Drought stress effects on photosystem I content and photosystem II thermotolerance analyzed using Chl a fluorescence kinetics in barley varieties differing in their drought tolerance

Abstract

Drought stress has multiple effects on the photosynthetic system. Here, we show that a decrease of the relative contribution of the I-P phase, DeltaV(IP) = -V(I) = (F(M)-F(I))/(F(M)- F(o)), to the fluorescence transient OJIP is observed in 10 drought-stressed barley and 9 chickpea varieties. The extent of the I-P loss in the barley varieties depended on their drought tolerance. The relative loss of the I-P phase seems to be related to a loss of photosystem (PS) I reaction centers as determined by 820-nm transmission measurements. In the second part of this study, the interaction of drought and heat stress in two barley varieties (the drought tolerant variety Aït Baha and the drought sensitive variety Lannaceur) was studied using a new approach. Heat stress was induced by exposing the plant leaves to temperatures of 25-45 degrees C and the inactivation of the O(2)-evolving complex (OEC) was followed measuring chlorophyll a (Chl a) fluorescence using a protocol consisting of two 5-ms pulses spaced 2.3 ms apart. In active reaction centers, the dark interval is long enough to allow the OEC to recover from the first pulse; whereas in heat-inactivated reaction centers it is not. In the latter category of reaction centers, no further fluorescence rise is induced by the second pulse. Lannaceur, under well-watered conditions, was more heat tolerant than Aït Baha. However, this difference was lost following drought stress. Drought stress considerably increased the thermostability of PS II of both varieties.

Natural leaf senescence: probed by chlorophyll fluorescence, CO2 photosynthetic rate and antioxidant enzyme activities during grain filling in different rice cultivars

“…Fv/Fm depends only from the fluorescence extrema Fo and Fm and not of the trajectory between these values. Therefore Fv/Fm is not a sensitive parameter to assess the senescence index in rice (Van Heerden et al 2004;Oukarroum et al 2009;Panda et al 2008;Falqueto et al 2009). The decline in the value of Fm 0 ABS kF/kN can reflect a decrease in the ability of PS II to reduce the primary acceptor Q A (Calatayud and Barreno 2001).…”

Photosynthetic proton and electron transport in wheat leaves under prolonged moderate drought stress

“…The plot of variable fluorescence shows the clear difference in I-P amplitude. The decrease of IP-amplitude is typical for drought stress [67]; however, in some species it occurs only at severe drought stress [68] and it disappears after rehydration [69]. Although the full interpretation of J-I-P kinetics is rather complicated [70,71], the IP amplitude was suggested to be a measure of relative abundance of PSI with respect to PSII [72,73], and its decrease was previously ascribed to decrease of PSI content in leaves [67,74].…”

Chlorophyll a fluorescence as a tool to monitor physiological status of plants under abiotic stress conditions

“…The I-P phase seems to be related to the content of PSI reaction centers (Ceppi et al 2012) or availability of linear electron transport as determined by 820-nm transmission measurements (Zivcak et al 2014a). For example, the extent of the I-P loss in barley varieties depends on their drought tolerance (Oukarroum et al 2009;Ceppi et al 2012). ChlF is emitted following a dark-to-light transition of a photosynthetic sample, while delayed fluorescence emission (DF) occurs during light-to-dark transitions (Goltsev et al 2009;Strasser et al 2010;Kalaji et al 2012).…”