Phospholipase A (PLA) catalyses the hydrolysis of phospholipids into lysophospholipids and free fatty acids. Physiological studies have indicated that PLA is involved in stomatal movement. However, genetic evidence of a role of PLA in guard cell signalling has not yet been reported. To identify PLA gene(s) that is (are) involved in light-induced stomatal opening, stomatal movement was examined in Arabidopsis thaliana plants in which the expression of PLA isoforms was reduced or knocked-out. Light-induced stomatal opening in PLAl knockout plants did not differ from wild-type plants. Plants in which PLAo was silenced by RNA interference exhibited delayed light-induced stomatal opening, and this phenotype was reversed by exogenous lysophospholipids, which are products of PLA. Stomatal opening in transgenic plants that over-expressed PLAo was faster than wild-type plants. The expression of PLAo was localized to the endoplasmic reticulum of guard cells, and increased in response to light in the mature leaf. Aristolochic acid, which inhibits light-induced stomatal opening, inhibited the activity of purified PLAo. Collectively, these results provide evidence that PLAo is involved in light-induced stomatal opening in ARABIDOPSIS:
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