Effect of growth arrest on carotene accumulation and photosynthesis in Dunaliella

Abstract

The halotolerant green alga Dunaliella bardawil is known to accumulate /3-carotene in response to stress factors such as high light intensity, high salt concentrations and nutrient limitation. In this report, the accumulation of ficarotene was studied in cells from nitrate-limited chemostat cultures, in comparison with those of D. salina, a strain that does not accumulate /3-carotene under stress conditions. D. bardawil responded to growth arrest by accumulating /3-carotene and, to a lesser degree, lutein and zeaxanthin. A substantial fraction of Pcarotene and all the lutein and zeaxanthin was associated with the thylakoid fraction. The accumulation of carotenoids in D. bardawil occurred only in the light, but the light intensities were far below those where the photosynthetic rate is maximal. After growth arrest, the amount of chlorophyll (Chl) decreased in both strains. However, in D. bardawil Chl a decreased to a lesser extent in comparison with Chl b, which resulted in an increased Chl alb ratio. The maximum photosynthetic capacity declined rapidly in both strains after growth arrest. In contrast, the photosynthetic efficiency showed a temporary increase in D. bardawil and a decrease in D. salina. This increase did not occur when carotenogenesis was inhibited by diphenylamine, implying a causal relationship between enhanced carotenogenesis and increase of photosynthetic efficiency. The possible involvement of stress-accumulated carotenoids in photosynthetic activity is discussed.

Unusual occurrence of non carotenogenic strains of Dunaliella bardawil and Dunaliella parva in India

“…The continuance in the increase of carotenoids observed in the present study in the algal isolates even after cessation of growth i.e. between 24 -30 days could also be attrib-uted to nutrient depleted conditions [36,37]. This results demonstrates the maximum β-carotene exhibited by all the isolates in last day of the experiment was due to nutrient depleted condition, which have been previously observed in Dunaliella cultivated by Mojaat et al [38].…”

“…The observations indicated that the pigments such as Chl a and Chl b were predominant in the growth phase of Dunaliella while the amount of total carotenoids increased and accumulated to high levels in carotenogenic alga during the red orange phase. Maximal carotene accumulation depends upon various factors which include high light intensity [34], extreme temperatures [35], high salinity [35] and deprivation of mineral nutrients including nitrate, sulphate and possibly phosphate [36,37]. The continuance in the increase of carotenoids observed in the present study in the algal isolates even after cessation of growth i.e.…”

Regulation of Two Photosynthetic Pigment-related Genes During Stress-induced Pigment Formation in the Green Alga, Dunaliella salina

“…The halotolerant green alga Dunaliella salina is well known for its b-carotene production (Vorst et al 1994). b-Carotene production in D. salina is enhanced by suboptimal growth conditions such as high light intensity, salinity or temperature (Vorst et al 1994), or nutrient limitation (Marín et al 1998).…”

Comparison of the responses of two Dunaliella strains, Dunaliella salina CCAP 19/18 and Dunaliella bardawil to light intensity with special emphasis on carotenogenesis

“…However, in Ben-Amotz and Avron (1983) and Vorst et al (1994), the D. salina strain they used was not able to accumulate β-carotene. In Gómez and González (2005), they used the same strain as we did.…”

“…Some of Dunaliella strains are well known for the high production of carotenoids, especially β-carotene ). This alga produces large amount of β-carotene under stress conditions such as high light (HL) (Vorst et al 1994, Coesel et al 2008, Lamers et al 2010, high salinity (Vorst et al 1994, Hadi et al 2008, nutrient limitation (Marín et al 1998, Coesel et al 2008, and nitrogen starvation (Sánchez-Estudillo et al 2006, Lamers et al 2012. Ability of Dunaliella to thrive under extreme salinities gives a selective advantage that inhibits growth of other algae and its predators.…”