Alterations in ultrastructure and subcellular localization of Ca²⁺in poplar apical bud cells during the induction of dormancy

An electron microscopic-cytochemical localization of plasma membrane Ca2+-ATPase activity in poplar apical bud cells during the induction of dormancy by short-day photoperiods

“…Naturally, it may be expected that during this period of SD exposure the PM Ca 2+ pumping should be very low or inactive, and thus would result in no cerium phosphate grains on the interior face of the PM. When the plant has completed its dormancy process, we believe the plant should be back to the status of a resting low Ca 2+ concentration, as evidenced by the observation in poplar after a 70-d SD exposure in which the PM Ca 2+ pumping was restored (Fig 4) and a low concentration of intracellular Ca 2+ was observed [16]. As shown in Fig 2 and 3, many reaction products were present on the exterior face of the PM during the dormancy development.…”

“…Between the 28 and 42 d of SD exposure, when the dormancy was developing, no reaction products of the enzymatic activity were seen on the interior face of the PM. The dynamic of Ca 2+ -ATPase activity appears to be an adaptive nature corresponding to the alterations of the intracellular Ca 2+ concentration [16].…”

“…Active calcium pumping is necessary in order to maintain a Ca 2+ -homeostasis, as plants such as poplar are actively growing. When poplar plants were exposed to SD, e.g., between the 28-42 d period, the dormancy was developing, and intracellular Ca 2+ concentration was increased [16]. Naturally, it may be expected that during this period of SD exposure the PM Ca 2+ pumping should be very low or inactive, and thus would result in no cerium phosphate grains on the interior face of the PM.…”

“…ex March) plants were established as previously described [16]. They were grown in a greenhouse with 16 h light (long day, LD) at 25/21 o C day/night (D/N).…”

“…Because of its high affinity for calcium, this enzyme can either reduce the cytoplasmic concentration of free calcium ions to extremely low levels (thus maintaining a Ca 2+ homeostasis), or restore it after a specific stimulus causes an increase in cytosolic Ca 2+ concentration [11], [15]. We previously found a dynamic change in calcium distribution in poplar apical bud meristematic cells when dormancy was induced by short days (SD) [16]. For example, during SD exposures of up to 20 d (prior to a measurable level of dormancy), Ca 2+ increased in cytosol and nuclei.…”