Changes In Levels Of Cellular Constituents Of Dunaliella Parva Associated With Inorganic Phosphate Depletion

Middle-East Journal of Scientific Research 4 (2): 94-99, 2009
ISSN 1990-9233
© IDOSI Publications, 2009

Changes in Levels of Cellular Constituents of Dunaliella parva
Associated with Inorganic Phosphate Depletion
Hanan A. Said
Department of Botany, Faculty of Science, Fayoum University, Egypt
Abstract: The effect of phosphorous limitation on some physiological and biochemical parametersof the green
alga Dunaliella parva have been examined. Algal cells were cultured under conditions of either Pi limitation
or nutrient sufficiency. At the end of the experiment and under phosphorus limitation conditions the percent
of decrease in number of cells and growth rate reached 58.4% and 36.3% respectively, while the generation time
increased by 2.21 days compared to nutrient sufficientmedium. The content of chlorophyll fractions, glycerol,
$-carotene, total soluble carbohydrates and proteins were also significantly reduced in response to
phosphorus limitation. The photosynthetic and respiratory activities in nutrient sufficient control medium
increased gradually till the 12th days of culturing where at the 16 th day they decreased by 8.9% and 17.8% for
photosynthesis andrespiration, respectively. Phosphorous limitation resulted in 36.8% lower rate of respiration
and 65.5% decline in rate of photosynthesis at the 16th day of culturing compared to control. The results cleared
also that D. parva when cultured under phosphorous starvation conditions, growth of the alga was the most
sensitive parameter followed by photosynthesis then respiration.
Key words:Phosphorous limitation % Photosynthesis % Respiration % Growth rate % Dunaliella parva % Algae
INTRODUCTION

Phosphate appears also to be required for the
active transport of metals into the cell [7]. Phosphate
limitation should thus directly reduce metal uptake as has
been observed in studies of nickel uptake by
Phaeodactylum tricornutum [8]. Phosphate may complex
or precipitate metals makingboth toxic metal and
phosphate unavailable to the cell [9]. When the
phosphate concentration is increased, excess metal is
complexed reducing toxicity and the surplus phosphate
produces growth stimulation.
This work was designed to assess the effect of
phosphorous nutrition on some physiological and
biochemical parameters of the green alga Dunaliella
parva cultured under conditions of eitherphosphorous
limitation or nutrient sufficiency.

Inspite of its absence in nature phosphate is
frequently the limiting nutrient in many environments
since it is mainly found in forms not readily available such
as insoluble salts [1, 2]. However, Keasling et al. [3] found
that synthesis and degradation are influenced by the
energy state of the cell and extracellular phosphate level.Tillberg and Rowley [4] studied the effect of phosphorous
starvation on morphology, intracellular structure and on
reactions related to the energy metabolism of the
unicellular green alga Scenedesmus obtusiusculus.
Increase in cell size, shape and cell wall thickness and
disorganization in the internal structure are the
dominating features of phosphorous starvation. In
addition, Theodorou et al.[5] found that Selenastrum
minutum cultured under conditions of phosphorous
limitation resulted in noticeable decrease in rate of
respiration, rate of photosynthesis and significant
increase in activities of phosphoenol pyruvate (PEP),
carboxylase and PEP phosphates. Also, El-Sheikh and
Rady [6] obtained the same results for the effect of
phosphorus starvation on growth, photosynthesis andsome metabolic processes in the unicellular green alga
Chlorella kessleri.

MATERIALS AND METHODS
Biological Material: The biological material used in this
work was the unicellular marine green alga Dunaliella
parva, obtained from UTEX at Austin, USA. The axenic
culture of D. parva was grown on MH medium [10].
Culture Conditions: The axenic inoculum was grown in
100 ml MH medium with...