Chlorophyll b reduction during senescence of barley seedlings

Abstract

During senescence of flowering plants, only breakdown products derived from chlorophyll a were detected although b disappears, too (Matile et al., 1996, Plant Physiol 112: 1403-1409). We investigated the possibility of chlorophyll b reduction during dark-induced senescence of barley (Hordeum vulgare L.) leaves. Plastids isolated from senescing leaves were lysed and incubated with NADPH. We found 7(1)-hydroxy-chlorophyll a, 7(1)-hydroxy-chlorophyllide a, and, after incubation with Zn-pheophorbide b, also Zn-7(1)-hydroxy-pheophorbide a, indicating activity of chlorophyll(ide) b reductase. The highest activity was found at day 2 of senescence when chlorophyll breakdown reached its highest rate. Chlorophyllase reached its highest activity under the same conditions only at days 4-6 of senescence. Based on the chlorophyll b reductase activity of plastids at day 2.5 of senescence (=100%), the bulk of activity (83%) was found in the thylakoids and only traces (5%) in the envelope fraction. Chlorophyll b reduction is considered to be an early and obligatory step of chlorophyll b breakdown.

Stay-green protein, defective in Mendel’s green cotyledon mutant, acts independent and upstream of pheophorbide a oxygenase in the chlorophyll catabolic pathway

“…Increase in the chl a to b ratio is a characteristic of senescence-related chl breakdown (Pružinská et al, 2005). This is caused by chl b to a reduction, which is a prerequisite of breakdown beyond the level of pheide (Scheumann et al, 1999). Consequently, the chl a:b ratio increased during darkincubation of JI4 leaves, but not in JI2775, indicating that both chl a and b are retained to the same extend in the mutant (Fig.…”

Seasonal fluctuations of photosynthetic pigments content in Taxus baccata needles

“…Similar course of changes in Chl a/b ratio to that observed by our group in T. baccata was also present in Piper betle L. (Kumar et al, 2006) for which it reached the highest value in November (that is a month earlier than T. baccata observed by our group), and these values were slightly higher for male in comparison to female individuals. Higher value of Chl a/b ratio in male individuals may be caused by a higher degree of conversion of Chl b into Chl a by specific enzymes (Folly & Engel, 1999;Scheumann et al, 1999) or higher membrane sensitivity (Zu et al, 2010).…”

Update on the biochemistry of chlorophyll breakdown

“…The two enzymes catalyzing these consecutive reactions, Chl b reductase and hydroxymethyl Chl a reductase (HCAR), have different biochemical properties; while the latter is a ferredoxin-dependent, stroma-localized enzyme, Chl b reductase localizes to the thylakoid membrane and requires NADPH as electron source (Ito et al 1996;Scheumann et al 1998Scheumann et al , 1999. Genes encoding both enzymes have recently been identified Meguro et al 2011).…”

“…thylakoid (NYC1), stroma (NOL, PPH, RCCR) and envelope (PAO) (Scheumann et al 1999;Sato et al 2009;Rodoni et al 1997;Matile and Schellenberg 1996;Schelbert et al 2009). As a consequence, Chl pigment shuttling mechanisms between the thylakoid and the envelope have been postulated in the past (Matile et al 1999;Hörtensteiner 2006).…”