Effect of Defoliation or Excision of Growing Axillary Shoots on the Composition of Labeled Products of Photosynthesis in the Leaves and Xylem Sap of Kidney Bean

摘要

The content of ~(14)C in the products of photosynthesis of the source leaf and xylem sap was investigated in kidney bean (Phaseolus vulgaris L.) plants during the stage of mass tillering. C partition was measured a day after two-minute photoassimilation of ~(14)CO_2 by an individual mature leaf located in the middle part of the shoot. The source-sink relations were disturbed by the excision of all mature leaves (except the source leaf) or all growing axillary shoots. The leaves or growing axillary shoots were excised 15 min after leaf feeding with ~(14)CO_2. A day later, in plants with excised growing axillary shoots, the content of ~(14)C in the source leaf was by 18% higher and in those with removed leaves by 15% lower than in control plants. Thenext day after the excision of growing axillary shoots, radioactivity of the xylem sap increased; after defoliation, both the volume of the xylem sap and its specific radioactivity decreased. In the xylem sap of defoliated plants, the proportion of ~(14)C in malate decreased more than six times, whereas the proportion of ~(14)C in amino acids somewhat increased (1.5 times). In two days, the volume of the xylem sap exuded by treated plants became the same as in control plants and its radioactivity decreased almost by an order of magnitude but essentially did not differ in the both types of treatment. It is concluded that the processes occurring in the roots are governed by photosynthesis but its regulatory effect is limited by a photoperiod and largelydepends on changes in the ratio between biosynthesis of amino acids in the roots and leaves.