Changes in the pools of carotenoids and protochlorophyll(ide) were investigated in etiolated cucumber cotyledons treated with norflurazon (NF) and an experimental herbicide KC 6361 (KC). Both the NF- and the KC-treated tissues considerably accumulated the colourless carotenes phytoene and phytofluene with a concomitant depletion of the coloured carotenoids lutein and β-carotene in darkness. However, the profiles of changes in chlorophylls (Chls) and carotenoids were different for the two herbicides. The plants were also influenced by the photosynthetic photon flux densities (PPFD's), with a more pronounced decline of Chl under high PPFD than under low PPFD. The ratios of protochlorophyll (PChl)/protochlorophyllide (PChlide) were greatly altered due to a decrease and an increase of PChl in the NF- and the KC-treated etiolated tissues, respectively, whereas the PChlide content was not significantly influenced by the inhibitors. Large increase of PChls in the KC-treated tissues seems to derive from the binding of accumulated geranylgeraniol (GG) equivalents, through carotenogenic inhibition, to PChlide. Therefore, the alterations of PChl and PChlide occurring under disturbed carotenogenesis may suggest an interaction between the biosynthetic pathways of Chls and carotenoids. In addition, the great proportion of PChl GG and PChl dihydro-GG in the KC-treated tissues implies that PChl formation is regulated at the level of hydrogenation. and S. Jung ... [et al.].
In addition to other factors, high altitude (HA) environment is characterized by high photosynthetic photon flux density (PPFD). Photosynthetic characteristics of wild and cultivated plants were studied at different irradiances at Losar, India (altitude 4 200 m). Wild plants were tolerant to high PPFDs. Slopes of curve between net photosynthetic rate (PN) and intercellular CO2 concentration
(Ci) or stomatal conductance (gs) increased with increase in irradiance suggesting insensitivity or tolerance of these plants to higher PPFD. Cultivated plants, however, were sensitive to higher PPFD, their slopes of curves between PN and Ci or gs decreased with increased PPFD. Tolerance or insensitivity to higher PPFD was an important parameter affecting plant performance at HA. and N. Kumar, S. Kumar, P. S. Ahuja.
Diurnal and seasonal trends in net photosynthetic rate (PN), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum PN in D. sissoo ranged from 21.40±2.60 µmol m-2 s-1 in rainy season I to 13.21±2.64 µmol m-2 s-1 in summer whereas in H. binata it was 20.04±1.20 µmol m-2 s-1 in summer and 13.64±0.16 µmol m-2 s-1 in winter. There was a linear relationship between daily maximum PN and gs in D. sissoo but there was no strong linear relationship between PN and gs in H. binata. In D. sissoo, the reduction in gs led to a reduction in both PN and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in gs causes an increase of PN and E with a significant moderate WUE. and S. G. Saraswathi, K. Paliwal.
Rates of net photosynthesis (PN) and transpiration (E), and leaf temperature (TL) of maintenance leaves of tea under plucking were affected by photosynthetic photon flux densities (PPFD) of 200-2 200 µmol m-2 s-1. PN gradually increased with the increase of PPFD from 200 to 1 200 µmol m-2 s-1 and thereafter sharply declined. Maximum PN was 13.95 µmol m-2 s-1 at 1 200 µmol m-2 s-1 PPFD. There was no significant variation of PN among PPFD at 1 400-1 800 µmol m-2 s-1. Significant drop of PN occurred at 2 000 µmol m-2 s-1. PPFD at 2 200 µmol m-2 s-1 reduced photosynthesis to 6.92 µmol m-2 s-1. PPFD had a strong correlation with TL and E. Both TL and E linearly increased from 200 to 2 200 µmol m-2 s-1 PPFD. TL and E were highly correlated. The optimum TL for maximum PN was 26.0 °C after which PN declined significantly. E had a positive correlation with PN. and T. S. Barman, U. Baruah, J. K. Saikia.
A mathematical model for photoinhibition of leaf photosynthesis was developed by formalising the assumptions that (1) the rate of photoinhibition is proportional to irradiance; and (2) the rate of recovery, derived from the formulae for a pseudo first-order process, is proportional to the extent of inhibition. The photoinhibition model to calculate initial photo yield is integrated into a photosynthesis-stomatal conductance (gs) model that combines net photosynthetic rate (PN), transpiration rate (E), and gs, and also the leaf energy balance. The model was run to simulate the diurnal courses of PN, E, gs, photochemical efficiency, i.e., ratio of intercellular CO2 concentration and CO2 concentration over leaf surface (Ci/Cs), and leaf temperature (T1) under different irradiances, air temperature, and humidity separately with fixed time courses of others. When midday depression occurred under high temperature, gs decreased the most and E the least. The duration of midday depression of gs was the longest and that in E the shortest. E increased with increasing vapour pressure deficit (VPD) initially, but when VPD exceeded a certain value, it decreased with increasing VPD; this was caused by a rapid decrease in gs. When air temperature exceeded a certain value, an increase in solar irradiance raised T1 and the degree of midday depression. High solar radiation caused large decrease in initial photon efficiency (α). PN, E, and gs showed reasonable decreases under conditions causing photoinhibition compared with non-photoinhibition condition under high irradiance. The T1 under photoinhibition was higher than that under non-photoinhibition conditions, which was evident under high solar irradiance around noon. The decrease in Ci/Cs at midday implies that stomatal closure is a factor causing midday depression of photosynthesis. and Qiang Yu, J. Goudriaan, Tian-Duo Wang.
