The Physiological Mechanism of Melatonin Enhancing the Tolerance of Oat Seedlings under Saline–Alkali Stress

Round 1

Reviewer 1 Report

The manuscript titled ' The Physiological Mechanism of Melatonin Enhancing the Re-sistance of Oat Seedlings Under Saline–Alkali Stress' by Wang et al analyzed the effects of exogenous MT on morphogenesis, photosynthetic physiology, hormone levels and ionic homeostasis of oat seedlings under saline stress however some clarifications are needed to improve the study as below.

1. Section 2.4 MT treatment, the cultured seedlings were subjected to three different treatments, S45, S+MT, and seedlings grown generally in 50% Hoagland nutrient solution as CK, why no Hoagland nutrient solution was added to S45 and S+MT.

2. Recent studies have shown that melatonin plays an important role in coping with biotic and abiotic stresses, while role of melatonin in plants is still unknown, and researchers are debating whether it acts as an antioxidant or a growth regulator. In this study, the author measured a series of physiological indicators, what were the authors' conclusions through this study?

3. Li−6400XT is a product of LI-COR Corporate, please correct it.

Moderate editing of English language required

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Interesting work. It was good to see that melatonin could significantly enhance the ability of oat seedlings to resist saline-alkali stress. However, I still have some questions and suggestions about the manuscript.

1.  A discussion on hierarchical clustering analysis of agronomic and physiological indicators should be added to the manuscript.

2.  The antioxidant defence system of plants plays an important role in stress resistance, but why did this study not determine relevant indicators of antioxidant defence system?

3. The nitrogen form in the Hoagland nrtrient solution was mainly nitrate nitrogen, why nitrate nitrogen was chosen as the nitrogen source, and wheather too much nitrate nitrogen would inhibit the root growth and development of seedlings and affect the physiological and metabolic activities of plants?

4. Why did most of the physiological indicators differ at 0 d, were there differences in the seedlings themselvves, and did this affect the results of this experiment?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The MS "The Physiological Mechanism of Melatonin Enhancing the Resistance of Oat Seedlings Under Saline–Alkali Stress' is the result of extensive reseach with anormous parameters measured. The results are clear. However, the MS is lacking the emphasized novelty. In the introduction it should be said what physiological mechanisms are already known for the effects of MT on plant tolerance to abiotic stresses and to saline-alkali stress in particular. In the conclusion the authors should state what new information to the available earlier knowledge this study added as it is the the aim of this research. Otherwise it is not clear  how "results of this study provide a new basis for further elucidate the physiological mechanisms of exogenous MT application for improving saline–alkali tolerance".

The lines are not numbered, which makes difficult to indicate other minor concerns.  Still they are as foolows:

First two sentences of the abstract are not acceptable. Fist one is a nonsense as Melatonin ... plays an important role in regulating plant growth and development NOT IN ORDER to enhance plant tolerance to abiotic stresses. It is the opposite - effects of MT on plant tolerance result in improved growth and development. Besides, MT has direct effects on growth and development. The second sentence is not understandable and needs editing.  In some places extensive editing of English is requited as well. 

References 12-15 can be added by available extensive reviews on MT effects.

Please, indicate the origin of MT used in the experiments.

Is there ref to the preparation of MT solution? What is Tween-20?

2.4. Oat is a monocot and therefore has one cotyledon.  Why do you write  "after the two cotyledons of oat seedlings were fully opened"?

2..3.  - Why 'seedling breeding'? What do you mean by breeding?

Round the figures to the wholes, for example 21% instread of 21.28%

Fig. 1. Why seedling height in CK do not increase with time? (no differnce between day 0 and 4).

Fig. 1.  There is no significant effect of MT on main root length, but in the text it is described like 21 and 6% increase.

3.2. Chlorophyll a and b - a and b should be italicazed throughout the text.

Authors write that MT alleviated chl degradation, then that MT had an effect on chl synthesis. In fact, it is not known what process was affected, You can just state the content of chl. 

All the discussions on the correlations are very doubtful. Correlation may mean changes in the same direction, but the processes may not be related. Just parallel changes. I doubt that Pn, Gs, Ci, Tr and chl content changes related solely to the changes in IAA and GAs content.  

The authors use both terms "resistance" and "tolerance". They are not absolute synonyms. Please, choose. 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I consider this revised manuscript suitable for publication.

Reviewer 3 Report

The revised version of MS is improved according to recommentations.