Plant embryology: leaf making feedback controls (Introduction)

by David Turell , Wednesday, June 06, 2018, 19:42 (2363 days ago) @ David Turell

All life regulates itself by circular feedback loops, especially in creating new parts:

https://www.sciencedaily.com/releases/2018/06/180606132652.htm

"During growth, plants constantly form new leaves, branches, and roots over weeks, months, and years. These are initially formed via cell division, where cells develop in highly complex, yet orderly processes. One result of these developmental programs is the vascular tissue of the plants, which is visible to the human eye in the form of leaf veins. Vascular tissue pervades the entire plant body, supplying the plant with water and salts from the ground via the xylem, and with metabolic products such as sugars from photosynthesis via the phloem.

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"'Back in 2009, the team in Lausanne demonstrated that plants which were lacking a certain protein (BRX) have problems forming phloem cells," states co-author Lanassa Bassukas .."At the same time, they also observed that it has a highly sensitive response to the plant hormone auxin. Depending on whether the auxin value was low or high, the protein was located in the cell membrane or was degraded inside the cell."

"This became relevant when the TUM researchers discovered a new regulator called PAX. With the help of this regulator, the hormone auxin can be transferred out of the cell via transporter proteins. Just as in plants with a defect in the BRX protein, plants without PAX had fewer phloem cells.

"'For us, it was noteworthy, on the one hand, that the PAX regulator could be retarded by the BRX protein, and on the other, that PAX became more active as the auxin level in the cell increased," explains Martina Kolb and Ulrich Hammes from TU Munich, who provided important findings for the new model with their auxin transporter studies.

"According to their findings, auxin initially accumulates in a newly developed cell. This is because BRX prevents the hormone coming from the other phloem cells from being transported out of the cell with the help of the PAX regulator. The auxin which accumulates over time then leads to the degradation of BRX, causing the PAX regulator, which has now been activated, to export the auxin from the cell. Because the BRX protein is formed again with a certain time delay upon which it blocks auxin transport, the system regulates itself repeatedly like a rheostat.

"Many plant development processes are dependent on auxin transport and regulators similar to PAX. With the development of the negative regulation via the protein, a new control level has been discovered which could be just as applicable in other processes.

Comment: Another feedback loop control. Since they are circular, they require design to create the mechanism. A loop cannot design itself by chance and meet itself on the other side of the loop.