Abstract:
Sulfur dioxide (SO
2
) is one of the most common and harmful air polluta
nts. High
concentrations of SO
2
can cause stress and limit growth in plants. Some
of the plants can
resist stress by bacterial symbiosis such as
Rhizobium
symbiosis.
Rhizobium
is a beneficial
bacterium that enhances plant growth and yield. To
study the effects of SO
2
pollution on
growth indexes, protein, proline and sulfur content
s, 31 days old plants of
Trifolium
resupinatum
(Persian clover), inoculated with native and standa
rd
Rhizobium
were
exposed to the different concentrations of SO
2
(0 as control, 0.5, 1, 1.5 and 2 ppm) for 5
consecutive days. Results showed that inoculation i
ncreased leaf area, leaf number, shoot
height, root length, shoot fresh and dry weight and
protein content of Persian clover but
didn’t show any significant effect on proline and s
ulfur contents. Different concentrations
of SO
2
had a significant effect on leaf number, shoot hei
ght, root length, shoot fresh and
dry weight, protein, proline and sulfur contents bu
t didn’t have effects on leaf area. 0.5
ppm concentration of SO
2
increased growth indexes and protein content. Prol
ine and
sulfur contents didn’t change in 0.5 ppm. Increasin
g SO
2
decreased growth indexes and
protein, and increased proline and sulfur contents.
Interaction between
Rhizobium
inoculation and SO
2
treatment improved the stress effects of high conc
entrations of SO
2
on growth indexes, protein, proline and sulfur cont
ents. It was therefore concluded that
Rhizobium
can increase tolerance and resistance of this plan
t to the abiotic stresses such
as SO
2
pollution
.
Keywords
: Air pollution, Persian clover, Protein,
Rhizobium
, Sulfur
