EFFECTS OF SILICON DEFICIENCY ON LIPID COMPOSITION AND METABOLISM IN THE DIATOM CYCLOTELLA CRYPTICA1

The effects of silicon deficiency on the metabolism and composition of lipids in Cyclotella cryptica T13L Reimann, Lewin, and Guillard were examined. Silicon-deficient cells had higher levels of neutral lipids (primarily triacylglycerols) and higher proportions of saturated and monounsaturated fatty acids than silicon-replete cells. After 4 h of silicon deficiency, the percentage of newly assimilated NaH¹⁴CO₃ partitioned into lipids increased from 27.6% to 54.1%, whereas the percentage partitioned into chrysolaminarin decreased from 21.6% to 10.6%. In addition, pulse-chase experiments with NaH¹⁴CO₃ indicated that the amount of ¹⁴C in the total cellular lipid fraction increased by 32% after 12 h of silicon deficiency despite the absence of additional photoassimilable ¹⁴C. Therefore, the accumulation of lipids in response to silicon deficiency appears to be due to two distinct processes: (a) an increase in the proportion of newly assimilated carbon partioned into lipids, and (2) a slow conversion of previously assimilated carbon from non-lipid compounds into lipids     

Red–blue plots for detecting clusters in count data

A new index and four new graphical displays, termed "red–blue" plots, are presented to study and measure clustering in spatially referenced count data. The index can detect clusters in the form of patches, comprising several nearby large counts, and in the form of gaps, comprising several nearby small counts. The new methods quantify the degree to which the count for each sample unit contributes towards the overall degree of clustering, either as part of a patch or as a gap; provide tests of nonrandomness to detect clustering; and facilitate a comprehensive definition of the size and dimension of a cluster. The methods are illustrated using aphid field data.     

Characteristics of Pustula tragopogonis (syn. Albugo tragopogonis) Newly Occurring on Cultivated Sunflower in Germany

In temperate climates, Pustula tragopogonis is rarely found on cultivated sunflower. In Europe, it was so far of little economic impact on other Asteraceae, except for some regions in the Mediterranean. In 2003, P. tragopogonis was found for the first time in sunflower fields in southern Germany. The pathogen has a widespread occurrence there, especially in the region around Stuttgart, BW. Fatty acid profiling, ultrastructural investigation and ITS sequencing revealed a high similarity to an 2002 isolate from southern Africa and an 2005 isolate from Australia, but revealed significant differences to P. tragopogonis s.l. on Cirsium arvense, a common weed, growing on or in the vicinity of sunflower fields in Germany. P. tragopogonis from this host can therefore be excluded from being the source of the reported infection.     

Are Sulfurous Soil Amendments (S0, Fe(II)SO4, Fe(III)SO4) an Effective Tool in the Restoration of Heathland and Acidic Grassland after Four Decades of Rock Phosphate Fertilization?

This paper deals with the complex issue of reversing long‐term improvements of fertility in soils derived from heathlands and acidic grasslands using sulfur‐based amendments. The experiment was conducted on a former heathland and acid grassland in the U.K. that was heavily fertilized and limed with rock phosphate, chalk, and marl. The experimental work had three aims. First, to determine whether sulfurous soil amendments are able to lower pH to a level suitable for heathland and acidic grassland re‐creation (approximately 3 pH units). Second, to determine what effect the soil amendments have on the available pool of some basic cations and some potentially toxic acidic cations that may affect the plant community. Third, to determine whether the addition of Fe to the soil system would sequester PO₄^? ions that might be liberated from rock phosphate by the experimental treatments. The application of S⁰ and Fe^(II)SO₄^? to the soil was able to reduce pH. However, only the highest S⁰ treatment (2,000 kg/ha S) lowered pH sufficiently for heathland restoration purposes but effectively so. Where pH was lowered, basic cations were lost from the exchangeable pool and replaced by acidic cations. Where Fe was added to the soil, there was no evidence of PO₄^? sequestration from soil test data (Olsen P), but sequestration was apparent because of lower foliar P in the grass sward. The ability of the forb Rumex acetosella to apparently detoxify Al³⁺, prevalent in acidified soils, appeared to give it a competitive advantage over other less tolerant species. We would anticipate further changes in plant community structure through time, driven by Al³⁺ toxicity, leading to the competitive exclusion of less tolerant species. This, we suggest, is a key abiotic driver in the restoration of biotic (acidic plant) communities.     

