h时,Pro预处理黄瓜幼苗叶片单脱氢抗坏血酸还原酶(MDAR)活性、GSH(还原型谷胱甘肽)/GSSG(氧化型谷胱甘肽)比值及GSH含量显著升高;(2)在高温胁迫8 h时,Pro预处理幼苗的净光合速率(P_n)、气孔导度(G_s)及PSⅡ的最大光化学效率(F_v/F_m)、光化学淬灭系数(q_P)均显著升高,而蒸腾速率(T_r)和非光化学淬灭系数(NPQ)降低.研究表明,外源Pro预处理可显著提高高温胁迫下黄瓜幼苗叶片抗坏血酸-谷胱甘肽循环清除H_2O_2能力和叶片光合能力,有效缓解高温胁迫对黄瓜叶片抗氧化系统和光合系统的伤害,从而增强植株的耐热性.     

Water relations of cotton plants under nitrogen deficiency

Nitrogen deficiency in cotton plants (Gossypium hirsutum L.) increased the threshold water potentials for both stomatal closure and leaf senescence (defined as loss of chlorophyll and protein) during drought. These studies attempted to answer two questions: (1) What is the basis for the N/water interaction on senescence? (2) Is there a direct relationship between stomatal closure and senescence? Young and old leaves from N-deficient and N-sufficient plants maintained their relative sensitivities to water stress when excised leaf discs were floated on solutions of polyethylene glycol in dim light. In this leaf disc system, both leaf aging and N deficiency increased the threshold water potential for senescence. Leaf aging and N deficiency also decreased the concentration of exogenous abscisic acid necessary to initiate senescence in discs. A role for cytokinins in controlling senescence could not be clearly shown. In young leaves of both N-deficient and N-sufficient plants, stomata closed at water potentials much higher than those causing senescence. During leaf aging, the water potentials causing senescence increased more than those causing stomatal closure. The two processes thus occurred at about the same potentials in the oldest leaves. These data argue against a general cause-and-effect relationship between stomatal closure and senescence. Rather, each process apparently responded independently to absicsic acid accumulated during drought.     

外源脯氨酸对自然干旱下白刺叶片气孔的影响

以大田环境内多年生荒漠植物白刺（Nitraria tangutorum）为研究对象,采用扫描电子显微镜对不同外源脯氨酸质量浓度处理下白刺叶片气孔进行微观结构观察并测定叶片表皮气孔器长度、宽度、面积和密度,比较同一指标在不同脯氨酸质量浓度处理下的差异。采用室外试验研究自然干旱胁迫下喷施质量浓度为50、100、150、200、250 mg·L^-1的外源脯氨酸（Proline,缩写为Pro或P）研究白刺的耐旱性。观察结果显示,白刺叶片气孔保卫细胞为肾形,气孔在叶片表皮随机分布,气孔器多为无规则型,气孔呈椭圆形且叶片表面蜡质较少,并且叶片细胞出现褶皱和下陷。与对照相比,在不同质量浓度处理和不同采样时间时,气孔长度、宽度及面积下降,气孔密度增大,随着浓度的升高以及采样时间的变化,气孔长度整体呈现下降趋势,当浓度达到200 mg·L^-1时,下降幅度增大,宽度和面积整体呈现先降低后升高再降低的趋势,而气孔密度则整体呈现上升趋势,其中,气孔长度、宽度和面积在质量浓度为50 mg·L^-1、采样第1天时达到最大值,气孔密度在质量浓度为150 mg·L^-1、采样第9天时达到最大值。此外,气孔长度在不同浓度脯氨酸处理下第1、6和9天存在显著差异,而气孔宽度和面积差异不显著,除第0天外,气孔密度因脯氨酸质量浓度不同均差异显著（P<0.05）。研究结果表明,自然干旱胁迫下对白刺叶片喷施不同质量浓度的外源脯氨酸,可减小气孔长度、宽度和面积,而增加气孔密度,以期为白刺抗旱提供理论依据。     

