Regulation of Transpiration to Improve Crop Water Use

Abstract

Decreasing fresh water supplies and increasing agricultural drought threaten sustainable worldwide crop production. Consequently, there is a global priority to develop crops with higher water use efficiency (WUE): biomass production or yield per unit of water used. Water use efficiency varies substantially among species and genotypes within a species, and a major effort is now underway to identify the genetic determinants of WUE. Today, it is known that genotypes in primary gene pools exhibit allelic variation for WUE through mechanisms that regulate transpiration, which is the conductance of water through stomata, the cuticle, and the boundary layer. Because of the differential diffusion properties of water and carbon dioxide (CO₂) through these pathways, it is feasible that WUE could be improved by decreasing transpiration without a concomitant reduction in CO₂ uptake. Since CO₂ uptake and transpirational water loss occur predominantly through stomatal pores, it is not surprising that genes involved in stomatal development and stomatal opening/closing impact WUE. Furthermore, loss- and gain-of-function genetic screens have identified genes that regulate transpiration and WUE by yet undetermined mechanisms. This review will discuss the genetic determinants that regulate transpiration and WUE in the context of the modern agricultural goal of improving WUE while sustaining biomass and yield.

Keywords:

• water use efficiency
• stomatal transpiration
• cuticular transpiration
• boundary layer
• nighttime transpiration
• stomatal movement
• stomatal density
• water availability
• drought
• water conservation

ACKNOWLEDGMENTS

National Science Foundation awards MCB-0424850 and IBN-0416773 supported research in the laboratory of PMH. Purdue Agricultural Research Programs supported research in the laboratory of MVM. We thank Robert Heath, Matthew Jenks, Richard Meilan, Tom Sharkey, and Tom Sinclair for their thoughtful reviews of this manuscript.

Notes

^a Age is given in weeks, except where ^y indicates years.

^b Location (Loc) where plants were grown and measured.