Cytokinins

Functions:

• Cell Division...Cyto-kinin=cell-division
• Delays Senescence
• Nutrient Mobilization
• Chloroplast Maturation
• Cotyledon Expansion
• Overcomes Apical Dominance
• Shoot initiation

1970s Cytokinins stimulate mature cells to divide...totipotency!

Development terms

• undifferentiated-multiple cell fates
• determined-destined for a particular fate (may "dedifferentiate")
• canalized-locked into destiny for particular fate (cannot "dedifferentiate")
• differentiated-distinctly different and already IN particular fate

Discovery

Heat tumor to 42 C, bacteria die, callus continues to grow! 1958
*bacteria alter genes of host!

Ti plasmid genes for cytokinin synthesis and auxin synthesis

transformed into plant genome and expressed (like viruses!)

First genetic engineering protocols to produce transgenic plants!

Synthetic genes replace hormone synthesis genes and voila!

Tissue culture of plant cells

minerals, vitamins, sucrose, coconut milk (?)

What is the active ingredient of coconut milk?
Adenine minimal effect (look for stuff in DNA) Skoog & Miller 1955
Museum herring sperm DNA--works great
New herring sperm DNA--fails
Autoclave new herring sperm--works great
Active principle = kinetin = 6 furfuryl amino purine (Letham 1974)

6-furfuryl = derivative of deoxyribose
aminopurine = derivative of adenine

Actual cytokinin in Coconut milk = Zeatin

Level control

• Synthesis: adenine = nitrogenous base + isoprene from mevalonic acid
  mostly in roots
• Transport: nonpolar...via xylem?
• Conjugation: Free- vs sugar-bound forms (riboside, ribotide(inactive))
• Degradation: Polymerization into DNA/RNA + Cytokinin oxidase
• Found as an altered base in tRNA
• Embryo gets jump-start from endosperm but then makes own!

Function

But maybe this is merely for alignment of certain tRNAs?

Does the receptor activate a Calcium intake pump that turns on second-messenger calmodulin?

Activating Cell Division:

Cell Cycle Review

Leaf Cutting:

Go back to the Course Schedule.