Influence of heat shock on chlorophyll fluorescence of white oak (Quercus pubescens Willd.) leaves

Abstract

Chlorophyll fluorescence parameters of Quercus pubescens Willd. as response to heat shock (HS) by immersing leaves for 5 and 15 min in water of temperatures between 38 and 59 o C were examined. Fluorescence was measured after different periods of recovery (15, 30, 90, 210, and 1 440 min at 24/26 ºC night/day temperature and 100 % humidity). The effective quantum yield of photosystem 2 (Y) in control and HS-treated leaves was always measured after previous 15 min irradiation. Under a 5 min HS, Y did not change after using temperatures below 44 o C, was rapidly restored after HS of moderate temperatures (44-48 o C), and progressively decreased and recovered eventually to the initial value after HS of high temperatures (48-52 o C). Y did not recover after HS with temperatures higher than 52 o C. Increase in the duration of HS from 5 to 15 min lead to change of the initial Y at each HS temperature, but the recovery processes were similar to those characteristic after 5 min incubation. The processes of recovery may depend mainly on the specificity of injuries caused by different heat shock temperatures. Thus Q. pubescens is able to preserve and recover the functional potential of its photosynthetic apparatus in response to HS up to 52 o C.Additional key words: photosystem 2; temperature. --The growth and survival of plants can be determined by the thermotolerance capabilities of photosynthesis (Sharkey 2000). The composition of thylakoid membranes of chloroplasts, which contain the light-absorbing system, electron transport chain, and ATP synthase, is important in determining a plant's ability for growth and photosynthesis at high temperatures (Murakami et al. 2000). Heating followed by cooling causes deleterious changes in many physiological processes and disrupts the intricate organization of the thylakoid membrane, which has a high content of unsaturated fatty acids (Berry and Björkman 1980). These membranes must be sufficiently fluid to allow the "spinning" of ATP synthase, yet solid enough to produce the proton-motive force needed to propel this spinning (Gounaris et al. 1984). The thylakoid membrane is heterogeneous, and the lipids must be kept properly dispersed to prevent them from concentrating and forming non-bilayer structures.We examined the influence of the temperature of HS and the period of recovery after shock on the fluorescence of Quercus pubescens leaves. The experiment was set up in a completely randomized block design with 6 replicates. Leaves were collected in August 2005 from the white oak trees that grow in forests of the Leova area of Moldova. As humidity strongly influences the sensitivity of plants to the growing temperature, we incubated the isolated leaves in glass crystallizers on wet filter paper, at a relative humidity of 100 %. The crystallizers were exposed to 60 PAR from luminescent lamps with 16 h daylength, and 26/24 o C day/night temperature for the duration of the experiments. In order to assess the effect of temperature on the photosynthetic machinery, leaves were pre-treated by...

The Influence of Heat Shock and Dessication on Boxwood (Buxus Sempervirens L.) Leaves' Photosystem Ii and Antioxidant Systems Activity

“…In general, the results presented confirm the data obtained by us previously with oak leaves [8,5]. They demonstrate that extending HS duration (extension factor) only quantitatively affects the ability of leaves to recover from HS damage.…”

“…Due to this, the summary response of the box leaves to action of HS at different temperatures can be characterized by determining the parameters quantum yield of PSII in days 10-12 after its application. In general terms, the response of box leaves to HS at different temperatures was similar to that obtained with oak leaves [8].…”

“…To assess the effect of temperature on the photosynthetic machinery, the leaves were pre-treated by immersing them for 5 minutes in distilled water at various temperatures between 50 and 61 o C, maintained at accuracy ±0.05 o C with the help of the ultrathermostat U-10 (Germany). In experiments previously carried out with oak leaves [8] and here repeated with those of box, we demonstrated that at the mentioned duration of exposure to excessive temperatures, the damage to the leaves mainly depends on the extensive factor (temperature). In these conditions, the influence of the phenomena of extension of deterioration caused by the extensive factor (duration of exposure) is minimized.…”

Species-Level Differences in Osmoprotectants and Antioxidants Contribute to Stress Tolerance of Quercus robur L., and Q. cerris L. Seedlings under Water Deficit and High Temperatures

“…9-16 µmol m −2 s −1 in Q. robur) [46,53,62,63]. Similarly, thermotolerance of the investigated species was revealed by the maintenance of significant photosynthetic functionality, together with the lack of irreversible damage to the photosynthetic apparatus (i.e., photoinhibition of the PSII) even at the highest temperature (47 • C; [52,64]).…”

“…9-11%. The duration of the drought treatment was chosen to induce an almost natural, reversible drought stress, thus allowing the plant enough time to acclimate and to recover [52,63]; (3) Heat stress (HS): plants were exposed to daily air temperatures ranging between 33-47 • C (night temperatures were about 25-30 • C), using a small enclosure chamber in the greenhouse for 6 days [64]. During the heat treatment, plants were regularly watered to maintain the soil's maximum water capacity, and the daily air temperature was continuously monitored with thermo-sensors.…”