Boric acid-phenolic relationships within the Pinus echinata-Pisolithus tinctorius ectomycorrhizal association

At germination, container-grown shortleaf pine seedlings were inoculated with Pisolithus tinctorius (Pers.) Coker & Couch or left uninoculated, and both groups were fertilized semiweekly with a modified Hoagland's solution supplemented with 0 or 0.4 mM boric acid. After 12, 16 and 24 weeks, seedling root tissue was analyzed for ectomycorrhizal colonization, phenolic concentration and phenoloxidase activity. In addition, phenoloxidase activity was assayed in P. tinctorius that had been cultured in a liquid medium containing boric acid. Inoculation with P. tinctorius increased the root phenolic concentration of 16- and 24-week-old seedlings, and increased root phenoloxidase activity in 12-, 16- and 24-week-old seedlings. Fertilization with boric acid reduced the phenolic concentration of P. tinctorius ectomycorrhizae after 24 weeks. Although boric acid fertilization did not affect the phenoloxidase activity of 12-, 16- and 24-week-old inoculated roots, or that of 16- and 24-week-old uninoculated roots, it increased the phenoloxidase activity of P. tinctorius grown in vitro and 12-week-old uninoculated roots. We conclude that boric acid fertilization influences the phenolic relations of the shortleaf pine-P. tinctorius ectomycorrhizal association, possibly through a boric acid-induced increase in phenoloxidase activity.     

Seasonal changes in bud dormancy in relation to bud morphology, water and starch content, and abscisic acid concentration in adult trees of Betula pubescens

Annual cycles of change in bud morphology, bud burst ability, abscisic acid (ABA) concentration, and starch and water content were studied in mid-crown terminal buds of short shoots and underground basal buds of Betula pubescens Ehrh. In particular, we investigated the roles of ABA and bud water content in the regulation of bud growth. Basal buds differed morphologically from terminal buds of short shoots in that their leaf initials did not develop into embryonic foliage leaves and their total size did not increase significantly during summer. Bud burst ability, measured by forcing detached short shoots and stumps under controlled conditions, was maintained in the basal buds throughout the year, whereas the terminal buds of short shoots remained dormant until October, thereafter their bud burst ability increased gradually and reached a maximum in March-April. The ABA concentration of the basal buds was relatively constant throughout the sampling period (1-3 micro g g(DW) (-1)), whereas that of the terminal buds of short shoots, which was much higher (5-10 micro g g(DW) (-1)), showed a distinct seasonal cycle with a maximum from August to November. Bud ABA concentration decreased during the first 10 days of forcing, especially in basal buds. In both bud types, the amount of starch increased toward the autumn, declined in November, and was negligible in the terminal buds of short shoots between January and March, but in April, the amount was high again in both bud types. Water content varied characteristically in both bud types, although more distinctly in the terminal buds of short shoots, with an increase in spring before bud burst and a decrease during the summer until September. The significant morphological and physiological differences between the mid-crown terminal buds of short shoots and the underground basal buds may partly explain the characteristic growth habit of the basal buds and their development into coppice shoots after cutting the tree. The results also indicate a role for ABA in maintaining dormancy of the terminal buds of short shoots and emphasize the relationship between tissue water status and ABA concentration.