机械损伤对拟南芥莲座叶芥子油苷含量和组成的影响

植物可以利用体内次生代谢产物的变化来抵御昆虫取食和机械损伤.芥子油苷是拟南芥的主要次生代谢产物.通过剪刀剪取叶片(40%面积)对温室培养的拟南芥幼苗莲座叶进行机械损伤处理,观察机械损伤后8个时间点拟南芥叶片中不同种类芥子油苷含量和组合模式的变化.结果表明机械损伤后3 h叶片中芥子油苷总含量开始明显上升,脂肪族和吲哚族芥子油苷含量在损伤后3 h也都显著高于损伤前.在检测到的12种芥子油苷中,4-甲基亚磺酰丁基芥子油苷(4-methylsulphinylbutyl GS,4MSOB)的含量最多,占芥子油苷总量的48.5%,并且在损伤3 h后含量增加.4MSOB含量的变化成为影响莲座叶中芥子油苷组合模式的主导因素.其它各种芥子油苷在损伤后不同时间点的变化也存在差异.     

寄主植物物理性状及营养物质对地红蝽寄主选择性的影响

【目的】地红蝽Pyrrhocoris tibialis是一种重要的农业植食性害虫,寄主范围广泛。本研究测定地红蝽对不同植物的取食偏好及分析寄主植物物理性状和营养物质在地红蝽成虫寄主选择行为中的作用,以期从寄主理化性状的角度来探讨地红蝽寄主选择行为机制,为指导作物抗虫育种提供依据。【方法】通过自由选择方法研究地红蝽成虫对5种寄主植物(谷子Setaria italica、高粱Sorghum bicolor、绿豆Vigna radiata、大豆Glycine max和玉米Zea mays)叶片的取食选择性;使用Y型嗅觉仪进一步检测地红蝽对5种植物叶片气味的趋性反应;测定分析5种植物叶片物理性状及主要营养物质含量与地红蝽取食选择性的相关性。【结果】地红蝽成虫对5种寄主植物叶片的取食选择率存在显著性差异,依次为谷子＞高粱＞绿豆＝大豆＞玉米,与对这5种寄主植物叶片气味的趋性反应百分率结果一致。相关性分析表明,地红蝽成虫的取食选择性与叶片长宽比、含水量和背面茸毛密度呈显著正相关,相关系数分别为0.881, 0.884和0.906,而与地红蝽成虫取食前后寄主植物叶片可溶性糖含量变化和总蛋白质含量变化呈显著负相关,相关系数分别为-0.915和-0.951。通径分析表明,寄主植物叶片背面茸毛密度和总蛋白质含量变化是地红蝽寄主选择性的重要决定因素。【结论】地红蝽成虫对不同寄主植物存在取食选择和趋向性差异,地红蝽成虫取食选择与寄主植物叶片长宽比、背面茸毛密度、含水量以及可溶性糖和总蛋白质含量变化有关。     

不同损伤形式诱导合作杨叶片中酚类物质含量的差异

采用机械损伤、舞毒蛾(Lymantria dispar)幼虫取食、机械损伤伤口涂抹舞毒蛾口腔分泌物3种方法处理合作杨(Populus simonii×P.pyramidalis 'Opera 8277')扦插苗叶片,24 h后用高效液相色谱(HPLC)检测叶片中香豆酸等9种酚类物质的含量,比较不同损伤形式诱导的酚类物质含量的变化差异,以探讨酚类物质含量变化的原因.结果表明,机械损伤和舞毒蛾取食诱导的酚类物质含量变化存在显著差异,而机械损伤伤口涂抹舞毒蛾口腔分泌物与舞毒蛾取食处理诱导的酚类物质含量变化相似,推测舞毒蛾口腔分泌物是造成机械损伤与昆虫取食处理间酚类物质含量变化差异的关键因素.     

