Spatial-temporal variations in rose leaves under water stress conditions studied by chlorophyll fluorescence imaging

Abstract

Spatial-temporal changes were examined by imaging chlorophyll (Chl) a fluorescence in four leaf areas, two central and two external of rose plants ( Rosa x hybrida) cv. Grand Gala for 9 days, under progressive water stress. New fluorescence parameters based on the lake model have recently been used to determine Q A redox state and excitation energy fluxes in order to gain a better understanding of the mechanisms that occur under drought stress. Chlorophyll fluorescence images showed a spatial variation in the leaves. The lower values for F o, F M, φ 2, q P and q L were found in the internal leaf area while higher values of non-photochemical quenching calculated from Stern–Volmer quenching (NPQ) and φ NPQ. φ Po were more homogeneous throughout leaf. Temporal changes were also observed during the experiment, a 10% decrease in relative water content (RWC) (between day 1 and 2), led to a decrease in photochemical quenching and an increase in non-photochemical processes. Chlorophyll fluorescence parameters were more or less constant till day 8. At the end of the experiment (day 9), energy dissipation by downregulation, electron transport and Q A redox state, decreased and φ NO increased to compensate the change. Chlorophyll fluorescence parameters based on the lake model q L, φ NPQ and φ NO have been found more appropriate for estimating the fraction of open centres, the quantum yield of regulated energy dissipation in photosystem II (PSII) and the quantum yield of non-regulated energy dissipation in PSII, respectively. The F s/ F o ratio is strongly correlated with NPQ and φ NPQ up to a RWC of 20%. This coincides with a greater decrease in photochemical quenching and non-photochemical quenching and an increase in φ NO.