Lipid transformations in greening and senescing leaf tissue

Changes in lipid profile during growth and senescence of Catharanthus roseus leaf

Various lipid classes and compounds were monitored during the period of leaf emergence to leaf drop of Catharanthus roseus. The expansion to early maturation phase was accompanied by cellular build-up of all major lipid classes, whilst aging and senescence were characterized by their substantial decline, except for the neutral lipids; the leaf monogalactosyl diglyceride/digalactosyl diglyceride ratio decreased from 4.3 (complete maturity) to 2.1 (abscised stage). The early maturation stage was the earliest stage when appreciable amounts of free sterols and fatty acids could be observed. Sterol/phospholipids ratios increased by 68-fold in the abscised leaf as compared to that at full maturity. The unsaturated/saturated fatty acid ratio was far lower in the senescent leaf as compared to that of the fully expanded leaf. The spatial alterations in lipid profiles may be suggestive of concomitant changes in membrane ultrastructure and functions, putatively leading to perturbation of indole alkaloid sequestration capability of the tissues of a species of pharmaceutical significance.

[Changes of glyco- and phospholipid contents during leaf senescence]

The glyco- and phospholipid levels in green, green-yellow and yellow leaves of Impatients balsamina L., Daucus carota L. and Cucurbita pepo L. were determined on a leaf area basis. In Fagus silvatica L. leaves the kinetics of lipid breakdown during autumnal senescence was analysed. It was shown that yellow tissues still contain 40% to 50% of galactolipids and 50% to 60% of phospholipids present in green tissues. In the early stages of senescence of autumnal Fagus leaves we found a more rapid decline in the levels of the galactolipids and of the phospholipids phosphatidylglycerol and phosphatidylcholine, whereas in the later stages the breakdown of these lipids is slower than that of chlorophyll. The last yellow stage still contains 30% of the galactolipids and about 23% of the phospholipids present in fully greened leaves. Phosphatidylinositol shows a different behavior during senescence.

Compositional changes in developing rape seed (Brassica napus L.)

The growth and composition of siliquas and seeds of oilseed rape was followed over 12 weeks from shortly after anthesis to maturity. Each plant produced 220 siliquas, this number being constant throughout development. Seed numbers per siliqua fell from 19 to 9 by week 5 and declined to 7 at maturity. Hull(1) and seed growth followed a sigmoid pattern, but were not in phase. Seed development could be divided into 3 phases: In Phase 1, seed weight was low and starch and ethanol soluble compounds accounted for 80% DM. Phase 2, seed growth increased and storage oil and proteins were deposited accounting for 40% and 20% DM respectively at the end of this stage. Starch, glucose and fructose were utilized in this process. Phase 3 was largely concerned with the deposition of oil and protein in fixed proportions. Seed weight more than doubled while DM composition remained constant. Sugars were transferred from the hull to the seed to support this growth.The proportion of hull lipids remained constant throughout development until shortly before maturity when MGDG and DGDG fell due to chloroplast breakdown as indicated by chlorophyll disappearance. The FA composition of the hull lipids resembled that of photosynthetic tissue. In the seeds, the neutral lipids increased from 20% of the total lipids in Phase 1 to 93% at maturity. The proportion of structural lipids declined as the storage lipids increased. In Phase 1 the FA composition of the lipid resembled that of photosynthetic tissue (high in C16:0; C18:2; C18:3). In Phase 2, FA typical of storage triglycerides (C20:1; C22:1, appeared, C18:1 transitorily increased, but C18:2 and C18:3 fell dramatically. In Phase 3, the content of C22:1 continued to rise, but the proportions of the other FA remained constant.