PEP Carboxylase Activity Supports Organic Acid Metabolism of Maize (Zea mays ) under Salt Stress Sarah Hatzig, Ashwani Kumar, Anja Neubert and Sven Schubert Shb Institute t of Plant Nutrition Justus Liebig University Heinrich Buff Ring 26 32 35392 Giessen Germany http://www.uni giessen.de//plant nutrition//
Surprising result PEP-carb boxylase activity µmol C O 2 / g FW min 30 1 mm NaCl 100 mm NaCl 25 20 15 10 5 Effect of salt stress on the PEPcarboxylase activity in young shoots of various maize hybrids 0 Pioneer SR03 SR12 SR13 30 25 1 mm NaCl 100 mm NaCl Effect of salt stress on the PEPcarboxylase activity in old shoots of various maize hybrids PEP-carboxylase activity µmol CO 2 / g FW min 20 15 10 5 0 Pioneer SR03 SR12 SR13
Hypotheses EnhancedPEP carboxylase activity in youngshootsincreases CO sugar concentrations 2 PEP PEP carboxylase Oxaloacetate Pyruvate Calvin cycle sugar Malate CO 2 Mesophyll cell Bundlesheath cell Enhanced PEP carboxylase activity in young shoots increases organic acid concentrations COOH C O ~ P PEP carboxylase COOH C O CH 2 CO 2 + OH P i CH 2 PEP COO Oxaloacetate
Experimental approaches Comparison of maize (Zea mays L. hybrid SR 03) as a C 4 plant with wheat (Triticum aestivum L. cv. Thasos) as a C 3 plant Effect of two different light intensities on the Effect of two different light intensities on the concentrations of sugars and organic acids in young shoots
Material: Material and Methods Maize (Zea mays L. hb hybrid SR 03 ) Weizen (Triticum aestivum L. cv. Thasos) Plant cultivation: growth chamber 330 W m 2 and 200 W m 2 26 C C, 16 h (day); 18 C C, 8 h (night) standard nutrient solution (± salt) Sl Salt treatment 100 mm NCl NaCl 13th day: 25 mm NaCl 14th day: 50 mm NaCl 15th day: 75 mm NaCl 16. 20th day: 100 mm NaCl, 20th day: harvest Information on the development and salt resistance of maize hybrid SR 03: Schubert et al.: Plant Sci. 177, 196 202 (2009) Pitann et al.: J. Plant Nutr. Soil Sci. 172, 535 543 (2009)
Material and Methods Parameters: Fresh weight PEP carboxylase activity Glucose, fructose and sucrose concentrations Malate concentrations Alkalinity
Determination of alkalinity Conversion of organic anions into carbonates by ashing at 500 C Solubilization of carbonates with excess acid Back titration with NaOH for the determination of residual acid http://upload.wikimedia.org/wikipedia/commons/8/8c/titolazione.gif
Effect of salt stress on the shoot fresh weights of wheat and maize under two different light intensities 160 Shoot Fresh weigh ht(g) 140 120 100 80 60 40 Control 100 mm NaCl 20 0 Wheat Maize Wheat Maize 330 W m 2 200 W m 2
Effect of salt stress on the PEP carboxylase activity in young shoots of wheat and maize under two different light intensities 1.4 1.2 PEP carboxyl lase activity (µmol CO 2 /g FW min) 1.0 0.8 0.6 0.4 Control 100 mm NaCl 0.2 0.0 Wheat Maize Wheat Maize 330 W m 2 200 W m 2
Effect of salt stress on the glucose and fructose concentrations of young shoots of wheat and maize under two different light intensities t) Glucose (mg g/g fresh weight 0.5 0.0 Control 100mM NaCl Wheat Maize Wheat Maize 330 W m 2 200 Wm 2 ructose fresh weight) F (mg/g f 0.5 0.0 Wheat Maize Wheat Maize 330 W m 22 200 W m 22
Regeneration of PP i as substrate for the pyrophosphatase H + pump Cytoplasm Vacuole H + PP i 2 P i Fructose-1,6-bisphosphate+P i Fructose-6-phosphate Phosphofructokinase Costa dos Santos et al.: Plant Physiol. 133, 885 892 (2003)
Effect of salt stress on the sucrose concentrations of young shootsof wheat and maize undertwodifferent light intensities 3.5 3.0 Control 100 mm NaCl concentration fresh weight) Sucrose (mg/g f 2.5 2.0 15 1.5 1.0 0.5 0.0 Wheat Maize Wheat Maize 330 W m 2 200 Wm 2
Effect of salt stress on the alkalinity in young shoots of wheat and maize under two different light intensities iti 0.25 020 0.20 Control 100 mm NaCl Alkalin nity (mequ / g fres shweight) 0.15 0.10 0.05 0.00 Wheat Maize Wheat Maize 330 W m 22 200 W m 2 2
Effect of salt stress on the malate concentrations in young shoots of wheat and maize under two different light intensities 1.6 1.4 1.2 alate resh weight) M (mg / g fr 1.0 0.8 0.6 0.4 0.2 0.0 Wheat Maize Wheat Maize 330 W m 2 200 W m 2
Conclusions Enhanced PEP carboxylase activity in young shoots of maize under salt stress does not increase sugar supply via the C 4 pathway. This is in agreement with the finding that osmotic adjustment does not limit growth. Enhanced PEP carboxylase activity in young shoots of maize maintains organic acid metabolism under salt stress. De Costa et al.: Physiol. Plant. 131, 311 321 (2007) Hatzig et al.: J. Agron. Crop Sci. (accepted)
Acknowledgment We thank Anita Langer and Christa Lein for excellent technical assistance