Over-production of reactive oxygen species (ROS) in plants under stress conditions is a common phenomenon. Plants tend to counter this problem through their ability to synthesize ROS neutralizing substances including non-enzymatic and enzymatic antioxidants. In this context, ascorbic acid (AsA) is one of the universal non-enzymatic antioxidants having substantial potential of not only scavenging ROS, but also modulating a number of fundamental functions in plants both under stress and non-stress conditions. In the present review, the role of AsA, its biosynthesis, and cross-talk with different hormones have been discussed comprehensively. Furthermore, the possible involvement of AsA-hormone crosstalk in the regulation of several key physiological and biochemical processes like seed germination, photosynthesis, floral induction, fruit expansion, ROS regulation and senescence has also been described. A simplified and schematic AsA biosynthetic pathway has been drawn, which reflects key intermediates involved therein. This could pave the way for future research to elucidate the modulation of plant AsA biosynthesis and subsequent responses to environmental stresses. Apart from discussing the role of different ascorbate peroxidase isoforms, the comparative role of two key enzymes, ascorbate peroxidase (APX) and ascorbate oxidase (AO) involved in AsA metabolism in plant cell apoplast is also discussed particularly focusing on oxidative stress perception and amplification. Limited progress has been made so far in terms of developing transgenics which could over-produce AsA. The prospects of generation of transgenics overexpressing AsA related genes and exogenous application of AsA have been discussed at length in the review.

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Ascorbic Acid-A Potential Oxidant Scavenger and Its Role in Plant Development and Abiotic Stress Tolerance.

A study was conducted to find out the role of ascorbic acid (AsA) in modulating growth and different physio-biochemical attributes of canola plants under well-watered as well as water-deficit conditions. Drought stress imposed on 60 % field capacity significantly decreased the shoot and root fresh and dry weights, leaf chlorophyll contents, shoot and root P, root K+, and activity of CAT enzyme, while increased chlorophyll a/b contents, MDA, NPQ, leaf total phenolics, free proline and GB contents in both canola cultivars. Foliar-applied varying levels (50, 100 and 150 mg L−1) of AsA enhanced shoot and root fresh and root dry weights, qN, NPQ, shoot and root P, AsA as well as the activity of POD enzyme particularly under drought stress conditions. Of both canola cultivars, cv. Dunkeld was higher in shoot fresh weights, ETR and F
 v
 /F
 m, MDA, proline and GB contents, and POD activity, however, cv. Cyclone in total phenolics and qN under well-watered and water-deficit conditions. Overall, the foliar-applied AsA had a positive effect, though not marked, on salt sensitive cv. Cyclone in terms of improved growth and other attributes, whereas exogenously applied AsA had a non-significant effect on relatively salt tolerant cv. Dunkeld.

Synergistic effects of drought and ascorbic acid on growth, mineral nutrients and oxidative defense system in canola ( Brassica napus L.) plants

Alpha-tocopherol (α-Toc) is a member of the vitamin E family and is lipid soluble. Its biosynthesis is by the reaction of isopentyl diphosphate and homogentisic acid in plastid membranes. The putative biochemical activities of tocopherols are linked with the formation of tocopherol quinone species, which subsequently undergo degradation and recycling within cells/tissues. α-Toc plays a key role in a variety of plant metabolic processes throughout the ontogeny of plants. It can maintain the integrity and fluidity of photosynthesizing membranes. It can also neutralize lipid peroxy radicals, consequently blocking lipid peroxidation by quenching oxidative cations. It preserves membrane integrity by retaining membranous structural components under environmental constraints such as water deficiency, high salt content, toxic metals, high/low temperatures, and radiations. α-Toc also induces cellular signalling pathways within biological membranes. Its biosynthesis varies during growth and developmental stages as well as under different environmental conditions. The current review primarily focuses on how α-Toc can regulate various metabolic processes involved in promoting plant growth and development under stress and non-stress and how it can effectively counteract the stress-induced high accumulation of reactive oxygen species (ROS). Currently, exogenous application of α-Toc has been widely reported as a potential means of promoting resistance in plants to a variety of stressful environments.

Alpha-Tocopherol-Induced Regulation of Growth and Metabolism in Plants Under Non-stress and Stress Conditions

Ascorbic acid is considered to be one of the most important antioxidants in plants and plays a vital role in the adaptation of plants to unfavorable conditions. In the present study, an ascorbate oxidase gene (Solyc04g054690) was over-expressed in cherry tomato cv. West Virginia 106 lines and compared with previously studied RNAi silenced ascorbate oxidase lines. Two lines with lower ascorbate oxidase activity (AO−15 and AO−42), two lines with elevated activity (AO+14 and AO+16), and the non-transgenic line (WVa106) were grown and irrigated with 75 mM and 150 mM NaCl in 2015 and 2016. Growth, yield, and chemical composition of the lines under salinity stress were evaluated. Lines with lower ascorbate oxidase activity resulted in higher plant growth parameters (plant height, leaf number, flower, and cluster number in 2015 and stem diameter and flower number in 2016), and improved fruit quality (firmness in 2016 and soluble solid content in 2015) and total yield per plant under salinity stress over both years. In addition, we show that ascorbic acid, lycopene, and carotene contents of fruits were higher in lines with lower ascorbate oxidase activity compared to lines with elevated activity and the non-transgenic line under conditions of moderate and high salinity in both years.

https://www.mdpi.com/2073-4395/9/2/51/pdf

Increasing Ascorbic Acid Content and Salinity Tolerance of Cherry Tomato Plants by Suppressed Expression of the Ascorbate Oxidase Gene

Protective role of α-tocopherol on two Vicia faba cultivars against seawater-induced lipid peroxidation by enhancing capacity of anti-oxidative system

A pot experiment was carried out during 2007 and 2008 seasons at Research and Production Station of National Research Centre ,Nubaria, Cairo, Egypt. The aim of this work to study the effect of foliar spray of ascorbic acid (0, 50 and 100 ppm) and � - tocopherol (0, 50 and 100 ppm) and their interaction on vegetative growth and some chemical composition of Hibiscus rosa sineses L. plant. Most criteria on vegetative growth expressed as plant height, number of branches and leaves/plant, stem diameter, leaf area, fresh and dry weight of plant organs were significantly affected by application of ascorbic acid and � - tocopherol separately or collectively promoted all the a forementioned characters in this study. Chemical constituents i.e. chl (a), chl (b), carotenoids, soluble sugars, nitrogen, phosphorus and potassium contents were increased compared with untreated plants. The highest recorded data were obtained in plants treated with ascorbic acid 100 ppm + � - tocopherol 100 ppm and ascorbic acid 50 ppm + � - tocopherol 100 ppm. Foliar application of the two factors under study separately or collectively on Hibiscus rosa sineses L. plant significantly increased number of flowers/plant, as well as fresh and dry weights of flowers as compared with control plants.

Magda M. Kandil

Papers

Some studies on the effect of ascorbic acid and - tocopherol on the growth and some chemical composition of Hibiscus rosa sineses L. at Nubaria