Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Abstract

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 lmol m -2 s -1 ) were investigated in onemonth-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 lmol m -2 s -1 , while net CO 2 assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 lmol m -2 s -1 , indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and b-glucosidase (b-GS) activities increased to a maximum in acclimatised plants at 300 lmol m -2 s -1 . A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 lmol m -2 s -1 . The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 lmol m -2 s -1 was suitable for acclimatisation when plants were transferred from in vitro conditions.

Methyl Jasmonate and Salicylic Acid Induced Oxidative Stress and Accumulation of Phenolics in Panax ginseng Bioreactor Root Suspension Cultures

“…The parallel increases of phenolics and flavonoids levels and DPPH activity indicated that the increased free radical scavenging activity might be due to the increased phenolic compound levels induced by MJ and SA treatments. Our results are in accordance with a previous report, which has shown that higher phenolic compound levels increase the antioxidant activity [2] and also showed a linear correlation between phenolics contents and antioxidant activity [18]. Such an induced effect is a possible indication of oxidative stress mediated enhancement, as evidenced by the accumulation of H 2 O 2 and carbonyl content up to 7 days (Figures 1A and B).…”

“…Defense responses to stress induce the production of several secondary metabolites such as phenolics, flavonoids and other low molecular weight substances [2]. In the present study, there was a significant increase in total phenolics, flavonoids, ascorbic acid, NPSH and cysteine contents and DPPH activity in response to MJ or SA treatment.…”

“…Proline has multiple functions, such as osmotic pressure regulation, protection of membrane integrity, stabilization of enzymes/proteins, maintaining appropriate NADP + /NADPH ratios and scavenger of free radicals [21]. Accumulation of proline under stress conditions such as high salinity, high photosynthetic photon flux, including jasmonic acid presence in plants, has been correlated with stress tolerance [22,23,2]. We observed a substantial increase in proline levels with both treatments, which might be attributed to the strategies adapted by plants to cope up with stress conditions.…”

“…Under biotic and abiotic stresses such as pathogen attack, physical wounding, and UV-light exposure, plants can induce a defense response and increase secondary metabolite levels [2]. In relation to this, increased activity of phenylalanine ammonia lyase (PAL) and other related enzymes such as peroxidase has been reported in plants subjected to various stresses [3].…”

Effects of Foliar of the Application Chitosan and Reduced Irrigation on Essential Oil Yield, Total Phenol Content and Antioxidant Activity of Extracts From Green and Purple Basil

“…On the other hand, under abiotic stresses such as drought stress plants it can induce a defense response and increase secondary metabolite levels [Ali et al 2006]. Moisture deficit has a significant influence on growth and metabolic activities of plant species.…”