ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
INTRACELLULAR CALCIUM DYNAMICS: REGULATION OF CELL FUNCTION AND IMPLICATIONS FOR STRESS TOLERANCE |
| Author: | V.S. Polito |
| Abstract:
The role of calcium, particularly fluxes in free cytoplasmic Ca2+ concentration ([Ca2+]cyt), in the regulation of such plant cell activities as cell division, polarized growth and cytoplasmic streaming is becoming well established (Hepler and Wayne, 1984; Hepler and Wolniak, 1984; Williamson, 1981). In addition, the involvement of Ca2+ in at least some hormone-and growth regulator-mediated events is becoming increasingly evident. Elliott (1983), Elliott, et al (1983) and Saunders and Hepler (1981, 1982) have shown a relationship between Ca2+ and cytokinin. Polar auxin transport and Ca2+ have been shown to be related with auxin moving in a direction opposite to that of Ca2+ (Lee, et al. 1984). DeGuzman and DeLa Fuente (1984) found that acropetal efflux of Ca2+ from Helianthus hypocotyl segments is promoted by IAA and inhibited by TIBA suggesting that Ca2+-influx regulates IAA efflux. [Ca2+]cyt in higher plant cells remains somewhat uncertain although indirect evidence and evidence from algal cells (Williamson, 1981; Williamson and Ashley, 1982) indicates that the situation is similar to that in animal cells where [Ca2+]cyt is orders of magnitude lower than extracellular [Ca2+]. In addition, plant cells also contain a pool of Ca2+ in the vacuole, whose [Ca2+] remains unknown, although implications from algal cells (Williamson and Ashley, 1982) indicate that it is at least two orders of magnitude greater than that of the cytoplasm. Low intracellular Ca2+ must be maintained in the presence of millimolar levels in the extracellular space and values likely approaching millimolar in the vacuole. This requires active pumping of Ca2+ out of the cytoplasm in order to maintain [Ca2+]cyt at 0.1 μM. Factors leading to the breakdown of Ca2+ homeostasis may be associated with some stress-related dysfunctions. In animal cells it is clear that various signals lead to increases in [Ca2+]cyt thereby triggering cellular activities via Ca2+-dependent regulatory proteins. Similar functions are widely suspected in plants although adequate experimental data are in many cases, particularly in cells of higher plants, lacking. Additionally, calcium has an important role as a membrane component where it is involved in maintaining membrane integrity and in membrane-fusion events. In my lab we have been investigating aspects of cell calcium dynamics particularly in stressed plant cells. Chlorotetracycline (CTC), a probe for membrane calcium, has been an important tool in this work. CTC forms a fluorescent complex with Ca2+ whose fluorescence emission intensity in the apolar, membrane environment is five times that of the complex in the polar environments of the cytoplasm, vacuole or apoplast. Thus, changes in fluorescence signals from cells | |
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