J. Aquat. Plant Manage. 40: 2002. 105 J. Aquat. Plant Manage. 40: 105-109 Inhibition of Onion Germination and Root Growth by Cattail Extracts Involves Reduced Cell Proliferation and Disruption of Cell Wall Integrity MARIA T. GALLARDO-WILLIAMS 1,2 , REBECCA L. BARTON 1 , PATRICIA M. DOORIS 3 AND DEAN F. MARTIN 1,4 ABSTRACT The effects of cattail (Typha domingensis P.) aqueous ex- tracts on germination of onion (Allium cepa L.) seeds and development of onion roots were studied using a standard germination bioassay and microscopic examination. Cattail extracts delayed and inhibited growth of onion roots and in- duced inversion in a significant percentage of germinating seedlings. Inhibitory effects correlated well with organic car- bon content of the extracts. Aqueous extracts of cattail roots were more inhibitory than aqueous extracts of stem materi- als, which in turn were more inhibitory than extracts of cat- tail leaves. When actively growing onion roots were exposed to cattail extracts changes observed included loss of root caps, intense desiccation, reduced number of mitotic figures, impaired cell proliferation, and disruption of the cell wall in- tegrity. Key words: Bioassays, colchicine, mitotic figures, nocoda- zole, phytotoxins, Allium cepa, Typha domingensis. INTRODUCTION In Florida public waters, cattails including Typha domingen- sis, are the most dominant emergent aquatic plant species (Schardt 1997). Several factors allow cattails to accomplish this opportunistic expansion, including size, growth habit, adaptability to changes in their surroundings, and the re- lease of compounds that can prevent the growth of other species. We have been concerned with the effects of cattail on other wetland species and with the determination of the chemical compounds that cattails release into surrounding waters. Cat- tail phytotoxins include fatty acids (linoleic and a-linolenic acid) and phenolic compounds (caffeic, p -coumaric and gal- lic acid) (Gallardo-Williams et al. 2002). Both extracts and phytotoxins isolated from extracts have the potential to in- hibit the growth and chlorophyll production of several spe- cies. Prindle and Martin (1996) found that aqueous extracts from different portions of cattail inhibited growth of lettuce 1 Institute for Environmental Studies, Department of Chemistry, Univer- sity of South Florida, Tampa, FL 33620. 2 Current address: Laboratory of Molecular Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709. 3 Environmental Section, Southwest Florida Water Management District, 2379 Broad Street, Brooksville, FL 34604. 4 Corresponding author. Received for publication March 16, 2002 and in revised form May 23, 2002. and radish seeds; the same extracts also inhibited oxygen production by Lyngbya majuscula (Prindle and Martin 1996). We have also shown that aqueous cattail extracts inhibit the growth of salvinia (Salvinia minima Baker) (Gallardo et al. 1998) and reduce its rate of oxygen production (Gallardo et al. 1999). A short-term exposure bioassay showed that oxy- gen production by Valisneria americana Michx., Elodea cana- densis Rich., and Myriophyllum spicatum L. was also inhibited by exposure to aqueous cattail extracts (Ambrogio et al. 2000). A closely related cattail species (T. latifolia), which produces similar phytotoxins, has been shown to inhibit algal growth in vitro (Aliotta et al. 1990). We have reached a certain understanding of the relation- ship between extract concentration and the toxicity of the re- sulting compounds. In order to further clarify the mode of action of cattail-derived substances on ecological targets, we investigated the cellular effects after exposing germinating roots to cattail extracts. Microscopy studies have been a very useful tool to eluci- date the mode of action of natural toxins at the cellular level. Comparison of affected and unaffected tissue can easily re- veal subtle changes, including loss of membrane integrity, changes in starch allocation, degradation of ribosomes, and protrusion of mitochondrial membranes (Dooris et al. 1988, Kupidlowska et al. 1994). A limited number of sensitive, diagnostic bioassays are available to characterize and define the mode of action of compounds produced by aquatic weeds. In this study, we present our results of the inhibition of germination of onion seeds by cattail aqueous extracts, as well as the effects of cat- tail extracts on developing onion roots at the cellular level. MATERIALS AND METHODS Plant material. Mature cattail samples were taken from a storm-water ditch near the University of South Florida cam- pus in Tampa, FL and were identified by Dr. Richard Wunderlin, USF Herbarium, as T. domingensis. Samples were rinsed with deionized water and maintained in half-strength Hoagland’s medium (Steward and Elliston, 1973) in a con- trolled environment Phytotron room (Environmental Growth Chambers, Chagrin Falls, OH) for 1.0 month prior to use. Conditions in the growth chamber were constant with a tem- perature of 26C, 12-hour photoperiod with a light intensity of 190 μE per m 2 per sec at floor level, and 80% relative humidity. Plants were set in plastic trays with dimensions of 59 cm in length by 40.5 cm in width by 17 cm in height with acid-washed sand as a support substrate.