模拟酸雨对毛竹叶片抗氧化酶活性及释放绿叶挥发物的影响

为了探讨酸雨胁迫与毛竹(Phyllostachys pubescens)绿叶挥发物(green leaf volatiles, GLVs)释放规律以及抗氧化酶活性的关系, 通过盆栽试验, 采用不同pH值(5.6、4.0、2.5)的模拟酸雨对毛竹三年生实生苗进行处理, 研究酸雨对毛竹叶片可溶性蛋白质含量、丙二醛(MDA)含量和抗氧化酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对毛竹释放的GLVs成分和含量进行分析。结果表明: 酸雨胁迫下毛竹叶片MDA含量明显增加, pH 2.5模拟酸雨胁迫处理45天毛竹叶片MDA含量与对照相比增加了43.0% (p < 0.01); pH 4.0处理MDA含量增加缓慢, 处理75天时MDA含量比对照增加了0.36倍(p < 0.01)。pH 4.0和pH 2.5模拟酸雨胁迫处理45天时, 毛竹叶片可溶性蛋白质含量极显著增加, 与对照相比分别增加了32.0%和65.0% (p < 0.01)。在酸雨胁迫下, 毛竹叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的响应时间存在一定差异, 表现为互相协调, pH 2.5模拟酸雨胁迫处理SOD活性和POD活性分别在45天和60天时达到最大值, 分别为对照的1.67倍和1.31倍(p < 0.01), 随后降低。pH 4.0和pH 2.5模拟酸雨胁迫处理, 毛竹叶片GLVs含量比对照分别增加26.4%和132.9% (p < 0.01), 新增GLVs为 (E)-2-辛烯醛、2-乙基己醛、(E)-2-己烯醛和(E)-2-壬烯醛。研究表明: 酸雨胁迫条件下, 毛竹可以通过调节保护酶活性、可溶性蛋白质含量和释放GLVs来提高适应环境的能力。     

Effects of simulated acid rain on the activity of antioxidant enzyme and the emission of induced green leaf volatiles in Phyllostachys pubescens

为了探讨酸雨胁迫与毛竹(Phyllostachys pubescens)绿叶挥发物(green leaf volatiles, GLVs)释放规律以及抗氧化酶活性的关系, 通过盆栽试验, 采用不同pH值(5.6、4.0、2.5)的模拟酸雨对毛竹三年生实生苗进行处理, 研究酸雨对毛竹叶片可溶性蛋白质含量、丙二醛(MDA)含量和抗氧化酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对毛竹释放的GLVs成分和含量进行分析。结果表明: 酸雨胁迫下毛竹叶片MDA含量明显增加, pH 2.5模拟酸雨胁迫处理45天毛竹叶片MDA含量与对照相比增加了43.0% (p < 0.01); pH 4.0处理MDA含量增加缓慢, 处理75天时MDA含量比对照增加了0.36倍(p < 0.01)。pH 4.0和pH 2.5模拟酸雨胁迫处理45天时, 毛竹叶片可溶性蛋白质含量极显著增加, 与对照相比分别增加了32.0%和65.0% (p < 0.01)。在酸雨胁迫下, 毛竹叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的响应时间存在一定差异, 表现为互相协调, pH 2.5模拟酸雨胁迫处理SOD活性和POD活性分别在45天和60天时达到最大值, 分别为对照的1.67倍和1.31倍(p < 0.01), 随后降低。pH 4.0和pH 2.5模拟酸雨胁迫处理, 毛竹叶片GLVs含量比对照分别增加26.4%和132.9% (p < 0.01), 新增GLVs为 (E)-2-辛烯醛、2-乙基己醛、(E)-2-己烯醛和(E)-2-壬烯醛。研究表明: 酸雨胁迫条件下, 毛竹可以通过调节保护酶活性、可溶性蛋白质含量和释放GLVs来提高适应环境的能力。     

