Temperature Effects on Oxidative Metabolism of Dormant Sugar Pine Seeds

When dormant sugar pine (Pinus lambertiana L.) seeds were imbibed at 5 degrees C, they showed a rapid increase in O(2) uptake, ATP level, and moisture content during the first 4 days. This was followed by a plateau phase until 60 days, after which a second significant increase in all three features occurred as dormancy was broken. During the plateau phase, conventional CN-sensitive respiration accounted for 74 to 79% of the total O(2) uptake. When dormant sugar pine seeds were imbibed at and maintained at 25 degrees C, a different pattern occurred. Water uptake was much more rapid during the first 4 days and no second increase occurred after 60 days because the seeds did not break dormancy. There was an initial burst of O(2) uptake and ATP formation, but these both declined abruptly after 24 to 48 hours. Levels about half those of seeds at 5 degrees C were maintained through the rest of a 90-day period. CN-sensitive respiration declined during imbibition at 25 degrees C, and accounted for only 55 to 61% of the total O(2) uptake. The inability of dormant sugar pine seeds to germinate at temperatures above about 17 degrees C may therefore result from initial temperature effects on membrane properties, leading to reduced O(2) uptake, reduced cytochrome oxidase electron transport activity, and lowered ATP levels.