A new image instrumentation system for quantitative analysis of the rapid change in intensity of chlorophyll fluorescence during dark-light transition (CFI, chlorophyll fluorescence induction), which is a sensitive indicator of the various reactions of photosynthesis, was developed and its performance was evaluated. This system made it possible to resolve CFI at any small leaf area (about 1 square millimeter) of a whole leaf when the plant was illuminated by blue-reen light at more than 50 micromoles photons per square meter per second. In order to test the usefulness of this system, we applied it to analyze the effect of S02 on photosynthetic apparatus in attached sunflower leaves. Dynamic CFI imaging over the whole single leaf, where there was no visible injury, indicated not only the local changes in photosynthetic activity but also the site of inhibition in photosynthetic electron transport system in chloroplasts. The new instrumentation system will be useful for the analytical diagnosis of various stress-actions on plants in situ. transport system. Therefore, the measurement and analysis of CFI in plant leaves in situ has been developed as a sensitive and nondestructive assay for the functional state of the photosynthetic apparatus (26,29,(31)(32)(33). The conventional methods (27,28) give only the spatially averaged CR at a definite area because these use point sensors. The static imaging of Chl fluorescence such as photography (8, 15) reveals the location of impairment for the whole leaf in a similar manner as the DLE imaging method, but it does not give any information involving in CFI.We therefore developed a new instrumentation system using a CCD image sensor for a quantitative analysis ofCFI, the system of which would give the information not only on the localized differences in photosynthetic activity on whole leaf in situ but also on the inhibition site in the photosynthetic system. In order to test the usefulness of this system, we successfully applied it to analyze the stress induced by SO2, a major phytotoxic air pollutant (10,12,17), on the photosynthetic apparatus of attached sunflower leaves. MATERIALS AND METHODSAbiotic and biotic stresses such as air pollutants, water deficit, high or low temperature, and virus infection cause a spatially heterogeneous impairment in attached leaves. The heterogeneous impairment was indicated in stomatal responses and photosynthetic activity. For example, recent investigations employing thermal imaging methods (9,19,21,22) and DLE2 imaging methods (6, 7) have shown evidence of spatially different responses of stomata in situ to various stresses. The DLE imaging method, furthermore, clarified localized changes in photosynthetic activity induced by the stresses (2, 5). However, these techniques did not provide any information about the site of inhibition in the photosynthetic apparatus.Rapid changes in intensity of Chl a fluorescence during darklight transition (CFI) reflect the various reactions of photosynthesis (4,11,13,18,24)
We conducted in situ measurements of gas exchange and O 2 concentration in pneumatophores of Sonneratia alba, Avicennia marina and Bruguiera gymnorrhiza and prop roots of Rhizophora stylosa. The mean rates of photosynthesis were 0.6 and 0.2 µmol CO 2 m -2 s -1 in the raised pneumatophores of S. alba and A. marina, respectively, at a photosynthetic photon flux density of 100 µmol m -2 s -1 . Photosynthetic activity was also detected in the prop roots of R. stylosa but the photosynthetic rate was lower than in A. marina. B. gymnorrhiza had no photosynthetic activity in knee pneumatophores. O 2 concentrations in the pneumatophores of these four species decreased by 4-8% when the pneumatophores were submerged under water. The O 2 concentrations in submerged pneumatophores of S. alba and A. marina were higher with higher solar radiation. Such photosynthetically generated O 2 could diffuse down through the pneumatophores into the roots, particularly when sunlit pneumatophores were submerged by high tide. This may contribute to the success of S. alba and A. marina in zones where tidal inundation is common.
We examined the relationships between O3 sorption and the acute effects of the O3 on sunflower leaves, such as changes in stomatal response and visible injury, using an image instrumentation method. The results obtained were as follows:1) Changes in stomatal response to O3 varied randomly at different sites on a leaf, and were not dependent on the integrated O3 sorption at these sites. This result suggests that there are differences in stomatal sensitivity to O3 among local sites on a leaf.2) The degree of visible injury at local sites on a leaf, which reached chlorosis and necrosis, was not related to the integrated O3 sorption at these sites. This result suggests that the differences in the degree of the visible injury among local sites on a leaf are dependent on differences not only in factors related to O3 sorption, but also in other physiological factors among these sites.Ozone is a major air pollutant of photochemical oxidant, which is produced in the atmosphere by a series of photochemical reactions involving nitrogen oxides and gaseous hydrocarbones.1,2) Entry of O3 into a leaf through the stomata causes various effects on leaves.3-6) The degree of the effects varies at different sites on a leaf. For example, chlorotic and necrotic visible injuries caused by O3, which are conspicuous symptoms of the acute effect, are generally characterized by numerous discrete lesions scattered over all or a large portion of the leaf surface. Depending on the plant species and the severity of the injury, the lesions range from small superficial spots to a large necrotic area.7-8) Therefore, to better understand the effects of O3 sorption, it is necessary to define relationships between local gas sorption, factors governing the sorption, and the degree of the gas sorption effects at local sites.As described in the preceding papers,9,10) we have developed an instrumentation method for studying the distribution of the sorption of air pollutants, transpiration, and stomatal diffusion resistance of leaves using a thermal infrared image instrumentation system, and have examined quantitatively the relationships between the acute effects, such as changes in stomatal response and visible injury, of SO2 or NO2 on a leaf and gas sorption. However, the relationships between O3 sorption and its effects all over the leaf surface have not been clarified.We therefore made the present study to elucidate the relationships between the distribution patterns of O3 sorption and its acute effects such as changes in stomatal response and visible injury on a leaf.
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