Please also take a look at this old RG discussion thread.

https://www.researchgate.net/post/Is_chlorophyll_b_content_higher_than_chlorophyll_a_in_the_leaves

Well done good question. Heavy metals affect the activity of photosynthesis in the plant. In other words, it affects chlorophyll A as it is important in the process of photosynthesis because the chloroplast contains chlorophyll a higher than B and when exposed to stress with heavy metals the opposite will happen, ie, the less chlorophyll A and become less than the amount of chlorophyll b. Thank you and good luck.

Its a natural composition of plants, but it also varied depending on the environment.

Chlorophyll a content is always higher than chlorophyll b. Chlorophyll b is more adaptive to stress condition.

Dear Samrina,

the onset of senescence in your plants may be the cause of the low chl a/b ratio: this has been observed in many instances (see, for example, Kura-Hotta et al., Plant and Cell Physiology 28 (1987) 1321–1329). Moreover, if you grew your plants in a controlled environment under a low PPFD, the chl a/b ratio might have been relatively low since the early stages of development.

Best wishes,

Carlo

Thanks a lot

so it means that under heavy metal stress condition chlorophyll "a" is lower and "b" is higher,and under control condition (without any stress) plant should have opposite situation i.e., chlorophyll "a" higher and "b" is lower.

am i right??

Dear Samrina Ahmed if heavy metal is disturbing chloroplast biogenesis chl b synthesis could be favoured. but if your plants are growing up under low light conditions, in that case, the chl a/b ratio decreases. I recommend to make a search in google scholar for cases where chl b is increased (or chl a/b ratio decreased) related or not to plant stress, heavy metal stress, low light growth and chlorophyll a biogenesis.

Dear Samrina Ahmed. I am facing the same problem where my chlorophyll b content is increasing and a decreasing under heavy metal stress. I have gone through all the answers. Kindly can anyone please suggest any suitable reference to explain the above fact? Thankyou in advance

How even a recommended answer here is just a Copy-Pasted exactly copy from other Web sites and online books? Plagiarism? Let's see, for example this one:

http://www.phschool.com/science/biology_place/biocoach/photosynth/chlorophyll.html

but why?

By typing a simple search here in RG( "chl a/b ratio metal stress" ), I did find these articles may help you to understand the mechanism that regulates Chl a/b ratio and metal stress:

Article The chl a fluorescence intensity is remarkably insensitive t...

Article Magnesium-Deficiency Effects on Pigments, Photosynthesis and...

Chapter Regulation of Photosynthesis Under Metal Stress

There are many more articles here in RG, about that quite interesting topic

Thankyou so much Dr. Ronald Maldonado Rodriguez.