Responses of Photosynthesis and Photosystem II to Higher Temperature and Salt Stress in Sorghum

Abstract

Gas exchange and chlorophyll a fluorescence transient were examined in leaves of sorghum under salt stress and high temperature. During salt treatment with 50 and 150 mm NaCl, photosynthetic rate (Pn) decreased, which could be ascribed to stomatal limitation. Salt stress had no effect on photosystem II (PSII) activity. At high temperatures, PSII function was inhibited in leaves of sorghum, indicated by the decrease in PSII performance index on absorption base and PSII maximal photochemistry efficiency (Fv/Fm); however, the decrease was lower in salt‐treated sorghum, suggesting that salt adaption enhanced heat tolerance of PSII. The enhanced heat resistance can be expressed on all the components of PSII including reaction centre, donor side and acceptor side. Consistently, a slight decrease in Pn was found in salt‐treated sorghum at high temperatures, indicating that salt adaption also enhanced heat tolerance of photosynthesis. Proline plays an important protective role in plant response to environmental stress, and its large accumulation in salt‐treated sorghum might be the underlying reason leading to the enhanced heat tolerance. As for this pattern of photosynthetic response, sorghum seems to be a reliable crop species for human beings in the face of global warming and increasing salinity of agricultural land.

Salt priming improved salt tolerance in sweet sorghum by enhancing osmotic resistance and reducing root Na+ uptake

“…Salt stress reduced g s in the leaves of sweet sorghum (Fig. 3b), which could restrict water loss from transpiration and enhance water use efficiency (Yan et al 2012). However, the declined g s inevitably led to stomatal limitation of photosynthesis.…”

“…Glacial acetic acid (2 ml) and ninhydrin reagent (3 ml) were added to the supernatant (2 ml) and incubated at 100°C for 40 min. Toluene (5 ml) was added to the mixture after cooling, and then proline content (mg g -1 DW) was analyzed by the absorbance of chromophore-containing toluene at 520 nm (Yan et al 2012). …”

Exogenously applied nitric oxide confers tolerance to salinity-induced oxidativestress in two maize (Zea mays L.) cultivars differing in salinity tolerance

“…Several recent studies have reported that saline stress can result in alterations of leaf fluorescence in a broad range of crops such as sunflower (Akram et al, 2009), okra (Saleem et al, 2011), wheat (Habib et al, 2013;Perveen et al, 2013), and eggplant (Shaheen et al, 2012). This reduction in maximum fluorescence yield (F v /F m ) by salinity stress might be due to the inactivation and destruction of the PS-II reaction center (Santos et al, 2001;Yan et al, 2012;Ashraf and Harris, 2013;Dong et al, 2014). In the present study, PS-II activity (F v /F m ) of both maize cultivars increased due to exogenously applied NO in salt-stressed maize plants, which is analogous to the findings of , who documented improved chlorophyll fluorescence in salt-stressed wheat plants due to exogenously applied NO.…”

Salt pretreatment alleviated salt-induced photoinhibition in sweet sorghum

“…1a). Stomatal aperture often declines under salt stress for reducing water loss from transpiration (Chaves et al 2009;Yan et al 2012). The lower salt-induced decrease in leaf relative water content suggested the enhanced osmotic resistance in pretreated plants (Table 1).…”