SALT ABSORPTION AND ACCUMULATION IN VARIOUS REGIONS OF ROOTS

Abstract

THIS STUDY was made to provide more information concerning the relative amounts of salt accumulated in various regions of roots and the amounts translocated to the shoot from various regions of roots. For soine years it was believed that the greatest amount of salt always is accumulated near the root tip and that this also is the region through which most of the salt absorbed enters the plant (Prevot and Steward, 1936; Steward et al., 1942; Overstreet and Jacobson, 1946), Kramer and Wiebe (1952) found, however, that in roots of barley, tomato, and pine there is as much acicumulation of P32 in a region one to several centimeters behind the root tips as in the apical region, and there is typically a region of low accumulation a few millimeters behind the tip. This appears to be in the region of cell enlargement. Later Wiebe and Kramer (1954) found that very little of the salt accumulated in the root tips of barley seedlings was translocated to the shoots, but considerable translocation occurred from the regions 10-60 mm. behind the tip. This was true for Rb86, Is3 and S35, as well as for P32, when roots were exposed to the isotopes for a period of 6 hr. In view of the results obtained with barley seedlings it was decided to study accumulation in and translocation out of various zones of the roots of several other species of plants. MATERIALS AND METHODS.-The plants used were Golden Cross Bantam sweet corn, Thomas Laxton peas, and Pima S-1 cotton. The seeds were surface sterilized for 15 min. in a 5 per cent solution of Clorox (a commercial preparation of sodium hypochlorite) and rinsed several times in distilled water before starting germination. The corn was germinated on moist filter paper in finger bowls in darkness at 25?C. for 48 hr. The cotton seeds were soaked in water for 30 min. and then germinated on moist paper in an incubator at 35?C. for 48 hr. The peas were soaked in water over-night and germinated in dilute nutrient solution (0.02 per cent Hoagland solution) at 25?C. in darkness for 48 hr. The full strength Hoagland solution contained 5 mM. of KNO3, 5 mM. of Ca(NO3)2, 2mM. Of MgSO4, and one mM. of KH2PO4 per liter. After germination the seeds were laid on lucite plates provided with holes through which the roots projected downward into jars of dilute nutrient solution. The jars were wrapped in aluminum foil and the lucite plates were painted with black asphalt to exclude light. Dilute, aerated nutrient solution