Nkomo Mbukeni, Gokul Arun, Ndimba Roya, Badiwe Mihlali, Keyster Marshall, Klein Ashwil
Plant Omics Laboratory, Department of Biotechnology, Life Science Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7530, South Africa.
Department of Plant Sciences, Qwaqwa Campus, University of the Free State, Phuthadithjaba 9866, South Africa.
AoB Plants. 2022 May 26;14(3):plac025. doi: 10.1093/aobpla/plac025. eCollection 2022 Jun.
-Coumaric acid synthesis in plants involves the conversion of phenylalanine to -cinnamic acid via phenylalanine ammonia-lyase (PAL), which is then hydroxylated at the para-position under the action of -cinnamic acid 4-hydroxylase. Alternatively, some PAL enzymes accept tyrosine as an alternative substrate and convert tyrosine directly to coumaric acid without the intermediary of -cinnamic acid. In recent years, the contrasting roles of coumaric acid in regulating the growth and development of plants have been well-documented. To understand the contribution of -cinnamic acid 4-hydroxylase activity in -coumaric acid-mediated plant growth, mineral content accumulation and the regulation of reactive oxygen species (ROS), we investigated the effect of piperonylic acid (a -cinnamic acid 4-hydroxylase inhibitor) on plant growth, essential macroelements, osmolyte content, ROS-induced oxidative damage, antioxidant enzyme activities and phytohormone levels in chia seedlings. Piperonylic acid restricted chia seedling growth by reducing shoot length, fresh weight, leaf area measurements and -coumaric acid content. Apart from sodium, piperonylic acid significantly reduced the accumulation of other essential macroelements (such as K, P, Ca and Mg) relative to the untreated control. Enhanced proline, superoxide, hydrogen peroxide and malondialdehyde contents were observed. The inhibition of -cinnamic acid 4-hydroxylase activity significantly increased the enzymatic activities of ROS-scavenging enzymes such as superoxide dismutase, ascorbate peroxidase, catalase and guaiacol peroxidase. In addition, piperonylic acid caused a reduction in indole-3-acetic acid and salicylic acid content. In conclusion, the reduction in chia seedling growth in response to piperonylic acid may be attributed to a reduction in -coumaric acid content coupled with elevated ROS-induced oxidative damage, and restricted mineral and phytohormone (indole-3-acetic acid and salicylic) levels.
植物中香豆酸的合成涉及苯丙氨酸通过苯丙氨酸解氨酶（PAL）转化为肉桂酸，然后在肉桂酸4-羟化酶的作用下在对位发生羟基化。另外，一些PAL酶接受酪氨酸作为替代底物，直接将酪氨酸转化为香豆酸，而无需肉桂酸作为中间产物。近年来，香豆酸在调节植物生长发育中的不同作用已得到充分证明。为了了解肉桂酸4-羟化酶活性在香豆酸介导的植物生长、矿物质含量积累和活性氧（ROS）调节中的作用，我们研究了胡椒酸（一种肉桂酸4-羟化酶抑制剂）对奇亚籽幼苗的植物生长、必需大量元素、渗透溶质含量、ROS诱导的氧化损伤、抗氧化酶活性和植物激素水平的影响。胡椒酸通过降低茎长、鲜重、叶面积测量值和香豆酸含量来限制奇亚籽幼苗的生长。除了钠之外，相对于未处理的对照，胡椒酸显著降低了其他必需大量元素（如钾、磷、钙和镁）的积累。观察到脯氨酸、超氧化物、过氧化氢和丙二醛含量增加。肉桂酸4-羟化酶活性的抑制显著增加了超氧化物歧化酶、抗坏血酸过氧化物酶、过氧化氢酶和愈创木酚过氧化物酶等ROS清除酶的酶活性。此外，胡椒酸导致吲哚-3-乙酸和水杨酸含量降低。总之，奇亚籽幼苗对胡椒酸反应生长减少可能归因于香豆酸含量的降低，以及ROS诱导的氧化损伤增加，以及矿物质和植物激素（吲哚-3-乙酸和水杨酸）水平受限。
