Shoot differentiation from Dendrocalamus brandisii callus and the related physiological roles of sugar and hormones during shoot differentiation

Abstract Only a few calli regeneration systems of bamboos were successfully established, which limited the research on the physiological mechanism of callus differentiation. In this study, we successfully established the callus differentiation systems of Dendrocalamus brandisii (Munro) via seeds. The results showed that the best medium for the callus induction of D. brandisii seeds was basal Murashige and Skoog (1962) (MS) media amended with 5.0 mg l−1 2,4-D and 0.5 mg l−1 kinetin (KT), and the optimal medium for shoot differentiation was the basal MS media supplemented with 4.0 mg l−1 6-benzylaminopurine (6-BA) and 0.5 mg l−1 1-Naphthaleneacetic acid (NAA). Callus tissues had apparent polarity in cell arrangement and developed their own meristematic cell layers. Alpha-amylase (α-amylase), starch phosphorylase (STP) and sucrose synthase (SUSY) played a dominant role in carbohydrate degradation in callus during shoot differentiation. The pentose phosphate pathway (PPP) and TCA pathways were up-regulated in the shoot-differentiated calli. The dynamics of 6-BA and KT contents in calli were consistent with their concentrations applied in medium. Indoleacetic acid (IAA) synthesis and the related signal transduction were down-regulated, whereas the endogenous CTK contents were up-regulated by the exogenous cytokinin (CTK) application in shoot-differentiated calli, and their related synthesis, transport and signal transduction pathways were also up-regulated. The down-regulated signal transduction pathways of IAA and abscisic acid (ABA) revealed that they did not play the key role in the shoot differentiation of bamboos. Gibberellins (GAs) also played a role in shoot differentiation based on the down-regulation of DELLA and the up-regulation of PIF4 genes. The overexpression of DbSNRK2 and DbFIF4 genes further confirmed the negative role of ABA and the positive role of GAs in shoot differentiation.