Levchenko V, Guinot D R, Klein M, Roelfsema M R G, Hedrich R, Dietrich P
Molecular Plant Physiology and Biophysics, Julius von Sachs Institute for Biosciences, Würzburg University, Würzburg.
Protoplasma. 2008;233(1-2):61-72. doi: 10.1007/s00709-008-0307-x. Epub 2008 Jul 22.
Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca(2+) signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca(2+) homeostasis and stimulus-induced Ca(2+) signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca(2+)-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca(2+) concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca(2+) concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca(2+) concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca(2+) concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca(2+) concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.
细胞质钙浓度的升高、瞬变和振荡被认为编码了触发植物细胞中各种生理反应的信息。然而，由单一刺激诱导的Ca(2+)信号会有所不同，这取决于细胞的生理状态和实验条件。我们比较了完整植物、表皮条和分离原生质体的保卫细胞中的Ca(2+)稳态和刺激诱导的Ca(2+)信号。将对Ca(2+)敏感的染料Fura 2用于单细胞比率成像，并结合电生理记录。通过膜片吸管将Fura 2加载到保卫细胞原生质体中，发现在-47 mV时细胞质游离Ca(2+)浓度约为80 nM。当质膜超极化至-107 mV时，Ca(2+)浓度增加到超过400 nM的水平。完整的保卫细胞在超极化电位下能够维持低得多的细胞质游离Ca(2+)浓度，在-100 mV时，表皮条和完整植物中的平均浓度分别为183和90 nM。质膜进一步超极化至-160 mV会导致保卫细胞细胞质Ca(2+)浓度持续升高，在完整植物中该浓度会缓慢恢复到刺激前水平，但在表皮条中不会。我们的结果表明，完整植物保卫细胞中的细胞质Ca(2+)浓度受到严格控制，但在表皮条和分离原生质体中对质膜电位变化越来越敏感。
