untreated lemons); however, from this point on the SS activity
showed a pronounced decrease. Similarly to flavedo, the SS activity
of albedo was increased by UV-B treatment. The highest value
of SS activity (0.021mol sucrose min−1 g−1 FW) was reached at
0.5 min time–dose being 2.8-fold higher than control. The SS activity
also showed a different activity pattern in UVB-treated flavedo
and albedo (Fig. 4a). Contrary to SS, the SPS activity did not increase
in UVB-treated flavedo, being at 0.5, 1 and 5min time–dose significantly
decreased (Fig. 4b). Noteworthy at 5min time–dose the
SPS activity only represents 11.0% of the control activity. In albedo
tissue the SPS activity showed at 0.5 and 5min time–dose a significantly
increase compared with no UVB-treated albedo, but at 2
and 3min time–dose it was strongly decreased. Although the SPS
activity was, in general, higher in flavedo than in albedo, the highest
activity (0.021mol sucrose 6-P min−1 g−1 FW)was observed in
the latter at 5 min UV-B time–dose. The pattern of SPS activity was
also different in albedo and flavedo. The flavedo/albedo enzyme
ratio showed a different pattern of changes for all tested activities
indicating a differential time–dose effect of UV-B radiation (Fig. 5).