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Regulation of correlative inhibition of axillary bud outgrowth by basal branches varies with growth stage in Trifolium repens.

ABSTRACT: In Trifolium repens the decline in bud outgrowth that occurs with distance from basal root systems is due to correlative inhibition by the first-formed basal branches. The apical and axillary buds on these basal branches are the source of the inhibitory effect, but their mode of action is unclear. Inhibition might occur via basal branches being a sink for xylem-transported branching stimulants or alternatively by providing a source of inhibitory signals, or by both mechanisms. To distinguish between these mechanisms, four experiments were conducted on plants varying in initial growth stage from 10 to 19 nodes along their main stems to determine any variation in the relative importance of the operative mechanisms of correlative inhibition. Inhibitory signal exported into the main stem, detected as a branching response to girdling of basal branches, was relatively more significant in smaller (initially with 10-15 nodes on the main stem) than in larger (>19 nodes on main stem) plants. This signal was shown not to involve auxin fluxes, and is unidentified. However, across all stages of growth, the predominant mechanism driving correlative inhibition was the action of axillary and apical buds of basal branches as sinks for the stimulatory signal. This study indicates that the relative importance of the mechanisms regulating bud outgrowth in T. repens varies with growth stage and that, during intermediate stages, regulation has some similarity to that in Pisum.

SUBMITTER: Thomas RG

PROVIDER: S-EPMC4473983 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Aims: To determine the changes in the Arabidopsis axillary bud transcriptome in response to changes in the red light (R) to far red light (FR) ratio (R:FR). Background: The branching habit of plants is a key determinant of overall plant form and function with great relevance to modern agriculture. Shade signals transduced by phytochromes are major regulators of axillary bud outgrowth, and in turn control branching in both natural and agricultural environments. To continue our investigations into the regulation of branching by R:FR, we have developed a system using supplemental FR LEDs to tightly control the outgrowth of Arabidopsis axillary buds. Depending on the position of the bud in the rosette, outgrowth is either repressed (uppermost bud) or rapidly promoted (bud in the axil of the third leaf down) by the transition from low to high R:FR. Treatment: Two separate experiments were conducted to evaluate the effects of R:FR on transcriptome changes in the uppermost rosette bud (bud n) and the axillary bud in the axil of the third leaf from the top (bud n-2). WT Col-60000 was used as the experimental material. Plants were grown individually in 25 by 50 mm tubes and watered and fertilized optimally. Plants were grown in a split growth chamber (providing uniform temperature and PPFD but allowing for differential R:FR) with 18 h photoperiods (185 Moles m-2 s-1 PPFD provided by T12 VHO CW fluorescent lamps) and 24 C/18 C day/night temperatures. One day after sowing, the R:FR was reduced on both sides of the chamber from 3.5 to 0.08 using FR LEDs fixed in clear overhead arrays. Prior to anthesis, the plants were matched and split into two treatment groups. In experiment 1, the FR source for one of the groups was switched off at 12:00 pm on the day of anthesis, causing the R:FR to increase to 3.5. Unelongated axillary buds in the axil of the uppermost leaves (approx. 2.5 mm long) were harvested for RNA preparation from both groups (low and transiently increased R:FR) 3 h after changing the R:FR. Each treatment was composed of three biological replicates, each containing buds from about 15-18 plants. Experiment 2 was conducted exactly the same as experiment 1, except the R:FR was altered 3 days after anthesis and the unelongated axillary buds in the axils of the third leaves down (approx. 1 mm long) were harvested for RNA preparation. 12 samples (3 bud n and low R:FR, 3 bud n and high R:FR, 3 bud n-2 and low R:FR, 3 bud n-2 and high R:FR) were used in this experiment.

Project description:Aims: To determine the changes in the Arabidopsis axillary bud transcriptome in response to changes in the red light (R) to far red light (FR) ratio (R:FR). Background: The branching habit of plants is a key determinant of overall plant form and function with great relevance to modern agriculture. Shade signals transduced by phytochromes are major regulators of axillary bud outgrowth, and in turn control branching in both natural and agricultural environments. To continue our investigations into the regulation of branching by R:FR, we have developed a system using supplemental FR LEDs to tightly control the outgrowth of Arabidopsis axillary buds. Depending on the position of the bud in the rosette, outgrowth is either repressed (uppermost bud) or rapidly promoted (bud in the axil of the third leaf down) by the transition from low to high R:FR. Treatment: Two separate experiments were conducted to evaluate the effects of R:FR on transcriptome changes in the uppermost rosette bud (bud n) and the axillary bud in the axil of the third leaf from the top (bud n-2). WT Col-60000 was used as the experimental material. Plants were grown individually in 25 by 50 mm tubes and watered and fertilized optimally. Plants were grown in a split growth chamber (providing uniform temperature and PPFD but allowing for differential R:FR) with 18 h photoperiods (185 Moles m-2 s-1 PPFD provided by T12 VHO CW fluorescent lamps) and 24oC/18oC day/night temperatures. One day after sowing, the R:FR was reduced on both sides of the chamber from 3.5 to 0.08 using FR LEDs fixed in clear overhead arrays. Prior to anthesis, the plants were matched and split into two treatment groups. In experiment 1, the FR source for one of the groups was switched off at 12:00 pm on the day of anthesis, causing the R:FR to increase to 3.5. Unelongated axillary buds in the axil of the uppermost leaves (approx. 2.5 mm long) were harvested for RNA preparation from both groups (low and transiently increased R:FR) 3 h after changing the R:FR. Each treatment was composed of three biological replicates, each containing buds from about 15-18 plants. Experiment 2 was conducted exactly the same as experiment 1, except the R:FR was altered 3 days after anthesis and the unelongated axillary buds in the axils of the third leaves down (approx. 1 mm long) were harvested for RNA preparation.

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Regulation of correlative inhibition of axillary bud outgrowth by basal branches varies with growth stage in Trifolium repens.

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