| Abstract: | Seedlings of Pinus sylvestris were grown in long days at day/nighttemperatures of 27.5/20 °C. 22.5/15 °C, and 17.5/10°C to determine effects of temperature on tracheid expansionand wall thickening. Inbuilt regulatory systems make it unlikely that mean temperaturedifferences account for much of the normal seasonal variationin tracheid dimensions, for while an increase in temperatureincreased rates of both tracheid expansion and wall thickening,the duration of both was reduced. Though wall thickness increasedwith decreasing temperature in tracheids at the same distancefrom the pith, this was offset by a slower rate of tracheidproduction at lower temperatures. While rates of wall accumulation increased with increase intemperature, storage starch grain sizes were smaller at highertemperatures. It is suggested that wall thickness is not limitedby available substrates in these conditions. |
