ABA supplied directly and continuou

ABA supplied directly and continuously to the cytosol via a patch pipette inhibited K+ in channels, which are required for stomatal opening (Schwartz et al. 1994).

Microinjection of an inactive “caged” form of ABA into guard cells of Commelina resulted in stomatal closure after the stomata were treated briefly with UV irradiation to activate the hormone—that is, release it from its molecular cage (Figure 23.7) (Allan et al.1994). Control guard cells injected with a nonphotolyzable form of the caged ABA
did not close after UV irradiation.


Taken together, these results indicate that extracellular perception of ABA can prevent stomatal opening and regulate gene expression, and intracellular ABA can both induce stomatal closure and inhibit the K+ current required for opening. Thus there appear to be both extra- cellular and intracellular ABA receptors. However, they have yet to be identified or localized.

ABA Increases Cytosolic Ca 2+, Raises Cytosolic pH, and Depolarizes the Membrane
As discussed in Chapter 18, stomatal closure is driven by a reduction in guard cell turgor pressure caused by a massive long-term efflux of K+ and anions from the cell. During the subsequent shrinkage of the cell due to water loss, the surface area of the plasma membrane may contract by as much as 50%. Where does the extra membrane go? The answer seems to be that it is taken up as small vesicles by endocytosis—a process that also involves reorganization of the actin cytoskeleton. However, the first changes detected after exposure of guard cells to ABA are transient membrane depolarization caused by the net influx of positive charge, and transient increases in the cytosolic calcium concentration (Figure 23.8).

ABAstimulates elevations in the concentration of cytosolic Ca2+ by inducing both influx through plasma membrane channels and release of calcium into the cytosol from internal compartments, such as the central vacuole (Schroeder et al. 2001). Stimulation of influx occurs via a pathway that uses reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) or superoxide (O2), as secondary messengers leading to plasma membrane channel activation (Pei et al. 2000). Calcium release from intracellular stores can be induced by a variety of second messengers, including inositol 1,4,5- trisphosphate (IP3), cyclic ADP-ribose (cADPR), and self.

amplifying (calcium-induced) Ca2+ release. Recent studies have shown that ABA stimulates nitric oxide (NO) synthesis in guard cells, which induces stomatal closure in a cADPR-dependent manner, indicating that NO is an even earlier secondary messenger in this response pathway (Neill et al. 2002) (for background on NO, see Chapter 14
on the Web site).
The combination of calcium influx and the release of calcium from internal stores raises the cytosolic calcium concentration from 50 to 350 n M to as high as 1100 nM (1.1m M) (Figure 23.9) (Mansfield and McAinsh, in Davies 1995). This increase is sufficient to cause stomatal closure, as demonstrated by the following experiment.

As in the experiment described earlier, calcium was microinjected into guard cells in a caged form that could be hydrolyzed by a pulse of UV light. This method allowed the investigators to control both the concentration of free calcium and the time of release to the cytosol. At Cytosolic concentrations of 600 n M or more, release of calcium from its cage triggered stomatal closure (Gilroy et al. 1990). This level of intracellular calcium is well within the concentration range observed after ABA treatment. In the preceding studies, intracellular free calcium was measured by the use of microinjected calcium-sensitive ratiometric fluorescent dyes, such as fura-2 or indo-1. However, microinjections of fluorescent dyes into single plant cells are difficult and often result in cell death. Success rates of viable injections into Arabidopsis guard cells can be less than 3%. In contrast, transgenic plants expressing the gene for the calcium indicator protein yellow cameleon make it possible to monitor several fluorescing cells in parallel, without the need for invasive injections (Allen et al. 1999b) (see Web Topic 23.9). Such studies have demonstrated that the cytosolic Ca jected calcium-sensitive ratiometric fluorescent dyes2+ concentration oscillates with distinct periodicities, depending on the signals received (Figure 23.10).


These results support the hypothesis that an increase in cytosolic calcium, partly derived from intracellular stores, is esponsible for ABA-induced stomatal closure. However, the growth hormone auxin can induce stomatal opening, and this auxin-induced stomatal opening, like ABA-induced stomatal closure, is accompanied by increases in cytosolic calcium. This finding suggests that the detailed characteristics of the location and periodicity of Ca 2+ oscillations (the “Ca signature”), rather than the overall concentration of cytosolic calcium, determine the cellular response.

