The interrelationship between the lower oxygen limit, chlorophyll fluorescence and the xanthophyll cycle in plants

Abstract

The lower oxygen limit (LOL) in plants may be identified through the measure of respiratory gases [i.e. the anaerobic compensation point (ACP) or the respiratory quotient breakpoint (RQB)], but recent work shows it may also be identified by a sudden rise in dark minimum fluorescence (F(o)). The interrelationship between aerobic respiration and fermentative metabolism, which occur in the mitochondria and cytosol, respectively, and fluorescence, which emanates from the chloroplasts, is not well documented in the literature. Using spinach (Spinacia oleracea), this study showed that F(o) and photochemical quenching (q(P)) remained relatively unchanged until O(2) levels dropped below the LOL. An over-reduction of the plastoquinone (PQ) pool is believed to increase F(o) under dark + anoxic conditions. It is proposed that excess cytosolic reductant due to inhibition of the mitochondria's cytochrome oxidase under low-O(2), may be the primary reductant source. The maximum fluorescence (F(m)) is largely unaffected by low-O(2) in the dark, but was severely quenched, mirroring changes to the xanthophyll de-epoxidation state (DEPS), under even low-intensity light (≈4 μmol m(-2) s(-1)). In low light, the low-O(2)-induced increase in F(o) was also quenched, likely by non-photochemical and photochemical means. The degree of quenching in the light was negatively correlated with the level of ethanol fermentation in the dark. A discussion detailing the possible roles of cyclic electron flow, the xanthophyll cycle, chlororespiration and a pathway we termed 'chlorofermentation' were used to interpret fluorescence phenomena of both spinach and apple (Malus domestica) over a range of atmospheric conditions under both dark and low-light.

Activation of violaxanthin cycle in darkness is a common response to different abiotic stresses: a case study in Pelvetia canaliculata

“…Both these examples suggest that chlororespiration may represent a plausible explanation for the activation of V de-epoxidation showed by P. canaliculata in darkness. This may be the case of desiccating or overheated tissues, but under anoxia, it is unlikely that PTOX would be able to oxidize PQH 2 due to the absence of the electron acceptor (oxygen), even when it is considered that under these conditions the PQ pool should be over-reduced [42]. Furthermore, the inhibition of PTOX by n-PG did not block the de-epoxidation of V-cycle pigments that occurred in darkness during desiccation (Figure 8).…”

A Shoot-Specific Hypoxic Response of Arabidopsis Sheds Light on the Role of the Phosphate-Responsive Transcription Factor PHOSPHATE STARVATION RESPONSE1

“…5D). The increase in zeaxanthin is an indication for enhanced nonphotochemical quenching due to excessive excitation energy (Wright et al, 2011). Because of the closure of stomata upon oxygen deficiency (Else et al, 1996), CO 2 rapidly becomes limiting, and therefore, the Calvin-Benson cycle is strongly inhibited.…”

Photosynthetic analysis of mid-vein and leaf lamina in high-yield hybrid rice in fields during senescence

“…The extraction and analysis of xanthophyll by high performance liquid chromatography (HPLC) was performed as previously described (Wright et al 2011). Under dimmed room lighting, a sample was extracted separately with 85% acetone and 100% acetone, before centrifugation for 4 min at 12,000 g at 4°C.…”