斜纹夜蛾幼虫诱导的油菜抗虫性及其与茉莉酸信号途径的关系

植物在受植食性昆虫为害时能产生防御反应,并且植物的茉莉酸信号转导途径在这一过程中发挥着重要作用。然而, 迄今为止对于油菜Brassica campestris的诱导防御反应很少有研究报道。为此, 本实验通过测定油菜内茉莉酸和胰蛋白酶抑制剂含量研究了油菜在斜纹夜蛾Spodoptera litura幼虫为害后的抗虫性和胰蛋白酶抑制剂含量的变化,并分析这些变化在油菜诱导抗虫性与茉莉酸信号转导途径中的关系。结果表明：斜纹夜蛾幼虫取食能导致油菜体内茉莉酸和胰蛋白酶抑制剂含量系统性上升,外用茉莉酸甲酯处理也能系统性增加油菜的胰蛋白酶抑制剂含量,并且取食茉莉酸甲酯处理或斜纹夜蛾幼虫取食过的叶片能显著降低斜纹夜蛾幼虫的体重,两者的体重分别为对照植株上的67.5%和60.2%。机械损伤加斜纹夜蛾幼虫口腔分泌物处理能引起处理叶中茉莉酸和胰蛋白酶抑制剂含量的增加,但其诱导效果与机械损伤加水没有显著差异,并且两者明显低于虫害的诱导效果,两种处理的茉莉酸和胰蛋白酶抑制剂含量分别为虫害诱导的68.4%和24.4%及62.9%和36.9%;多次连续机械损伤的诱导效果与一次损伤的没有明显差异。结果说明斜纹夜蛾幼虫诱导的油菜抗虫性与茉莉酸信号转导途径有关,而其激活油菜抗虫反应的机理则可能与其特定的取食行为相关。     

蒙古沙冬青对灰斑古毒蛾重复取食响应的代谢组学分析

植物对同种昆虫重复取食做出更有效的响应是植物适应自然界虫害周期性爆发的重要策略。为了研究蒙古沙冬青对其主要害虫灰斑古毒蛾幼虫重复取食响应的代谢基础,本实验采用基于核磁共振（NMR）的代谢组学技术,分析了遭受同一年不同代灰斑古毒蛾幼虫取食的蒙古沙冬青叶片和对照组幼苗叶片的代谢差异。结果表明,仅遭受第一代幼虫取食叶片在第二代幼虫期与对照之间代谢物存在较小差异,而仅遭受第二代幼虫取食叶片与遭受两代幼虫取食叶片代谢差异显著,仅遭受第一代与仅遭受第二代幼虫取食的植株相邻分枝叶片差异显著。另外,只有仅遭受第二代幼虫取食组幼苗表现出处理叶片与相邻分枝叶片的显著代谢差异,并且这种代谢差异为总体代谢的变化,而并未表现为特定代谢物含量变化。由此可见,蒙古沙冬青能在代谢水平以很小的代谢变化来保存昆虫取食信息,在遭受同种昆虫取食后,代谢差异被放大,而且这种信息保存在遭受取食叶片中表现更明显。     

青藏高原高寒草甸门源草原毛虫取食偏好及其与植物C、N含量的关系

草食性昆虫对不同植物物种的取食存在偏好,这种取食偏好可能受其自身对蛋白质和碳水化合物的需求及二者平衡的调节。以青藏高原高寒矮嵩草草甸31种常见植物及门源草原毛虫为对象,通过饲喂实验,研究了草食性昆虫对不同物种和不同功能群植物的取食偏好,及其与植物叶片C、N含量和C∶N之间的关系。在31种植物中,门源草原毛虫对19种植物进行了取食,尤其对矮嵩草、红棕薹草、藏异燕麦和垂穗披碱草四种植物表现出强烈的取食偏好,而对另外12种植物未进行任何取食。在物种水平上,门源草原毛虫取食量与植物叶片N含量呈显著负相关,与叶片C∶N呈正相关。从功能群水平上看,门源草原毛虫对莎草类的取食偏好最大,而对豆科植物取食偏好最低;相应地,莎草类植物叶片N含量最低、C∶N最高,而豆科植物叶片N含量最高、C∶N最低。因此,即使在土壤有效氮匮乏、植物生长受氮素限制的高寒草甸生态系统,植物体内N含量的增加也可能不利于草食性昆虫的取食。门源草原毛虫对优势植物矮嵩草和垂穗披碱草的取食对高寒矮嵩草草甸物种共存和生物多样性维持可能具有重要的作用。     

