FIGURE 1.

Photosynthetic capacities, nocturnal retention of starch, and vein densities of fully expanded leaves acclimated to high light (HL), low light (LL), and 1 week after transfer from low to high light. Photosynthetic capacity (light- and CO₂-saturated rates of oxygen evolution determined in a leaf disc oxygen electrode at 25°C; Delieu and Walker, 1981) relative to that determined from fully expanded leaves of spinach (A) and pumpkin (D) grown under HL, fractional area of the chloroplasts filled with starch grains in spinach (B) and pumpkin (E) quantified from cross-sections of palisade cells (examined with electron microscopy) from fully expanded leaves collected predawn, and vein densities of fully expanded leaves of spinach (C) and pumpkin (F). Plants were germinated and grown under a 9-h photoperiod of 150 (spinach) or 100 (pumpkin) μmol photons m^-2 s^-1(low light = LL), or under a 14-h photoperiod of 1000 μmol photons m^-2 s^-1 (high light = HL), or developed under LL and subsequently transferred for 1 week to HL (LL→HL), all at 25°C/20°C day/night temperature. Only leaves that had expanded fully under LL (hatched portion of the LL→HL column) were characterized 1 week after transfer to HL (filled portions of the LL→HL column). Means (n = 3) ± standard deviation depicted in B, C, E, and F. Asterisk (*) and ** indicate significant differences at p < 0.05 and p < 0.01, respectively, and n.s. = not significantly different (Students t-test). Data redrawn or recalculated from Amiard et al. (2005). Photosynthetic capacities of leaves from HL plants and LL transferred to HL plants were both significantly higher than leaves of LL spinach plants (A), and photosynthetic capacities of pumpkin leaves were significantly different from each other for all three growth conditions (D).