Classical macroautophagy in Lobivia rauschii (Cactaceae) and possible plastidial autophagy in Tillandsia albida (Bromeliaceae) tapetum cells

Abstract

Two-component signal transduction systems (TCSs) consist of sensor histidine kinases and response regulators. TCSs mediate adaptation to environmental changes in bacteria, plants, fungi and protists. Histidine kinase 2 (Hik2) is a sensor histidine kinase found in all known cyanobacteria and as chloroplast sensor kinase in eukaryotic algae and plants. Sodium ions have been shown to inhibit the autophosphorylation activity of Hik2 that precedes phosphoryl transfer to response regulators, but the mechanism of inhibition has not been determined. We report on the mechanism of Hik2 activation and inactivation probed by chemical crosslinking and size exclusion chromatography together with direct visualisation of the kinase using negative-stain transmission electron microscopy of single particles. We show that the functional form of Hik2 is a higher-order oligomer such as a hexamer or octamer. Increased NaCl concentration converts the active hexamer into an inactive tetramer. The action of NaCl appears to be confined to the Hik2 kinase domain.

Macroautophagy and microautophagy in relation to vacuole formation in mesophyll cells of Dendrobium tepals

“…Some structures similar to those in Fig. 1D and E were also shown in tapetum cells of Lobivia rauschii (Papini et al, 2014).…”

Crystalloids in apparent autophagic plastids: Remnants of plastids or peroxisomes?

“…We previously showed evidence for autophagy carried out by plastids of Tillandsia albida, one of the species presently used (Papini et al, 2014). In the present experiments crystalloids were found in what was apparently the intraplastidial space of autophagic plastids.…”

The effects of elevated CO2 (0.5%) on chloroplasts in the tetraploid black locust (Robinia pseudoacacia L.)

“…And Bréhélin also found that the tocopherols stored in osmiophilic globules would be delivered to thylakoid membranes to scavenge ROS under oxidative stress (Bréhélin, Kessler, & van Wijk, 2007). In Tillandsia albida (Bromeliaceae), Papini found an increase in plastoglobules in plastids involved in autophagy (Papini, Mosti, & van Doorn, 2014). And Sallas et al also reported that a non significant decrease in the number of plastoglobules in response to elevated CO 2 in Norway spruce while an increase in number of chloroplast plastoglobules in Scots pine (Sallas, Luomala, Utriainen, Kainulainen, & Holopainen, 2003).…”

“…And Bréhélin also found that the tocopherols stored in osmiophilic globules would be delivered to thylakoid membranes to scavenge ROS under oxidative stress (Bréhélin, Kessler, & van Wijk, ). In Tillandsia albida (Bromeliaceae), Papini found an increase in plastoglobules in plastids involved in autophagy (Papini, Mosti, & van Doorn, ). And Sallas et al.…”