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Abscission was studied in immature apple fruits (cv Golden Delicious) during the physiological drop. Fruitlet shedding is preceded by a stimulation of ethylene biosynthesis and a gain in sensitivity to the hormone. Experiments were performed on abscising fruitlet (AF) and non-abscising fruitlet (NAF) populations. AF were obtained from lateral fruitlets of trees sprayed with benzylaminopurine (BAP) at 200 ppm, 17 days after petal fall (APF) with a fruit cross diameter of about 10–12 mm.

In zucchini (), different cultivars present a distinctive floral abscission capacity. In greenhouses in the south-east of Spain, the summer conditions (high temperatures and long days) promote the production of bisexual flowers with an inhibition in the floral abscission during fruit formation (‘sticky flower’ syndrome) (Gòmez , 2004).

To protect themselves from disease, plants have evolved sophisticated defense mechanisms in which the signal molecules salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) often play crucial role (Pieterse and Van Loon, 1999). Elucidation of signaling pathways controlling disease resistance is a major objective in research on plant–pathogen interactions. The capacity of a plant to develop a broad-spectrum, systemic acquired resistance (SAR) after primary infection with a necrotizing pathogen is well known and its signal transduction pathway extensively studied (Durrant and Dong, 2004).

Ethylene has long been regarded as a stress hormone. However, the roles of the ethylene signaling in abiotic stress responses remain an open question. Previously, we have cloned tobacco ethylene receptor genes and , and studied their expression in response to different abiotic stresses. We found that both genes were induced by wounding and dehydration (Zhang ., 2001a; Zhang ., 2001b).

Chemical-induced cell death was studied in suspension-cultured tomato ( Mill.) cells (line MsK8) treated with the anticancer drug camptothecin (CPT) and the heavy metal CdSO4. Within 24 h, chemical treatment induced cell death in a concentration-dependent manner.

Herbivore-induced plant volatiles (HIPVs) contribute to attracting the natural enemies of the herbivores and, hence, benefit the plant indirectly. Volatile terpenoids are the major products among the HIPVs from legumes, e.g., lima bean (Phaseolus lunatus) and Medicago truncatula (Leitner et ., 2005).

(teleomorph, ), more commonly known as the cause of grey mould, has a wide host range of over 200 plant species, including many economically important crops such as tomato, grape and potato. This necrotrophic fungus secretes cell wall degrading enzymes which kill host plant tissue in advance of its own growth, metabolising any nutrients that are released (Govrin and Levine, 2000).

The regulation of eukaryotic gene activity at the transcriptional level involves multiprotein complexes and requires the concerted action of transcription factors and coactivator proteins. Transcription factors bind to DNA in a sequence-specific manner and essentially mark a gene for activation or repression through the recruitment of coactivator or corepressor proteins (Spiegelman and Heinrich, 2004).

A model was previously proposed to explain how ACC deaminasecontaining plant growth-promoting bacteria can lower plant ethylene levels and in turn stimulate plant growth (Glick , 1998), especially under stress conditions.

Stratospheric ozone (O3) protects life from detrimental ultraviolet-B radiation, but tropospheric O3 is a serious world-wide pollutant. It is generally accepted that O3 initiates an oxidative burst and an active production of reactive oxygen species (ROS). Several signal molecules like ethylene (ET), jasmonic acid (JA), salicylic acid (SA) and nitric oxide (NO) have been hypothesized to act as a second or third messengers for O3-induced gene expression. Using a pharmacological approach, the aim of this work was to inspect the time course of the NO, SA and ET accumulation under ozone stress in the O3-sensitive tobacco cv BelW3 and the cross talk between these signaling molecules.