Studies on the Early Development of the Eugregarine Gregarina garnhami

SYNOPSIS. The Eugregarine Gregarina garnhami is parasitic in the mid-intestine and caecae of the desert locust Schistocerra gregaria (Forsk). The penetration oi the sporozoite and its development into a three-segmented cephalont is described. At no time in its development is the Fregarine completely intracellular; the so-called intracellular stages of other workers are shown to be the breakdoan products of the intestinal host cells themselves.
After penetrating the host intestinal cell the sporozoite grows rapidly and the anterior intracellular region outgrows the posterior estracellular region. Once the intracellular region reaches a size 13–16 μ in diameter. growth oi this region ceases and growth is now concentrated in the posterior region. When this latter region has reached 20 μ in diameter an annulus appears. This, by growing diametrically across the posterior epimerite region, divides the extracellular region into protomerite and deutomerite.
Detachment of the cephalont is considered to be a passive and not an active process and is dependent on the breakdown and extrusion of host cells. In this process the epimerite may or may not become detached from the protomerite.
A system of lonpitudinal fibres (myonemes) exists within the protomerite, and these play an important role in converting the protomerite into an adhesil-e disc prior to conjugation.
Extensive folding of the epicyte occurs in both the protomerite and deutomerite in the three-segmented cephalont; this folding could not be observed prior to the division of the gregarine into three regions. The epimerite has a dual function in the early stages of development, serving both as an attachment organelle and as an absorptive region across which iood materials may pass from the host cell.     

Land management affects grass biomass in the Eucalyptus tetrodonta savannas of monsoonal Australia

Abstract We surveyed herbaceous biomass across the range of Eucalyptus tetrodonta savannas in north‐western Australia. Sample sites (n = 211) were stratified within four broad geographical regions characterized by different mixes of land management regimes. Grasses dominated (87% mean) the herbaceous biomass. After controlling for climatic and edaphic gradients, herbaceous biomass was highest in the Greater Darwin region (2.2 t ha⁻¹) which is managed predominantly by Europeans, and least under semi‐traditional Aboriginal management in Arnhem Land region (1.1 t ha⁻¹). In the drier Gulf of Carpentaria and Kimberley regions, where a mix of Aboriginal, conservation and pastoral land uses occurs, fuel loads were higher than in Arnhem Land region but still considerably lower than around Darwin. Sarga was recorded in all regions except the Gulf of Carpentaria and had the highest biomass in Darwin (0.88 t ha⁻¹) and lowest biomass in the Kimberley (0.54 t ha⁻¹). The proportion of herbaceous biomass made up of perennial grasses was least in Darwin (17%) and greatest in the Gulf (77%) regions. We suggest that climate, soils and land management account for differences between the drier pastoral regions of the Gulf of Carpentaria and the Kimberley and the wet Greater Darwin region relative to the Arnhem Land region. The high frequency, and larger spatial scale, of fires in the Greater Darwin region relative to the Arnhem Land region underpins the contrasting trends in total herbaceous biomass and abundance of flammable annual grasses.     

Arabidopsis ATG4 cysteine proteases specificity toward ATG8 substrates

Macroautophagy (hereafter autophagy) is a regulated intracellular process during which cytoplasmic cargo engulfed by double-membrane autophagosomes is delivered to the vacuole or lysosome for degradation and recycling. Atg8 that is conjugated to phosphatidylethanolamine (PE) during autophagy plays an important role not only in autophagosome biogenesis but also in cargo recruitment. Conjugation of PE to Atg8 requires processing of the C-terminal conserved glycine residue in Atg8 by the Atg4 cysteine protease. The Arabidopsis plant genome contains 9 Atg8 (AtATG8a to AtATG8i) and 2 Atg4 (AtATG4a and AtATG4b) family members. To understand AtATG4’s specificity toward different AtATG8 substrates, we generated a unique synthetic substrate C-AtATG8-ShR (citrine-AtATG8-Renilla luciferase SuperhRLUC). In vitro analyses indicated that AtATG4a is catalytically more active and has broad AtATG8 substrate specificity compared with AtATG4b. Arabidopsis transgenic plants expressing the synthetic substrate C-AtAtg8a-ShR is efficiently processed by endogenous AtATG4s and targeted to the vacuole during nitrogen starvation. These results indicate that the synthetic substrate mimics endogenous AtATG8, and its processing can be monitored in vivo by a bioluminescence resonance energy transfer (BRET) assay. The synthetic Atg8 substrates provide an easy and versatile method to study plant autophagy during different biological processes.