Flavonoids are thought to participate in protection of the photosynthetic apparatus against photoinhibition under excessive light. Flavone glycoside, scutellarin, is a main active ingredient extracted from Erigeron breviscapus, the plant used in Chinese medicine. Shade-developed leaves of E. breviscapus were transferred from shade to full sunlight to quantify a relationship between the concentration of leaf scutellarin and tolerance to high radiation stress or the recovery from photoinhibition. The maximal quantum yield of PSII photochemistry showed a diurnal fluctuation in both shaded and sunlit leaves throughout the day. It indicated dynamic photoinhibition in the leaves of Erigeron, i.e., higher photoinhibition at solar noon and lower one in the morning and late afternoon. The sun-developed leaves reached the higher scutellarin content and values of nonphotochemical quenching coefficient with a lower degree of photoinhibition than the shade-developed leaves. When the shade-developed leaves were transferred to full sunlight, the content of scutellarin was declining continuously for 10 d and then was increasing for 15 d. After 50 d, all leaves became the sun-developed leaves with their scutellarin contents of about 138.5 ± 5.2 mg g-1(dry mass, DM) which was significantly higher than that of the shade-developed leaves [107.8 ± 9.8 mg g-1(DM)]. During acclimatization, the degree of photoinhibition was negatively correlated with the scutellarin content. Our results demonstrated a synchronous fluctuation between the flavonoid content and degree of protection against photoinhibition., R. Zhou, W. H. Su, G. F. Zhang, Y. N. Zhang, X. R. Guo., and Obsahuje seznam literatury
Leaf protein content and net photosynthetíc rate (P^) were estimated at monthly intervals in seven tropical deciduous tree species, námely Chukrasia tabularis, Dolichandrone atrovirens, Eugenia Jambolana, Gmelina arborea, Lannea coromandelica, Terminalia arjuna and Terminalia bellerica firom September 1990 to August 1991. Among the seven tree species examined, Terminalia arjuna exhibited a significant positive correlation (r = 0.81; p < 0.05) between leaf protein content and while in others it was found insignificant.
The relationship between net photosynthetic (PN) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and PN during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean PN (16.4±2.4 µmol m-2 s-1) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 µmol m-2 s-1). The highest R (1.89±0.30 µmol m-2 s-1, mean of the species), associated to a significant PN decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/PN ratio 0.447±0.091). Q10, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/PN determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher PN and lower R during stress periods. and L. Gratani, L. Varone, R. Catoni.
Field studies with segregating populations under short days showed a significant positive correlation between tuber yield and the light-saturated net photosynthetic rate (Fn) in the 4th leaf from the top, at the tuber formation stage, in two seasons. The leaf area per plant {A) at this stage and also at the tuber bulking stage had a significant positive correlation with tuber yield. The product of PN and A also showed a significant positive correlation with tuber yield at both of these stages, a stronger one than that between tuber yield and A at the tuber formation stage.
Simultaneous measurements of net photosynthetic rate {P^ and fluorescence were taken on flag leaves of fíeld-grown wheat {Triíicum aestivum L., Thlicum durum L.) from anthesis to senescence. By using leaf discs inaintained in saturating CO2 in tlie O2 electrode we found that the electron transport measured by fluorescence, and that calculated from O2 evolution rate were similar througliout the experimental period, which indicated that fluorescence might be ušed to measure the linear electron transport rate. In field measurements on intact attached leaves, the electron transport rate declined less than during leaf senescence, Measurements taken in the aftemoon indicated that the electron transport remained constant during the day while slightly decreased. Thus, in fíeld-grown wheat leaves photoinhibition was not a relevant phenomenon. When the alternativě electron routes were negligible, the increasing discrepancy between Pn and the electron transport during leaf senescence could be explained by an increment in photorespiration rate (Pp), The change of oxygenation to carboxylation ratio (Vq/Vj,) might be caused by increasing resistances to CO2 diffusion in the leaf CO2 lost through photorespiration was about half of that fixed with Pn in the sun-exposed leaves. Yet Pp was lower in the basal part of leaves which mostly grew in shade. Fluorescence coupled with gas exchange proved to be a useful method for evaluation of the photorespiratory losses in field conditions.
