Auxin and cytokinin relationship

auxin and cytokinin relationship

Cytokinin (CK), synthesized in the root cap, promot. Adventitious roots, apical dominance, Arabidopsis thaliana, auxin, cytokinin, ethylene, lateral .. The same basic rules on phloem and xylem relationships occur in both. The phytohormones auxin and cytokinin interact to regulate many plant to mind plants and their integral relationship with light and shadow. petioles results in a decline of cytokinin content and an increase of auxin levels. The addition of plant growth regulators (PGRs) to the medium lead to recovery of .

The absence of isopentenyltransferase IPT expression in shoot apical meristems Miyawaki et al. The suggestion of Letham that the main site of CK synthesis is the root tip, specifically the root cap cells, was confirmed by Aloni et al.

PLANT HORMONES - Auxin Gibberellin Cytokinin Ethylene Abscisic Acid

CKs have opposing roles in shoots and roots; in young shoot organs the CKs positively regulate development and promote shoot growth Howell et al. GUS transformant of 5-week-old Arabidopsis grown under long-day conditions described in Aloni et al. A Root of wind-protected plant with strong ARR GUS expression reflecting high bioactive CK concentration in the cap arrowconsiderable concentration in the vascular cylinder arrowhead and lower concentration in the cortex.

The Yin-Yang of Hormones: Cytokinin and Auxin Interactions in Plant Development

C Plant from the same experiment as in A and B, but exposed to gentle wind of 0. GUS expression in the young apical flower buds arrow. This suggests that synthesis of CK in the shoot could guarantee CK availability under conditions of insufficient CK supply from the root, e.

View large Download slide Schematic diagrams at the root's differentiation zone, showing free-IAA transport pathways in a triarch root at a phloem plane Aand in the same root at a xylem plane B ; the xylem plane location is marked by a dotted line a—b in A. The long arrows in the diagrams illustrate IAA movement in a polar manner preferably in the vascular cylinder the internal route: In the peripheral route from the shoot to the root's differentiation zonethe IAA arriving from the young leaves moves downward in a polar manner see Terasaka et al.

Auxin–Cytokinin Interaction Regulates Meristem Development

This probably induces the meristematic cortical downward IAA movement detected by the polar pattern of PIN1 in the acropetal membranes of the differentiating cortex near the root tip.

In the non-polar route, IAA moves up and down illustrated by broken-line arrows in mature protophloem sieve tubes S. The auxin hormone and its polar movement, originating in young shoot organs Jacobs, ; Aloni et al. IAA regulates the development of the primary and lateral roots Sabatini et al.

The PINFORMED1 PIN1an essential protein component involved in auxin efflux, cycles between the plasma membrane and intracellular vesicular compartments, facilitating rapid transfer and accumulation of the protein in various sites of the plasma membrane Geldner et al.

auxin and cytokinin relationship

Polar accumulation of PIN proteins at specific sites of the plasma membrane enables detection of the polar IAA transport direction Friml et al. However, further away from the apices, perhaps owing to decreased local IAA concentrations, the polar IAA movement might not be enough to induce detectable polar patterns of PINs, and therefore further away from the tips the IAA routes remain obscure.

Like auxin, cytokinin is also a key regulator for various aspects of plant growth and development.

auxin and cytokinin relationship

Cytokinin homeostasis is spatially and temporally regulated by a fine balance between synthesis and catabolism. The first enzyme identified in the Arabidopsis cytokinin biosynthetic pathway is adenosine phosphate-isopentenyltransferases IPTs. Another landmark is the identification of two cytochrome P monooxygenases, CYPA1 and CYPA2, which catalyze the hydroxylation at the prenyl side chain of the iP-nucleotides to synthesize tZ-nucleotides Takei et al.

In contrast to auxin, cytokinin is perceived in plants through a multi-step phosphorelay pathway similar to the bacterial two-component signaling system Kakimoto, ; To and Kieber, Recent analyses on these three receptors have revealed a largely overlap expression pattern and partially redundant functions in cytokinin perception Higuchi et al.

The Yin-Yang of Hormones: Cytokinin and Auxin Interactions in Plant Development

Furthermore, the arr1, arr10, arr12 triple mutants show a strong reduction in cytokinin induction of multiple type-A ARR transcripts Mason et al. Mutation analysis has indicated that at least eight of the 10 type-A ARRs are negative regulators of cytokinin signaling again with overlapping functions To et al. For the past few years, genetic and molecular evidence has revealed the interaction between auxin and cytokinin during plant development Dettmer et al.

Many recent biochemical and genetic investigations have further confirmed that the intricate cross-talk and integration of hormone signaling are required for differentiation and maintenance of plant meristems.

Auxin–Cytokinin Interaction Regulates Meristem Development

Hereafter, we shall focus our discussion on the interaction between auxin and cytokinin in the regulation of meristem development.

The first step of embryonic patterning is the establishment of the apical—basal axis, in which asymmetric distribution of auxin mediated by PIN proteins plays a major role. A zygote undergoes an asymmetric division to produce a smaller apical cell and a larger basal cell. At this two-cell embryo stage, PIN7 is expressed in the basal cell to transport auxin to the apical cell Friml et al.

auxin and cytokinin relationship

After two more rounds of cell division, PIN7 localizes to the apical membrane of suspensor cells, resulting in the accumulation of auxin in the whole pro-embryos Friml et al. This WUS induction might be related to auxin accumulation. However, PIN7 polarity is reversed at the cell stage, resulting in the transport of auxin towards the suspensor cells Friml et al.

The transported auxin accumulates in the uppermost cell of the suspensor to form the hypophysis, the founder of the stem-cell niche of the embryonic root Friml et al.

At a later transition stage of the embryo, auxin is directed towards the center of the cotyledon primordia in the apical domain to establish the cotyledons. Therefore, auxin transport is critical for the maintenance of the polar axis and the formation of two types of meristems in the embryo.

auxin and cytokinin relationship

Loss-of-function of MP or gain-of-function of BDL causes the aberrant specification of the apical cell, and prevented the formation of the embryonic root Weijers et al. Embryos of the mp mutants are abnormal at their early globular stages. In addition, heart-stage mp embryos lack the central pro-vascular cylinder. The gain-of-function bdl mutants show milder defects than mp mutants and have a reduced vascular system and a hypocotyl of variable length without primary root meristem Hamann et al.