Salt stress is a major problem in
global crop production. Sugar beet which is one of the world’s leading sugar
crops has strong salt tolerant features than other crops. To investigate this,
the response of sugar beet towards various levels of salt stress, sugar beet
was grown hydroponically under 70mM, 140, 210 and 280mM NaCl concentrations
with a control of 3mM concentration.
There was no difference in the
dry weight of the aerial parts and leaf area of the plant treated with 70mM
salt stress and that of the control conditions. Dry weight of the root and the
entire plant treated with 70mM salt conditions was less than that of the
controls. The growth was arrested with increase in salt concentrations.
The tissues of petioles and old
leaves were with highest concentrations of Na+ and Cl-, which is nothing but salt
stress. With the rise in NaCl concentrations, the content of nitrogen and
potassium in the tissues of leaf, petiole and roots were decreased quickly and
the content of phosphorus increased. The antioxidant enzymes like superoxide
dismutase, catalase, ascorbate peroxidase and glutathione peroxidase showed higher
activities in the high salt concentrations.
As the external salt
concentrations increased, osmoprotectants such as free aminoacids and betaine
increased in their concentrations. Two organic acids such as malate and citrate
that are involved in tricarboxylic acid cycle showed increased contents under the
salt stress. It was also found that the activity of Rubisco also reduced with
increase in salt stress. The activities of enzymes like NADP-malic enzyme, NADP
malate dehydrogenase and phosphoenol pyruvate carboxylase first increased and
then decreased. Their activities were seen higher with salinity at 140mM NaCl.
This research study revealed the mechanisms
of physiological and metabolic responses of sugar beet at various levels of
salt stress.
