暑さと干ばつに強い農作物(Critical crops’ alternative way to succeed in heat and drought)

2024-09-14 バーミンガム大学

Maize plants

<関連情報>

• https://www.birmingham.ac.uk/news/2024/critical-crops-alternative-way-to-succeed-in-heat-and-drought
• https://www.pnas.org/doi/abs/10.1073/pnas.2402233121

メソフィル空隙の不飽和化が蒸気圧不足ストレス下でのC4植物の成育に貢献 Mesophyll airspace unsaturation drives C4 plant success under vapor pressure deficit stress

Diego A. Márquez, Suan Chin Wong, Hilary Stuart-Williams, +1, and Graham D. Farquhar
Proceedings of the National Academy of Sciences  Published:September 16, 2024
DOI:https://doi.org/10.1073/pnas.2402233121

Significance

C₄ plants such as maize, millet, and sorghum are crucial for global food security, and our research marks a significant advance in understanding their physiological mechanisms. We demonstrate the existence of nonstomatal control of water loss in C₄ plants and its vital role in maintaining favorable CO₂ conditions to achieve high assimilation rates under increased evaporative demand. Our findings reveal substantial unsaturation within the substomatal cavity even under moderate vapor pressure deficit (VPD), challenging traditional interpretations of C₄ photosynthetic efficiency under VPD stress. This research reframes water use efficiency in C₄ plants, highlighting the crucial role of mesophyll hydraulic properties (i.e., nonstomatal control of water loss) beyond the usual focus on CO₂ concentration mechanisms.

Abstract

A fundamental assumption in plant science posits that leaf air spaces remain vapor saturated, leading to the predominant view that stomata alone control leaf water loss. This concept has been pivotal in photosynthesis and water-use efficiency research. However, recent evidence has refuted this longstanding assumption by providing evidence of unsaturation in the leaf air space of C₃ plants under relatively mild vapor pressure deficit (VPD) stress. This phenomenon represents a nonstomatal mechanism restricting water loss from the mesophyll. The potential ubiquity and physiological implications of this phenomenon, its driving mechanisms in different plant species and habitats, and its interaction with other ecological adaptations have. In this context, C₄ plants spark particular interest for their importance as crops, bundle sheath cells’ unique anatomical characteristics and specialized functions, and notably higher water-use efficiency relative to C₃ plants. Here, we confirm reduced relative humidities in the substomatal cavity of the C₄ plants maize, sorghum, and proso millet down to 80% under mild VPD stress. We demonstrate the critical role of nonstomatal control in these plants, indicating that the role of the CO₂ concentration mechanism in CO₂ management at a high VPD may have been overestimated. Our findings offer a mechanistic reconciliation between discrepancies in CO₂ and VPD responses reported in C₄ species. They also reveal that nonstomatal control is integral to maintaining an advantageous microclimate of relatively higher CO₂ concentrations in the mesophyll air space of C₄ plants for carbon fixation, proving vital when these plants face VPD stress.