Significant linear relationships between photosynthetic capacity and principal components loaded by phloem cell numbers and tracheary elements per minor vein as well as the latter two normalized for vein density (proxy for apoplastic phloem loading capacity involving membrane transporters) were revealed for all apoplastic loaders (summer annuals and winter annual Arabidopsis thaliana). In addition, significant linear relationships between photosynthetic capacity and a principal component loaded by tracheary element cross-sectional areas and volumes per unit of leaf area (water flux capacity proxy) was present for symplastic and apoplastic loaders. Lastly, a significant linear relationship between photosynthetic capacity and a principal component loaded by phloem cell cross-sectional areas and volumes per unit of leaf area (proxy for symplastic loading capacity involving cytosolic enzymes for companion cells) was revealed for summer annual symplastic loaders as well as for A. thaliana (in the case of sieve elements, a proxy for sugar export capacity from the leaves)., S. K. Polutchko, J. J. Stewart, B. Demmig-Adams, W. W. Adams., and Obsahuje bibliografické odkazy
Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of three foliose lichen species was studied using Chl fluorescence imaging (CFI) and slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most physiologically active zones within fully hydrated thalli: marginal thallus parts (Hypogymnia physodes), central part and close-to-umbilicus spots (Lasallia pustulata), and irregulary-distributed zones within thallus (Umbilicaria hirsuta). During gradual desiccation of lichen thalli, decrease in Chl fluorescence parameters (FO - minimum Chl fluorescence at point O, FP - maximum Chl fluorescence at P point, Φ2 - effective quantum yield of photochemical energy conversion in photosystem 2) was observed. Under severe desiccation (>85 % of water saturation deficit), substantial thalli parts lost their apparent physiological activity and the resting parts exhibited only a small Chl fluorescence. Distribution of these active patches was identical with the most active areas found under full hydration. Thus spatial heterogeneity of Chl fluorescence in foliose lichens may reflect location of growth zones (pseudomeristems) within thalli and adjacent newly produced biomass. When exposed to high irradiance, fully-hydrated thalli of L. pustulata and U. hirsuta showed either an increase or no change in FO, and a decrease in FP. Distribution of Chl fluorescence after the high irradiance treatment, however, remained the same as before the treatment. After 60 min of recovery in the dark, FO and FP did not recover to initial values, which may indicate that the lichen used underwent a photoinhibition. The CFI method is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus before application of single-spot fluorometric techniques in lichens. and M. Barták, J. Hájek, J. Gloser.
Photosynthesis is amongst the plant cell functions that are highly sensitive to any type of changes. Sun and shade conditions are prevalent in fields as well as dense forests. Dense forests face extreme sun and shade conditions, and plants adapt themselves accordingly. Sun flecks cause changes in plant metabolic processes. In the field, plants have to face high light intensity and survive under such conditions. Sun and shade type of plants develops a respective type of chloroplasts which help plants to survive and perform photosynthesis under adverse conditions. PSII and Rubisco behave differently under different sun and shade conditions. In this review, morphological, physiological, and biochemical changes under conditions of sun (high light) and shade (low light) on the process of photosynthesis, as well as the tolerance and adaptive mechanisms involved for the same, were summarized., S. Mathur, L. Jain, A. Jajoo., and Obsahuje bibliografické odkazy
Photoinhibition is a significant constraint for improvement of radiation-use efficiency and yield potential in cereal crops. In this work, attached fully expanded leaves of seedlings were used to assay the factors determining photoinhibition and for evaluation of tolerance to photoinhibition in wheat (Triticum aestivum L.). Our results showed that even 1 h under PPFD of 600 µmol(photon) m-2 s-1 could significantly reduce maximal quantum yield of PSII photochemistry (Fv/Fm) and performance index (PI) compared to low light [300 µmol(photon) m-2 s-1]. The decrease of Fv/Fm and PI was more noticeable with the increase of light intensity; irradiance higher than 800 µmol(photon) m-2 s-1 resulted in photoinhibition. Compared to 25°C, lower (20°C) or higher temperature (≥ 35°C) aggravated photoinhibition, while slightly high temperature (28°) alleviated photoinhibition. At 25°C, irradiance of 1,000 µmol(photon) m-2 s-1 for 1 h was enough to cause photoinhibition and a significant decrease of Fv/Fm, PI, trapped energy flux, electron transport flux, and density of reaction center as well as increase of dissipated energy flux per cross section were observed. In addition, seedlings at 21-32 days after planting showed a relatively stable phenotype, while the younger or older seedlings indicated an increased susceptibility to photoinhibition, especially in senescing leaves. Finally, six wheat varieties with relative tolerance to photoinhibition were identified from 22 Chinese winter wheat varieties by exposing attached leaves of the 25-d old seedlings for 1 h to 1,000 µmol(photon) m-2 s-1 at 25°C. Therefore, our work established a possible method for development of new wheat varieties with enhanced tolerance to photoinhibition., H. Li, Q. Zheng, J. Zhang, B. Li, Z. Li., and Obsahuje bibliografii