Gokare Aswathanarayana Ravishankar

Influence of abiotic stress signals on secondary metabolites in plants

Plant secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, and industrially important biochemicals. Accumulation of such metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. Secondary metabolites play a major role in the adaptation of plants to the environment and in overcoming stress conditions. Environmental factors viz. temperature, humidity, light intensity, the supply of water, minerals, and CO2 influence the growth of a plant and secondary metabolite production. Drought, high salinity, and freezing temperatures are environmental conditions that cause adverse effects on the growth of plants and the productivity of crops. Plant cell culture technologies have been effective tools for both studying and producing plant secondary metabolites under in vitro conditions and for plant improvement. This brief review summarizes the influence of different abiotic factors include salt, drought, light, heavy metals, frost etc. on secondary metabolites in plants. The focus of the present review is the influence of abiotic factors on secondary metabolite production and some of important plant pharmaceuticals. Also, we describe the results of in vitro cultures and production of some important secondary metabolites obtained in our laboratory.

Antioxidant and antimicrobial activity of Cissus quadrangularis L.

Extracts of Cissus quadrangularis L. were tested for antioxidant activity by beta-carotene linoleic acid model and also by 1,1-diphenyl-2-picrylhydrazyl model. The ethyl acetate fraction of both fresh and dry stem extracts at a concentration of 100 ppm showed 64.8% antioxidant activity in the beta-carotene linoleic acid system and 61.6% in the 1,1-diphenyl-2-picrylhydrazyl system. This fraction showed the presence of sterols, vitamin C, and tannins as phytoconstituents. The antioxidant activity of methanol extract and aqueous extract were comparatively less significant than that of ethyl acetate extract, and n-hexane extract showed the least activity. The ethyl acetate extract and methanol extract of both fresh and dry stems further exhibited antimicrobial activity against Gram-positive bacteria, including Bacillus subtilis, Bacillus cereus, Staphylococcus aureus, and Streptococcus species. The results of the study have implications in the use of C. quadrangularis as an antibacterial agent and more so as an antioxidant in several applications requiring these properties.

Phytoserotonin: A review

Serotonin (5-hydroxytryptamine; SER) is one of the well-studied indoleamine neurotransmitter in vertebrates. Recently SER has also been reported in wide range of plant species. The precise function of SER at the physiological level, particularly growth regulation, flowering, xylem sap exudation, ion permeability and plant morphogenesis in plant system has not been clear. Though SER is found in different parts of plant species including leaves, stems, roots, fruits and seeds, the quantity of SER within plant tissues varies widely. SER has been recently shown as a plant hormone in view of its auxin-like activity. This brief review provide an overview of SER biosynthesis, localization, its role in plant morphogenesis and possible physiological functions in plants. This would certainly help to elucidate further the multiple roles of SER in plant morphogenesis. In the future it may form the basis for studies on involvement of SER in cellular signaling mechanisms in plants. Apart from these gaps in understanding the role of SER in ontogeny of plant physiology and ecological, adaptations have been emphasized. Thus, overall perspectives in this area of research and its possible implications have been presented.

Indoleamines and calcium channels influence morphogenesis in in vitro cultures of Mimosa pudica L.

The present article reports the interply of indoleamine neurohormones viz. serotonin, melatonin and calcium channels on shoot organogenesis in Mimosa pudica L. In vitro grown nodal segments were cultured on MS medium with B5 vitamins containing Serotonin (SER) and Melatonin (MEL) at 100 µM and indoleamine inhibitors viz. serotonin to melatonin conversion inhibitor p-chlorophenylalanine (p-CPA) at 40 µM, serotonin reuptake inhibitor (Prozac) 20 µM. In another set of experiment, calcium at 5 mM, calcium ionophore (A23187) 100 µM, and calcium channel blocker varapamil hydrochloride (1mM) a calcium chelator EGTA (100 µM) were administered to the culture medium. The percentage of shoot multiplication, endogenous MEL and SER were monitored during shoot organogenesis. At 100 µM SER and MEL treatment 60% and 70% explants responded for shoot multiplication respectively. Medium supplemented with either SER or MEL along with calcium (5mM) 75% - 80% explants responded for organogenesis. SER or MEL along with calcium ionophore (A23187) at 100 µM 70% explants responded for shoot multiplication. p-CPA, prozac, verapamil and EGTA, shoot multiplication was reduced and endogenous pools of SER, MEL decreased by 40-70%. The results clearly demonstrated that indoleamines and calcium channels positively influenced shoot organogenesis in M. pudica L.

Functional validation of Capsicum frutescens aminotransferase gene involved in vanillylamine biosynthesis using Agrobacterium mediated genetic transformation studies in Nicotiana tabacum and Capsicum frutescens calli cultures

Capsaicinoid biosynthesis involves the participation of two substrates viz. vanillylamine and C(9)-C(11) fatty acid moieties. Vanillylamine which is a derivative of vanillin is synthesized through a transaminase reaction in the phenylpropanoid pathway of capsaicinoid synthesis. Here we report the functional validation of earlier reported putative aminotransferase gene for vanillylamine biosynthesis in heterologous system using Agrobacterium mediated genetic transformation studies in Nicotiana tabacum and Capsicum frutescens calli cultures. Molecular analysis tools comprising PCR and Southern blot analysis have shown the integration of the foreign gene in N. tabacum and C. frutescens calli cultures. The study shows the production of vanillylamine in transformed N. tabacum callus cultures and also the reduction of vanillylamine production when whole gene based antisense binary vector construct was used in transformation of C. frutescens callus cultures. Vanillylamine production, aminotransferase assay with Western blot analysis for crude proteins of transformants established the production of putative aminotransferase (pAMT) protein in alternate plant. The result is a clear evidence of involvement of the reported putative aminotransferase responsible for vanillylamine biosynthesis in capsaicinoid biosynthesis pathway, confirming the gene function through functional validation.