The effect of ascorbic acid and dehydroascorbic acid on the root gravitropic response in Arabidopsis thaliana

Characterization and Identification of Drought-Responsive ABA-Aldehyde Oxidase (AAO) Genes in Potato (Solanum tuberosum L.)

Abscisic acid (ABA) is an important stress hormone that affects plants' tolerance to stress. Changes in the content of abscisic can have an impact on plant responses to abiotic stress. The abscisic acid aldehyde oxidase (AAO) plays a crucial role in the final step in the synthesis of abscisic acid; therefore, understanding the function of the AAO gene family is of great significance for insight into plants' response to abiotic stresses. In this study, Solanum tuberosum AAO (StAAO) members were exhaustively explored using genome databases, and nine StAAOs were identified. Chromosomal location analysis indicated that StAAO genes mapped to 4 of the 14 potato chromosomes. Further analyses of gene structure and motif composition showed that members of the specific StAAO subfamily showed relatively conserved characteristics. Phylogenetic relationship analysis indicated that StAAOs proteins were divided into three major clades. Promoter analysis showed that most StAAO promoters contained cis-elements related to abiotic stress response and plant hormones. The results of tissue-specific expression analysis indicated that StAAO4 was predominantly expressed in the roots. Analysis of transcriptome data revealed that StAAO2/4/6 genes responded significantly to drought treatments. Moreover, further qRT-PCR analysis results indicated that StAAO2/4/6 not only significantly responded to drought stress but also to various phytohormone (ABA, SA, and MeJA) and abiotic stresses (salt and low temperature), albeit with different expression patterns. In summary, our study provides comprehensive insights into the sequence characteristics, structural properties, evolutionary relationships, and expression patterns of the StAAO gene family. These findings lay the foundation for a deeper understanding of the StAAO gene family and offer a potential genetic resource for breeding drought-resistant potato varieties.

Cytosolic ascorbate peroxidase 1 modulates ascorbic acid metabolism through cooperating with nitrogen regulatory protein P-II in tea plant under nitrogen deficiency stress

Nitrogen (N) element is essential nutrient, and affect metabolism of secondary metabolites in higher plants. Ascorbate peroxidase (APX) plays an important role in ascorbic acid (AsA) metabolism of tea plant. However, the roles of cytosolic ascorbate peroxidase 1 (CsAPX1) in AsA metabolism under N deficiency stress in tea plant remains unclear in detail. In this work, nitrogen regulatory protein P-II (CsGLB1) and CsAPX1 were identified by isobaric tags for relative and absolute quantitation (iTRAQ) from tea plant. The cell growth rates in transgenic Escherichia coli overexpressing CsAPX1 and CsGLB1 were higher than empty vector under N sufficiency condition. Phenotype of shoots and roots, AsA accumulation, and expression levels of AtAPX1 and AtGLB1 genes were changed in transgenic Arabidopsis hosting CsAPX1 under N deficiency stress. These findings suggested that cytosolic CsAPX1 acted a regulator in AsA accumulation through cooperating with GLB1 under N deficiency stress in tea plant.

Cyanide produced with ethylene by ACS and its incomplete detoxification by β-CAS in mango inflorescence leads to malformation

Malformation of mango inflorescences (MMI) disease causes severe economic losses worldwide. Present research investigates the underlying causes of MMI. Results revealed significantly higher levels of cyanide, a by-product of ethylene biosynthesis, in malformed inflorescences (MI) of mango cultivars. There was a significant rise in ACS transcripts, ACS enzyme activity and cyanide and ethylene levels in MI as compared to healthy inflorescences (HI). Significant differences in levels of methionine, phosphate, S-adenosyl-L-methionine, S-adenosyl-L-homocysteine, ascorbate and glutathione, and activities of dehydroascorbate reductase and glutathione reductase were seen in MI over HI. Further, a lower expression of β-cyanoalanine synthase (β-CAS) transcript was associated with decreased cellular β-CAS activity in MI, indicating accumulation of unmetabolized cyanide. TEM studies showed increased gum-resinosis and necrotic cell organelles, which might be attributed to unmetabolized cyanide. In field trials, increased malformed-necrotic-inflorescence (MNI) by spraying ethrel and decreased MNI by treating with ethylene inhibitors (silver and cobalt ions) further confirmed the involvement of cyanide in MMI. Implying a role for cyanide in MMI at the physiological and molecular level, this study will contribute to better understanding of the etiology of mango inflorescence malformation, and also help manipulate mango varieties genetically for resistance to malformation.

