BioPL 3420Spring 2016Lecture Topic 27Answer to Assigned Study QuestionAbiotic InteractionsPlant Physiology LecturesBioPL 3420Spring 2016Lecture Topic 27 Answer to Assigned Study QuestionAbiotic InteractionsStudy Question. Reactive oxygen species in some ways seem to be the new Ca2+ ofabiotic stress-related signaling. Curiously, ROS seem to play two different roles. One isas a real stress response in which the ROS is generated directly from the stress. Thesecond is where ROS is produced as a part of both cellular and intercellular signalingpathways. This distinction can be seen in Figure 24.4 where ROS are produced bymany types of stresses, but as you see later in the chapter, ROS are also produced as apart of stress-induced signal transduction. Keep in mind that singlet oxygen, hydrogenperoxide or other ROS produced directly as a consequence of the stress cannot bedistinguished from ROS produced as a part of signaling pathways. Explain how ROSare produced by these two mechanisms and if there is a need to distinguish betweenthe two in terms of the type of response the cell produces. I am not looking for specificshere. Rather, does your understanding of abiotic stress and signal transduction giveyou clues about the answers to these questions.Answer: The most common pathways that produce ROS directly in response to stress involveO2 acting as an electron acceptor under circumstances when the normal electronacceptors are in limited supply. Similarly, the most common pathway for production ofROS associated with signaling pathways is again, reduction of O2. The difference isthat in the first, O2 is not the intended electron acceptor, but in the second, O2 is theintended acceptor. One of the main processes in which stress directly produces ROS iswhen the stress decreases the cells capacity to do photosynthesis. This means that thelight reactions are trying to go faster than the carbon reactions, and NADP+ is in shortsupply, allowing O2 to act as an electron acceptor from reduced plastoquinone (PQ) orferredoxin (Fd). In contrast, in stress-induced signaling pathways, ROS are producedby proteins that oxidize NADH (made in the cytoplasm in glycolysis and the citric acidcycle), typically producing ROS in the apoplast. (Note that these enzymes play a keyrole in secondary cell wall formation by producing ROS that initiate free radicalformation required for lignin formation.There is no reason that these two need to be distinguished. In fact, the production ofROS as a consequence of stress-induced signaling can be seen as a way of amplifyingthe original ROS produced directly by the stress. Note that pathway for signal-relatedROS production has a positive feedback loop which results in even more