Na+ and Cl-are the principal solutes utilized for osmotic adjustment in cells of Nicotiana tabacum L. var Wisconsin 38 (tobacco) adapted to NaCi, accumulating to levels of 472 and 386 millimolar, respectively, in cells adapted to 428 millimolar NaCI. X-ray microanalysis of unetched frozen-hydrated cells adapted to salt indicated that Na+ and Cl-were compartmentalized in the vacuole, at concentrations of 780 and 624 millimolar, respectively, while cytoplasmic concentrations of the ions were maintained at 96 millimolar. The morphometric differences which existed between unadapted and salt adapted cells, (cytoplasmic volume of 22 and 45% of the cell, respectively), facilitated containment of the excited volume of the x-ray signal in the cytoplasm of the adapted cells. Confirmation of ion compartmentation in salt adapted cells was obtained based on kinetic analyses of 22NaI and 36CI-efflux from cells in steady state. These data provide evidence that ion compartmentation is a component of salt adaptation of glycophyte ceUs.A typical response of many plants to saline environments, particularly halophytes, is to accumulate high intracellular concentrations of Na+ and Cl- (9,11,23,26,28). Since the in vitro activities of enzymes isolated from glycophytes or halophytes are inhibited equally by NaCl (9, 11), it has been generally accepted that the accumulated ions are sequestered in the vacuole and 'compatible solutes,' such as sugars, proline, and glycinebetaine, function to balance the osmotic pressure of the cytoplasm (9,11,26). This ability to compartmentalize Na+ and Cl-has been considered to be a mechanism of tolerance of halophytes (26).Although salt tolerance of glycophytes, particularly agronomic species, is usually attributed to the ability to exclude Na+ and Cl-, especially from the shoot (8, 11), intracellular ion compartmentation also may occur in these species. Despite indications of negative correlations between ion accumulation and salt tolerance in glycophytes, such as tomato (22), rice (29), wheat (27), and maize (12), examination of the data reveals that, even in tolerant genotypes, the accumulated levels of Na+ and Clare substantial. In some instances whole cell Na+ and Cl-accumulation was similar for both tolerant and sensitive genotypes (22,27,29). Thus, the ability to compartmentalize Na+ and Clmay be an underlying determinant of the tolerance not only of halophytes but also of many crop species.Verification of ion compartmentation has been restricted by the difficulty in obtaining reliable measurements of subcellular ion concentrations (7,15,23,30). Despite this, cytoplasmic Na + concentration in leaf cells of Suaeda maritima was determined to be 165 mm by efflux analysis when the whole cell concentration was about 600 mM (28). Data obtained by x-ray microanalysis of frozen hydrated leaves of Atriplex spongiosa (23) revealed that cytoplasmic ion concentrations were considerably lower than those in the vacuole.Results from investigations of glycophytes exposed to salinity have been less conc...

How surfactants modify the characteristics of a spray liquid is now reasonably well understood. Beneficial effects are primarily associated with reduction in surface tension. However, the mechanisms whereby surfactants enhance the diffusion of herbicides across the plant cuticle are less clear. Generally, hydrophilic surfactants with a high hydrophile/lipophile balance (HLB) are most effective at enhancing penetration of herbicides with high water solubility, whereas lipophilic surfactants with a low HLB are most effective for enhancing uptake of herbicides with low water solubility. Both high- and low-HLB surfactants are absorbed into the cuticle, but current theory suggests different mechanisms are involved in enhancing diffusion of hydrophilic and lipophilic herbicides across the cuticle. Surfactants having a high HLB are absorbed into the cuticle and enhance the water-holding capacity (hydration state) of the cuticle. With increased cuticle hydration, the permeance of hydrophilic herbicides into the cuticle is increased, which increases the herbicide diffusion rate at a constant concentration gradient. Surfactants having a low HLB are absorbed into the cuticle and increase the fluidity of waxes, as measured by a small reduction in melting point. This increased fluidity increases the permeance of lipophilic herbicides in the cuticle, which, in turn, increases their diffusion rate at a set concentration gradient.

Leaf surface morphology and physical characteristics of herbicide deposits on leaf surfaces can influence herbicide performance. Leaf surface topography, the degree and type of epicuticular wax formation, and the presence, type, and distribution of trichomes all influence the distribution of a given herbicide formulation sprayed onto a leaf surface. Depressions above anticlinal cell walls accumulate herbicide, thus lessening uniform distribution. As the amount of particulate wax increases, the size of individual spray drop deposits on the leaf decreases, thus resulting in reduced coverage. In many instances the presence of trichomes reduces optimal epidermal coverage by intercepting spray drops before they reach the epidermal surface. Adjuvants reduce the adverse influence of leaf topography, epicuticular wax, and trichomes on herbicide distribution, but their use usually does not yield an even coating over the entire leaf surface. Many herbicides, in pure form, are solids (i.e., crystals) rather than liquids. For most applications, herbicides are dissolved, dispersed, or emulsified in a water-based spray solution. After spraying, water and any solvents evaporate from the leaf surface and herbicides often return to their solid crystalline form. In the few cases that have been studied, less herbicide is absorbed when present on the leaf surface as a solid rather than as a liquid. In many instances, greater effectiveness of a postemergence herbicide may be obtained if attention is given to optimizing the distribution and physical form on sprayed leaf surfaces.

Absorption and translocation of glyphosate [N-(phosphonomethyl)glycine] with and without adjuvants were examined in field bindweed (Convolvulus arvensisL. # CONAR) to develop an understanding of the influence of selected adjuvants and environment before application on glyphosate activity. Light intensity and humidity during plant development resulted in differences in14C-glyphosate absorption. When applied in water or with an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) adjuvant, an average of 9% of the glyphosate was absorbed in plants grown in high light intensity, low humidity (HLLH) before treatment, compared to an average of 21% in plants grown in low light, high humidity (LLHH) before treatment, respectively. Amounts of epicuticular wax on HLLH field bindweed were almost three times as great as on LLHH leaves and may explain absorption differences. No differences in glyphosate absorption were observed between glyphosate applied with oxysorbic or no adjuvant even though the oxysorbic adjuvant effectively reduces surface tension. Absorption was increased two- to threefold with a polyethoxylated tallow amine adjuvant (MON 0818) compared to no adjuvant. Unlike absorption without adjuvant or with oxysorbic adjuvant, there were few absorption differences in plants grown in different environments before application. Absorption continued for 24 to 36 h after application regardless of adjuvant. Reductions in MON 0818 concentration and subsequent necrosis resulted in increased movement of radioactivity away from the site of application.

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