不同BR施用方式诱导黄瓜幼苗对Ca(NO_3)_2胁迫抗性的研究

为探讨外源油菜素内酯(brassinosteroid,BR)诱导黄瓜幼苗对Ca(NO3)2胁迫抗性的效果,研究了3种外源BR施用方法(0.01mg·L-1 BR浸种、0.1mg·L-1 BR喷叶及其二者结合施用)对Ca(NO3)2胁迫(60mmol·L-1)下黄瓜幼苗生长、生理活动以及光合作用的影响。结果表明:(1)3种外源BR方法处理后,Ca(NO3)2胁迫下的黄瓜幼苗株高、茎粗、展开叶片数、叶面积、干重含水量均显著提高,同时其叶片游离脯氨酸和可溶性糖含量上升,过氧化物酶活性提高,而其丙二醛(MDA)含量趋于无Ca(NO3)2胁迫对照的水平;(2)外源BR处理还提高了Ca(NO3)2胁迫下黄瓜幼苗的净光合速率、蒸腾速率和气孔导度,却抑制了Ca(NO3)2胁迫下胞间CO2浓度的升高。研究认为,适宜浓度的外源BR浸种和喷叶处理均可有效增强黄瓜幼苗渗透调节能力,降低细胞膜质过氧化伤害程度,提高抗氧化酶活性和光合效率,从而表现出对Ca(NO3)2胁迫的抗性,并以操作简便、用量极低的0.01mg·L-1 BR浸种方法效果最佳。     

Epidermal structures and stomatal parameters of Chinese endemic Glyptostrobus pensilis (Taxodiaceae)

Glyptostrobus pensilis K. Koch, the only living species, is endemic to southern China. Epidermal structures of G .  pensilis have been studied on leaves collected from Guangzhou, southern China, the native locality of the species, and from Hangzhou, eastern China, the cultivated locality. Leaves are linear, linear-subulate and scale-like. Epidermal cells are rectangular and elongate parallel to the mid-vein on areas lacking stomata, and short, with rounded corners, on intrastomatal areas. Stomatal bands lie parallel to the mid-vein on both surfaces of leaves. Commonly the stomata have five or six subsidiary cells. Stomatal parameters (density and index) of the same surfaces of linear leaves from Guangzhou and Hangzhou show no statistically significant differences ( P  > 0.05). Considering the stomatal parameters of the same surfaces of linear-subulate leaves between the two localities, the stomatal index of the abaxial surfaces reveals no significant differences ( P  > 0.05), while the stomatal index of the adaxial surfaces and the stomatal density of both surfaces exhibit significant differences ( P  < 0.05). Intra-individual variation in stomatal index is smaller than that in stomatal density based on the coefficient of variability of stomatal parameters of the same areas of leaves. When studying the correlation between stomatal parameters of G. pensilis and atmospheric CO₂ concentrations, the stomatal parameters of linear leaves are mostly significant, and stomatal index is more useful than stomatal density.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 153–162.     

Proline biosynthesis in a proline-accumulating barley mutant

A barley (Hordeum vulgare L.) mutant, R5201, selected for resistance to 4? mM trans-4-hydroxyproline had a 3–6 fold increase in the soluble proline content of the leaf compared with the parent cultivar, Maris Mink. The mutant converted more [U-⁴C]glutamic acid to free proline in the leaves than Maris Mink but incorporation into protein proline was similar. Incorporation of radioactivity into proline was inhibited by exogenous proline more in Maris Mink than R5201, suggesting that feedback inhibition of proline biosynthesis is relaxed, but not absent in the mutant. When [1-¹⁴C]ornithine was the precursor, both R5201 and Maris Mink incorporated similar small amounts of label into soluble and protein proline. More protein proline was formed by both genotypes from labelled glutamic acid than from labelled ornithine. There may exist two routes of proline formation, where the glutamate pathway is synthetic and the ornithine pathway is catabolic.     

