Figure 7.

Comparison of C requirements for leaf growth and maintenance in the sampled leaf zones with C provided through depletion of profiled C reserves. This figure compares, for each leaf interval, the amount of C needed to support the measured leaf growth and respiration in the mature leaf area to the amount of C provided from C reserves in the growth zones and the mature leaf tissue and, during the day, photosynthesis. C provided from reserves was estimated by calculating the difference in these resources at the beginning and end of each time interval. Values were summarized for the three growth zones and interpolated for the total mature area of the leaf based on iodine staining for starch. The middle part of the leaf is not accounted for. “Carbohydrates” refers to starch, Suc, Glc, and Fru; “other C resources” accounts for malate, fumarate, and amino acids. “Accumulation of sucrose and AAs in ExN” refers to the increase in the levels of amino acids (AAs) and Suc in the growth zones toward the end of the extended night time course, which will represent an additional C requirement at this time. Photosynthesis and respiration of the mature leaf tissue was determined by gas exchange measurement (Supplemental Fig. S13). For details of the calculations, please refer to the main text and Supplemental Datafile S3. Time points: ED, end of day; EN, end of night; ExN 6h/14h/24h, extension of the night by 6 h/14 h/24 h.