Narváez-Vásquez Javier, Ryan Clarence A
Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
Planta. 2004 Jan;218(3):360-9. doi: 10.1007/s00425-003-1115-3. Epub 2003 Oct 8.
The systemin precursor, prosystemin, has been previously shown to be sequestered in vascular bundles of tomato ( Lycopersicon esculentum Mill.) plants, but its subcellular compartmentalization and association with a specific cell type has not been established. We present in situ hybridization and immunocytochemical evidence at the light, confocal, and transmission electron microscopy levels that wound-induced and methyl jasmonate-induced prosystemin mRNA and protein are exclusively found in vascular phloem parenchyma cells of minor veins and midribs of leaves, and in the bicollateral phloem bundles of petioles and stems of tomato. Prosystemin protein was also found constitutively in parenchyma cells of various floral organs, including sepals, petals and anthers. At the subcellular level, prosystemin was found compartmentalized in the cytosol and the nucleus of vascular parenchyma cells. The cumulative data indicate that vascular phloem parenchyma cells are the sites for the synthesis and processing of prosystemin as a first line of defense signaling in response to herbivore and pathogen attacks.
系统素前体，即前系统素，此前已被证明存在于番茄（Lycopersicon esculentum Mill.）植株的维管束中，但其亚细胞定位以及与特定细胞类型的关联尚未明确。我们通过原位杂交以及光镜、共聚焦显微镜和透射电子显微镜水平的免疫细胞化学证据表明，创伤诱导和茉莉酸甲酯诱导的前系统素mRNA和蛋白质仅存在于叶片小叶脉和中脉的维管束韧皮薄壁细胞中，以及番茄叶柄和茎的双韧皮部维管束中。前系统素蛋白也组成性地存在于包括萼片、花瓣和花药在内的各种花器官的薄壁细胞中。在亚细胞水平上，发现前系统素定位于维管束薄壁细胞的细胞质和细胞核中。累积的数据表明，维管束韧皮薄壁细胞是前系统素合成和加工的场所，作为对食草动物和病原体攻击的第一道防御信号。
