JXB Advance Access originally published online on July 3, 2007
Journal of Experimental Botany 2007 58(11):2733-2744; doi:10.1093/jxb/erm138
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Xylella fastidiosa disturbs nitrogen metabolism and causes a stress response in sweet orange Citrus sinensis cv. Pêra
1Departamento de Fisiologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, 13083-970, Campinas, SP, Brazil
2Universidade Federal Rural do Rio de Janeiro, Km 7 Rodovia BR 465, 23850-000, Seropédica, RJ, Brazil
3Conplant, Rua Francisco Andreo Aledo, 22, 13084-200, Campinas, SP, Brazil
4Departamento de Bioquímica, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, 13083-970, Campinas, SP, Brazil
5Instituto Agronômico de Campinas, Centro de Ecofisiologia e Biofísica, Av. Barão de Itapura 1481, CP 28, 13012-970, Campinas, SP, Brazil
6Instituto Agronômico de Campinas, Centro APTA Citros Sylvio Moreira, CP 04, 13490-970, Cordeirópolis, SP, Brazil
* To whom correspondence should be addressed. E-mail: pmazza{at}unicamp.br
Xylella fastidiosa (Xf) is a fastidious bacterium that grows exclusively in the xylem of several important crop species, including grape and sweet orange (Citrus sinensis L. Osb.) causing Pierce disease and citrus variegated chlorosis (CVC), respectively. The aim of this work was to study the nitrogen metabolism of a highly susceptible variety of sweet orange cv. ‘Pêra’ (C. sinensis L. Osbeck) infected with Xf. Plants were artificially infected and maintained in the greenhouse until they have developed clear disease symptoms. The content of nitrogen compounds and enzymes of the nitrogen metabolism and proteases in the xylem sap and leaves of diseased (DP) and uninfected healthy (HP) plants was studied. The activity of nitrate reductase in leaves did not change in DP, however, the activity of glutamine synthetase was significantly higher in these leaves. Although amino acid concentration was slightly higher in the xylem sap of DP, the level dropped drastically in the leaves. The protein contents were lower in the sap and in leaves of DP. DP and HP showed the same amino acid profiles, but different proportions were observed among them, mainly for asparagine, glutamine, and arginine. The polyamine putrescine was found in high concentrations only in DP. Protease activity was higher in leaves of DP while, in the xylem sap, activity was detected only in DP. Bidimensional electrophoresis showed a marked change in the protein pattern in DP. Five differentially expressed proteins were identified (2 from HP and 3 from DP), but none showed similarity with the genomic (translated) and proteomic database of Xf, but do show similarity with the proteins thaumatin, mucin, peroxidase, ABC-transporter, and strictosidine synthase. These results showed that significant changes take place in the nitrogen metabolism of DP, probably as a response to the alterations in the absorption, assimilation and distribution of N in the plant.
Key words: Amino acids, citrus variegated chlorosis, nitrate reductase, polyamines, proteases, xylem sap, Xylella fastidiosa
Received 21 February 2007; Revised 18 May 2007 Accepted 25 May 2007