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1. Oleh : YOSEHI MEKIUW NIM. G3IP22001 AGRICULTURAL SCIENCES DOCTORAL STUDY GRADUATE PROGRAM HALU OLEO UNIVERSITY YEAR 2023 REACTIVE OXYGEN SPECIES (ROS), BIOTIC STRESS AND COMBINATIONS OF STRESS IN PLANT SIGNALING ”

2. Reaktive Oksigen Species (ROS) Compounds that contain reactive oxygen so that they easily form new compounds with other molecules around them ROS Free radical oxygen N on radikal Has one or more unpaired electrons in its outermost orbital, e.g. superoxide Has no unpaired electrons but is a reactive compound that can be converted into free radical ROS, for example peroxide (H 2 O 2 ) is converted into hydroxyl radicals. The two main sources of ROS during abiotic stress can be shown in Figure beside that Metabolic ROS which can directly change the redox status of rate-limiting enzymes and control metabolic flows in cells thereby changing different metabolic reactions to counteract the effects of stress During abiotic stress, metabolic ROS and their signaling, were shown to interact and form ROS signatures that control plant acclimatization to stress through redox reactions that regulate transcription and translation of stress acclimatization proteins and enzymes.

3. PRODUCTION, SCAVENGING, AND SIGNALING OF ROS Kloroplas Apoplast Mitokondria Peroksisom As a marker of changes in internal or external conditions that require acclimatization or adjustment of metabolism Mitochondrial redox balance can serve as an indicator of various environmental cues and is intrinsically linked to chloroplast function Peroxisomes are central to a variety of metabolic processes, many of which lead to the formation of ROS Exchange of nutrients and signals between plant cells and the environment Recent studies have shown that under stress conditions chloroplast, peroxisomes and mitochondria can extend membrane structures ( stromules , peroxules and matrixules , respectively) that will contact the nuclear envelope and could directly alter the ROS status of the nuclei ( Noctor and Foyer, 2016). However, if labile Fe  2+ exist in cells, ROS such as H 2  O 2 can react with it to generate the highly toxic hydroxyl radical that would lead to oxidative stress and cell damage

4. The production of 1 O 2 in chloroplasts can also cause reprogramming of nuclear gene expression leading to chlorosis and programmed cell death, as well as induce a wide range of responses related to biotic and abiotic stresses through the function of EXECUTER1 (EX1) and EX2, two nuclear-encoded chloroplast proteins associated with thylakoid membranes   Mitochondrial ROS accumulation during abiotic stress is usually processed via electron leakage from complexes I and III to produce O 2 -, which can be converted to H 2 O 2  by Mn-SOD. This process can be mitigated by alternative oxidases (AOX), NAD(P)H type II dehydrogenase and uncoupling proteins in the inner mitochondrial membrane. Production of ROS in peroxisomes during abiotic stress is the result of increased photorespiration resulting in H 2 O 2 production by glycolate oxidase ROS production in apoplasts during abiotic stress is processed via at least four distinct mechanisms. The most studied of the four are proteins, PM, NADPH and RBOH-oxidase which link calcium and ROS signaling during stress and generate superoxide in the apoplast.

5. ROS-INDUCED PROTEIN MODIFICATIONS AND THEIR ROLE IN STRESS ACCLIMATION ROS-INDUCED PROTEIN MODIFICATIONS S- nitrosylation S ulfonilasi K arbonilasi G lutathionylation ROLE IN STRESS ACCLIMATION One of the main mechanisms that regulate enzyme activity in plants May regulate the function of some proteins during stress As a redox regulator of signal transduction cascades and metabolic pathways May cause a slowdown of flow to the TCA cycle and a consequent decrease in the energy state of the cell

6. INTERACTIONS OF ROS WITH STRESS HORMONES Plant hormones play a key role in shaping the acclimatization response of plants to abiotic stresses During abiotic stress affects the level and function of different plant hormones, such as abscisic acid (ABA), auxins, brassinosteroids (BRs), gibberellins (GAs) ROS AND STRESS COMBINATION Combined stress is the term used to describe a situation in which a plant is simultaneously subjected to two or more abiotic stresses Abiotic stress was shown to result in the formation of ROS signatures that mediate plant acclimatization and cell death.

7. ROS IN PLANT DEVELOPMENT ROS in the regulation of stomatal closure RBOHD and RBOHF are required to perform stomatal closure in response to abscisic acid (ABA) and high CO 2 levels ARE ROS GOOD OR BAD FOR ABIOTIC STRESS During abiotic stress in plants, ROS can have several important beneficial roles. For example, ROS production in chloroplasts can divert electrons away from the photosynthetic apparatus to prevent antenna overload and subsequent damage Negative aspects of ROS function during abiotic stress are their potential toxicity and the energetic costs associated with their detoxification Developmental processes that involve the production of apoplastic ROS are pollen formation and root hair growth. RBOHC is the main ROS-producing enzyme required for root hair elongation, as the rbohC mutant is deficient in this process Two isoforms of RBOH, RBOHH and RBOHJ, serve as sources of apoplastic ROS and are essential for pollen growth.

8. Conclusion Types of reactive oxygen (ROS) play a key role in the acclimatization process of plants to abiotic stresses. primarily functions as a signaling transduction molecule that regulates different pathways during plant acclimatization to stress, but is also a toxic by-product of metabolic stress .

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