广聚萤叶甲取食对豚草挥发物组分的影响

植物在遭受植食性昆虫为害后,会系统性地释放虫害诱导挥发物(HIPVs).为探明广聚萤叶甲取食对豚草挥发物组分的影响,本研究采用动态顶空吸附法和气相色谱-质谱联用仪(GC-MS),收集并分析了豚草在受机械损伤和受广聚萤叶甲取食损伤前后挥发物组分及相对含量的变化.结果表明,豚草健康植株与损伤植株的挥发物组分和相对含量具有明显的差异.与健康植株相比,受机械损伤后的豚草挥发物中新出现了乙酸芳樟酯、桉树醇、十二醛、γ-木罗烯、植物醇、β-波旁烯,这些化合物在受损后立即释放,表明它们是组成型豚草挥发性有机化合物(VOCs);受取食损伤后,挥发物中大根香叶烯D的相对含量显著增加,表明大根香叶烯D为诱发型VOCs;而较于健康植株和机械损伤植株,取食损伤后的豚草VOCs中增加了桧烯、辛醛、β-罗勒烯、香茅醇,表明这些化合物为HIPVs.此外,机械损伤与取食损伤对豚草VOCs组分的影响有所不同.受机械损伤后,挥发物的种类减少后(损伤后第3天)很快又恢复到健康水平,而受取食损伤后,VOCs的种类逐渐减少(损伤后3d内).受损后不同时期挥发物的种类和相对含量亦有显著差异.受损后的早期(1 d),释放的多为一些豚草绿叶性物质,而在后期有一些诱导物释放.本研究结果为利用豚草VOCs和HIPVs组分提高广聚萤叶甲对豚草的防控效果奠定了重要基础.     

西花蓟马取食与机械损伤对菜豆叶片抗氧化系统的影响

本文研究了西花蓟马Frankliniella occidentalis(Pergande)取食和机械损伤诱导对菜豆抗氧化系统的影响,比较了不同损伤形式诱导的抗氧化酶活力和抗氧化物质含量的变化差异。结果表明,西花蓟马取食和机械损伤均可诱导菜豆叶片内过氧化物酶(POD)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)3种抗氧化酶活性有不同程度的升高,但两种处理诱导的抗氧化酶活性变化规律不完全相同,各种酶活性达到最高点时间不同,西花蓟马取食对抗氧化酶活力的诱导作用大于机械损伤的。两种处理诱导下的类胡萝卜素的含量变化不大,但不论西花蓟马取食还是机械损伤均导致菜豆叶片内类黄酮和总酚含量整体呈下降趋势,西花蓟马的取食诱导的下降幅度大于机械损伤的。因此,西花蓟马取食诱导明显高于机械损伤对菜豆抗氧化系统的影响。     

小麦叶片胞间洗脱液的蛋白质组学检测分析

植物叶片胞间液蛋白主要是一些低丰度蛋白,其中某些种类在植物抗病反应中起着重要的作用.通过改进已有的技术方法,结合超滤和丙酮沉淀处理,从500 9抗条锈病近等基因系小麦Taichung29*6/Yr5的叶片中获得了1.5mg可溶性的胞间洗脱液蛋白.SDS-PAGE电泳分析显示,胞间洗脱液蛋白样品和总蛋白样品存在着明显的差异.进一步的双向电泳分析证实,两个样品在胶图上可分别检测到1 241±59(n ＝3)和1 849±138(n ＝3)个蛋白点,其中胞间洗脱液样品有1 042±47(n ＝3)个不同于总蛋白样品的蛋白点,与总蛋白样品共有的蛋白点仅198±13(n ＝3)个.随意取100个差异蛋白点进行MALDI-TOF质谱分析,鉴定到一些已被确证存在于小麦胞间液中的蛋白质,如β-1,3-萄聚糖酶、葡聚糖-β-D-1,3-葡萄糖苷内切酶、几丁质酶、过氧化物酶等.从蛋白质组学角度初步分析了小麦叶片胞间洗脱液的组成,为进一步探索小麦叶片胞间液中低丰度蛋白的抗病功能提供依据.     

