W. Thies

Chemotaxonomic value of tocopherols in Brassicaceae

The significance of tocopherols as chemotaxonomic markers and their relationship withoil content and fatty acid profile was investigated in a collection of 91 species of the familyBrassicaceae. Total tocopherols content ranged from 68 mg kg−1 oil in Diplotaxis viminea to2479 mg kg−1 oil in Schivereckia doerfleri. The collection also showed wide variability fortocopherol composition. The average tocopherol profile consisted of 65.4% g-, 28.7% a-, 5.1%d- and 0.8% β-tocopherol. Individual tocopherols were found to have great taxonomic value inthe Brassicaceae.

Contribution of Leaves, Stem, Siliques and Seeds to Dry Matter Accumulation in Ripening Seeds of Rapeseed, Brassica napus L.

Summary 14CO2 was fed to single leaves and to whole plants of B. napus at different stages of plant development. 14C activity was assayed at various intervals after labeling. The experiments showed that younger leaves of the rapeseed plant are supported by the older ones during pre-anthesis growth. Photosynthates from the upper leaves are mainly utilized in the development of the upper stem and buds. However nearly 75% of the assimilates from the topmost (flag) leaf were translocated to the growing fruits. During the period of the most intensive accumulation of dry matter in the seeds, the net photosynthetic activity (dpm/mg dry weight) of the seeds, the fruit walls and the stem parts bearing the siliques was 2%, 28% and 41%, respectively (leaves = 100%). The share of the assimilated 14C delivered by these organs to the growing seeds (dpm/organ, sum of the translocated 14C = 100%) was 37% for the leaves, 32% for the fruit walls and 31% for the stem. The contribution of the seeds to their own development was thus relatively small (ca. 1%). In an induced mutant «M 11», the photosynthetic activities of the fruit walls and seeds were markedly higher at all stages of seed development than those of the parental cultivar «Oro». As compared to «Oro», «M 11» has a genetically lower content of linolenic acid in its seeds and fruit walls. No direct relationship could be determined, however, between the 14CO2 assimilation and the linolenic acid content of the two varieties.

Quantitative determination of tocopherols in single seeds of rapeseed (Brassica napus L.)

A high-performance liquid chromatography (HPLC) method was developed to determine tocopherols in single seeds of oilseed rape (Brassica napus L.). Single seeds were extracted with isooctane, centrifuged, and the overlayer extract injected into the HPLC instrument without further purification. Separation was performed on a diol-column (250 mm × 3 mm I.D.) using a mobile phase consisting of 94% isooctane and 6% tert-butyl methyl ether. Quantification of individual tocopherols was done by fluorescence detection and with β-tocopherol as internal standard. The standard error (SE) of the present method for total tocopherol content, as determined with 30 ground samples of Samourai (mean = 304 mg kg -1 dry seed) and 20 ground samples of Lirabon (mean = 350 mg kg -1 dry seed), was 9.5 mg tocopherol/kg dry seed. The SEs of the method for the determination of α- and γ-tocopherol percentages were 1.2% and 1.3%, respectively. The low SE values indicate that the method can be effectively used to detect small differences for tocopherol content and composition in studies requiring the analysis of reduced amounts of plant material. In particular, the comparison between the SE of the method and the SD of single seeds within individual plants of Samourai (36.8 mg kg -1 dry seed) and Lirabon (37.6 mg kg -1 dry seed) shows the potential of the present method for the detection of the tocopherol content within plant differences.