Function in plants

In milk fat, cholesterol is associated with Hpoproteins in the milk fat globule. It is also a component of animal membranes and controls rigidity and permeabihty of the membranes. Cholesterol has interesting surface properties and can occur in Hquid crystalline forms. Plants contain sterols such as P-sitosterol [83-46-5] (4b) or stigmasterol [83-48-7] (4c). Their functions in plant metaboHsm are not yet well understood. Analysis of sterols has proven useful for detection of adulteration of edible fats (9). 

Bouvier, F. et al., Oxidative tailoring of carotenoids a prospect towards novel functions in plants, Trends Plant ScL, 10, 187, 2005. 

Flavonoids and other phenolic compounds released by plant roots have important functions in plant-pathogenic interactions, feeding deterrence, nematode resistance, and allelopathic interactions they also serve as signal molecules for the establishment of symbiotic associations (72,149). However, a detailed analysis of signaling pathways involved in these interactions is currently available in only a limited number of cases (see also Chap. 7). 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Theis N and Lerdau, M (2003), The evolution of function in plant secondary metabolites , Int. J. Plant Sci., 164 (3 Suppl.), S93-S102. 

Heldt HW and Heldt F. 2005. A large diversity of isoprenoids has multiple functions in plant metabolism. In Plant Biochemistry, 3rd ed. San Diego, CA Elsevier Academic Press, pp. 413 134. 

Smallwood M, Knox JP, Bowles D. Membrane Specialized Functions in Plants, Bios Scientific Publishers, Herndon, VA, 1996. 

Figure 8.7 Simplified model of nicotiniamine (NA) function in plant cells. Iron is transported across the plasma membrane by the Strategy I or Strategy II uptake systems. Once inside the cell, NA is the default chelator of iron to avoid precipitation and catalysis of radical oxygen species. The iron is then donated to proteins, iron-sulfur clusters and haem, while ferritin and iron precipitation are only present during iron excess. (From Hell and Stephan, 2003. With kind permission of Springer Science and Business Media.)...

The spatial structure of ACS isozymes Do they function in plants as monomers,... 

Gould KS, Lister C (2006) Flavonoid functions in plants. In Anderson DM, Markham KR (eds) Flavonoids chemistry, biochemistry, and applications. CRC Press, Boca Raton, FL, pp 397-442... 

Wink, M. 1987. Quinolizidine alkaloids Biochemistry, metabolism, and function in plants and cell suspension cultures. Planta Medica, 53 509-514. 

The flavonoids are a remarkable group of plant metabolites. No other class of secondary product has been credited with so many — or such diverse — key functions in plant growth and development. Many of these tasks are critical for survival, such as attraction of animal vectors for pollination and seed dispersal, stimulation of Rhizobium bacteria for nitrogen fixation. 

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