Counting stomata
Stomata close after they receive a calcium current. How quickly, that is dependent on the trigger of this current. But how the stomata distinguishes those calcium signals was up till now unknown. A recently in Current Biology published study shows how stomata differentiate between the different signals.
By using a light activated calcium channel the researchers could subject the cells to different calcium signalling regimes. This enabled them to discover that the number of calcium pulses influences stomata closure. After one of two pulses only a small number of stomata closed slowly. By six pulses the majority of stomata were closing a lot quicker, and by twelve pulses all stomata were closed.
The frequency of the pulses also influenced stomata closure. When the calcium pulses occurred with an interval of 60 seconds, the stomata closed after 15 minutes. But when the researchers shortened the frequency of the pulses to 30 seconds, then the stomata closed after 10 minutes. The difference between 60 and 30 seconds intervals appears to come from the merging together of the pulses during a quicker frequency.
The expectation now is that the triggers of calcium signals like CO2 and drought, each trigger a specific pulse frequency and pulse number. In this way the cell knows if the stomata needs to close right away, or that it has more time.
Literature
Huang et al., Guard cells count the number of unitary cytosolic Ca2+ signals to regulate stomatal dynamics, Current Biology (2024), https://doi.org/10.1016/j.cub.2024.07.086
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