Photoperiodic control of tetrasporangium formation in the red alga Rhodochorton purpureum

Publisher Website
Google Scholar
Abstract
Six geographical isolates of Rhodochorton purpureum (Lightfoot) Rosenvinge (Rhodophyta, Nemalionales) formed tetrasporangia only in short days at 10°C. For most isolates, the critical day-length increased with latitude of origin from 9.5 h for an isolate from California to 14.5 h for one from Antarctica. Tetrasporangium production could be induced by 9–15 short-day cycles followed by a further 22–28 cycles in long days. A night-break consisting of 1 h of white light in the middle of a 16-h dark period inhibited the short-day response of isolates from low latitudes, but not those from higher latitudes. When a similar night-break was given in the middle of a 14-h dark period, however, the response of all isolates was at least partially inhibited. Night-breaks given at any time in the central 7 h of a 14-h dark period were equally inhibitory. Broad-band red light (0.3–0.4 mmol m-2), given as a night-break, caused 50% inhibition of the short-day response. At a slightly higher photon exposure (0.6 mmol m-2, given as 1 μmol m-2 s-1 for 10 min), narrow-band red (662 nm) and blue (448 nm) light caused similar inhibition, but green (547 nm) and far-red (731 nm) were ineffective as night-breaks. The inhibitory effect of a 10-min night-break with red light could not be reversed by subsequent exposure to an equal photon exposure of far-red light. These results add to the existing evidence that the pigments mediating photoperiodic responses among algae are more varied than those among flowering plants.