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JXB Advance Access published online on January 11, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erl270
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© The Author [2007]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Vacuolar cysteine proteases of wheat (Triticum aestivum L.) are common to leaf senescence induced by different factors

Dana E. Martínez1, Carlos G. Bartoli1, Vojislava Grbic2 and Juan J. Guiamet1,*

1Instituto de Fisiología Vegetal, Universidad Nacional de La Plata, cc 327, 1900-La Plata, Argentina
2Department of Plant Sciences, University of Western Ontario, 1155 Richmond St., London, ON N6A 5B8, Canada

* To whom correspondence should be addressed. E-mail: jguiamet{at}fcnym.unlp.edu.ar

Cellular proteins are extensively degraded during leaf senescence, and this correlates with an up-regulation of protease gene expression, particularly cysteine proteases. The objectives of this work were (i) to detect cysteine proteases associated with senescence of wheat leaves under different conditions and (ii) to find out their subcellular location. Activity labelling of cysteine proteases with the biotinylated inhibitor DCG-04 detected five bands at 27, 36, 39, 42, and 46 kDa in leaves of wheat senescing under continuous darkness. In-gel activity assays showed that these proteases are only active in an acid milieu (pH 4), and their activity increased several-fold in senescing leaves. Fractionation experiments showed that the senescence-associated cysteine proteases of 36, 39, 42, and 46 kDa localize to a vacuolar-enriched fraction. The vacuolar cysteine proteases of 36, 39, and 42 kDa increased in activity in attached flag leaves senescing naturally during post-anthesis, and in attached leaves of plants subjected to a period of water deficit. Thus, the activity of these vacuolar cysteine proteases is associated with developmental (post-anthesis) senescence and with senescence induced by stress factors (i.e. protracted darkness or drought). This suggests that vacuoles are involved in senescence-associated cellular degradation, and that different senescence-inducing factors may converge on a single degradation pathway.

Key words: Cysteine proteases, leaf senescence, protein degradation, vacuole, wheat


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