Abstract
Plants need to respond to various environmental stresses such as abiotic stress for proper development and growth. The responses to abiotic stress can be biochemically demanding, resulting in a trade-off that negatively affects plant growth and development. Thus, plant stress responses must be fine-tuned depending on the stress severity and duration. Abscisic acid, a phytohormone, plays a key role in responses to abiotic stress. Here, we investigated time-dependent physiological and molecular responses to long-term ABA treatment in Arabidopsis as an approach to gain insight into the plant responses to long-term abiotic stress. Upon ABA treatment, the amount of cellular ABA increased to higher levels, reaching to a peak at 24 h after treatment (HAT), and then gradually decreased with time whereas ABA-GE was maintained at lower levels until 24 HAT and then abruptly increased to higher levels at 48 HAT followed by a gradual decline at later time points. Many genes involved in dehydration stress responses, ABA metabolism, chloroplast biogenesis, and chlorophyll degradation were strongly expressed at early time points with a peak at 24 or 48 HAT followed by gradual decreases in induction fold or even suppression at later time points. At the physiological level, long-term ABA treatment caused leaf yellowing, reduced chlorophyll levels, and inhibited chloroplast division in addition to the growth suppression whereas short-term ABA treatment did not affect chlorophyll levels. Our results indicate that the duration of ABA treatment is a crucial factor in determining the mode of ABA-mediated signaling and plant responses: active mobilization of cellular resources at early time points and suppressive responses at later time points.
Highlights
Plants have evolved complex signaling pathways to respond and adapt to changes in environmental conditions
We reasoned that long-term abscisic acid (ABA) treatment may provide an insight into plant responses to the long-term abiotic stress
We systematically investigated the temporal aspects of plant responses to exogenous ABA at both molecular and physiological levels
Summary
Plants have evolved complex signaling pathways to respond and adapt to changes in environmental conditions. Extensive studies have been carried out to understand the mechanisms by which ABA-mediated signaling contributes to plant responses to abiotic stresses such as dehydration and osmotic stresses at the molecular and physiological levels (Tuteja, 2007). The activation of SnRK2s induces a large number of cellular responses including stomatal closure to prevent water loss and the expression of many genes whose products are important for stress responses and tolerance such as enzymes for osmoprotectant synthesis (Fujita et al, 2009) These responses contribute to the enhanced resistance to abiotic stress. The expression of genes involved in dehydration stress responses, chloroplast biogenesis, ABA biosynthesis, and chlorophyll degradation was strongly induced during the first 24 ∼ 48 h after ABA treatment, but gradually declined or became suppressed thereafter
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