Cell Cycle-related and Endogenously Controlled Circadian Photosynthetic Rhythms in Euglena

Abstract

The data presented for three strains of Euglena gracilis corroborate previous reports of a diel rhythm in photosynthetic capacity in divisionsynchrnized cultures of this alga and extend these studies to free nning, dividing and nondividing (stationary) Circadian rhythms in photosynthesis have been observed in a number of higher plants as well as in algae (16). Several studies have reported a rhythm of photosynthetic capacity during the cell cycle of the alga flagellate Euglena (3,4,22,32), although the results are often conflicting. Walther and Edmunds (32) demonstrated a clear 24-h rhythm in the capacity of Euglena to fix CO2 in cultures synchronized by appropriately chosen light (12,000 lux) cycles (LD: l0,14 This lack of long term persistence of the photosynthetic capacity rhythm and hence the inability to conclude that an endogenous circadian clock underlies the overt periodicity, could have been

Circadian rhythm of photosynthesis inKappaphycus alvarezii(Rhodophyta): independence of the cell cycle and possible photosynthetic clock targets

“…The finding (2) that the photosynthetic rhythm was apparent in both growing and nongrowing parts of the thallus indicates that the factors causing the photosynthetic rhythm in Kappaphycus may be independent from the cell cycle, as in Euglena (Walther & Edmunds, 1973;Laval-Martin et al, 1979). In the second part of the present investigation it was shown, in step (3), that oxygen evolution rates changed rhythmically in LL (Fig.…”

“…In the latter alga, maximum PSII capacity was detected at noon and declined during the afternoon when the cells divide and the altered morphology and composition of the thylakoid membranes in the daughter cells may inhibit optimum operation of the PSII-repair cycle (Kaftan et al, 1999). In contrast, the rhythm of photosynthetic capacity in Euglena was independent of the cell cycle and still continued for at least 10 days under non-dividing conditions (Walther & Edmunds, 1973), and circadian rhythmicity in cellular chlorophyll was detected in non-dividing cells of Euglena (Laval-Martin et al, 1979).…”

Change in Photosynthetic Capacity over the Cell Cycle in Light/Dark-Synchronized Amphidinium carteri Is Due Solely to the Photocycle

“…Since such changes are not apparent as cells progress through their cell cycle in a constant light environment, it is clear that they are not the direct result of cell cycle variation; rather, they are induced by periodicity in the environment. Although others have attempted to dissect these two factors using other experimental designs (6,13,29) this study is the first in which (14). It is agreed by most that electron transfer activity through PSI is constant in cells that exhibit diel variation in photosynthesis (15, 18, A very intriguing phenomenon observed in our cells when maintained on a periodic L/D cycle was the midlight period photoinhibition.…”

“…In cells grown on the L/D cycle, Chl per cell began to increase in the middle of the dark period, suggesting increased synthesis long before the onset of the light period. In the absence of evidence for cell cycle control over this phenomenon, we must hypothesize some form of endogenous control (13 …”

“…For example, a plant cell transferred into the light may respond to its changed energy status regardless of its cell cycle or clock position. The well known periodic change in photosynthetic capacity in cells grown in photocycle is an example of such an ambiguous situation; while photosynthetic rhythms have been described in detail (6, [13][14][15], the relative contributions of the clock, the photocycle, and the cell cycle in controlling such rhythms have not been well established. In particular, the contribution of the cell cycle per se (i.e.…”