Feedback Regulation of Xylem Cytokinin Content Is Conserved in Pea and Arabidopsis

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Eloise Foo; Suzanne E. Morris; Kathy Parmenter; Naomi Young; Huiting Wang; Alun Jones; Catherine Rameau; Colin G.N. Turnbull; Christine A. Beveridge


Scholarcy highlights

  • Increased-branching mutants of garden pea and Arabidopsis were used to investigate control of cytokinin export from roots in relation to shoot branching
  • A small reduction in X-CK is observed when wild-type plants are induced to branch by cytokinin applied directly to axillary buds. These findings indicate that regulation of X-CK is dependent on the shoot branching phenotype and requires a longdistance signal that is modulated during the process of axillary bud outgrowth
  • To test whether down-regulation of X-CK is conserved in species other than pea, xylem sap was collected from mature, short-day-grown Arabidopsis plants of Columbia-0 and branching mutants max1, max2, max3, and max4
  • Predominant X-CKs detected in wild-type xylem sap were trans-zeatin riboside, isopentenyl adenosine, and trans-zeatin, together with smaller amounts of cis-ZR and isopentenyl adenine
  • In the case of trans-zeatin riboside and iPR, the mutant xylem sap contained between 6-fold less and 50-fold less cytokinin, with levels being almost undetectable in some samples
  • We suggest that feedback control of X-CK may be one essential component of the homeostatic control of shoot branching
  • Presence of the sax1 mutation resulted in a 7-fold reduction in total lateral branch length compared with rms4 scions and suppression of axillary meristem formation at a majority of nodes, yet these rms4 sax1 double mutant scions were as effective as rms4 scions at suppressing X-CK in wild-type rootstocks

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