le MDA est la conséquence de la peroxydation des lipides membranaires

Le stress thermique provoque un stress oxydatif induit et donc la peroxydation des lipides; si vous avez des variétes où le MDA est plus faible que dans les témoins et donc il semblerait que ces variétés soient les plus résistantes au stress

MDA is the consequence of the peroxydation of membrane lipids. Heat stress provoque an oxydatif stress and the peroxydation of lipids. If you have some stressed plants with low MDA perhaps theses plants are less sensitive

same variety showing less MDA in stress and more MDA in control. How it possible??

Its true that one expects higher levels of ROS production and in turn increased levels of MDA under high temperature stress conditions. But MDA is not just one criteria and there are many more physiological assays (electrolytic leakage (EL), Fv/Fm, total Chl estimation etc.) to confirm these findings.

Possibly you can try above assays and

1- Do verify your findings by repeating atleast twice and to sure of what you got.

2- If still you find your certain varieties having less MDA content than respective non-treated control, possibly these varieties have enhanced inherent thermotolerance and their this capability is effective only when they are subjected to heat stress.

Tolerance to heat is one of the inherent mechanisms of plants linked to oxidative stress. Lipid peroxidation is just one of the several parameters to measure oxidative stress. It is possible that rice vairieties differ in their sinsitivity to heat stress. The ones which are more sinsitive are expected to show up increased lipid peroxidation than the ones which are more heat-tolerant. Your findings should be corroborated with other oxidative parameters like antioixidative enzyme activities, memebrane damage, and generation of ROS under heat stress.

in sensitive plants MDA content should be more, less in tolerant lines in stress condition

should be equal or light variation in un stress condition in both sensitive and tolerant ones.

MDA contents are reduced in tolerant crop under stress condition while in sensitive crop these are increased. Lipid peroxidation is just one of the parameter to measure oxidative stress. Your should be compared it with other oxidative parameters like antioixidative enzyme activities, memebrane damage, and generation of ROS under heat stress.

MDA contents are reduced in tolerant crop under stress condition while in sensitive crop these are increased. Lipid peroxidation is just one of the parameter to measure oxidative stress. You should be compared it with other oxidative parameters like antioixidative enzyme activities, memebrane damage, and generation of ROS under heat stress. You can down load my paper from research gate

Oxidative stress physiology is much sensitive one to abiotic stress. Normally, high oxidative damage to lipids (lipid peroxidatin: LPx) and proteins (protein carbonylation) occurs as a function of the level of abiotic stress. If you are getting less LPx under stress condition then irrespective of the antioxidant levels, be sure that same higher pattern you are getting for protein or DNA damage (DNA fragmentation or unwinding) along with ROS level. The reason is (high) ROS normally do not discriminate to attack all the above three macromolecules. If only LPx is low under stress but not protein and DNA damage are low then you may have to repeat the experiment carefully to estimate LPx. Even you then get the same result then just go for estimating the lipid content of your tissue. Possibly due to low lipid content in the tissue under stress condition than control, you are getting low LPx under stress condition.

First you have to identify what sort of stress you were provided. It is really important to know the nature of stress,I dont know weather you provided biotic or abiotic stress.. So please identify. Second Please select other physiological and biochemical paramters to confirm the rice either sensitive or tolerance. Rice plants are really sensitive to enivormental factors

you should be very careful while designing the protocol to asses varieties

Under heat stress, there is generation of ROS under oxidative stress for both tolerant and sensitive plants. However, for tolerant the level of ROS is less than for sensitive ones but compared to their control this level is greater for both tolerant and sensitive. ROS attack membranes, nucleic acids, lipids, etc..So, I suggest verifying the antioixidative enzyme activities, memebrane damage, and generation of ROS under heat stress with lipid peroxydation (by MDA content) that you determined. Normally, control plants can't show quantity of MDA more than stressed ones but as I said verify by studying the other parameters.

Some of the above discussions emphasize on antioxidants molecules. I do not think he has to give importance on that if he is already getting low MDA under stress than control. Because MDA content is a reflection of oxidant (ROS) and antioxidant balance in cell. That means antioxidant guys have already did their job and still which might not be sufficient to reduce ROS in control and as a result high MDA level has obtained in control. Some times high or low antioxidant levels are observed at high ROS and their (ROS ) mediated MDA level or any other damage level. So antioxidants are measured only to complete the story to describe the high or low oxidative stress. Means, oxidative stress (high MDA in this case) are the consequence that has already happened irrespective of antioxidant activities in control. I think he must repeat his experiment after checking all aspect correct then to quantify lipid contents at the stress condition. Because if lipid content could be low at the experimental condition then irrespective of low or normal ROS level than control, he might get low MDA. In his case he might have a very high antioxidant levels also experimental groups. It ion s not a surprising result. The simple reason might be that he may have high antioxidants or very low lipid contents (that to PUFA) in experimental groups

I agreed Dr. Paital point of view. That is why I suggest to repeat the experiment and carefully designed. Dont forget rice is not an easy plant to study. I am also working the some korean Trangenic rcie plant here ta GM Criop center. I suggest you should have atleat ten plants per replicate and you should have 4 replicates it means your data would be the mean of forty plant

Hi

you know lipid peroxidation is resulted by oxidative stress and caused by active oxygen like H2o2. ROS production caused by oxidative stress results lipid peroxidation and consequently causes the accumulation of MDA which is an important index of hazard of all stresses, therefore when plants are subjected to all kinds of stress, tolerant plants show lower amount of lipid peroxidation measured by (MDA) than sensitive plants, because tolerant plants have more antioxidant activities than sensitive plants.

Allsalamo alekom

First ,you had not determine the heat stress precisely ,because slite increase in many factors( abiotic ) and applying low amount or weakend (avirulent) biotic you get phsiological state called priming or conditioning the tissue for later increase giving the tissue tollerance to the factor ,add to this from all the above answers i recomend to also estimate antioxident substances ,enzymes, hydrogen peroxide content,DNA and read carefully your protein profile your heat may evoke heat stress protein which provide defence way to your rice via which alleviate the abiotic stress.

Thank you very much to all for your response.

I think that for these varieties control is not a real control and in the condition of control these varieties are stressed

If choosing variety is a problem then you may contact CRRI, Cuttack, odisha, India.

It would be better to study other antioxidant parameters along with MDA. Also monitor damage to DNA and protein. It could be possible that your control group was stressed by other factors.

MDA is done to check the cell damage (Lipid per-oxidation level). Your results are contrary. Better to correlate the data with ROS levels and electrolyte content. if possible check any genetic aberrations/DNA damage. Also check the reproduciblity of your data with large sample values.

MDA  level is not the only way to identify plant stress response. I think you have to examine some other attributes including physiological mechanism. However, if you want to interpret the results regarding your hypothesis it could be possible but you need to thorough study of research articles 

MDA content is correlated with cell membrane integrity that could be identified by measuring electrolyte leakage. For control plants MDA content should be less than stressed plants and so the electrolyte conductivity. However, the cell membrane integrity should be more in control plants than stressed ones. I suggest checking electrolyte leakage, membrane integrity, ROS levels, etc.