GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. V. ETHYLENE AND THE EARLY EVENTS OF SPORE GERMINATION

Abstract

Early events during the germination of spores of the fern Onoclea sensibilis were studied to determine the time during germination when ethylene had its greatest inhibiting effect. Water imbibition by dry spores was rapid and did not appear to be inhibited by ethylene. During normal germination DNA synthesis occurred about four hours before the nucleus moved from a central position to the spore periphery. Following nuclear movement, mitosis and cell division occurred, partitioning the spore into a small rhizoid cell and a large protonemal cell. Cell division was complete approximately six hours after nuclear movement. Ethylene treatment of the spores blocked DNA synthesis, nuclear movement, and cell division. The earliest DNA replication in uninhibited spores was observed after 14 hours of germination, and the maximal rate of spore labeling with 3H‐thymidine was between 16 and 20 hours. Spores were most sensitive to ethylene, however, during the stages of germination prior to DNA synthesis, and it was concluded that ethylene did not directly inhibit DNA replication but blocked germination at some earlier fundamental step. The effects of ethylene were reversible. since complete recovery from inhibition of germination was possible if ethylene was released and the spores were kept in light. Recovery was much slower in darkness. It was hypothesized that light acted photosynthetically to overcome the ethylene inhibition of germination. Consistent with this, it was shown that spores exhibit net photosynthesis after only two hours of germination.