Effects of ABA dynamics on poplar acclimation to drought

Characterisation of the biochemical and genetic mechanisms that underpin plant responses to water deficit are central to the development of more productive drought-tolerant biomass crops, including fast-growing poplars.

Cecilia Brunetti and colleagues have demonstrated how abscisic acid (ABA) tightly regulates photosynthetic machinery in different plant organs on a daily basis. This occured under both well-watered and water deficit conditions. Their findings show how ABA enables the optimisation of intrinsic water use efficiency (WUEint) and coordination of whole plant acclimation responses to reduced water availability. “To the best of knowledge, our data provide the first report of a possible relationship between ABA and soluble carbohydrates in the leaves and stem, suggesting further potential roles of this hormone in carbohydrate metabolism,” say the authors.

Brunetti and colleagues examined how stomatal (gs), mesophyll (gm) and leaf hydraulic (Kleaf) conductance varied under well-watered and water-stressed conditions in Populus nigra L. (black poplar, Salicaceae).

“[T]he results of this study expand our understanding of the impact of water stress on the daily trends of gm, gm and Kleaf and the close coordination of these parameters in the optimization of water transport and CO2 assimilation in water-stressed plants,” said the authors. “In addition, the finding that WW [well-watered] plants restrict gs during the day while keeping photosynthesis constant provides evidence that unstressed plants can operate in a more water-efficient mode by increasing WUEint without curbing CO2 fixation.”

“This study supports previous results showing a role of both hydraulic and hormonal signals in the regulation of gs under water stress… Moreover, these two signals are strictly coupled and have a different influence on gs and gm depending on the time of the day and the intensity of the stress. In particular, we suggest that in well-watered plants a slight increase in leaf ABA content is enough to decrease gs , but reducing gm in water-stressed plants may require higher leaf levels of ABA, probably associated with reductions in water potential.”