Sean F. Clarke

The influence of 6-benzylaminopurine on post-harvest senescence of floral tissues of broccoli (Brassica oleracea var Italica)

The pattern of post-harvest senescence of broccoli (Brassica oleracea) and the effect of the cytokinin 6-benzylaminopurine (6-BAP) were investigated. Chlorophyll degraded before ammonia production increased and this was earlier in florets at the edge of the head than those at the centre. Application of 6-BAP delayed the onset of both chlorophyll degradation and ammonia production. Pedicels contained low levels of chlorophyll which changed little over the duration of the experiment. Pedicels were unresponsive to 6-BAP treatment with no differences between chlorophyll degradation or ammonia accumulation between the treated and non-treated tissues.Application of 6-BAP to the carpel delayed chlorophyll degradation in the sepals, stimulated growth of the carpel and, when over-mature heads of broccoli were used, stimulated petal emergence.Treatment of florets with 1-aminocyclopropane carboxylic acid (ACC) and silver ions indicated that ethylene may be involved in the control of chlorophyll degradation. Cytokinin application negated the ACC-stimulated senescence.

Hormone-Virus Interactions in Plants

Symptoms of virus infection may be simplistically ascribed to a change in quantity of a particular plant hormone, and frequently virus-induced symptoms can be mimicked by application or removal of a plant hormone. In this review, we look critically at the information available concerning changes in the biosynthesis and metabolism of plant hormones following virus infection. In addition, we briefly review the effects of virus infection on endogenous jasmonates and salicylic acid. We also briefly assess the involvement of the classical plant hormones, jasmonic acid and salicylic acid in the induction of defense-related genes.

Influence of white clover mosaic potexvirus infection on the endogenous levels of jasmonic acid and related compounds in Phaseolus vulgaris L. seedlings

Summary Primary leaves of 16-day-old Phaseolus vulgaris L. seedlings were inoculated with either white clover mosaic potexvirus (WClMV) or water. The concentrations of jasmonic acid JA), dihydrojasmonic acid (DHJA) and cucurbic acid (CA), and virus titre were measured over a ten day period following inoculation. A transient increase in the concentration of JA occurred immediately following inoculation with water or WClMV, which we attribute to wounding. A second increase in JA occurred only in virus-infected leaves. Concentrations of cucurbic and dihydrojasmonic acids were not affected by wounding, but virus-infection resulted in a decline in the concentration of CA and an increase in DHJA. Reasons for the changes in jasmonate concentrations after virus infection are discussed.

Neuropathology of wild-type and nef-attenuated T cell tropic simian immunodeficiency virus (SIVmac32H) and macrophage tropic neurovirulent SIVmac17E-Fr in cynomolgus macaques

The neuropathology of simian immunodeficiency (SIV) infection in cynomolgus macaques (Macaca fascicularis) was investigated following infection with either T cell tropic SIVmacJ5, SIVmacC8 or macrophage tropic SIVmac17E-Fr. Formalin fixed, paraffin embedded brain tissue sections were analysed using a combination of in situ techniques. Macaques infected with either wild-type SIVmacJ5 or neurovirulent SIVmac17E-Fr showed evidence of neuronal dephosphorylation, loss of oligodendrocyte and CCR5 staining, lack of microglial MHC II expression, infiltration by CD4+ and CD8+ T cells and mild astrocytosis. SIVmacJ5-infected animals exhibited activation of microglia whilst those infected with SIVmac17E-Fr demonstrated a loss of microglia staining. These results are suggestive of impaired central nervous system (CNS) physiology. Furthermore, infiltration by T cells into the brain parenchyma indicated disruption of the blood brain barrier (BBB). Animals infected with the Δnef-attenuated SIVmacC8 showed microglial activation and astrogliosis indicative of an inflammatory response, lack of MHC II and CCR5 staining and infiltration by CD8+ T cells. These results demonstrate that the SIV infection of cynomolgus macaque can be used as a model to replicate the range of CNS pathologies observed following HIV infection of humans and to investigate the pathogenesis of HIV associated neuropathology.

