Comparison of the Calcium and Sulphur Content of Plant Fluids Expressed from Tissues Killed by Autoclaving and by Freezing with Solid Carbon Dioxide.

Sap analysis in combination with analysis of the complete tissue is particularly useful in gaining information concerning the distribution of elements between fluids and solids of a given tissue and the relative availability of elements for conditioning metabolic processes of the plant. Two methods, killing by heat and killing by freezing with solid carbon dioxide, are readily adapted to the pretreatment of plant tissues in the field for subsequent studies on the expressed sap. Both procedures have been used but few comparisons of results of mineral analyses of sap obtained by the two methods have been published. Results reported in this paper are intended to call to the attention of investigators of plant tissues the possibility of obtaining expressed fluids of different composition depending upon the methods of pretreating the materials. Particular emphasis is placed on the calcium and total sulphur of such saps because these two constituents showed the greatest change as a result of the type of pretreatment for the plants and elements studied. With other plants, other constituents may differ. BROYER (1) recently reviewed methods for preparing tissues for analysis in physiological studies with plants, but most of the investigators he cited have been primarily interested in the osmotic concentration, the carbohydrate content, or the nitrogen fractions of the expressed saps. Freezing of plant tissues at low temperatures prior to expression of the sap has been studied and used by BROYER and HOAGLAND (2), MASON and PHILLIS (6), GREATHOUSE (4), MEYER (7), and others. DONEEN (3) found no difference in the freezing point depression, total solids, total sugars, or nitrate-nitrogen in the sap of small wheat plants as a result of freezing or heating. A decrease in the calcium content of sap as a result of heating has been noted by ILJIN (5) for several different plants. While studyina the "partition indices" of potassium, magnesium, and calcium in cotton leaves, PHILLIs and MASON (9) noted a difference in the concentrations of potassium and calcium between sap expressed from frozen and from boiled leaves and attributed this to the occurrence of base exchange during boiling. Experimental technique Tissues from cotton and tomato plants grown in nutrient solutions containing added chloride and sulphate salts were chopped into pieces approximately one centimeter or less in length, mixed thoroughly, and divided into equal parts. Each portion was sealed in a pint glass fruit jar. One series was placed in contact with "dry ice" for 16 to 20 hours in a small