Gebhard Bufler’s research while affiliated with University of Hohenheim and other places

The kinetics and activity of pyruvate decarboxylase of ‘Golden Delicious’ apples under different storage conditions were investigated. The capability of a partially purified enzyme preparation from preclimacteric apples to decarboxylate pyruvate and to synthesize acetoin in vitro was tested by removing and adding co-factors (thiamine pyrophosphate (TPP), Mg2+). The results show the presence of a TPP- and Mg2+-dependent enzyme in the partially purified enzyme preparation which catalyses the synthesis of acetoin.There was an increase of pyruvate decarboxylase activity in crude extracts of ‘Golden Delicious’ apples in cold storage (+4°C), low pressure (LPS), LPS + O2, LPS + C2H4 and controlled atmosphere (CA). The highest increase was found in apples from LPS and LPS + C2H4. However, no ethanol or acetoin accumulated in these apples. Ethanol and acetoin accumulation was detected in ripe apples during cold storage and LPS + O2. The significance of in vitro pyruvate decarboxylase activity as an indicator of a metabolic shift towards fermentation in stored apples is discussed.

The rise in ethylene production accompanying the respiration climacteric and senescence of cut carnation flowers (Dianthus caryophyllus L. cv. White Sim) was associated with a 30-fold increase in the concentration of 1-aminocyclopropane-1-carboxylic acid (ACC) in the petals (initial content 0.3 nmol/g fresh weight). Pretreatment of the flowers with silver thiosulfate (STS) retarded flower senescence and prevented the increase in ACC concentration in the petals. An increase in ACC in the remaining flower parts, which appeared to precede the increase in the petals, was only partially prevented by the STS pretreatment. Addition of aminoxyacetic acid (2 mM) to the solution in which the flowers were kept completely inhibited accumulation of ACC in all flower parts.

Nuclear ribosomal DNA of advanced and primitive cultivars of avocado (Persea americana Mill.) collected in Mexico was surveyed for repeat length and restriction site variation. The ribosomal repeat encoding the 18S to 25S ribosomal RNA yields informative fragments after digestion with the restriction enzymes Pstl, Eco Rl and Sstl. Digestion with either Pstl and Sstl or Eco Rl and Sstl are sufficient to identify the botanical variety of an avocado cultivar. Moreover, cultivars representing Persea americana var. guatemalensis Williams and var. americana Mill, reveal a similar fragment pattern with either Pstl or Eco Rl, while the fragment patterns of cultivars of var. drymifolia (Schlecht. and Cham.) Blake are different from the fragment patterns of cultivars of the other two varieties. Assay of 5S ribosomal DNA, which is unlinked to the 18S to 25S ribosomal DNA, support these observations; these preliminary results suggest a closer phylogenetic relationship of var. guatemalensis and var. americana, compared to a more distant lineage of var. drymifolia. In a recent review on the origin and taxonomy of avocado (Persea americana Mill.), Scora and Bergh (1990) described P. americana as a polymorphic species consisting of the wild varieties floccosa Mez., steyermarckii Allen, nubigena (Williams) Kopp, and the cultivated varieties americana Mill., drymifolia (Schlecht. and Cham.) Blake and guatemalensis Williams. Furnier et al. (1990) examined the phylogenetic relationships among these taxa by analyzing DNA restriction fragment length polymorphisms (RFLPs) in the chloroplast DNA and nuclear genes coding for cellulase and ribosomal RNA (rDNA). The assay of the variation of rDNA has proven to be a useful tool in plant systematic studies (Hemleben et al., 1988). In the present study we examined the variation of 18S to 25S rDNA and 5S rDNA of advanced and primitive cvs. of avocado collected in Mexico in order to check the identification of the collected material and to gain further insight into the phylogenetic relationships in the subgenus Persea. The results of a selection of representative cvs. are presented.

Internal ethylene concentration, ability toconvert 1-amino-cyclopro- pane-l-carboxylic acid(ACC)toethylene (ethylene-forming enzyme IEFEI activity) andACCcontent inthepeel ofapples (Malus domestica Borkh., cvGolden Delicious) increased only slightly during fruit matu- ration onthetree. Treatment ofimmature apples with100microliters ethylene perliter for24hours increased EFEactivity inthepeel tissue, butdidnotinduce anincrease inethylene production. Thisability of apple peeltissue torespond toethylene withelevated EFEactivity increased exponentially during maturation onthetree. After harvest of mature preclimacteric apples previously treated withaminoethoxyvinyl- glycine, 0.05microliter perliter ethylene didnotimmediately causea rapid increase ofdevelopment inEFEactivity inpeel tissue. However, 0.5microliter perliter ethylene andhigher concentrations did.The ethylene concentration forhalf-maximal promotion ofEFEdevelopment wasestimated tobeapproximately 0.9microliter perliter. CO2partially inhibited therapid increase ofethylene-promoted development ofEFE activity. Itissuggested thatethylene-promoted CO2production isin- volved intheregulation ofautocatalytic ethylene production inapples.

Until now starch and its metabolites malto-oligosaccharides have been overlooked as potentially important constituents of carbohydrates in carrots. A comparison of the organically bred cultivars Rodelika and Robila with the hybrid cultivars Maestro F 1 and Starca F 1 revealed that the content of malto-oligosaccharides in the organic cultivars (126 and 191 mg g -1 dry matter, respectively) surpassed the content in the two hybrid cultivars (86 and 89 mg g -1 dry matter, respectively), although the starch content was similar in all cultivars (between 50 and 70 mg g -1 dry matter). There were also cultivar differences in the pattern of glucose, fructose, and sucrose, however, the total amount of water-soluble carbohydrates (between 550 and 600 mg g -1 dry matter) was similar in each cultivar. Relatively high contents of starch and malto-oligosaccharides in carrot cultivars may be a key factor for their storage potential and quality.

Parsnip (Pastinaca sativa L.) is one of the few cultivated plants domesticated in Europe. The crop is underutilised and the number of available varieties is small in Central Europe. On-farm management of genetic resources can be an important means to increase infraspecific diversity, and to improve the quality of crops. In the present experiment quality-improvement by progeny selection on-farm was investigated. In a first step parsnips were selected for organoleptic quality by a technique that allows to harvest seeds from the plant tested. In a second step, progenies of positive-and negative-selected plants were compared with the original population. The experiment was carried out with the varieties Aromata (2006) and White King (2008) in biodynamic management. Organoleptic quality was determined according to a key developed for parsnip. Sugar contents were determined. Organoleptic selection significantly improved sweetness and flavour and can be recommended. However, selection was not efficient to improve texture.