Browsing by Author "Singh, Namrata"

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Nitrate nutrition influences multiple factors in order to increase energy efficiency under hypoxia in Arabidopsis
(Oxford University Press, 2019) Wany, Aakanksha; Gupta, Alok Kumar; Kumari, Aprajita; Mishra, Sonal; Singh, Namrata; Pandey, Sonika; Vanvari, Rhythm; Igamberdiev, Abir U.; Fernie, Alisdair R.; Gupta, Kapuganti Jagadis
BACKGROUND AND AIMS: Nitrogen (N) levels vary between ecosystems, while the form of available N has a substantial impact on growth, development and perception of stress. Plants have the capacity to assimilate N in the form of either nitrate (NO3-) or ammonium (NH4+). Recent studies revealed that NO3- nutrition increases nitric oxide (NO) levels under hypoxia. When oxygen availability changes, plants need to generate energy to protect themselves against hypoxia-induced damage. As the effects of NO3- or NH4+ nutrition on energy production remain unresolved, this study was conducted to investigate the role of N source on group VII transcription factors, fermentative genes, energy metabolism and respiration under normoxic and hypoxic conditions. METHODS : We used Arabidopsis plants grown on Hoagland medium with either NO3- or NH4+ as a source of N and exposed to 0.8 % oxygen environment. In both roots and seedlings, we investigated the phytoglobin-nitric oxide cycle and the pathways of fermentation and respiration; furthermore, NO levels were tested using a combination of techniques including diaminofluorescein fluorescence, the gas phase Griess reagent assay, respiration by using an oxygen sensor and gene expression analysis by real-time quantitative reverse transcription-PCR methods. KEY RESULTS : Under NO3- nutrition, hypoxic stress leads to increases in nitrate reductase activity, NO production, class 1 phytoglobin transcript abundance and metphytoglobin reductase activity. In contrast, none of these processes responded to hypoxia under NH4+ nutrition. Under NO3- nutrition, a decreased total respiratory rate and increased alternative oxidase capacity and expression were observed during hypoxia. Data correlated with decreased reactive oxygen species and lipid peroxidation levels. Moreover, increased fermentation and NAD+ recycling as well as increased ATP production concomitant with the increased expression of transcription factor genes HRE1, HRE2, RAP2.2 and RAP2.12 were observed during hypoxia under NO3- nutrition. CONCLUSIONS: The results of this study collectively indicate that nitrate nutrition influences multiple factors in order to increase energy efficiency under hypoxia.
Serine hydroxymethyltransferase6 is involved in growth and resistance against pathogens via ethylene and lignin production in Arabidopsis
(John Wiley & Sons, 2024) Singh, Pooja; Kumari, Aprajita; Khaladhar, Vemula Chandra; Singh, Namrata; Pathak, Pradeep Kumar; Kumar, Vinod; Kumar, Ritika Jantu; Jain, Priyanka; Thakur, Jitendra K.; Fernie, Alisdair R.; Bauwe, Hermann; Raghavendra, A.S.; Gupta, Kapuganti Jagadis
Photorespiratory serine hydroxymethyltransferases (SHMTs) are important enzymes of cellular one-carbon metabolism. In this study, we investigated the potential role of SHMT6 in Arabidopsis thaliana. We found that SHMT6 is localized in the nucleus and expressed in different tissues during development. Interestingly SHMT6 is inducible in response to avirulent, virulent Pseudomonas syringae and to Fusarium oxysporum infection. Overexpression of SHMT6 leads to larger flowers, siliques, seeds, roots, and consequently an enhanced overall biomass. This enhanced growth was accompanied by increased stomatal conductance and photosynthetic capacity as well as ATP, protein, and chlorophyll levels. By contrast, a shmt6 knockout mutant displayed reduced growth. When challenged with Pseudomonas syringae pv tomato (Pst) DC3000 expressing AvrRpm1, SHMT6 overexpression lines displayed a clear hypersensitive response which was characterized by enhanced electrolyte leakage and reduced bacterial growth. In response to virulent Pst DC3000, the shmt6 mutant developed severe disease symptoms and becomes very susceptible, whereas SHMT6 overexpression lines showed enhanced resistance with increased expression of defense pathway associated genes. In response to Fusarium oxysporum, overexpression lines showed a reduction in symptoms. Moreover, SHMT6 overexpression lead to enhanced production of ethylene and lignin, which are important components of the defense response. Collectively, our data revealed that SHMT6 plays an important role in development and defense against pathogens.
Using different forms of nitrogen to study hypersensitive response elicited by avirulent Pseudomonas syringae
(Springer Nature Publishing AG, 2020) Singh, Namrata; Singh, Pooja; Pathak, Pradeep Kumar; Gupta, Kapuganti Jagadis
Nitrate, ammonium, or a combination of both is the form of N available for nitrogen assimilation from soil by the plants. Nitrogen is an important and integral part of amino acids, nucleotides, and defense molecules. Hence it is very important to study the role of nitrate and ammonium nutrition in plant defense via hypersensitive response (HR). Shifting plants from ammonium nitrate Hoagland solution to nitrate Hoagland nutrition slightly enhances root length and leaf area. HR phenotype is different in nitrate and ammonium grown plants when challenged with avirulent Pseudomonas syringae DC3000 avrRpm1. HR is also associated with increased production of reactive oxygen species (ROS) and nitric oxide (NO). Hence to understand HR development it is essential to measure HR lesions, cell death, ROS, NO, and bacterial growth. Here we provide a stepwise protocol of various parameters to study HR in Arabidopsis in response to nitrate and ammonium nutrition.