The Radical Pair Mechanism and Its Quantum Role in Plant Reactive Oxygen Species Production Under Hypomagnetic Fields

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The topic of this review is timely and important. The manuscript assembles disparate findings into a multi-level narrative linking hMF to ROS modulation and plant phenotype. Several sections are clearly written and potentially useful to the field. 

Comments

1. The term "quantum signature" appears repeatedly from the abstract onward but lacks a clear operational definition. The author should provide an explicit definition early in the introduction: what specific measurement constitutes a quantum signature in plants, under what controls, and what alternative classical explanations must be ruled out to validate the claim.

2. Section 4.3 suggests that plant responses to hMF "in continuous darkness" exclude a direct role for photoreceptors. This conclusion should be revised. There is significant in vivo evidence demonstrating that cryptochrome's magnetic sensitivity occurs during its light-independent flavin reoxidation phase, which proceeds in the dark after initial photoactivation. Therefore, a dark response does not exclude cryptochrome but rather helps to pinpoint the specific, magnetically sensitive step in its photocycle. The argument should be reframed to use the dark-response data as evidence for phase-specific magnetosensitivity, which would strengthen the overall mechanistic discussion.

3. To add mechanistic precision, the review would benefit from explicitly distinguishing the "conventional" RPM (light-dependent formation of a radical pair involving tryptophan) from the "alternative" RPM (light-independent reoxidation involving a radical pair with superoxide). The manuscript's focus on ROS reduction under hMF aligns strongly with the alternative RPM, and framing the discussion within this context would provide a clearer interpretation of the evidence.

4. The review proposes that lower ROS levels under hMF lead to generally "improved plant health." This appears to be an oversimplification. The manuscript itself cites evidence of negative developmental effects under hMF, such as delayed flowering, reduced leaf area, and shorter stems in Arabidopsis. The outcomes are clearly not always positive. The author should revise the conclusions and figure legends to reflect that the effects of hMF are context-dependent, sometimes benefiting certain traits while impairing others. A more balanced perspective is required.

5. The review rightly notes that some observations are not fully explained by current RPM theory. This presents an opportunity to articulate testable predictions that could discriminate between a cryptochrome-centric RPM and alternative quantum mechanisms. A dedicated subsection proposing discriminative experiments (e.g., orientation and resonance protocols, phase-specific light paradigms, use of cryptochrome and RBOH mutants, isotope-sensitive tests) would significantly enhance the manuscript's forward-looking value.

6. In figure 1, the multi-level model is a strong conceptual tool. At the Subatomic Level, the diagram could be made more specific by depicting the proposed radical pair (e.g., FADH• and O₂•−) instead of generic spheres. Furthermore, the figure would benefit from the inclusion of typical timescales for each level (from nanoseconds for spin dynamics to days for developmental traits) and an indication of the strength of evidence (e.g., well-established, likely, speculative) for each step.

7. The statement that peroxisomal oxidases "do not have a defined RPM" is too categorical. Many are flavin-dependent and could plausibly generate spin-correlated intermediates. The language should be softened to state that there is "no experimental demonstration to date of MF-sensitive radical pairs in peroxisomes."

8. The discussion on quantum tunnelling should more clearly distinguish between established principles of tunnelling in enzymatic electron transfer and the specific hypothesis that MF-sensitive spin dynamics create ET bottlenecks in plant organelles. The latter remains a prediction that requires direct experimental testing.

9. Terminology and Typos such as recobination, phonotypic

Comments on the Quality of English Language

-

Author Response

Comment 1: The topic of this review is timely and important. The manuscript assembles disparate findings into a multi-level narrative linking hMF to ROS modulation and plant phenotype. Several sections are clearly written and potentially useful to the field.

Response 1: I thank the reviewer for the careful and insightful evaluation of the manuscript. The comments are highly constructive and have allowed me to significantly enhance the scientific rigor and forward-looking value of this review. The point-by-point response is detailed below, and all changes have been incorporated into the revised manuscript.

 

Comment 2: The term "quantum signature" appears repeatedly from the abstract onward but lacks a clear operational definition. The author should provide an explicit definition early in the introduction: what specific measurement constitutes a quantum signature in plants, under what controls, and what alternative classical explanations must be ruled out to validate the claim.

