Abstract Brassinosteroids have been extensively used
to overcome various abiotic stresses. But its role in
combined stress of salt and excess copper remains
unexplored. Seeds of two cultivars (Rocket and
Jumbo) of Cucumis sativus were grown in sand
amended with copper (100 mgkg−1), and developed
seedlings were exposed to salt stress in the form of
NaCl (150mM) at the 30-day stage of growth for 3 days.
These seedlings were subsequently sprayed with 0 or
0.01 μM of 24-epibrassinolide (EBL) at the 35-day
stage. The plants exposed to NaCl and Cu in combination
exhibited a significant decline in fresh and dry mass
of plant, chlorophyll content, activities of carbonic
anhydrase, net photosynthetic rate and maximum quantum
yield of the PSII primary photochemistry followed
by NaCl and Cu stress alone, more severely in Jumbo
than in Rocket. However, the follow-up treatment with
EBL to the stressed and nonstressed plant improved
growth, chlorophyll content, carbonic anhydrase activity
and photosynthetic efficiency, and further enhanced
the activity of various antioxidant enzymes viz. catalase,
peroxidase and superoxide dismutase and content of
proline at the 40-day stage of growth, and the response
of the hormone was more effective in Rocket than in
Jumbo. The elevated level of antioxidant enzymes as
well as proline could have conferred tolerance to the
NaCl- and/or Cu-stressed plants resulting in improved
growth, water relations and photosynthetic attributes.
Furthermore, antioxidant enzyme activity and proline
content were more enhanced in Rocket than in Jumbo
cultivar. |
