Effects of phosphorus stress on the growth and secondary metabolism of Artemisia argyi.

Phosphorus is essential in critical plant processes such as signaling, photosynthesis, energy metabolism, and enzyme activity during respiration. Phosphorus stress therefore has a significant impact on plant growth and metabolism. Here, we characterized the biochemical responses of Artemisia argyi Level. et Vant to low phosphorus (LP) and high phosphorus (HP) stress. Plants were treated with 0 g (LP), 1.5 g (control), or 3 g (HP) P per 10 kg of soil. The results demonstrated that CK encouraged the most plant growth, as quantified by leaf size and plant biomass. We also found that the total amounts of phenolic and flavonoid compounds (such as chlorogenic acid, isochlorogenic acid A, isochlorogenic acid B, isochlorogenic acid C, cryptochlorogenic acid, neochlorogenic acid, hispidulin, jaceosidin, eupatilin, and casticin) were increased in the leaves of A. argyi plants exposed to LP stress compared to those raised under CK conditions. The levels of these compounds were inversely related to the amount of phosphorus added, and therefore peaked in plants treated with LP stress. Levels of terpenoids were also found to fluctuate under LP and HP stress compared to CK conditions. Furthermore, transcriptomic analyses showed up-regulation of several genes encoding key enzymes in the flavonoid and phenolic acid metabolic pathways under LP stress. There were also alterations in the expression levels of genes in the methylerythritol 4-phosphate and mevalonate pathways of terpene synthesis. This study contributes to a deeper understanding of the physiological and molecular mechanisms underlying phosphorus stress responses and their impacts on the growth and quality of the economically important species A. argyi.

Weed Suppression and Molecular Mechanisms of Isochlorogenic Acid A Isolated from Artemisia argyi Extract via an Activity-Guided Method.

Allelopathy is considered an environmentally friendly and resource-conserving approach to weed control because allelochemicals degrade easily and cause less pollution than traditional chemical herbicides. In this study, the allelopathic active constituents of Artemisia argyi were elucidated by activity-guided isolation and ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). First, a crude extract prepared in water was fractionated using macroporous resin D101 to obtain three fractions (Fr.A-C). Combined with the allelopathic activity assay on Setaria viridis and Portulaca oleracea, Fr.C was determined to be the most active fraction. We identified 14 compounds in the active fraction (Fr.C) using UPLC-QTOF-MS, including 13 phenolic compounds. Accordingly, phenolic components have been suggested as the main allelochemicals in A. argyi. Thereafter, Fr.C was further isolated by octadecylsilyl (ODS) chromatography to obtain eight subfractions (Fr.C-1-Fr.C-8). Finally, isochlorogenic acid A (ICGAA) was purified from Fr.C-3 by semipreparative liquid chromatography, which was detected in the growth environment of A. argyi. Furthermore, we evaluated the allelopathic effects of ICGAA on six weeds from different families and genera for the first time. The results showed that ICGAA is a novel allelochemical with broad herbicidal activity. In addition, we analyzed the inhibitory effect and molecular mechanism of ICGAA on the growth of S. viridis seedlings. Optical microscopy and transmission electron microscopy (TEM) revealed the degradation of membrane structures and organelles after ICGAA treatment. Transcriptome and real-time polymerase chain reaction (RT-qPCR) analysis showed that ICGAA inhibited the growth of weeds mainly by inhibiting the diterpenoid biosynthesis pathway (especially gibberellins, GAs). The decrease of gibberellin (GA) contents after ICGAA treatment also confirmed these results. In brief, this study provides new material sources and theoretical support for developing biological herbicides for agroecosystems.

Caffeic Acid, an Allelochemical in Artemisia argyi, Inhibits Weed Growth via Suppression of Mitogen-Activated Protein Kinase Signaling Pathway and the Biosynthesis of Gibberellin and Phytoalexin.

Artemisia argyi is widely distributed in Asia, and it often becomes the dominant population in the field because of its strong ecological niche competitiveness. Allelochemicals secreted by plants are generally considered an important reason for their dominance in ecological competition. In this study, the allelochemicals in A. argyi were screened by a series of experiments and their mechanisms were explored via transcriptomics. First, the inhibitory effects of A. argyi on Echinochloa crusgalli, Setaria viridis, Portulaca oleracea and Amaranthus retroflexus were evaluated. Then, we carried out a qualitative and quantitative analysis of the chemical composition of the aqueous extract of A. argyi to screen for potential allelochemicals that can inhibit weed growth. Four potential allelochemicals were quantified: neochlorogenic acid (5-CQA), chlorogenic acid (3-CQA), cryptochlorogenic acid (4-CQA), and caffeic acid (CA). Coincidentally, their allelopathic effects on weeds seemed to be identical to their content, in the order CA>4-CQA>5-CQA>3-CQA. These findings suggested that CA might be the main allelopathic compound in the aqueous extract of A. argyi. Subsequently, the allelopathic effect and molecular mechanism of CA on S. viridis leaves were investigated. The physiological results showed that CA significantly induced reactive oxygen species (ROS) production, led to malondialdehyde (MDA) accumulation, and disrupted enzyme activities (POD, SOD, CAT) in S. viridis leaves. Moreover, transcriptome results revealed that CA inhibited S. viridis growth by downregulating multiple genes involved in gibberellin (GA) and phytoalexin biosynthesis and Mitogen-activated protein kinase (MAPK) signaling pathways. In addition, differentially expressed genes (DEGs) related to the biosynthesis and signaling pathways of phytohormones were verified by Quantitative Real-Time PCR (RT-qPCR). Taken together, this study may be the first to identify allelochemicals and explore their molecular mechanism about A. argyi. Importantly, the ecological advantages of A. argyi could be applied to ecological regulation and the development of botanical herbicides.