The plant hormone abscisic acid (ABA) regulates potassium and chloride ion
channels at the plasma membrane of guard cells, Leading to stomatal closure
that reduces transpirational water loss from the leaf. The tobacco Nt-SYR1
gene encodes a syntaxin that is associated with the plasma membrane. Synta
xins and related SNARE proteins aid intracellular vesicle trafficking, fusi
on, and secretion. Disrupting Nt-Syr1 function by cleavage with Clostridium
botulinum type C toxin or competition with a soluble fragment of Nt-Syr1 p
revents potassium and chloride ion channel response to ABA in guard cells a
nd implicates Nt-Syr1 in an ABA-signaling cascade.