Drought‐induced changes in xylem pH, ionic composition, and ABA concentration act as early signals in field‐grown maize (Zea mays L.)

Abstract

Early signals potentially regulating leaf growth and stomatal aperture in field-grown maize ( Zea mays L.) subjected to drought were investigated. Plants grown in a field lysimeter on two soil types were subjected to progressive drought during vegetative growth. Leaf ABA content, water status, extension rate, conductance, photosynthesis, nitrogen content, and xylem sap composition were measured daily. Maize responded similarly to progressive drought on both soil types. Effects on loam were less pronounced than on sand. Relative to fully-watered controls, xylem pH increased by about 0.2 units one day after withholding irrigation (DAWI) and conductivity decreased by about 0.25 mS cm À1 1-3 DAWI. Xylem nitrate, ammonium, and phosphate concentrations decreased by about 50% at 1-5 DAWI and potassium concentration decreased by about 50% at 7-8 DAWI. Xylem ABA concentration consistently increased by 45 -70 pmol ml À1 at 7 DAWI. Leaf extension rate decreased 5 DAWI, after the changes in xylem chemical composition had occurred. Leaf nitrogen significantly decreased 8 -16 DAWI in droughted plants. Midday leaf water potential and photosynthesis were significantly decreased in droughted plants late in the drying period. Xylem nitrate concentration was the only ionic xylem sap component significantly correlated to increasing soil moisture deficit and decreasing leaf nitrogen concentration. Predawn leaf ABA content in droughted plants increased by 100-200 ng g À1 dry weight at 7 DAWI coinciding with a decrease in stomatal conductance before any significant decrease in midday leaf water potential was observed. Based on the observed sequence, a chain of signal events is suggested eventually leading to stomatal closure and leaf surface reduction through interactive effects of reduced nitrogen supply and plant growth regulators under drought.

Multiple exposures to drought 'train' transcriptional responses in Arabidopsis

“…Our method for applying multiple dehydration stress/recovery treatments in a relatively short time, as opposed to prolonged soil-water withdrawal/recovery treatments, allowed us to observe this phenomenon and may explain why it has evaded detection in Arabidopsis so far. It is particularly relevant to point out that our experimental system is similar to the day/night oscillations in the leaf water potential that plants experience in the field during low soil water potential conditions [22][23][24] . It is tempting to suggest that under natural conditions stress memory is activated by the previous day's dehydration stress, persists through the recovery period at night (when transpiration is less and leaf water potential recovers) and then facilitates the plant's response to dehydration stress encountered during the next day, when adequate soil water is unavailable to maintain leaf water potentials at the higher transpiration rates occurring during the day.…”

Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis

“…Similarly, cytokinins have been implicated as long-distance signals that communicate the nitrogen status from the root to the shoot (Takei et al, 2001; see also Kudo et al, 2010). The signal that communicates drought conditions from the root to the shoot is widely believed to be mediated through abscisic acid (Bahrun et al, 2002). Although there are some examples of root-to-shoot signaling regulating developmental phenotype and hormone translocation, there is no information that dictates the existence of a shoot-to-root intraplant signal relaying a plant's response with beneficial microbes.…”

Corn yield response to partial rootzone drying and deficit irrigation strategies applied with drip system

“…The idea of using PRD as a tool to manipulate plant water deficit response has its origin in the observation that root-generated ABA can be transported to shoot regulating stomata of the leaves as shown in a number of crop species, such as corn (Bahrun et al 2002) and soybean (Liu et al 2003). As a consequence of plant response, the aperture of stomata can be regulated so that a partial closure of stomata at a certain level of soil water deficit may lead to an increase in WUE (Liu et al 2005).…”