  Citation: Hessini, K.; Wasli, H.; Al-Yasi, H.M.; Ali, E.F.; Issa, A.A.; Hassan, F.A.S.; Siddique, K.H.M. Graded Moisture Deficit Effect on Secondary Metabolites, Antioxidant, and Inhibitory Enzyme Activities in Leaf Extracts of Rosa damascena Mill. var. trigentipetala. Horticulturae 2022, 8, 177. https://doi.org/10.3390/ horticulturae8020177 Academic Editors: Stefania Toscano, Giulia Franzoni and Sara Álvarez Received: 22 January 2022 Accepted: 17 February 2022 Published: 21 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). horticulturae Article Graded Moisture Deficit Effect on Secondary Metabolites, Antioxidant, and Inhibitory Enzyme Activities in Leaf Extracts of Rosa damascena Mill. var. trigentipetala Kamel Hessini 1, * , Hanen Wasli 2 , Hatim M. Al-Yasi 1 , Esmat F. Ali 1 , Ahmed A. Issa 1 , Fahmy A. S. Hassan 3 and Kadambot H. M. Siddique 4 1 Department of Biology, College of Sciences, Taïf University, P.O. Box 888, Taif 21974, Saudi Arabia; h.alyasi@tu.edu.sa (H.M.A.-Y.); a.esmat@tu.edu.sa (E.F.A.); a.hissa@tu.edu.sa (A.A.I.) 2 Laboratoire des Plantes Aromatiques et Médicinales, Centre de Biotechnologie de Borj-Cédria (LR15CBBC06), BP 901, Hammam Lif 2050, Tunisia; hanenwasli@gmail.com 3 Horticulture Department, Faculty of Agriculture, Tanta University, Tanta 31527, Egypt; fahmy_hssn@yahoo.com 4 The UWA Institute of Agriculture, The University of Western Australia, Perth, WA 6001, Australia; kadambot.siddique@uwa.edu.au * Correspondence: k.youssef@tu.edu.sa Abstract: Drought affects plant growth and yield in many agricultural areas worldwide by producing negative water potentials in the root zone that reduce water availability, affecting plant development and metabolism. This study investigated the effect of varying moisture regimes (100% field capacity (FC), well-watered plants, 50% FC (moderate water stress), and 25% FC (severe water stress)) on growth parameters, chlorophyll content, and bioactive molecule patterns, and the impact on an- tioxidant, lipoxygenase (LOX), and acetylcholinesterase (AChE) activities in Rosa damascena. The water deficit treatments reduced biomass production for both treatments (−29 and −33%, respec- tively, for MWS and SWS) and total chlorophyll (−18 and −38% respectively for MWS and SWS), relative to the control. The 50% FC treatment had the greatest effect on the phenolic profiles and their respective functionalities, with significant increases in the levels of total phenolic, benzoic (gallic, p-coumaric, and syringic acids) (+32%), and cinnamic (caffeic and trans-cinnamic acid) acids (+19%) and flavonoids (epicatechin-3-O-gallate) (+15%) compared to well-watered leaves (control leaves). The 50% FC treatment also exhibited the highest potential antioxidant activities (apart from NO-quenching activity), evidenced by the lowest IC 50 and EC 50 values. The inhibitory LOX and AChE capacities varied depending on the severity of stress, with superior activity in the 50% FC treatment. Overall, the drought tolerance in rose was associated mainly with its suitable manipulation of antioxidant production and orderly regulation of LOX and AChE activities. Keywords: AChE activity; antioxidant; drought stress; LOX activity; phenolics; damask rose 1. Introduction The severity and incidence of drought are expected to increase with the predicted change in typical precipitation patterns associated with climate change [1]. Water deficits are anticipated to reduce world crop production by up to 30% by 2025 compared to current yields [2]. In arid and semi-arid zones, the potential of water resources to expand landscapes and grow ornamental plants is threatened. Water distribution to the floral industry is in strong competition with other demands, such as agriculture, urban management, and human consumption [3], and should be used optimally and with high efficiency [4]. Limited water supply to plants incites a chemical signal in the aerial system through xylem sap, eliciting partial stomatal closure to avert water loss by evaporation. As a result, plants shift to a water-saving strategy that decreases intracellular CO 2 , reducing Horticulturae 2022, 8, 177. https://doi.org/10.3390/horticulturae8020177 https://www.mdpi.com/journal/horticulturae