Phospholipid and free sterol composition of hypocotyl plasma membranes of ageing Mung bean seedlings
Stalleart, V.M. | Geuns, J.M.C.
Plasma membrane fractions were prepared from different hypocotyl segments ('top', 'middle' and 'lower' segments) of ageing Mung bean seedlings (four-seven days old) and analysed for the composition of phospholipids (headgroups) and free sterols. Effects of progressing seedling age were most striking at the base of the hypocotyl. Net phospholipid content decreased from the top to the base of the hypocotyl, and demonstrated increased susceptibility to degradation in the physiologically oldest (lower) segments. Breakdown of phosphatidylethanolamine and phosphatidylcholine resulted in increased amounts of phosphatidic acid. In top segments the membrane phospholipid composition remained essentially unchanged, which could be expected since the physiological age of these segments was identical during the four days of the experiment. Similarly, top segments did not show marked sterol changes. In middle segments, the rapid increase (2.4 times) of stigmasterol between day 4 and 5 reflected a final step in the membrane maturation process. Lower segments demonstrated a 40% decrease of both stigmasterol and sitosterol. Cholesterol and campesterol remained unchanged in all three segments.
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