NUCLEAR EVENTS DURING EARLY DEVELOPMENT IN GAMETOPHYTES OF MACROCYSTIS-PYRIFERA, AND THE TEMPORAL EFFECTS OF A MARINE CONTAMINANT

The time course of DNA synthesis in developing haploid gametophytes of the giant kelp Macrocystis pyrifera was determined, and the effects o f arsenic (As) on the temporally distinct nuclear events, DNA synthesi s and subsequent nuclear division/translocation, were investigated to establish which of these specific events may be disrupted by this cont aminant. Experiments were carried out on material collected from kelp beds near Santa Barbara, California from 1993-1994. Timing of DNA synt hesis was determined during development by use of the fluorochrome, DA PI (4',6-diamidino-2-phenylindole), and single-cell microspectrofluoro metry. Zoospores, which result from meiosis, had already undergone two rounds of DNA synthesis at the time of release. The developing gameto phytes underwent an additional two rounds of replication of DNA by 16 h of development, and following the first nuclear division/translocati on, the gametophyte contained eight times the minimum DNA level throug hout subsequent development. Both DNA synthesis and nuclear division/t ranslocation, were found to be inhibited by As. Phosphate enrichment r educed the inhibitory effects of As on division/translocation of the n ucleus, supporting the hypothesis As interferes with phosphorylation. Gametophytes were more severely affected by As under light conditions, as opposed to dark, suggesting that photosynthesis may be more sensit ive than dark metabolism.