Soybean [Glycine max (L.) cv. Jack] grown in open top chambers under controlled laboratory and field conditions was ušed to study the acclimation of leaf gas exchange processes to CO2 enrichment. Air inside the open top chambers was maintained at either 700-800 or 350-400 pmol(C02) mol'^(air). Leaf gas exchange rates were measured for some plants switched between treatments. When measmed in the C02-emiched atmosphere, stomatal conductances (gg) were higher in leaves grown in C02-enriched atmospheres than in those grown under ambient conditions, and the lower gg values for plants in the C02-enriched atmospheres were limiting to leaf net photosynthetic CO2 exchange rates (Pn). of enriched leaves was higher than those of the ambient Controls when measured at elevated CO2 levels in both controlled environment and field studies, while it was depressed in enriched leaves when measured imder ambient CO2 conditions, and this drop in Pn did not recover until 6-15 d after plants were placed back in ambient conditions.
Diumal changes in chlorophyll (Chl) a fluorescence characteristics of sun-exposed and shade leaves of some tropical and temperate tree species growing under fíeld conditions on sunny and cloudy days during summer were recorded. Significant reduction in photochemical efficiency of photosystem (PS) 2 measured as ratio during periods of maximum irradiance was observed in sun-exposed leaves of some plants. The extent of this reduction was probably a function of the plant species. Among the tropical species tested, Boehmeria rugulosa, Celíis ausíralis, Dalbergia sissoo, Eugenia jambolana and Grewia optiva showed maximum reduction (15-22 %), whereas species like Ficus racemosa and Sapium sebiferum showed least dechne (< 7 %) in the F^/F^ ratio. On the other hand, no significant reduction in this ratio was observed in Bauhinia purpurea. Temperate species, v/z. Acer oblongum and Aesculus indica, were most susceptible to high irradiances. Prolonged exposure of these plants to high irradiances resulted in lesion development in their leaves characterized by reduction in pigment contents and Fy/F^, ratio. Plant species with considerable midday dechne in Fy/Fn, ratio showed (7) slight but significant rise in initial fluorescence (Fq), (2) pronounced decrease in F^ value, and (3) significant reduction in area over the curve between Fq and Fj„ indicating the pool size of electron acceptors on the reducing side of PS2. The depression in Fy/F^ ratio though reversible could not be alleviated even after watering the plants at hourly intervals. No reduction in Fy/F^, was observed in shade leaves of the same plants and/or when measurements were taken on cloudy days. Hence high solar radiation and high atmospheric evaporative demand existing during summer period could probably be the major contributoiy factors for this reduction.
A theory of spectra and excitation dynamics in antenna based on the notion of exciton interactions in the cyclic structures of light-harvesting pigments is reported. The theory provides an explanation for the picosecond absorbance difference spectra, the induced absorption anisotropy decay, the anomalously high bleaching valné, as well as for the fluorescence spectra, kinetics and depolarizatio
Spectral absoiptance of greenhouse tomato (Lycopersicon esculentum Milí.) canopy (sunny day, LAI = 2.54) varied between 87-89 %. Absoiptance of smáli tomato fruits was 77 % of PAR energy (spectral reflectance was 22 % and transmittance 1 %). The difíusion resistance to COj of the parenchyma extemal layer with epidermis in smáli fruits reached 25 s cm‘i and in large green fruits 75 s cm-i. At the atmospheric CO2 concentration (330 cm^ m*^) and the quantum flux density of PAR 800 pmol m'2 s'* the steady statě CO2 evolution rate was found to be slightly below its compensation value [-0.06 mg(C02) kg-i(d.m.) s-i]. The net photosynthetic rate in smail tomato fruits was 0.3 mg(C02) kg-i(d.m.) s'*, whereas in a large green tomato it reached 0.16 mg(C02) kg-i(d.m.) s’T Intemal CO2 concentration in smáli tomato frnits by the light was 2 300 cm3(C02) m-3 and in the dark 2 900 cm3(C02) m*3. Even under the optimal irradiance CO2 difíusion proceeded always from fruits to the environment.
Effects of heat pre-treatment (60 oC for 15 min) on the chlorophyll (Chl) bleaching and excitation energy transfer in thylakoids, isolated from the cucumber cotyledons, were studied by anaiysis of the overlapping absorption and the low temperature fluorescence spectra. The Chl forms C678 and C672 appeared to be the most heat-susceptible components, whereas C684 was found to be very heat-stable. Subsequent exposure of the thylakoid suspension to a high photon flux density (ca. 3 500 pmol m‘2 s'i) caused further bleaching of all the tested forms: ca. 8-20 or 2-5 % of chlorophyll was degraded duríng the initial (0-4 min) or later (4-10 min) period of irradiation, respectively. The heat pre-treatment of thylakoids led to the decrease of the 472 and 486 nm bands in Chl fluorescence excitation spectrum and the 730 nm band in the Chl fluorescence emission spectrum. The F730/F685 ratio decreased by ca. 4-, 3- or 2-fold when excited with the wavelengths of 437, 742 or 486 nm, respectively. These ratios increased by 60-90 % after 10 min irradiation with high photon flnx density.
Pathway of protochlorophyilide (Pchlide) biosynthesis, properties of Pchlide in vitro and in vivo, its in vivo localization, structure, localization and properties of the enzyme NADPH-Pchlide oxidoreductase, and phototransfonnation and dark reduction of Pchlide to chlorophyllide are reviewed.
Room temperature absorbance and 77 K fluorescence measurements were ušed in order to identity Pchlide and Chlide spectral forms involved in protochlorophyllide photoreductíon in greening leaves of barley. Pchlide55o (the subscript refers to the in vivo absorbance maximum of the pigment) is the main photoactíve Pchlide throughout the first 8 h of greening. Its photoreductíon triggers a succession of Chl(ide) spectral forms that are identícal to those normally found after photoreductíon in uitírradiated leaves. Afler an actinic radiation pulse, Chlide5g4 appears within 2 s from an intermediate at shorter wavelength and is transformed to Chlide572 in less than 2 min. The time-scale of the shifts is remarkably shorter than in unirradiated leaves, which is consistent with the acceleratíon of Chl accumulatíon during greening. Pchlide63o and Pchlide64o act as precursors of Pchlide65o during its regeneration, which exhibits a marked inhibition at temperatures above 30 °C.