Fig. 4.

Expression of arginine biosynthetic genes in various poplar tissues during or after senescence. (A) Expression of AS, OTC, CPS and CP genes in laminae. Cysteine protease (CP) was used as a marker of the senescence state (Bhalerao et al., 2003). (B) Expression of AS, OTC and CPS genes in petioles. (C) Expression of AS, OTC and CPS in 2-year-old stems. Total RNAs were extracted at different time periods during autumn and winter and 300 ng of total RNAs were reverse transcribed into cDNA. The ubiquitin (Ubq) gene was amplified and used as internal control. Analyses were performed by RT–PCR in triplicate. Signal intensities were normalized to the constitutively expressed poplar ubiquitin gene. Values are expressed as the mean ± s.e. of three replicate experiments. For a given gene, values with the same letter are not significantly different, according to ANOVA at P < 0·05.