Increased Stability of LHCII by Aggregate Formation during Dark-Induced Leaf Senescence in the Arabidopsis Mutant, ore10

Abstract

Leaf senescence in a stay-green mutant of Arabidopsis thaliana, ore10, was investigated during dark-incubation of its detached leaves. During this dark-induced senescence (DIS), Chl loss was delayed in ore10 mutants, as compared with wild type, but the rate of decline in the photochemical efficiency of PSII was not delayed in mutant leaves. After 2 d of DIS, native green gel electrophoresis of ore 10 leaf proteins resulted in a significant amount of pigment remaining as aggregates on top of the stacking gel. In addition, the accumulation of aggregates coincided with the emergence of a new band near 700 nm (F 699 ) in the 77 K fluorescence emission spectrum of the aggregates. At 4 d, F 699 became a major band, both in the isolated aggregates and in intact leaves. Prolonged treatment with detergents revealed that light-harvesting complex II (LHCII) remaining after 2 d was highly stable, and the accumulation of aggregates coincided with the appearance of truncated LHCII in senescing ore10 leaves. These results suggest that increased LHCII stability is due to the formation of aggregates of trimmed LHCII. Thus, the LHCII protein degradation step that follows proteolysis of its terminal peptides is a possible lesion site of the ore10 mutant.

ETHYLENE-INSENSITIVE3 Is a Senescence-Associated Gene That Accelerates Age-Dependent Leaf Senescence by Directly Repressing miR164 Transcription in Arabidopsis

“…We also measured the transcript levels of NAP (for NAC-LIKE, ACTIVATED BY AP3/PI) and WRKY53, two known positive regulators of leaf senescence (Hinderhofer and Zentgraf, 2001;Guo and Gan, 2006), and found that their transcript levels increased with leaf ageing, whereas the expression levels of RBCS1A (for RIBULOSE BISPHOSPHATE CARBOXYLASE SMALL CHAIN1A) and CAB1 (for CHLOROPHYLL A/B INDING PROTEIN1), two photosynthesis genes, decreased ( Figure 1B). We also measured the expression levels of EIN3 and other SAGs in detached leaves upon dark treatment (see Supplemental Figure 2 online), a procedure that is commonly used to induce senescence (Weaver and Amasino, 2001;del Río et al, 2003;Oh et al, 2003;Chrost et al, 2004). Upon dark treatment for 1 d, the level of EIN3 transcript evidently increased, suggesting that EIN3 may be one of the early-acting regulators to initiate leaf senescence.…”

“…The level of EIN3 transcript is elevated in senescing leaves, and its transcription gradually increases during the progression of plant ageing. EIN3 transcription is also upregulated by dark treatment, a condition used to quickly induce non-natural leaf senescence (Weaver and Amasino, 2001;del Río et al, 2003;Oh et al, 2003;Chrost et al, 2004). Furthermore, transgenic plants constitutively overexpressing EIN3 showed early senescence symptoms, as indicated by faster and greater chlorophyll loss and quicker SAG12 induction when plants age (Figure 3).…”

Pheophytin Pheophorbide Hydrolase (Pheophytinase) Is Involved in Chlorophyll Breakdown during Leaf Senescence in Arabidopsis

“…Chloroplast membranes were isolated according to established procedures (Oh et al, 2003). Membranes were subsequently solubilized on ice for 30 min with 0.8% (w/v) dodecylmaltoside in 13 PBS.…”

The Senescence-Induced Staygreen Protein Regulates Chlorophyll Degradation

“…The nonfunctional type C stay-green mutants share a number of unusual features, such as the high stability of Chl binding thylakoid proteins among chloroplast proteins, especially LHCPII, and the persistence of unstacked thylakoid membranes in senescing leaf cells (Thomas, 1977(Thomas, , 1982Hilditch, 1986;Hilditch et al, 1989;Guiamé t et al, 1991;Thomas et al, 2002;Oh et al, 2003). Thus, we further examined the stabilities of thylakoid proteins and membranes in the senescing mesophyll cells of sgr.…”