In Arabidopsis thaliana the basal leaves are green to slightly purplish in colour, with maximum chlorophyll pigment activity in blue wavelength on this plant particularly at 642-665 nm. Chlorophyll a (C55H72O5N4Mg) and Chlorophyll b (C55H70O6N4Mg) while Chlorophyll-a is a universal pigment and its counterpart Chlorophyll-b is found in the higher plants. Structurally chlorophyll-a molecule is having a molecule less of water and hence may be seen to a step towards adaptation toward the terrestrial life from water during evolution. Keeping in mind constant light supply scenario ideally it should be chlorophyll-b should have more concentration than chlorophyll-a in saline conditions. In drought conditions therefore there would be more of Chlorophyll-b than that of Chlorophyll-a. The critical balance lies in availability of water. Chloroplast being a pigment with autonomous DNA influences most of this maternal traits such as leaf colour, pigment concentration and thereby chlorophyll content.

Hello. Drought stress often brings other stresses, such as the alterations in micro-and macronutrients, and this may lead to the changes in pigment composition. Additionally, the conversion of Chl a into Chl b in any conditions is possible. Have you considered such hypothesis?

That's it! And an increase in PSII reaction centres while the antennae size decrease. Dear Muhammad, I am quite interested whether you have checked Chls pools after rehydration?

Stress might causes the conversion of chlorophyll to pheophytin...

drought and saline stress decrease the content of chlorophyll. For a good function of photosyntthesis chla/chlb wille be constant; we know also that chla is more sensitive than chlb and the decrease is higner

Considering such aged Arabidopsis plants (6 weeks!), probably you should better to think about chlorophyll degradation, but not biosynthesis. It is known that chlorophyll degradation occurs from Chl a. For degradation of Chl b, this pigment must be first converted to Chl a by two sequential enzymes, Chl b reductase and hydroxyl methyl Chl a reductase (HMCR). Higher Chl b accumulation under drought stress condition may suggest that either or both enzyme activities or expression may be decreased compared to the salt stress condition. I think there is no report about such drought-stress dependent reduction of both enzymes. Probably, it is better to compare the expression levels of Chl b reductase (NOL/NYC) and HMCR in both conditions.

Osmotic stresses are known to induce a decrease in the effeciency of the photosynthesis, a decrease in total chlorophyll (chla and chlorophyll b will be both decreasing). Chlorophyll a's variation is more important. You might observe the decrease in chlorophyll b later (for a plant water content ranged between 50 and 25%). My advice is to do an optimization test for all your measurements and applied stresses before proceeding to final results and conclusions (for eg.: apply diferent types of drought stress in different planters and different water deprivation, measure chlorophyll 3 times for the same sample and calculate the mean..)

Dear all,

I worked in senescence leaves and at the initial stage of leaf senescence I often found an increase of chlorophyll b.Tatsuru Masuda in the previuos answer explained very well the process and I believe that it is your case.

Dear Muhammad,

Although I’m specialized in cyanobacteria that contain Chl a only, I’ll try to give you some clues. However, you didn’t provide very important information. Namely, comparison of the total Chl a+b amounts and the Chl a/Chl b ratio in the plants under both salt and drought stresses with the unstressed plants of the same age (importantly, leaves of the same order should be analyzed in all plants). As I know, both kinds of stress should result in reduction of the total Chl a+b content. However, the magnitude of such reduction depending on the particular stress may be informative. Additionally, this would be very informative to compare alteration in the Chl a / Chl b ratios in the stressed plants with that in the control plants. Upon these comparisons, one can judge about Chl species under stress conditions more precisely, i.e., whether amount of particular Chl species increases/or decreases (and to what extend) or remains essentially the same. The thing is that Chl b (along with Chl a) specifically associates with the outer light-harvesting complexes, LHCs (LHCI and LHCII), whereas Chl a is the only Chl present in both PSI and PSII core complexes (PSI binds about 70% of Chl if compared with PSII). Thus, change in Chl a/Chl b ratio is likely a result of change in stoichiometry of particular Chl-binding pigment-protein complexes, i.e., LHCI, LHCII, PSI and PSII that in turn reflects alterations in biogenesis (accumulation) of all these complexes under particular conditions. There are a lot of approaches to detect accumulation of these complexes in plants, especially in Arabidopsis as it is the famous plant model in study of photosynthesis. However, before planning any experiments, read literature. I’m 100% sure that you will find enough answers with regard to your data in publications because salt and drought stresses have been studied for a long time, especially on Arabidopsis, and Chl a/b levels are among the most important parameters assessed in any experiments. Try literature search in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) or just in Google Scholar (http://scholar.google.com) using word combinations as follows: “plant drought stress”, “plant salt stress”, “Arabidopsis drought stress”, “Arabidopsis salt stress”. If you have no free access to any paper of your interest, contact me at [email protected]. I will send you the enquired PDF(s).

