Seed germination in Chenopodium album L.: further evidence for the dependence of the effects of growth regulators on nitrate availability

Abstract Chenopodium album L. plants, grown under controlled environmental conditions on different levels of soil nitrate, produced seeds with proportionately different NO^?₃ contents. Regardless of the endogenous NO^?₃ content, few seeds germinated in water or upon treatment with KNO₃. Ethylene promoted germination, and the extent of germination was positively correlated with the endogenous seed NO^?₃ content. Combined application of ethylene and KNO₃ in the dark had a synergistic effect on NO^?₃ -deficient seed. The synergism between ethylene and KNO₃ was attributable to the NO^?₃ moiety of the nitrate salt. Ethylene and light showed moderate synergism in seeds with low or high endogenous nitrate. Addition of nitrate, however, masked the interaction between ethylene and light. Gibberellic acid₄₊₇ (GA₄₊₇) or red light, each alone or combined with KNO₃, had little effect on germination. When applied together in the dark, ethylene and GA₄₊₇ synergistically enhanced the germination of NO^?₃-deficient seed. The combined effects of the two hormones on this seed were further enhanced by the addition of KNO₃. There was no synergism between ethylene and GA₄₊₇ in NO^?₃-rich seed. These interactions among GA₄₊₇, ethylene and KNO₃ were not affected by light. The results confirm and further elaborate our earlier finding that the sensitivity of C. album seeds to ethylene may depend on nitrate availability.     

Effects of plant chemical extracts and physical characteristics of Apium graveolens and Chenopodium murale on host choice by Spodoptera exigua larvae

Choice tests with whole plants and leaf discs indicated that fourth instar Spodoptera exigua (Hübner) (Noctuidae: Amphypyrini) were found more frequently and ate significantly more of the weed Chenopodium murale than the associated crop plant Apium graveolens. In order to explain the preference, plant extracts, plant volatiles, soluble protein concentrations, water contents, and leaf toughness of the two plants were investigated. Bioassays of aqueous methanol (90%) and hexane extracts of leaves on cellulose discs indicated that neither attractants in C. murale nor repellents in A. graveolens could account for the observed preference. No significant difference could be found between the effects of plant volatiles from C. murale, A. graveolens and a control on larval dispersal by S. exigua. Selective feeding for higher levels of proteins also was not a factor, because A. graveolens had nearly twice the soluble protein of C. murale. Water content was approximately 6% higher (by weight) in C. murale than A. graveolens but most polyphagous larvae do not typically show compensatory feeding for water alone. However, the potentially related characteristic of leaf toughness was significantly different, with A. graveolens exhibiting 1.53 times the toughness of C. murale. Studies comparing five types of larval behavior on both plant species showed that the time spent in swallowing behavior was significantly greater on the tougher A. graveolens leaves relative to C. murale. To test the hypothesis that leaf toughness was affecting larval host choice, both plants were finely ground and incorporated into agar blocks. No differences in feeding behavior were detected. The implications of leaf toughness for larval diet and host choice are discussed.     

Changes in distribution of chloroplast adenylate kinase isoforms during floral induction

In the short day plant Chenopodium rubrum and the long day plant Nicotiana tabacum cv. Havana 425, adenylate kinase (EC 2.7.4.3) occurs as a family of isoforms, with at least two members localized in the chloroplast representing the main isoforms. In this work, isoforms were separated by anion exchange chromatography and relative isoform activities were compared between vegetative plants and plants induced to flowering. In both species examined, a light regime leading to floral induction resulted in a significant decrease in the activity of one chloroplast isoform. This decrease modified considerably the relative distribution of isoform activities, especially that between the two chloroplast activities.     

Prediction of a low dose herbicide effect from studies on binding of metribuzin to the chloroplasts of Chenopodium album L.

Chenopodium album L. seedlings at the 4- and 8-leaf stage were exposed to low concentrations metribuzin [4-amino-6-(l, l-dimethyl)-3-(methylthio)-l,2,4-triazin (4 H )-one] in nutrient solution to study herbicide uptake and the effects of low-dose rates. Chlorophyll fluorescence was measured to relate the inhibition of photosynthesis to herbicide dose. The minimum rate at which metribuzin fully inhibited photosynthesis was less than 1 μM for seedlings at the 4-leaf stage of development, and between 1 and 5 μM for the 8-leaf stage seedlings. With isolated chloroplasts, experiments were conducted to establish the relationship between the amount of herbicide molecules bound to each chloroplast and the inhibition of photosynthesis. From the dose-response curves obtained it was calculated that photosynthesis was fully inhibited when 7.5 10⁵ molecules metribuzin were bound to each chloroplast. This amount of binding was used to estimate minimum-lethal dose rates of metribuzin required for seedlings differing in fresh weight of leaves and amounts of chloroplasts present. It is suggested that prediction of a low dose herbicide effect from studies on binding of photosystem-II inhibitors in combination with chlorophyll fluorescence measurements may lead to the development of a new weed management strategy.     

