Handbook of Plant and Crop Physiology

414 LEONARDOS AND GRODZINSKI

Figure 3 Total^14 C fixation,^14 C retention,^14 C export, and^14 C partitioning in major intermediates during a
2-hr^14 CO 2 feeding of source leaves. Data are those for species that transport sucrose [a C 3 species,P. bisulca-
tum(A, E, I, and M); a C 3 -C 4 intermediate species, P. decipiens(B, F, J, and N); and a C 4 species,P. miliaceum
(C, G, K, and O] and for a species that transports auxiliary sugars as well as sucrose [a C 3 species,C. sativus
(D, H, L, and P)]. Measurements were made under saturating irradiance (1500, 1600, and 1750 mol m^2 sec^1
for the C 3 , C 3 -C 4 intermediate, and C 4 species, respectively), 35 Pa CO 2 , 21 kPa O 2 , and 30°C. Cumulative net
C fixation (dashed line in A, B, C, and D) was calculated from IRGA data, whereas^14 C retention in the leaf was
measured both nondestructively by monitoring^14 C with a GM detector continuously (solid line) and destruc-
tively at the end of the feeding. Export (dotted line) was estimated as the difference between total fixation
(dashed line) and^14 C retention in the leaf (solid line). Panels E, F, G, and H show partitioning of total^14 C in
the total sugar fraction () and in ethanol insolubles (starch, ). Panels I, J, K, and L show partitioning of to-
tal^14 C into sugars (sucrose and auxiliary sugars), and panels M, N, O, and P show the specific activity of the
transport sugars, sucrose (Suc, ), raffinose (Raf, ), and stachyose (Sta, ). Each point is the average of at
least four leaves on four different plants and each error bar represents the SE of the mean. The shaded areas rep-
resent the 90–120 min period during which export was estimated.