The function of the apoplastic enzyme ascorbate oxidase (AO) was investigated in tobacco (Nicotiana tabacum). The abundance of AO mRNA was up-regulated by light. Cytosolic ascorbate peroxidase (APX1) transcripts were also highest in the light. In contrast, l-galactono-␥-lactone dehydrogenase, stromal APX, and thylakoid APX transcripts remained constant over the day/night cycle. Salicylic acid inhibited growth, increased expression of the pathogenesis-related protein (PR) 1a, and decreased AO transcript abundance. In contrast, the application of auxin enhanced growth and increased AO and PR 1a gene expression. Therefore, AO transcript abundance varied in a manner similar to hormone-mediated changes in plant growth. To study the effects of modified AO expression on growth, transformed tobacco plants expressing AO in the sense and antisense orientations were generated. The resultant large changes in apoplastic AO activity in the transformed tobacco plants had little effect on whole leaf ascorbate (AA) content, but they had dramatic effects on apoplastic AA levels. Enhanced AO activity oxidized the apoplastic AA pool, whereas decreased AO activity increased the amount of AA compared with dehydroascorbate. A relationship was observed between AO activity and plant height and biomass. Native AO transcript levels were no longer subject to light/dark regulation in AO sense and antisense plants. Taken together, these data show that there is an interaction between hormone, redox, and light signals at the level of the apoplast via modulation of ion of AA content.Ascorbate (AA) plays a key role in defense against oxidative stress and is particularly abundant in photosynthetic tissues (Foyer et al., 1983; Smirnoff, 2000). Most (over 90%) of the AA is localized in the cytoplasm, but unlike other soluble antioxidants, a substantial proportion is exported to the apoplast, where it is present at millimolar concentrations. Apoplastic AA is believed to represent the first line of defense against potentially damaging external oxidants such as ozone, SO 2 , and NO 2 (Plö chl et al., 2000; Barnes et al., 2002). In the apoplast, AA is oxidized to monodehydroascorbate (MDHA) by the enzyme ascorbate oxidase (AO). MDHA is an unstable radical and rapidly disproportionates to yield DHA and AA. DHA is then transported into the cytosol through the plasma membrane by a specific carrier that preferentially translocates the oxidized form in exchange for the reduced form, ensuring a continuous flux of reducing power to the cell wall (Horemans et al., 2000). Perhaps the most intriguing and poorly understood of the enzymes involved in AA metabolism in plants is the apoplastic AO. No clear biological functions for AO have been described to date. However, it is widely believed that AO plays a role in cell elongation because of its extracellular localization and its high activity in rapidly expanding tissues (Esaka et al., 1992; Moser and Kanellis, 1994; Ohkawa et al., 1994; Kato and Esaka, 1999). Recent work has shown that tobacco (Nicotiana taba...

It is well known that feelings of happiness transfer between individuals through mimicry induced by vision and hearing. The evidence is inconclusive, however, as to whether happiness can be communicated through the sense of smell via chemosignals. As chemosignals are a known medium for transferring negative emotions from a sender to a receiver, we examined whether chemosignals are also involved in the transmission of positive emotions. Positive emotions are important for overall well-being and yet relatively neglected in research on chemosignaling, arguably because of the stronger survival benefits linked with negative emotions. We observed that exposure to body odor collected from senders of chemosignals in a happy state induced a facial expression and perceptual-processing style indicative of happiness in the receivers of those signals. Our findings suggest that not only negative affect but also a positive state (happiness) can be transferred by means of odors.

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