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Abstract
Physiological Studies on the Effect of some Antioxidants on
Germination, Growth and some Metabolic Activities of
Cowpea (Vigna unguiculata) Plant
Eman Zakaria Ahmed
(Botany& Microbiology Dept., Faculty of Science,
HelwanUniversity)
Abstract
The present work aimed to study the effect of four antioxidants
on growth and some metabolic activities of cowpea (Vigna
unguiculata L.) plant under normal and salinity stress
conditions. This included chemical synthesis and
characterization of selenium nanoparticles (SeNPs ≡ 33.4 nm)
using sodium selenate and ascorbic acid. Seeds soking for 2h
in different concentrations of four antioxidants (Ascorbic acid
(AsA) and gallic acid (GA), sodium selenate (NaSeO4) and
nanoselenium (SeNPs), or NaCl for assessing the suitable
treatments that might improve cowpea growth and yield under
normal and salinity stress conditions in pot experiment.
Soaking cowpea seeds in AsA and GA up to 150 ppm, NaSeO4
and SeNPs up to 25 μM significantly increased seedling length
(plumule and radicle lengths) accompanied with increase in
activity of hydrolytic (α, ß amylase and protease) enzymes,
soluble sugars and proteins, whereas a reverse situation was
observed with salinity, where increasing salinity from 50 to
250 mM, decreased germination percent, seedling length,
activity of hydrolytic enzymes, soluble sugars and proteins
compared to control seedling.
[Abstract]
During the first season: Foliar spray of cowpea plant with four
antioxidant compounds (AsA and GA at 50, 100, 150, 200,
ppm, NaSeO4 and SeNPs at 6.25, 12.5 and 25 μM)
significantly increased almost all growth criteria (i.e. length of
roots and stem, fresh and dry weights of root, stem and leaves,
No. of leaves and total leaves area cm2/plant), as well as weight
of 100 seed and quality of seed. During the second season a
revese situation was obtained with salinity, where NaCl at 100
mM decreased growth criteria, weight and quality of seed as
compared with untreated control plants, while foliar spray with
four antioxidants compounds at low concetrations alleviated
the adverse effect of salinity stress on growth of cowpea
plants.
Furthermore, GA was more effective than AsA at 100 ppm and
SeNPs was more effective than Na2SeO4 at 6.25 μM in
enhancing nodule formation, increasing nitrogenase activity,
the levels of the growth hormones indole acetic acid (IAA),
gibberellic acid (GA3) and cytokinins (CKs) of cowpea leaves,
with a relatively lower abscisic acid (ABA) content and higher
GA3/ ABA ratios, which explains the increase in growth
parameters and seed weight in treated plants compared to
control, but salinity decreased the level of growth promoters
hormones and increased ABA content of cowpea leaves.
Application of AsA, GA, NaSeO4 and SeNPs at low
concentration alleviated the adverse the effect of salinity on
cowpea plants by increasing the level of growth promoters
hormones as compared to control and salinity stress plants.In
addition, application of AsA, GA, Na2SeO4 and SeNPs,
especially at low concentration increased the total
photosynthetic pigments (TPP), total carbohydrate (TC), total
[Abstract]
soluble proteins (TSP), DNA, RNA, different minerals, non
enzymatic antioxidants (i.e. ascorbic acid, total antioxidant
capacity, total phenols and flavonoids), activities of
antioxidant enzymes (catalase, peroxidase, ascorbic
peroxidase, ascorbic oxidase, superoxide dismutase,
glutathione peroxidase and glutathione reductase) and
oxidative enzyme (polyphenol oxidase) accompanied by
decrease in total soluble sugars (TSS) in leaves, stress markers
(lipid peroxidation, the percentage of electrolyte leakage (EL)
and H2O2 content) and activity of IAAoxidase enzyme
compared to control plants. A revese situation was obtained
with salinity, where NaCl at 100 mM decreased photosynthetic
pigments and activity, TC, TSP, DNA, RNA, different
minerals, while increased TSS, non enzymatic antioxidants,
stress markers and activities of antioxidants enzymes, PPO,
and IAA oxidase as compared with untreated control plants.
Application of four antioxidants compounds at low
concentration alleviated the adverse effect of salinity on the
previous measured activities.
Transmission electron microscopy showed small, dark deposits
in leaf and seed of plants treated with SeNPs at 6.25 and 50
μM, which probably originated from the nanoparticles
absorbed on to the leaves and deposits in seeds.
In conclusion, application of AsA and GA at 100 ppm, SeNPs
and Na2SeO4 at 6.25 μM improved vegetative growth, yield
of seed, nutritional value and quality of cowpea plants under
normal and salinity stress conditions.
Key Words: Cowpea; Vigna unguiculata; Antioxidants;
Ascorbic acid; Gallic acid; Selenium; NanoSelenium.