The Effects of Plant Growth Regulators on Cell Growth, Protein, Carotenoid, PUFAs and Lipid Production of Chlorella pyrenoidosa ZF Strain

Abstract

Abstract:In the present study, eight kinds plant growth regulators-salicylic acid (SA), 1-naphthaleneacetic acid (NAA), gibberellic acid (GA 3 ), 6-benzylaminopurine (6-BA), 2, 4-epi-brassinolide (EBR), abscisic acid (ABA), ethephon (ETH), and spermidine (SPD)-were used to investigate the impact on microalgal biomass, lipid, total soluble protein, carotenoids, and polyunsaturated fatty acids (PUFAS) production of Chlorella pyrenoidosa ZF strain. The results showed the quickest biomass enhancement was induced by 50 mg·L −1 NAA, with a 6.3-fold increase over the control; the highest protein content was increased by 0.005 mg·L −1 ETH, which produced 3.5-fold over the control; total carotenoids content was induced most effectively by 1 mg·L −1 NAA with 3.6-fold higher production than the control; the most efficient elicitor for lipid production was 5 mg·L −1 GA 3 at 1.9-fold of the control; 0.2 mg·L −1 ETH induced the abundant production of 1.82 ± 0.23% linoleic acid; 0.65 ± 0.01% linolenic acid was induced by 1 mg·L −1 NAA; 2.53 ± 0.15% arachidonic acid and 0.44 ± 0.05% docosahexaenoic acid were induced by 5 mg·L −1 GA 3 . Transcriptional expression levels of seven lipid-related genes, including ACP, BC, FAD, FATA, KAS, MCTK, and SAD, were studied by real-time RT-q-PCR. 5 mg·L −1 GA 3 was the most effective regulator for transcriptional expressions of these seven genes, producing 23-fold ACP, 31-fold BC, 25-fold FAD, 6-fold KAS, 12-fold MCTK compared with the controls, respectively.

Plant hormone induced enrichment of Chlorella sp. omega-3 fatty acids

“…Similar to salt stress, oxidative stress created by plant hormone in the present study also increased the carbon chain length and desaturation. The results in the present study were in agreement with those of Du et al [40] which showed that the plant hormone treatment and stress created by plant hormone especially IAA increased the carbon chain length and desaturation. Sivaramakrishnan and Incharoensakdi Biotechnol Biofuels (2020) 13:7 In case of gibberellic acid treatment which did not improve the omega-3 fatty acid content, it showed variations in the contents of linoleic and linolenic acid.…”

“…(Table 2). Similarly, other plant hormones showed higher fatty acid desaturase expression than did the ABA treatment [40]. In addition, plant hormones could stimulate fatty acid elongation process.…”

“…Lei et al [61] reported that the various fatty genes were upregulated under stress condition and showed high fatty acid content in Haematococcus pluvialis. In another study, mRNA levels of fatty acid biosynthesis genes in H. pluvialis were upregulated by plant hormones [62]. Lin et al [63] studied the effect of plant growth regulators on fatty acid synthesis genes transcription level in C. vulgaris and found that the fatty acid synthesis genes were upregulated after ABA treatment and showed high omega-3 fatty acid content.…”

“…On the other hand, DHA and EPA production was less stimulated by ABA treatment when compared to IAA treatment ( Table 2). Du et al [40] studied the fatty acid desaturation and lipid content after ABA treatment on C. pyrenoidosa, which showed the absence of linoleic acid and arachidonic acid and a decreased PUFA content, as well as the reduced fatty acid desaturase expression. ABA treatment in the present study also resulted in very low PUFA content in Chlorella sp.…”

“…The highest carbon chain length fatty acid appearing in C. pyrenoidosa was C20:4, whereas plant hormone treatment increased the carbon chain length with the occurrence of new fatty acid C22:4 in the fatty acid profile. The expression of several genes related to fatty acid metabolism was differentially affected by different plant growth regulators in microalgae including fatty acid elongation [40]. Azachi et al [41] studied the induction of fatty acid elongase in the microalgae Dunaliella salina and found that the salt stress induced the elongation and desaturase which increased the carbon chain length and desaturation of fatty acids.…”