Have fun!

Alex

One note to the previous writing, LHC complexes assigned to PSI (LHCI) and PSII (LHCII) also may have various compositions per se, i.e., may be composed of various particular Chl-binding proteins depending on conditions (I can send you a couple of papers). Therefore, I assume that the thing, which should be taken into account, is not only a stoichiometry between main Chl-binding complexes (PSI, PSII, LHCI, LHCII) but the composition of the LHC complexes (particular, LHSII) itself. Additionally, as far as I know, at least photosystems (e.g., PSI) may bind various Chl amounts retaining the same apo-protein content, i.e., at the given time point some Chl-binding niches can be occupied by Chl molecules or can be empty. This concerns antennae Chls a within PSs. Perhaps, this is also the case for the LHC complexes – I don’t know exactly. Look in literature, as suggested above.

And also look for the information about regulation of the Chl a-Chl b cycle in context of the biogenesis of photosynthetic apparatus in plants. Chl b is synthesized from Chl a (in some minor cased from chlorophyllide a with following esterification of the chlorophyllide b) and degraded via Chl as well. Namely, firstly, Chl b is converted to Chl a and then Chl a is degraded. Importantly, Chl a-Chl b cycle is crucial for differential biogenesis (i.e., differential accumulation) of the particular Chl-binding complexes (PSI/II, LHCI/II) as this Chl cycle is involved in re-distribution of Chl species between the above complexes.

To my mind, the above comments from Yagut Allahverdiyeva, Aid Fatiha, Fatima Awwad, Tatsuru Masuda and Antonio Ferrante are of impotence.

To explain the changes in chl-a/chl-b ratio, follow the advices Tatsuru Masuda wrote, he is absolutely right! Besides the possibility of biosynthesis inhibition, one always should consider the possibility of break-down processes, especially under stress conditions.

Otherwise, it would be interesting to isolate and separate the chlorophyll-protein complexes on green PAGE and identify the changes of separate complexes. Other possibility is to isolate intact chloroplasts, dilute their suspensions to low concentration (and to the same chlorophyll contents of stressed and control leaves) to avoid reabsoption and measure the fluorescence emission (possibly 77 K) or absorption spectra. The differences in the spectral characteristics would indicate the changes in the pigment-protein complexes what influences the photosynthetic activity.

Drs Masuda and Boeddi as well others have well explained the complex system of photosynthesis RC and Antennae, but it is still crucial to point out that here you got an evidence reversed under salinity. It is advisable to better clarify other macro characters like leaf thickness, leaf specific weight, light absorption, type of light and possibly leaf duration. Another question that may arise is if these are adaptations possibly reversible, or stresses. Water stress in ephemerals is a relative thought. Death and apoptosis with pheophorbide a CHla catabolite is a possibility but is the beginning of an end.

Dear Bela Böddi, I agree. However, to discern between biosynthetic and degradation process more or less clearly, we should know concrete experimental conditions applied. Actually, they are not mentioned in the question. For instance, if plants grown under standard conditions were quickly shifted to strong stress conditions and rapid reduction of, e.g., Chl, level(s) is observed, one really may make a conclusion about degradation processes (e.g., degradation of pigment-protein complexes, activation of Chl catabolism enzymes, etc.). This is short-term response. On the other hand, if the stressful conditions are moderate, and the plants were initially adapted to them and grow under these conditions for a long time, one may conclude that reduction of pigment (pigment-protein complex) level is not due to activation of degradation processes but rather due to inhibition of biosynthesis processes. This is long-term response.

And, of course Dr. Tatsuru Masuda is right, but change in activity of the enzymes involved in Chl metabolism (anabolism or catabolism either) can not be considered a priori as the major primary reason of alteration of Chl (Chl a or Chl b either) content because one should consider levels of the Chl-binding complexes – not Chl itself. Namely, change in rates of biosynthesis or degradation of the Chl-binding apo-proteins may be the primary reason determining levels of the pigment-protein complexes, and the activation/inhibition of Chl metabolic enzymes may be the secondary events.

