Fig. 4.

Model of hormonal and metabolic regulation of AR formation in shoot tip cuttings in the context of the plant genotype and selected environmental factors at the stock plant and the cutting levels. The genotype as indicated by the blue circular area provides the genetic background for all responses. The parenthesized number of illustrated cuttings and orange arrows indicate the chronological situations, when cuttings are developing on the stock plant (1), freshly excised (2a) and thereafter either immediately planted and cultivated under light (3) or first incubated in the dark (storage or transport, 2b) before planting (3). A, B and S in circles indicate the shoot apex, stem base and fully developed source leaves as important functional units of the cuttings. Following initially balanced (bal) sink activity between A and B (stage 2a), plus vs. minus signs at B vs. A (stages 2b and 3) indicate the relatively higher sink activity in B compared with A. Black arrows indicate the directions of action. Red arrows indicate the direction of polar auxin transport (PAT). AA, amino acids; CH, carbohydrates; Suc, sucrose; Gln, glutamine; Asn, asparagine; SE, sink establishment; RC, recovery; MT, maintenance. Further explanations are provided in the text.