Biological Clock Found in Plants

Joe the Lesser writes "This CNN article discusses how scientists have found that a chemical 'clock' that tells a plant to prepare for the sun. The clock controls an enzyme that modifies a protein called D1. This protein is critical for photosynthesis, the process whereby plants extract light and convert it to food. When D1 binds with phosphorus, it creates a modified protein found in chloroplast -- a special structure in the cell that's made of carbohydrates, fat and proteins."

Comments

link to paper + abstract

[mlush]

link2paper

Phosphorylation of the D1 Photosystem II Reaction Center Protein Is Controlled by an Endogenous Circadian Rhythm

Isabelle S. Booij-James, W. Mark Swegle, Marvin Edelman, and Autar K. Mattoo*

Vegetable Laboratory, The Henry A. Wallace Beltsville Agricultural Research Center-West, United States Department of Agriculture-Agricultural Research Service, Beltsville, Maryland 20705-2350 (I.S.B.-J., M.S., A.K.M.); and Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel (M.E.)

The light dependence of D1 phosphorylation is unique to higher plants, being constitutive in cyanobacteria and algae. In a photoautotrophic higher plant, Spirodela oligorrhiza, grown in greenhouse conditions under natural diurnal cycles of solar irradiation, the ratio of phosphorylated versus total D1 protein (D1-P index: [D1-P]/[D1] + [D1-P]) of photosystem II is shown to undergo reproducible diurnal oscillation. These oscillations were clearly out of phase with the period of maximum in light intensity. The timing of the D1-P index maximum was not affected by changes in temperature, the amount of D1 kinase activity present in the thylakoid membranes, the rate of D1 protein synthesis, or photoinhibition. However, when the dark period in a normal diurnal cycle was cut short artificially by transferring plants to continuous light conditions, the D1-P index timing shifted and reached a maximum within 4 to 5 h of light illumination. The resultant diurnal oscillation persisted for at least two cycles in continuous light, suggesting that the rhythm is endogenous (circadian) and is entrained by an external signal.

Plant ageing clock

[tlambert]

The plant ageing clock is the same as the human ageing clock; it's based on something called "the Hayflick limit", which is the limit on the number of times a cell can divide.

You can look it up on the web, but the short version is that each time a cell divides, it shortens the telomeres on the ends of its genes; when it runs out of telomeres, the cell dies (or becomes cancerous, or is subject to other age-related disease processes).

Baby humans and plants don't have this limit, since, in gametogenesis, the telomeres are lengthened by a chemical called "telomerase", effectively resetting the clock for the newly created entity.

-- Terry