EFFECTS OF TEMPERATURE ON CELL-DIVISION IN ROOT-MERISTEMS OF NATURAL-POPULATIONS OF DACTYLIS-GLOMERATA OF CONTRASTING LATITUDINAL ORIGINS

The effect of temperature on cell division was studied in the root meristems of five natural populations of Dactylis glomerata from contrasting latitudes and altitudes within mainland Europe to determine which aspects of the cell cycle were most sensitive to temperature change and to what extent this was related to latitude and altitude of origin. Cell doubling times (cdts), and the duration of the cell cycle (Tc) were determined in primary root meristems of the five populations which were grown at 15-degrees-C for 10 days and then maintained at this temperature or transferred to either 10 or 20-degrees-C for a further 4 days. Cdts were measured using the colchicine-metaphase arrest technique while Tcs were determined with the percentage H-3-labelled mitoses method. The growth fraction: mean labelling index divided-by fraction of labelled mitoses over one cell cycle, or Tc divided-by cdt, were also calculated. The relative sensitivity of the cell cycle to lowered root temperature (Tc 10/20) was less in populations from high latitudes/altitudes compared with populations from lower latitudes/altitudes. Growth fraction measured at all temperatures for all populations was correlated positively with the duration of the cell cycle and separately for the data at 10 and 15-degrees-C but not at 20-degrees-C. Thus, for these natural populations of Dactylis glomerata grown over a 10-20-degrees-C temperature range, the longer cell cycles were compensated for by larger growth fractions.