Figure 8.

Carbonyl, ubiquitin conjugates and 20S content of total proteins extracted from Arabidopsis root seedlings. The roots of eleven-day-old seedlings grown in control medium without (A) and with paraquat (PQ; B), or in the hydrotropic assay medium without (C) or with PQ (D). Equal amounts of total protein (5 mg) were used to measure protein carbonyl, ubiquitin (Ub) conjugates and 20S proteasome content by slot blot, as described in Materials and Methods. Ub conjugate content was the most responsive and sensitive parameter (A–D). Root seedlings of the nhr1 and wav2-1 mutants had higher Ub conjugate content under control conditions (A), while in the presence of paraquat (PQ) or in the hydroptropism assay medium, the same mutants showed a clear decrements (B–C), indicative of more active Ub conjugate-degrading machinery. The ahr1 mutant had the highest Ub conjugate content in the hydrotropism assay medium, whether with or without PQ. Carbonyl and 20S content showed minor but significant variations. Values are expressed as fold increases, where the wild type (Wt) in control medium is considered as 1. Means and standard deviations (SD) were calculated from three biological replicates.