Pool RNA samples

[ifhmn]

I got low concentration of RNA samples in mature plant compared to the immatured using Qiagen RNA extraction kit. The concentrations are around 50-80ng/uL and using these concentrations, I cannot synthesis 1 ug of cDNA. I've been tried to pool identical samples by ethanol and isopropanol precipitation few times and resulted in degradation of RNA when I checked on gel.
Is there are any way to improve the concentration of my RNA?
Should I pooled them before of after the DNase treatment?
Usually, how much RNA can be used to synthesis cDNA for qPCR? Is it still ok if I used 0.5ug or lower for my qPCR?

[relaxin]

If you use RNeasy mini kit, you can follow its RNA cleanup protocol to concentrate the pooled RNA on one spin column, treat with DNase, and elute the pooled RNA in 50 ul.

My qPCR protocol uses 2 ug total RNA for cDNA synthesis, but only 2 ul of 1:10 dilution of the cDNA per tube are used for qPCR. So 0.5 ug total RNA may be sufficient for cDNA synthesis. You may dilute cDNA 1:2 instead of 1:10.