毛竹出笋后快速生长期内茎秆中光合色素和光合酶活性的变化

为了探讨毛竹(Phyllostachys pubescens)非同化器官茎秆的光合特性, 测定了毛竹出笋后快速生长期内(2011年4月13日到6月2日)的光合色素含量以及光合酶活性, 并通过激光共聚焦显微镜对其叶绿体分布进行了观察。结果表明: 毛竹茎秆中的叶绿体主要集中分布在表皮以下的基本组织中, 此外维管束鞘周围的细胞内也存在大量的叶绿体, 此特征类似于C₄植物的花环结构。在毛竹出笋后快速生长期内, 随着茎秆不断生长, 叶绿素a、叶绿素b和类胡萝卜素含量均极显著(p < 0.01)增加。在出笋10天时, 茎秆中核酮糖-1,5-二磷酸羧化酶/加氧酶(Rubisco)活性、磷酸烯醇式丙酮酸羧化酶(PEPC)活性和NADP-苹果酸酶(NADP-ME)活性最高, 之后随茎秆生长逐渐降低, 生长30天时酶活性与10天时相比分别降低了88.55% (p < 0.01)、77.46% (p < 0.01)和72.50% (p < 0.01), 而PEPC/Rubisco比值则随茎秆生长逐渐增加, 30天时比值达到12.83, 明显高于C₃植物。这表明毛竹茎秆内可能存在C₄光合途径, 此途径有利于毛竹提高光合效率, 进而促进其出笋后的快速生长。     

民勤绿洲—荒漠过渡带植物叶性状的研究

以民勤绿洲—荒漠过渡带20种主要植物为研究对象,通过对叶片6个功能性状的测定,分析荒漠植物叶性状的变异及相关性,比较不同功能群植物叶性状的差异性,探讨荒漠植物对环境的适应性,为该地区植被的恢复和重建提供理论依据。结果表明：①叶性状存在种间差异且变异程度不同,变异范围为14.11%~47.63%,叶绿素含量（ChlC）变异系数最大,叶片全氮含量（LCC）变异系数最小。②叶干物质含量（LDMC）与ChlC、LCC均呈极显著正相关（P＜0.01）,ChlC与LCC呈极显著正相关（P＜0.01）,其他叶性状间相关性不显著。③不同功能群植物叶性状存在显著差异。其中,豆科植物叶片LDMC、ChlC、LCC极显著高于藜科植物（P＜0.01）。草本植物叶片比叶面积（SLA）极显著高于灌木植物叶片（P＜0.01）。一年生植物叶片SLA、LNC显著高于多年生植物（P＜0.05）;多年生植物叶片LDMC极显著高于一年生植物（P＜0.01）;多年生植物叶片C含量显著高于一年生植物（P＜0.05）。C₃植物叶片LDMC、ChlC显著高于C₄植物（P＜0.05）;C₄植物叶片δ¹³C极显著高于C₃植物 （P＜0.01）;C₃植物叶片LCC极显著（P＜0.01）高于C₄植物。     

镉胁迫对平邑甜茶脂肪酸构成及脂质过氧化的影响

以平邑甜茶幼苗为试材,研究了镉胁迫下幼苗叶片和根系膜脂肪酸构成、活性氧、脂氧合酶和丙二醛含量的变化.结果表明：氯化镉处理后7～12 h,脂肪酸种类及其相对含量变化最为明显.处理后7 h,叶片和根系脂肪酸不饱和水平升至最高,含量分别达8282%和7243%;叶片可检测到的脂肪酸在处理后12 h由11种增至14种,根系则在处理17 h后由4种增至6种.O₂^.-产生速率在处理3 h、H₂O₂含量在处理7 h时升至最高,丙二醛含量和脂氧合酶活性则随着处理时间的延长逐渐增加.镉胁迫通过诱导活性氧和脂氧合酶来改变平邑甜茶脂肪酸构成,并引起脂质过氧化;镉处理12 h前,脂质过氧化是活性氧和脂氧合酶的共同结果;但处理12 h后,脂质过氧化加剧主要在于脂氧合酶活性的持续增加.     