Leaf Age as a Determinant in Stomatal Control of Water Loss from Cotton during Water Stress

The stomatal resistance of individual leaves of young cotton plants (Gossypium hirsutum L. var. Stoneville 213) was measured during a period of soil moisture stress under conditions of constant evaporative demand. When plants were subjected to increasing soil water stress, increases in stomatal resistance occurred first on the lower leaves and the stomata on the upper surfaces were the most sensitive to decreasing leaf-water potential. Stomatal closure proceeded from the oldest leaves to the youngest as the stress became more severe. This apparent effect of leaf age was not due to radiation differences during the stress period. Radiation adjustments on individual leaves during their development altered the stomatal closure potential for all leaves, but did not change the within-plant pattern. Our data indicate that no single value of leaf water potential will adequately represent a threshold for stomatal closure in cotton. Rather, the stomatal resistance of each leaf is uniquely related to its own water potential as modified by age and radiation regime during development. The effect of age on stress-induced stomatal closure was not associated with a loss of potassium from older leaves. Increases in both the free and bound forms of abscisic acid were observed in water-stressed plants, but the largest accumulations occurred in the youngest leaves. Thus, the pattern of abscisic acid accumulation in response to water stress did not parallel the pattern of stomatal closure induced by water stress.     

Water relations of the upper and lower surfaces of maize leaves

The objective of this study was to determine if the two surfaces of a leaf had different, or the same, water potentials. Maize (Zea mays L. cv. Cargill 805) was the test plant. During an 11 day period, the water potentials of the upper and lower surfaces of the maize leaves were measured daily with anin situ thermocouple psychrometer under growth-room conditions. Plants were grown in pots with a well-watered, commercial greenhouse soil. Stomatal resistance also was measured. The water potential of the upper surface was less negative (more wet) than that of the lower surface. The overall average of the water potential of the upper and lower surfaces was ?1.48 and ?2.07 MPa, respectively. The stomatal resistance of the upper surface was greater than that of the lower surface. The average stomatal resistance during the experiment was 780 and 600 s m^?1 for the upper and lower surfaces, respectively. Since the upper and lower surfaces were not at the same water potential, the results indicated that the parallel-resistance equation, used to combine resistances on the two surfaces of a leaf, was not strictly valid when applied to the maize leaves, as the law assumes equal potentials on the two surfaces.     

Stomatal Responses of Phaseolus vulgaris L. Seedlings to Potassium Chloride in the Nutrient Solution

Alteration in KNO₃ and KCl levels of culture solutions resultedin the production of a series of Phaseolus vulgaris seedlingscontaining a range of chloride levels in the primary leaves;such treatments did not affect leaf potassium content. Irrespectiveof the leaf chloride content the stomata responded to increasedlight intensity by a decrease in stomatal resistance. The stomataof seedlings grown in culture solutions containing KCI offeredhigher diffusive resistances than those of seedlings not receivingthis treatment. This increase in stomatal resistance was foundover the whole range of elevated leaf chloride contents produced.Presence of chloride in the leaf tissue did not, however, affectstomatal responses to fluctuations in atmospheric CO₂ concentration.     

落羽杉属(杉科)叶表皮结构及气孔参数

落羽杉属Taxodium Rich.现生3种植物——落羽杉T. distichum (L.) Rich.、池杉T. ascendens Brongn.和墨西哥落羽杉T. mucronatum Tenore.的条形叶为双面气孔型或单面气孔型。叶片远轴面气孔分布于中脉两侧,每侧各有4-8列气孔。叶片中部气孔数量稳定,顶部和基部气孔数量比中部略少。近轴面气孔在中脉两侧各有1-4行,有时仅少数几个气孔或没有气孔分布。非气孔分布区内,表皮细胞长方形,细胞壁直或稍微呈波状,细胞长轴与叶片长轴一致。气孔分布区内的表皮细胞有时为多边形。气孔器椭圆形,长轴与叶片长轴垂直或成一定的角度。保卫细胞壁加厚明显,极端联合形成极层结构。落羽杉属3种现生植物的气孔密度和气孔指数差异显著,不同采集地的落羽杉气孔密度和气孔指数差异不显著。这3种植物的气孔指数的变异系数均小于气孔密度的变异系数,用气孔指数指示大气CO2浓度比用气孔密度可靠。     

