Using transgenic Nicotiana plumbaginifolia seedlings in which the @entity460 reporter aequorin is targeted to the chloroplast stroma, we found that darkness stimulates a considerable flux of @entity141 into the stroma. This @entity141 flux did not occur immediately after the light-to-dark transition but began approximately 5 min after lights off and increased to a peak at approximately 20 to 30 min after the onset of darkness. Imaging of aequorin emission confirmed that the dark-stimulated luminescence emanated from chloroplast-containing tissues of the seedling. The magnitude of the @entity141 flux was proportional to the duration of light exposure (24 to 120 h) before lights off; the longer the duration of light exposure, the larger the dark-stimulated @entity141 flux. On the other hand, the magnitude of the dark-stimulated @entity141 flux did not appear to vary as a function of circadian time. When seedlings were maintained on a 24-h light/dark cycle, there was a stromal @entity141 burst after lights off every day. Moreover, the waveform of the @entity141 spike was different during long-day versus short-day light/dark cycles. The dark-stimulated @entity141 flux into the chloroplastidic stroma appeared to affect transient changes in cytosolic @entity141 levels. @entity11079 , an inhibitor of photosynthetic electron transport, caused a significant increase in stromal @entity141 levels in the light but did not affect the magnitude of the dark-stimulated @entity141 flux. This robust @entity141 flux likely plays regulatory roles in the sensing of both light/dark transitions and photoperiod.

Dark-stimulated XXXX ion fluxes in the chloroplast stroma and cytosol.

@entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca(2+)'] @entity11079 :: ('MESH:D004237', 'Chemical') :: ['DCMU'] @entity460 :: ('MESH:D002118', 'Chemical') :: ['calcium']
@entity460 :: (MESH:D002118,Chemical) :: ['calcium']
