Figure 3 shows the effect of NOS inhibitor, L-NAME, on
ABA inhibition of stomatal opening. Application of 25 mM
L-NAME completely abolished the ABA-induced stomatal
closure (Fig. 1a) and also reversed the ABA inhibition of
stomatal opening to about 50%. Similar results were
obtained (data not shown) when a higher concentration
(100 mM) of L-NAME was used. Application of D-NAME,
an inactive isomer, did not markedly affect the inhibition of
stomatal opening.
The effects of arginine on stomatal closure and inhibition
of stomatal opening are shown in Fig. 4. Arginine, a substrate
of NOS, inhibited stomatal opening. L-NAME and
cPTIO prevented arginine inhibition of stomatal opening