Photo- and antioxidative protection during summer leaf senescence in Pistacia lentiscus L. grown under Mediterranean field conditions.

Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the oldest leaves to the youngest ones, and therefore contributes to plant survival during the adverse climatic conditions typical of Mediterranean summers, i.e. water deficit superimposed on high solar radiation and high temperatures. To evaluate the extent of photo- and antioxidative protection during leaf senescence of this species, changes in carotenoids, including xanthophyll cycle pigments, and in the levels of ascorbate and alpha-tocopherol were measured prior to and during summer leaf senescence in 3-year-old plants grown under Mediterranean field conditions. Although a chlorophyll loss of approx. 20% was observed during the first stages of leaf senescence, no damage to the photosynthetic apparatus occurred as indicated by constant maximum efficiencies of photosystem II photochemistry. During this period the de-epoxidation state of the xanthophyll cycle, and lutein, neoxanthin and ascorbate levels were kept constant. At the same time beta-carotene and alpha-tocopherol levels increased by approx. 9 and 70%, respectively, presumably conferring photo- and antioxidative protection to the photosynthetic apparatus. By contrast, during the later stages of leaf senescence, characterized by severe chlorophyll loss, carotenoids were moderately degraded (neoxanthin by approx. 20%, and both lutein and beta-carotene by approx. 35%), ascorbate decreased by approx. 80% and alpha-tocopherol was not detected in senescing leaves. This study demonstrates that mechanisms of photo- and antioxidative protection may play a major role in maintaining chloroplast function during the first stages of leaf senescence, while antioxidant defences are lost during the latest stages of senescence.

[1]  E. Elstner.  Mechanisms of oxygen activation in different compartments of plant cells , 1991 .

[2]  T. Kozlowski.  CHAPTER 5 – WATER SUPPLY AND LEAF SHEDDING , 1976 .

[3]  T. Kuroiwa,et al.  Three-dimensional analysis of the senescence program in rice (Oryza sativa L.) coleoptiles: Investigations by fluorescence microscopy and electron microscopy , 1998 .

[4]  R. Amasino,et al.  Making Sense of Senescence (Molecular Genetic Regulation and Manipulation of Leaf Senescence) , 1997, Plant physiology.

[5]  W. W. Adams,et al.  Acclimation of leaf carotenoid composition and ascorbate levels to gradients in the light environment within an Australian rainforest , 1996 .

[6]  J. M. Chandlee,et al.  Current molecular understanding of the genetically programmed process of leaf senescence , 2001 .

[7]  The Function of Tocopherols and Tocotrienols in Plants , 2002 .

[8]  V. Shuvalov,et al.  Protection of the photosynthetic apparatus against damage by excessive illumination in homoiohydric leaves and poikilohydric mosses and lichens. , 2001, Journal of experimental botany.

[9]  R. Legge,et al.  THE ROLE OF FREE RADICALS IN SENESCENCE AND WOUNDING. , 1987, The New phytologist.

[10]  J. Briantais,et al.  The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence , 1989 .

[11]  L. Alegre,et al.  Plant aging increases oxidative stress in chloroplasts , 2002, Planta.

[12]  R. Amasino,et al.  Molecular aspects of leaf senescence. , 2000, Trends in plant science.

[13]  W. Gruszecki,et al.  Does the xanthophyll cycle take part in the regulation of fluidity of the thylakoid membrane , 1991 .

[14]  E. Pfündel,et al.  A few molecules of zeaxanthin per reaction centre of photosystem II permit effective thermal dissipation of light energy in photosystem II of a poikilohydric moss , 2001, Planta.

[15]  N. Smirnoff.  THE FUNCTION AND METABOLISM OF ASCORBIC ACID IN PLANTS , 1996 .

[16]  Christine H. Foyer,et al.  Photooxidative stress in plants , 1994 .

[17]  Y Y Leshem,et al.  Plant senescence processes and free radicals. , 1988, Free radical biology & medicine.

[18]  S. Munné-Bosch,et al.  Drought‐induced senescence is characterized by a loss of antioxidant defences in chloroplasts , 2001 .

[19]  B. Halliwell,et al.  Free radicals in biology and medicine , 1985 .

