Bruce R J, West C A
Molecular Biology Institute, University of California, Los Angeles, California 90024.
Plant Physiol. 1989 Nov;91(3):889-97. doi: 10.1104/pp.91.3.889.
Suspension cultures of castor bean (Ricinus communis L.) which have been treated with pectic fragment elicitor rapidly accumulate lignin as measured by derivatization with thioglycolic acid. The responsiveness of cultured cells to elicitor is dependent on the stage of culture growth. In 6-day (maximally responsive) cultures, increases in lignin are first evident 3 hours after addition of pectic fragment elicitor with maximal rates of lignin synthesis between 4 and 10 hours. The abundance of lignin in cultures after 12 hours of elicitor treatment is 10- to 20-fold higher than in untreated control cultures and can thereby account for as much as 2% of the dry cell weight. Only intermediate sizes of pectic oligomer are active as elicitors of lignin. Half-maximal accumulation of lignin occurs at 250 to 300 micrograms per milliliter of an optimal elicitor preparation with an average degree of polymerization of seven. We consider the synthesis of lignin in elicited cultures to be a mechanism of plant disease resistance which is induced by the elicitor. Plant peroxidases have been proposed to catalyze the last enzymatic steps in the biosynthesis of both lignin and hydrogen peroxide. Six extracellular isoenzymes of peroxidase (two anionic, designated A1 and A2, and four cationic, designated C2, C3, C4, and C7) are detectable in healthy suspension cultures of castor bean by native gel electrophoresis. Treatment of cultures with elicitor causes substantial changes in the activity of four of these species (A1, C2, C3, and C7). Elicitor treatment also results in the appearance of three new peroxidase isoenzymes that are not readily detectable in healthy cultures (C1, C5, and C6). Increases in the activities of these isoenzymes are concurrent with or slightly precede the accumulation of lignin in elicited 6-day cultures. By 12 hours after addition of elicitor, C1 becomes the most abundant extracellular isoperoxidase. The differential regulation of expression of peroxidase isoenzymes following elicitor treatment suggests that individual isoenzymes of peroxidase may have specific functional roles in the biosynthesis of disease-lignin.
用果胶片段激发子处理的蓖麻（Ricinus communis L.）悬浮培养物，通过巯基乙酸衍生化测定，木质素迅速积累。培养细胞对激发子的反应性取决于培养生长阶段。在6天（反应最大）的培养物中，添加果胶片段激发子3小时后，木质素的增加首先明显，木质素合成的最大速率在4至10小时之间。激发子处理12小时后，培养物中木质素的丰度比未处理的对照培养物高10至20倍，因此可占干细胞重量的2%。只有中等大小的果胶寡聚物作为木质素的激发子具有活性。木质素积累达到最大值的一半时，每毫升含有平均聚合度为7的最佳激发子制剂250至300微克。我们认为在诱导培养物中木质素的合成是植物抗病性的一种机制，由激发子诱导。有人提出植物过氧化物酶催化木质素和过氧化氢生物合成中的最后酶促步骤。通过天然凝胶电泳在蓖麻健康悬浮培养物中可检测到六种细胞外过氧化物酶同工酶（两种阴离子型，命名为A1和A2，四种阳离子型，命名为C2、C3、C4和C7）。用激发子处理培养物会导致其中四种同工酶（A1、C2、C3和C7）的活性发生显著变化。激发子处理还导致出现三种新的过氧化物酶同工酶，在健康培养物中不易检测到（C1、C5和C6）。在诱导的6天培养物中，这些同工酶活性的增加与木质素积累同时发生或略早于木质素积累。添加激发子12小时后，C1成为最丰富的细胞外同功过氧化物酶。激发子处理后过氧化物酶同工酶表达的差异调节表明，过氧化物酶的个别同工酶可能在病害木质素的生物合成中具有特定的功能作用。
