Tillering promotion by paclobutrazol in wheat and its relationship with plant carbohydrate status

In grasses, tillering is at least in part controlled by auxins and cytokinins. The participation of other hormones is less clear, but there is evidence that gibberellins may also play a role, as suggested by earlier tillering in plants treated with gibberellin synthesis inhibitors. This study evaluates the effect of paclobutrazol (PBZ), a gibberellin synthesis inhibitor, on tiller development in wheat. Experiments were conducted under controlled conditions, and PBZ was supplied to the root medium. PBZ caused a significant advancement of the onset of tillering compared with the controls. However, no effects on site filling were observed. Earlier tillering in PBZ-treated plants was associated with a promotive effect on the rate of leaf appearance. PBZ-treated plants had lower height, higher chlorophyll content, a trend to a higher quantum yield of photosystem II, increased dry matter content and a higher concentration of soluble sugars. The results suggest that an increased carbohydrate status in PBZ-treated plants may lead to a faster leaf and tiller development without modifying site filling. A proposed model of the relationships between gibberellins, carbohydrates, rate of leaf appearance and tillering is discussed.