普通丝瓜叶片成分和物理结构对黄足黑守瓜取食和定位的影响

黄足黑守瓜是普通丝瓜生长过程中危害叶片的主要害虫.本文对普通丝瓜不同部位叶片挥发性成分、营养成分和物理结构对黄足黑守瓜取食和定位的影响进行了系统研究.本实验采用顶空固相微萃取-气相色谱-质谱法分析了普通丝瓜不同部位叶片挥发性成分,研究结果表明,嫩叶主要挥发性成分有(Z)-3-己烯-1-醇(27.65%)和植醇(45.77%),成熟叶挥发性成分主要有(Z)-3-己烯-1-醇(49.34%),老叶挥发性成分主要有植醇(63.25%),且挥发性成分对黄足黑守瓜远距离定位起到了引导作用.同时,本研究还采用5点取样法、3,5-二硝基水杨酸法和考马斯亮蓝法分别研究了普通丝瓜不同部位叶片营养成分含量与黄足黑守瓜取食之间的关系,实验结果表明,黄足黑守瓜喜食植物叶片嫩叶部位,喜食部位叶片的总糖与还原糖含量、蛋白质含量都最高,且总糖含量与蛋白质含量比值最高.叶片物理结构调查采用石蜡切片法,发现叶片的物理结构对于黄足黑守瓜取食很少造成影响.通过研究,使我们充分地了解影响黄足黑守瓜取食不同部位叶片的因素,便于今后的育种和栽培过程中加强不利于黄足黑守瓜取食的因素,以达到安全、环保地进行农业生产的目的.     

Differential responses of Brassica napus and Petunia hybrida to leaf protoplast isolation stress

Changes in the response to abiotic stress during the isolation of leaf protoplasts were compared between a recalcitrant species of Brassica napus and regenerating species of Petunia hybrida . Initially, levels of soluble free putrescine (put), spermidine (spd) and spermine (spm) in leaves and protoplasts were determined. The sum of these three polyamines increased in petunia and B. napus leaf protoplasts by 1.6-fold and 1.1-fold, respectively. The soluble free fraction of spd and spm decreased in B. napus but not in petunia protoplasts. During the isolation of leaf protoplasts from B. napus , the ratio of soluble free put to the total PAs almost doubled, but that of spd and spm declined significantly. Petunia leaf protoplasts treated with cyclohexylamine (CHA), an inhibitor of spermidine synthase, accumulated ammonia and soluble putrescine, but lost the soluble spermidine. The soluble polyamine levels of CHA-treated petunia leaf protoplasts corresponded with those in B. napus . Leaves were subjected to abiotic stress during the isolation of protoplasts, namely wounding and osmotic stress which changed soluble free polyamine levels in B. napus and petunia, respectively. Both B. napus and petunia leaf protoplasts showed an increase in ammonia, but total free amino acid content and activation of proteases were only enhanced in B. napus leaf protoplasts. These results suggest that in B. napus wounding initiated senescence of leaf protoplasts during their isolation, leading to a constant production of ethylene early in the culture.     

Analysis of the native forms of the 90 kDa heat shock protein (hsp90) in plant cytosolic extracts

A polyclonal antibody, R2, was raised against a fusion protein consisting of a portion of plant hsp90 fused to the trpE protein of Escherichia coli. This antibody was found to be specific towards plant hsp90, showing little or no cross-reactivity with mouse and human hsp90 proteins. The R2 antibody identified an 83 kDa protein as the hsp90 homologue in cytosolic extracts of several dicot and monocot plants. Two-dimensional gel electrophoresis indicated that at least two different isoforms of hsp90 are expressed in Brassica napus seedlings. An examination of the native state of hsp90 by non-denaturing gel electrophoresis showed that this protein exists as a monomer, dimer and as a high-molecular-mass complex of ca. 680 kDa in cell extracts of spinach cotyledons and leaves, B. napus seedlings and wheat germ. Native gel analysis and cross-linking studies of purified hsp90 showed that plant hsp90 exists predominantly as a monomer. When 35S-labelled B. napus cytosolic extracts were immunoprecipitated with the R2 antiserum, hsp90 and two additional proteins with approximate molecular masses of 49 and 45 kDa were detected in the immunoprecipitates. These results are consistent with the idea that hsp90:protein heterocomplexes exist in plant cells.     

Two-Dimensional Electrophoretic Analysis of Salicylic Acid-Induced Changes in Polypeptide Pattern of Barley Leaves

The salicylic acid-induced changes in the polypeptide patterns of barley (Hordeum vulgare L.) leaves have been analysed using two-dimensional gel electrophoresis. An optimized 2-D PAGE protocol was used and gave reproducible 2-D gels from leaf crude protein extracts with a high number of detected polypeptides. When applied for 24 h SA affected the expression of a number of soluble proteins. Most of them appeared to be down-regulated. Although no abundant expression of specific proteins was observed, we detected three polypeptides that were present only in SA-treated leaves.     

