Senescence in wheat leaves: is a cysteine endopeptidase involved in the degradation of the large subunit of Rubisco?

Abstract

In wheat (Triticum aestivum L.), leaf senescence can be initiated by different factors. Depending on the plant system (intact plants or detached leaves) or the environmental conditions (light, nutrient availability), the symptoms of senescence differ. The aim of this work was to elucidate the catabolism of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco, EC. 4.1.1.39) under various senescence-inducing conditions. Leaf senescence was initiated in intact plants by darkness or by N-deprivation and in leaf segments by exposure to light or darkness. Depending on the treatment, a 50 kDa fragment of Rubisco was observed. The formation of this fragment was enhanced by leaf detachment and low light. In segments exposed to high light and in intact plants induced to senesce by N-deprivation, the fragment was essentially absent. Since an antibody against the N-terminus of a large subunit of Rubisco (LSU) did not cross-react with the fragment, it appears likely that a smaller fragment was removed from the Nterminus of LSU. Inhibitor studies suggest that a cysteine endopeptidase was involved in the formation of the 50 kDa fragment. Non-denaturing-PAGE followed by SDS-PAGE revealed that the fragment was produced while LSU was integrated in the holoenzyme complex, and that it remained there after being produced. It remains open how the putative endopeptidase reaches the stromal protein Rubisco. The results indicate that depending on the senescence-inducing conditions, different proteolytic enzymes may be involved. The involvement of vacuolar proteases must be considered as occurring during LSU degradation, which takes place in darkness, low light or under carbon limitation.

Drought stress and carbon assimilation in a warming climate: Reversible and irreversible impacts

“…1 D, 2 C, D, E). Besides the onset and the velocity of leaf senescence, mechanisms involved in the catabolism of leaf constituents may be altered under abiotic stresses (Thoenen et al, 2007;Feller et al, 2008;Simova-Stoilova et al, 2010). In general, photosynthetic capacity declines before other cellular functions (e.g.…”

Dynamic "Symbionts" Linked over Two Centuries: A Tribute to Lynn Margulis (1938–2011)

“…RbcL identified in band A is the catalytic domain which participates in CO 2 assimilation and mobilization in plants. Rubisco is degraded under stress (Thoenen et al, 2007) via ATP-dependant ubiquitination (Shanklin et al, 1995;Vierstra, 1996) and usually is present as fragments rather than intact protein. The pronounced accumulation of Rubisco as the RbcL fragment in Castle rock plants at 50 mM NaCL may indicate increased degradation of it under salt stress (Chattoapadhyay et al, 2011).…”

Gamma Ray Irradiation for Crop Protection Against Salt Stress

“…In wheat, amylolytic degradation of starch increased with an increase in the dose of gamma irradiation, however, the activities of α and β-amylases did not change significantly [81][82] . Rribulose-1,5-bisphosphate carboxylase (RUBISCO) which accounts for more than thirty percent of the total leaf nitrogen 83 and catalyses the production of two molecules of 3-phosphoglyceric acid (PGA) by a reaction between carbon dioxide and RUBP 84 , is a sensitive enzyme and declines both in terms of Rubisco proein and Rubisco activity under stressful condition of growth [85][86] . However, Rubisco activity did not decline in response to gamma irradiation treatment in wheat and that an increase in total carboxylation efficiency was measured in comparison to the unirradiated control at low doses.…”