Abstract
Drought is a severe environmental stress that exerts negative effects on plant growth. In trees, drought leads to reduced secondary growth and altered wood anatomy. The mechanisms underlying wood stress adaptation are not well understood. Here, we investigated the physiological, anatomical, hormonal, and transcriptional responses of poplar to strong drought. Drought-stressed xylem was characterized by higher vessel frequencies, smaller vessel lumina, and thicker secondary fiber cell walls. These changes were accompanied by strong increases in abscisic acid (ABA) and antagonistic changes in salicylic acid in wood. Transcriptional evidence supported ABA biosynthesis and signaling in wood. Since ABA signaling activates the fiber-thickening factor NST1, we expected upregulation of the secondary cell wall (SCW) cascade under stress. By contrast, transcription factors and biosynthesis genes for SCW formation were down-regulated, whereas a small set of cellulose synthase-like genes and a huge array of genes involved in cell wall modification were up-regulated in drought-stressed wood. Therefore, we suggest that ABA signaling monitors normal SCW biosynthesis and that drought causes a switch from normal to “stress wood” formation recruiting a dedicated set of genes for cell wall biosynthesis and remodeling. This proposition implies that drought-induced changes in cell wall properties underlie regulatory mechanisms distinct from those of normal wood.
Highlights
Wood is an important commodity for construction materials, biofuels, and as a feedstock for cellulose production [1,2]
abscisic acid (ABA) Is Strongly Regulated in Drought-Stressed Wood
ABA is instrumental for dormancy [78], but its role in the transcriptional regulation of wood formation is just emerging
Summary
Wood is an important commodity for construction materials, biofuels, and as a feedstock for cellulose production [1,2]. Wood (botanically: xylem) is formed by the secondary growth of stems of trees. Tree growth is severely constrained by harsh environmental conditions such as drought [3,4]. In order to reduce water loss and acclimate to drought, several physiological changes occur, including stomatal closure, reductions in photosynthetic CO2 assimilation, leaf area reduction, shoot growth cessation, leaf desiccation and abscission [5,6]. Plant height and stem diameter growth are impeded and the aboveground biomass production is diminished. Root growth is often maintained or even enhanced when sensing drought to adjust the uptake of dwindling water resources [7]
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