Dissection of Photosynthetic Electron Transport Process in Sweet Sorghum under Heat Stress

Abstract

Plant photosynthesis and photosystem II (PSII) are susceptible to high temperature. However, photosynthetic electron transport process under heat stress remains unclear. To reveal this issue, chlorophyll a fluorescence and modulated 820 nm reflection were simultaneously detected in sweet sorghum. At 43°C, J step in the chlorophyll a fluorescence transient was significantly elevated, suggesting that electron transport beyond primary quinone of PSII (QA) (primary quinone electron acceptor of PSII) was inhibited. PSI (Photosystem I) photochemical capacity was not influenced even under severe heat stress at 48°C. Thus, PSI oxidation was prolonged and PSI re-reduction did not reach normal level. The inhibition of electron transport between PSII and PSI can reduce the possibility of PSI photoinhibition under heat stress. PSII function recovered entirely one day after heat stress at 43°C, implying that sweet sorghum has certain self-remediation capacity. When the temperature reached 48°C, the maximum quantum yield for primary photochemistry and the electron transport from PSII donor side were remarkably decreased, which greatly limited the electron flow to PSI, and PSI re-reduction suspended. The efficiency of an electron transferred from the intersystem electron carrier (plastoquinol, PQH2) to the end electron acceptors at the PSI acceptor side increased significantly at 48°C, and the reason was the greater inhibition of electron transport before PQH2. Thus, the fragment from QA to PQH2 is the most heat sensitive in the electron transport chain between PSII and PSI in sweet sorghum.

Characterization of photosynthetic electron transport chain in bioenergy crop Jerusalem artichoke (Helianthus tuberosus L.) under heat stress for sustainable cultivation

“…4a). It should be pointed out that increase in W k with an elevated K step around 300 s is commonly accepted as a specific indicator of injury on OEC, although increased V k is also a reasonable candidate (Wen et al, 2005;Yang et al, 2007;Li et al, 2009;Brestic et al, 2012;Yan et al, 2013). However, just increased V k was observed in this study ( Fig.…”

Salt pretreatment alleviated salt-induced photoinhibition in sweet sorghum

“…Thus, PSI seems more susceptible to salt stress than PSII in sweet sorghum. On one hand, PSII photoinhibition can alleviate or prevent PSI photoinhibition by reducing electron flow to PSI, and they do not change in the same way, as severe PSII photoinhibition appears without PSI photoinhibition (Yan et al 2013a;Yang et al 2014). On the other hand, PSI photoinhibition can result in PSII photoinhibition due to the feedback inhibition on electron transport at PSII acceptor side, and they share the same change pattern and have positive correlation .…”

Chlorophyll fluorescence in the evaluation of photosynthetic electron transport chain inhibitors in the pea

“…Modulated reflection at 820 nm has recently been studied to evaluate the photosynthetic capacity of PSI, by analysing the redox state of the P 700 reaction centre and the PC (YAN et al, 2013). The signals of the modulated reflection at 820 nm are shown in Figure 3.…”

“…It has been proposed that the kinetics of modulated reflection at 820 nm (MR 820 ) may reflect PSI activity (STRASSER et al, 2010;YAN et al, 2012), indicating alterations in the redox state of the PC and of the PSI (P 700 ) reaction centre (RC) (OUKARROUM; GOLTSEV; STRASSER, 2013;YAN et al, 2013). Strasser et al (2010) emphasize that simultaneous measurements of the FT, DF and MR 820 are essential for complete correlation of the information on the different dominions of the ETC.…”