Controlling stomatal aperture in semi-arid regions—The dilemma of saving water or being cool?

• Published in: Plant science (Limerick) Vol. 251; pp. 54 - 64
• Main Authors: Chaves, M.M., Costa, J.M., Zarrouk, O., Pinheiro, C., Lopes, C.M., Pereira, J.S.
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.10.2016
• Subjects: carbon dioxide; Conservation of Natural Resources; cooling; Crop management; Crop Production - methods; crops; Crops, Agricultural - physiology; drought; energy balance; evaporative demand; gas exchange; heat; Leaf temperature; molecular genetics; Night-time transpiration; plant adaptation; Plant Stomata - physiology; Plant Transpiration - genetics; roots; screening; Semi-arid regions, Heat wave; semiarid zones; Stomata; stomatal conductance; stomatal movement; temperature; Water - metabolism; water conservation; water use efficiency; water vapor; WUE; A; ST; RV; E; WUE; Night-time transpiration; Stomata; Semi-arid regions, Heat wave; WUEi; VPD; gs; Leaf temperature; WUEl; E/∂A; Enight; SD; gsnight; S; WUEc; Crop management; gsmax; Amax
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2016.06.015

•Given the expected water restrictions in semiarid climates, the best adapted genotypes should be able to compromise between high water use efficiency and leaf cooling capacity.•High WUE genotypes avoid dehydration by closing stomata but under hot spells they may reach supra-optimal temperatures. Therefore they must possess high mesophyll resilience to heat stress.•Heat avoiders genotypes will maintain stomata open and benefit from leaf evaporative cooling. Because they tend to over-expend water they require precise monitoring of water status to prevent excessive dehydration under hot spells.•Night-time transpiration can result in significant water loss and major reduction of WUE. The time sequence of nocturnal stomatal aperture suggests an endogenous regulation, possibly as part of circadian rhythms rather than a direct response to changes in evaporative demand.•Among the best characterized genes affecting drought tolerance are ERECTA genes. They are related to the perception of drought stress signals across cell membrane and were associated with improved transpiration efficiency and thermo-tolerance. Stomatal regulation of leaf gas exchange with the atmosphere is a key process in plant adaptation to the environment, particularly in semi-arid regions with high atmospheric evaporative demand. Development of stomata, integrating internal signaling and environmental cues sets the limit for maximum diffusive capacity of stomata, through size and density and is under a complex genetic control, thus providing multiple levels of regulation. Operational stomatal conductance to water vapor and CO2 results from feed-back and/or feed-forward mechanisms and is the end-result of a plethora of signals originated in leaves and/or in roots at each moment. CO2 assimilation versus water vapor loss, proposed to be the subject of optimal regulation, is species dependent and defines the water use efficiency (WUE). WUE has been a topic of intense research involving areas from genetics to physiology. In crop plants, especially in semi-arid regions, the question that arises is how the compromise of reducing transpiration to save water will impact on plant performance through leaf temperature. Indeed, plant transpiration by providing evaporative cooling, is a major component of the leaf energy balance. In this paper we discuss the dilemma of ‘saving water or being cool’ bringing about recent findings from molecular genetics, to development and physiology of stomata. The question of ‘how relevant is screening for high/low WUE in crops for semi-arid regions, where drought and heat co-occur’ is discussed.