Heat stress effects on ribulose-1,5-bisphosphate carboxylase/oxygenase, Rubisco binding protein and Rubisco activase in wheat leaves

Changes in chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) binding protein (RBP), Rubisco activase (RA), Rubisco large (LS) and small (SS) subunits, and electrolyte leakage were investigated in wheat leaf segments during heat stress (HS) for 1 h and for 24 h at 40 °C in darkness or in light, as well as after recovery from heat stress (HSR) for 24 h at 25 °C in light. The 24-h HS treatment in darkness decreased irreversibly photosynthetic pigments, soluble proteins, RBP, RA, Rubisco LS and SS. An increase in RA and RBP protein contents was observed under 24-h HS and HSR in light. This increase was in accordance with their role as chaperones and the function of RBP as a heat shock protein.

Dithiothreitol triggers photooxidative stress and fragmentation of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase in intact pea chloroplasts

In intact chloroplasts isolated from mature pea leaves (Pisum sativum L.), the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) was rapidly fragmented into several products upon illumination in the presence of 1 mM dithiothreitol (DTT). Very similar effects on LSU stability could be observed when illuminated chloroplasts were poisoned with cyanide which, like DTT, inhibits important plastid antioxidant enzymes, or when a light-dependent hydroxyl radical-producing system was added to the incubation medium. Moreover, DTT-stimulated light degradation of LSU was markedly delayed in the presence of scavengers of active oxygen species (AOS). It is therefore suggested that light degradation of LSU in the presence of DTT is mainly due to inhibition of the chloroplast antioxidant defense system and the subsequent accumulation of AOS in intact organelles. When chloroplasts were isolated from nonsenescent or senescent leaves, LSU remained very stable upon incubation without DTT, indicating that the antioxidant system was still functional in the isolated chloroplasts during leaf ageing. Our data support the notion that AOS might be important for the degradation of Rubisco in vivo under oxidative stress.

The quest for planarizing distortions in hydrocarbons: two stereoisomeric 4.5.5.5 fenestranes

According to semiempirical calculations the planarizing distortions in the central C(C)4 substructure of fenestranes, represented as 1, can be enhanced by a variety of structural modifications. Based on these results we selected the 7-hydroxy-c,c,c,c- and c,t,c,c[4.5.5.5]fenestranones 13 and 16 as precursors for the introduction of a bridgehead double bond. The efficient synthesis of these precursors and their chemical transformations are reported. Attempts to activate the hydroxyl group in 16 for introduction of a bridgehead double bond led to the rearrangement of the [4.5.5.5]fenestrane to a triquinacane skeleton. (C) 2011 Elsevier Ltd. All rights reserved.

Synthesis and reactions of two stereoisomeric 4.5.5.5 fenestranes with bridgehead substituents

The [4.5.5.5]fenestranes 2 and 3 with two different functionalities were prepared in seven steps with overall yields of 5% and 10%, respectively. For introduction of a bridgehead double bond the removal of the tertiary hydroxy group was investigated in the two stereoisomeric hydroxyketones 12 and 15. Whereas the dehydration readily occurred in 12, a ring opening reaction was observed for 15. (C) 2011 Elsevier Ltd. All rights reserved.