Figure 1. Semi-quantitative RT–PCR analysis of AtPPC1–AtPPC3, and AtPPCK1 and AtPPCK2 gene expression in +P_i and −P_i Arabidopsis suspension cells (A) and seedlings (B).

Levels of mRNA were measured using primers specific for AtPPC1–AtPPC3, AtPPCK1 and AtPPCK2, and AtACTIN2. AtACTIN2 was used as a reference to ensure equal template loading. All PCR products were measured at cycle numbers determined to be non-saturating. Template concentrations needed to achieve non-saturating conditions for primer pairs as tested for −P_i cells or roots of −P_i seedlings are indicated in parentheses. Control RT–PCR reactions lacking reverse transcriptase did not show any bands. ‘P_i refed’ (A) denotes 7-day-old −P_i suspension cells that were supplied with 2.5 mM P_i and cultured for an additional 24 and 48 h. d, day.