THE EFFECT OF NODE TEMPERATURE ON ASSIMILATION AND TRANSLOCATION OF C14 IN THE SQUASH

Abstract

Varying the primary leaf node temperature from 0 to 45 °C did not alter the rate of either C14O2 assimilation or transpiration of the leaf blade. In contrast, the rate of C14-sugar export from the blade was markedly influenced by the node temperature. At 0 °C there was no significant movement of C14 through the node, but a slow export of C14-stachyose and C14-sucrose did continue from the blade into the petiole above the chilled node. This was associated with an abnormal accumulation of C14-sugars in the blade, where the accumulated C14-stachyose showed little metabolic turnover. Above 0 °C and typical of the response of many physiological mechanisms to temperature, the rate of C14 movement through the node increased to a maximum at 25 °C and fell again to zero at 55 °C. The exports from the blade of C14-stachyose and C14-sucrose were equally affected by the different temperature treatments at the node. The inhibitory effect of chilling on translocation was reversible, whereas the effect of heating to 55 °C was irreversible. When the node was rapidly returned from 0 to 25 °C a slow export from the blade began immediately but the normal rate was not restored until approximately 60 minutes later. It is concluded that translocation of sugar through the node and basal region of the squash petiole is under direct physiological control. The process does not appear to be closely correlated with protoplasmic streaming.