ACCUMULATION OF VARIOUS SUBSTANCES IN GIRDLED STEM OF TOMATO PLANTS

Abstract

IN EARLIER papers (Bonner, 1942; Bonner and Dorland, 1943a, 1943b) observations have been reported concerning the distribution of various vitamins in tomato plants as well as the behavior of these vitamins in girdled stems. It was found that thiamin, pyridoxine and pantothenic acid accumulated above basal girdles of tomato stems, while riboflavin was accumulated little or not at all. In the present paper the simultaneous accumulation of the above named substances in the same girdled tomato stems will be considered, especially in relation to proposed mechanismsu of the transport of organic solutes in the plant. For comparison with the behavior of the vitamins, data on the soluble carbohydrates and on nitrogen fractions will also be presented. Three experiments were carried out in this investigation, a preliminary one in which use was made of 300 plants and two larger ones in which 1500 and 2100 plants, respectively, were used. Only the data from the two larger experiments will be here presented. ANALYTICAL METHODS.-Thiamin was assayed by means of Phycomyces Blakesleanus, accordinig to the method previously outlined (Bonner, 1942). Pantothenic acid and riboflavin were determined with Lactobacillus casei, according to the methods of Pennington, Snell and,Williams (1940), and Snell and Strong (1939). Pyridoxine was determined with a mutant of Neurospora sitophila, which is unable to synthesize the substance. Use of this organism for assay of pyridoxine has been described elsewhere (Bonner and Dorland, 1943b). In the present case assays were conducted in a basal medium containing supplements of thiamin (100y/liter) and casein hydrolysate. Thiamin was assayed in samples which were weighed directly into the Phycomyces culture flasks. Pantothenic acid, riboflavin and pyridoxine were analyzed in extracts prepared by autoclaving the sample in water (1 mg. sample per 1 cc. H20) at fifteen pounds pressure for thirty minutes. Reducing sugars were determined.by the method of Shaffer and Somogyi (1933) or of Hassid (1937) on 80 per cent alcohol extracts of dried tissue. The concentrated extracts were cleared with neutral lead acetate. Total nitrogen was determined by microKjeldahl, and non-protein nitrogen was determined on aqueous extracts of the dried sample. EXPERIMENT 2.Plants.-Tomato seeds of the variety Marglobe were germinated in soil contained in flats. When the seedlings had reached a height of 10-12 cm., 1800 of them were transplanted to fourinch clay pots containing washed sand. The plants, which were then placed on well lighted greenhouse benches, were supplied with nutrient solution daily. Six weeks after the transplanting, when the plants 1 Received for publication July 5, 1944. had attained an average height of approximately 50 cm., they were used for the experiment. Fifteen hundred plants were selected for uniformity and divided randomly into three lots of 500 plants each. Each lot of 500 plants was in turn divided randomly into ten samples of fifty plants each. One lot of 500 plants was then harvested as the initial control. In harvesting, sections 1.5 cm. long were cut from the stem of each plant at the second node. The ten samples each of fifty sections were then dried, weighed, and subjected to analysis. The second lot of 500 plants was subjected to girdling at the second node by application of a jet of superheated steam to each plant. Each plant was steamed sufficiently long so that all living tissues were killed. Each plant of this lot was also staked for support of the top. The plants of the third lot were reserved as the final control. Five days after steaming, stem sections 1.5 cm. long were harvested from immediately above and immediately below the steamed region of the girdled plants, and similar sections were removed from the region of the second node of the final control plants. All of the stem sections were then dried, weighed, and subjected to analysis.