ENVIRONMENTAL AND HORMONAL CONTROL OF TURION GERMINATION IN MYRIOPHYLLUM VERTICILLATUM

Germination, or outgrowth, of Myriophyllum verticillatum turions involves a series of visible changes starting with reflexing of leaves followed by extension and curving of the axis, and then by root formation. Before abscission, turions grow out in response to long days (16 hr) but not short days (8 hr). After abscission, turions show maximal dormancy which can be fully broken by a cold treatment (4 C). Turions are heterogeneous in degree of dormancy and ability to respond to less complete dormancy-breaking treatments, e.g., long days at 20 C. Cytokinins (106 M) break dormancy of non-cold-treated turions, whereas gibberellic acid (GA3) is ineffective except at high concentrations (10-3 M). Continuous treatment with cytokinins causes abnormal development after germination. GA3, on the other hand, induces apparently normal development even at high concentration. Indoleacetic acid (IAA) induces outgrowth only at high concentrations (10-3 10-' M), but these concentrations also produce abnormal development. Abscisic acid (ABA, 10' M) retards outgrowth of cold-treated turions and can completely suppress it in non-cold-treated turions. The activity of ABA-like substances in turions remains about the same before and during germination, whereas other (unidentified) acidic inhibitors decrease markedly. The cytokinin activity changes in a complex pattern. THE ENVIRONMENTAL and hormonal control of dormancy and germination, or outgrowth, of turions have been studied in only a few species. These specialized buds of vascular hydrophytes are of interest, because they can be very important in propagation as well as overwintering of the plants (Weber, 1972). Temperature and light have been found to affect the germination of some turions. For example, turions of some clones of Spirodela polyrhiza (L.) Schleiden require cold-treatments for germination, but other clones do not (Jacobs, 1947; Perry, 1968). Hydrocharis morsus-ranae L. turions require either a cold (0-4 C) or a warm (greater than 40 C) treatment for germination (Vegis, 1932; 1955). Light has been shown to stimulate germination of turions of H. morsusranae (Terras, 1900). Hormonal control of turion germination appears to be similar to that found in other buds. Kummerow (1958) and Lacor (1969), who studied H. morsus-ranae and S. polyrhiza, respectively, found that kinetin would promote turion germination, but that indoleacetic acid (IAA) antagonized 1 Received for publication 28 July 1975. 2 Present address: Biological Station, University of Michigan, Ann Arbor, 48109. This publication represents a portion of a dissertation presented to the H. H. Rackham School of Graduate studies at The University of Michigan in partial fulfillment of the requirements for the degree of Doctor of Philosophy (J. A. W.). We wish to thank the HoffmanLaRoche Co. for the gift of 100 mg of + ABA and the Amchem Products, Inc. for providing the Ethephon used in this study. this action in H. morsus-ranae. Gibberellins were shown to promote turion germination in S. polyrhiza (Perry, 1968; Lacor, 1969). Pieterse, Bhalla, and Sabharwal (1971) found a lower level of gibberellin activity in turions than in actively growing plants of Wolffiella f loridana (J. D. Smith) Thompson. In order to extend our knowledge of the control of turion development and germination, a broad study of the turions of Myriophyllum verticillatum L., a submerged aquatic vascular plant, was undertaken. In this species, turions are distinct from normal vegetative buds; they abscise from the parent plant at maturity and are important in propagation and overwintering (Weber and Nooden, 1974a). Data on the environmental and hormonal control of dormancy and germination of M. verticillatum turions will be presented. Some of these data have been presented in other reports (Weber and Nooden, 1972, 1974b). MATERIALS AND METHODS-Myriophyllum verticillatum turions were collected periodically during the fall and winter from local lakes and prepared for culture or extraction as described earlier (Weber and Nooden, 1976). Attached turions were collected from late September through October (Weber and Nooden, 1974a). Abscised, dormant turions were collected from late October through early November before the lake temperature dropped to 10 C. Some turions were also collected in the winter when ice covered the lake. Since it was not practical to produce large quantities of turions in growth chambers, or even in