Bacterial endobionts in the big non-mycorrhizal roots of Scots pine (Pinussylvestris L.)

Subsurface bacterial growth occurred in an N-free medium inoculated with in terior tissues of big non-mycorrhizal roots (7 to 8 mm diameter) of 15-20 y ears-old Scots pine (Pinus sylvestris L.) growing on sand dunes at the Balt ic Sea of Poland. The bacteria were not N-2 fixers as determined by the ace tylene reduction method. Light microscopic and scanning electron microscopi c observations revealed massive bacterial clusters residing in the cortical cells underlying epidermis and parenchyma. The bacteria produced yellow-gr een pigments on King's medium, which fluoresced under ultraviolet (UV) irra diation at 366 nm wavelength, and could be a siderophore-producing Pseudomo nas.