Effects of drought preconditioning on thermotolerance of photosystem II and susceptibility of photosynthesis to heat stress in cedar seedlings

Abstract

Changes in photosystem II (PSII) thermotolerance during drought and recovery were studied under controlled conditions in three Mediterranean cedar species (Cedrus brevifolia Henry, C. libani Loudon and C. atlantica Manetti). The temperature at which the quantum yield of PSII photochemistry was reduced by 15% of its value at 25 degrees C was 3 to 4 degrees C higher in drought-treated plants than in well-watered plants. The drought-induced increase in PSII thermotolerance was already evident 8 days after water had been withheld from the seedlings, when net CO(2) assimilation was still at 80% of its initial value, and was visible for up to 12 days after re-watering. When seedlings of the three species were exposed to temperatures above 45 degrees C for 5 h, both maximal quantum yield of PSII photochemistry and net CO(2) assimilation rate were significantly reduced in unconditioned seedlings, whereas drought-preconditioned seedlings were almost unaffected by the heat treatment. Drought-preconditioned seedlings still exhibited a higher tolerance to heat stress than unconditioned seedlings 60 days after re-watering, although the transient, drought-induced osmotic adjustment had fully disappeared. Among species, C. atlantica was the most heat sensitive, whereas the heat treatment had no significant effect on the parameters measured in C. brevifolia.

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

“…This was the case in Cedrus atlantica (Epron, 1997a;Ladjal et al, 2000). In Q. suber, a 10 • C increase of T c was evidenced during the course of a severe drought that resulted in complete stomatal closure (Ghouil et al, 2003).…”

“…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).…”

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

“…High temperatures induce visible damage on leaves [23], growth reductions in trees [22,38] and affect photosynthesis primarily by severely impairing light driven electron transport and thylakoid stability [33]. Among the processes related to photochemistry, the most sensitive to 236 F. Froux et al…”

“…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]. Finally, increased CO 2 resulted also in a larger thermostability of the photosynthetic apparatus [37].…”

Field performance of maize (Zea mays L.) cultivars under drought stress

“…2A) may be partly resulted from low nitrogen uptake (Rimski-Korsakov et al, 2009), oxidative damage of reactive oxygen species and disorganization of thylakoid membranes (Ladjal et al, 2000). Decreased or unchanged chlorophyll levels during drought stress have been reported in many species, depending on the duration, severity of drought (Anjum et al, 2011) and sensitivity of cultivars (Valifard et al, 2012).…”