苯丙氨酸解氨酶在诱导黄瓜幼苗抗寒性中的作用

为了探讨苯丙氨酸解氨酶(PAL)在诱导黄瓜幼苗抗寒性中的作用,采用喷施特异抑制剂(AOPP)的方法控制PAL活性,测定幼苗抗寒性的变化.结果表明： 低温可以诱导黄瓜幼苗叶片中PAL的基因表达和活性升高;喷施AOPP显著抑制了叶片中PAL活性,减少了酚类和类黄酮物质的积累.低温对黄瓜幼苗造成显著伤害,AOPP预处理加剧了低温对幼苗的损伤,幼苗抗寒性降低.与对照相比,幼苗叶片中相对电解质渗漏率和丙二醛(MDA)含量显著升高,PSII最大光化学效率(F_v/F_m)降低,光化学猝灭参数Y(NO)升高,胁迫相关基因(PR1-1a、COR47、P5CS、HSP70)的诱导表达受到抑制.低温导致黄瓜幼苗叶片中H₂O₂积累,还原型抗坏血酸(AsA)含量降低,脱氢抗坏血酸(DHA)含量升高,AsA∶DHA减小;喷施AOPP的幼苗中抗氧化酶(过氧化氢酶CAT、抗坏血酸过氧化物酶APX)活性显著低于对照,H₂O₂过量积累,AsA∶DHA更低.施用H₂O₂清除剂可以有效缓解喷施AOPP引起的低温损伤加剧,而施用CAT抑制剂的幼苗对低温胁迫更敏感.表明低温诱导了PAL活性升高,促进了苯丙烷类次生代谢产物的合成,提高了胞内抗氧化酶活性,可有效清除活性氧分子,维持AsA氧化还原状态,缓解低温引起的光损伤和氧化损伤.     

迷迭香对干旱胁迫的生理响应及其诱导挥发性有机化合物的释放

为探讨干旱胁迫对迷迭香(Rosmarinus officinalis)生理生化特性及挥发性有机化合物(VOC)释放规律的影响, 该文采用盆栽称重控水法研究了轻度(LD)、中度(MD)和重度(SD)干旱胁迫对迷迭香二年生实生苗叶片细胞膜透性、可溶性糖、可溶性蛋白质和丙二醛(MDA)含量以及脂氧合酶和抗氧化保护酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对不同干旱胁迫下迷迭香释放的挥发性有机化合物成分进行了分析。结果表明: 干旱胁迫对迷迭香叶片可溶性糖和可溶性蛋白质含量有明显的影响, MD和SD处理12天时其含量极显著地增加(p < 0.01), 与对照相比可溶性糖分别增加了51.5%和87.4%, 可溶性蛋白质含量分别增加了0.82和1.40倍。在MD和SD胁迫下, 超氧化物歧化酶、过氧化物酶和过氧化氢酶对干旱胁迫的响应存在一定差异, 表现为相互协调的作用。随着干旱胁迫时间的延长, 迷迭香体内MDA含量极显著地增加(p < 0.01), 细胞膜损伤率显著增加。分析显示, 迷迭香释放的VOC主要是萜烯类化合物, 占总量的46.0%以上; 随着干旱胁迫增强, 迷迭香释放的VOCs总量减少, 种类增多; LD、MD和SD胁迫处理萜烯类化合物相对含量与对照相比分别增加了14.4%、17.0%和23.7%; 干旱胁迫还明显诱导绿叶挥发物(green leaf volatiles)和醛类化合物的释放, 诱导产生了2-己烯醛、叶醇、山梨醛和癸醛4种新组分。研究表明: 干旱胁迫条件下, 迷迭香能够通过调节保护酶活性、渗透调节物质含量和释放VOCs来提高抗旱性。     