Live attenuated simian immunodeficiency virus vaccination confers superinfection resistance against macrophage-tropic and neurovirulent wild-type SIV challenge.

Vaccination with live attenuated simian immunodeficiency virus (SIV) in non-human primate species provides a means of characterizing the protective processes of retroviral superinfection and may lead to novel advances of human immunodeficiency virus (HIV)/AIDS vaccine design. The minimally attenuated SIVmacC8 vaccine has been demonstrated to elicit early potent protection against pathogenic rechallenge with genetically diverse viral isolates in cynomolgus macaques (Macaca fascicularis). In this study, we have characterized further the biological breadth of this vaccine protection by assessing the ability of both the nef-disrupted SIVmacC8 and its nef-intact counterpart SIVmacJ5 viruses to prevent superinfection with the macrophage/neurotropic SIVmac239/17E-Fr (SIVmac17E-Fr) isolate. Inoculation with either SIVmacC8 or SIVmacJ5 and subsequent detailed characterization of the viral replication kinetics revealed a wide range of virus–host outcomes. Both nef-disrupted and nef-intact immunizing viruses were able to prevent establishment of SIVmac17E-Fr in peripheral blood and secondary lymphoid tissues. Differences in virus kinetics, indicative of an active process, identified uncontrolled replication in one macaque which although able to prevent SIVmac17E-Fr superinfection led to extensive neuropathological complications. The ability to prevent a biologically heterologous, CD4-independent/CCR5+ viral isolate and the macrophage-tropic SIVmac316 strain from establishing infection supports the hypothesis that direct target cell blocking is unlikely to be a central feature of live lentivirus vaccination. These data provide further evidence to demonstrate that inoculation of a live retroviral vaccine can deliver broad spectrum protection against both macrophage-tropic as well as lymphocytotropic viruses. These data add to our knowledge of live attenuated SIV vaccines but further highlight potential safety concerns of vaccinating with a live retrovirus.

Attenuated SIV causes persisting neuroinflammation in the absence of a chronic viral load and neurotoxic antiretroviral therapy

Objectives:Using simian models, where SIV chronic viral loads are naturally controlled in the absence of potentially neurotoxic therapies, we investigated the neuropathological events occurring during times of suppressed viraemia and when these events were initiated. Design:Cynomolgus macaques were infected with SIV strains that are naturally controlled to low levels of chronic viraemia. Study 1: animals were maintained up to 300 days after inoculation and analysed for viral-induced neuropathology following sustained suppression of chronic viral loads. Study 2: initiation and development of lesion was examined following 3, 10, 21, or 125 days SIVmacC8 infection. Methods:Formalin-fixed, paraffin-embedded brain sections were analysed following immunohistochemical staining for simian immunodeficiency virus (SIV) (KK41), blood–brain barrier leakage (ZO-1, fibrinogen), apoptosis (active caspase 3), neuroinflammation [GFAP, cyclooxygenase (COX)-1, COX-2], microglia and macrophage (Iba-1, CD68, and CD16), oligodendrocytes (CNPase1), MHC class II expression, and T cells (CD3 and CD8). Replicating SIV was detected through in-situ hybridization. Results:Study 1: neuroinflammation was present despite prolonged suppressed viraemia. Study 2: attenuated SIV entered the brain rapidly triggering acute phase neuroinflammatory responses. These did not return to naive levels and GFAP and COX-2 responses continued to develop during a chronic phase with a suppressed viral load. Conclusion:Neuroinflammatory responses similar to those in HIV neurocognitively impaired patients are present within macaque brains during prolonged periods of suppressed SIV viral load and in the absence of potentially neurotoxic antiretroviral drugs. These responses, initiated during acute infection, do not resolve despite the lack of on-going peripheral viraemia to potentially reseed the brain.