Effects of NaCl on Aerenchyma Development in Roots

The basic anatomical structures appeared unchanged by salt stress. Control roots showed some cell collapse at 5-10 mm from the root tip in the mid-cortex. More extensive cortical cavities were evident in older parts further from the root tip. The percentage aerenchyma was measured for cross sections of 20 mm and 30 mm long roots. Maximum gas spaces of about 25% for 20 mm long roots and about 30% for 30 mm roots were recorded in control roots. Under salt stress, significantly less aerenchyma was observed throughout the roots irrespective of growth stage. No more than 12% gas space was found in the middle portions (15-20 mm from root tip) of 30 mm roots. To observe the progress of cell death with time, aerenchyma formation in roots at different intervals was analyzed. Only a limited amount of aerenchyma was observed under salinity stress from 60 h after germination, while in controls gas spaces were clearly developed after only 36 h.

Effects of NaCl on Cell Number and Cell Size in Cortical Cells of Roots

Cell number, cell length and cell diameter measurement in cortical tissues of 20 and 30 mm roots are given, respectively. The cell number was substantially limited in almost every portion of the root tip (0-1.2 mm) under saline conditions. The cell length increased earlier and more closer to the root tip in salt-stressed roots, shortening the phase between cell division and cell elongation. Final cell length (~80 ^m) in root portions proximal to the root tip was similar in control and salt-stressed roots. With the exception of cells in the apical 1 mm, there was no significant difference in cell diameter between treatments. The average diameter for mature cells in the middle cell position was approximately 25 ^m.

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