The objective of this study is to explore the
response of an activated Rhizobium tibeticum inoculum
with a mixture of hesperetin (H) and apigenin (A) to
improve the growth, nodulation, and nitrogen fixation of
fenugreek (Trigonella foenum graecum L.) grown under
nickel (Ni) stress. Three different sets of fenugreek seed
treatments were conducted, in order to investigate the
activated R. tibeticum pre-incubation effects on nodulation,
nitrogen fixation and growth of fenugreek under Ni stress.
Group (I): uninoculated seeds with R. tibeticum, group (II):
inoculated seeds with uninduced R. tibeticum group (III):
inoculated seeds with induced R. tibeticum. The present
study revealed that Ni induced deleterious effects on rhizobial
growth, nod gene expression, nodulation, phenylalanine
ammonia-lyase (PAL) and glutamine synthetase
activities, total flavonoids content and nitrogen fixation,
while the inoculation with an activated R. tibeticum significantly
improved these values compared with plants
inoculated with uninduced R. tibeticum. PAL activity of
roots plants inoculated with induced R. tibeticum and
grown hydroponically at 75 and 100 mg L-1 Ni and was
significantly increased compared with plants receiving
uninduced R. tibeticum. The total number and fresh mass
of nodules, nitrogenase activity of plants inoculated with
induced cells grown in soil treated up to 200 mg kg-1 Ni
were significantly increased compared with plants inoculated
with uninduced cells. Plants inoculated with induced
R. tibeticum dispalyed a significant increase in the dry
mass compared with those treated with uninduced R.
tibeticum. Activation of R. tibeticum inoculum with a
mixture of hesperetin and apigenin has been proven to be
practically important in enhancing nodule formation,
nitrogen fixation and growth of fenugreek grown in Ni
contaminated soils.