FOLIAR PENETRATION OF NAPHTHALENEACETIC ACID: ENHANCEMENT BY LIGHT AND ROLE OF STOMATA

Light enhanced the penetration of naphthaleneacetic-1-¹⁴C acid (NAA) into the stomatous lower surface of pear (Pyrus communis L. cv. Bartlett) leaf discs. The light effect was rapidly lost on transfer to the dark and was diminished by pretreatment of leaf discs with a Hill reaction inhibitor (2-chloro-4-ethylamino-6-isopropyl-amino-s-triazine). The effect of light on NAA penetration was isolated from its effect on stomatal opening. A similar stimulation of NAA penetration was obtained with stomata opened and closed, providing evidence that penetration did not take place by mass movement into the substomatal chamber.     

The role of calcium on protein secretion of the albumen gland in Helisoma duryi (Gastropoda)

Abstract. The albumen gland of the freshwater pulmonate snail Helisoma duryi produces and secretes the perivitelline fluid, which coats fertilized eggs and provides nutrients to the developing embryos. It is known that perivitelline fluid secretion is stimulated by dopamine through the activation of a dopamine D₁‐like receptor, which in turn stimulates cAMP production leading to the secretion of perivitelline fluid. This paper examines the glandular release of perivitelline fluid and provides evidence for the role of Ca²⁺ in the regulated secretion of perivitelline fluid based on protein secretion experiments and inositol 1,4,5‐trisphosphate assays. Dopamine‐stimulated protein secretion by the albumen gland is reduced in Ca²⁺‐free medium or in the presence of plasma membrane Ca²⁺ channel blockers, although the Ca²⁺ channel subtype involved is unclear. In addition, dopamine‐stimulated protein secretion does not directly involve phospholipase C‐generated signaling pathways and Ca²⁺ release from intracellular stores. Sarcoplasmic/endoplasmic reticulum Ca²⁺‐ATPase inhibitors had little effect on protein secretion when applied alone; however, they potentiated dopamine‐stimulated protein secretion. Dantrolene, an inhibitor of ryanodine receptors, 8‐(N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxybenzoate hydrochloride, a nonspecific inhibitor of intracellular Ca²⁺ channels, and 2‐aminoethyldiphenylborate, an inhibitor of inositol 1,4,5‐trisphosphate receptors, did not suppress protein secretion, suggesting Ca²⁺ release from internal stores does not directly regulate protein secretion. Thus, the influx of Ca²⁺ from the extracellular space appears to be the major pathway mediating protein secretion by the albumen gland. The results are discussed with respect to the role of Ca²⁺ in controlling exocytosis of proteins from the albumen gland secretory cells.     

Preferential polar pathways in the cuticle and their relationship to ectodesmata

Summary Ectodesmata-like structures, referred to here as mercurous or mercury precipitates (MP) and considered to be identical to precipitates observed after treatment of leaf tissue with Gilson solution for demonstration of ectodesmata, were demonstrated with cuticle enzymatically isolated from Allium bulb scales and leaves mounted on ascorbic acid-enriched agar or gelatin. The MP distribution patterns obtained with isolated cuticle, in the absence of a cell wall, were identical to those observed with living tissue. Since the distribution in either the presence or absence of the cell wall was similar, the distribution pattern must be determined by the cuticle and not by the cell wall. Disruption of the physical arrangement of epicuticular wax by brushing or removal with chloroform altered the distribution pattern and increased the frequency of MP. This was interpreted to mean that epicuticular wax plays an important role and also that the necessary reductant was not localized in specific structures in the cell wall. Based on this evidence, it appears that ectodesmata, as demonstrated with Gilson solution, are not specific cell-wall structures, whether plasmic or not plasmic. More likely, the MP observed in the cell wall reflect areas in the cuticle permeable to mercuric chloride and undoubtedly to other polar compounds. The presence of such pathways in the cuticle, long established as the prime barrier to penetration of polar compounds, has marked implications in foliar uptake and excretion.Michigan Agricultural Experiment Station Journal Article No. 4971. This study was supported-in-part by Public Health Service Grant CC 00246 from the National Communicable Disease Center, Atlanta, Georgia, and Food and Drug Administration Grant FD 00223.     

Cuticular penetration of abscisic acid

Summary Penetration of 2-¹⁴C abscisic acid (ABA) through enzymatically isolated cuticles from tomato fruit and from the upper epidermis of apricot, pear and orange leaves was assessed. Penetration was linear with time, greater as the undissociated than the dissociated ion, and greater through dewaxed than non-dewaxed cuticles. Significantly less (3–6 times) (2-¹⁴C)ABA penetrated the tomato fruit cuticle than NAA or 2,4-D. The leaf cuticles were less permeable than the tomato fruit cuticle. There was no evidence that the ABA was altered during transfer across the cuticle.     

Anatomical characteristics and antioxidant properties of Euphorbia nicaeensis ssp. glareosa

Anatomical analyses found that leaves of Euphorbia nicaeensis ssp. glareosa are isolateral, amphistomatous, with two layers of palisade cells on the adaxial and one on the abaxial side. Laticifers are present by vascular bundles, in palisade and spongy tissue. Stem laticifers are located in the pericyclic ring, adjacent to the phloem, in cylinder parenchyma and medullar rays. The structure of pleiochasium and dichasium peduncle is similar to the stem structure. Plants from typical steppe habitat show more xeromorphic features. Phytochemical screening of extracts showed presence of catecholes, flavonoids, tannins, saponins, free quinone derivatives and absence of anthocyanins, leucoanthocyanins, alkaloids, steroid compounds and essential oils. Our results showed that the examined taxon was partially susceptible to the action of reactive oxygen species, such as O₂·⁻ and ·OH. The higher quantities of ROS thus provoked an antioxidative response from the plant, both in an enzymatic and non-enzymatic manner. Stable anatomical structure, presence and distribution of laticifers and effective antioxidant properties when exposed to ROS, make Euphorbia nicaeensis subsp. glareosa potentially interesting for further pharmaceutical and phytochemical examinations.     

The nature of precipitates formed in the outer cell wall following fixation of leaf tissue with Gilson solution

Summary The nature of precipitates formed in the outer cell walls of leaf tissue fixed in Gilson solution, used extensively to demonstrate ectodesmata, is described. Electron-microbe X-ray analysis established that the crystalline precipitates contained both mercury and chlorine. Based on solubility in water and ethanol, birefringence and ratio of mercury to chlorine, the chemical form is probably mercurous chloride. Further treatment of the leaf tissue with potassium iodide caused the crystalline precipitate to turn black and lose birefringence when viewed with plane-polarized light. Analysis of this precipitate showed the presence of only mercury, chlorine having been lost.     

Identification of a region in G protein γ subunits conserved across species but hypervariable among subunit isoforms

The heterotrimeric GTP binding proteins, G proteins, consist of three distinct subunits: alpha, beta, and gamma. There are 12 known mammalian gamma subunit genes whose products are the smallest and most variable of the G protein subunits. Sequencing of the bovine brain gamma(10) protein by electrospray mass spectrometry revealed that it differs from the human protein by an Ala to Val substitution near the N-terminus. Comparison of gamma isoform subunit sequences indicated that they vary substantially more at the N-terminus than at other parts of the protein. Thus, species variation of this region might reflect the lack of conservation of a functionally unimportant part of the protein. Analysis of 38 gamma subunit sequences from four different species shows that the N-terminus of a given gamma subunit isoform is as conserved between different species as any other part of the protein, including highly conserved regions. These data suggest that the N-terminus of gamma is a functionally important part of the protein exhibiting substantial isoform-specific variation.