Finally, you mentioned right experimental approaches. However, as I mentioned in the former comment, many data have already been published about plants and concretely Arabidopsis stressed by increased salt concentration or drought (ass well as many other data that also may be relevant). Thus, one, first, should study literature before doing any experiments to avoid wasting time and money.

P.S. Guido Bongi also is absolutely correct. In fact, we know nothing about exact experimental conditions applied, measurements performed and the data obtained to judge the phenomenon indicated in the question. A lot of factors and aspects have to be taken into account to make more or less adequate conclusion.

… on the other hand, Chl availability per se may influence the rate of accumulation of photosynthetic apo-proteins, therefore levels of photosynthetic pigment-protein complexes. This was demonstrated concretely for accumulation of D1, PsaA, PsaB, etc. in plants and cyanobacteria as well. The question about the primary reasons causing specific alterations in photosynthetic apparatus under specific conditions is one of the most difficult to answer. This is the subject of many studies concerning sensing and transduction (adaptive response to) environmental signals. Anyway, we should know concrete experimental conditions – all details, including specificity of the measured samples – leaves, tissues, tissue amounts, light regime, etc., as assumed by Dr. Guido Bongi.

Dear all and especially Alexey Shpilyov Thanks for comprehensive detail, now I would like to provide the conditions of experiment briefly. After 2 weeks of drought stress, I measured Relative Water Content (RWC). Then the whole plant was grounded to fine powder in liquid nitrogen. The weighed amount of powder was used to measure chlorophyll contents as mg per gram Dry weight, rather than Fresh weight as after drought stress how can I get Fresh weight. The RWC was used to determine dry weight.

I am using reporter line as Wild type whose Chla/Chlb ratio is 0,61, and two mutants M1 with 1,01 and M2 with 0,67 ratio after drought stress. These mutants are not chlorophyll mutants.

These ratio(s) have same trend even when I used the weight of plant samples unadjusted with RWC.

And for total chlorophyll contents Reporter line 2,705, M1 2,226 and M2 with 2,252 mg/g DW.

Hello. Maybe it would be worthy to check all the parameters not only aftee the stres stage, but also after the recovery. Good luck!

Dear Muhammad,

Actually, it is still difficult to judge your results even basing on the additional data you provided. First of all, you should have an idea, what you want to see in your experiment or what you are looking/testing for. To have such an idea, you should know what already is known about phenotypic and molecular alterations in Arabidopsis (and other plants) under salt and drought stresses. To plant you experiment, you should know how such stress conditions are provided for in laboratory – mild stress, strong stress – and what data are observed under such stress conditions. Then, basing on your purposes, you should choose some, already published protocol, to stress the plants in your lab. Following the chosen protocol, measure Chl a & Chl b contents (and other parameters of the interest) so as it is described in publication(s) representing respective experimental stress protocol(s). After performing the experiment, compare your data with the published data with regard to the wild type. Judge, whether your data are solid or require additional repetitive experiment (the later also are usually carried out to obtain statistically valid data). ‘Judge’ means how much your data are similar to the data published (for the WT plant) if you applied essentially the same stress conditions (in comparison with the described in publication(s)). If your aim is to test some mutants – test them in parallel with the WT, i.e., run the mutants through all conditions applied for the WT in the experiment. Then, see whether the mutant(s) display(s) some difference vs. WT in the experiment. But, first, study from literature, how other researches perform such experiment(s) and what is already known from such experiment(s). Go step by step accurately to compare every your step (and the observations on the steps) with analogous steps described by other researches in publications. Fix all your data and then give them to others for interpretation if required. But, I think, you will be able to interpret your data yourself pretty well after primary reading necessary literature about salt and drought stresses made on Arabidopsis :) Good luck!

P.S. If you need some papers (PDFs), let me know.

You should analyze the Pheophytin a and b contents in order to understand if the Chl a and b are being degraded or simply if they are not being synthesized.