Hasil (Bahasa Indonesia) 1:

ABA disediakan langsung dan terus-menerus untuk sitosol melalui patch pipette menghambat K + di saluran, yang dibutuhkan untuk stomatal pembukaan (Schwartz et al. 1994). Microinjection bentuk aktif "sangkar" ABA ke sel-sel penjaga Commelina mengakibatkan penutupan stomatal setelah stomata diperlakukan secara singkat dengan UV iradiasi untuk mengaktifkan hormon — yaitu mengeluarkannya dari kandangnya molekuler (gambar 23.7) (Allan et al.1994). Kontrol penjaga sel-sel disuntik dengan bentuk nonphotolyzable ABA sangkartidak menutup setelah iradiasi UV.Diambil bersama-sama, hasil ini menunjukkan bahwa persepsi ekstraseluler ABA dapat mencegah stomatal pembukaan dan mengatur ekspresi gen, dan intraseluler ABA dapat menginduksi stomatal penutupan maupun menghambat K + saat ini diperlukan untuk membuka. Jadi tampaknya ada tambahan-seluler maupun intraseluler ABA reseptor. Namun, mereka belum diidentifikasi atau lokal.ABA meningkatkan aktif denganrasio Ca 2+, pH menimbulkan aktif denganrasio, dan Depolarizes membranAs discussed in Chapter 18, stomatal closure is driven by a reduction in guard cell turgor pressure caused by a massive long-term efflux of K+ and anions from the cell. During the subsequent shrinkage of the cell due to water loss, the surface area of the plasma membrane may contract by as much as 50%. Where does the extra membrane go? The answer seems to be that it is taken up as small vesicles by endocytosis—a process that also involves reorganization of the actin cytoskeleton. However, the first changes detected after exposure of guard cells to ABA are transient membrane depolarization caused by the net influx of positive charge, and transient increases in the cytosolic calcium concentration (Figure 23.8).ABAstimulates elevations in the concentration of cytosolic Ca2+ by inducing both influx through plasma membrane channels and release of calcium into the cytosol from internal compartments, such as the central vacuole (Schroeder et al. 2001). Stimulation of influx occurs via a pathway that uses reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) or superoxide (O2), as secondary messengers leading to plasma membrane channel activation (Pei et al. 2000). Calcium release from intracellular stores can be induced by a variety of second messengers, including inositol 1,4,5- trisphosphate (IP3), cyclic ADP-ribose (cADPR), and self.amplifying (calcium-induced) Ca2+ release. Recent studies have shown that ABA stimulates nitric oxide (NO) synthesis in guard cells, which induces stomatal closure in a cADPR-dependent manner, indicating that NO is an even earlier secondary messenger in this response pathway (Neill et al. 2002) (for background on NO, see Chapter 14on the Web site). The combination of calcium influx and the release of calcium from internal stores raises the cytosolic calcium concentration from 50 to 350 n M to as high as 1100 nM (1.1m M) (Figure 23.9) (Mansfield and McAinsh, in Davies 1995). This increase is sufficient to cause stomatal closure, as demonstrated by the following experiment.As in the experiment described earlier, calcium was microinjected into guard cells in a caged form that could be hydrolyzed by a pulse of UV light. This method allowed the investigators to control both the concentration of free calcium and the time of release to the cytosol. At Cytosolic concentrations of 600 n M or more, release of calcium from its cage triggered stomatal closure (Gilroy et al. 1990). This level of intracellular calcium is well within the concentration range observed after ABA treatment. In the preceding studies, intracellular free calcium was measured by the use of microinjected calcium-sensitive ratiometric fluorescent dyes, such as fura-2 or indo-1. However, microinjections of fluorescent dyes into single plant cells are difficult and often result in cell death. Success rates of viable injections into Arabidopsis guard cells can be less than 3%. In contrast, transgenic plants expressing the gene for the calcium indicator protein yellow cameleon make it possible to monitor several fluorescing cells in parallel, without the need for invasive injections (Allen et al. 1999b) (see Web Topic 23.9). Such studies have demonstrated that the cytosolic Ca jected calcium-sensitive ratiometric fluorescent dyes2+ concentration oscillates with distinct periodicities, depending on the signals received (Figure 23.10).

These results support the hypothesis that an increase in cytosolic calcium, partly derived from intracellular stores, is esponsible for ABA-induced stomatal closure. However, the growth hormone auxin can induce stomatal opening, and this auxin-induced stomatal opening, like ABA-induced stomatal closure, is accompanied by increases in cytosolic calcium. This finding suggests that the detailed characteristics of the location and periodicity of Ca 2+ oscillations (the “Ca signature”), rather than the overall concentration of cytosolic calcium, determine the cellular response.