Saleem Aladaileh

Phagocytosis of the protozoan parasite, Marteilia sydneyi, by Sydney rock oyster (Saccostrea glomerata) hemocytes.

QX disease is a fatal disease in Sydney rock oysters caused by the protozoan parasite Marteilia sydneyi. The current study investigates the phagocytosis of M. sydneyi by Sydney rock oyster hemocytes. It also compares the in vitro phagocytic activities of hemocytes from oysters bred for QX disease resistance (QXR) with those of wild-type oysters. After ingestion of M. sydneyi, hemocyte granules fused with phagosome membranes and the pH of phagosomes decreased. Significantly (p=<0.05) more phagosomes in QXR hemocytes showed obvious changes in pH within 40 min of phagocytosis, when compared with wild-type hemocytes. Phenoloxidase deposition was also evident in phagosomes after in vitro phagocytosis. Most importantly, ingested and melanised M. sydneyi were detected in vivo among hemocytes from infected oysters. Overall, the data suggest that Sydney rock oyster hemocytes can recognise and phagocytose M. sydneyi, and that resistance against QX disease may be associated with enhanced phagolysosomal activity in QXR oysters.

In vitro effects of noradrenaline on Sydney rock oyster (Saccostrea glomerata) hemocytes.

Our prior work has shown that the catecholamine hormone, noradrenaline, mediates environmental stress responses in Sydney rock oysters, resulting in impaired immunological function. In the current study, we tested the cellular basis of this stress response. Hemocytes were exposed to noradrenaline in vitro before cell morphology and viability were analyzed. Noradrenaline was shown to induce apoptotic markers, including the loss of mitochondrial membrane potential, DNA fragmentation and plasma membrane blebbing. F-actin appeared to play an important role in the changes observed in hemocytes, being concentrated mostly in the plasma membrane blebs of noradrenaline-treated hemocytes. This may explain why hemocyte adhesion and pseudopodia formation were inhibited by noradrenaline. Cellular dysfunction induced by norarenaline mainly affected the hyalinocyte sub-population of hemocytes, whilst the other major cell type, granulocytes, remained unaffected. Given that hyalinocytes are important immunological effectors, the results of this study help to explain why immunosuppression accompanies noradrenaline-mediated stress responses in oysters.

Anatomy and cytology of the thymus in juvenile Australian lungfish, Neoceratodus forsteri

The anatomy, histology and ultrastructure of the thymus of a dipnoan, the Australian lungfish, Neoceratodus forsteri, was studied by light and transmission electron microscopy. The thymic tissue showed clear demarcation into a cortex and medulla with ample vascularization. Large cells including foamy and giant multinucleated cells with periodic acid Schiff/Alcian blue positive staining properties were localized mainly in the medulla. The major cellular components were epithelial cells and lymphoid cells. The epithelial cells were classified by location and ultrastructure into six sub‐populations: capsular cells, cortical and medullary reticular cells, perivascular endothelial cells, intermediate cells, nurse‐like cells and Hassall‐like corpuscles. Myoid cells were found mainly in the cortico‐medullary boundary and medulla. Macrophages and secretory‐like cells were also present. These findings will provide a base of knowledge about the cellular immune system of lungfish.

Infectious microbial diseases and host defense responses in Sydney rock oysters

Aquaculture has long been seen as a sustainable solution to some of the worlds growing food shortages. However, experience over the past 50 years indicates that infectious diseases caused by viruses, bacteria, and eukaryotes limit the productivity of aquaculture. In extreme cases, these types of infectious agents threaten the viability of entire aquaculture industries. This article describes the threats from infectious diseases in aquaculture and then focuses on one example (QX disease in Sydney rock oysters) as a case study. QX appears to be typical of many emerging diseases in aquaculture, particularly because environmental factors seem to play a crucial role in disease outbreaks. Evidence is presented that modulation of a generic subcellular stress response pathway in oysters is responsible for both resistance and susceptibility to infectious microbes. Understanding and being able to manipulate this pathway may be the key to sustainable aquaculture.

Contribution of the IAM Pathway to IAA Pool in Developing Rice Grains

A possible role for the indole-3-acetamide (IAM) pathway in the indole-3-acetic acid (IAA) production was investigated in developing rice grains. IAM-hydrolase proposed to convert IAM to IAA primarily through the identification of IAM and IAM-hydrolase activity in some plant species. Expression profiles of the two putative rice IAM-hydrolase genes, OsAMI1&2, were compared to the previously quantified IAA level. The abrupt increase in IAA level between 4 and 7 days after anthesis (DAF) was not found to correlate with changes in the expression of OsAMI1 or OsAMID2 suggesting that the IAM pathway may not contribute significantly to IAA pool in rice grains. Production of a biological compound other than IAA may explain the high activity of OsAMI1&2 in developing rice grains. OsAMI1 that reported to be conserved across the plant kingdom showed higher expression level in most analyzed reproductive rice tissues whereas OsAMID2 showed more fluctuation in expression comparing to OsAMI1. Role of the IAM pathway in IAA production was also discussed in other plant systems and Arabidopsis seed was recommended as an ideal tissue to identify enzyme(s) convert(s) tryptophan to IAM as well as physiological effects of IAA produced via this pathway.