Correct

For analysis of chlorophyll ,you could use Dimethyl sulfoxide as solvent .Take the fresh leaf sample and incubate in Dimethyl sulfoxide in dark for 24 hr. Then you measure the chl.Then there will not be any degradation of Chl a. Chl a degrades in bright light. automatically concentration of Chl. b will be more .It may be one of the reason. Chlorophyll analysis should be done in dim / dull light

In this respect, salt stress is known to reduce the life span of plant leaves, resulting in accelerated senescence and as a consequence pigment degradation. Generally, when the leaves of plants started to senesce, there was a gradual loss of chlorophylls. Moreover, salinity could affect chlorophyll of leaves through the inhibition of its synthesis and/or the acceleration of its degradation or through impairment of the carhoxylation capacity which in turn inhibits electron transport . Furthermore, it was declared that the suppression of plant pigments under salt stress is probably due to the interference with Mg2+ ion absorption which is involved in chlorophyll build-up and/or to the increase in growth inhibitors, particularly ethylene and ABA. .The reduced pigment content under salt stress may be due to the interference of salt ions with the de novo synthesis of proteins, the structural component of chlorophyll, rather than the breakdown of chlorophyll. However, Djanaguiraman and Ramadass (2004) ascribed the suppressed pigment contents under salt stress to the increased activity of chlorophyllase enzyme or disruption of fine structure of the chloroplast as well as the instability of pigment-protein complex. Additionally, ROS generated due to salt stress can cause pigment breakdown leading to the loss of carbon-fixing ability in chloroplasts.

There is a common observation that leaf yellowing can occur when leaves have had low water potentials for a considerable time. Chlorophyll is more sensitive to drought than carotenoids and consequently the ratio of total chlorophyll to carotenoids decreases with increasing drought severity. Kamel et al. (1995) working with cotton plants (Gossypium barbadense cv Giza 75) reported two opposite trends regarding the relative concentration of photosynthetic pigments throughout the experimental period in plants under constant water stress. The first was a reduction in the different photosynthetic pigments comparing to the normally irrigated plants, while the second was an enhancing effect. Subjecting cotton plants to drought whether during the vegetative growth or at maximum flowering, showed a decrease in the concentration of chlorophylls a and b and carotenoids. However, at budding or flowering a remarkable increase occurred compared with controls.

For degradation of Chl b, this pigment must be first converted to Chl a by two sequential enzymes, Chl b reductase and hydroxyl methyl Chl a reductase (HMCR). Higher Chl b accumulation under drought stress condition may suggest that either or both enzyme activities or expression may be decreased compared to the salt stress condition.

leaf thickness and specific leaf weight SLW, variations coupled to apoptotic agents like chlorophyll a degradation intermediates, can generate a panoplia of responses from early senescence to photooxidation to apparent Chla increases for SLW. I think in reports there is little space for speculation, but we can not estimate vriables a posteriori after grinding. Probably next time a complete pigment analysis, pheopytins, and growth cycle and analysis. P.see Ibasami an PPB the pheophorbide induced apotosis and take care in speculations valuable at chloroplast level. Good question anyway

I missed an H, please take the previous as Hibasami and PPB . Incidentally he talks about cancer but any PPB activity can be guessed also at plant level. All obscure art the way of guess if a way

The occurence of chlorophyll a and b in plants particularly fungi play an important role for their life. generally all pigments are necessary for photosynthetic processes. the domination of each pigment according the type of fungal group.

The reduced pigment content under salt stress may be due to the interference of salt ions with the de novo synthesis of proteins, the structural component of chlorophyll, rather than the breakdown of chlorophyll. However, the suppressed pigment contents under salt stress to the increased activity of chlorophyllase enzyme or disruption of fine structure of the chloroplast as well as the instability of pigment-protein complex. Additionally, ROS generated due to salt stress can cause pigment breakdown leading to the loss of carbon-fixing ability in chloroplasts

Yes, ROS generation is usually the secondary stress accompanying primary impairment of plant tissue integrity.

If you want to know if the diminution of chlorophyll is the consequence of the degradation you can measure the pheophytin a and the pheophytin b

I give up with this topic. The question was about Chl a b ratios in LN ground tissue. Given the short life cycle of the species and the lack of biochemical tests run at that time, there is no way for a diagnosis, chloroplasts are not leaves, fungi are out of question and ephemerals shorten life on stress. ROS and oxidations usually follow an apoptotic signal, but we can spend of lot of might be and science wanderings. With the best

ehmmm… Really, I don’t know what to say more on the basis of the data provided by Dr. Muhammad. To my mind, some accurate experiments definitely are required to derive sufficient batch of reliable data for interpretations/speculations. Anyway, there is some discussion/speculations below… Somewhat borrowing, I’d say. Sorry... ha ha :)

Muhammad Shafiq wrote:

‘2 weeks of drought stress … I am using reporter line as Wild type whose Chla/Chlb ratio is 0,61, and two mutants M1 with 1,01 and M2 with 0,67 ratio after drought stress. These mutants are not chlorophyll mutants. These ratio(s) have same trend even when I used the weight of plant samples unadjusted with RWC. And for total chlorophyll contents Reporter line 2,705, M1 2,226 and M2 with 2,252 mg/g DW.’

