3.8. Water potential and osmotic potential in tips of spikes treated
with various carbohydrates
Osmotic potential in the spike tips treated with sucrose and sorbitol rapidly decreased with time (Fig. 8A). Glucose treatment also decreased osmotic potential on 15th day. In contrast, the mannitol treatment maintained the osmotic potential at relatively high levels compared with other carbohydrate treatments. Osmotic potential in the spike tips during the first 10 day decreased to 0.43, 3.76, and 1.92 kPa in glucose, sucrose, and sorbitol treatments, respectively. On the basis of data in Fig. 7, osmotic potential due to total soluble carbohydrates in spike tips during this time is calculated to decrease 0.64, 2.68, and 1.09 kPa in the abovementioned carbohydrate treatments, respectively. The water potential in the spike tips showed a trend similar to that for osmotic potential (Fig. 8B).
3.9. Translocated carbohydrate
Leaves were exposed to 14CO2, and then phloem exudates were collected from the cut ends of the pedicel. The phloem exudates were separated with HPLC, and 14C-carbohydrate was detected. Only a peak corresponding to that of sucrose was detected in the phloem exudates (data not shown).