Large solutes induce structural perturbations in proteins and membranes

The alternative oxidase mediated respiration contributes to growth, resistance to hyperosmotic media and accumulation of secondary metabolites in three species

Plant respiration, similar to respiration in animal mitochondria, exhibits both osmosensitive and insensitive components with the clear distinction that the insensitive respiration in plants is quantitatively better described as 'less' sensitive rather than 'insensitive'. Salicylic hydroxamic acid (SHAM)-sensitive respiration was compared with the respiration sensitive to other inhibitors in rice, yeast and Dunaliella salina. The influence of SHAM was largely in the osmotically less sensitive component and enhanced with external osmotic pressure unlike other inhibitors that inhibited the osmotically sensitive component. SHAM inhibited germination and root growth but not shoot growth. Osmotic remediation of respiration that developed in due course of time with rice seedlings was abolished by SHAM and was not due to water and ionic uptake mechanisms. Yeast and Dunaliella also showed susceptibility of growth and respiration to SHAM. Glycerol retention was influenced by all inhibitors, while growth was inhibited demonstrably by SHAM in Dunaliella. Respiration in plants needs to be seen as a positive contribution to overall growth and not merely for burning away of the biomass.

Shape anisotropy of lipid molecules and voids

Biological polymers, viz., proteins, membranes and micelles exhibit structural discontinuities in terms of spaces unfilled by the polymeric phase, termed voids. These voids exhibit dynamics and lead to interesting properties which are experimentally demonstrable. In the specific case of phospholipid membranes, numerical simulations on a two-dimensional model system showed that voids are induced primarily due to the shape anisotropy in binary mixtures of interacting disks. The results offer a minimal description required to explain the unusually large permeation seen in liposomes made up of specific lipid mixtures (Mathai & Sitaramam, 1994). The results are of wider interest, voids being ubiquitous in biopolymers.