Early stomatal closure in waterlogged pea plants is mediated by abscisic acid in the absence of foliar water deficits

Abstract Soil waterlogging decreased leaf conductance (interpreted as stomatal closure) of vegetative pea plants (Pisuin sativum L. cv. ‘Sprite’) approximately 24 h after the start of flooding, i.e. from the beginning of the second 16 h-long photo-period. Both adaxial and abaxial surfaces of leaves of various ages and the stipules were affected. Stomatal closure was sustained for at least 3 d with no decrease in foliar hydration measured as water content per unit area, leaf water potential or leaf water saturation deficit. Instead, leaves became increasingly hydrated in association with slower transpiration. These changes in the waterlogged plants over 3 d were accompanied by up to 10-fold increases in the concentration of endogenous abscisic acid (ABA). Waterlogging also increased foliar hydration and ABA concentrations in the dark. Leaves detached from non-waterlogged plants and maintained in vials of water for up to 3 d behaved in a similar way to leaves on flooded plants, i.e. stomata closed in the absence of a water deficit but in association with increased ABA content. Applying ABA through the transpiration stream to freshly detached leaflets partially closed stomata within 15 min. The extractable concentrations of ABA associated with this closure were similar to those found in flooded plants. When an ABA-deficient ‘wilty’ mutant of pea was waterlogged, the extent of stomatal closure was less pronounced than that in ordinary non-mutant plants, and the associated increase in foliar ABA was correspondingly smaller. Similarly, waterlogging closed stomata of tomato plants within 24 h, but no such closure was seen in ‘flacca’, a corresponding ABA-deficient mutant. The results provide an example of stomatal closure brought about by stress in the root environment in the absence of water deficiency. The correlative factor operating between the roots and shoots appeared to be an inhibition of ABA transport out of the shoots of flooded plants, causing the hormone to accumulate in the leaves.     

cDNA and protein sequence of a major pea seed albumin (PA 2 : Mr≈26 000)

Summary Pea albumin 2 (PA2:M_r26000) is a major component of the albumin fraction derived from aqueous salt extracts of pea seed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and chromatography on DEAE-Sephacel resolve PA2 into two closely related components (PA2a and PA2b). A cDNA clone coding for one of these components has been sequenced and the deduced amino acid sequence compared with partial, chemically-determined sequences for cyanogen bromide peptides from both PA2 components. Complete amino acid sequences were obtained for the C-terminal peptides. The PA2 molecule of 230 amino acids contains four imperfect repeat sequences each of approximately 57 amino acids in length.The combined sequence data, together with a comparison of PA2-related polypeptides produced in vitro and in vivo, indicate that PA2 is synthesized without a signal sequence and does not undergo significant post-translational modification. Although both forms of PA2 contain Asn-X-Thr consensus sequences, neither form is glycosylated. Accumulation of PA2 contributes approximately 11% of the sulfur-amino acids in pea seeds (cysteine plus methionine equals 2.6 residues percent). Suppression of levels of PA2 polypeptides and their mRNAs in developing seeds of sulfur-deficient plants is less marked than that for legumin, in spite of the lower content of sulfur-amino acids in legumin.     

Photoinactivation of δ-aminolevulinic acid dehydratase from maize by flavin mononuclotide

The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD -aminolevulinic acid dehydratase - FMN flavin mononucleotide - O₂ ^- superoxide - H₂O₂ hydrogen peroxide - 10₂ singlet oxygen - LA levulinic acid - PBG porphobilinogen - BSA bovine serum albumin - BME 2-mercaptoethanol - SOD superoxide dismutase - pHMB para-hydroxymercuribenzoate - DTT dithiothreitol - FAD flavin adenine dinucleotide - NADH nicotinamide adenine dinucleotide