PHYSIOLOGIA PLANTARUM 115: 87–92. 2002 Copyright C Physiologia Plantarum 2002 Printed in Denmark – all rights reserved ISSN 0031-9317 Silicification in sorghum (Sorghum bicolor) cultivars with different drought tolerance Alexander Lux a, *, Miroslava Luxova ´ b , Taiichiro Hattori c , Shinobu Inanaga c and Yukihiro Sugimoto c a Department of Plant Physiology, Faculty of Natural Sciences, Comenius University, Mlynska ´ dolina B-2, SK-842 15 Bratislava, Slovak Republic b Institute of Botany, Slovak Academy of Sciences, Du ´bravska ´ cesta 14, SK-842 23 Bratislava, Slovak Republic c Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680–001, Japan *Corresponding author, e-mail: lux/fns.uniba.sk Received 10 July 2001; revised 31 October 2001 Sorghum belongs to a group of economically important, sili- con accumulating plants. X-ray microanalysis coupled with environmental scanning electron microscopy (ESEM) of fresh root endodermal and leaf epidermal samples confirms histo- logical and cultivar specificity of silicification. In sorghum roots, silicon is accumulated mostly in endodermal cells. Spe- cialized silica aggregates are formed predominantly in a single row in the form of wall outgrowths on the inner tangential endodermal walls. The density of silica aggregates per square mm of inner tangential endodermal cell wall is around 2700 and there is no significant difference in the cultivars with dif- ferent content of silicon in roots. In the leaf epidermis, silicon deposits were present in the outer walls of all cells, with the Introduction The evidence is overwhelming that silicon (Si) should be included among the elements having a major bearing on plant life (Epstein 1999). Recently it has been necessary to modify the traditional view that silicon deposition in the cell walls was a purely physical process leading to mechanical strengthening of the tissue. Silicon depo- sition is under rather strict metabolic and temporal con- trol (Marschner 1995). The changes in cell wall metabo- lites interacting with silicic acid lead to bulk deposition of silicon into the mature cell wall structure (Perry et al. 1986). A dynamic component of redistribution of silicon is also involved in the protective effects of silicon against insects and pathogens, in addition to a mechanical bar- rier (Heath and Stumpf 1986). Takahashi and Miyake (1977) distinguished between silicon accumulators and silicon non-accumulators. Sor- ghum (Sorghum bicolor) is one of the important silicon Physiol. Plant. 115, 2002 87 highest concentration in specialized idioblasts termed ‘silica cells’. These cells are dumb-bell shaped in sorghum. In both the root endodermis and leaf epidermis, silicification was higher in a drought tolerant cultivar Gadambalia compared with drought sensitive cultivar Tabat. Silicon content per dry mass was higher in leaves than in roots in both cultivars. The values for cv. Gadambalia in roots and leaves are 3.5 and 4.1% Si, respectively, and for cv. Tabat 2.2 and 3.3%. How- ever, based on X-ray microanalysis the amount of Si deposited in endodermal cell walls in drought tolerant cultivar (unlike the drought susceptible cultivar) is higher than that deposited in the leaf epidermis. The high root endodermal silicification might be related to a higher drought resistance. accumulators. Most of the silicon in sorghum, as well as in other graminaceous species, is deposited in the outer walls of the epidermal cells of the leaves and in the in- florescence bracts (Hodson and Sangster 1989). The epi- dermal cell walls are impregnated with a layer of silicon and become an effective barrier against both water loss by cuticular transpiration and fungal infections. In sor- ghum, and many other grasses, a high proportion of sili- con in the leaf epidermis is also located intracellularly in specialized idioblasts called silica cells (Sangster 1970, Esau 1977). In accumulator species, silicon uptake is closely re- lated to root metabolism and not greatly affected by the transpiration rate (Okuda and Takahashi 1965). Silic- ification of root tissues occurs in several species of grass- es. Three basic patterns of silicon distribution were rec- ognized in roots. It can be (1) restricted to the uniseriate