Abstract
Root pressure, also manifested as profusive sap flowing from cut stems, is a phenomenon in some species that has perplexed biologists for much of the last century. It is associated with increased crop production under drought, but its function and regulation remain largely unknown. In this study, we investigated the initiation, mechanisms, and possible adaptive function of root pressure in six genotypes of Sorghum bicolor during a drought experiment in the greenhouse. We observed that root pressure was induced in plants exposed to drought followed by re-watering but possibly inhibited by 100% re-watering in some genotypes. We found that root pressure in drought stressed and re-watered plants was associated with greater ratio of fine: coarse root length and shoot biomass production, indicating a possible role of root allocation in creating root pressure and adaptive benefit of root pressure for shoot biomass production. Using RNA-Seq, we identified gene transcripts that were up- and down-regulated in plants with root pressure expression, focusing on genes for aquaporins, membrane transporters, and ATPases that could regulate inter- and intra-cellular transport of water and ions to generate positive xylem pressure in root tissue.
Highlights
Root pressure is a phenomenon that has long puzzled plant scientists (Hales, 1727; Priestley, 1920; Pickard, 2003; Wegner, 2014; Singh, 2016)
The clearest result of this study is that sorghum requires prior exposure to drought to generate root pressure
Other studies have found that pre-exposure to drought increased root pressure (Stiller et al, 2003; Barrios-Masias et al, 2015) but in this study, re-watered individuals in the control group did not produce significant root pressure (> 5 kPa, Figure 2)
Summary
Root pressure is a phenomenon that has long puzzled plant scientists (Hales, 1727; Priestley, 1920; Pickard, 2003; Wegner, 2014; Singh, 2016). One posits that root pressure is generated by xylem parenchyma acting as an osmometer, structuring the osmotic potential of cell compartments to passively pull water into the mature xylem from the apoplast or bulk medium (Enns et al, 2000). Another suggests a hydraulic pressure scenario driving water into vessels via membrane asymmetry and compartmentalization of
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