Light-dependent utilization of two radiolabelled carbon sources, sodium bicarbonate and sodium acetate, and relationships with long chain polyunsaturated fatty acid synthesis in the microalga Pavlova lutheri (Haptophyta)

Figures & data

Fig. 1. Effect of light intensity on the radioactivity incorporated (pmol ¹⁴C × 10⁻⁶ cells) into whole cells (a) and total lipids (b) after incubating for 10 h with [¹⁴C] bicarbonate (Bc, unshaded columns) and [1-¹⁴C] acetate (Ac, hatched columns). For explanation of statistical assessments of significance, see footnote to Table 1.

Table 1.  Effect of light intensity on radioactivity incorporated into total lipids, expressed as the percentage of ¹⁴C incorporated into lipids out of the total radioactivity incorporated into the cells, after incubating for 10 h with [¹⁴C] bicarbonate and [1-¹⁴C] acetate.¹ Results are expressed as mean ± SD (n = 3). LL-20: 20 µmol photons m⁻² s⁻¹; ML-100: 100 µmol photons m⁻² s⁻¹; HL-340: 340 µmol photons m⁻² s⁻¹.

Light intensity	LL-20		ML-100		HL-340
Carbon source (^14C)	Bicarbonate	Acetate	Bicarbonate	Acetate	Bicarbonate	Acetate
% radioactivity	36.6 ± 0.3^a	37.4 ± 3.7^β	34.4 ± 2.8^a	29.7 ± 1.0^α,*	40.2 ± 3.5^b	34.5 ± 5.2^αβ
^1After two-way ANOVA, Student–Newman–Keuls (SNK) multiple comparison test results are arranged in increasing order: a < b < c (effect of light intensity with bicarbonate) and α < β < γ (effect of light intensity with acetate). For each light intensity, mean acetate values designated by an asterisk (*) are significantly different from those for bicarbonate (SNK test, P < 0.05).

Table 2.  Effect of light intensity on the distribution (%) of the radioactivity incorporated into the different lipid fractions, expressed as percentage of total radiolabelled lipids, after incubating for 10 h with [¹⁴C] bicarbonate and [1-¹⁴C] acetate. For explanation of statistical assessments of significance, see footnote to Table 1.

Light intensity	LL-20		ML-100		HL-340
Carbon source (^14C)	Bicarbonate	Acetate	Bicarbonate	Acetate	Bicarbonate	Acetate
NL	23.6 ± 0.2^c	29.8 ± 0.5^β,*	18.7 ± 0.7^b	23.9 ± 3.5^α	15.4 ± 0.1^a	19.0 ± 6.0^α
GL	58.5 ± 1.0^a	50.8 ± 2.2^α,*	58.4 ± 1.2^a	52.5 ± 3.0^α,*	64.0 ± 0.7^b	61.2 ± 4.2^β
PL	18.0 ± 1.2^a	19.4 ± 2.6^α	22.9 ± 0.5^b	23.6 ± 0.5^β	20.6 ± 0.6^ab	19.8 ± 1.8^α
Sum GL + PL	76.4 ± 0.2^a	70.2 ± 0.5^α,*	81.3 ± 0.7^b	76.1 ± 3.5^β	84.6 ± 0.1^c	81.0 ± 6.0^β
NL: neutral lipids, GL: galactolipids, PL: phospholipids.

Table 3.  Effect of light intensity on the radioactivity incorporated into the different lipid fractions, expressed as pmol ¹⁴C × 10⁻⁶ cells, after incubating for 10 h with [¹⁴C] bicarbonate and [1-¹⁴C] acetate. For explanation of statistical assessments of significance, see footnote to Table 1.

Light intensity	LL-20		ML-100		HL-340
Carbon source (^14C)	Bicarbonate	Acetate	Bicarbonate	Acetate	Bicarbonate	Acetate
NL	9.9 ± 0.4	6.0 ± 1.1*	9.6 ± 0.2	4.8 ± 1.3*	10.4 ± 1.0	6.0 ± 3.0*
GL	24.4 ± 0.9 ^a	10.4 ± 2.1^α,*	29.9 ± 1.1^b	10.5 ± 0.6^α,*	43.3 ± 3.4^c	18.5 ± 2.6^β,*
PL	7.5 ± 0.9 ^a	3.9 ± 0.1^α,*	11.8 ± 0.1^b	4.7 ± 0.5^αβ,*	14.0 ± 1.6^c	6.0 ± 0.7^β,*
NL: neutral lipids, GL: galactolipids, PL: phospholipids.

Table 4.  Effect of light intensity on distribution of the radioactivity incorporated into each fatty acid, expressed as percentage of total radiolabelled fatty acids, after incubating for 10 h with [¹⁴C] bicarbonate and [1-¹⁴C] acetate. For explanation of statistical assessments of significance, see footnote to Table 1.

Light intensity	LL-20		ML-100		HL-340
Carbon source (^14C)	Bicarbonate	Acetate	Bicarbonate	Acetate	Bicarbonate	Acetate
14:0	17.5 ± 1.8^a	14.0 ± 0.5^α,*	20.6 ± 0.9^ab	15.9 ± 1.1^α,*	22.0 ± 0.5^b	19.6 ± 2.1^β,*
16:0	29.8 ± 0.4^c	20.3 ± 0.8^γ,*	26.1 ± 0.8^a	16.3 ± 1.2^α,*	28.3 ± 0.8^b	17.8 ± 0.6^β,*
18:0	0.7 ± 0.3	1.2 ± 0.2	0.4 ± 0.1	1.3 ± 0.6	0.5 ± 0.1	1.4 ± 1.1
16:1 n-7	18.9 ± 0.9^a	11.4 ± 0.6^α,*	21.9 ± 0.9^b	11.9 ± 0.7^α,*	25.1 ± 0.8^c	13.1 ± 0.5^β,*
18:1 n-9	2.9 ± 0.4	33.9 ± 1.3^β,*	2.4 ± 0.1	35.6 ± 1.8^β,*	2.8 ± 0.1	31.0 ± 0.8^α,*
18:3^1	1.9 ± 0.6^b	1.6 ± 0.4^β	1.3 ± 0.1^ab	1.4 ± 0.4^αβ	0.9 ± 0.1^a	0.9 ± 0.2^α
18:4 n-3	1.5 ± 0.3	1.1 ± 0.4	1.8 ± 0.2	1.2 ± 0.2*	1.3 ± 0.1	1.1 ± 0.3
20:4^1	1.3 ± 0.4^b	1.3 ± 0.4^β	0.9 ± 0.4^ab	1.0 ± 0.4^αβ	0.6 ± 0.1^a	0.7 ± 0.1^α
20:5 n-3	19.1 ± 0.6^b	11.3 ± 0.7*	18.3 ± 0.5^b	11.1 ± 0.2*	14.4 ± 0.9^a	10.9 ± 0.4*
22:6 n-3	6.4 ± 0.8^b	4.0 ± 0.4*	6.3 ± 0.3^b	4.3 ± 0.1*	4.2 ± 0.5^a	3.5 ± 0.8
^1The n-3 and n-6 isomers of linolenic (18:3) and eicosatetraenoic (20:4) acid are not separated by the HPLC system used.