Response 2: I appreciate the reviewer's concern regarding the precise definition of "quantum signature." I agree that, for a field transitioning from theoretical to experimental validation, a clear, operational definition is critical. I have now added an explicit definition of "quantum signature" at the beginning of section 4. This definition clarifies the specific criteria necessary to validate a magnetic field effect as a quantum phenomenon, particularly within the context of the radical-pair mechanism (RPM). Crucially, the revised text now includes the Isotope Effect (IE) as the most definitive criterion for RPM validation, alongside Magnetic Field Dependence (MFD) and Spin-State Dependence (SSD).

 

Comment 3: Section 4.3 suggests that plant responses to hMF "in continuous darkness" exclude a direct role for photoreceptors. This conclusion should be revised. There is significant in vivo evidence demonstrating that cryptochrome's magnetic sensitivity occurs during its light-independent flavin reoxidation phase, which proceeds in the dark after initial photoactivation. Therefore, a dark response does not exclude cryptochrome but rather helps to pinpoint the specific, magnetically sensitive step in its photocycle. The argument should be reframed to use the dark-response data as evidence for phase-specific magnetosensitivity, which would strengthen the overall mechanistic discussion.

Response 3: I thank the reviewer for this highly insightful and important clarification regarding the magnetosensitivity of cryptochromes. I agree that stating a response in "continuous darkness" excludes photoreceptors is an oversimplification that neglects the key magnetic-sensitive step of the flavin reoxidation cycle. I have revised Section 4.3 to reflect the current understanding that cryptochrome's magnetic sensitivity persists in the dark reoxidation phase following initial photoactivation. This reframing not only corrects the previous logical error but also allows me to use the dark-response data as strengthening evidence for phase-specific magnetosensitivity, thereby deepening the mechanistic discussion related to RPM. The revised text now acknowledges that, while the continuous darkness response rules out the initial photoactivation step as the direct magnetic sensor, it points directly to the magnetically sensitive radical-pair formation and decay during the light-independent reoxidation phase.

 

Comment 4: To add mechanistic precision, the review would benefit from explicitly distinguishing the "conventional" RPM (light-dependent formation of a radical pair involving tryptophan) from the "alternative" RPM (light-independent reoxidation involving a radical pair with superoxide). The manuscript's focus on ROS reduction under hMF aligns strongly with the alternative RPM, and framing the discussion within this context would provide a clearer interpretation of the evidence.

Response 4: I fully agree with the reviewer that explicitly distinguishing between the light-dependent and light-independent radical-pair mechanisms (RPMs) within the cryptochrome cycle is essential for mechanistic precision. This distinction directly strengthens my interpretation, as the observed hMF-induced reduction in Reactive Oxygen Species (ROS) production aligns perfectly with the characteristics of the alternative, light-independent RPM involving the radical-pair with superoxide. I have revised Section 4.3 to explicitly define and differentiate these two mechanistic pathways—the "conventional" (light-dependent) and the "alternative" (light-independent reoxidation) RPM—and to frame my discussion of the ROS data within the context of the latter. This revision provides a clearer and more focused interpretation of the evidence.

 

Comment 5: The review proposes that lower ROS levels under hMF lead to generally "improved plant health." This appears to be an oversimplification. The manuscript itself cites evidence of negative developmental effects under hMF, such as delayed flowering, reduced leaf area, and shorter stems in Arabidopsis. The outcomes are clearly not always positive. The author should revise the conclusions and figure legends to reflect that the effects of hMF are context-dependent, sometimes benefiting certain traits while impairing others. A more balanced perspective is required.

Response 5: I sincerely thank the reviewer for highlighting the need for a more balanced and nuanced conclusion. We agree that summarizing the complex, multi-level responses to a hMF as simply "improved plant health" is an oversimplification, especially when considering the documented evidence of negative developmental effects (e.g., delayed flowering, reduced leaf area) cited within the manuscript. I have revised the concluding paragraph and ensure the corresponding Figure 1 legend is also updated. The conclusion now clearly states that hMF effects are context- and trait-dependent, simultaneously exhibiting both beneficial traits (e.g., reduced ROS and increased stress tolerance in some conditions) and inhibitory effects on development. The revised conclusion now emphasizes that the model demonstrates a causal link from the quantum trigger to a modulated physiological state, rather than a universally positive outcome. This provides a more accurate and scientifically rigorous summary of the current state of research.

