Response of the photosynthetic apparatus of cotton (Gossypium hirsutum) to the onset of drought stress under field conditions studied by gas-exchange analysis and chlorophyll fluorescence imaging

Diurnal courses of photosystem II (PS II) activity of Xanthoria elegans were continuously monitored using a novel technique of chlorophyll fluorescence imaging in the field (maritime Antarctica) over a period of 7 days. The lichen specimens grew on rock surfaces in a north-facing coastal area of Galindez Island (Argentine Islands). A portable fluorometer FluorCam equipped with a CCD camera and image analysis software was placed over a thallus so that false colour images of FV/FM and quantum yield of photochemical processes in PS II (ΦII) distribution over the thallus could be taken over the course of a day. Simultaneously, microclimatic parameters of the habitat were recorded: air and thallus temperatures, relative air humidity, PPFR (photosynthetic photon fluence rate) and global radiation. Photosynthetic processes in X. elegans were activated by rainfall or water from melting snow. After thallus hydration, FV/FM and ΦII gradually decreased from their maximum values due to evaporation and progressive loss of water from the thallus. Chlorophyll fluorescence imaging showed that the thallus dehydration started from the margins and moved towards the central thicker thallus zones. These zones exhibited higher activity of PS II than the margins throughout the day. The rate of inhibition of photosynthetic processes in PS II was faster at the margins than in the centre of the thallus. Dependence of ΦII on thallus water potential (WP) was investigated during gradual dehydration under laboratory conditions. After a decrease in WP from zero to −7 MPa, X. elegans exhibited only a 13·8% decrease in ΦII from its maximal value. Within the range of WP of from −8 to −20 MPa, the ΦII decrease was more rapid reaching the critical point (ΦII=0) at WP of approximately −25 MPa. Chlorophyll fluorescence imaging and WP measurements showed that X. elegans is capable of maintaining detectable photosynthetic activity even at extremely low WP. Based on our microclimatological data, X. elegans may be photosynthetically active under field conditions for several hours after being wetted by rain or snowfall. It is suggested that chlorophyll fluorescence imaging is a powerful technique, transferable to field conditions and capable of visualizing heterogeneity of photosyntetic processes over a lichen thallus subjected to periodic dehydration.

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Misurare la vitalità delle piante per mezzo della fluorescenza della clorofilla

10.36253/978-88-6655-216-1 ◽

2012 ◽

Author(s):

Filippo Bussotti ◽

Mohamed Hazem Kalaji ◽

Rosanna Desotgiu ◽

Martina Pollastrini ◽

Tadeusz Loboda ◽

...

Keyword(s):

Chlorophyll Fluorescence ◽

Fluorescence Imaging ◽

Low Temperatures ◽

Photosynthetic Apparatus ◽

Delayed Fluorescence ◽

Chlorophyll Fluorescence Imaging ◽

Strong Light ◽

Fluorescence Techniques ◽

Modulated Fluorescence ◽

High And Low Temperatures

The book begins with a detailed description of the characteristics of the photosynthetic apparatus and the processes that take place there, to then present the general principles of fluorescence. After that, it gives a description of the characteristics of direct and modulated fluorescence and a presentation of the shared and distinctive parameters of these two techniques. Then a brief presentation is made of other innovative approaches to the analysis of fluorescence (Chlorophyll Fluorescence Imaging - CFI, P700 absorbance, delayed fluorescence) and the relative tools. An important part of the book comprises a description of the possible applications of fluorescence techniques for the analysis of various types of stress (aridity, strong light radiations, UV, high and low temperatures, salinity, weedkillers, pollution, etc.) and, consequently, their possible use in agriculture, forestry and to protect the environment.

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Enhanced sensitivity of Arabidopsis anthocyanin mutants to photooxidation: a study with fluorescence imaging

Functional Plant Biology ◽

10.1071/fp08069 ◽

2008 ◽

Vol 35 (8) ◽

pp. 714 ◽

Cited By ~ 30

Author(s):

Ling Shao ◽

Zhan Shu ◽

Chang-Lian Peng ◽

Zhi-Fang Lin ◽

Cheng-Wei Yang ◽

...

Keyword(s):

Oxidative Stress ◽

Chlorophyll Fluorescence ◽

Fluorescence Imaging ◽

Photosynthetic Apparatus ◽

Chlorophyll Fluorescence Imaging ◽

Prolonged Treatment ◽

Partial Recovery ◽

Wild Type ◽

Short Term Treatment ◽

Chlorophyll Fluorescence Parameters

Chlorophyll fluorescence imaging and antioxidative capability in detached leaves of the wild-type Arabidopsis thaliana ecotype Landsberg erecta (Ler) and in three mutants deficient in anthocyanin biosynthesis (tt3, tt4 and tt3tt4) were investigated under photooxidation stress induced by methyl viologen (5 μm) in the light. In comparison with the wild-type (WT) plant, photooxidation resulted in significant decreases in the contents of total phenolics and flavonoid, total antioxidative capability and chlorophyll fluorescence parameters (Fv/Fm, qP, ΦPSII, NPQ and ETR) as determined by chlorophyll fluorescence imaging, and in an increase in cell-membrane leakiness in the three anthocyanin mutants. The sequence of sensitivity to photooxidation in the leaves of the four phenotypes were tt3tt4 (deficient in both chalcone synthase locus (CHS) and dihydroflavonol 4-reductase locus (DFR)) > tt4 (deficient in CHS) > tt3 (deficient in DFR) > WT. The results demonstrate that anthocyanins might, along with other antioxidants, protect the photosynthetic apparatus against photooxidative damage. An interesting phenomenon was observed over the 270 min of the photooxidative treatment, that is, fluorescence imaging revealed that qP, ΦPSII and ETR appeared in three phases (fall → partial recovery → rapid fall). This was considered to be a modulation of reversible deactivation in PSII to cope with the moderate oxidative stress in the first two stages of short-term treatment (<150 min), followed finally by damage to PSII under severe oxidative stress with prolonged treatment.

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