内蒙古荒漠草原植物叶片功能性状关系及其经济谱分析

气候变化和人为干扰导致草原荒漠化加剧, 引发了严重的环境问题。因此, 对荒漠草原植物与环境变化关系的研究愈加迫切, 分析比较荒漠草原不同功能型物种叶片经济谱具有重要意义。该研究通过测定内蒙古荒漠草原生态系统不同功能型植物叶片的光合及叶绿素荧光参数、比叶面积和叶片氮素含量, 验证了荒漠草原植物叶片经济谱的存在, 明确了各功能型植物叶片性状间的关系及其在叶片经济谱中的位置。荒漠草原不同功能型植物叶片性状差异明显, 草本植物的比叶面积(SLA)、单位质量叶氮含量(N_mass)分别是灌木的2.39倍和1.20倍; 一年生植物单位面积最大净光合速率(A_area)、SLA、光合氮利用效率(PNUE)分别是多年生植物的1.93倍、2.13倍和4.24倍; C₄植物的A_area、SLA、PNUE分别是C₃植物的2.25倍、1.73倍和3.61倍。除A_area与单位面积叶氮含量(N_area)、PSII的实际光化学效率(Φ_PSII)与SLA之间不存在显著相关关系外, 叶片性状间存在广泛的相关关系, 且均达到极显著水平。这验证了叶片经济谱在内蒙古荒漠草原植物中也同样存在。进一步分析表明, 一年生植物、草本植物、C₄植物叶片在叶片经济谱中位于靠近薄叶、光合能力强、寿命短的一端; 而多年生植物、灌木、C₃植物叶片靠近厚叶、光合能力弱、寿命长的一端。这说明荒漠草原中不同功能型植物可通过权衡其经济性状间的关系而采取不同的适应策略, 对于荒漠草原生态系统管理具有重要的理论指导意义。     

祁连山两种优势乔木叶片δ13C的海拔响应及其机理

以分布于祁连山北麓中段的两种优势乔木祁连圆柏(Sabina przewalskii)和青海云杉(Picea crassifolia)为研究对象, 分析了高山乔木叶片δ¹³C值对海拔(2 600-3 600 m)、土壤含水量和叶片含水量、叶片碳氮含量的响应及其机理。结果表明, 这两种乔木叶片δ¹³C值均随海拔升高呈增重趋势, 与海拔呈显著正相关关系(p < 0.000 1)。海拔2 600-3 600 m阳坡树种祁连圆柏叶片的δ¹³C值显著高于同海拔梯度阴坡树种青海云杉。祁连圆柏和青海云杉叶片的δ¹³C值均与年平均气温呈显著负相关关系(p < 0.000 1), 与年平均降水量呈显著正相关关系(p < 0.000 1)。祁连圆柏叶片δ¹³C值与土壤含水量(p < 0.000 1)、叶片含水量(p = 0.01)和叶片碳氮比(C/N) (p < 0.000 1)呈显著正相关关系, 与叶片全氮呈显著负相关关系(p < 0.000 1)。而青海云杉叶片δ¹³C值与土壤含水量、叶片全氮、叶片碳氮比和叶片含水量不相关。说明海拔变化引起的水热条件的改变, 尤其是温度变化对高山乔木叶片碳同位素分馏起主要作用, 但各个因子综合对高山植物叶片碳同位素分馏的作用机制可能比较复杂, 需进一步深入研究。     