Dear Muhammad,

Firsts, you didn’t tell what was going on with the unstressed plants, i.e, WT, M1 & M2. These are the real controls (especially the WT) to compare your data. Second, you stressed the plants for 2 weeks (by drought). Did they grow under stress conditions or just died slowly? If the plants grew, one may presume some adaptive responses in them, i.e., inhibition of some biosynthetic processes, which however occurred and were predominating vs. catabolic processes in the plants despite the stress. But the rate of biosynthetic processes was just inhibited (but not abolished at all), and, perhaps, the metabolic network was re-arranged. On the other hand, if the plants died (slowly), one may presume that the break-down processes were predominating vs. biosynthetic processes. Is that difference clear? This is rather important thing to judge your results and the stress impact(s) generally, i.e., either in terms of inhibition/re-arrangement of biosynthetic processes or in terms of predominating of the destructive processes.

Anyway (although I don’t know exactly), let’s consider that (during two weeks) your plants didn’t die or at leas were in a dormant state. What can we see from your data? The first fact is that both mutants possess less total Chl content than the WT. The second fact is that the mutants (especially M1) have higher relative Chl-a content (higher Chl-a/Chl-b ratio). As I mentioned in one of the former messages to you, Chl-b is specifically bound to the LHC (LHCI & LHCII) complexes in the plant photosynthetic apparatus. As you probably know, these complexes are external antennae in plants providing more excitation energy for PSI and PSII to optimize photosynthetic performance. As some researches mentioned here correctly, drought stress (which essentially mimics senescence) has secondary effect such as photo-oxidative stress (due to generation of higher level of reactive oxygen species (ROS), particularly singlet oxygen). Thus, under photo-oxidative stress conditions (caused by the drought stress) the plants may reduce external antenna size, i.e., either degrade LHCI & LHCII (if they stopped grow) or synthesize less amounts of these complexes (this may happens in growing or not growing plants as well). The first reason of such regulatory response (degradation or inhibited synthesis either) is to reduce excitation pressure on photosystems, thereby to reduce level of generated ROS. Here, I don’t discriminate between LHCI and LHCII because it’s just impossible to do basing on your data. But, among other photosynthetic complexes, PSII (D1 protein in it) is known to be the most vulnerable to photoinactivation by absorbing excess light energy. Thus, reduction of LHCII may be the case to avoid overexcitation of PSII. However, THE RESPECTIVE PARAMETERS IN THE UNSTRESSED PLANTS ARE UNKNOWN FOR US to make such a conclusion. [However, I’m sure that something informative has already been published in literature by other researches to interpret your data, at least with regard to the WT of Arabidopsis.]

The second reason (which, however, doesn’t contradict the former one, but may be predominant) may be that the plant (I mean WT) reduce(s) content of subcellular structures and the rate of metabolisms to pass through the difficult time safely, i.e., just to save vitally important nutrients during stress.

Actually, stress conditions (especially strong ones) cause rather broad and sharp physiological and structural alterations. Change of one parameter, e.g. Chl content(s) may be just a tip of the iceberg and may be caused by other underlying reasons. However, change in some parameters may be indicative to make conclusion(s) about other physiologic/structural alterations as, for instance, Chl content(s) may somehow be indicative for the level of photosynthetic complexes.

