No abstract

Bilins are open‐chain tetrapyrroles with a wide range of visible and nearly visible‐light absorption and emission properties. The linear tetrapyrrole molecules function as chromophores of the light‐harvesting phycobiliproteins and phytochrome‐mediated light sensing in photosynthetic organisms. They are derived from the cyclic precursor haem. The initial step in bilin biosynthesis is the conversion of haem into biliverdin (BV IX α) catalysed by haem oxygenase, which is subsequently reduced to specific bilins by ferredoxin‐dependent bilin reductases (FDBRs). Bilins usually bound to apoproteins via single or double covalent bonds to form a macromolecular complex phycobilisomes. The attachment of apoproteins to bilin is an autocatalytic process, but bilin lyases are required for the specific attachment of bilin chromophores to phycobiliprotein apoproteins. Besides the biosynthesis, structure and functions of bilins, this article also aims to recapitulate and discuss the current progress in the field of bilins and to emphasise the emerging areas. Key Concepts Bilins are open‐chain tetrapyrrole non‐metallic colour compounds formed as a metabolic product of protoporphyrin IX. Biliverdin IX α is the common precursor of all naturally occurring bilins. Haem oxygenase (HO) and ferredoxin‐dependent bilin reductases (FDBRs) are the two key enzymes involved in the biosynthesis of bilins. Phycobiliproteins assemble with bilins to form phycobilisomes, which help in light harvesting and energy transfer. Bilin plays a significant role in various physiological processes, namely, photosynthesis, respiration, light perception, signalling, cell defence against oxidative stress, nitrate and sulfate assimilation and programmed cell death.

The study illustrates the system for enhanced production of a medicinally important unexplored compound, carvone occurring naturally in Anethum graveolens. The effect of salicylic acid (SA) on biomass yield, carvone biosynthesis, growth and major enzymatic antioxidant parameters in A. graveolens was evaluated. The effects of different combinations of benzyl adenine (BA) and 1-Naphthalene acetic acid (NAA) were tested. Murashige and Skoog (MS) medium comprising 1.76 µM BA + 3.24 µM NAA was the best for friable callus induction. The friable callus was used for the initiation of cell suspension culture. MS salts in combination with 4.4 µM BA and 2.6 µM NAA, 3% sucrose was appropriate for cell growth and bioactive compound accumulation. The cell suspension cultures were then treated with SA (0.1, 0.75 and 1.5 mM) as an elicitor for four weeks. An up regulation of enzymatic antioxidants, ascorbate peroxidase (APX); superoxide dismutase (SOD) and catalase (CAT) activity with increasing concentrations of SA whereas a reduction in guaiacol peroxidase (GPX) activity was recorded at the end of the growth phase. The results also showed that higher concentrations of SA significantly increased malondialdehyde (MDA) and Proline content. Cell suspension culture was then subjected to extraction and isolation. The quantification of carvone through HPLC analysis revealed highest amount of carvone (0.063%) in cell suspension culture treated with 0.1 mM concentration of SA whereas higher concentration 0.75 mM SA showed reduction in amount (0.035%) of carvone. SA elicited cell suspension culture offered an effective and favorable in vitro method to improve the production of carvone for its potential use in pharmaceuticals.

No abstract