DAILY DYNAMICS IN XYLEM CELL RADIAL GROWTH OF SCOTS PINE (PINUS-SYLVESTRIS L)

Daily dynamics of radial cell expansion during wood formation within t he stems of 25-year-old Scots pine trees (Pinus sylvestris L.), growin g in field conditions, were studied. The samples of forming wood layer s were extracted 4 times per day for 3 days. Possible variations in th e growth on different sides of the stem, duration of cell development in radial cell expansion phase and dynamics of cell growth in this pha se were taken into account. The perimeters of tracheid cross-sections as a reflection of primary cell wall growth were the criterion of grow th in a radial direction. For the evaluation of growing cell perimeter s a special system for digital processing and image analysis of trache id cross-sections of the forming wood was used. Growth rate for certai n time intervals was estimated by the change in the relation of the pe rimeter of each observed cell in each of ten tracheid rows in each of 12 trees to the perimeter of the xylem cell of the same row before the expansion. Temporal differences in average values of the relations we re estimated by Analyses of Variance. The existence of daily dynamics of Scots pine xylem cell radial growth has been proved. Intensive grow th of pine tracheids has been shown to occur at any time of the day an d to depend on the temperature regime of the day and the night as well as water supply of stem tissues. Moreover, reliable differences (P = 0.95) in the increment of cell walls during tracheid radial expansion have been found. Pulsing changes of the water potentials both of the c ell and the apoplast, as the reason for the fluctuations of radial cel l growth rate, were discussed.