No abstract

The Bambusoideae subfamily includes the fastest-growing plants worldwide, as a consequence of fast internode elongation. However, few studies have evaluated the temporal and spatial distribution of endogenous hormones during internode elongation. In this paper, endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) were detected in different developmental internodes during shoot elongation by immunolocalization. Immunohistochemistry showed that IAA was mainly present in the shoot apex, leaf sheath primordia, parenchymal cells, and vascular tissues. During internode elongation and maturation, the IAA signals decreased significantly and then increased slightly, with the weakest signals observed in the rapidly elongating internode. Based on immunogold localization, most IAA signals were detected in the cytoplasm and nuclei of both parenchymal and fiber cells, and few signals were detected in cell walls in the unelongated and elongating internodes. After the completion of internode elongation, additional IAA signals were detected in the secondary walls of both parenchymal and fiber cells. Immunohistochemical localization of ABA showed that ABA signals decreased with internode elongation and maturation, with the weakest signal observed in the internodes of 3-month-old shoots. In addition, few ABA signals were detected in the shoot apex. The strongest IAA and ABA signals in unelongated internodes suggested that both hormones participated in the mediation of internode differentiation but not in the rapid elongation. Moreover, IAA was involved in secondary cell wall deposition.