Differential Germination of Fern and Moss Spores in Response to Mercuric Chloride

Abstract

The pervasive use of toxic substances and the synthesis of myriad new such compounds requires that toxic substance limits be set and that environmental monitoring be maintained in order to insure the health and integrity of the biosphere. Bioassays are the primary mechanism for meeting these two requirements. A bioassay designed to determine the environmental impact of a particular toxic substance, for example divalent mercury, should have the following attributes: ease of performance, low cost, brevity, sensitivity, and high overall reflectivity of environmental stress induced by the presence of the toxic substance. The appropriateness of a bioassay is based on the selection of its two primary components-the living system employed and the parameter measured. Petersen et al. (1980) have demonstrated the feasibility of using the germination of Onoclea sensibilis spores to gauge the toxicity of various heavy metal ions. It was found that for the three metal ions tested, toxicity was directly proportional to atomic weight. Hg ++ is twice as toxic as Cd++ and four times as toxic as Co+ +. The present study is a comparison of the germination responses of different fern and moss spores to divalent mercury. There are few investigations on the effects of metal ions and other potential pollutants on fern spores and gametophytes that yield data pertinent to pollution research and control. Nakazawa and Tsusaki (1959) determined that the fern spore cytoplasm associated with rhizoid differentiation has a marked affinity for metal ions. Nakazawa and Otaki (1962) demonstrated the affinity of developed rhizoids for metal ions. Fern rhizoids apparently function like the root hairs of vascular plants in absorbing water and minerals from the soil. Therefore, their affinity for metal ions is not surprising. Co++ and Ni++ were shown to prolong filamentous (onedimensiqnal) growth in Lygodium smithianum gametophytes (Pares, 1958) resulting in a retardation of their development sequence. LiCl caused a precocious differentiation of terminal papillae (gland-like hair cells produced by some fern gametophytes) in Dryopteris varia (Nakazawa, 1960a, b). Several metal chlorides at concentrations of 0.005-0.08M decreased the period of fern sperm motility (Igura, 1958). A few papers on ferns with direct application to pollution monitoring have been published. Klekowski (1976), Klekowski and Berger (1976), and Klekowski and Poppel (1976) found that meiotic chromosome behavior during fern sporogenesis was correlated with the presence of toxic substances in the environment. Howard and Haigh (1972) studied the effects of increasing doses of X-radiation on the first mitotic division of Osmunda regalis spores. Edwards and Miller (1970, 1972a, b) studied the quantitative effects of ethylene on Onoclea sensibilis spore germination and gametophyte growth. Fern gametophytes also have been successfully employed in bioassay procedures for the plant hormones kinetin, gibberelic acid, and antheridogen (Bopp, 1968; Brandes, 1973).