We analyzed several approaches dealing with the components of non-photochemical energy dissipation and introduced improved versions of the equations used to calculate this parameter. The usage of these formulae depends on the conditions of the sample (acclimation to dark or irradiation, presence or absence of the "actinic light"). The parameter known as "excess" cannot be used as a component of energy partitioning. In reality, this parameter reflects the differences between potential and actual quantum yields of photochemistry. and D. Kornyeyev, A. S. Holaday.
We describe an instrument that allows the rapid measurement of fluorescence lifetime-resolved images of leaves as well as sub-cellular structures of intact plants or single cells of algae. Lifetime and intensity fluorescence images can be acquired and displayed in real time (up to 55 lifetime-resolved images per s). Our imaging technique therefore allows rapid measurements that are necessary to determine the fluorescence lifetimes at the maximum (P level) fluorescence following initial illumination during the chlorophyll (Chl) a fluorescence transient (induction) in photosynthetic organisms. We demonstrate the application of this new instrument and methodology to measurements of: (1) Arabidopsis thaliana leaves showing the effect of dehydration on the fluorescence lifetime images; (2) Zea mays leaves showing differences in the fluorescence lifetimes due to differences in the bundle sheath cells (having a higher amount of low yield photosystem 1) and the mesophyll cells (having a higher amount of high yield photosystem 2); and (3) single cells of wild type Chlamydomonas reinhardtii and its non-photochemical quenching mutant NPQ2 (where the conversion of zeaxanthin to violaxanthin is blocked), with NPQ2 showing lowered lifetime of Chl a fluorescence. In addition to the lifetime differences referred to in (1) and (2), structural dependent heterogeneities in the fluorescence lifetimes were generally observed when imaging mesophyll cells in leaves. and O. Holub ... [et al.].
Photoinactivation of photosystem 2 (PS2) results from absorption of so-called "excessive" photon energy. Chlorophyll a fluorescence can be applied to quantitatively estimate the portion of excessive photons by means of the parameter E = (F - F0')/Fm', which reflects the share of the absorbed photon energy that reaches the reaction centers (RCs) of PS2 complexes with QA in the reduced state ('closed' RCs). Data obtained for cotton (Gossypium hirsutum), bean (Phaseolus vulgaris), and arabidopsis (Arabidopsis thaliana) suggest a linear relationship between the total amount of the photon energy absorbed in excess (excessive irradiation) and the decline in PS2 activity, though the slope may differ depending on the species. This relationship was sensitive not only to the leaf temperature but also to treatment with methyl viologen. Such observations imply that the intensity of the oxidative stress as well as the plant's ability to detoxify active oxygen species may interact to determine the damaging potential of the excessive photons absorbed by PS2 antennae. Energy partitioning in PS2 complexes was adjusted during adaptation to irradiation and in response to a decrease in leaf temperature to minimize the excitation energy that is trapped by 'closed' PS2 RCs. The same amount of the excessive photons absorbed by PS2 antennae led to a greater decrease in PS2 activity at warmer temperatures, however, the delay in the development of non-photochemical and photochemical energy quenching under lower temperature resulted in faster accumulation of excessive photons during induction. Irradiance response curves of EF suggest that, at high irradiance (above 700 μmol m-2 s-1), steady-state levels of this parameter tend to be similar regardless of the leaf temperature. and D. Kornyeyev, A. S. Holaday, B. A. Logan.
In this historical review we summarize discoveries related to the flowering genes in controlling leaf area index (LAI, the leaf area per unit ground area) in sorghum, soybean, or pea crop stands. We also analyze similar work on Arabidopsis and dwarf and intermediate stem height genes in wheat and rice. and G. B. Begonia, M. T. Begonia.
Adverse effect of caffeine consumption has been well documented in animals and in human beings. However, here we studied the influence of caffeine exposure on seedling growth of Arabidopsis and tobacco plants. Retardation in the seedling growth of these plants was observed when grown on MS medium plates containing 1 mM caffeine and their growth retarded further upon increasing the concentration of caffeine to 5 mM. Retardation in seedling size including both root and shoot size, yellowing and decrease in chlorophyll content of seedlings upon caffeine treatment indicated that caffeine exposure induced early senescence in plants. Therefore, the influence of caffeine exposure on transcript expression and activity of Rubisco in tobacco and Arabidopsis seedlings was monitored. Caffeine exposure has been found to decrease the expression and activity of Rubisco in both the plants. Hence, this study documents that caffeine exposure retarded seedling growth and one reason for this could be its negative effect on Rubisco. and P. Mohanpuria, S. K. Yadav.