Dear Shobhita

i send you my best wishes and respect, the following article will help you

I wish you all the best

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC540261/

Some people autoclave the soil before planting. Are these wild-type plants?

I am not entirely sure about the problem you have. But we have had problems with thrips which results in white spots on leaves and damaged flowers. We used biocontrol methods (specific mite species) and good sanitary practices in the growth chamber rooms to control them and have had success ever since. 

thanks everyone for your suggestions. 

actually we are facing drooping of inflorescence at the reproductive phase of the plant and after some whole plant get collapsed so that no seeds set. vegetative phase is quite good only face problem after flowering.

I know this is an old post, but just in case you still need advice I thought I'd make a comment. What ecotype are you using? The only ecotype of Arabidopsis plants that will stand up on their own after bolting is Landsberg erecta (Ler). Other common ecotypes (Columbia, Ws, etc.) all have stems that are not strong enough to stand upright without support. I'd carefully tie my plants to wooden skewers with string and to keep them separate from each other. So, what you are seeing is completely normal for the most of the common ecotypes.