Boron deficiency affects early infection events in the pea-Rhizobium symbiotic interaction

The effects of the deprivation of boron (B) on Rhizobium-legume signaling a nd 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 fro m B-deficient pea plants led to a low level of nod-gene expression that cou ld be correlated with poor root hair curling. However, inoculation of B-def icient 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, a nd it was not recovered by hesperetin. Both phenomena provoked a reduction in nodulation of more than 50%. Furthermore, infection thread development w as arrested at very early stages, and cell invasion by endocytosis was prec luded, leading to almost empty of bacteria B-deficient nodules.