Plant Molecular Biology Group, Biotechnology Department, Indian Institute of Technology Roorkee, Roorkee 247 667, India.
Protein Biochemistry Laboratory, Biotechnology Department, Indian Institute of Technology Roorkee, Roorkee 247 667, India.
J Plant Physiol. 2018 Feb;221:66-73. doi: 10.1016/j.jplph.2017.12.002. Epub 2017 Dec 6.
Salicylic acid (SA) is known to trigger a number of plant defense responses upon pathogen attack. It is well known that apple (Malus domestica) plants respond to pathogen invasion by synthesizing SA, but its biosynthesis is not well understood. In this study, we report salicylaldehyde synthase (SAS) activity from Venturia inaequalis elicitor (VIE)-treated cell suspension cultures of apple (Malus domestica 'Florina'). SAS catalyzes non-oxidative C-side chain cleavage of 2-coumaric acid to form salicylaldehyde (SALD) in the presence of a reducing agent such as cysteine. The side chain cleavage mechanism was found to be very similar to that of salicylaldehyde synthase activity from tobacco and 4-hydroxybenzaldehyde synthase activity from Vanilla planifolia and Daucus carota. A basal SAS activity was observed in the non-elicited cell cultures, and a 7-fold increase in SAS activity was observed upon elicitation. In parallel to SAS activity, the level of total SA accumulation increased by 5.6-fold after elicitation compared to the untreated control cells. Elicitor treatment further resulted in an 8.7-fold increase in the activity of the phenylalanine ammonia-lyase (PAL) enzyme that preceded the peak of SAS activity and total SA accumulation, suggesting the involvement of the phenylpropanoid pathway in SA metabolism. The preferred substrate for SAS was 2-coumaric acid (Km = 0.35 mM), with cysteine being the preferred reducing agent. In addition, a 1.8-fold enhancement in the SA content and 0.7-fold enhancement in the SALD content was observed when elicited cell cultures were fed with 2-coumaric acid. These observations suggest the involvement of SAS in SALD biosynthesis.
水杨酸（SA）在受到病原体攻击时会引发许多植物防御反应。众所周知，苹果（Malus domestica）植物通过合成 SA 来应对病原体的入侵，但对其生物合成知之甚少。在这项研究中，我们报道了来自苹果（Malus domestica 'Florina'）细胞悬浮培养物中 VIE 处理的 Venturia inaequalis 诱导物的水杨醛合酶（SAS）活性。SAS 在还原剂（如半胱氨酸）存在下催化 2-肉桂酸的非氧化 C-侧链裂解，形成水杨醛（SALD）。侧链裂解机制与烟草中的水杨醛合酶活性和香草醛合酶活性以及胡萝卜中的 4-羟基苯甲醛合酶活性非常相似。在未诱导的细胞培养物中观察到基础 SAS 活性，诱导后 SAS 活性增加了 7 倍。与 SAS 活性平行的是，与未处理的对照细胞相比，诱导后总 SA 积累增加了 5.6 倍。诱导处理进一步导致苯丙氨酸解氨酶（PAL）酶的活性增加了 8.7 倍，该酶的活性先于 SAS 活性和总 SA 积累的峰值，表明苯丙烷途径参与了 SA 代谢。SAS 的首选底物是 2-肉桂酸（Km=0.35 mM），半胱氨酸是首选还原剂。此外，当用 2-肉桂酸喂养被诱导的细胞培养物时，SA 含量增加了 1.8 倍，SALD 含量增加了 0.7 倍。这些观察结果表明 SAS 参与了 SALD 的生物合成。
