DAYLENGTH AND LIGHT RESPONSES IN GROWTH AND FERTILITY OF GLOSSOPHORA-KUNTHII (PHAEOPHYTA, DICTYOTALES) FROM PACIFIC SOUTH-AMERICA
Abstract
Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4-24 h and photon fluence rates of 10-75 .mu.mol .cntdot. m-2 .cntdot. s-1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long-day regimes with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short-day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short-day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short-day regimes and low irradiances; differentiation was completely inhibited at long-day conditions and high irradiance.