The reduced photosynthetic capacity relative to light harvesting maintains photon PKC inhibitor absorption high in the light limited shade conditions, whereas investment in a high photosynthetic capacity would not result in sufficient return as photosynthetic rates are predominantly low.

The reduced amount of photosynthetic proteins per area in shade requires a lower number of chloroplasts. This in turn requires less space in mesophyll cells (Terashima et al. 2011), which makes the shade-grown leaf thinner. Shade leaves thus have reduced costs per area in terms of nitrogen (Pons and Anten 2004) and of carbon as the leaf dry mass per area (LMA) is lower (Poorter et al. 2009). A similar shift in the balance between light harvesting and photosynthetic capacity is observed with variation in growth temperature (Hikosaka et al. 2006). The amount of Rubisco and other components that determine photosynthetic capacity expressed per unit area and per chlorophyll increases at low temperature. This compensates for the reduced activity of the photosynthetic proteins, whereas light harvesting is largely unaffected by temperature (Hikosaka 1997). Acclimation to high growth irradiance and learn more low growth temperature is thus generally reflected in high Rubisco content per unit leaf area and per chlorophyll, a high chlorophyll a/b ratio and

thick leaves (Hikosaka 2005; Muller et al. 2005). An additional phenomenon associated with acclimation to low growth temperature is increased investment in the capacity of assimilate processing. Warm-grown plants measured at low temperatures typically show inhibition of photosynthesis at high [CO2] and/or low [O2] (Sage and Sharkey 1987; Atkin et al. 2006; Sage and Kubien 2007). The high rate of production of triose-phosphate by the chloroplast cannot be met by the reduced capacity of its utilization in sucrose synthesis as a result of a lower protein activity at low temperature. This leads to sequestering of phosphate in the cytosol, which limits ATP production in the chloroplast. The Compound C cost Limitation of photosynthesis by triose-phosphate utilization (TPU) is avoided in the cold by increasing

the capacity of sucrose synthesis (Stitt and Hurry 2002). The light saturated photosynthetic rate in the next absence of limitation by TPU can be limited by two processes. Limitation by the carboxylation capacity of Rubisco at ribulose-bisphosphate (RuBP) saturation (V Cmax) occurs at low [CO2], whereas at higher [CO2] the regeneration of RuBP as determined by the electron transport capacity (J max) limits photosynthesis. The limitation by these two processes can be distinguished in CO2 response curves (Farquhar et al. 1980). The J max /V Cmax ratio varies little between species (Wullschleger 1993; Leuning 1997) causing the [CO2] where co-limitation by the two processes occurs to be close to the intercellular CO2 partial pressure (C i) at ambient values or somewhat above (Stitt 1991).