Abstract
ABSTRACT Selaginella martensii is a living member of lycophytes, an early divergent group of vascular plants. This shade‐adapted species can acclimate to various light regimes, from deep shade to high light, with a gain in carboxylation capacity accompanied by modulations in thylakoid composition, including increased relative amount of photosystem I (PSI) compared to photosystem II (PSII). It was hypothesized that, as in angiosperms, the photosynthetic acclimation of S. martensii to high light may lead to increased cyclic electron flow around PSI (CEF), with changes in excitation distribution between PSI and PSII and with modulations of electron carrier pools. After long‐term acclimation to deep shade (LL), intermediate shade (ML) and high light (HL) regimes, plants were compared using chlorophyll a fluorescence, P700 oxidation, electrochromic bandshift, and transmission electron microscopy of the thylakoid system. As expected, a 75% increase in CEF occurred from LL to HL plants, facilitated by a preferential energy distribution to PSI. However, some unique characteristics distinguish S. martensii from common models of long‐term thylakoid photoregulation. The pools of electron transporters did not increase linearly with the electron fluxes from LL to HL plants; rather, the enhancement of electron transport depended on unique combinations of capacity and mobility of the electron carriers, the latter determined by the extent of thylakoid shrinkage. Moreover, especially in shade‐acclimated plants, the fraction of oxidized PSI exceeded that of reduced Q A , therefore keeping PSI under a persistent shortage of electrons already at low light intensities.
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Claims 7
Claim · model-written summary
Cyclic electron flow increased 75% from deep shade to high light.
- Taxon
- Selaginella martensii
Selaginella martensiit0 - Treatment
- HLe0
- Outcome
- CEFe0
- Direction
- increasee0
- Value
- 75%e0
- Comparator
- LLe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a 75% increase in CEF occurred from LL to HL plants”
t0“Selaginella martensii”
Claim · model-written summary
Preferential energy distribution to PSI facilitated the increase in cyclic electron flow.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- preferential energy distribution to PSIe0
- Qualifier
- preferential energy distribution to PSIe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“facilitated by a preferential energy distribution to PSI”
t0“Selaginella martensii”
Claim · model-written summary
Electron transporter pools did not increase linearly with electron fluxes from deep shade to high light.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- pools of electron transporterse0
- Direction
- did not increase linearlye0
- Comparator
- electron fluxese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The pools of electron transporters did not increase linearly with the electron fluxes from LL to HL plants”
t0“Selaginella martensii”
Claim · model-written summary
Enhanced electron transport depended on combinations of electron carrier capacity and mobility.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- enhancement of electron transporte0
- Qualifier
- capacity and mobility of the electron carrierse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the enhancement of electron transport depended on unique combinations of capacity and mobility of the electron carriers”
t0“Selaginella martensii”
Claim · model-written summary
Electron carrier mobility was determined by the extent of thylakoid shrinkage.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- thylakoid shrinkagee0
- Qualifier
- extent of thylakoid shrinkagee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the latter determined by the extent of thylakoid shrinkage”
t0“Selaginella martensii”
Claim · model-written summary
Especially in shade-acclimated plants, the oxidized PSI fraction exceeded reduced Q A.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- fraction of oxidized PSIe0
- Direction
- exceedede0
- Qualifier
- shade‐acclimated plantse0
- Comparator
- reduced Q Ae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“especially in shade‐acclimated plants, the fraction of oxidized PSI exceeded that of reduced Q A”
t0“Selaginella martensii”
Claim · model-written summary
PSI remained short of electrons even at low light intensities.
- Taxon
- Selaginella martensiiSelaginella martensiit0
- Outcome
- persistent shortage of electronse0
- Qualifier
- low light intensitiese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“keeping PSI under a persistent shortage of electrons already at low light intensities”
t0“Selaginella martensii”