Barto E Kathryn, Cipollini Don
Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA.
Oecologia. 2005 Dec;146(2):169-78. doi: 10.1007/s00442-005-0207-0. Epub 2005 Oct 28.
Two prominent theories proposed to explain patterns of chemical defense expression in plants are the optimal defense theory (ODT) and the growth-differentiation balance hypothesis (GDBH). The ODT predicts that plant parts with high fitness value will be highly defended, and the GDBH predicts that slow growing plant parts will have more resources available for defense and thus will have higher defense levels than faster growing tissues. We examined growth rate, fitness value, and defense protein levels in leaves of a wild and lab ecotype of Arabidopsis thaliana to address whether patterns of defense protein expression in this plant conform to predictions of either the ODT or the GDBH. We divided leaves of A. thaliana into six leaf classes based on three developmental stages: vegetative, bolting, and flowering; with two leaf ages at each stage: young and old. We assessed the fitness value of leaves by determining the impact of the removal of each leaf class on total seed production and germination rates. Although A. thaliana was highly tolerant to defoliation, young leaves were more valuable than old in general, and young leaves on bolting plants were the most valuable leaf class in particular. Young leaves on vegetative plants grew fastest in both ecotypes, while old leaves on bolting and flowering plants grew slowest. Finally, defense levels were assessed in each leaf class by quantifying the constitutive and inducible expression of four defense-related proteins. Expression of guaiacol peroxidase and chitinase activity conformed largely to GDBH predictions. Expression of trypsin inhibitor and polyphenoloxidase activity varied by leaf class and treatment, but conformed to neither GDBH nor ODT predictions.
为解释植物化学防御表达模式而提出的两个重要理论是最优防御理论（ODT）和生长 - 分化平衡假说（GDBH）。最优防御理论预测，具有高适合度值的植物部分将受到高度防御，而生长 - 分化平衡假说预测，生长缓慢的植物部分将有更多资源用于防御，因此其防御水平将高于生长较快的组织。我们研究了野生型和实验室生态型拟南芥叶片的生长速率、适合度值和防御蛋白水平，以探讨该植物中防御蛋白的表达模式是否符合最优防御理论或生长 - 分化平衡假说的预测。我们根据三个发育阶段：营养期、抽薹期和开花期，将拟南芥叶片分为六个叶类；每个阶段有两个叶龄：幼叶和老叶。我们通过确定去除每个叶类对总种子产量和发芽率的影响来评估叶片的适合度值。尽管拟南芥对去叶具有高度耐受性，但总体而言幼叶比老叶更有价值，特别是抽薹植物上的幼叶是最有价值的叶类。营养期植物上的幼叶在两种生态型中生长最快，而抽薹期和开花期植物上的老叶生长最慢。最后，通过量化四种防御相关蛋白的组成型和诱导型表达来评估每个叶类的防御水平。愈创木酚过氧化物酶的表达和几丁质酶活性在很大程度上符合生长 - 分化平衡假说的预测。胰蛋白酶抑制剂和多酚氧化酶活性的表达因叶类和处理而异，但既不符合生长 - 分化平衡假说也不符合最优防御理论的预测。
