Salinity Eustress Increases the Biosynthesis and Accumulation of Phenolic Compounds That Improve the Functional and Antioxidant Quality of Red Lettuce

Round 1

Reviewer 1 Report

The manuscript entitled “Salinity eustress increases biosynthesis and accumulation of phenolic compounds that improve functional and antioxidant quality of red lettuce “seems to be interesting, however the quality has to be improved. I have some comments, please find them below:

 

In Food vegetables as Red lettuce, quality parameters and secondary metabolites production are so important. However, the yield and commercial parameters are essential as well. The author used root dry biomass as a parameter which is not essential for a plant whose edible part is the shoot!! Also leaf dry biomass is better used as a parameter for medicinal plants and spices. At the same time the authors ignore some essential yield parameters such as shoot fresh weight, shoot length and plant size or width that could indicate the commercial status of a vegetable plant under stress. So I highly recommend adding these parameters to figure1.

I also recommend adding a photo or scheme diagram to show the difference in plant size under different salt treatments.

 

Some minor English spelling and grammar check is also needed

Author Response

Reviewer 1:

The manuscript entitled “Salinity eustress increases biosynthesis and accumulation of phenolic compounds that improve functional and antioxidant quality of red lettuce “seems to be interesting, however the quality has to be improved. I have some comments, please find them below:

R: Thank you for the positive global evaluation of our manuscript. We are pleased since our complete and hard work was well understood and in your opinion is a good and interesting contribution.

In Food vegetables as Red lettuce, quality parameters and secondary metabolites production are so important. However, the yield and commercial parameters are essential as well. The author used root dry biomass as a parameter which is not essential for a plant whose edible part is the shoot!! Also leaf dry biomass is better used as a parameter for medicinal plants and spices. At the same time the authors ignore some essential yield parameters such as shoot fresh weight, shoot length and plant size or width that could indicate the commercial status of a vegetable plant under stress. So I highly recommend adding these.

R: Thank you very much for your positive comments. We have incorporated shoot fresh weight and number of leaves as essential yield parameters, please see figure 1.

I also recommend adding a photo or scheme diagram to show the difference in plant size under different salt treatments.

 R: Thank you for this valuable observation, we agree. Please see the figure 2.

Some minor English spelling and grammar check is also needed

R: Done, please see the body text of the new manuscript version.

Reviewer 2 Report

In this study, authors conducted quite a lot of work for the determination of phenolic compounds from red lettuce leaves by HPLC-DAD-ESI-MS/MS and indicated that the highest phenolic concentration and antioxidant activity, were reached by moderate salt stress (50 mM NaCl) applied for 15 days without affecting photosynthetic activity and biomass production of lettuce plants, and showed that the moderate stress (50 mM NaCl) application across fifteen days in red lettuce grown in a hydroponic system,induced a stimulation on the biosynthesis of polyphenols, flavonoids, and improved antioxidant activity, while increasing DPPH scavenging capacity, without significantly affecting the growth and biomass production of lettuce plants. This work provided a potential use as tool to increase the biosynthesis and accumulation of bioactive secondary metabolites through the application of moderate stress in red lettuce as eustressor on functional quality of red lettuce under hydroponic conditions and subjected to increasing salinity. The study would help to provide new information for further study on the elucidation of the positive stress (eustress) mechanism in red lettuce.

The authors conducted extensive physiological and biochemical analysis of red lettuce plants growing under hydroponic conditions and subjected to different levels of salinity (0, 50, 100, 150 and 200 mM NaCl) to explore the moderate salt stress (50 mM NaCl) application across fifteen days in red lettuce grown in a hydroponic system, could enhance nutritional and functional attributes of red lettuce, which could be very interesting for the readers of this journal.However, I have some important concerns for this manuscript, the comments as follows:

 

Minor Comments:

1. Authors should double check the writing typos in the article and be consistent with the writing standard and style of the abbreviations, figure and table legends.
2. Since the authors displayed the experiment results under moderate salt stress or severe salt stress, but almost all information is not about their molecular mechanism of salt stress in the introduction part. Please authors supplement and add some important references.
3. Please authors provide the high-definition photos about experimental materials.