 

Comment 6: The review rightly notes that some observations are not fully explained by current RPM theory. This presents an opportunity to articulate testable predictions that could discriminate between a cryptochrome-centric RPM and alternative quantum mechanisms. A dedicated subsection proposing discriminative experiments (e.g., orientation and resonance protocols, phase-specific light paradigms, use of cryptochrome and RBOH mutants, isotope-sensitive tests) would significantly enhance the manuscript's forward-looking value.

Response 6: I fully agree with the reviewer that articulating specific, testable predictions is crucial for advancing the field beyond the current limitations of the cryptochrome-centric RPM and for exploring alternative quantum mechanisms. This feedback significantly enhances the forward-looking value of the review. I have incorporated a new, dedicated Section 5 titled: Discriminating RPM from alternative quantum mechanisms. This new section now serves as a clear roadmap for future research, allowing scientists to conclusively discriminate between the proposed quantum mechanisms.

 

Comment 7: In figure 1, the multi-level model is a strong conceptual tool. At the Subatomic Level, the diagram could be made more specific by depicting the proposed radical pair (e.g., FADH• and O₂•−) instead of generic spheres. Furthermore, the figure would benefit from the inclusion of typical timescales for each level (from nanoseconds for spin dynamics to days for developmental traits) and an indication of the strength of evidence (e.g., well-established, likely, speculative) for each step.

Response 7: I highly appreciate the reviewer's detailed and constructive suggestions for refining Figure 1. I agree that incorporating specific mechanistic details, timescales, and evidence strength will significantly enhance the scientific value and rigor of the conceptual model. I have extensively revised Figure 1 accordingly.

 

Comment 8: The statement that peroxisomal oxidases "do not have a defined RPM" is too categorical. Many are flavin-dependent and could plausibly generate spin-correlated intermediates. The language should be softened to state that there is "no experimental demonstration to date of MF-sensitive radical pairs in peroxisomes."

Response 8: I thank the reviewer for this important clarification. I agree that the original statement—that peroxisomal oxidases "do not have a defined RPM”—is too categorical and potentially overlooks the mechanistic plausibility given their flavin-dependent nature. I have revised this sentence to reflect the current state of experimental evidence accurately. The revised text now acknowledges that while RPM is theoretically possible, there is currently no experimental demonstration of magnetic field-sensitive radical pairs operating within peroxisomes. This revision maintains scientific rigor while avoiding a premature negative conclusion about a potential mechanism.

 

Comment 9: The discussion on quantum tunnelling should more clearly distinguish between established principles of tunnelling in enzymatic electron transfer and the specific hypothesis that MF-sensitive spin dynamics create ET bottlenecks in plant organelles. The latter remains a prediction that requires direct experimental testing.

Response 9: I thank the reviewer for this crucial comment regarding the discussion of quantum tunnelling. I have revised Section 3 to explicitly and clearly distinguish between the established principle of electron tunnelling in ET (a widely accepted quantum phenomenon) and the specific hypothesis that MF-sensitive spin dynamics might create ET bottlenecks in plant organelles. I now state that this latter concept remains a prediction that requires direct experimental testing.

 

Comment 10: Terminology and Typos such as recobination, phonotypic

Response 10: All noted typos have been fixed (recombination, phenotypic). Thank you for noticing these.

Reviewer 2 Report

Comments and Suggestions for Authors

The author is to be congratulated for their valuable contribution to a topic of great relevance in the field. The manuscript highlights an important research area where further investigation is clearly needed to deepen our understanding of the subject. In particular, when discussing clock genes (line 249), it would be highly informative to address the main plant clock genes, their associated metabolites and their functions, as well as how these elements might be influenced by variations in the electromagnetic field.

Similarly, when focusing on antioxidant metabolites (line 252), the discussion could be strengthened by including the analysis of the principal antioxidant metabolites present in the studied plant species and the changes caused by the effect of MF; that could provide a broader and more integrative perspective on the underlying biochemical and physiological processes.

Finally, emphasizing the potential applications of this line of research (Conclusions, line 295), such as improving plant stress tolerance, optimizing crop productivity, or developing strategies for sustainable agriculture, would further enhance the impact and relevance of the study.

Author Response

Comment 1: The author is to be congratulated for their valuable contribution to a topic of great relevance in the field. The manuscript highlights an important research area where further investigation is clearly needed to deepen our understanding of the subject.

