Effects of abiotic stress on gene transcription in European beech: ozone affects ethylene biosynthesis in saplings of Fagus sylvatica L.

Abstract

© iForest -Biogeosciences and Forestry IntroductionEuropean beech is the most abundant broadleaf tree in Germany (Schütt et al. 1992). It is also of major importance for the European forest industry and was therefore chosen as an experimental species for our studies, to obtain deeper molecular insights into the potentially detrimental effects of ozone on European broadleaf forest ecosystems. Plants have long been known to exhibit responses to ozone exposure resembling the hypersensitive response following pathogen attack. Ozone has been qualified as an abiotic elicitor of plant defence reactions (Sandermann et al. 1998). These responses include phytoalexin production and synthesis of pathogenesis-related (PR) proteins, accompanied by the formation of various aromatic metabolites like lignins and flavonoids .Another well-known plant response to ozone exposure is the stimulation of ethylene biosynthesis (Tuomainen et al. 1997, Rao et al. 2002, Langebartels & Kangasjärvi 2004. Activation of ethylene biosynthesis is one of the fastest ozone-dependent biochemical responses so far observed in herbaceous plants, occurring within 5 hours, or even more rapidly (Schlagnhaufer et al. 1997, Nakajima et al. 2001, Moeder et al. 2002. This response was similarly rapid in birch (Vahala et al. 2003) and in an ozone-sensitive poplar clone (Diara et al. 2005). ACC synthase (ACS) and ACC oxidase (ACO), the two enzymes of ethylene biosynthesis, are encoded by gene families in herbaceous plants; several ACS and ACO isoforms have been reported to be induced by ozone (Nakajima et al. 2001, Moeder et al. 2002. In ozone-sensitive as well as ozone-tolerant birch clones, ozoneinduced accumulation of ACS and ACO transcripts was found (Vahala et al. 2003). Similarly, ozone fumigation of beech saplings (180-200 nl L -1 ) showed enhanced transcript levels of ACS2 and ACO1 (Nunn et al. 2005a). We therefore extended our study by reporting the cloning of ACS2 and ACO2, and analysing over a period of 3 month an ozone-induced expression of the ethylene biosynthesis genes (ACS1, ACS2, ACO1, ACO2), the accumulation of the ethylene precursor free ACC and conjugated ACC, and the emission of the end product of this pathway, ethylene, using beech saplings. Materials and methods Plant material and growth conditionsThree-year-old European beech saplings (Fagus sylvatica L., provenance 81024; Schlegel Baumschulen, Riedlingen, Germany) were planted in 14-L pots filled with natural forest soil (site Höglwald, Bavaria, Germany -Betz et al. 2009b). Saplings were maintained during winter under a wooden pergola. Before bud burst, the plants were treated with Promanal ® (Neudorff, Emmerthal, Germany), to prevent insect infestation. In spring the 4-year-old saplings were transferred to climate-controlled cabinets (39 m 2 ) of a greenhouse covered with UV-permeable glass sheets (http://www.helmholtz-muen chen.de/eus/index.php -Olbrich et al. , Betz et al. 2009a. Each cabinet contained 8 tables (2 m 2 per table) and 12 saplings were placed on a single table. The sap...

Involvement of Phytohormones in Plant Responses to Ozone

“…In O 3 -fumigated tomato plants, LE-ACS1A, LE-ACS2, and LE-ACS6 are induced, and the expression of ST-ACS4 and ST-ACS5 is increased in potato (Schlagnhaufer et al 1997;Tuomainen et al 1997). This response was similarly rapid in birch (Vahala et al 2003) and in an O 3 -sensitive poplar clone (Diara et al 2005 , for 6 consecutive months), the transcript levels of ACS1, ACS2, and ACO1 were significantly enhanced (Nunn et al 2005;Betz et al 2009). …”

Histological, physiological and molecular investigations of Fagus sylvatica seedlings infected with Phytophthora citricola

“…There was no correlation between ACO1 with the second ethylene peak. At the time writing this manuscript, cDNA sequences and specific PCR primers for ACC oxidase 2 (ACO2) and for ACC synthases 1 and 2 (ACS1, ACS2) of F. sylvatica were published by Betz et al 2009. However, a possible correlation between the expression of these genes with the second ethylene peak could not be measured anymore.…”

“…There was no correlation between ACO1 with the second ethylene peak. At the time writing this manuscript, cDNA sequences and specific PCR primers for ACC oxidase 2 (ACO2) and for ACC synthases 1 and 2 (ACS1, ACS2) of F. sylvatica were published by Betz et al. 2009.…”

Plant Hormones under Challenging Environmental Factors

“…This response was similarly rapid in birch (Vahala et al 2003) and in an O 3sensitive poplar clone (Diara et al 2005). In O 3 -exposed beech plants (180-200 ppb, 8 h d −1 , for 6 consecutive months), the transcript levels of ACS1, ACS2, and ACO1 were significantly enhanced (Nunn et al 2005;Betz et al 2009). …”