Effects of light quality on reproduction, growth and pigment content of &lt;em&gt;Gracilaria birdiae&lt;/em&gt; (Rhodophyta: Gracilariales)

Estela M Plastino,Félix L Figueroa,José Bonomi Barufi

doi:10.3989/scimar.04049.12a

Abstract

Gracilaria species are the main source of agar worldwide. Since laboratory cultivation is an important means of sustaining such production, this study aimed to assess the influence of two fundamental strategies of physiological algae adjustment, photoacclimation and photomorphogenesis, on G. birdiae physiology. Specifically, the effects of different spectral light qualities on reproduction, growth, and pigment content in two distinct photoperiods (8 and 14 hours) were examined. Tetrasporophytes and gametophytes were submitted to different light qualities: white, green, red, and blue over the course of nine weeks. At the end of this period, chlorophyll a, allophycocyanin, phycocyanin, and phycoerythrin contents were analysed. Gametophytes showed reproductive structures only under monochromatic radiation. A stimulatory effect on tetrasporangium differentiation was mainly observed under red light, but this high fertility was negatively correlated with growth rate, i.e. algae cultivated under red light showed the lowest growth rate. However, while growth rates were higher in algae exposed to white light, they were similar to those observed in algae subjected to green light and 14 hours of daylight. PE was the predominant pigment, irrespective of light quality. Phycocyanin and phycoerythrin concentration increased when algae were cultivated under green and blue light. Therefore, considering future management prospects for G. birdiae mariculture, we suggest that red light could be utilized as a reproductive inductor to produce tetraspores. Furthermore, if the aim is to achieve high phycoerythrin content, continuous blue light could be applied during a short photoperiod. Indeed, the combination of different wavelengths could allow better economic resource exploitation.

Highlights

Light is primarily used as a source of energy, enabling organisms to adapt to a steadily changing environment
chlorophyll a (Chl a) was extracted after dissolving the pellet in 90% acetone and centrifuging at 12000 g for 15 min (Kursar et al 1983a, modified by Plastino and Guimarães 2001)
Pigments were quantified in a spectrophotometer (HP 8452A), and concentrations of phycobiliproteins and Chl a were calculated according to Kursar et al (1983a) and Jeffrey and Humphrey (1975), respectively

Summary

Introduction

Light is primarily used as a source of energy, enabling organisms to adapt to a steadily changing environment. Light can be used as an environmental signal to control metabolic and reproductive processes (Rüdiger and Figueroa 1992). Monochromatic light can provide the signalling necessary to regulate algal metabolism, reproduction and growth (Dring 1988), prompting, in turn, a variety of photomorphogenetic strategies, such as the control of cell growth or induced enzymatic activation (Lüning 1992). Marine red algae occur in environments subjected to wide variations of irradiance and spectral distribution, and their pigment contents are regulated by irradiance and light qualities. These responses may be the result of photomorphogenetic signalling processes with photoreceptor control that regulate growth and metabolism (Talarico and Maranzana 2000). Photosynthetic changes can result from an imbalance of photosystems, a difference in the rate at which photosystems turn over, a deficiency in the electron transport chain, or a major change in the spatial relationship between the two photosystem (Gantt 1990)

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