Fine Structure of Peanut Root Nodules Induced by Nod+Fix- Strains of Bradyrhizobium with Special Reference to Lipid Bodies

Ineffective nodules of peanut induced by two nod⁺fix^–strains of Bradyrhizobium sp. were compared with the ones inducedby nod⁺fix⁺ strain NC92. One of the fix^– strains, 639is a transconjugate Tn5 mutant of NC92, while the other, 7091,is an isolate from ICRISAT soil. Both induce small nodules lackingleghemoglobin and nitrogen-fixing activity. Ultrastructuralobservations revealed that the nodules of 639, have enlargedperibacteroid space and lack persistence of nodule function.The 7091-induced nodules showed impediment in bacteroid releaseand differentiation. In both the ineffective nodules large amountsof lipid bodies were found to accumulate several times in excess,compared to the effective NC92 nodules. The large lipid accumulationin absence of nitrogen fixation supports the hypothesis thatin peanut nodules lipid bodies are utilized as a supplementarysource of carbon and energy for nitrogen fixation. Peanut, lipid bodies, nitrogen fixation, nod⁺fix^– Bradyrhizobium, ultrastructure     

Western Palaearctic phylogeography of an inquiline oak gall wasp,Synergus umbraculus

Insect‐induced galls on plants comprise species‐rich but self‐contained communities of herbivores and natural enemies. In the present study, we focus on galls induced by cynipid gall wasps on oaks, and on the least‐known trophic level that these galls contain: inquilines. These insects, also cynipids, feed on gall tissue and are an abundant but taxonomically poorly understood part of an otherwise well‐studied system. We used DNA sequence data to examine spatial patterns in the genetic diversity of Synergus umbraculus Olivier 1791 (Hymenoptera: Cynipidae: Synergini), a widespread species attacking many host galls across the Western Palaearctic. Analysis of 239 cytochrome b sequences revealed eight haplogroups showing significant phylogeographic pattern across the Western Palaearctic, corresponding to putative glacial refugia in Iberia, Central Europe, Turkey, and Iran. There were significant genetic discontinuities across the Pyrenees and the Anatolian diagonal but no impact of the Alps, suggesting that significant discontinuities have biotic rather than physical causes. Detailed analysis of sites in the Carpathian Basin reveal a high diversity and low spatial structure, and identify Central Europe as the source of colonists for Quaternary colonization of Germany, France, and Britain. We found no evidence for host‐associated differentiation of S. umbraculus lineages associated with the most common cynipid host galls, suggesting frequent shifts within the host gall assemblage by inquiline lineages. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 750–764.     

Systematic re‐appraisal of the gall‐usurping wasp genus Synophrus Hartig, 1843 (Hymenoptera: Cynipidae: Synergini)

Several unanswered questions remain regarding the taxonomy and phylogeny of inquiline gallwasps (Cynipidae: Synergini), obligate inhabitants of plant galls induced primarily by other gallwasps (Cynipidae: Cynipini and Diplolepidini). Here we use morphological and molecular data to revise the inquiline genus Synophrus, members of which are notable for extensively modifying the structure of galls induced by oak gallwasp hosts on oaks in the section Cerris of Quercus subgenus Quercus in the Western Palaearctic. Previous taxonomic treatments have recognized three Western Palaearctic species of Synophrus: S. pilulae, S. politus and S. olivieri. Our results support the establishment of four additional Western Palaearctic species: Synophrus hungaricus sp.n. , S. libani sp.n. , S. syriacus sp.n. and S. hispanicus sp.n. We describe and diagnose these new taxa, analyse their phylogenetic relationships, and show that Synophrus inquilines are able to impose their own gall phenotypes on those of their hosts. We provide an updated key to Synophrus.     

STUDIES IN THE QUIESCENT ROOT MERISTEM OF THE BULB OF ALLIUM CEPA L.: FINE STRUCTURE AND DNA SYNTHESIS *

Study of the quiescent root meristem of Allium cepa L. bulbs has revealed that its histological organization does not differ significantly from the growing meristem, except for the fact that the cells are all arrested in interphase. Ultrastructure of the quiescent tissue is, however, different in the organization of the nucleolus and in the absence of prominent endoplasmic reticulum, microtubules and golgi complexes. A variety of lomasome-like structures, plasma membrane modifications and vacuoles have been recorded. Most of the cells except for the ones in the root cap and quiescent center are highly vacuolated; vacuolation is maximum in the cortical zone of the meristem. The pattern of ³H thymidine incorporation during early stages of sprouting indicates that asynchrony of the mitotic cycle, which is the characteristic of the growing meristem, is maintained during quiescence by the arrest of nuclei at different subphases of interphase.     

Oleosomes (lipid bodies) in nitrogen-fixing peanut nodules

Abstract. Nitrogen-fixing peanut root nodules have oleosomes (lipid bodies) in the infected cells. The oleosomes have been characterized and compared with their counterparts in the seed tissue. Eighty per cent of the nodule oleosomes were found to be of smaller size (0.16–1.0 μm diameter [dia.]) while in the seeds the larger size (2.0–5.5 μm dia.) dominated. The larger oleosomes were exclusively found in the uninfected three layers of cortical cells adjacent to the infected zone. Morphometric analyses have revealed significantly higher numbers of oleosomes covering about 8% of the infected cell area in immature (white) nodules, whereas the mature/old (pink) nodules had lesser numbers occupying about 4–5% of the cell area. The decrease in the amount of oleosomes possibly reflects their utilization in mature/old nodules which effectively fix nitrogen. The oleosomes were distinctly stained by p-phenylenediamine (pPD) at both light and electron microscopic levels. An electron-dense rim was observed around the nodule oleosomes; where lipolytic activity was also demonstrated using cytochemical methods. The rim was absent in the seed oleosomes. The defatted oleosomes were found to be surrounded by a 'half unit membrane' and a non-extractable rim of possible pro-teinaceous substance. Gas chromatographic analyses of the lipid from the isolated oleosomes indicated the presence of higher amounts of saturated fatty acids in the nodule oleosomes than the ones in the seed. The study indicates that the nodule oleosomes differ from seed oleosomes, with respect to the presence of (1) an electron-dense rim showing (2) lipolytic activity and (3) higher amounts of saturated fatty acids. Nodule oleosomes seem to be transient storage organelles to be metabolized, while in the seed they are meant for long-term storage.     

Activation of geminivirus V‐sense promoters in roots is restricted to nematode feeding sites

Obligate sedentary endoparasitic nematodes, such as the root‐knot and cyst nematodes, elicit the differentiation of specialized nematode nurse or feeding cells [nematode feeding sites (NFS), giant cells and syncytia, respectively]. During NFS differentiation, marked changes in cell cycle progression occur, partly similar to those induced by some geminiviruses. In this work, we describe the activation of V‐sense promoters from the Maize streak virus (MSV) and Wheat dwarf virus (WDV) in NFS formed by root‐knot and cyst nematodes. Both promoters were transiently active in microinjection experiments. In tobacco and Arabidopsis transgenic lines carrying promoter–β‐glucuronidase fusions, the MSV V‐sense promoter was activated in the vascular tissues of aerial plant parts, primarily leaf and cotyledon phloem tissue and some floral structures. Interestingly, in roots, promoter activation was restricted to syncytia and giant cells tested with four different nematode populations, but undetectable in the rest of the root system. As the activity of the promoter in transgenic rootstocks should be restricted to NFS only, the MSV promoter may have utility in engineering grafted crops for nematode control. Therefore, this study represents a step in the provision of some of the much needed additional data on promoters with restricted activation in NFS useful in biotechnological nematode control strategies.