The influence of ascorbic acid on root growth and the root apical meristem in Arabidopsis thaliana

Cell division is a fundamental biological process governed by molecular networks that are initiated in the apical meristems of plants. l-ascorbic acid (AsA) commonly known as vitamin C is a crucial molecular modulator involved in cell proliferation. In this study, we used AsA application to Arabidopsis and four AsA pathway mutants to investigate the influence of AsA on the root apical meristem (RAM) and root growth. Treatment of seeds of wild-type Col-0 with AsA prior to sowing showed a significant increase in the activity of cell division of the RAM, root growth rate and root length when compared with untreated seeds. Seedlings of the AsA pathway mutant vtc1-1 showed a significant reduction in the level of AsA and a significant increase in the number of quiescent cells in the RAM when compared with Col-0. Cell proliferation was reduced in the AsA pathway mutants vtc1-1, dhar1, vtc5-1, apx1, respectively, however, root growth decreased significantly only in vtc1-1 when compared with Col-0. In addition, hydrogen peroxide (H₂O₂) levels were shown to increase in the AsA pathway mutants, with the highest level of H₂O₂ found in vtc1-1. AsA is also shown to have an indirect influence in inducing periclinal division as a reduced level was found in vtc1-1. Therefore, in this study, we found that AsA had an influence on cell proliferation and root growth and VTC1 was shown to be a key modulator of H₂O₂ levels. These findings open the door for further studies to reveal the involvement of AsA in cell proliferation and the interaction between AsA and H₂O₂ on cell polarity in the RAM and potentially the shoot apical meristem.

Ascorbate-Deficient vtc2 Mutants in Arabidopsis Do Not Exhibit Decreased Growth

In higher plants the L-galactose pathway represents the major route for ascorbate biosynthesis. The first committed step of this pathway is catalyzed by the enzyme GDP-L-galactose phosphorylase and is encoded by two paralogs in Arabidopsis - VITAMIN C2 (VTC2) and VTC5. The first mutant of this enzyme, vtc2-1, isolated via an EMS mutagenesis screen, has approximately 20-30% of wildtype ascorbate levels and has been reported to have decreased growth under standard laboratory conditions. Here, we show that a T-DNA insertion into the VTC2 causes a similar reduction in ascorbate levels, but does not greatly affect plant growth. Subsequent segregation analysis revealed the growth defects of vtc2-1 mutants segregate independently of the vtc2-1 mutation. These observations suggest that it is the presence of an independent cryptic mutation that affects growth of vtc2-1 mutants, and not the 70-80% decrease in ascorbate levels that has been assumed in past studies.

Expression profiling of genes involved in ascorbate biosynthesis and recycling during fleshy root development in radish

Ascorbate is a primary antioxidant and an essential enzyme cofactor in plants, which has an important effect on the development of plant root system. To investigate the molecular mechanisms of ascorbate accumulation during root development and reveal the key genes of the ascorbate biosynthesis and recycling pathways, the expression of 16 related genes together with ascorbate abundance were analyzed in the flesh and skin of radish (Raphanus sativus L.) fleshy root. The content of ascorbate decreased with root growth in both the flesh and skin. Expression of GDP-d-mannose pyrophosphorylase, GDP-d-mannose-3',5'-epimerase and d-galacturonate reductase were also decreased and correlated with ascorbate levels in the flesh. In the skin, the expression of GDP-d-mannose pyrophosphorylase and l-galactose dehydrogenase was correlated with ascorbate levels. These results suggested that ascorbate accumulation is affected mainly by biosynthesis rather than recycling in radish root, and the l-galactose pathway may be the major biosynthetic route of ascorbate, and moreover, the salvage pathway may also contribute to ascorbate accumulation. The data suggested that GDP-d-mannose pyrophosphorylase could play an important role in the regulation of ascorbate accumulation during radish fleshy taproot development.

Cereal grass pulvini: agronomically significant models for studying gravitropism signaling and tissue polarity

Cereal grass pulvini have emerged as model systems that are not only valuable for the study of gravitropism, but are also of agricultural and economic significance. The pulvini are regions of tissue that are apical to each node and collectively return a reoriented stem to a more vertical position. They have proven to be useful for the study of gravisensing and response and are also providing clues about the establishment of polarity across tissues. This review will first highlight the agronomic significance of these stem regions and their benefits for use as model systems and provide a brief historical overview. A detailed discussion of the literature focusing on cell signaling and early changes in gene expression will follow, culminating in a temporal framework outlining events in the signaling and early growth phases of gravitropism in this tissue. Changes in cell wall composition and gene expression that occur well into the growth phase will be touched upon briefly. Finally, some ongoing research involving both maize and wheat pulvini will be introduced along with prospects for future investigations.