qPCR. Sugarcane seedlings inoculated either with or without 33.1::
pNKGFP were sampled, and the roots and aerial parts of these plants were
separated. To separate the bacterial cells from the sugarcane surface, the
root was incubated in 2 ml of PBS buffer at 28°C for 2 h, and the bacterial
cells were harvested by centrifugation. Total bacterial DNA was extracted
as described by Araújo et al. (1). After this surface sterilization, the total
DNA of the root and aerial plant parts was extracted by the cetyltrimethylammonium
bromide method, according to Doyle and Doyle (22).
The qPCR analysis was performed in a 25-l final volume, which
contained 12.5 l of the master mix of Platinum SYBR green qPCR
SuperMix-UDG (Invitrogen) and the PPNKF and PPNKRII primers (10
Meach). Aliquots of the master mix (20 l) were dispensed in the wells,
and 5 g of DNA (50 ng/l) was added as a PCR template. The qPCR
cycles consisted of a denaturation step at 94°C for 5 min, 40 cycles at 94°C
for 30 s, and a final step at 61°C for 15 s. The plasmid fragment quantification
was performed using an iCycler iQ real-time PCR instrument (Bio-
Rad Laboratories Inc.). Four replicates in duplicate were used, and a standard
curve was obtained for every run using a known copy number (105 to
108) of the linearized plasmid pNKGFP.