Research article Physiological and metabolic changes of Cucurbita pepo leaves in response to zucchini yellow mosaic virus (ZYMV) infection and salicylic acid treatments Deya Eldeen Mohammed Radwan a,b , Khalaf Ali Fayez b , Sabry Younis Mahmoud c , Ahmed Hamad d , Guoquan Lu a, * a College of Agriculture & Biotechnology, Zhejiang University, 268 Kaixuan Road, Hangzhou 310029, Zhejiang, China b Botany Department, Faculty of Science, Sohag University, Sohag 82524, Egypt c Virology Department, Faculty of Agriculture, Sohag University, Sohag 82786, Egypt d Botany Department, Faculty of Science, Assiut University, Assiut, Egypt Received 26 July 2006; accepted 5 March 2007 Available online 12 March 2007 Abstract The changes of some physiological and biochemical parameters in pumpkin (Cucurbita pepo cv Eskandarani) leaves associated with zucchini yellow mosaic virus (ZYMV) infection and the effect of exogenous application of salicylic acid (SA) were studied in this paper. In comparison to the untreated leaves, ZYMV infected leaves showed many symptoms, including severe mosaic, size reduction, stunting and deformation. Results from analysis of physiological parameters indicated that viral infection and SA treatments affected metabolism. Viral infection decreased pig- ment, protein and carbohydrate levels. But with all SA treatments, the protein and carbohydrate contents are noticeably increased. Moreover, the other biochemical parameters showed variable alterations. The peroxidase (POX, EC 1.11.1.7) activity and proline contents were induced by both viral infection and SA treatments. In addition, protein patterns represent some newly synthesized polypeptides which reflect formation of pathogenesis related proteins in all treatments. SA treatment increases the plant resistance against ZYMV. This can be noticed through re- duction of percentage of the infected plants, decrease in disease severity and virus concentration of the plants treated with SA then inoculated with virus. All results show significant changes in metabolism affected by either viral infection or SA treatments and also indicate that exog- enous SA plays an important role in induction of defense mechanism against ZYMV infection. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Metabolism; Peroxidase; Pigments; Pumpkin; Salicylic acid; Systemic acquired resistance; Zucchini yellow mosaic virus 1. Introduction Many types of environmental stresses both biotic and abiotic produce characteristic changes in physiology and metabolic processes of higher plants [26]. Among these stresses, attack by pathogens which cause many biochemical changes lead to harmful effects on plant health. There are more than 20 viruses infecting cucurbit crops [8]. Zucchini yellow mosaic virus (ZYMV) is one of the most im- portant viruses affect cucurbit production. It causes destructive diseases to a large variety of economically important cucurbit plants including zucchini squash (Cucurbita pepo) [44]. ZYMV was reported in many African countries including Algeria, Egypt, Madagascar, Mauritius, Morocco, Reunion, Swaziland and Tunisia [22]. Morphological symptoms Abbreviations: Chl, chlorophyll; POX, peroxidase; SA, salicylic acid; SAR, systemic acquired resistance; SA þ V, treated with salicylic acid then in- oculated with virus; ZYMV, zucchini yellow mosaic virus. * Corresponding author. Tel./fax: þ86 571 8697 1117. E-mail addresses: deya90@yahoo.com (D.E.M. Radwan), lugq10@zju. edu.cn (G. Lu). 0981-9428/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.plaphy.2007.03.002 Plant Physiology and Biochemistry 45 (2007) 480e489 www.elsevier.com/locate/plaphy