Effects of Glyphosate on Metabolism of Phenolic Compounds

Light enhanced the inhibiting effect of root-fed glyphosate (5 × 10^?4M) on dry weight accumulation of soybean [Glycine max. (L.) Merr.] seedling axes. Inhibition of growth by light was greatest in hypocotyls, whereas by glyphosate it was greatest in roots. A synergistic effect of light and glyphosate on stimulation of phenylalanine ammonia-Iyase (PAL, E.C. 4.3.1.5) activity was also demonstrated. In continuous white light PAL activity increased linearly for 4 days in axes of seedlings exposed to glyphosate. Evidence of phytochrome involvement in the light effect was shown. The stimulatory effect of glyphosate on PAL activity was greater in roots than in hypocotyls. Soluble hydroxyphenolic compound levels were reduced by glyphosate but were increased by light on a per axis basis. On a fresh weight basis, hydroxyphenolics were more concentrated in glyphosate-treated than in control tissues in the light. When compared to other amino acids, disproportionate decreases in free pools of phenylalanine and tyrosine occurred in axes of seedlings treated with glyphosate and light. The effect of light on all measured parameters was mainly in the hypocotyl, while that of glyphosate was primarily in the root. In the light, glyphosate caused increases in levels of glutamine and other amino acids that may be the result of amination reactions, protecting from excess ammonia generated by enhanced PAL activity. These results suggest that PAL has a strong influence on its substrate levels in this system and/or that glyphosate inhibits synthesis of aromatic amino acids.     

Tentoxin effects on infrastructure and greening of ivyleaf morningglory (Ipomoea hederacea var. hederacea) cotyledons

The effects of 20 μM tentoxin on mesophyll chloroplast ultra-structural development, chlorophyll organization and accumulation, and pigment transformations in cotyledons of dark-grown, 4-day-old ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea]were monitored. After 6 h of white light (200 μEm^?2T.s^?1), many plastids of tentoxin-treated tissues contained prolamellar bodies or inconsistent internal membrane orientation in contrast to the uniform internal membrane orientation and absence of prolamellar bodies in controls. Grana stacking did not progress beyond three to four disc loculi in tentoxin-treatments, and fret membranes were usually discontinuous and reduced. Cylindrical or cupped grana appeared in many chloroplasts after 3 days of light, while other chloroplasts in which disruption was more pronounced had few grana except for remnants, but usually did possess vesicles or structures resembling prolamellar bodies. Tentoxin had no apparent effect on stroma density or plastoglobuli size and number. No starch grains appeared in any of the tentoxin treatments, whereas they appeared after 24 h in controls. Initial protochlorophyllide content and its photoconversion to chlorophyllide and subsequent Shibata shift were not affected by tentoxin. Chlorophyll accumulation rates in tentoxin-treated cotyledons were about 10% of control rates during the first 24 h of greening and about 20% of controls from 48 to 72 h of greening. Chlorophyll alb ratio and PSU size (total Chl/P700) were not significantly affected by tentoxin.     

Glutamate Dehydrogenase Activity in Roots: Distribution in a Seedling and Storage Root, and the Effects of Red and Far-red Illuminations

Pisum seedling and Pastinaca storage roots contained high glutanrate dehydrogenase (GDH) activity in areas of reported rapid growth and high phytoctrome content. A similar distribution was observed for malate dehydrogenase. Freeze-thawings of mitochondrial preparations from Pisum roots always resulted in increases of GDH specific activity; however, the observed increases were much larger with basal than apical sections. Both intact and freeze-thawed mitochondrial preparations from seedling roots exhibited increases in GDH activity with time after isolation. In intact mitochondrial preparations from roots of etiolated seedlings, an increase in malate dehydrogenase activity was observed similar to that of GDH activity; however, no increased malate dehydrogenase activity was noted in preparations from light-grown seedlings. Illuminating Pisum seedlings with far-red light slowly increased GDH activity in roots over a period of two weeks. Since these observed increases were not due to direct exposure of roots to light, other factors were likely involved.     

In situ localization of the sites of paraquat action

Abstract. Effects of paraquat were monitored by electron microscopic, cytochemical, and in vivo spectrophotometric procedures. Electron microscopy of paraquat-treated pea leaf discs indicates that the chloroplasts are affected primarily with both thylakoid dilation and apparent lamellar fusions, resulting in a 'honeycomb' of lamellae. No ultra-structural effects were noted when leaf discs were incubated in both DCMU and paraquat. Paraquat-induced peroxide was located cytochemically along the stroma lamellae, on the ends of the grana stack and in the dilated thylakoids. Less destruction was noted in those samples where peroxide was precipitated by cerium chloride, indicating that peroxide or one of its products is one of the major causes of paraquat toxicily. In C₄ plants mesophyll plastids exhibited much more peroxide deposition than was detected in bundle sheath plastids. No plastid peroxide depositions were noted in a photobleaching mutant that is resistant to paraquat. In situ cytochrome f oxidation-reduction was followed during paraquat treatments and resulted in a hastening of the dark re-reduction of cytochrome f after only 1 h of treatment. This effect was prevented by DCMU or CeCI₃. Electron transport, as measured by cytochrome f oxidation-reduction, was completely obliterated by a 24 h paraquat treatment. These in situ studies on paraquat confirm previous studies that the primary effect in the light is on the plastid and involves peroxide or further products generated by peroxide.     