The relationship between chlorophyll (Chl) content and net photosynthetic rate (PN) in an isolated Quercus ilex tree, growing inside Villa Pamphili Park in Rome, was explored. The highest PN was in March, May, and September (10.1 μmol m-2 s-1, maximum rate). PN decreased by 65 % (with respect to the yearly maximum) when leaf temperature reached 34 °C, and by 50 % when leaf temperature was 9 °C. The highest Chl contents were in April, October [1.47 g kg-1 (d.m.), maximum value], and December. The lowest Chl content was found in July (0.78 g kg-1). The decrease of PN in July was in close connection with the decrease of Chl content. On the contrary, the high Chl content during winter did not correspond with PN of this season. Discordances between Chl content and PN over the year influenced the regression analysis, which although positive did not show very high correlation coefficients (r = 0.7). The high Chl (a+b) content during most of the year indicated that the photosynthetic apparatus remained basically intact also during stress periods. and L. Gratani, P. Pesoli, M. F. Crescente.
To assess the relationship between chlorophyll (Chl) fluorescence (CF) and photosynthetic pigments, soybean was grown under varying phosphorus (P) nutrition at ambient and elevated CO2 (EC). The EC stimulated, but P deficiency decreased plant height, node numbers, and leaf area concomitantly with the rates of stem elongation, node addition, and leaf area expansion. Under P deficiency, CF parameters and pigments declined except that carotenoids (Car) were relatively stable indicating its role in photoprotection. The CF parameters were strongly related with Chl concentration but not with Chl a/b or Car. However, total Chl/Car showed the strongest association with CF parameters such as quantum efficiency and yield of photosystem II. This relationship was not affected by CO2 treatment. The high correlation between CF and total Chl/Car underscores the significance of the quantification of both, Chl and Car concentrations, to understand the photochemistry and underlying processes of photoprotection and mechanisms of excess energy dissipation in a given environment., S. K. Singh, V. R. Reddy, D. H. Fleisher, D. J. Timlin., and Obsahuje bibliografii
Specific leaf area (SLA) is a key trait to screen plants for ecological performance and productivity; however, the relationship between SLA and photosynthesis is not always up-scalable to growth when comparing multiple species with different life cycles. We explored leaf anatomy in annual and perennial species of Physaria, and related it to photosynthesis and water loss. The annual Physaria gracilis had higher SLA, thinner leaves, and lower investment in protective tissues, than perennial P. mendocina. Physaria angustifolia (annual), and P. pinetorum (perennial) showed intermediate values. Both perennials had a thicker palisade and high photosynthesis, relative to annuals. The larger leaf veins of perennials should allow high water availability to the mesophyll. The thicker palisade should determine high resistance to water flow and help explain their high water-use efficiency. These leaf functions reflect the construction of long-lived leaves that efficiently use resources under environmental limitations of arid environments., L. Gonzalez-Paleo, D. A. Ravetta., and Obsahuje bibliografii
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (PN) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (μmol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 μmol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi - Fo)/(Fm - Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 μmol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs - Fo')/Fm' - Fo')], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (μmol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 μmol m-2 s-1 and photoinhibition occurred above PPFD 900 μmol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 μmol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 μmol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter PN and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves. and Husen Jia, Dequan Li.
During the last century, the world soybean yield has been constantly enhancing at a remarkable rate. Factors limiting the soybean yield may be multiple. It is widely acknowledged that changes of root metabolism can influence aboveground characteristics, such as the seed yield and photosynthesis. In this study, we considered root bleeding sap mass (BSM) and root activity (RA) as indicators of the root growth vigour. We used 27 soybean cultivars, spanning from 1923 to 2009, to evaluate the contribution of root characteristic improvement to efficient photosynthesis and dry matter production. The BSM, RA, net photosynthetic rate (P N), and organ biomass were measured at different growth stages, such as the fourth leaf node, flowering, podding, and seed-filling stage. Our results showed that the soybean cultivars increased their biomass and P N thanks to genetic improvement. At the same time, BSM and RA also increased in dependence on a year of cultivar release. However, both P N and biomass were positively correlated with root characteristics only at the podding stage. Our data revealed that the improved root characteristic may have contributed to the enhanced photosynthesis, biomass, and yield of soybean cultivars during last 87 years of genetic improvement. We suggest that BSM and RA could be used as important indexes for further practice in soybean production improvement., X. Cui, Y. Dong, P. Gi, H. Wang, K. Xu, Z. Zhang., and Obsahuje seznam literatury