586 Studies on the Mode of Action of NH4NO3 as a Spray Additive on Penetration of 14C-NAA through Isolated Tomato Fruit Cuticle

NAA, a weak organic acid plant growth regulator (pKa 4.2), penetrates the plant cuticle preferentially as an undissociated molecule (<10% dissociated at pH 3.2). We have reported, using a finite dose diffusion system, that NH4NO3 (AN, 8 mM) at pH 5.2 (>90% dissociated) enhanced the penetration of 14C-NAA through isolated tomato fruit cuticular membranes (CM). AN appears to preferentially enhance penetration of the dissociated NAA molecule over the nondissociated form. A possible mode of action is that AN affects the cuticle matrix, allowing for greater NAA penetration. Acid treatment (4 N HCl) of the cuticle, which alters the cuticle's ionic characteristics, resulted in a 10% reduction in NAA penetration from droplets in the presence of AN. When AN (80 mM) was included in the receiver solution of the diffusion cell in an effort to infuse the cuticle matrix, NAA penetration was not increased compared to when AN was present in the applied droplet. AN (8 mM) also increased NAA penetration through dewaxed tomato cuticular membranes (DCM; +252% for DCM vs. +190% for CM in 120 h). Since AN only enhances NAA penetration when included with the NAA in the treatment droplet, the AN effect may be related to the role of the droplet/deposit (droplet residue) as a donor. This conclusion is further supported with sorption studies, where AN over a 100-fold concentration range (0.8–80 mM) did not increase NAA sorption by tomato fruit CM and where no deposit is present. The role of the physicochemical nature of the deposit, including the chemical/ionic characteristics of any additive (i.e., AN) and active ingredient will be discussed.

Absorption and Translocation of Picloram by Lindheimer Pricklypear (Opuntia lindheimeri)

Removing the epicuticular wax from mature pads (cladophylls) of Lindheimer pricklypear increased picloram absorption by four- to sixfold in the laboratory, while the addition of surfactant had little effect on absorption. Absorption decreased with increasing pH of the picloram solution, indicating that picloram diffused through the cuticle as the undissociated molecule. Picloram entered detached pads at the areoles more readily than through the surrounding cuticle. In the glasshouse, whole plants consisting of an old, mature pad supporting a young, growing pad absorbed picloram very slowly whether picloam was applied as a spray to old or young pads or to the soil. About 90 and 80% of the applied picloram remained on the waxy surface of old and new pads, respectively, and about 2% of the applied picloram was recovered from within the epicuticular wax after 30 days. Picloram concentrations within pads treated in the glasshouse were greater when the herbicide was applied to new pads (4.6 μg/g) than old pads (1.9 μg/g) after 30 days. More picloram was translocated basipetally from treated new pads to untreated old pads than in the opposite direction, but concentrations in untreated pads were low (<1 μg/g). Little picloram was absorbed by roots, compared to pads, and little was translocated into or out of roots. These results conflict with the view that the effectiveness of picloram for pricklypear control is attributable to extensive root uptake and acropetal transport. However, observations of plants 6 months after treatment indicated that soil applications were more effective than sprays in the glasshouse.

Uptake and Release of Abscisic Acid by Runner Bean Root Tip Segments

Uptake of abscisic acid by 5 mm long decapped root tips is a linear function of the external ABA concentration in the range of 2.9 × 10-8m to 10-4м and decreases dramatically with in­creasing pH. At pH 8.0 uptake rate is extremely low, even at high ABA concentrations. This indicated that nearly all of the ABA is taken up as the undissociated molecule ABAH. Uptake of ABA is influenced by agents modifying the pH gradients between the medium and the tissue such as salts of weak acids incubated at low external pH (inhibition of uptake and stimulation of ABA release by abolishing the pH gradients), protonophores such as CCCP (inhibition of uptake) and fusicoccin (stimulation of uptake by increasing the pH between medium and cytoplasm). It is concluded that ABA distributes between the compartments of the root cells according to the pH gradients with the undissociated molecule as the only penetrating species. Uptake and release occur without participation of a saturable component by diffusion. In contrast IAA permeates the plasmalemma as both IAAH and IAA-.

The combination curves, hydrogen ion regulating power and dissociation constants of gelatin

The existing titrations of gelatin with acid and alkali have been found to refer mainly to solutions containing approximately 1 per cent. of the dry material, while the few titrations in 0·1 per cent. solutions are not in agreement. A series of titrations with alkali at both concentrations of gelatin has been made with a view to deciding whether the combining weight is really affected by the concentration. From the collected data, the combining or equivalent weight has been calculated by a new method based on the theory of buffer mixtures, and incidentally, the buffer capacities at the different concentrations have been determined. The equivalent so found has been compared with those which have been deduced by other methods. The equivalents of the 1·0 per cent. and 0·1 per cent. solutions in the alkaline range have also been calculated by another method using constants, and found to differ from one another. The equivalents as acid and as base have been deduced in various ways from the combination curves and also from the cleavage products, and these acid/base ratios have been compared. Finally by treating gelatin as a simple ampholyte, apparent constants have been calculated both on the undissociated molecule or older and on the "amphoteric ion" or newer theory. Although gelatin is undoubtedly amphoteric in its nature, yet its curves of combination ( p H plotted against x = added acid or alkali) differ greatly from those of simple amino-acids such as glycine, as is easily seen by comparing the types which have been portrayed by Harris (1923, 1925, 1930).

MECHANISM OF THE ACCUMULATION OF DYE IN NITELLA ON THE BASIS OF THE ENTRANCE OF THE DYE AS UNDISSOCIATED MOLECULES

The rate of penetration of brilliant cresyl blue into the living cells of Nitella indicates that the dye enters only in the form of the undissociated molecule. At equilibrium the total concentration of the dye in the sap is proportional to the concentration of the free base in the outside solution.