CO2浓度升高和降水增加协同作用对玉米产量及生长发育的影响

关于[CO₂]升高和降水变化等多因子共同作用对植物的影响报道较少, 制约着人们对植物对全球气候变化响应的认识和预测。玉米(Zea mays)作为重要的C₄植物, 受[CO₂]和降水影响显著, 但鲜有[CO₂]升高和降水增加协同作用对其产量及生长发育影响的报道。该研究利用开顶式生长箱模拟[CO₂]升高(390 (环境)、450和550 μmol·mol^-1), 降水增加量设置为增加自然降水量的15% (以试验地锦州1981-2010年6至8月月平均降水量为基准), 从而形成6个处理: C₅₅₀W_+15%、C₅₅₀W₀、C₄₅₀W_+15%、C₄₅₀W₀、C₃₉₀W_+15%和C₃₉₀W₀。试验材料选用玉米品种‘丹玉39’。结果表明: [CO₂]升高和降水增加的协同作用在玉米的籽粒产量和生物产量上均达到了显著水平(p< 0.05), 二因子均起正作用, 使籽粒产量和生物产量均升高。籽粒产量在[CO₂] 390、450和550 μmol·mol^-1水平下的降水增加处理较自然降水处理分别增加15.94%、9.95%和9.45%, 而生物产量分别增加13.06%、8.13%和6.49%。因为籽粒产量的增幅略大于生物产量的增幅, 所以促进了经济系数的升高。穗部性状变化显著, 其中, 穗粒数、穗粒重、穗长和穗粗等性状值均随[CO₂]升高而升高, 且各[CO₂]水平下均表现为降水增加处理>自然降水处理, 而瘪粒数相反。但是, [CO₂]升高和降水增加的协同作用也促进了轴粗的升高, 对玉米产量的增加起着限制作用。二因子协同作用在净光合速率(P_n)和叶面积上达到了极显著水平(p< 0.01), 而在株高和干物质积累量上达到了显著水平(p< 0.05)。二因子协同作用使玉米叶片的P_n升高, 植株高度升高, 穗位高升高, 茎粗增加, 叶面积变大, 从而促进了干物质积累量的升高, 为玉米增产打下了良好的基础。这表明: 在未来[CO₂]升高条件下, 一定程度的降水增加对玉米的产量具有正向促进作用。     

Overexpression of hydroperoxide lyase,peroxygenase and epoxide hydrolase in tobacco for the biotechnological production of flavours and polymer precursors

Plants produce short‐chain aldehydes and hydroxy fatty acids, which are important industrial materials, through the lipoxygenase pathway. Based on the information that lipoxygenase activity is up‐regulated in tobacco leaves upon infection with tobacco mosaic virus (TMV), we introduced a melon hydroperoxide lyase (CmHPL) gene, a tomato peroxygenase (SlPXG) gene and a potato epoxide hydrolase (StEH) into tobacco leaves using a TMV‐based viral vector system to afford aldehyde and hydroxy fatty acid production. Ten days after infiltration, tobacco leaves infiltrated with CmHPL displayed high enzyme activities of 9‐LOX and 9‐HPL, which could efficiently transform linoleic acid into C₉ aldehydes. Protein extracts prepared from 1 g of CmHPL‐infiltrated tobacco leaves (fresh weight) in combination with protein extracts prepared from 1 g of control vector‐infiltrated tobacco leaves (as an additional 9‐LOX source) produced 758 ± 75 μg total C₉ aldehydes in 30 min. The yield of C₉ aldehydes from linoleic acid was 60%. Besides, leaves infiltrated with SlPXG and StEH showed considerable enzyme activities of 9‐LOX/PXG and 9‐LOX/EH, respectively, enabling the production of 9,12,13‐trihydroxy‐10(E)‐octadecenoic acid from linoleic acid. Protein extracts prepared from 1 g of SlPXG‐infiltrated tobacco leaves (fresh weight) in combination with protein extracts prepared from 1 g of StEH‐infiltrated tobacco leaves produced 1738 ± 27 μg total 9,12,13‐trihydroxy‐10(E)‐octadecenoic acid isomers in 30 min. The yield of trihydroxyoctadecenoic acids from linoleic acid was 58%. C₉ aldehydes and trihydroxy fatty acids could likely be produced on a larger scale using this expression system with many advantages including easy handling, time‐saving and low production cost.     

Light/dark modulation of phosphoenolpyruvate carboxylase in C3 and C4 species

In this report, the effects of light on the activity and allosteric properties of phosphoenolpyruvate (PEP) carboxylase were examined in newly matured leaves of several C₃ and C₄ species. Illumination of previously darkened leaves increased the enzyme activity 1.1 to 1.3 fold in C₃ species and 1.4 to 2.3 fold in C₄ species, when assayed under suboptimal conditions (pH 7) without allosteric effectors. The sensitivities of PEP carboxylase to the allosteric effectors malate and glucose-6-phosphate were markedly different between C₃ and C₄ species. In the presence of 5 mM malate, the activity of the enzyme extracted from illuminated leaves was 3 to 10 fold higher than that from darkened leaves in C₄ species due to reduced malate inhibition of the enzyme from illuminated leaves, whereas it increased only slightly in C₃ species. The Ki(malate) for the enzyme increased about 3 fold by illumination in C₄ species, but increased only slightly in C₃ species. Also, the addition of the positive effector glucose-6-phosphate provided much greater protection against malate inhibition of the enzyme from C₄ species than C₃ species. Feeding nitrate to excised leaves of nitrogen deficient plants enhanced the degree of light activation of PEP carboxylase in the C₄ species maize, but had little or no effect in the C₃ species wheat. These results suggest that post-translational modification by light affects the activity and allosteric properties of PEP carboxylase to a much greater extend in C₄ than in C₃ species.     

