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In the present study carbon partitioning was investigated in the Usterapfel (Malus domestica Borkh.), a variety in which a sweet-tasting form and an acid-tasting mutant is known. The high concentration of malic acid, which was increased 10-fold up to 800 μmol/g DW when compared to the low-acid or sweet-tasting form, accounted for the elevated acid content in the mutant. Fruit from the high-acid mutant was larger but showed the same total dry weight as the sweet form. The difference in fresh weight is therefore the result of enhanced water retention in the high-acid mutant. To elucidate the biochemical background with respect to the different ability of the two apple forms to store malic acid, enzyme activities related to malate metabolism were compared. The activity of phosphoenolpyruvate carboxylase (PEPC) was slightly increased in the-low acid apple and for the activity of phosphoenolpyruvate carboxykinase (PEPCK) a 3-fold activation in the same fruit was found. There was no difference in the activity of NAD-dependent malic acid dehydrogenase (MDH) and NADP-dependent malic enzyme (ME). It is suggested that in the low-acid fruit, in which there was no decrease in the activity of the enzymes involved in malate metabolism, it is an inability to accumulate malate that is responsible for the low-acid content of the apple.

The abscission of young fruit occurring in apple trees was measured under various conditions in order to locate the possible source of the signal that induces fruit drop. The effect on fruit abscission of shading of leaves, girdling of conducting tissue, extracting seeds and defruiting pedicels was investigated. Complete shading of whole trees for 5 days, steam girdling of defoliated fruiting wood proximal to the abscission zone and removal of seeds from attached fruit resulted in 100% fruit drop when treatment was carried out prior to the June drop period. When the same treatment was applied after June drop no fruit abscised. However, fruit abscission took place before and after June drop when steam girdling was applied to the pedicel distal to the abscission zone. The same effect was observed in defruited pedicels, which always abscised after fruit removal throughout fruit development. The results show that during the pre-June drop period, abscission can be induced by treatments which reduce or block nutrient supply to the abscission zone of fruit. After that period the growing fruit becomes a sugar storage organ which is resistant to abscission. It is though likely that inhibition of abscission is related to the presence of stored carbohydrates already accumulated in the young fruit. An indication for the involvement of the sugar level, in particular glucose, in the control of the abscission process was provided by the results of measurements of individual sugar levels in conducting tissue distal and proximal to the abscission zone. It was found that during fruit development, glucose concentration in the pedicel was normally above the concentration found in fruiting wood proximal to the abscission zone. However, when abscission during the June drop period was induced, the glucose level dropped to a minimum in the pedicel, reaching the same value as in the fruiting wood. It is suggested that the glucose level in the pedicel of growing fruit may therefore be a factor in the control of the abscission process in young apple fruit, abscission occuring only in those fruit in which the glucose content in the pedicel is below a critical level. Fruit which remain on the tree have most likely reached a stage in their development at which sufficient amounts of sugar have accumulated to prevent abscission.

Besides the synthesis of urea, ammonia detoxication at high concentrations can also be effected through enzyme reactions involved in glutamic acid metabolism. These mechanisms are also operative in extrahepatic tissues. Hyperammonemia is also found in the animal model of the portacaval shunt (PCS) rat. This model was chosen to study the activities of glutamate dehydrogenase, glutamine synthetase and glutaminase I in liver, brain and kidney 10, 20 and 30 days after PCS. In brain and kidney ammonia is detoxified mainly by the glutamate dehydrogenase and glutamine synthetase reactions whereas in the liver these enzyme reactions play a minor role.

At high systemic blood concentrations ammonia may be partially deviated into the pathway of pyrimidine synthesis, as has been observed in different genetic defects of the urea cycle. The portacaval shunt (PCS) rat presents an animal model to study ammonia detoxication without an underlying enzyme defect in the urea cycle. Since ammonia may induce a deviation into the pyrimidine pathway by influencing enzymatic reactions involved in this pathway, the activity of carbamylphosphate synthetase and aspartate transcarbamylase in liver as well as the excretion of orotic acid in the urine were measured in rats 10, 20 and 30 days after PCS. The results suggest that in this experimental model ammonia may be channeled into the pyrimidine pathway leading to a stimulation of the first enzymatic step and to an increased excretion of orotic acid.

Die Isolierung eines Stoffes mit Antithiaminwirkung aus Farnkraut und seine Identifizierung mit 3,4-Dihydroxyzimtsaure wird beschrieben.

Oxygen evolution of isolated chloroplasts ofImperata cylindrica is half inhibited by 10−6M Simazin, a herbicide which is unable to kill this resistant tropical weed.