ANATOMICAL ADAPTATIONS IN BEACH ALTERNANTHERA AND WHITE MOUTH DAYFLOWER UNDER SALINITY STRESS

Specific anatomical features of two halophytes, Alternanthera maritima (Mart.) A.St.-Hil. and Commelina erecta subsp. maritima, distributed exclusively on coastal sand dunes in Nigeria, were investigated to deepen scientific knowledge on the anatomical responses of strand plants growing under salt stress. Potted plants were raised from vegetative stem cuttings in perforated plastic pots (20x26 cm) filled with 2:1 mixture (v/v) of river sand to topsoil. Plants were treated with 0 (control), 70, 140, 280 and 560 mM NaCl solution for 12 weeks in a Greenhouse study. Free hand sections of the leaf, stem and root were examined under the microscope, and cell dimensions were measured using an ocular micrometer. C. erecta subsp. maritima did not survive beyond 280 mM NaCl treatment. Stomata were found only on the abaxial side of the leaves in both plants. Stomatal density and number of stomata/leaf were remarkably higher in plants grown in the absence of salt and decreased with increasing salt concentration. Salinity induced leaf succulence in A. maritima by increasing spongy and palisade cells size and layers. The variables however remained fairly constant for all the parameters in C. erecta subsp. maritima. Salinity increased A. maritima stem diameter and cross-sectional area at 70-280 mM NaCl by increasing the stele dimension but decreased at higher salt concentration. C. erecta subsp. maritima had a reduced stem diameter and cross-sectional area with increasing salt concentration as the proportion of the cortex was negatively affected. A reduction in root diameter and cross-sectional area in both plants increased as salt concentration increased due to reduction in cortex and stele.