Stress Tolerance of Photosystem II in Vivo

Abstract

The in vivo photochemical activity of photosystem 11 was inferred from modulated chlorophyll fluorescence and photoacoustic measurements in intact leaves of several plant species (Lycopersicon esculentum Mill., Solanum tuberosum L., Solanum nigrum L.) exposed to various environmental stresses (drought, heat, strong light) applied separately or in combination. Photosystem II was shown to be highly drought-resistant: even a drastic desiccation in air of detached leaf samples only marginally affected the quantum yield for photochemistry in photosystem 11. However, water stress markedly modified the responses of photosystem 11 to superimposed constraints. The stability of photosystem 11 to heat was observed to increase strongly in leaves exposed to water stress conditions: heat treatments (e.g. 42°C in the dark), which caused a complete and irreversible inhibition of photosystem 11 in wellwatered (tomato) leaves, resulted in a small and fully reversible reduction of the photochemical efficiency of photosystem 11 in drought-stressed leaves. In vivo photoacoustic data indicated that photosystem I was highly resistant to both heat and water stresses. When leaves were illuminated with intense white light at 25°C, photoinhibition damage of photosystem 11 was more pronounced in water-stressed leaves than in undesiccated controls. However, in nondehydrated leaves, photoinhibition of photosystem 11 was strongly temperature dependent, being drastically stimulated at high temperatures above 38 to 40°C. As a consequence, when exposed to strong light at high temperature, photosystem 11 photochemistry was significantly less inhibited in dehydrated leaves than in control well-hydrated leaves. Our results demonstrate the existence of a marked antagonism between physicochemical stresses, with water stress enhancing the resistance of photosystem 11 to constraints (heat, strong light at high temperature) that are usually associated with drought in the field.For a given plant material, the thermolability of PSII has been reported to vary substantially due to influence from various environmental factors. For instance, light has been shown to markedly reduce damage to PSII during heat stress depending on its intensity and spectral characteristics (12, 31, 36). Increased thermostability of PSII has been observed in leaves exposed to physicochemical stresses such as high salinity (21) or hypertonic stress (17). It was also reported that changes in the leaf water potential and osmotic potential influence the thermal tolerance of photosynthesis (14, 32). Observations of this nature suggest the existence of antagonistic interactions between environmental stresses, with one constraint enhancing the tolerance of photosynthesis toward another, superimposed constraint. With regard to temperature stress, this is clearly very important from an ecophysiological viewpoint because under natural conditions, heat stress is often combined with other constraints such as water deficit and strong light. For this reason, we examined the effects of ...

Seasonal variations and acclimation potential of the thermostability of photochemistry in four Mediterranean conifers

“…High temperatures associated with large salt concentrations induced a significant increase of thermostability in Vigna unguiculata [24]. Similarly, light has been shown to protect to some extent PS II against high temperature induced damage [13]. A moderate drought stress increased significantly the thermostability in a range of species like Cedrus atlantica [7,8,23] or Triticum sativum [27] and exogenous abscisic acid (ABA) increased PS II termostability in barley [19] and in cucumber [25].…”

Interactions between water stress, sun‐shade acclimation, heat tolerance and photoinhibition in the sclerophyll Heteromeles arbutifolia

“…In agreement with the findings of Havaux (1993), dynamic adaptation of the photosynthetic system to the rapidly changing temperatures of natural environments could be a more important component of the thermotolerance of plants than the intrinsic resistance of PSII. Havaux (1992) demonstrated the existance of an antagonism between physicochemical stresses in detached, dehydrated leaves of Lycopersicon esculentum and Solcinum sp. with water stress enhancing the resistance of PSII to high PFD at high temperature.…”

“…Since transpiration is drastically reduced by drought, it has proved very difficult to separate the direct effects of high temperature from those of water deficit (Gates 1968). To complicate the matter further, leaf desiccation enhanced resistance of PSII to high temperature stress in certain species (Havaux 1992). Stomatal closure caused by water stress inhibits photosynthesis by limiting the availability of CO2 within the leaf (Boyer 1976;Chaves 1991).…”

Responses of photosynthesis to high temperatures in oak saplings assessed by chlorophyll-a fluorescence: inter-specific diversity and temperature-induced plasticity

“…T c can be influenced by a series of environmental parameters like ambient temperature (Dreyer et al, 2001;Havaux, 1993;Robakowski et al, 2002), water availability (Epron, 1997a;Havaux, 1992;Ladjal et al, 2000) and plant growth regulators like ABA (Havaux, 1992;Ivanov et al, 1992). T c varies largely with season, in parallel to ambient temperatures, and increases during summer and decreases during autumn (Froux et al, 2004;Hüve et al, 2006).…”