Irradiance data software developed by the NREL Solar Radiation Laboratory (Simple Model of Atmospheric Radiative Transfer of Sunshine, SMARTS) has been used for modelling photosynthesis. Spectra and total irradiance were expressed in terms of quanta [mol m-2 s-1, photosynthetic photon flux density, PPFD (400-700 nm)]. Using the SMARTS software it is possible to (1) calculate the solar spectrum for a planar surface for any given solar elevation angle, allowing for the attenuating effects of the atmosphere on extraterrestrial irradiance at each wavelength in the 400-700 nm range and for the thickness of atmosphere the light must pass through during the course of a day, (2) calculate PPFD vs. solar time for any latitude and date and (3) estimate total daily irradiance for any latitude and date and hence calculate the total photon irradiance for a whole year or for a growing season. Models of photosynthetic activity vs. PPFD are discussed. Gross photosynthesis (Pg) vs. photosynthetic photon flux density (PPFD) (Pg vs. I) characteristics of single leaves compared to that of a canopy of leaves are different. It is shown that that the optimum irradiance for a leaf (Iopt) is the half-saturation irradiance for a battery of leaves in series. A C3 plant, with leaves having an optimum photosynthetic rate at 700 μmol m-2 s-1 PPFD, was used as a realistic worked example. The model gives good estimates of gross photosynthesis (Pg) for a given date and latitude. Seasonal and annual estimates of Pg can be made. Taking cloudiness into account, the model predicts maximum Pg rates of about 10 g(C) m-2 d-1, which is close to the maximum reported Pg experimental measurements. and R. J. Ritchie.
Changes in pigment composition and chlorophyll (Chl) fluorescence parameters were studied in 20 year-old Scots pine (Pinus sylvestris L.) trees grown in environment-controlled chambers and subjected to ambient conditions (CON), doubled ambient CO2 concentration (EC), elevated temperature (ambient +2-6 °C, ET), or a combination of EC and ET (ECT) for four years. EC did not significantly alter the optimal photochemical efficiency of photosystem 2 (PS2; Fv/Fm), or Chl a+b content during the main growth season (days 150-240) but it reduced Fv/Fm and the Chl a+b content and increased the ratio of total carotenoids to Chl a+b during the 'off season'. By contrast, ET significantly enhanced the efficiency of PS2 in terms of increases in Fv/Fm and Chl a+b content throughout the year, but with more pronounced enhancement in the 'off season'. The reduction in Fv/Fm during autumn could be associated with the CO2-induced earlier yellowing of the leaves, whereas the temperature-stimulated increase in the photochemical efficiency of PS2 during the 'off season' could be attributed to the maintenance of a high sink capacity. The pigment and fluorescence responses in the case of ECT showed a similar pattern to that for ET, implying the importance of the temperature factor in future climate changes in the boreal zone. and K. Y. Wang, S. Kellomäki, T. Zha.
Photosynthetic characteristics were compared between plants of low altitude (LA) grown at LA (Palampur; 1 300 m) and at high altitude, HA (Kibber; 4 200 m), and plants naturally occurring at different altitudes (Palampur, 1 300 m; Palchan, 2 250 m; and Marhi, 3 250 m). Net photosynthetic rate (PN) was not significantly different between altitudes. However, the slopes of the curve relating PN to intercellular CO2 concentration (Ci) were higher in plants at Palchan, Marhi, and Kibber compared to those at Palampur, indicating that plants had higher efficiency of carbon uptake (the initial slope of PN/Ci curve is an indication) at HA. They had also higher stomatal conductance (gs), transpiration rate, and lower water use efficiency at HA. gs was insensitive to photosynthetic photon flux density (PPFD) for plants naturally occurring at Palampur, Palchan, and Marhi, whereas plants from LA grown at Palampur and Kibber responded linearly to increasing PPFD. Insensitivity of gs to PPFD could be one of the adaptive features allowing wider altitudinal distribution of the plants. and N. Kumar, S. Kumar, P.S. Ahuja.
Net photosynthetic rate (PN) of Valeriana jatamansi plants, grown under nylon net shade or under different tree canopies, was saturated with photons at 1 000 μmol m-2 s-1 photosynthetic photon-flux-density (PPFD), whereas open-grown plants were able to photosynthesise even at higher PPFD, e.g. of 2 000 μmol m-2 s-1. Plants grown under net shade had higher total chlorophyll (Chl) content per unit area of leaf surface. However, Chl a/b ratio was maximal in open-grown plants, but remained unchanged in plants grown in nylon net shade and under different tree canopies. Sun-grown plants had thicker leaves (higher leaf mass per leaf area unit), higher wax content, and higher PN than shade grown plants. Thus V. jatamansi is able to acclimate to high PPFD and therefore this Himalayan species may be cultivated in open habitat to meet the ever-increasing industrial demand. and S. K. Vats, S. Pandey, P. K. Nagar.
Seasonal changes in leaf gas exchange, assimilation response to light and leaf area were monitored in bearing and nonbearing pistachio shoots. Shoot bearing status did not directly affect leaf photosynthetic rate. However, photosynthetic light-response curves strongly varied during the season demonstrating the dominant effect of the tree’s seasonal phenology on assimilation. Early in the season low photosynthetic rates were associated with high rates of dark respiration indicating limited photosynthesis in the young leaves. As leaves matured, dark respiration decreased and assimilation reached maximum values. Photosynthetic efficiency was strongly reduced late in the season due to leaf age and senescence. Fruit load precipitated an early leaf senescence and drop that resulted in a 53% decrease in leaf area in bearing vs. nonbearing shoots, strongly decreasing the seasonal photosynthetic performance of bearing shoots. Bearing shoots produced a 26% lower seasonal carbon gain compared to nonbearing shoots., G. Marino, M. La Mantia, T. Caruso, F. P. Marra., and Obsahuje bibliografii