Phosphoinositides, Biosynthesis

Amongst the cyclic polyols, inositols are most widely distributed in the plant kingdom.234 Out of nine stereoisomers, myo-inositol has the most widespread metabolic significance.235 The derivatives of myoinositol are also widespread. In plants, myo-inositol plays an important role in the biosynthesis of hemicelluloses and oligosaccharides it also occurs as a storage product (phytic acid), a coenzyme for sugar-transport, a precursor of phosphoinositides, and esters of in-doleacetic acid.47,113,238... 

Our results show that the components of the phosphatidyl inositol cycle are present in suspension cultured tobacco cells, which is in agreement with previous report (5). The incorporation of [ P] into phosphoinositides was rather fast, preferentially into PIP which peaked at 5 min (70% of tot. inc.) and then levell (fig lb). The fast incorporation of [ P] into PIP, PIP2 and PA is considered as a the result of rapid phosphoinositide turnover (3). Moreover, changes in the [ P] PA to PI ratio are good indicators of the rapid biosynthesis of the major membrane phospholipids. In tobacco cells we noted a lack of response of PIP2 to cold stress or to added substances as choline chloride or ABA to the culture medium. Cold temperature resulted in an enhanced level of PA and PIP suggesting that Pl-kinase and the enzymes involved in PA formation (e.g. DAG-kinase and phospholipases C and D) remained active in cold. 

Figure 5. Biosynthesis of phosphoinositides. Figures in parentheses refer to equations in text.

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