Induction of Antibody Synthesis by Purified Immunogenic RNA <Emphasis Type="Italic">in vitro</Emphasis>

WE have described an RNA fraction derived from phenol-extracted livers of immunized rabbits, which induced specific antibody production when mixed with normal rabbit spleen cells in vitro^1,2. Similar fractions have been described by others using spleen, lymph node or peritoneal exudate cells of mice, rats or rabbits^3–12 as sources of the RNA fraction. In all cases it has been assumed that the RNA-donor cell type was a macrophage. Considerable controversy has been generated by these experiments and data have been published to show that (a) the RNA is neither specific¹³ nor newly synthesized¹⁴ and (b) the RNA fraction contains antigen or fragments thereof^15–18. Here we show that the data obtained with the rabbit-DNP system² extend to another laboratory model, the mouse-sheep red blood cell (RBC) system. Our earlier work^1,2 suggested that the immunogenic RNA is produced in the macrophage cell, that it is specific and that it is confined to a discrete fraction of the extractable RNA. For these reasons we thought it desirable (a) to compare directly the capacities of both liver and spleen tissue RNA extracts to induce antibody-plaque-forming cells in vitro, (b) to compare the effects of RNAase and pronase on the immunogenic capacity of the RNA fraction and (c) to investigate the distribution of the immunogenic RNA fraction relative to the total RNA fractions.     

Light Control of Anthocyanin Biosynthesis in Zea Seedlings

Evidence for involvement of two non-photosynthetic pigments in photoinduction of anthocyanin biosynthesis in the roots and mesocotyls of Zea mays L. seedlings is presented. Short (5 min), low energy (4.5 × 10³ J m^?2) fluences of red light neither induced anthocyanin synthesis nor enhanced phenylalanine ammonia-lyase activity in dark-grown maize seedlings. Little anthocyanin synthesis and no enhancement of phenylalanine ammonia-lyase activity was induced by continuous far-red light. Continuous white or blue light induced both anthocyanin synthesis and enhanced phenylalanine ammonia-lyase activity. These results show that phytochrome alone cannot induce anthocyanin synthesis in maize seedlings. However, a strong phytochrome mediation of white light induced pigment synthesis was demonstrated. This effect was not demonstrable with white light enhanced phenylalanine ammonia-lyase activity, indicating that phytochrome controls another step in anthocyanin biosynthesis.     

Phytochrome Control of Longitudinal Growth and Phytochrome Synthesis in Maize Seedlings

The active, far-red light absorbing, form of phytochrome was found to inhibit growth and phytochrome levels in the mesocotyl and coleoptile of 4- to 5.5-day-old seedlings of Zea mays L. Short, low-irradiance red or far-red light treatments were used to produce different proportions of active phytochrome at the end of highdirradiance white-light periods, which left different levels of total phytochrome in the plants. After light treatments which left relatively high levels of spectrophotometrically assayable phytochrome in the seedlings, apparent phytochrome synthesis in the subsequent dark period was low regardless of the proportions of each form of the pigment present at the beginning of the dark period. In light treatments producing relatively low levels of assayable phytochrome, levels of apparent phytochrome synthesis in both red and far-red treatments and differences between apparent synthesis in red and far-red treatments were maximal. No simple correlation was found between growth and apparent phytochrome synthesis. However, growth and total phytochrome levels were positively correlated in both organs. Using a subtractive method of correlation, in which only phytochrome effects were plotted, strong linear relationships between phytochrome levels or longitudinal growth and P_fr levels were found in those light treatments leaving greater than 8% of dark control levels of phytochrome in the tissues. Using this technique non-linear, inverse relationships between P_fr and apparent phytochrome synthesis was found, indicating that modes of phytochrome control over phytochrome synthesis and growth differ. Our results are consistent with the view that in vivo assays of “bulk’ phytochrome reflect levels and states of the physiologically active phytochrome fraction under our experimental conditions in maize.     

On the mechanism of enzyme action. LIII. The amphoteric properties of trypsin

Several methods were employed for the preparation of salt-free trypsin samples which were used to determine the electrometric titration curves of the enzyme. These curves point to a maximum acid-binding capacity below pH 2. Stoichiometric analysis indicates the presence of 6 carboxyl groups per 10,000 g. of proteins, 1 imidazole group, and 13 hydroxyl-binding groups. Calcium has a specific effect on the titration curves by increasing the acidity of the carboxyl groups in the pH range 3.5 – 5. This effect is not shown by potassium, sodium, or even the bivalent magnesium ion. It is attributed to the formation of a specific complex between the enzyme and the calcium ions, involving the carboxyl groups of the protein. The equally specific protective effect of calcium on the self-digestion of trypsin can therefore be explained by assuming the formation of a complex which stabilizes the enzyme.     

Insect herbivory on mangrove leaves in North Queensland*

Estimates of leaf damage by insect herbivores are presented for 25 species of mangrove plants, comprising canopy and understorey species. Leaf area loss was highly variable among the species sampled, with means ranging from 0.3 to 35.0% of expanded leaf area. There was also great variability amongst leaves within species, and the mean coefficient of variation for leaf loss from the 25 species was 266%. Of the 12 species sampled at more than one site in North Queensland, eight exhibited small, but significant, between-site differences in herbivory. In general, it did not appear that height in the canopy influenced herbivory. For the dominant mangrove forest community type at Missionary Bay, an estimated mean of 2.1% of leaf production, or 11 g m^-2 per year, entered the direct grazing pathway. This very low figure is compared with estimates from other studies on mangrove forests and estimates from a variety of Australian terrestrial forests.