高大气CO2浓度下氮素对小麦叶片光能利用的影响

关于氮素对高大气CO₂浓度下C₃植物光合作用适应现象的调节机理已有较为深入的研究, 但对其光合作用适应现象的光合能量转化和分配机制缺乏系统分析。该文以大气CO₂浓度和施氮量为处理手段, 通过测定小麦(Triticum aestivum)抽穗期叶片的光合作用-胞间CO₂浓度响应曲线以及荧光动力学参数来测算光合电子传递速率和分配去向, 研究了长期高大气CO₂浓度下小麦叶片光合电子传递和分配对施氮量的响应。结果表明, 与正常大气CO₂浓度处理相比, 高大气CO₂浓度下小麦叶片较多的激发能以热量的形式耗散, 增施氮素可使更多的激发能向光化学反应方向的分配, 降低光合能量的热耗散速率; 大气CO₂浓度升高后小麦叶片光化学淬灭系数无明显变化, 高氮叶片的非光化学猝灭降低而低氮叶片明显升高, 施氮促进PSII反应中心的开放比例, 降低光能的热耗散; 高大气CO₂浓度下高氮叶片通过PSII反应中心的光合电子传递速率(J_F)较高, 而且参与光呼吸的非环式电子流速率(J₀)显著降低, 较正常大气CO₂浓度处理的高氮叶片下降了88.40%, 光合速率增加46.47%; 高大气CO₂浓度下小麦叶片J_F-J₀升高而J₀/J_F显著下降, 光呼吸耗能被抑制, 更多的光合电子分配至光合还原过程。因此, 大气CO₂浓度增高条件下, 小麦叶片激发能的热耗散速率增加, 但增施氮素后小麦叶片PSII反应中心开放比例提高, 光化学速率增加, 进入PSII反应中心的电子流速率明显升高, 光呼吸作用被抑制, 光合电子较多地进入光化学过程, 这可能是高氮条件下光合作用适应性下调被缓解的一个原因。     

Upregulation of bundle sheath electron transport capacity under limiting light in C4 Setaria viridis

C₄ photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO₂ concentration at the site of CO₂ fixation. C₄ plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity. Plants grown under low light (LL) maintained CO₂ assimilation rates similar to high light plants but had an increased chlorophyll and light-harvesting-protein content, predominantly in BS cells. Photosystem II (PSII) protein abundance, oxygen-evolving activity and the PSII/PSI ratio were enhanced in LL BS cells, indicating a higher capacity for linear electron flow. Abundances of PSI, ATP synthase, Cytochrome b₆f and the chloroplast NAD(P)H dehydrogenase complex, which constitute the BS cyclic electron flow machinery, were also increased in LL plants. A decline in PEP carboxylase activity in mesophyll cells and a consequent shortage of reducing power in BS chloroplasts were associated with a more oxidised plastoquinone pool in LL plants and the formation of PSII – light-harvesting complex II supercomplexes with an increased oxygen evolution rate. Our results suggest that the supramolecular composition of PSII in BS cells is adjusted according to the redox state of the plastoquinone pool. This discovery contributes to the understanding of the acclimation of PSII activity in C₄ plants and will support the development of strategies for crop improvement, including the engineering of C₄ photosynthesis into C₃ plants.     

