Accumulation and Radial Transport of Ions from Potassium Salts by Cucumber Roots

Abstract

Accumulation of K+ is insensitive to the anion supplied with it at a solution concentration below 1 mM. Rates of K+ transport to the xylem from the same solutions are, however, dependent upon the anion present and decrease in the order NO3->> Cl-> SOI2-. Parallel effects on rates of exudation and anion transport result from kind and concentration of anion supplied and time of exposure to the solution. When high K salt concentrations are used, only linear relationships are found between solution concentrations and transport rates. However, ion concentration in the exudate increases more than external solution concentration, while exudation rate is unaffected. It is suggested that some of the ions transported are from compartments within the cells. At high solution concentrations KNO3 results in more exudation and in higher ion concentration in the exudate than is found with KCI.The processes involved in transport of ions from the external medium into the xylem of roots continue to evoke controversy and have been discussed in several recent reviews (1,18,19,27). Liittge and Laties (22) Cucumber roots can be induced to exude from the xylem profusely. These roots reduce little of the NO3-that is absorbed, and most of it is transported to the stems and leaves (3). As with tobacco (30, 31), cucumber roots depleted of NO3-respond to a new supply of this ion with increased rates of exudation and salt transport. These properties make the cucumber root ideal for studying ion transport to the xylem.This report compares patterns of accumulation and radial transport in cucumber roots of K salt ions supplied at concentrations below 1 mm, and transport at concentrations of 0.5 to 10 mM. MATERIALS AND METHODSPlant Culture. Seeds of Cucumnis sativus L. cv. Burpeeana Hybrid were soaked in deionized water with continuous aeration for 24 hr, then planted in moist vermiculite and allowed to germinate in the dark for about 65 hr at 23 to 25 C. The seedlings were next exposed to indirect light for about 24 hr. Single plants were then transferred to 4-liter glass jars of continuously areated nutrient solution consisting of 1 mM Ca (N03)

Nitrate Translocation by Detopped Corn Seedlings

“…It is not yet known whether the enhancement in organic nitrogen translocation in the presence of ambient nitrate resulted from translocation of organic nitrogen sythesized from the entering nitrate or from the nitrate causing an increased translocation from endogenous organic nitrogen sources. Enhanced translocation of cations under nitrate nutrition has been frequently reported (1,3,5,8,19,21). With the detopped corn seedlings used in the present investigations, the effect of nitrate on potassium translocation was not observed until 4 or 5 hr elapsed (Fig.…”

Mannitol inhibits growth of intact cucumber but not pea seedlings by mechanically collapsing the root pressure

“…Note, however, that the potassium transport characteristics of eucumber roots differed from those found in corn roots. Cueumber roots permit the penetration of potassium salts (P^ shows transient or biphasie response curves; see also Cooil 1974) whereas corn roots do not (P^ shows monophasie response curves to potassium salts; Azaizeh & Steudle 1991).…”