Metabolic Changes Associated with the Sink-Source Transition During Sprouting of the Axillary Buds on the Sugarcane Culm Gino Boussiengui-Boussiengui 1 & Jan-Hendrik Groenewald 1 & Frederik C. Botha 2,3 Received: 16 June 2015 /Accepted: 8 December 2015 # Springer Science+Business Media New York 2015 Abstract Sucrose, glucose and fructose concentrations, and sucrolytic enzyme activities were measured in the developing shoots and internodes of sprouting sugarcane setts (Saccharum spp, variety N19). The most striking change dur- ing the sink-source transition of the internode and germination of the axillary bud is a more than five-fold induction of cell wall invertase in the germinating bud. In contrast, soluble acid invertase is the main sucrose hydrolytic activity induced in the internodal tissue. A cycle of breakdown and synthesis of su- crose was evident in both the internodes and the shoots. During shoot establishment, the sucrose content decreased and the hexose content increased in the internodal tissues while both sucrose and hexoses continuously accumulated in the shoots. Over the sprouting period internode, dry mass was reduced by 25 and 30 % in plants incubated in a dark/light cycle or total darkness, respectively. Sucrose accounted for 90 % of the dry mass loss. The most significant changes in SuSy activity are in the synthesis direction in the shoots resulting in a decrease in the breakdown/synthesis ratio. In contrast the SuSy activity in the internodal tissue decrease and more so in the synthesis activity resulting in an increase in the breakdown to synthesis ratio. Keywords Sugarcane (Saccharum spp) . Sucrose . Germination . Cell wall invertase . Invertases sucrose synthase Abbreviations CWI Cell wall invertase (EC. 3.2.1.26) NI Neutral invertase (EC 3.2.1.26) SAI Soluble acid invertase (EC. 3.2.1.26) SuSy Sucrose synthase (EC 2.4.1.13) Bq Becquerel V max Maximum catalytic activity HEPES N-2-hydroxyethylpiperazine-N’-2-ethanesulfonic acid EDTA Ethylenediaminetetraacetic acid NAD β-nicotinamide adenine dinucleotide HK Hexokinase G6PDH Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) ATP Adenosine 5′-triphosphate PGI Phosphoglucose isomerase (EC 5.3.1.9) UDP Uridine 5′-diphosphate ATP Adenosine 5′-triphosphate PVPP Polyvinyl polypyrrolidone Introduction The regulatory mechanisms which determine the pattern of carbon allocation between the different plant organs and regulate source-sink transitions are of prime impor- tance in determining crop establishment and perfor- mance (Roitsch 1999). Sugars play an important role in the regulation of carbon partitioning between source and sink (Herbers and Sonnewald 1998; Roitsch 1999). Communicated by: Ray Ming * Frederik C. Botha fbotha@sugarresearch.com.au 1 Institute for Plant Biotechnology, University of Stellenbosch, Private Bag XI, Matieland 7602, South Africa 2 Sugar Research Australia, PO Box 68, Indooroopilly 4068, Australia 3 The Queensland Alliance for Agriculture and Food Innovation (QAAFI) University of Queensland, Saint Lucia, Australia Tropical Plant Biol. DOI 10.1007/s12042-015-9158-8