Fluorescence as a tool in photosynthesis research: application in studies of photoinhibition, cold acclimation and freezing stress

Abstract

Chlorophyll fluorescence induction (at 20 °C and 77 K) and quenching were analysed in relation to effects of environmental stresses imposed by chilling in high light and by freezing and thawing of spinach ( Spinacia oleracea L.) leaves. The data indicate that cold acclimation of spinach plants, which leads to increased frost tolerance of the leaves, results in decreased susceptibility to photoinhibition of photosynthesis at chilling temperatures. When plants acclimated to 18 °C and 260-300 µmol quanta m -2 s -1 were exposed to higher light (550 µmol quanta m -2 s -1 ) at 4 °C, they developed strong photoinhibition, as characterized by decreased quantum yield of O 2 evolution and decreased ratio of variable: maximum fluorescence (F V /F M ) of photosystem II. The decrease in F V /F M resulted from a decline in F V and an increase in F 0 . The F V /F M ratio was lowered to a significantly greater extent when induction was recorded at 20 °C, as compared with 77 K. The effects related to photoinhibition were fully reversible at 18 °C in dim light. Plants that had been cold-acclimated for 10 days exhibited slightly decreased quantum yield and lowered F V /F M ratio. However, they did not show further photoinhibition on exposure to 550 µmol quanta m -2 s -1 at 4 °C. The reversible photoinhibition is discussed as a protective pathway serving for thermal dissipation of excessive light energy. It is hypothesized that such a mechanism prevents destruction of the photosynthetic apparatus, until other means of protection become effective during long-term acclimation to high light. Inhibition of photosynthetic carbon assimilation caused by freezing and thawing of leaves in the dark was closely correlated with inhibition of photochemical fluorescence quenching (q Q ). As a sensitive response of the thylakoid membranes to freezing stress, the energy-dependent quenching, q E , was inhibited. Only more severe impact of freezing caused a significant decline in the F V /F M ratio. It is concluded that measurements of fluorescence induction signals ( F V /F M ratios) provide a sensitive tool with which to investigate photoinhibition, whereas freezing damage to the photosynthetic system can be detected more readily by the quenching coefficients q Q and q E than by F V /F M ratios.

Chlorophyll fluorescence emission as a reporter on cold tolerance inArabidopsis thalianaaccessions

“…Low temperature reduction of chlorophyll quenching may also be caused by inhibition of oxygen evolving complexes, 43 a slowdown of the Calvin cycle and hence the electron transport rate. 44 Subsequent cooling causes F s to attain the level of P, indicating that photosynthesis was completely abolished similar to what is observed when the electron transport was completely stopped by the application of the electron transport inhibitor DCMU [3-(3,4-Dichlorophenyl)-1,1-dimethylurea].…”

Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

“…In wild-type plants, the stomatal closing after 3 d of water stress correlated well with the decrease in carboxylation efficiency. The maintenance of a constant ratio of variable to maximal chlorophyll fluorescence (F v /F m ), an indicator of the maximum quantum efficiency of PSII and stress-induced photoinhibition (Krause et al, 1989), further supported the ability of the transgenic plants to maintain C assimilation during the stress episode (Fig. 1I).…”

Sudden Exposure to Solar UV-B Radiation Reduces Net CO2 Uptake and Photosystem I Efficiency in Shade-Acclimated Tropical Tree Seedlings

“…When rates of CO 2 uptake were plotted versus F V /F M , pictures similar to Figure 4 were obtained (data not shown). These results contrast with those of studies using artificial visible light, where a close empirical correlation between optimal quantum yield of photosynthesis and F V /F M (at room temperature) was observed, with regression lines extending to the origin (Leverenz and Ö quist, 1987;Krause and Somersalo, 1989;Giersch and Krause, 1991;Krause and Weis, 1991). Figure 4 indicates a large increase in the degree of inhibition of CO 2 assimilation when only small changes in potential PSII efficiency occur. )…”