T. Klockenbring et al., THE STOMATAL PHOSPHOENOLPYRUVATE CARBOXYLASE - A POTENTIAL TARGET FORSELECTIVE PROTEOLYSIS DURING STOMATAL CLOSURE, Journal of plant physiology, 152(2-3), 1998, pp. 222-229
The activity of the stomatal key enzyme phosphoenolpyruvate carboxylas
e (PEPCase, EC 4.1.1.31) is known to be decreased during ABA-induced s
tomatal closure, in parallel the level of the second messenger inosito
l 1,4,5 trisphosphate (ins(1,4,5)P-3) is increased. Since ins(1,4,5)P-
3 itself induces stomatal closure, the effect of the second messenger
on protein-selective degradation of PEPCase and the specificity for PE
PCase guard cell isoforms was investigated. PEPCase was immunoprecipit
ated from ins(1,4,5)P-3 treated epidermal crude extracts. Analysis of
the precipitates gave hints to an ins(1,4,5)P-3-induced selective ubiq
uitin-dependent proteolysis preferentially of guard cell specific PEPC
ase isoforms (110,112,116 kDa). The role of the second messenger ins(1
,4,5)P-3 as a possible mediator between signal-mediated cascades and t
he ubiquitin-specific PEPCase degradation is discussed on the basis of
PEPCase functioning as a target for selected proteolysis during stoma
tal closure. Moreover, the diurnal rhythmicity of guard cell protein t
urnover was analysed, especially with respect to ubiquitin-dependent p
rocesses.