THE PRESENT work is concerned with the distribution of riboflavin and of pantothenic acid in vegetative tomato plants and the behavior of these substances in plants girdled by steaming at various levels. METHODS.-Plants.-The tomato plants used for these studies were of the variety San Jose Canner. Seeds were germinated in flats of washed river sand, and when the seedlings had attained an age of three weeks they were transplanted to similar sand contained in clay pots. Hoagland's nutrient solution was supplied daily and additional water given as needed. The plants were used in the experiments when they were from six to twelve weeks old. All of the plants were greenhousegrown, and all of the experiments were conducted in the greenhouse. At the time of harvest the plants were dried in a current of air at 600C., weighed, and ground in a Wiley mill. Pantothenic acid assay.-For the assay of pantothenic acid, Lactobacillus casei was grown in medium deficient pantothenic acid according to the method of Pennington, Snell, and Williams (1940). Growth was measured by turbidity (determined with a Fisher electrophotometer) after twenty-four hours incubation at 36?C. This procedure possessed the disadvantage that the response to crystalline calcium pantothenate was not linear over any useable range but was sigmoid as shown in figure 1. 1 Received for publication February 10, 1943. Report of work carried out with the cooperation of the Works Projects Administration, 0. P. Number 365-1-07-2.. The curve in figure 1, however, was highly reproducible in the fifty-one experiments which were carried out. Pantothenic acid concentrations in extracts of tomato samples were, therefore, estimated by reference to the calibration curve, and in each assay such a calibration curve with crystalline calcium pantothenate was included. Table 1 shows that this method yielded consistent values for the apparent pantothenic acid content (calculated as calcium pantothenate) of samples assayed at different concentration levels, as well as satisfactory recovery of pantothenic acid added to tomato leaf extracts. It would appear, therefore, that substances interfering with the determination of pantothenic acid by this method are not present in tomato extracts. Table 2 shows that autoclaving of ground tomato leaf samples in water (2 mgs. dried and ground sample per cc.) for thirty minutes extracted as much pantothenic acid as two successive fifteenminute autoclavings, and that further extraction did not increase this yield. Extraction by boiling for thirty minutes in water was as satisfactorv as autoclaving but proved less convenient on a large scale. Extraction with dilute HCI gave greatly reduced yields. The standard procedure adopted for the experiments reported below consisted of extraction of the sample by autoclaving in distilled water for thirty minutes at fifteen pounds pressure. In all cases two mgs. of sample per cc. of water were used, and assays were conducted on samples representing 2.5 to 5.0 mgs. of dry tissue.
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Apr 30, 2023
Younghyeon Jang + 2
Open Access
