100 Effects of chelated iron on gametogenesis in kelp gametophytes

Abstract

Gametogenesis in several species of kelp gametophytes was investigated in relation to the supply of chelated iron (Fe‐EDTA) in the culture medium. Spores of Laminaria setchellii, Egregia menziesii, Alaria marginata, Dictyoneurum californicum, and Macrocystis pyrifera were grown in Provasoli's Enriched Seawater with and without added Fe‐EDTA. All species showed a decrease in gametogenesis without added Fe‐EDTA. Gametophytes of E. menziesii showed predominant gametogenesis even without supplied iron, resulting in all cells being converted to gametes so that vegetative growth did not continue. Vegetative gametophytes were obtained in the other species. M. pyrifera did not show any gametogenesis without added Fe‐EDTA. L. setchellii, A. marginata and D. californicum were intermediate in their response. In addition, Fe‐EDTA supply was delayed by 1, 2 and 3 weeks with spores of M. pyrifera, resulting in an intermediate degree of gametogenesis which decreased as the delay grew longer. Fe‐EDTA supply was also investigated using isolated female gametophytes of two strains of M. pyrifera and one of Macrocystis integrifolia. None of the three strains produced gametes without the addition of Fe‐EDTA. Gametophytes of M. integrifolia required the least amount of added Fe‐EDTA to achieve gametogenesis while gametophytes of M. pyrifera required higher amounts, with the two strains showing different responses. Thus, by varying the supply of chelated iron, it is possible to control vegetative growth or gametogenesis in most of these kelp species. In addition, different species and individuals show varied responses to added chelated iron.