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

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors is: Christine A

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

2007

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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