The Effect of Heat Shock on Morphogenesis in Barley

Abstract

The effect of daily heat-shock treatments on gene expression and morphogenesis of etiolated barley (Hordeum vulgare) was investigated. Heat-shock treatments in the dark induced shortening of the primary leaves and the coleoptiles to the length of those in light-grown plantlets. In addition, the mRNA levels of the lightinduced genes that were investigated were raised under these conditions and showed distinct oscillations over a period of at least 3 d. While the mRNA levels for chlorophyll a/b binding protein (LHC II), plastocyanin, and the small subunit of ribulose-1,5-bisphosphate carboxylase had maxima between 8 and 12 PM (12-16 h after the last heat-shock treatment), the mRNA levels for thionin oscillated with a phase opposed to that of LHC II. Etiolated barley, the circadian oscillator of which was synchronized by cyclic heatshock treatments, was illuminated for a constant interval at different times of the day; this led to the finding that greening was fastest at the time when the maximal levels of mRNA for LHC II were also observed. Whereas After the discovery of circadian regulation of mRNA levels (19), evidence accumulated suggesting that transcription of light-regulated genes is primarily under the control of the circadian clock (14) and that signal perception occurs via phytochrome (27). Moreover, the phase of the endogeneous clock can be shifted via phytochrome (27). Thus, a primary synchronization between the circadian rhythm of gene expression and the external factor light can be achieved. These findings imply an interaction of phytochrome with the mechanism of the circadian oscillator itself. The signal chain(s) that leads from the receptor(s) via the endogeneous clock mechanism to the transcription of genes is not yet known.To understand more closely the potential effect of circadian rhythm on gene expression and morphogenesis, we studied the influence of external signals (zeitgeber) other than light. Of these, temperature shifts appeared well suited because alterations in the ambient temperature affect the phase of the circadian rhythm (26). The positive effect of temperature oscillations on development was shown in experiments in which it was found that plants grown under constant environmental conditions do not develop properly, whereas a diurnal fluctuation of temperature under otherwise constant conditions has a normalizing effect on plant development (16).In previous studies (20), we have shown that HS2 treatments and diurnal temperature shifts during emergence of pea seedlings in the dark cause morphogenetic changes that are very similar to those induced by far-red light: plumulae are developed, the hooks opened, and the stems shortened. These 'photomorphogenetic' characteristics are accompanied by elevated levels of nuclear-coded, light-inducible mRNAs for LHC II and SSU. ELIPs are another group of lightregulated genes (15); the regulation in their steady-state mRNA level remains entirely light dependent in etiolated pea seedlings whose circadian oscillations were entrained by te...

Arabidopsis Transcriptome Profiling Indicates That Multiple Regulatory Pathways Are Activated during Cold Acclimation in Addition to the CBF Cold Response Pathway[W]

“…GI is a novel protein with roles in the promotion of flowering by photoperiod and circadian clock function (Fowler et al, 1999;Park et al, 1999), but it has not been associated with acclimation to low temperature. Interestingly, however, it is known that in addition to entrainment by light/dark cycles, the circadian clock in plants can be entrained by temperature cycles (Kloppstech et al, 1991;Beator et al, 1992;Heintzen et al, 1994;McWatters et al, 2000). Park et al (1999) proposed that GI functions in a light input pathway to the clock.…”

?Circadian clock? directs the expression of plant genes

“…Experiments performed with tomato, pea and barley clearly demonstrated that alternating high and low temperatures (simulation of day and night temperatures) and cyclic heat-shock treatments can function as entraining signal(s) to synchronize Lhc, rbcS and elip mRNA oscillations [3,25,42,48]. Furthermore, it was demonstrated that low temperature suspended the timing of the rhythm and upon rewarming, the circadian control was reestablished but was displaced from the actual time of day by the length of the chilling exposure [29].…”

Heat Shock–Induced Fluctuations in Clock and Light Signaling Enhance Phytochrome B–Mediated Arabidopsis Deetiolation

“…In dark-grown pea (Pisum sativum) seedlings, daily heat shock induces some responses typically triggered by the exposure to light, such as inhibition of stem growth, leaf expansion, opening of the apical hook, and increased expression of genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and chlorophyll a/b binding proteins (Kloppstech et al, 1991), and also enhances the responses of the latter genes and of chloroplast development to light (Otto et al, 1992). In dark-grown barley (Hordeum vulgare), daily heat shocks generate circadian rhythms of expression of several lightregulated genes (Beator et al, 1992). While our understanding of the molecular mechanisms that account for the opposite effects of light and average temperature has advanced significantly (Franklin et al, 2011), we are largely ignorant of the signaling players involved in the synergistic actions of light and heat shocks.…”