Physiologia Plantarum 134: 293–302. 2008 Copyright ª Physiologia Plantarum 2008, ISSN 0031-9317 Effect of growth temperature and total non-structural carbohydrate accumulation on growth coefficient in Petunia  hybrida petals Takushi Hachiya a,b, * and Ko Noguchi b a Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan b Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Correspondence *Corresponding author, e-mail: takushi@biol.s.u-tokyo.ac.jp Received 15 November 2007; revised 1 May 2008 doi: 10.1111/j.1399-3054.2008.01132.x 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  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 construc- tion 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. Introduction Respiration has been partitioned into two functional components, construction respiration and maintenance respiration (Hesketh et al. 1971, Thornley 1970). Con- struction respiration is defined as respiration involved with the supplies of carbon skeletons and biosynthetic energy (ATP and NAD[P]H) for the production of new tissue. The construction respiration rate (R g ) can be cal- culated as follows: R g ¼ gGR ¼ gRGRDW; where g, GR, RGR and DW denote growth coefficient, growth rate, relative growth rate, and dry weight, respectively. The growth coefficient, g, is the respiratory cost (usually expressed as glucose or carbon equivalent) consumed per unit DW synthesized. This coefficient has been estimated from linear regression of the specific respiration rate vs RGR (regression method; Hesketh et al. 1971, Thornley 1970, van Iersel 2003) or from chemical composition or heat of combustion of biomass (theoret- ical method; McDermitt and Loomis 1981, Nobel et al. 1992, Vertregt and Penning de Vries 1987, Williams et al. 1987). Carbohydrates are substrates for respiration and energy production and for the biosynthesis of other compounds (McDermitt and Loomis 1981, Penning de Vries et al. 1974, Poorter 1994, Williams et al. 1987). In most Abbreviations – CC, construction cost; DW, dry weight; EABP, estimated annual aboveground biomass produced; FW, fresh weight; g, growth coefficient; GR, growth rate; R g , construction respiration rate; RGR, relative growth rate; TNC, total non- structural carbohydrate. Physiol. Plant. 134, 2008 293