Interspecific competition affects growth and herbivore damage of Brassica napus in the field

Resource competition can influence plant fitness either directly, or indirectly by influencing the amount of herbivore damage received by plants in the field. We previously found that competition could constrain the constitutive and woundinduced expression of defensive trypsin inhibitors in pot-grown Brassica napus seedlings in the greenhouse, suggesting that the ability of a plant to chemically defend itself could be constrained by competition in the field. Guided by these results, we investigated whether competition would affect growth and the presence of herbivores and herbivore damage on B. napus plants in the field. We established sixteen 1 m 2 plots in the field in a 7 x7 mgrid. Nine two-week-old B. napus seedlings were transplanted from the greenhouse into each 1 m 2 plot. Half of the plots were kept weed-free and half were left to develop interspecific weed competi-tors.After six weeks, three randomly chosen plants in each plot were measured for height, number of leaves, leaf area removed by herbivores, and the presence of aphids, leaf miners, and eggs of ladybird beetles. Consistent with the induction of the shade-avoidance response, plants in plots with weed competitors were significantly taller and had half as many leaves as plants in weed-free plots. Competing plants also had 60% more leaf arearemoved by herbivores, an 80% higher proportion of leaves with aphids, and an equal proportion of leaves with leaf miners. In this study, weed competition had dramatic effects on growth, leaf area removal by herbivores, and the presence of aphids on B. napus plants in the field. Together with our demonstration that competition can constrain the expression of trypsin inhibitor activity, these results suggest that resource competition may limit theability of a plant to defend itself from natural enemies, leading to greater herbivory. In turn, increased herbivory on competing plants could exacerbate the direct effects of competition on plant fitness.     

洱海三种生活型水生植物叶片中碳、氮与总酚含量的比较研究

植物体内的C、N和总酚是影响其被牧食和凋落物降解的重要因素,从而影响C和N在食物链的传递和生物地化循环。本研究测定了云南洱海3种生活型（挺水、沉水和浮叶）26种水生植物叶片中C、N和总酚含量以及C/N比率,并分析了它们与总酚的关系。结果表明:挺水植物叶片的C、N和总酚平均含量为448.08、39.30和24.70 mg/g,浮叶植物叶片的C、N和总酚平均含量为433.32、35.16和28.05 mg/g,沉水植物叶片的C、N和总酚平均含量为378.36、27.31和10.28 mg/g;总体上看,植物叶片C和N含量:挺水植物 浮叶植物 沉水植物;挺水和浮叶植物叶片的总酚含量差异不显著,且均远高于沉水植物叶片的总酚含量;26种植物叶片中C和N与总酚含量均呈显著正相关。在富营养化条件下,3种生活型植物所处生境的光照和CO2供给均差异显著,会对这些植物叶片的C、N和总酚含量有一定影响,此外由于应对生境中的胁迫（草食性昆虫、病原体及紫外线辐射等）压力以及自身的生长策略的不同也可能导致C、N和酚在三者中形成差异;通过对13种沉水植物叶片总酚含量比较,推测光叶眼子菜和微齿眼子菜较为适合作为洱海耐牧食恢复先锋物种;N与总酚正相关的关系可能在富营养化进程中加速湖泊沼泽化。     

过氧化氢参与了黑暗诱导的盐地碱蓬叶片甜菜红素积累

该文比较研究了黑暗和光照条件下C₃盐生植物盐地碱蓬(Suaeda salsa)叶片甜菜红素积累和H₂O₂含量及其抗氧化酶活性的关系,实验分析了甜菜红素体外抗氧化性能,以期揭示诱导盐地碱蓬甜菜红素积累的可能机制以及甜菜红素积累的生理生态意义。结果表明:暗期处理和营养液中加入一定浓度的H₂O₂都明显促进盐地碱蓬叶片H₂O₂含量、甜菜红素的含量、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)的活性,而且叶片中 H₂O₂含量与甜菜红含量、SOD和CAT活性具有正相关性;盐地碱蓬甜菜红素体外清除羟自由基的能力明显强于维生素C,而清除超氧阴离子能力低于维生素C。这些结果表明:黑暗作为一种环境胁迫因子诱导盐地碱蓬叶片甜菜红素的积累可能是由自由基介导的,甜菜红素的积累可能与提高植物的抗氧化能力有关。     

Comparative proteomic analysis provides new insights into mulberry dwarf responses in mulberry (Morus alba L.)

