The age dependence of the photosynthetic performance, chlorophyll fluorescence and chloroplast ultrastructure of green form and Chl ft-deficient form (aurea) of tobacco Su/su mutant were compared. The most pronounced differences between the aurea and green tobacco found in young leaves diminished with leaf age. Slower accumulation of the photosynthetic pigments during the development of aurea leaves was accompanied by a slower accumulation of LHC antennae of both photosystems, particularly that of PS2, and by retention of an increase in the capacity of PS2 photochemistry, measured as Fy/FM The ratio Fv/Fm, however, increased rapidly during maturation of aurea leaves, and fmally the mature aurea leaves exhibited higher values of this ratio than the green ones. Rates of photosynthesis at saturating irradiance (Epiax) saturating CO2 concentration (/’sat) decreased with leaf age for both aurea and green tobacco, being always higher in aurea leaves than in leaves of green tobacco of comparable age. AU these characteristics indicated retarded development of aurea leaves. Also the chloroplast ultrastructure, particularly grana formation, exhibited slower development. The decrease in /Wx and with leaf age in both tobacco forms and retardation in the development of aurea leaves can explain higher value of usually found in aurea tobacco.
When exposed to Y-radiation (12, 8 and 3.5 kGy), the growth of beán seedlings {Phaseolus vulgaris L.) was stopped and after some hours or days the plants began to wilt in a dose-dependent manner, starting from the leaf rim. The rate of the dark respiration {R) of leaves increased and that of net photosynthesis {P^ was strongly reduced. The regulation of stomata opening and closure was lost and the stomatal conductance (g^) of the y-ray exposed plants was strongly reduced. The reduced was only partly due to either the partial or almost Ml stomata closure. Chlorophyll (Chl) fluorescence measurements with a two-wavelength fluorometer and a PAM fluorometer showed an increasingly reduced variable fluorescence Fy, lower values of Rfj, of ground fluorescence Fq, and of the fluorescence ratios Fy/F,n and Fy/F^. This indicated a damage to the photosynthetic apparatus. The increasing loss of photosynthetic pigments in the 350 krad exposed plants was also detected via an increase in the fluorescence ratio F690/F730. The performance of the light driven xanthophyll cycle (violaxanthin/zeaxanthin transformation) proceeded in the y-ray treated plants only at reduced rates. The y-ray damage of plants can best be detected by measurements of stomatal conductance, and various Chl fluorescence ratios such as Rf(j, Fy/Fj, and Fy/F^,.
Changes in the chlorophyll (Chl) and carotenoid (Car) contents and photosynthetic activity of leaves of three-year-old maple trees were studied under an extremely high irradiance (HI) (5 000 and 7 000 pmol m-2 s‘*) and subsequent low irradiance (LI) (10 pmol m-2 s‘*). Speciál attention was paid to a possible linear correlation between zeaxanthin (z) accumulation and the decrease in variable Chl fluorescence (ratio Fy/FnO during photoinhibitory treatment. Hl-induced violaxanthin (v) transformation into z was a fast one-step response proceeding within 2-5 min. Changes in the Chl a and b contents or in non-xanthophyll cycle Car were either not observed (30 min at 5 000 pmol m*2 s‘i) or a slight decline of the Chl a, lutein, 3-carotene and z contents only occurred at prolonged exposure (60 min at 7 000 pmol m'^ s'i)- Photosynthetic activity measured via the ratios (Fy/F^, Fy/F^, Rfj 690, Rfj 735) sank during this treatment to a much higher extent at 7 000 than at 5 000 pmol m'^ s'*. Ratios Fy/F<„ Rfd 690 and Rfj 735 proved to be better indicators of photoinhibition with a larger amplitudě ťhan the ratio Fy/F,„. Unlike literatuře reports, no linear correlation was found between Hl-induced decrease of fluorescence ratios and the z accumulation. Decrease of the fluorescence ratios appears to be biphasic in nátuře: fast initial fall which parallels the z formation is followed by a phase when ratios Fy/F^,, Fy/F^,, Rj^ 690 and Rf^ 735 sink further without any changes in the z pool. Regeneration of photosynthetic activity under LI also proceeded in two steps; a relatively fast increase in ratios with little or no changes in the z pool followed by a slow many hours' restoring of the former fluorescence ratios, paralleled by the z transformation into v. The back-reaction of z to v under LI was increasingly retarded with higher irradiance. Z formation and decrease in the fluorescence ratios are thus probably two Hl-induced processes which may be mutually independent.
Primary leaves of barley (Hordeum vulgare L.) plants, growing either in complete (H) oř nitrogen deficient nutrítion (H-N), were subjected to complex chlorophyll (Chl) a fluorescence measurement after an 8 or 14 d cultivation period. Ilie fluorescence spectra of H-N plants exhibited a higher ratio of the two maxima F690/F73S, caused predominantly by drastic decrease in Chl content. The ratio of Chl to carotenoids (a+b/x+c) decreased considerably in H-N leaves. In špite of high Rfd values (ratio of fluorescence decrease) in H-N leaves, indicating high efficiency of photochemical energy conversion, quenching analysis of H-N leaves showed a significantly higher coefiicient of non-photochemicď quenching, qjsip (i.e. higher proportion of heat loss). Fast fluorescence kinetics indicated slower reoxidation of primáty quencher (Q^) in H-N leaves.
Differences between photosynthetic characteristics of chlorophyll (Chl) 6-deficient aurea mutant (Su/su) and the green (su/su) variety of Nicotiana tabacum were tested. Fully mature leaves of 3-5-month-old plants grown in potted soil were investigated. Main differences were found as follows: Respective Chl a and b contents were 3 and 5 times lower in aurea plants, while xanthophylls and carotenes contents per unit of Chl were higher. The content of light-harvesting complex (LHC) was lower and LHC composition differed in aurea mutant. PS 1 activity calculated per unit of Chl content was higher in aurea mutant. The green variety showed the lower photosynthetic rates (Pn) at saturating irradiances whether calculated on the Chl or leaf area basis. At excessive light declined with green plants. Carboxylation efficiency (CE) (CO2 response slope of Pjj at low CO2 concentrations) was higher for aurea mutant. Time- integrated intercellular CO2 concentrations derived from ^^C discrimination were higher for aurea mutant (304 cm^ m'^) than for green plants (283 cm^ m'^), which together with higher mean stomatal conductance in aurea matched CE differences.
On the occasion of the 50th anniversary of the international journal Photosynthetica in 2017 we briefly report on the establishment of this journal and on Dr. Zdeněk Šesták, the renowned researcher of photosynthesis processes who, in cooperation with the Czechoslovak Academy of Sciences, founded this essential science journal in Prague in 1967., H. K. Lichtenthaler., Obsahuje bibliografii, and Ozvláštněné číslování stránek článku 1-6. teprve na ně se napojuje pokračování stránkování navazující na 1. číslo časopisu