Effects of allelochemical stress produced by Sicyos deppei on seedling root ultrastructure of Phaseolus vulgaris and Cucurbita ficifolia

The allelopathic potential of the cucurbit Sicyos deppei has been reported. Aqueous leachates (1% w/v) of S. deppei significantly inhibited the radicle growth of several test plants. Root tips of treated plants were thicker, with a brownish color as compared to control roots. Light microscope observations of treated root tips of Phaseolus vulgaris showed that cells around the quiescent center appeared compressed. Tissues were disorganized and lacked evident cell differentiation. Cucurbita ficifolia did not show these differences in root morphology. Scanning and electron microscope observations showed that treated roots of both P. vulgaris and C. ficifolia had ultrastructural alterations of certain organelles, the plasma membrane, and cell walls. Root cap cells of treated roots showed amorphous and inactivated (nondividing) nuclei, mitochondria, and endoplasmic reticulum. Vacuoles in treated cells showed invaginations that may correspond to engulfing of damaged cellular components.