Interactions of Applied Hormones in the Germination of Lepidium Virginicum Seeds

Tests of the germination response of light sensitive Lepidium virginicum seeds to applied gibberellic acid confirmed earlier reports that gibberellic acid can substitute for red light. Further tests indicated that promotion of germination by either red light or gibberellic acid can be nullified by abscisic acid. Dark incubation of the seeds in kinetin alone resulted in only slight promotion of germination. Combinations of suboptimal gibberellic acid plus kinetin did not enhance germination to a level greater than that for kinetin alone. Optimal concentrations of gibberellic acid plus kinetin can reverse inhibition of certain abscisic acid concentrations. A comparison of these responses with those of Grand Rapids variety of lettuce seed was made. OHIO J. SCI. 77(5): 236, 1977 Seeds of Lepidium virginicum L. require light for germination. Red light (660 nm) is most effective in promoting germination, and far-red light is inhibitory (Toole et al 1955a, b). Alternating exposures of the seeds to red and far-red light have demonstrated that the germination response is photoreversible and implicates the involvement of the phytochrome system (Toole et al 1955a, b). In terms of the photoresponse, therefore, seeds of Lepidium resemble the much studied seeds of lettuce (Lactuca sativa L. var. Grand Rapids). The effects of exogenously applied growth regulators on germination have been more thoroughly studied for Grand Rapids lettuce seeds than for Lepidium. Germination responses with lettuce have been studied in terms of such growth regulators as gibberellic acid (GA), kinetin, auxin and abscisic acid (ABA) (Ikuma and Thimann 1963; Kahn 1967a, b; Kahn et al 1957; Kahn and Tolbert 1965, 1966; Kahn 1968). The relatively limited work involving application of growth regulators to Lepidium seeds includes a study by Toole and Cathey (1961), who demonstrated that the red Manuscript received February 14, 1977 and in revised form June 24, 1977 (#77-21). Present address: Biology Department, Rutgers University, Camdcn, NJ 08102. light requirement for germination can be replaced by applied GA. It is the objective of the present work to further test the germination response of Lepidium seeds to applied hormones to determine if these seeds respond in a manner similar to that of lettuce. METHODS AND MATERIALS Seeds of Lepidium virginicum (obtained through the courtesy of V. K. Toole, Seed Research Laboratory, U.S.D.A., Beltsville, Maryland) were kept in cold storage at —11° to — 13°C for approximately 4 years before use in these experiments. Test plates consisted of lots of 50 seeds placed on a single thickness of Whatman #1, 7.0 cm filter paper in pre-sterilized, plastic petri dishes to which the various test solutions, totaling 3 ml in volume, were added. The dishes were wrapped with aluminum foil immediately after the test solutions were added to the seeds. Using a modification of the methods of Toole et al (1955a, b), the seeds were first incubated at 15°C for 48 hr. The seeds were then transferred to a 25°C incubator for an additional 48 hr, after which time germination counts were made. Plates of seeds to receive a light treatment were unwrapped in the dark and given the required irradiation at the time of the temperature change, after which they were re-wrapped in foil and transferred to the 25°C incubator. The red (660 nm) irradiation used in some tests was achieved by passing light from eight 15 watt, cool-white fluorescent tubes through a 12 inch, square Carolina Biological Supply red 650 plastic filter. For the far-red (735 nm) irradiation, light from a single 300 watt Sylvania reflector flood light was passed first