Interaction Between Leaf Elongation, Photosynthesis, and Carbohydrate Levels of Mater-stressed Corn Seedlings
1976
Barlow, E. W. R. | Boersma, L.
Young rapidly expanding leaves of a corn (Zea mays L.) plant are major photosynthate sinks. Recent evidence indicates that expansion of these young leaves may be severely restricted for a considerable time during the diurnal light period by low leaf water potential and/or low soil temperature. To better understand effects on photosynthesis of prolonged diurnal reduction in leaf expansion, net photosynthetic rate of lower mature leaves, which act as a major source of photosynthate for young expanding leaves, was monitored under environmental conditions shown to restrict the expansion of the young leaves. When leaf elongation was restricted by lowering root temperature from 27.5 C to 15.0 C, net photosynthetic rate of the source leaf was reduced 47% and soluble carbohydrate content of the sink leaf increased 45% at the end of a 7-hour treatment period. Only about one-third of this reduction in net photosynthesis was due to the concurrent decrease in leaf water potential. When leaf elongation was restricted by cooling the shoot apical meristem region from 27.5 C to 6.0 C, net photosynthetic rate of the source leaf decreased 24% and its soluble carbohydrate content increased 23% while the soluble carbohydrate content of the sink leaf increased 40% at the end of a 7-hour treatment. These experiments support the hypothesis that environmental factors which limit leaf elongation may indirectly decrease photosynthetic potential of source leaves within the time limits of the diurnal stress cycle.
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