Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants

Abstract

under water deficit. The ratio P N /E o falls under stress while the To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P N ), stomatal conductance (g s ), ratio U o /E o increases. We conclude that tomato plants follow intercellular CO 2 concentration (c i ) and Chl a fluorescence a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted were investigated in control and drought-stressed tomato plants (Lycopersicon esculentum). Gross O 2 evolution (E o ) and as heat and PSII activity is downregulated. This results in a gross O 2 uptake (U o ) were determined by a mass spectrometric decrease in E o as well as P N and U o . Despite reduced charge separation at PSII, the decline of CO 2 assimilation because of 16 O 2 / 18 O 2 isotope technique. Under drought stress P N , g s , c i and U o decline. While photochemical fluorescence quenching lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is Oxygen is used as an alternative electron acceptor in photoresnot affected by drought; however, in the light, E o decreases piration or Mehler reaction and U o rises relative to E o .electron transport chain and damage to the photosynthetic apparatus (Aro et al. 1993). There are several mechanisms known to protect plants against photodamage, including the emission of surplus radiant energy as heat in parallel to decreased PSII activity (Horton et al. 1996) and the use of electron acceptors instead of CO 2 , such as oxygen in photorespiration or Mehler reaction (Park et al. 1996). Thermal dissipation of absorbed light energy, which can be determined by non-photochemical fluorescence quenching in relation to CO 2 gas exchange, is well established in studies with excessive irradiance and reduced CO 2 (Dietz et al. 1985, Krause andBehrend 1986). Drought also leads to an increase in non-photochemical quenching in leaves (Stuhlfauth et al. 1988, Scheuermann et al. 1991, Biehler et al. 1997. One factor contributing to non-photochemical quenching is DpH-dependent high energy quenching, which is correlated with a downregulation of PSII activity (Havaux et al. 1991, Horton et al. 1996. In some experiments,

Measurement of Gross Photosynthesis, Respiration in the Light, and Mesophyll Conductance Using H218O Labeling

“…159 (Berry, Osmond and Lorimer 1978;Canvin et al 1980;227 Biehler et al 1997;Badger et al 2000;Haupt-Herting and Fock 2000;. 228…”

“…Finally, compared to the techniques on attached leaves, enclosing a leaf, petiole, and water 249 supply reduces potential system leaks (Yakir et al 1992;Haupt-Herting and Fock 2000). 250…”

Drought Adaptation Mechanisms Should Guide Experimental Design

“…Damage avoidance may also have a buffering effect, were a given stress level leads to less damage (Figure 3). Examples include changing leaf orientation away from light [21], heat dissipation of excess absorbed energy by PSII [22], the Mehler reaction or photorespiration [23,24], and altered root to shoot ratios [25]. Damage avoidance is the preferred term as the similar term, stress tolerance, is commonly used in a general manner.…”

Photosynthetic carbon assimilation and associated metabolism in relation to water deficits in higher plants

“…there was no photoinhibition): obviously they could cope with high light using other protective mechanisms. Generally, PR consumes a substantial proportion of the total electron flux and plays an important part in redox regulation even if the rate of electron flux is decreased by down-regulation at low A (Biehler & Fock 1996;Cornic & Massacci 1996;Haupt-Herting & Fock 2000, 2002.…”