Effect of growth temperature and total non-structural carbohydrate accumulation on growth coefficient in Petunia x hybrida petals.

It is widely believed that growth coefficient [g, respiratory cost consumed for synthesis of a unit dry weight (DW)] is independent of growth temperature. However, some studies using regression analysis indicated an increase in g at high temperatures. These two conflicting conclusions may be affected by the differences in total non-structural carbohydrate (TNC) accumulation between growth temperatures. Here, we evaluated whether g is independent of growth temperature in Petunia x hybrida petal after excluding TNC from DW. We also examined changes in g during petal development. We measured amounts of carbon, nitrogen, minerals and TNC and theoretically estimated construction cost and g. The results showed that the estimated g greatly changed with age and differed between growth temperatures. The estimated g was markedly increased by excluding TNC from DW. The effect of accumulation of TNC on the estimated g was observed at later stage of petal development. At earlier stage, the estimated g depended on the N amount. These results indicate that g changes with growth temperature and suggest that TNC accumulation must be taken into account in the estimation.