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First published online February 16, 2007; 10.1104/pp.106.091827

Plant Physiology 143:1975-1981 (2007)
© 2007 American Society of Plant Biologists

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WHOLE PLANT AND ECOPHYSIOLOGY

Reduced Content of Homogalacturonan Does Not Alter the Ion-Mediated Increase in Xylem Hydraulic Conductivity in Tobacco

Andrea Nardini*, Antonio Gascó, Felice Cervone and Sebastiano Salleo

Dipartimento di Biologia, Università di Trieste, 34127 Trieste, Italy (A.N., A.G., S.S.); and Dipartimento di Biologia Vegetale, Università di Roma La Sapienza, 00185 Roma, Italy (F.C.)

Xylem hydraulic conductivity (Ks) in stems of tobacco (Nicotiana tabacum) wild-type SR1 was compared to that of PG7 and PG16, two transgenic lines with increased levels of expression of the gene encoding the Aspergillus niger endopolygalacturonase (AnPGII). Activity of AnPGII removes in planta blocks of homogalacturonan (HG) with deesterified carboxyls, thus increasing the degree of neutrality of pectins. The effect of K+ was tested in increasing stem Ks using model plants with more neutral polysaccharides in primary walls and, hence, in intervessel pit membranes. Ks measured with deionized water was compared to that with KCl solutions at increasing concentrations ({Delta}Ks, %). Plants transformed for HG degree of neutrality showed a dwarfed phenotype, but {Delta}Ks did not differ among the three experimental groups. The ion-mediated hydraulic effect saturated at a KCl concentration of 25 mM in SR1 plants. All the three tobacco lines showed {Delta}Ks of around +12.5% and +17.0% when perfused with 10 and 25 mM KCl, respectively. Because modification of HG content did not influence ion-mediated hydraulic enhancement, we suggest that pectin components other than HG, like rhamnogalacturonan-I and/or rhamnogalacturonan-II, might play important roles in the hydrogel behavior of pit membranes.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is Andrea Nardini (nardini{at}units.it).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.091827

* Corresponding author; e-mail nardini{at}units.it; fax 39–040–5583875.

Received October 23, 2006; accepted January 27, 2007; published February 16, 2007.




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S. Ferrari, R. Galletti, D. Pontiggia, C. Manfredini, V. Lionetti, D. Bellincampi, F. Cervone, and G. De Lorenzo
Transgenic Expression of a Fungal endo-Polygalacturonase Increases Plant Resistance to Pathogens and Reduces Auxin Sensitivity
Plant Physiology, February 1, 2008; 146(2): 669 - 681.
[Abstract] [Full Text] [PDF]


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