A cDNA and a corresponding genomic clone encoding a protein with partial identity to type II proteinase inhibitors from potato, tomato and Nicotiana alata, were isolated from tobacco libraries. The protein of 197 amino acids contains a putative signal peptide of 24 residues and three homologous domains, each with a different reactive site. The tobacco PI-II gene is not expressed in leaves of healthy plants, but is locally induced in leaves subjected to different types of stress (TMV infection, wounding, UV irradiation) and upon ethephon treatment. As opposed to the analogous PI-II genes of potato and tomato, the tobacco gene is not systemically induced by wounding or pathogenic infection. A far-upstream region in the PI-II promoter, containing various direct and indirect repeats, shares considerable sequence similarity to a similar region in the stress-inducible Cu/Zn-superoxide dismutase gene of N. plumbaginifolia.
We have identified a new plant gene, AtCOX17, encoding a protein that shares sequence similarity to COX17, a Cu-binding protein from yeast (Saccharomyces cerevisiae) and vertebrates that mediates the delivery of Cu to the mitochondria for the assembly of a functional cytochrome oxidase complex. The newly characterized Arabidopsis protein has six Cys residues at positions corresponding to those known to coordinate Cu binding in the yeast homolog. Moreover, we show that the Arabidopsis COX17 cDNA complements a COX17 mutant of yeast restoring the respiratory deficiency associated with that mutation. These two lines of evidence indicate that the plant protein identified here is a functional equivalent of yeast COX17 and might serve as a Cu delivery protein for the plant mitochondria. COX17 was identified by investigating the hypersensitive response-like necrotic response provoked in tobacco (Nicotiana tabacum) leaves after harpin inoculation. AtCOX17 expression was activated by high concentrations of Cu, bacterial inoculation, salicylic acid treatment, and treatments that generated NO and hydrogen peroxide. All of the conditions inducing COX17 are known to inhibit mitochondrial respiration and to produce an increase of reactive oxygen species, suggesting that gene induction occurs in response to stress situations that interfere with mitochondrial function.
In M. braunii, the uptake of NO3" and NO2~ is blue-lightdependent and is associated with alkalinization of the medium. In unbufTered cell suspensions irradiated with red light under a COj-free atmosphere, the pH started to rise 10 s after the exposure to blue light. When the cellular NO3~ and NO2~ reductases were active, the pH increased to values of around 10, since the NH4* generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H2SO4 of NOa" or NO2" uptake and reduction showed that two protons were consumed for every one NH/ released. The uptake of CI" was also triggered by blue light with a similar 10 s time response. However, the Cr-dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl") taken up by the cells were released to the medium. When the cells lacked NO3" and NO2~ reductases, the shape of the alkalinization traces in the presence of NO3" and NO2" was similar to that in the presence of cr, suggesting that NO3" or NO2" was also released to the medium. Both the NO3"-and Cl-dependent rates of alkalinization were independent of mono-and divalent cations.
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