Preliminary histological investigations of the defense reactions of three pines to Ceratocystisclavigera and two chemical elicitors

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Abstract
The histology of defense reactions in individual pine trees belonging to three species, Pinusponderosa, P. contorta, and P. monticola, to inoculation with Ceratocystisclavigera and injection with chitosan and a proteinase inhibitor inducing factor was investigated after resin fixation with cupric acetate. The synthesis of secondary resins was directly associated with parenchyma cells in the phloem and in the rays of both phloem and sapwood. However, these resins were largely located in the lumen of sieve cells and tracheids. In the case of the fungus and chitosan, resin soaking began in the outer phloem and latewood of the last growth rings, then spread into the inner phloem and earlywood. With the proteinase inhibitor inducing factor, resinosis was similar to that of the buffer control, being much less extensive than with the fungus or chitosan, and occurring mainly in the inner phloem and earlywood. In P. monticola, the reaction was complicated by the appearance of fissures in the phloem, probably caused by tension from resin pressure. Phloem resinosis was accompanied by apparent secretion of phenolic compounds, presumably from parenchyma cells. The possible origin of these secondary resins and the potential mode of action of the chemicals used are discussed.

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