consequence of starch accumulation in citrus leaves affected by HLB may be an impact on photosynthesis. Light energy absorbed by chlorophyll molecules can be used to drive photosynthesis, dissipated as heat, or re-emitted as light (chlorophyll fluorescence
. Chlorophyll fluorescence and the photochemistry of photosystem II (PSII) can be imaged using cameras, sophisticated data capture techniques, and synchronized light sources ( Baker, 2008 ). Both baseline chlorophyll fluorescence and the Fv/Fm can be imaged and
well as labor-intensive and time-consuming. More recently, chlorophyll fluorescence analysis has been used to evaluate plant responses to different environmental stresses ( Baker and Rosenqvist, 2004 ; Maxwell and Johnson, 2000 ). Chlorophyll
peach have not been described. Photochemistry, chlorophyll fluorescence, and heat dissipation represent three competing de-excitation pathways for the light energy absorbed by chlorophyll in plant leaves ( Maxwell and Johnson, 2000 ). A reduction in the
excitation pressure may occur as a consequence of a reduction in PSII antenna size ( Huner et al., 1998 ). These mechanisms avoid damage to photosystems but result in a decrease in photosynthesis ( D'Ambrosio et al., 2006 ). Hence, chlorophyll fluorescence is
fluorescence. Chlorophyll fluorescence measurements can be used to quickly and reliably determine Φ PSII ( Maxwell and Johnson, 2000 ). Generally, a decrease in Φ PSII indicates that either plants dissipate an increasing fraction of the absorbed light energy
plants. Book Graffers, Chelsea, MI Chen, Y. Lin, F. Yang, H. Yue, L. Hu, F. Wang, J. Luo, Y. Cao, F. 2014 Effect of varying NaCl doses on flavonoid production in suspension cells of Ginkgo biloba : Relationship to chlorophyll fluorescence, ion
Chlorophyll fluorescence over the course of stem cutting propagation was examined in 10 cultivars of Taxus ×media (Taxus baccata L. × T. cuspidata Sieb. & Zucc.), including `Brownii', `Dark Green Pyramidalis', `Dark Green Spreader', `Densiformis', `Densiformis Gem', `Hicksii', `L.C. Bobbink', `Runyan', `Tauntoni', and `Wardii'. The fluorescence value measured was the ratio of variable over maximum chlorophyll fluorescence (Fv/Fm). This value reflects the maximum dark-adapted photochemical efficiency of photosystem II (PSII) reaction centers involved in photosynthesis and is an indirect measure of plant stress. The objective of this study was to examine Fv/Fm as a method for stock plant selection and for monitoring rooting progress of various cultivars. Fv/Fm varied significantly (P ≤ 0.05) among cultivars, initially and over time. However, there was significant overlap among some cultivars. The Fv/Fm decreased dramatically during cold storage, but usually returned to original levels after several weeks in the propagation beds. This appeared to be a reflection of the reduction of water stress as the cuttings formed roots. Initial stock plant Fv/Fm was not correlated (P ≤ 0.05) with rooting percentage, root number, root dry weight, or root length, indicating that Fv/Fm is not a reliable indicator of stock plant rooting potential. Visual assessment is just as reliable.
The stress level in a plant may be directly associated with the intensity of the Kautsky effect (the sudden increase in fluorescence emission by chlorophyll following a dark adaptation). The decrease in photosynthetic efficiency, linked with the rate of photochemistry of plants under stress, provides a definitive signature (graphical pattern) that can be quantified and monitored, even for plants that have no visible stress symptoms. Using a prototype GrowScanner®, signature differences in plants under nitrogen and water stress, as compared with plants not under stress, could be detected and measured. Returning stressed plants to a nonstressed condition returned the stress signatures to that of control plants not under stress. Development of the technology may provide a relatively quick, presymptomatic methodology for detecting plant stress without sacrificing plant tissue.
about how P n is limited and whether there are changes in energy fluxes in the photosynthetic apparatus. The status of the photosynthetic apparatus may be investigated in vivo using fast chlorophyll a fluorescence transient analysis ( Strasser and