Dipartimento di Biologia e Protezione delle Piante, Universita di Udine, Udine, Italy.
Phytopathology. 2010 Apr;100(4):390-9. doi: 10.1094/PHYTO-100-4-0390.
Recovery of apple trees from apple proliferation was studied by combining ultrastructural, cytochemical, and gene expression analyses to possibly reveal changes linked to recovery-associated resistance. When compared with either healthy or visibly diseased plants, recovered apple trees showed abnormal callose and phloem-protein accumulation in their leaf phloem. Although cytochemical localization detected Ca(2+) ions in the phloem of all the three plant groups, Ca(2+) concentration was remarkably higher in the phloem cytosol of recovered trees. The expression patterns of five genes encoding callose synthase and of four genes encoding phloem proteins were analyzed by quantitative real-time reverse transcription-polymerase chain reaction. In comparison to both healthy and diseased plants, four of the above nine genes were remarkably up-regulated in recovered trees. As in infected apple trees, phytoplasma disappear from the crown during winter, but persist in the roots, and it is suggested that callose synthesis/deposition and phloem-protein plugging of the sieve tubes would form physical barriers preventing the recolonization of the crown during the following spring. Since callose deposition and phloem-protein aggregation are both Ca(2+)-dependent processes, the present results suggest that an inward flux of Ca(2+) across the phloem plasma membrane could act as a signal for activating defense reactions leading to recovery in phytoplasma-infected apple trees.
本研究通过结合超微结构、细胞化学和基因表达分析，研究了苹果树从苹果增殖中恢复的情况，以期揭示与恢复相关的抗性变化。与健康或明显患病的植物相比，恢复的苹果树叶片韧皮部表现出异常的胼胝质和韧皮部蛋白积累。虽然细胞化学定位在三组植物的韧皮部中都检测到了 Ca(2+)离子，但恢复树韧皮部细胞质中的 Ca(2+)浓度明显更高。通过定量实时逆转录聚合酶链反应分析了编码胼胝质合酶的五个基因和编码韧皮部蛋白的四个基因的表达模式。与健康和患病植物相比，上述九个基因中有四个在恢复树中显著上调。与感染苹果树一样，类菌质体在冬季从树冠中消失，但在根系中仍然存在，这表明胼胝质的合成/沉积和筛管的韧皮部蛋白堵塞会形成物理屏障，防止树冠在次年春天重新定植。由于胼胝质沉积和韧皮部蛋白聚集都是 Ca(2+)依赖性过程，因此本研究结果表明，Ca(2+)向内穿过韧皮部质膜的内流可能作为激活防御反应的信号，导致感染类菌质体的苹果树恢复。
