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Báo cáo lâm nghiệp: "Assessment of the effects of below-zero temperatures on photosynthesis and chlorophyll a fluorescence in leaf discs of Eucalyptus globulu"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài:Assessment of the effects of below-zero temperatures on photosynthesis and chlorophyll a fluorescence in leaf discs of Eucalyptus globulus...

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Nội dung Text: Báo cáo lâm nghiệp: "Assessment of the effects of below-zero temperatures on photosynthesis and chlorophyll a fluorescence in leaf discs of Eucalyptus globulu"

Assessment of the effects of below-zero temperatures on photosynthesis and chlorophyll a fluorescence in leaf discs of Eucalyptus globulus L.F. Serrano, M.M. Chaves, M.H. Almeida J.S. Pereira Inst. 1399 Lisbon Codex, Sup. Agronomia, Portugal measured slow fluorescence Introduction and -5°C, we kinetics of a and photosynthetic chlorophyll capacity at 25°C with saturating light and C0 2 concentration (provided by a bicarbonate/car- The sensitivity of plants to low tempera- bonate buffer, pH 8.7, giving rise to a C0 2 tures has been assessed by a number of concentration of approximately 5%), using an methods, including measurements of LD-2 Hansatech oxygen electrode + fluoro- meter. Leaf discs were illuminated with an LS-2 visible symptoms of injury, vital staining Hansatech light source. Fluorescence was techniques, protoplasmic streaming, plas- induced with red light at 650 mm and was molysis and changes in the pattern of detected at 760 nm. Control discs were kept in chlorophyll fluorescence kinetics (Baker the dark at 25°C for the same periods. et al., 1983; MacRae et al., 1986). The When the methods of injury assessment aim of our study was to test the possibility to be compared, whole plants were frozen were and the leaf discs collected for measurements of using changes in photosynthetic capaci- of photosynthetic oxygen evolution and fluores- ty and in slow fluorescence kinetics in leaf cence. Tissue necrosis was expressed in terms discs of Eucalyptus globulus to screen of mean % injury per leaf per plant. resistance to below-zero temperatures, which we compared with the classic tissue necrosis method. Results The effects of the temperature treatments Materials and Methods on photosynthetic capacity (P of the ) N eucalypt leaf discs are shown in Fig. 1. Leaf discs (10 ) 2 cm of E. globulus potted plants Values of P measured either at 700 or N subjected to low temperature treatments. were 2500 pmol quanta.m- are slightly 1 s- ’ 2 They were placed in the dark, inside an alumi- increased in treatments of 2 h at -2 and num box floating in a 10 I bath containing ethyl- - 3°C, whereas in treatments at -4 and ene glycol. After 2 h of exposure at -2, -3, -4
- 5°C photosynthesis dropped to values with R being the depen- 0.71, P
The increasing delay of the fluorescence used as reliable screening tests for the decrease kinetics to reach the final stea- detection of low temperature effects on leaves of E. globulus. dy-state fluorescence, which is well expressed by the decrease in R values fd when treatment temperatures declined, is in accordance with results reported by References several authors (MacRae et al., 1986; Smillie et al., 1987). Such alterations in the fluorescence kinetics indicate damage Baker N.R., East T.M. & Long S.P. (1983) Chil- of the photosynthetic function. However, ling damage to photosynthesis in young Zea mays. 11. Photochemical functioning of thyla- we cannot tell whether the disturbances koids in vivo. J. Cxp. Bot. 34, 189-197 occurred during the induction period, the Lichtenthaler H.K. & Rinderle U. (1988) The state I-state II transitions or the photo- role of chlorophyll fluorescence in the detection synthetic C0 fixation, since R values 2 td of stress conditions in plants. CRC Crit. Rev. cover the whole process of photosynthesis Anal. Chem. 19 (suppl. 1 ), S29-S85 (Lichtenthaler and Rinderle, 1988). MacRae E.A., Hardacre A.K. & Fergusson I.B. (1986) Comparison of chlorophyll fluorescence These results obtained using leaf discs with several other techniques used to assess in agreement with earlier work with are chilling sensitivity in plants. Physiol. Plant. 67, intact E. globulus plants. The degree of 659-665 correlation obtained between the percent- Smillie R.M., Nott R., Hetherington S. & Oquist age of tissue necrosis and either photo- G. (1987) Chilling injury and recovery in deta- synthetic capacity or fluorescence quench- ched and attached leaves measured by chloro- phyll fluorescence. Physio/. Plant. 69, 419-428 ing indicates that both techniques may be

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