The effects of the deprivation of boron (B) on
Rhizobium–legume signaling and preinfection events
have been investigated in pea (Pisum sativum L. cv.
Argona). The capacity of root exudates to induce the activity of nodulation
genes was modulated by B nutrition in the host plant. Exudates derived from
B-deficient pea plants led to a low level of nod-gene
expression that could be correlated with poor root hair curling. However,
inoculation of B-deficient plants with bacteria grown in the presence of the
nod-gene inducing hesperetin, restored root hair
curling. The attachment of bacteria to roots was also diminished in plants
grown in the absence of the micronutrient, and it was not recovered by
hesperetin. Both phenomena provoked a reduction in nodulation of more than
50%. Furthermore, infection thread development was arrested at very
early stages, and cell invasion by endocytosis was precluded, leading to
almost empty of bacteria B-deficient nodules.