Silicon effect on suberization and lignification in roots of rice (Oryza sativa)

This study was performed to study the effect of silicon (Si) nutrition on suberization and lignification in roots of rice. Besides physiological and histochemical examinations of the roots, transcription of candidate genes related to synthesis of suberin and lignin was investigated using microarray analysis. 14 days old rice seedlings (Oryza sativa, cv. Selenio) were cultivated for 28 days in non-aerated nutrient solution (mM: 1.43 NH4NO3, 0.32 NaH2PO4 x H2O, 0.51 K2SO4, 1 CaCl2 x 2 H2O, 1.6 MgSO4 x 7 H2O; µM: 1.82 MnSO4, 0.03 (NH4)6Mo7O24, 9 H3BO3, 0.3 ZnSO4 x 7 H2O and 0.15 CuSO4). The pH-value was adjusted to 6.0 by addition of 10 % (v/v) H2SO4 and 0.75 M KOH.Plants were supplied with Si in form of K2SiO3 at concentrations 0 ppm Si (control) and 50 ppm Si (1.78 mM) and potassium in the control treatment was balanced with K2SO4 supply. The plants were grown in a growth chamber (photoperiod: 14 h light, 10 h dark; temperature 25°C day / 20°C night; relative humidity 75 %; light intensity 220 µmol m2 s-1). Adventitious roots were harvested at 0-2 cm and 4-6 cm distance from the root tip and frozen immediately in liquid nitrogen. For RNA isolation, roots were ground under liquid nitrogen and total RNA was isolated using TRIsure® Reagent (Bioline, Luckenwalde, Germany) following the instructions of the manufacturer. To examine transcription of genes related to suberin and lignin synthesis, a self developed microarray containing amongst others ABC transporter, aclytransferases, ß-ketoacyl-CoA synthases and peroxidases was used . Results from four microarrays are summarized in this study. The samples originate from two root zones (0-2 and 4-6 cm) with each two Si treatments (0 ppm and 50 ppm Si) as mentioned above. Microarrays were hybridized in a dye swap approach: Dye-swap1: 0-2 cm with and without Silicon. Dye-swap2: 4-6 cm with and without silicon