Plasmalemma: The Seat of Dual Mechanisms of Ion Absorption in Chlorella pyrenoidosa

Dual mechanisms of absorption of rubidium were demonstrated in a nonvacuolate unicellular alga, Chlorella pyrenoidosa, in both the light and the dark. The two mechanisms were sensitive to metabolic inhibitors. At high concentrations rubidium enhanced the respiration of Chlorella cells. The findings support the conclusion that the mechanisms of rubidium absorption in both the low and high concentration ranges are active processes and reside in the plasmalemma.

Kinetics of iron absorption by excised rice roots

Studies on the rate of iron absorption by excised rice roots from solutions of different concentrations of FeSO4 showed the presence of two patterns, one in the low (0.005-0.5 mM) and the other in the high (1-30 mM) concentration range. The presence of CaSO4 or MnSO4 at 0.5 mM enhanced Fe(++) absorption in the low concentration range, while CaSO4 at 10 mM inhibited Fe absorption in the high concentration range in a competitive manner. Fe(++) absorption at both low and high concentrations was sensitive to metabolic inhibitors. The isotherm for Fe(++) absorption at O° exhibited an initial absorption shoulder in both low and high concentrations and was suggestive of a latent ion-transport capacity for Fe(++) in rice roots.

Effects of growth substances on the absorption and transport of iron plants

The effects of a number of growth substances on the absorption and translocation of iron were studied in bean plants. Gibberellic acid application to the trifoliate leaf enhanced absorption of Fe applied to the primary leaf. 2-Chloroethyltrimethylammonium chloride increased absorption by the primary leaf while 6-furfurylaminopurine (kinetin) increased the transport of Fe from the primary leaf to other parts. When the roots were pretreated with gibberellic acid, the absorption of Fe by the primary leaf and subsequent transport to the trifoliate leaves were increased. Triiodobenzoic acid reduced the absorption and transport of Fe.Absorption of Fe by roots and transport to other parts were increased by pretreatment of the roots with gibberellic acid, 2-chloroethyltrimethylammonium chloride or N,N-dimethylaminosuccinamic acid for 3 days. An increase in the transport to other parts of Fe absorbed by roots was obtained when roots were exposed to the growth substances following Fe absorption.Absorption and transport of Fe in corn plants were much less than those of Rb and phosphate. Absorption and transport of Fe were greater in plants with decorticated roots than in those with intact roots. N,N-Dimethylaminosuccinamic acid significantly promoted the transport of root-absorbed Fe to the shoots of corn plants.

Factors related to iron absorption by enzymically isolated leaf cells

The rate of Fe absorption by cells enzymically isolated from tobacco leaves is correlated with the age of the leaves from which the cells are derived. The cells obtained from younger leaves absorb Fe more rapidly than those from older ones. Ca inhibits Fe and Mn absorption. Fe and Mn are mutually antagonistic in their absorption by leaf cells. Ca enhances the inhibition of Mn absorption by Fe, but reduces the inhibition of Fe absorption by Mn. The affinity constant for Fe absorption by leaf cells is low. The chelate EDDHA (ethylenediamine di(o-hydroxyphenylacetate) competitively inhibits Fe absorption.

Penetration of iron and some organic substances through isolated cuticular membranes

Cuticular membranes were isolated enzymically from tomato fruits and from the dorsal and ventral surfaces of the leaves of Euonymus japonicus. Penetration of Fe from FeSO(4) and FeEDDHA (ferric ethylenediamine di(o-hydroxyphenylacetate) in the absence and presence of urea through the isolated cuticular membranes was studied. Fe from FeSO(4) penetrated more rapidly through the cuticles than Fe from FeEDDHA. Urea reduced the penetration of Fe from FeSO(4) and FeEDDHA. Binding of Fe on the inner surfaces of tomato fruit cuticles was also reduced by EDDHA.The results on the rates of penetration of (14)C-labeled organic substances suggest a possible relationship with their molecular weights. Permeability coefficients for these solutes have been derived for the 3 types of cuticles, using Fick's equation. The penetration rates of all substances through stomatous cuticles far exceeded those through astomatous cutioles.