The effects of domestic compost upon the germination and emergence of barley and six arable weeds

In a bioassay, leachate from composted household waste was found to decrease both cress germination and the germination of barley and six arable weeds, especially in the light. The effect of compost depth upon the emergence of these species was examined in a glasshouse experiment. Compost had no significant effect on barley emergence. However, weed emergence, particularly of those with small seeds, was reduced greatly by the physical effect of compost and, to a lesser extent, by its chemical effect. The emergence of the large-seeded species was relatively unaffected by increasing depths of compost, whereas that of the smaller-seeded weeds steadily decreased, being almost completely prevented by a 3 cm layer. The use of compost to control arable weeds in the field is discussed.     

Fluctuation of free IAA under inductive and non-inductive photoperiods in Chenopodium rubrum

Fluctuation in levels of endogenous free IAA has been followed in the SD plant Chenopodium rubrum under photoperiodic conditions inductive or not inductive of flowering. Endogenous IAA was measured fluorimetrically as -pyrone. The level of IAA shows little fluctuation under continuous illumination. An endogenous rhythm of IAA fluctuation was found in plants transferred from light to continuous darkness, with a natural period of 30 hrs. The troughs of minimum IAA level within the endogenous rhythm coincided with the peaks in the endogenous rhythm of flowering response, which possessed the same period length. The concentration of IAA in the shoot always decreased at the end of cycles of dark period that induce flowering. The results are discussed in relation to the role of IAA in flowering of SD plants.     

Turnover of O-Glucosides of Dihydrozeatin and Dihydrozeatin-9-riboside During the Cell Growth Cycle of Photoautotrophic Cell Suspension Cultures of Chenopodium rubrum

The cellular levels of O-glucosides of ³H-(diH)Z and ³H-(diH)[9R]Z, the major short-term metabolites of ³H-(diH)Z having been exogenously supplied to photoautotrophically growing suspension cell cultures of Chenopodium rubrum, decreased significantly during further culture, irrespective of whether the cells were maintained in the stationary phase or were transferred to conditions restoring cell divison. Metabolism of both compounds was more pronounced during the active growth phase than during the stationary phase. The O-glucosides were converted preferentially to polar compounds of as yet unknown nature, which were partly excreted into the medium. The cellular pools of both glycosides remained compartmented within the vacuole. In contrast to the O-glycosides, the small cellular pools of the aglycones ³H-(diH)Z and ³H-(diH)[9R]Z maintained their level during the experimental period of 30 days. Small amounts of the glucosides, as well as of the aglycones, were recovered from the medium and could have resulted from the lysis of a few cells. The results demonstrate, for the first time, that O-glucosides of cytokinins are not irreversibly deposited within the vacuole of plant cells but may serve to maintain a small, but more or less constant pool of extra-vacuolar, presumably cytosolic, aglycones. (DiH)Z and its derivatives could be demonstrated to be endogenous cytokinins of Chenopodium rubrum suspension cultured cells occurring along with those of the isopentenyladenine and zeatin types.     

The lysolipid sphingosine modulates pyrophosphatase activity in tonoplast vesicles and isolated vacuoles from a heterotrophic cell suspension culture of Chenopodium rubrum

The proton pumping activity of the tonoplast (vacuolar membrane) H⁺-ATPase and H⁺-pyrophosphatase (H⁺-PPase) has been studied on a tonoplast-enriched microsomal fraction and on intact vacuoles isolated from a heterotrophic cell suspension culture of Chenopodium rubrum L. in the presence of the lysosphingolipids D-sphingosine, psychosine (galactosylsphingosine) and lysosulfatide (sulfogalactosyl-sphingosine). Sphingosine strongly stimulates (K_a= 0.16 μ M ) the PPase activity, assayed both as ΔpH formation across the tonoplast vesicle membrane, and as reversible clamp current measured by the whole-vacuolar mode of the patch-clamp technique. Psychosine showed a minor, and lysosulfatide no stimulatory effect. No effect upon the ATPase activity has been observed. No sphingosine-induced change could be observed in the affinity of the PPase for its substrate (apparent K_m= 10 μ M MgPPi). We tentatively conclude that sphingosine, which is known as a potent inhibitor of the protein kinase C in animal cells, may be a regulator of the plant vacuolar PPase.