ABSTRACT

Acetylcholine (ACh) is well known as the neurotransmitter in the mammalian central and peripheral cholinergic nervous systems. ACh has been identified in a number of non-neuronal cells in animals, plants, fungi, and bacteria. Acetylcholinesterase (AChE) is an enzyme hydrolyzing ACh into acetate and choline. ACh-hydrolyzing activity also distributes not only neuronal cells but also non-neuronal ones in animals, plants, and microorganisms. Both ACh and ACh-hydrolyzing activity have been widely recognized in the plant kingdom. Although functions of plant AChEs have been speculated based on histochemical and biochemical studies about ACh-hydrolyzing activity in plant tissues or cells, its functions in plant signaling remain unclear. Recently, AChE genes were identified from maize (Zea mays L.), rice (Oryza sativa L. ssp. Japonica cv. Nipponbare), siratro (Macroptilium atropurpureum Urb.), and Salicornia (Salicornia europaea L.) plants. Thus, direct functional studies of plant AChEs are now possible based on a genetic study using transgenic plants overexpressing and/or suppressing the expression of plant AChE gene. This chapter focuses on recent progress in purification and identification of plant AChE and possible functions of AChEs in plants exposed to environmental stimuli such as heat and gravity.