Stimulation effect of carrageenan on enzymatic defense system of sweet basil against Cuscuta campestris infection

Sweet basil is an important medicinal plant used especially for therapeutical potentials. Sweet basil is a common host for Cuscuta campestris, which has a negative effect on infected plants. Therefore, natural friendly control of C. campestris seems to be useful. It has been shown that carrageenans can act as elicitors of plant defense responses. In this work, the effect of κ-carrageenans on protection against C. campestris and suppression of its invasion in basils were studied. Basils were sprayed with a solution of κ-carrageenan (1?g?L^?1), once a week, three times in total. Infection of basils with C. campestris was performed two days after the last carrageenan treatment. C. campestris stem and the leaves of basils were collected two weeks after C. campestris inoculation for biochemical studies. Treatment with carrageenan significantly increased shoot length and leaf area of basil and decreased C. campestris infestation by about 26%. The content of malondialdehyde, other aldehydes, hydrogen peroxide and lipoxygenase (LOX) activity increased significantly in basils parasitized by C. campestris. There were significant differences in phenylalanine ammonia lyase (PAL), catalase (CAT), superoxide dismutase (SOD) and peroxidase activity of parasitized basils by C. campestris compared with healthy basils. Carrageenan treatment of basils caused a significant increase in H₂O₂ content and the activity of PAL, CAT and SOD, but not of malondialdehyde, other aldehydes content and LOX, polyphenol oxidase (PPO) and peroxidases activity. The activated enzymatic defense system (PAL, PPO, CAT, SOD and peroxidase) in carrageenan-treated basils have a vital role in alleviating oxidative stress damage in infected plants, by removing excess reactive oxygen species and inhibiting LOX activity and lipid peroxidation that was observed in this study. Our results showed that the application of κ-carrageenan-induced beneficial effects in plants, with regard to growth stimulation and the activation of enzymatic defense system. Thus, carrageenan was recommended as a natural biostimulator for protection of plants against C. campestris.     

Expression of soybean-embryo lipoxygenase 2 in transgenic tobacco tissue

To assess the role of lipoxygenase (LOX; EC 1.13.11.12) in plants, we increased the expression of LOX in the tissues of Nicotiana tabacum L. cv. KY 14 by over-expression of the LOX2 gene from the soybean (Glycine max (L.) Merrill) embryo. The LOX2 cDNA was manipulated by replacing its 5-untranslated sequence with the translational enhancer of the alfalfa mosaic virus (AMV), and subcloned into a plant expression vector, 3 to a duplicated cauliflower mosaic virus 35S promoter. The AMV-LOX2 construct was transferred into tobacco using Agrobacterium tumefaciens strain A281. The LOX2 was expressed in transgenic tobacco calli, leaves of transgenic plants, and their seed progeny at levels up to 0.1–0.2% of the total extracted protein. The introduced LOX2 affected fatty-acid oxidative metabolism as evidenced by a 50–529% increase in C₆-aldehyde production. The impact on C₆-aldehyde formation was greater than the effect on production of fatty-acid hydroperoxides. This is consistent with other studies indicating the greater propensity of soybean embryo LOX2 in generating C₆-aldehydes than that of other well-characterized LOX isozymes.Abbreviations AMV alfalfa mosaic virus - CaMV cauliflower mosaic virus - IEF isoelectric focusing - kDa kilodalton - LOX lipoxygenase - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis We thank Bernard Axelrod (Purdue University) for supplying the lipoxygenase 2 cDNA, and Arthur G. Hunt (University of Kentucky) for supplying the pKYLX71² and pBS/AMV. The advice of Arthur G. Hunt, Chris L. Schardl, Sadik Tuzun and Dwight Tomes is greatly appreciated, as is the technical assistance of Udaya Chand and Robert Versluys.     

In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate-deficient sunflower and maize leaves

The effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi-deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φ_e), the in vivo quantum yield of PSII photochemistry (φ_PSII) and the photochemical quenching co-efficient (q_P), and increased the non-photochemical quenching co-efficient (q_N) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi-deficient sunflower leaves reversed the long-term effects of Pi-deficiency on PSII photochemistry. Feeding Pi-sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long-term Pi-deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long-and short-term responses of photosynthetic machinery to Pi deficiency. The relationship between φ_PSII and the apparent quantum yield of CO₂ assimilation determined at varying light intensity and 21 kPa O₂ and 35 Pa CO₂ partial pressures in the ambient air was linear in Pi-sufficient and Pi-deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO₂ assimilated by the Pi-deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO₂ reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi-deficient leaves of sunflower and maize and that the decreased CO₂ assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1-5, bisphosphate, the acceptor for CO₂.     