[20]  Lijun Liu,et al.  Abscisic acid and cytokinins in the root exudates and leaves and their relationship to senescence and remobilization of carbon reserves in rice subjected to water stress during grain filling , 2002, Planta.

[21]  K. Asada,et al.  THE WATER-WATER CYCLE IN CHLOROPLASTS: Scavenging of Active Oxygens and Dissipation of Excess Photons. , 1999, Annual review of plant physiology and plant molecular biology.

[22]  S. I. Rosenthal,et al.  Photosynthetic decline and pigment loss during autumn foliar senescence in western larch (Larix occidentalis). , 1997, Tree physiology.

[23]  Barry Haluwell.  Oxidative Stress and the Molecular Biology of Antioxidant Defences , 1997 .

[24]  S. Munné-Bosch,et al.  Interplay between ascorbic acid and lipophilic antioxidant defences in chloroplasts of water‐stressed Arabidopsis plants , 2002, FEBS letters.

[25]  B. Demmig‐Adams,et al.  Photoprotection and Other Responses of Plants to High Light Stress , 1992 .

[26]  O. Björkman,et al.  Leaf Xanthophyll content and composition in sun and shade determined by HPLC , 1990, Photosynthesis Research.

[27]  E. Zeiger,et al.  A Putative Role of the Xanthophyll, Zeaxanthin, in Blue Light Photoreception of Corn Coleoptiles , 1994, Science.

[28]  Wilhelm Gruissem,et al.  Biochemistry & Molecular Biology of Plants , 2002 .

[29]  Nicholas Smirnoff,et al.  The role of active oxygen in the response of plants to water deficit and desiccation. , 1993, The New phytologist.

[30]  R. Leblanc,et al.  Increased heat emission and its relationship to the xanthophyll cycle in pea leaves exposed to strong light stress , 1991 .

[31]  J. Zeevaart,et al.  The 9-cis-epoxycarotenoid cleavage reaction is the key regulatory step of abscisic acid biosynthesis in water-stressed bean. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[32]  C. Forney,et al.  Improving the thiobarbituric acid-reactive-substances assay for estimating lipid peroxidation in plant tissues containing anthocyanin and other interfering compounds , 1999, Planta.

[33]  A. Trebst,et al.  A specific role for tocopherol and of chemical singlet oxygen quenchers in the maintenance of photosystem II structure and function in Chlamydomonas reinhardtii , 2002, FEBS letters.

[34]  R. Dhindsa,et al.  Leaf Senescence: Correlated with Increased Levels of Membrane Permeability and Lipid Peroxidation, and Decreased Levels of Superoxide Dismutase and Catalase , 1981 .

[35]  A. Kozaki,et al.  Photorespiration protects C3 plants from photooxidation , 1996, Nature.

[36]  E. Proebsting,et al.  The behavior of peach and pear trees under extreme drought stress. , 1980 .

[37]  H. Akerlund,et al.  The xanthophyll cycle, its regulation and components , 1997 .

[38]  Park S. Nobel,et al.  Physicochemical and Environmental Plant Physiology , 1991 .

[39]  L. Alegre,et al.  Changes in carotenoids, tocopherols and diterpenes during drought and recovery, and the biological significance of chlorophyll loss in Rosmarinus officinalis plants , 2000, Planta.

[40]  A. Altman,et al.  Xylem abscisic acid accelerates leaf abscission by modulating polyamine and ethylene synthesis in water-stressed intact poplar , 2001, Trees.

[41]  M. Havaux.  Carotenoids as membrane stabilizers in chloroplasts , 1998 .

[42]  Catherine M Smart,et al.  Gene expression during leaf senescence. , 1994, The New phytologist.

[43]  B. Osmond,et al.  Too many photons: photorespiration, photoinhibition and photooxidation , 1997 .

[44]  H. Frank,et al.  How carotenoids function in photosynthetic bacteria. , 1987, Biochimica et biophysica acta.

[45]  Hartmut K. Lichtenthaler,et al.  Chlorophyll Fluorescence Signatures of Leaves during the Autumnal Chlorophyll Breakdown , 1987 .