Inositol-containing lipids in higher plants

Abstract

Interest in the biochemistry and physiology of inositol and inositol-containing compounds in plants is not a new phenomenon. It is thus more than 100 years ago that Pf¢ffer first isolated phytic acid (inositol (1,2,3,4,5,6) hexakisphosphate) from seeds. In spite of considerable effort by plant scientists over the years, comparatively little is still known about this group of compounds, but that situation is beginning to change. Until 1983/84 the emphasis in this area of research was mainly on inositol phosphates involved in phytic acid metabolism, indole-3-acetic acid (IAA) esters of myo-inositol and inositol containing lipids such as phosphatidylinositol and the glycophosphosphingolipids. Around 1983 a major breakthrough was made by researchers in the mammalian field who discovered that a group of inositol-containing phospholipids (the phosphoinositides) play a central role in the cellular perception and transduction of a wide variety of extracellular signals. It is now generally recognised that these inositol lipids have similar functions in organisms as disparate as slime moulds, yeast, blowflies and humans. I In addition to the role played in transmembrane signalling inositol-containing lipids appear to have several additional important functions, these include: regulation of enzymic activity, anchoring of proteins to membranes and modulation of cytoskeletal dynamics. 2~2'49 The discovery of the mammalian phosphoinositidc systems has caused a major upsurge in interest in inositol lipids and inositol phosphates in all eukaryotes and has led plant scientists to ask the questions: Is a similar system involved in transmembrane signalling in plant cells? and Do inositol-containing lipids have other physiological functions in plants? Although definitive answers to these questions have yet to be found, it is becoming