A sat/chl measured at a common temperature decreased as a result of higher growth temperature and lower growth irradiance (Table 2). This was most clearly so when measured at 10 °C, whereas the growth temperature effect was small in HL-plants when measured at 22 °C, particularly in the Hel-1 accession (Tables 1, 2). Similar

responses were obtained when considering the other KPT-330 concentration capacity-related variables expressed per unit chlorophyll, Rubisco and V Cmax (Tables 1, 2). The growth irradiance effects are well known for many species including Arabidopsis (Murchie and Horton 1997; Walters et al. 1999; Evans and Poorter 2001; Bailey et al. 2004). The growth temperature effect on capacity variables per unit chlorophyll has not been specifically described for

Arabidopsis. However, it has been found for cold-tolerant species such as Plantago asiatica (Hikosaka 2005), S. oleracea (Yamori et al. 2005) and Aucuba japonica (Muller et al. 2005). Not surprisingly, the cold-tolerant A. thaliana is also capable of this form of acclimation to temperature. The shift in the Fedratinib molecular weight balance between light harvesting and photosynthetic capacity at the chloroplast level, as evident from the capacity-related variables per unit chlorophyll, was also reflected in the chlorophyll a/b ratio (Tables 1, 2). The low ratio at low growth irradiance and high growth temperature is associated with a large investment in LCHII and thus light harvesting (Anderson et al. 1995; Huner et al. 1998). Photosynthetic rates are necessarily low at a low growth irradiance, which does thus not require much investment in photochemistry. A low growth temperature requires a large investment in the see more photochemical apparatus to compensate for the reduced enzyme activity. The balance between photon absorption and utilization in photochemistry may be sensed by plants and used for the adjustment to the light and temperature condition (Huner et al. 1998; Bräutigam et al. 2009). The adjustment U0126 purchase thus contributes to an efficient utilization of resources for the

photosynthetic apparatus. The balance between the electron transport and carboxylation capacities The CO2 response curves (Fig. 2) were used to derive the carboxylation capacity (V Cmax) and the electron transport capacity (J max). The J max was difficult to derive from the curves of the HT-plants measured at 10 °C. The HTHL-plants showed a strong limitation by TPU, which prohibited the estimation of J max, but did not interfere with the estimation of the C i where V Cmax and RuBP-regeneration co-limit A sat. Some of the HTLL-plants of both accessions showed no clear transition from the RuBP-saturated to the RuBP-limited range at 10 °C, which indicates that the J max must be high relative to V Cmax, but it prohibited its quantitative estimation. The mean C i where V Cmax and J max co-limit A sat, further referred to as the co-limitation C i, was on average 45 Pa at the growth temperatures.