 

Author Response

Reviewer 2:

In this study, authors conducted quite a lot of work for the determination of phenolic compounds from red lettuce leaves by HPLC-DAD-ESI-MS/MS and indicated that the highest phenolic concentration and antioxidant activity, were reached by moderate salt stress (50 mM NaCl) applied for 15 days without affecting photosynthetic activity and biomass production of lettuce plants, and showed that the moderate stress (50 mM NaCl) application across fifteen days in red lettuce grown in a hydroponic system,induced a stimulation on the biosynthesis of polyphenols, flavonoids, and improved antioxidant activity, while increasing DPPH scavenging capacity, without significantly affecting the growth and biomass production of lettuce plants. This work provided a potential use as tool to increase the biosynthesis and accumulation of bioactive secondary metabolites through the application of moderate stress in red lettuce as eustressor on functional quality of red lettuce under hydroponic conditions and subjected to increasing salinity. The study would help to provide new information for further study on the elucidation of the positive stress (eustress) mechanism in red lettuce.

R: Dear reviewer, thank you for your positive consideration and understanding of our study. In fact, we also consider the possibilities to use saline eustress as a potential tool to improve the nutraceutical quality of lettuce, since also can represent the use of some water sources of low quality, which are day by day more abundant.

The authors conducted extensive physiological and biochemical analysis of red lettuce plants growing under hydroponic conditions and subjected to different levels of salinity (0, 50, 100, 150 and 200 mM NaCl) to explore the moderate salt stress (50 mM NaCl) application across fifteen days in red lettuce grown in a hydroponic system, could enhance nutritional and functional attributes of red lettuce, which could be very interesting for the readers of this journal. However, I have some important concerns for this manuscript, the comments as follows:

Authors should double check the writing typos in the article and be consistent with the writing standard and style of the abbreviations, figure, and table legends.

R: R: Thank you for your comment. We have fully checked all the manuscript. Please see the body text of this new version.

Since the authors displayed the experiment results under moderate salt stress or severe salt stress, but almost all information is not about their molecular mechanism of salt stress in the introduction part. Please authors supplement and add some important references.

R: Thank you very much for your positive comments, we have incorporated some key mechanistic pathways regarding salt stress. Please see lines 51-61.

Please authors provide the high-definition photos about experimental materials.

R: Done, this aspect was also mentioned by R1, please see the new figure 2.

Reviewer 3 Report

Dear Editor/Autors,

The work submitted for review: "Salinity eustress increases biosynthesis and accumulation of phenolic compounds that improve functional and antioxidant quality of red lettuce", is interesting due to the use of a potential stressor, which in a lower concentration can mobilize plant growth and increase the concentration of biologically active compounds. 

However, I have some comments to the Authors:

In the introduction, please re-arrange the first sentence, especially this fragment: "are associated with a lower risk of developing non-communicable diseases". 

Where did the choice of such a variety of lettuce come from? Is it less sensitive to salt ions than the other most commonly used lettuce varieties? Please include this information in the Material and Methods section. It would also be worth checking in the future: a few of the most popular varieties and the same concentrations of NaCl on stimulation of defense mechanisms, and thus the content of biologically active compounds.

Were there any changes, e.g. in the length and width of the leaves? in Plant Appearance? It was observed (although not statistically significant) a slight decrease in both the weight of the leaves and the roots after the application of the 50 mM dose. Maybe it is worth checking the dose, e.g. 30 mM.

 

 

 

Author Response

Reviewer 3:

The work submitted for review: "Salinity eustress increases biosynthesis and accumulation of phenolic compounds that improve functional and antioxidant quality of red lettuce", is interesting due to the use of a potential stressor, which in a lower concentration can mobilize plant growth and increase the concentration of biologically active compounds.

R: Thank you for the positive comments regarding our manuscript.

However, I have some comments to the Authors:

In the introduction, please re-arrange the first sentence, especially this fragment: "are associated with a lower risk of developing non-communicable diseases". 

R: Done, please see lines 31-32 in the new version.

Where did the choice of such a variety of lettuce come from? Is it less sensitive to salt ions than the other most commonly used lettuce varieties? Please include this information in the Material and Methods section. It would also be worth checking in the future: a few of the most popular varieties and the same concentrations of NaCl on stimulation of defense mechanisms, and thus the content of biologically active compounds.

R: Thank you for your comment. Please see line 90. Regarding your suggestion, we take note for incorporating in our next studies which can be of interest for the commercial production of lettuce under hydroponics.

Were there any changes, e.g. in the length and width of the leaves? in Plant Appearance? It was observed (although not statistically significant) a slight decrease in both the weight of the leaves and the roots after the application of the 50 mM dose. Maybe it is worth checking the dose, e.g. 30 mM.

R: Thank you for this valuable observation, we agree. Please see the figures 1 and 2 in the new manuscript version.