Abstract
Oscillations in cytosolic-free Ca(2+) concentration ([Ca(2+)]i) have been proposed to encode information that controls stomatal closure. [Ca(2+)]i oscillations with a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling. We have used a proven systems modeling platform to investigate these [Ca(2+)]i oscillations and analyze their origins in guard cell homeostasis and membrane transport. The model faithfully reproduced differences in stomatal closure as a function of oscillation frequency with an optimum period near 10 min under standard conditions. Analysis showed that this optimum was one of a range of frequencies that accelerated closure, each arising from a balance of transport and the prevailing ion gradients across the plasma membrane and tonoplast. These interactions emerge from the experimentally derived kinetics encoded in the model for each of the relevant transporters, without the need of any additional signaling component. The resulting frequencies are of sufficient duration to permit substantial changes in [Ca(2+)]i and, with the accompanying oscillations in voltage, drive the K(+) and anion efflux for stomatal closure. Thus, the frequency optima arise from emergent interactions of transport across the membrane system of the guard cell. Rather than encoding information for ion flux, these oscillations are a by-product of the transport activities that determine stomatal aperture.
Highlights
Oscillations in cytosolic-free Ca2+ closure. [Ca2+]i oscillations with concentration ([Ca2+]i) have been proposed to encode information that controls stomatal a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling
Our findings indicate that oscillations in voltage and [Ca2+]i, and their optima associated with stomatal closure, are most explained as emerging from the interactions between ion transporters that drive stomatal closure
To gain a better understanding of the drivers behind this optimum in closure rate, we examined the activities of the plasma membrane H+- and Ca2+-ATPases, as well as the IK,in, IK,out, influx by activating Ca2+ channels (ICa), ICl, and ALMT Mal22 channels at the plasma membrane
Summary
Oscillations in cytosolic-free Ca2+ closure. [Ca2+]i oscillations with concentration ([Ca2+]i) have been proposed to encode information that controls stomatal a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling. The model faithfully reproduced differences in stomatal closure as a function of oscillation frequency with an optimum period near 10 min under standard conditions Analysis showed that this optimum was one of a range of frequencies that accelerated closure, each arising from a balance of transport and the prevailing ion gradients across the plasma membrane and tonoplast. These interactions emerge from the experimentally derived kinetics encoded in the model for each of the relevant transporters, without the need of any additional signaling component. Minguet-Parramona et al.2010), elevate [Ca2+]i plasma membrane to by facilitating Ca2+ trigger Ca2+ release entry from at the endomembrane stores, a process often described as Ca2+-
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