The role of auxin in cell separation in the dehiscence zone of oilseed rape pods

Abstract

Concentrations of both free and conjugated indole-3-acetic acid (IAA) were studied during development of pod wall, dehiscence zone and seeds of Brassica napus pods. A decrease in auxin content prior to moisture loss in the pods was observed specifically in the dehiscence zone, which was correlated with a tissue specific increase in β-1,4-glucanase activity. Furthermore, treatment of the pods with the auxin mimic 2-methyl-4-chlorophenoxyacetic acid resulted in a delay of 10 d of β-1,4-glucanase activity and concomitant cell separation in the dehiscence zone. This indicates that the activity of hydrolytic enzymes involved in cell separation in the dehiscence zone is regulated by auxin activity. Comparison of parthenocarpic pods with seeded pods pointed to the seeds as the source of IAA. Levels in the dehiscence zone of these pods were low over the entire sampling period, while cell separation in the dehiscence zone was delayed by about 4 d. These results indicate that a low level of auxins in the dehiscence zone is necessary for dehiscence to take place, but other factors may also be important.