Cell size, nucleic acids, and synthetic efficiency in the wild type and a growth mutant of the multicellular alga Ulva mutabilis Føyn

Abstract

At a given light intensity the wild type of the green multicellular alga Ulva mutabilis Føyn grows at a slower rate than the mutant Slender. The mutant contains the same or a slightly greater amount of chlorophyll and RNA per unit DNA than the wild type, but much less protein and cell wall. The mutant and the wild type seem to absorb the same percentage of the incident light, and there seems to be no difference in the efficiency with which the absorbed energy is utilized. The amount of protein and cell wall synthesized per unit DNA (≈ per cell) per day is the same in the mutant and the wild type. The fact that the generation time of the mutant is shorter than the generation time of the wild type thus explains the difference in cell size. The amount of protein synthesized per unit total RNA per day appears to be less in the fast-growing mutant than in the slow-growing wild type. The data show that the proliferation rate of a cell population may increase without a corresponding increase in the amount or efficiency of the machinery responsible for increase of mass, and support the idea that the Slender mutation might be in a gene concerned with the control of the processes that prepare a cell for division.