Changes in the ultrastructure of Capsicum annuum L. seedlings roots under aluminum stress conditions

Agata Konarska

doi:10.5586/aa.2008.003

Abstract

The effect of aluminum was investigated on the cell ultrastructure of roots of fourteen-day-old 'Trapez' red pepper seedlings grown in water culture. Disorders in the cell structure were observed using transmission electron microscopy (TEM). An analysis of longitudinal sections of the apical region of the control plants' roots showed that cells of the cap and cells of the meristematic region had an arrangement and shape typical for these root regions, and cell organelles were properly developed. Changes in the cell structure under the influence of aluminum involved a reduction in the number of starch grains in the leucoplasts of the cap, the formation of lobate nuclei and a reduction in the number of cisternae in the dictyosomes as well as the damage of the cell membranes. Moreover, the swelling of mitochondria was observed with a simultaneous reduction in the number of mitochondrial cristae or the bursting of the membrane of these structures. In the vacuoles of the investigated root section, the presence of numerous electron-opaque large-sized formations was found, being most probably aluminum deposits. The cell wall, often thickened, was wavy or the formation of two walls in close distance was observed. The obtained results prove the high sensitivity of the studied red pepper cultivar to aluminum stress.

Highlights

Most plants respond to the presence of mobile aluminum in the substrate by a significant limitation of growth and yielding induced by development anomalies and metabolic disturbances as well as by insufficient supply of the plant with water and nutrients
The amyloplasts contained a smaller number of starch grains, but with much larger sizes compared to the control (Fig. 3)
Numerous mitochondria were characterised by the electron brighter matrix, as well as a reduced number of cristae and often degenerating contents (Fig. 4)

Summary

Introduction

Most plants respond to the presence of mobile aluminum in the substrate by a significant limitation of growth and yielding induced by development anomalies and metabolic disturbances as well as by insufficient supply of the plant with water and nutrients. The most characteristic morphological symptoms of aluminum toxicity are as follows: the shortening of the length of roots, their thickening and browning as well as the bending of the terminal section of the root (Weryszko - Chmielewska et al 1999; Malathi et al 2001; Ta buchi and Matsumoto , 2001; Konarska , 2004b; 2005). The effect of aluminum was frequently accompanied by the shortening of root regions and of the length of root hairs as well as their deformation (Szatanik - K l o c , 1999; Michałek , 2002). An increased thickness of cell walls in the outer layers of the root was observed, as well as the formation of cracks and losses in these tissues (Weryszko - Chmielewska and Chwil , 1998; Budiková , 1999; Vázquez et al 1999; Konarska , 2005). In the presence of aluminum ions, the programmed death of PCD cells was observed (P a n et al 2001), as well as the disintegration of microtubules and a change in polymerisation of the cytoskeleton (Horst et al 1999; Sivaguru et al 1999)

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