Loreto F, Mannozzi M, Maris C, Nascetti P, Ferranti F, Pasqualini S
Consiglio Nazionale delle Ricerche, Istituto di Biochimica ed Ecofisiologia Vegetali,Via Salaria Km 29,300, 00016 Monterotondo Scalo, Roma, Italy.
Plant Physiol. 2001 Jul;126(3):993-1000. doi: 10.1104/pp.126.3.993.
Isoprene is formed in and emitted by plants and the reason for this apparent carbon waste is still unclear. It has been proposed that isoprene stabilizes cell and particularly chloroplast thylakoid membranes. We tested if membrane stabilization or isoprene reactivity with ozone induces protection against acute ozone exposures. The reduction of visible, physiological, anatomical, and ultrastructural (chloroplast) damage shows that clones of plants sensitive to ozone and unable to emit isoprene become resistant to acute and short exposure to ozone if they are fumigated with exogenous isoprene, and that isoprene-emitting plants that are sensitive to ozone do not suffer damage when exposed to ozone. Isoprene-induced ozone resistance is associated with the maintenance of photochemical efficiency and with a low energy dissipation, as indicated by fluorescence quenching. This suggests that isoprene effectively stabilizes thylakoid membranes. However, when isoprene reacts with ozone within the leaves or in a humid atmosphere, it quenches the ozone concentration to levels that are less or non-toxic for plants. Thus, protection from ozone in plants fumigated with isoprene may be due to a direct ozone quenching rather than to an induced resistance at membrane level. Irrespective of the mechanism, isoprene is one of the most effective antioxidants in plants.
异戊二烯在植物体内形成并由植物释放，而这种明显的碳浪费现象的原因仍不明确。有人提出异戊二烯能稳定细胞尤其是叶绿体类囊体膜。我们测试了膜稳定作用或异戊二烯与臭氧的反应性是否能诱导植物抵御急性臭氧暴露。可见损伤、生理损伤、解剖损伤和超微结构（叶绿体）损伤的减轻表明，对臭氧敏感且无法释放异戊二烯的植物克隆体，如果用外源异戊二烯进行熏蒸，就会对急性和短期臭氧暴露产生抗性，并且对臭氧敏感的异戊二烯释放型植物在暴露于臭氧时不会受到损伤。如荧光猝灭所示，异戊二烯诱导的臭氧抗性与光化学效率的维持以及低能量耗散有关。这表明异戊二烯能有效稳定类囊体膜。然而，当异戊二烯在叶片内或潮湿大气中与臭氧反应时，它会将臭氧浓度猝灭至对植物毒性较小或无毒的水平。因此，用异戊二烯熏蒸的植物对臭氧的防护可能是由于直接的臭氧猝灭，而非膜水平上诱导的抗性。无论其机制如何，异戊二烯都是植物中最有效的抗氧化剂之一。