Response 1: I am very grateful to the reviewer for the positive assessment and valuable suggestions, which will significantly enhance the depth and relevance of the manuscript. I have addressed each point by incorporating more specific molecular details and strengthening the discussion of practical applications

 

Comment 2: In particular, when discussing clock genes (line 249), it would be highly informative to address the main plant clock genes, their associated metabolites and their functions, as well as how these elements might be influenced by variations in the electromagnetic field.

Response 2: I agree that a more detailed discussion on the plant circadian clock is necessary, as cryptochromes directly link magnetic sensing to clock function. I have revised the discussion to explicitly mention the principal plant clock genes and to hypothesize how MF variations might influence them via the RPM. Accordingly, I have added specific context to the manuscript.

 

Comment 3: Similarly, when focusing on antioxidant metabolites (line 252), the discussion could be strengthened by including the analysis of the principal antioxidant metabolites present in the studied plant species and the changes caused by the effect of MF; that could provide a broader and more integrative perspective on the underlying biochemical and physiological processes.

Response 3: This is an excellent suggestion for strengthening the biochemical component of the review. Given that the core quantum signature is the reduction of ROS, a detailed analysis of subsequent antioxidant changes is essential. We have expanded the discussion to include specific examples of antioxidant metabolites affected by magnetic fields.

 

Comment 4: Finally, emphasizing the potential applications of this line of research (Conclusions, line 295), such as improving plant stress tolerance, optimizing crop productivity, or developing strategies for sustainable agriculture, would further enhance the impact and relevance of the study.

Response 4: I fully agree that highlighting the practical implications of this research is crucial for enhancing its relevance. I have substantially revised the Conclusion section to explicitly detail the high-impact potential applications of manipulating the GMF.

Reviewer 3 Report

Comments and Suggestions for Authors

The review would benefit significantly from enhanced visual support, such as schematic diagrams illustrating key ROS-producing sites (e.g., chloroplasts, mitochondria, peroxisomes, plasma membrane) and the RPM’s molecular mechanism. Additionally, while the narrative is logically organized, the analysis draws on a relatively narrow subset of the available literature. Expanding the discussion to include alternative magnetoreception hypotheses (e.g., iron–sulfur clusters, magnetite-based sensing), a broader range of plant species, and transgenerational or epigenetic studies would strengthen the review’s depth and scholarly impact.

Author Response

Comment 1:The review would benefit significantly from enhanced visual support, such as schematic diagrams illustrating key ROS-producing sites (e.g., chloroplasts, mitochondria, peroxisomes, plasma membrane) and the RPM’s molecular mechanism. Additionally, while the narrative is logically organized, the analysis draws on a relatively narrow subset of the available literature. Expanding the discussion to include alternative magnetoreception hypotheses (e.g., iron–sulfur clusters, magnetite-based sensing), a broader range of plant species, and transgenerational or epigenetic studies would strengthen the review’s depth and scholarly impact.

 

Response 1: I am grateful to the reviewer for the insightful comments aimed at strengthening the visual and scholarly depth of the review. I agree that these topics are highly relevant to the broader field of plant biology.

I acknowledge the request for schematic diagrams. While I agree that the fundamental mechanisms of ROS production and the general RPM are well-illustrated in numerous primary and review articles (and thus fall outside the core focus of this specialized quantum biology review), I recognize the need to better visually connect the quantum trigger to the cellular outcome. Therefore, to enhance visual clarity without summarizing established general biology, I have significantly enhanced Figure 1, which serves as our central conceptual tool. This figure now explicitly includes a detailed depiction of the FADH/O2 - radical pair and integrates timescales and evidence strength for each mechanistic step, clearly linking the quantum event (ns) to the cellular outcome (min-h) and phenotype (weeks). This provides the necessary visual rigor while maintaining focus on the quantum core.

I appreciate the suggestion to broaden the discussion to alternative magnetoreception hypotheses and a wider range of plant species. However, as the mandate of this review is to provide a focused, mechanistic synthesis of the Radical-Pair Mechanism (RPM) and its direct quantum signature (the ROS reduction), I must maintain a sharp focus on the quantum biological pathway.

About alternative hypotheses, I respectfully decline to include extensive discussions on classical mechanisms like magnetite-based sensing or general Fe-S cluster physics, as these would divert the narrative from the RPM's quantum focus.

I fully agree that the future scope should be broadened. We have significantly expanded the final section on "Future Research" to include a detailed discussion on the potential for transgenerational effects via epigenetic mechanisms (DNA methylation and histone modification). This directly enhances the scholarly impact by addressing the long-term biological consequences of GMF variation.