About mutants:

By your data, the mutants, M1 & M2, may have lower content(s) of LHCI & LHCII if compared to the WT under drought stress conditions as they have higher Chl-a/Chl-b ratio (i.e., less relative Chl-b content) and reduced total Chl amount (i.e., reduction of the total Chl level may be because of reduction of Chl-b content that in turn may be due to lower content of the Chl-b-binding complexes, LHCs). Considering photosynthetic apparatus, I always mean Chl-binding complexes – not a Chl itself – because Chl (any species) doesn’t exist in a free form in vivo (probably, only very negligible amount). It is always bound to some protein matrix (the only exception is chlorosomes in green bacteria). Thus, when one determines Chl level (in general meaning), this means that one determines content of Chl-binding protein complexes. Also, one should take into account that the content of Chl-binding pigment-protein complexes may be resulting from the rate of synthesis/degradation of proteins (protein matrix), chlorophyll and other co-factors (carotenoids, lipids, etc.). So, in many cases (taking into account enormous complexity of the adaptive/regulatory network) the question about primary signal and sensor triggering micro and macro homeostatic alterations in an organism is frequently an open question. If one see altered Chl content, it doesn’t necessary mean that this alteration is due to change in activity of the chlorophyll biosynthesis/break-down enzymes. This phenomenon, for instance, may be due to alteration in synthesis (or stability) of the Chl-binding proteins. And vice versa, Chl (and Chl intermediate) availability is known to regulate accumulation of the Chl-binding proteins and biogenesis of the whole photosystems.

But.. in fact, these are bla bla speculations I’m making here :) Also.. many measurements may be really wasteful because one may assess hundreds of parameters for really nothing if there is no clear idea in the head. Actually, the thing you should find out (one among the most important things) is the gene(s) determining alteration(s) in your mutant(s). Thus:

First, study literature about stresses of your interest, i.e., how such stresses are performed. Different protocols may be published in reports with regard to the same stress (e.g., drought stress). Do trial stress tests in parallel using different conditional parameters: different, light intensities, different water supply, perhaps, varying some other parameters – nutrients and so on. The same for the salt stress, i.e., use different salt concentrations in media. Perform several trial stress tests simultaneously. One trial test should be different from another one by one parameter only. For example, you perform 3 stress experiments. In the 1st and 2d ones, the same light intensity is applied, but the water supplies are different (higher in the 2d one). In the 2d and 3d experiments, water supply is the same (higher than in the 1st one), but light intensity is different. And so on…

Second, chose the stress protocol that shows the most prominent phenotypic differences in the mutant(s) as compared with the WT: growth retardation, bleaching, some lesions, etc. Repeat the experiment (and also in additional experiment test State 1/State 2 transition as one of the basic parameters). And yes, as suggested here by Dr. Renata Baczek-Kwinta, also perform the recovery experiments and see what happens.

Third, measure the most notable parameters: total Chl contents, Chl-a, Chl-b, Chl-a/Chl b ratio, Chl biosynthesis intermediates (precursors and catabolites), photosynthetic capacity (by oxygen evolution or/and by usage of fluorometry), see PSI, PSII, LHCI, LHCII (by 77 K fluorescence emission spectroscopy on chloroplasts, isolated thylakoid membranes, photosynthetic complexes), native (green) protein electrophoresis, western-blot, microscopic analysis… In fact, almost unlimited number of parameters can be measured. But … to chose the parameters ‘number one’ read literature and judge the WT with the published data first. See, which changes WT displays, how they correlate with the literature data and how they are interpreted by the authors. Then, see how much your mutant(s) is(are) different from the WT with regard to the above mentioned parameters (parameters ‘number one’). But, before performing some sophisticated analyses (molecular, spectroscopic, etc), use simple methods to assess the parameters altered sharply: Chl & carotenoid content(s), oxygen evolution, sensitivity to inductors of oxidative stress, ability to recover after stress – up to you. Finally, assess these parameters in the mutant(s) with use of appropriate molecular biology, spectroscopic and other techniques.

Forth, continuing performance of some necessary biochemical/biophysical/physiologic assays, analyze genome in the mutant(s) to find out mutation(s), which led to the mutant phenotype(s). It’s not a simple thing, but you can find in literature how to proceed. When the gene (mutation) is localized, you will already know what to do next because that time you will already know enough :)

But first of all, again: )))

Before doing anything, go to PubMed or/and Google Scholar and try search using ‘Arabidopsis drought stress’, ‘Arabidopsis salt stress’, ‘plant drought stress’, ‘plant salt stress’ and other word combinations or your art :)

I don’t think that I can tell anything more. Good luck!

Vey simple. It can be done very precisely colorimetrically using the method of Arnon, D.I. (1949) using OD measurements at 645 and 663 nm. Acetone (80%) may be used as a solvent of extraction

In condition of drought stress chlorophyll a is more sensitive than chlorophyll b and the content of chlorophyll a is smaller than control conditions