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Plant Phenolics
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
In dicots, phenylalanine ammonia lyase, (PAL) (E.C. 4.3.1.5) catalyzes the anti-elimination of ammonia from l-Phe 26 to give E-(trans)-cinnamic acid 12 (Figure 4).19,20 The enzyme requires no co-factor for activity21 and removes the pro-3S hydrogen from Phe 26;22,23 it does not use Tyr 27 as a substrate. By contrast, in grasses, in addition to Phe 26, Tyr 27 can also undergo an enzymatically catalyzed deamination to yield p-coumarie acid 10; this transformation is putatively catalyzed by a distinct tyrosine ammonia lyase (TAL).24,25 It should be noted, however, that while in grasses both TAL and PAL activities have been observed, it has not been possible to obtain distinct enzymes capable of separately catalyzing p-coumaric 10 and cinnamic 12 acid formation, respectively.21 One interpretation of such findings is that in grasses, PAL and TAL are one and the same, i.e., the enzyme is simply less substrate specific and can catalyze deamination of either Phe 26 or Tyr 27. Detailed studies now need to be undertaken to prove (or disprove) this particular hypothesis.
Melatonin-stimulated biosynthesis of anti-microbial ZnONPs by enhancing bio-reductive prospective in callus cultures of Catharanthus roseus var. Alba
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Hafiza Rida Riaz, Syed Salman Hashmi, Tariq Khan, Christophe Hano, Nathalie Giglioli-Guivarc’h, Bilal Haider Abbasi
Phenolic profile of a plant represents its potential to overcome oxidative stress by scavenging free radical species actively [45]. Maximum TPC (35.2 mg of GAE g−1 DW) was recorded at the concentration of NAA (13.5 µM). Previously, TPC (30.8 mg of GAE g−1 DW) was reported by Akhtar et al. (2014) in C. roseus leaves [46]. Significant differences in TPC content (35.2 mg of GAE g−1 DW) was observed due to application of different PGRs in callus cultures of C. roseus (Figure 5(A)) [46–48]. Lowest TPC (15.8 mg of GAE g−1 DW) was recorded at 4.5 µM of TDZ (shown in the Figure 5(A)). TPC values were significantly increased with the application of melatonin. The highest value of TPC (42.23 mg of GAE g−1 DW) was recorded at 1.0 µM of melatonin and a notable increase in TPC content occurred when compared to the TPC value (35.2 mg of GAE g−1 DW) at 13.5 µM of NAA. Other concentrations of melatonin (0.5, 3, 5 and 10 µM) also showed considerable enhancement in TPC [38.5, 39.5, 39.40 and 40.33 mg of GAE g−1 DW; Figure 5(C)], respectively. Melatonin has been reported for enhanced phytochemical constituents and improved bio-reductive capacity [19]. Maximum TPP value (311.87 mg of GAE L−1) at NAA 13.5 µM was recorded (Figure 5(B)). Around 415.41 mg of GAE L−1 was recorded at melatonin 1.0 µM (Figure 5(C)). TPP values (352.3, 331.4, 369.3 and 347.4 mg of GAE L−1) recorded at 0.5, 3, 5 and 10 µM of melatonin, respectively, were remarkably different from TPP value of callus at the concentration of NAA (13.5 µM). Biomass accumulation and phenolic production are directly proportional and strongly dependent on the activation of key enzymes (tyrosine ammonia lyase) responsible for phytochemical production [41,49].