Biology subjects

Fluhr, R.

Publications and source records attributed to Fluhr, R..

3 recordsLinked to original sources

bioRxiv2024

Osmotic stress in roots drives lipoxygenase-dependent plastid remodeling through singlet oxygen production

Osmotic stress, caused by the lack of water or by high salinity, is a common environmental problem in roots. Osmotic stress can be reproducibly simulated with the application of solutions of the high-molecular-weight and impermeable polyethylene glycol. Different reactive oxygen species such as singlet oxygen, superoxide and hydrogen peroxide accompany this stress. Among them, singlet oxygen, produced as a byproduct of lipoxygenase activity, was shown to be associated with limiting root growth. To better understand the source and effect of singlet oxygen, its production was followed at the cellular level. Osmotic stress initiated profound changes in plastid morphology and vacuole structure. By confocal and electron microscopy the plastids were shown to be a source of singlet oxygen accompanied by the appearance of multiple small extraplastidic bodies that were also an intense source of singlet oxygen. A marker protein, CRUMPLED LEAF, indicated that these small bodies originated from the plastid outer membrane. Remarkably a type 9 lipoxygenase, LOX5, was shown to change its distribution from uniformly cytoplasmic to a more clumped distribution together with plastids and the small bodies. In addition, oxylipin products of type 9 lipoxygenase increased while products of type 13 lipoxygenases decreased. Inhibition of lipoxygenase by SHAM inhibitor or in down-regulated lipoxygenase lines prevented cells from initiating the cellular responses leading to cell death. In contrast, singlet oxygen scavenging halted terminal cell death. These findings underscore the reversible nature of osmotic stress-induced changes, emphasizing the pivotal roles of lipoxygenases and singlet oxygen in root stress physiology.

plant biology↗

bioRxiv2022

PGRL1A redox states alleviate photoinhibition in Arabidopsis during step changes in light intensity

Non-motile plants have evolved regulatory mechanisms to maintain homeostasis for optimal growth. Responses to environmental changes in light are particularly important not only during the diurnal transition from night to day but also to react to light changes caused by passing clouds or by wind. Thioredoxins rapidly orchestrate redox control during environmental change by modifying cysteine residues. Here, we assign a function to regulatory cysteines of PGRL1A, a constituent of the ferredoxin-dependent cyclic electron flow (Fd-CEF) pathway and show their role in the regulation of proton motive force (PMF) and nonphotochemical quenching (NPQ). During step increase of low light intensity (10-60 E*m-2*s-1), the intermolecular disulfide of the PGRL1A 59-kDa complex is reduced transiently within seconds to the 28 kDa form. In contrast, step increases to higher light intensity (60-600 E*m-2*s-1) stimulated a stable partially reduced redox state in PGRL1A. Measurements of NPQ, PMF and resultant photosynthetic controls Y(ND) and Y(NA) were found to correlate with the redox state of PGRL1A during step increases in light intensity but not in PGRL1mutant plants pgrl1ab or PGRL1A cysteine mutant (PGRL1AC1,2A). Continuous light regimes did not affect mutant growth; however, fluctuating regimes of light intensity showed significant growth reduction in the mutants. Inhibitors of photosynthesis placed control of the PGRL1A redox state as dependent on the penultimate ferredoxin redox state that fuels reducing equivalents to the large set of chloroplasts thioredoxins. Our results showed that redox state changes in PGRL1A are crucial to the optimization of photosynthesis and are regulated by the photosynthetic electron flux.

plant biology↗

bioRxiv2017

Pre-mature senescence in the oldest leaves of low nitrate-grown Atxdh1 mutant uncovers a role for purine catabolism in plant nitrogen metabolism

The nitrogen rich ureides allantoin and allantoate, are known to play a role in nitrogen delivery in Leguminosae, in addition to their role as reactive oxygen species scavengers. However, their role as a nitrogen source in non-legume plants has not been shown. Xanthine dehydrogenase1 (AtXDH1) activity is a catalytic bottleneck step in purine catabolism. Atxdh1 mutant exhibited early leaf senescence, lower soluble protein and organic-N levels as compared to wild-type (WT) older leaves when grown with 1 mM nitrate, whereas under 5mM, mutant plants were comparable to WT. Similar nitrate-dependent senescence phenotypes were evident in the older leaves of allantoinase (Ataln) and allantoate amidohydrolase (Ataah) mutants, impaired in further downstream steps of purine catabolism. Importantly, under low nitrate conditions, xanthine was accumulated in older leaves of Atxdh1, whereas allantoin in both older and younger leaves of Ataln but not in WT leaves, indicating remobilization of xanthine degraded products from older to younger leaves. Supporting this notion, ureide transporters UPS1, UPS2 and UPS5 were enhanced in older leaves of 1 mM nitrate-fed WT as compared to 5 mM. Enhanced AtXDH, AtAAH and purine catabolic transcripts, were detected in WT grown in low nitrate, indicating regulation at protein and transcript levels. Higher nitrate reductase activity in Atxdh1 than WT leaves, indicates their need for nitrate assimilation products. It is further demonstrated that the absence of remobilized purine-degraded N from older leaves is the cause for senescence symptoms, a result of higher chloroplastic protein degradation in older leaves of nitrate starved Atxdh1 plants.\n\nSummaryThe absence of remobilized purine-degraded N from older to the young growing leaves is the cause for senescence symptoms, a result of higher chloroplastic protein degradation in older leaves of nitrate starved Atxdh1 plants.

biochemistry↗