Energization and activation of inorganic carbon uptake by light in cyanobacteria

The requirement of the inorganic carbon (C_i) transport system for light in cyanobacteria was investigated in Anabaena variabilis by the filtering centrifugation technique and in a mutant (E₁) isolated from Anacystis nidulans using a gas exchange system. C_i transport capability increased with time of preillumination and decreased following darkening. Full activity could not be obtained by operating either photosystem II (PSII) or photosystem I alone. 3(3,4 Dichlorophenyl)-1,1 dimethylurea strongly inhibited C_i uptake. Very low activity of PSII was sufficient to activate C_i uptake. However, in the presence of dithiothreitol PSII activity was not required. We conclude that light may be required to activate as well as to energize C_i uptake in cyanobacteria.     

Electroantennogram responses of the oriental fruit fly, Dacus dorsalis, to a spectrum of alcohol and aldehyde plant volatiles

Electroantennograms (EAGs) were recorded from unmated, laboratory-reared, male and female oriental fruit flies, Dacus dorsalis, in response to a range of between C₁ and C₁₂ carbon chain-length saturated and unaturated aliphatic alcohols and aldehydes, most all of which are known host-plant volatiles. Only two of the 35 compounds tested elicited significantly larger EAGs from female than male antennae. For the two functional-group series tested, aldehydes elicited responses greater than or equal to the responses to the alcohols. In general, the unsaturated alcohols did not elicit responses significantly different from the saturated alcohols. However, the unsaturated aldehydes, (E)-2-hexenal and 10-undecenal, elicited larger amplitude EAGs than their saturated analogs. EAGs were significantly greater for a particular carbon chain-length, with responsiveness to primary alcohols peaking at C₆ and aldehydes peaking at C₇. The (E)-2- monoenic alcohols peaked at C₆, while the (E)-3-alcohols plateaued between C₅ and C₈. The greatest EAG responses of all compounds tested were elicited by the saturated and unsaturated C₆ alcohols and aldehydes which are constitutents of the general green-leaf volatile complex that emanates from most plants. The potential adapative benefit of selective sensitivity to green-leaf volatiles is discussed in regards to foraging behaviors of oriental fruit flies.

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Résumé Des électroantennogrammes (EAG) ont enregistré les réponses, en élevages de femelles et mâles vierges de Dacus dorsalis, à une gamme de chaînes de carbones de C₁ à C₁₂ saturés et non-saturés d'alcools aliphatiques et d'aldéhydes, dont beaucoup sont connus comme substances volatiles des végétaux. Seulement 2 des 35 composés examinés ont provoqué des EAG significativement plus importants chez les femelles que chez les mâles. Pour les séries des deux groupes fonctionnels examinés, les aldéhydes ont provoqué des réponses supérieures ou égales aux alcools. En général, les réponses aux alcools nonsaturés n'étaient pas significativement différentes des réponses aux alcools saturés. Cependant, les aldéhydes non-saturés, (E)-2-hexénal et 10-undécénal, ont induit des EAG de plus grande ampleur que leurs analogues saturés. Les EAG étaient significativement les plus importants pour une chaîne de longueur particulière, la réponse aux alcools primaires culminant en C₆ et les aldéhydes en C₇. Les alcools monoéniques (E)-2- culminaient en C₆, tandis que les alcools (E)-3- étaient étales entre C₅ et C₈. Les EAG les plus importants ont été obtenus pour tous les composés examinés avec les alcools et aldéhydes en C₆ qui appartiennent à l'odeur verte complexe émise par beaucoup de plantes. Le bénéfice adaptatif potentiel de la sensibilité sélective à l'odeur verte des feuilles est examinée en fonction du comportement de prospection de D. dorsalis.