Davies E, Vian A, Vian C, Stankovic B
Botany Department, North Carolina State University, NC 27695-7612, USA.
Acta Physiol Plant. 1997;19(4):571-6. doi: 10.1007/s11738-997-0055-0.
When one leaf of a tomato plant is electrically-stimulated or heat-wounded, proteinase inhibitor genes are rapidly up-regulated in distant leaves. The identity of the systemic wound signal(s) is not yet known, but major candidates include hormones transmitted via the phloem or the xylem, the electrically-stimulated self-propagating electrical signal in the phloem (the action potential, AP), or the heat-wound-induced surge in hydraulic pressure in the xylem evoking a local change in membrane potential in adjacent living cells (the variation potential, VP). In order to discriminate between these signals we have adopted two approaches. The first approach involves applying stimuli that evoke known signals and determining whether these signals have similar effects on the "model" transcripts for proteinase inhibitors (pin) and calmodulin (cal). Here we show that a heat wound almost invariably evokes a VP, while an electrical stimulation occasionally evokes an AP, and both of these signals induce accumulation of transcripts encoding proteinase inhibitors. The second approach involves identifying the array of genes turned on by heat-wounding. To this end, we have constructed a subtractive library for heat-wounded tissue, isolated over 800 putatively up-regulated clones, and shown that all but two of the fifty that we have analyzed by Northern hybridization are, indeed, up-regulated. Here we show the early kinetics of up-regulation of three of these transcripts in the terminal (4th) leaf in response to heat-wounding the 3rd leaf, about 5 cm away. Even though these transcripts show somewhat different time courses of induction, with one peaking at 30 min, another at 15 min, and another at 5 min after flaming of a distant leaf, they all exhibit a similar pattern, i.e., a transient period of transcript accumulation preceding a period of transcript decrease, followed by a second period of transcript accumulation.
当番茄植株的一片叶子受到电刺激或热损伤时，蛋白酶抑制剂基因会在远处的叶子中迅速上调。系统性创伤信号的身份尚不清楚，但主要候选信号包括通过韧皮部或木质部传输的激素、韧皮部中电刺激的自传播电信号（动作电位，AP），或热损伤诱导的木质部液压激增，从而引起相邻活细胞中膜电位的局部变化（变异电位，VP）。为了区分这些信号，我们采用了两种方法。第一种方法是施加能引发已知信号的刺激，并确定这些信号对蛋白酶抑制剂（pin）和钙调蛋白（cal）的“模型”转录本是否有类似影响。在这里我们表明，热损伤几乎总是会引发一个VP，而电刺激偶尔会引发一个AP，并且这两种信号都会诱导编码蛋白酶抑制剂的转录本积累。第二种方法是识别热损伤开启的基因阵列。为此，我们构建了一个热损伤组织的消减文库，分离出800多个假定上调的克隆，并表明我们通过Northern杂交分析的50个克隆中，除了两个之外，其余的确实都上调了。在这里我们展示了对距离约5厘米的第三片叶子进行热损伤时，末端（第四片）叶子中这三种转录本上调的早期动力学。尽管这些转录本显示出略有不同的诱导时间进程，其中一个在远处叶子燃烧后30分钟达到峰值，另一个在15分钟达到峰值，另一个在5分钟达到峰值，但它们都呈现出相似的模式，即转录本积累的短暂时期，接着是转录本减少的时期，随后是转录本积累的第二个时期。