Mulberry dwarf (MD) is a serious infectious disease of mulberry caused by phytoplasma. Infection with MD phytoplasma results in stress phenotypes of yellowing, phyllody, stunting, proliferation, and witches' broom. Physiological and biochemical analysis has shown that infection with MD phytoplasma causes an increase in soluble carbohydrate and starch content, and a decrease in the net photosynthesis rate, carboxylation efficiency, and pigment content of leaves. Furthermore, damage to the chloroplast ultrastructure was detected in infected leaves. To better understand the pathogen‐stress response of mulberry (Morus alba L.) to MD phytoplasma, we conducted a comparative proteomic analysis using 2‐DE of infected and healthy leaves. Among 500 protein spots that were reproducibly detected, 20 were down‐regulated and 17 were up‐regulated. MS identified 16 differentially expressed proteins. The photosynthetic proteins rubisco large subunit, rubisco activase, and sedoheptulose‐1,7‐bisphosphatase showed enhanced degradation in infected leaves. Based these results, a model for the occurrence mechanism of MD is proposed. In conclusion, this study provides new insights into the mulberry response to MD phytoplasma infection.     

泡桐叶片蛋白质多态性及其聚类分析

研究了9种泡桐叶片蛋白质的多态性,并根据其叶片蛋白质聚丙烯酰胺凝胶单向和双向电泳结果,将它们聚类为白花泡桐组［白花泡桐（Paulownia fortunei）和白花兰考泡桐（P. elongata f. alba）］、南方泡桐组［南方泡桐（P. australis）和成都泡桐(P. albiphloea var. chengtuensis)］和毛泡桐组［毛泡桐（P. tomentosa）、川泡桐（P. fargesii）、鄂川泡桐（P. albiphloea）、山明泡桐（P. lamprophylla）和兰考泡桐（P. elongata ）］。该结果可为了解泡桐属植物的亲缘关系和种的鉴定提供参考依据。     

In Vivo Photomodification of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Holoenzyme by Ultraviolet-B Radiation (Formation of a 66-Kilodalton Variant of the Large Subunit)

Increased levels of solar ultraviolet (290-320 nm) (UV-B) radiation could have profound effects on plant proteins because the aromatic amino acids in proteins absorb strongly in this spectral region. We have investigated the effects of UV-B radiation on plant proteins and have observed a novel 66-kD protein. This product was formed in vivo when Brassica napus L. plants grown for 21 d in 65 [mu]mol m-2 s-1 photosynthetically active radiation were subsequently exposed to 65 [mu]mol m-2 s-1 photosynthetically active radiation plus UV-B radiation (1.5 [mu]mol m-2 s-1). The protein appeared after 4 h of UV-B irradiation and accumulated during the next 16 h in UV-B. The 66-kD protein cross-reacted with an antiserum against the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) holoenzyme. Analysis of soluble leaf proteins revealed that the 66-kD product had a number of isoforms corresponding closely to those of the large subunit of Rubisco (LSU). Partial proteolytic digests of the LSU and the 66-kD protein resulted in an equivalent pattern of protein fragments, leading to the conclusion that the 66-kD protein was a photomodified form of the LSU. A similar high molecular mass variant of Rubisco was observed in soluble protein extracts from leaves of tomato (Lycopersicon esculentum), tobacco (Nicotiana tabacum), and pea (Pisum sativum L.) plants treated in vivo with UV-B, suggesting that it might be a common product, at least among C3 plants. It is interesting that the 66-kD product appears to be generated after incorporation of the LSU into holoenzyme complexes. This conclusion was drawn from two lines of evidence. First, the LSU variant co-purified with holoenzyme complexes isolated by nondenaturing polyacrylamide gel electrophoresis. Second, a UV-B-specific 66-kD protein did not accumulate in a tobacco mutant that synthesizes the Rubisco subunits but does not assemble them into normal holoenzyme complexes.