Heat-Shock-Induced Changes in Intracellular Ca2+Level in Tobacco Seedlings in Relation to Thermotolerance1

Abstract

Exposure of plants to elevated temperatures results in a complexThe responses of plants to HS have received increasing attention in recent years. Elevated temperatures initiate changes in transcription and selective translation of HS mRNA encoding HSPs, thereby enhancing thermotolerance of treated plants (Nover et al., 1989; Nover, 1991;Vierling, 1991; Howarth and Ougham, 1993;Waters et al., 1996). However, the pathways by which HS signals are perceived and transduced to activate gene expression of HSPs and to induced thermotolerance are not understood.In recent years a second-messenger Ca 2ϩ was found to be involved in the perception and regulation of many responses of plants to environmental signals (Gilroy et al., 1993; Poovaiah and Reddy, 1993; Gilroy and Trewavas, 1994; Bush, 1995;Braam et al., 1996;Webb et al., 1996). [Ca 2ϩ ] cyt often shows significant changes in plant cells under the influence of various stress signals such as touch, wind stimulation, cold shock, wounding, and mechanical stimulation (Knight et al., 1991(Knight et al., , 1992(Knight et al., , 1993 Haley et al., 1995;Campbell et al., 1996; Polisensky and Braam, 1996), oxidative stress (Price et al., 1994), salinity (Lynch et al., 1989; Bush, 1996; Okazaki et al., 1996), anoxia (Subbaiah et al., 1994a; Bush, 1996;Sedbrook et al., 1996), and hypoosmotic shock (Takahashi et al., 1997). It has been suggested that a stress-induced change in [Ca 2ϩ ] cyt might be one of the primary transduction mechanisms whereby gene expression and biochemical events are altered to adapt plant cells to environmental stresses (Monroy et al., 1993;Subbaiah et al., 1994aSubbaiah et al., , 1994b Monroy and Dhindsa, 1995;Braam et al., 1996).Several authors have suggested that Ca 2ϩ -mediated second-messenger systems might be involved in the HS responses of animal cells (Lamarche et al., 1985; Calderwood et al., 1988; Landry et al., 1988; Mosser et al., 1990), although other results indicated that Ca 2ϩ was not strictly required for some HSP synthesis (Drummond et al., 1986(Drummond et al., , 1988. In plant cells Klein and Ferguson (1987) observed that the uptake of Ca 2ϩ by suspension-cultured pear cells or protoplasts was significantly enhanced during heat stress. Braam (1992) demonstrated that HS induced a strongly up-regulated expression of calmodulin-related TCH genes in cultured Arabidopsis cells, and external Ca 2ϩ was required for maximal HS induction of these TCH genes. Wu et al. (1992) also indicated that pretreatment of hypocotyl segments and etiolated seedlings of Brassica napus with the Ca 2ϩ ionophore A23187 or the Ca 2ϩ chelator EGTA to modify Ca 2ϩ homeostasis resulted in changes in the synthesis of HSPs. Using the fluorescent dye Indo-1, Biyaseheva et al. (1993) reported that HS induced a 4-fold increase in [Ca 2ϩ ] cyt in pea mesophyll protoplasts, but the further dynamic changes in [Ca 2ϩ ] cyt during HS could not be detected because of limitations in the technique.We recently described a novel technology to measure [Ca 2ϩ ] ...

ABA Increased Soybean Yield by Enhancing Production of Carbohydrates and Their Allocation in Seed

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Cell- and Stimulus Type-Specific Intracellular Free Ca2+ Signals in Arabidopsis

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