Effect of auxin on xylem tracheids differentiation in decapitated stems of Pinus silvestris L. and its interaction with some vitamins and growth regulators

The effects of several vitamins and substances known as important agents in regulation of cell metabolism upon secondary xylem differentiation were studied in interaction with auxin (IAA) as applied in lanoline to decapitated stems of 5-year-old <i>Pinus silvestris</i> trees in early and late-summer. Tested substances were: gibberellic acid, kinetin, nicotinic acid, thiamine, pyridoxine, calcium panthotenate, choline chloride, riboflavin, inositol, ascorbic acid, vitamin, A (alcohol), vitamin A (ester), saponin. None of the effects of these substances appeared significant enough to indicate the involvement in the seasonal variation of the response of cambium or differentiating tracheids to auxin. However, several effects, especially those of inositol, vitamin A and pyridoxine upon cambial xylem production and further stages of tracheid differentiation were observed. Auxin (IAA) affected cambial activity and subsequent differentiation of tracheids during the earliest stages of cell ontogenesis. At these stages auxin treatment induced quantitative expression of the developmental processes involving radial growth and secondary wall formation by tracheids. In this respect, auxin did not affect cells advanced in differentiation, however, it proved to be an essential factor in the completion of the full cycle of tracheid ontogenesis.

Apical control of xylem formation in the pine stem. II. Responses of differentiating tracheids

The effect of auxin supplied to the main stem of 5-year-old <em>Pinus silvestris</em> trees during various periods after decapitation upon differentiation of the secondary xylem tracheids was investigated. The results revealed the complexity of auxin involvement in the regulatory system of tracheid differentiation of secondary xylem. It is manifested both as the inductive effect to which the cells respond in the meristematic phase and in the continuous control during the consecutive stages of radial growth and maturation. A lack of auxin during the meristematic phase resulted in smaller cell diameters and reduced the daily rate of cell wall deposition even though these cells progressively grew and matured in the presence of auxin. The intensity of these two processes increased and the cells deposited thicker walls when auxin was supplied during all stages of tracheid differentiation even though the period of maturation decreased. Under these conditions tracheids of compression wood type differentiated. Continuous availability of auxin causes earlier termination of tracheid maturation while lack of auxin results in a delay of autolysis of protoplasts. In this case auxin probably functions in a system specifying information concerning the position of the cells in respect to the cambial layer.

Effects of altitude on tracheid differentiation and lignification of Norway spruce

The effect of altitude on lignification is important in developing an understanding of what drives natural variation in wood properties. Cambia of two Norway spruce trees, growing at altitudes of 580 and 1260 m a.s.l., were periodically sampled to measure tracheid dimensions and cellular lignin content. The low-elevation tree showed a higher rate of cell division with thicker cell walls and wider growth rings. The maturation phase of tracheids at high elevation was completed by the end of October while low elevation latewood tracheids were still lignifying. As revealed by ultraviolet microscopy, lignin content in single cells, as well as in complete tree-rings, was higher at high elevation. Rank correlation analysis indicated high negative correlation between lignin content of tracheid cell walls and corresponding wall thickness. It is hypothesized that trees growing at higher altitudes compensate for the thinner cell walls with an increased lignin content which helps to maintain mechanical integrity of the xylem.Key words: altitude, lignin, tracheid, wood formation, ultraviolet microscopy.