Anatomical and Physiological Responses of the Tomato to Varying Concentrations of Sodium Chloride Sodium Sulphate, and Nutrient Solutions

Tomato plants were grown in three series of culture solutions: (a) a base nutrient series consisting of cultures adjusted to 0.5, 1.5, 3, 4.5, and 6 atmospheres osmotic concentration; (b) a sodium chloride series consisting of cultures containing base nutrient (0.5 atmosphere) plus sodium chloride to adjust the concentrations to 1.5, 3, 4.5, and 6 atmospheres osmotic concentration, respectively; and (c) a sodium sulphate series set up as in (b) but with sodium sulphate as the added salt instead of sodium chloride. 1. The concentration of the culture solution exerts an important influence on growth. In all series the growth of the plants as measured by height, diameter of stem, and dry weight was less at the high concentrations than at the control or 1.5 atmosphere levels. The greatest differences occurred in the sodium sulphate and the smallest in the base nutrient series. 2. The smaller diameters of stems at the high levels of salt concentration were correlated with significant differential reductions in the tissue systems. In general, the reduction of the vascular tissues, on the basis of percentage of total area, was greater than that of the parenchymatous tissue of the cortex and pith. 3. The reduction in the amount of vascular tissue at the high levels of salt concentration was related to more rapid maturation and consequent reduction in the size of the cells. The secondary xylem vessels were smaller in diameter at the high concentrations in all series, and the walls were thicker in proportion to the lumina of the vessel segments. 4. In the base nutrient and sodium sulphate series the proportion of secondary phloem to xylem was decreased at the high levels of salt concentration. In the sodium chloride series the proportionate amounts of secondary xylem and phloem remained approximately the same at all levels. 5. In all series the cells of the mechanical tissues were smaller in caliber and thicker walled in plants grown at high osmotic concentrations. 6. Cambial activity was inhibited by high concentrations of salts in all series. At isosmotic concentrations the cambial rate was greatest in the base nutrient and least in the sodium sulphate cultures. 7. The leaflets of plants grown at the high salt concentrations were significantly thicker in the sodium chloride and sodium sulphate series than in the base nutrient cultures. 8. The leaves of plants grown in high sodium chloride solutions were more succulent than those of the base nutrient and sodium sulphate series. This was correlated with the loose arrangement of the tissues of the mesophyll. In contrast, the palisade tissue in the leaves of plants grown in high sodium sulphate cultures was very compact. 9. The greater succulence of plants grown in high sodium chloride solutions was also indicated by the percentage of dry matter of tops. This remained essentially constant at all levels of concentration in the sodium chloride series, while it increased at the high concentrations in the base nutrient and sodium sulphate cultures. 10. Flower bud formation was retarded and probably reduced on plants grown in high sodium chloride solutions, and anthesis was delayed. There was a more pronounced effect in the high sodium sulphate cultures at the 4.5 atmosphere level, and no evident flower buds had developed up to the time of harvest. 11. High starch accumulation in the parenchymatous tissues of the basal stem was apparently correlated with high salt concentration in the culture solutions. This was most pronounced in the sodium sulphate cultures at 4.5 and 6 atmospheres osmotic concentration, but was also marked in the stems of plants grown at high sodium chloride levels. 12. Osmotic concentration of the sap increased in all series with increasing concentration of the culture solution. 13. With increasing concentration of the culture solutions there was increased accumulation of sodium and chloride ions in the tops of plants in the sodium chloride series. In the sodium sulphate series accumulation of the sodium ion increased as the concentration of the culture solution increased, but there was less correlation between the accumulation of the sulphate ion and the concentration of sulphate in the solutions.