Exogenous glycine betaine and proline play a protective role in heat-stressed barley leaves (Hordeum vulgare L.): A chlorophyll a fluorescence study

Abstract

Effects of drought and exogenous glycine betaine and proline on Photosystem II (PSII) photochemistry were studied in barley leaves under heat stress induced by exposing them to 45°C for 10 min. Polyphasic fluorescence transient (OJIP) was used to evaluate PSII photochemistry in leaves treated with either glycine betaine or proline, combined or not with heat treatment. A distinct K step in the fluorescence transient OJIP appeared in control leaves, indicating an inactivation of the oxygen evolving complex (OEC). Drought stress and exogenous glycine betaine and proline modified the shape of the OJIP curve of leaves heated at 45°C and the K step was not as pronounced. Increased thermostability of PSII may be associated with the resistance of OEC and increased energy connectivity between PSII units. The thermostability of PSII was also reflected by a lower decrease in maximum quantum yield of primary photochemistry (?_Po = F _V/F _M) and performance index (PI). Exogenous application of glycine betaine or proline can play an important role in enhancing plant stress tolerance and may help reduce effects of environmental stresses.     

Physiological Responses of <i>Dendrobium officinale</i> under Exposure to Cold Stress with Two Cultivars

This study aimed to explore the cold tolerance of two cultivars of Dendrobium officinale (MG1, MG2) grown in different regions of China. Under -2°C incubation, cultivar MG1 remained active after 3 d, and continued to grow after returning to room temperature. However, MG2 could only maintain its activity after 2 d treatment at −2°C, and the seedlings died with the low temperature treatment time. Investigation of the characteristics of the plants grown in the south (Hangzhou) or north (Zhengzhou) of China indicated that the leaves of MG1 also had reduced stomatal density, the highest thickness, and a compact microstructure. The contents of proline and soluble sugars were higher in MG1 than those in MG2. The cultivar MG1 had higher SOD enzyme activity than MG2, while CAT and POD activities in samples from Zhengzhou were higher than those from Hangzhou. The contents of polysaccharides and alkaloids in stems of in MG1 were higher than those in MG2, while the content of flavonoids in the Zhengzhou samples was higher than that in the Hangzhou samples. In addition, plant heights, stem diameters, and chlorophyll content were higher in MG1. Overall, MG1 had better cold resistance than MG2. MG1 is a cold tolerant cultivar with thick leaves and reduced stomatal density, higher contents of soluble sugars, proline, CAT, POD, polysaccharides, flavonoids and alkaloids, which together make it more adaptable to low temperatures. Thus, the cultivar MG1, with its demonstrated cold tolerance, can accordingly be grown on a large scale in cold regions, thereby expanding the available planting area for this important traditional medicinal plant to meet the increasing commercial demand for it.     

褪黑素调节烟草丁香假单胞菌抗性的功能研究

为分析褪黑素(N-乙酰-5-甲氧基色胺)在植物先天免疫中的功能及调控机理,研究以病原菌丁香假单胞杆菌(Pseudomonas syringae pv.tomato DC3000,Pst DC3000)—烟草互作系统为模型,检测了病原菌侵染对烟草褪黑素相关基因表达的影响,并探讨了褪黑素对植物叶片病原菌生长以及气孔开度和活性氧自由基(reactive oxygen species,ROS)含量的影响以及调控机理。结果表明:(1)Pst DC3000处理提高了烟草褪黑素合成(NtSNAT1)和受体(NtPMTR1)基因表达,且外源褪黑素处理降低了叶片中的病原菌含量。(2)与野生型植物相比,过表达大豆GmSNAT1基因显著提高了转基因烟草中内源褪黑素含量和NtPMTR1的表达,且转基因烟草叶片中的Pst DC3000菌落数显著下降。(3)外源褪黑素和细菌鞭毛蛋白多肽flg22处理诱导了野生型和转基因烟草保卫细胞中ROS产生和气孔关闭,且转基因植物对褪黑素和flg22诱导的气孔关闭和ROS产生比野生型烟草更加敏感。综上所述,研究表明褪黑素可能通过受体NtPMTR1介导的信号途径促进保卫细胞ROS产生,诱导气孔关闭,从而降低病原菌Pst DC3000的入侵。     

