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Abstract
ABSTRACT
Mohamed Mahmoud Aboul Fotouh Mesalhi: Biochemical and
Molecular Responses Associated with UV-Induced Resistance in
Plant. Unpublished M.Sc. Thesis, Department of Agricultural
Biochemistry, Faculty of Agriculture, University of Ain Shams, 2014.
Ultraviolet radiation is known to be one of the environmental
stresses that disturb biochemical and physiological processes in plant.
However, many studies declared that irradiation of plant tissues with low
doses of UV radiation should stimulate adaptive mechanisms, providing
better protection to other stresses. In the present investigation, dry and
germinated seeds of cucumber and green bean seeds were exposed to UVC
(254 nm) for periods of 7, 15, 30 and 60 min, then grown plants were
subjected to salinity stress (50 mM NaCl) as a challenge.
The ability of different doses to induce tolerance to salinity stress
was evaluated by determination of fresh weight, dry weight and root to
shoot ratios. Also, biochemical changes associated with UV-C induced
tolerance were investigated by determination of lipid peroxidation, total
phenols concentration, proline concentration, phenylalanine ammonia
lyase (PAL) activity and antioxidant enzymes activities (SOD, CAT, GPOD,
APX and PPO) in leaves and roots. As well, the behavior of POD
isozymes in leaves was also examined.
Results showed that plants grown from UV treated seeds were less
affected by salinity stress which was obvious in increased fresh and dry
weights of shoots and roots and increased root to shoot ratios under saline
conditions as compared with control. Also, one of the consequences of
salinity stress is increased MDA levels. UV treatment reduced MDA
levels in leaves and roots of cucumber seedlings under different
conditions which was not observed in the case of green bean plants in
spite of their better growth than control. Reduced MDA levels were
explained by the induced antioxidant system (total phenols, PAL, SOD,
CAT, G-POD, APX and PPO), while in green bean, the enhanced
tolerance despite the increased MDA was explained by the effect of MDA
in induction of survival mechanisms in plant. Also, elevated proline
concentration in leaves and roots contributed to protection from osmotic
shock resulted from salinity stress.
The isozymes pattern of POD of cucumber leaves declared that UVC
seed treatment did not result in synthesis of new POD isoform.
However, it was found that the increments in POD activity were attributed
to upregulation of the existing isoforms. The isozymes pattern of POD of
green bean leaves showed that the increments caused by treatment of dry
seeds was attributed to upregulation of the existing isoform, whereas
treatment of germinated seeds led to synthesis of a new isoform under
saline conditions. Both treatments enhanced G-POD under saline and non
saline conditions. Generally, it could be concluded that UV-C seed
treatment activated the antioxidant system in both plants, leading to
alleviation of adverse effects of salinity stress.
Keywords: UV radiation, Salinity stress, Seed treatment, Cucumber,
Green bean, Antioxidant system.