Role of Ca2+ in Mediating Plant Responses to Extracellular ATP and ADP

Abstract

Among the most recently discovered chemical regulators of plant growth and development are extracellular nucleotides, especially extracellular ATP (eATP) and extracellular ADP (eADP). Plant cells release ATP into their extracellular matrix under a variety of different circumstances, and this eATP can then function as an agonist that binds to a specific receptor and induces signaling changes, the earliest of which is an increase in the concentration of cytosolic calcium ([Ca2+]cyt). This initial change is then amplified into downstream-signaling changes that include increased levels of reactive oxygen species and nitric oxide, which ultimately lead to major changes in the growth rate, defense responses, and leaf stomatal apertures of plants. This review presents and discusses the evidence that links receptor activation to increased [Ca2+]cyt and, ultimately, to growth and diverse adaptive changes in plant development. It also discusses the evidence that increased [Ca2+]cyt also enhances the activity of apyrase (nucleoside triphosphate diphosphohydrolase) enzymes that function in multiple subcellular locales to hydrolyze ATP and ADP, and thus limit or terminate the effects of these potent regulators.

Early Extracellular ATP Signaling in Arabidopsis Root Epidermis: A Multi-Conductance Process

“…P2K1 has been shown to be required for the eATP-activated root epidermis PM HACC-like and NSCC-like conductances (Wang et al, 2018). Whether P2K1 (or an as yet unknown receptor; Clark and Roux, 2018) governs the eATP-induced HACC and anion currents remains, however, to be elucidated. The relationship between P2K1 and RBOHs in the root epidermis also needs to be tested, as does the possible role of ROS in activating the conductances found in the present study.…”

“…Adenosine 5′-triphosphate (ATP) is well known as an essential cellular energy source. However, the recognition of ATP as an extracellular signaling agent in plants is becoming more widespread (Clark and Roux, 2018). Extracellular ATP (eATP) has been shown to modulate growth and development, particularly of pollen and root hairs (Roux and Steinebrunner, 2007; Clark et al, 2010; Wu et al, 2018).…”

Actin Cytoskeleton as Actor in Upstream and Downstream of Calcium Signaling in Plant Cells

“…In plants, temporary and spatial changes in cellular Ca 2+ concentrations play vital roles in growth, development, and signal transduction, such as tip growth of pollen tubes and root hairs, stomatal movement, salt or osmotic stress response, temperature and hormone response, as well as beneficial and pathogenic associations with microorganisms [1,2,3,4,5]. Changes in Ca 2+ concentration often serve as triggers for calcium sensors or adapters, such as calcium-dependent protein kinases (CDPKs), calcineurin B-like protein (CBL) family, and Ca 2+ -dependent ABPs [1,2,6,7,8].…”

Iron availability modulates the Arabidopsis thaliana root calcium signature evoked by exogenous ATP

“…Extracellular purine nucleotide signaling is involved in wounding, immunity, growth regulation and guard cell dynamics. 5 eATP evoked a biphasic [Ca 2+ ] cyt increase in Arabidopsis root tips under full P nutrition (determined using cytosolic aequorin or YC3.6 as genetically encoded [Ca 2+ ] cyt reporters). 4 The first [Ca 2+ ] cyt increase in response to eATP occurred at the apex and the second [Ca 2+ ] cyt peak was sub-apical.…”