To show broader relevance without adding extensive, non-mechanistic tables, we have integrated new citations throughout the text that reference MF effects in various agricultural crop species (e.g., wheat, maize) where the ROS modulation is hypothesized to occur, demonstrating that the principles discussed are generalized across the plant kingdom.

These focused revisions directly enhance the scholarly depth of the manuscript while rigorously protecting its specialized focus on the quantum biology of the RPM.

Reviewer 4 Report

Comments and Suggestions for Authors

It is preferable not to have symbols in the title such as ROS. This is a mini review with only 53 references. I believe it needs more than 150 references for the study to be comprehensive and complete. At the very least, try to increase the number of references to be from 100 to 150. The review needs additional references and sources.

Comments for author File: Comments.pdf

Author Response

Comment 1: It is preferable not to have symbols in the title such as ROS. This is a mini review with only 53 references. I believe it needs more than 150 references for the study to be comprehensive and complete. At the very least, try to increase the number of references to be from 100 to 150. The review needs additional references and sources.

 

Response 1: I appreciate the reviewer's attention to the manuscript's presentation and scope. I have addressed the stylistic comments and provided a clear justification for the focused bibliography.

The title has been updated (e.g., changing "ROS" to "Reactive Oxygen Species") to adhere to conventional stylistic preferences and ensure clarity for the broadest audience.

I understand the reviewer's concern regarding the number of references in a comprehensive review. However, I respectfully assert that the manuscript's current bibliography is appropriate and scientifically sufficient, given the specialized focus and mandate of this work.

This manuscript is not intended to be a general review of plant physiology or oxidative stress. Its core focus is the intersection of quantum biology (specifically the RPM) and plant responses to the Geomagnetic Field (GMF). This is a highly specific, emerging field where the core literature linking the quantum mechanism to the biological outcome is inherently limited.

The current 61 references were strategically selected to represent the most foundational, high-impact, and mechanistically specific papers necessary to build the multi-level model from the quantum trigger to the phenotype. An arbitrary increase to 100-150 citations would necessitate including broad, general references on ROS production, plant stress, or GMF effects that do not directly contribute to the quantum mechanical narrative, thereby diluting the manuscript's core message and scholarly impact for a journal like Quantum Reports.

I am confident that the literature cited provides a rigorous and complete foundation for the quantum biological model proposed. While I have added several new references in response to the insightful comments of Reviewers 1 and 2 (e.g., on clock genes, metabolites, and transgenerational effects), I have done so strategically to enhance the mechanistic discussion, not merely to inflate the citation count.

Reviewer 5 Report

Comments and Suggestions for Authors

This is excellent review article on the radical-pair nechanism and its quantum role in plant ROS production.The topic is original and very important.The Earth's geomagnetic field is a fundamental environmental signal for life and cognition of organisms evolved on the Earth. The author summarizes published data and explains how radical-pair mechanisms and ROS are involved in metabolic processes and other life processes, with focus on plants.   This review paper manuscript is very useful as it excelently explains the quantum biology behind the radical pairs.  Figure 1 nicely summarizes the central message of this manuscript. All conclusions are consistent.All references are approriate. I am happy to suggest the acceptance of this manuscript. 

Author Response

Comment 1: This is excellent review article on the radical-pair mechanism and its quantum role in plant ROS production. The topic is original and very important. The Earth's geomagnetic field is a fundamental environmental signal for life and cognition of organisms evolved on the Earth. The author summarizes published data and explains how radical-pair mechanisms and ROS are involved in metabolic processes and other life processes, with focus on plants.   This review paper manuscript is very useful as it excellently explains the quantum biology behind the radical pairs.  Figure 1 nicely summarizes the central message of this manuscript. All conclusions are consistent. All references are appropriate. I am happy to suggest the acceptance of this manuscript.

 

Response 1: I am delighted by the positive assessment from the reviewer. I sincerely thank the reviewer for the strong support, kind remarks on the originality and importance of the topic, and their appreciation of the clarity of our explanation regarding the quantum biology of the radical-pair mechanism. The feedback on the consistency of the conclusions and the utility of Figure 1 is highly encouraging.

I appreciate the reviewer's suggestion for acceptance of the manuscript.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors carefully considered the reviewers’ comments and provided reasoned responses.

 

Reviewer 4 Report

Comments and Suggestions for Authors

good efforts