Drought-induced proline accumulation is uninvolved with increased nitric oxide,which alleviates drought stress by decreasing transpiration in rice

Accumulation of proline is trusted to be an adaptive response of plants against drought stress, and exogenous application of nitric oxide (NO) enhances proline accumulation in Cu-treated algae. In order to investigate whether NO works as a necessary signaling molecule in drought-induced proline accumulation in rice leaves, effects of drought stress on endogenous NO content and proline accumulation were studied in rice leaves, using sodium nitroprusside (SNP, a NO donor) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a NO scavenger). The results showed that drought treatment increased both endogenous NO and proline contents in rice leaves, while foliar spray of various concentrations of SNP failed to induce proline accumulation in the leaves of well-watered rice and foliar spray of cPTIO failed to inhibit proline accumulation in the leaves of drought-stressed rice. These results indicate that increase of endogenous NO is dispensable for proline accumulation in the leaves of rice under drought stress. Further studies indicate that exogenous application of NO alleviates drought-induced water loss and ion leakage by decreasing transpiration rate of rice leaves.     

施钾与蚜虫取食诱导的水杨酸对马铃薯抗虫性的影响

【目的】探讨施钾条件下,蚜虫取食诱导的水杨酸在促进马铃薯Solanum tuberosum抗虫性方面的作用机制,为提高作物抗虫性提供科学依据。【方法】施钾(外施硫酸钾6 g/株)、虫害(桃蚜Myzus persicae取食, 5头成虫/株)、施钾+虫害及外源水杨酸(浓度分别为15, 30和45 μmol/L,喷施量20 mL/株)条件下,测定马铃薯叶片中水杨酸和脯氨酸含量、苯丙氨酸解氨酶(PAL)活性及抗氧化酶［过氧化物酶(POD)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)］活性。【结果】结果表明：与未处理对照相比,施钾、虫害、施钾+虫害处理后马铃薯叶片中内源水杨酸含量分别增加了1.1,1.3和1.5倍,PAL活性分别增加了23.3%, 22.3%和35.0%。在施钾、虫害、施钾+虫害3个处理中,施钾+虫害处理的马铃薯叶片中内源水杨酸含量和PAL活性均为最高。用不同浓度外源水杨酸喷施马铃薯叶片,不论是否施钾,用浓度为15 μmol/L水杨酸喷施马铃薯植株后,其SOD活性均显著高于对照组。施钾后除喷施30 μmol/L水杨酸溶液外,喷施15和45 μmol/L水杨酸溶液的马铃薯植株POD活性均显著高于各自对照,活性分别为各自对照的1.7和1.8倍。施钾组中CAT活性在15和30 μmol/L水杨酸喷施后均显著高于对照,分别为对照的1.3和1.5倍。喷施15 μmol/L水杨酸后,马铃薯叶片中脯氨酸含量(1.2 OD/g pro)较对照(0.4 OD/g pro)显著升高。【结论】虫害、施钾+虫害处理均能提高马铃薯叶片中水杨酸含量和PAL活性。15 μmol/L外源水杨酸显著提高了施钾组中POD, SOD和CAT活性及脯氨酸含量,说明15 μmol/L是所用最适水杨酸浓度,该浓度下水杨酸与施钾具有正交互作用。结果提示虫害与施钾共同作用能增强水杨酸信号途径,从而提高植物的抗虫性。