During a 5-20 d growth at moderate salinity (7 dS m‘i) in rice seedlings of salt sensitive cultivars Ratna and Jaya a larger decrease in chlorophyll (Chl) a and b contents was observed than in tolerant cvs. CSR-1 and CSR-3. At higher salinity (14 dS m'i) about 40 % declines in both whole chain electron transport and photosystem (PS) 2 activities were observed in the tolerant cvs. and about 62 to 67 % declines in the sensitive ones. No apparent change in PSI activity was observed due to salinization in the both sets of cultivars. Higher rate of Hill reaction was observed in chloroplasts ffom salt stressed seedlings of tolerant cultivars whereas inhibition in this activity was found in the sensitive ones. Chloroplasts isolated from stressed seedlings of sensitive cultivars showed about 31 % reduction in fluorescence emission at 685 nm as well as a major decrease in absorption with shifts in peaks in the visible region of spectrum. Thus salt sensitivity in rice is associated with decreased contents of Chls and carotenoids, PS2 and Hill reaction activities, and fluorescence emission.
In the hypocotyls of Rhizophora mucronata Lamk. and R. apiculata Bl. during viviparous germination the concentrations of chlorophyll (Chl) and total sugars, and net photosynthetic rate (P^) were increased quadratically, while linear relationship existed between starch content and the developmental phase. R. apicuiata hypocotyls had a higher value of as well as higher Chl, sugar and starch contents than hypocotyls of R. mucronata.
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.
CO2 (40, 200, 400 loM) was added to the root systém of 10-d-old pea plants (Pisum sativum L. cv. Ran). The Co2'''-excess caused a reduction in the plant fresh and diy masses and water and chlorophyll contents. The rates of photosynthesis and transpiration decreased, while proline content and stomata resistance increased. The dramatic effect of Co2+-toxicity was expressed both in an inhibition of ribulose 1,5- bisphosphate (RuBP) carboxylase activity and a stimulation of RuBP-oxygenase and phosphoenolpyruvate carboxylase activities on the 4‘h day of cnltivation of plants in a solution of 400 pM C6^*.
Rice (Oryza sativa L.) plants were grown in nutríent solutíon containing concentrations of Cu vaiying from deficiency to toxicity [0.002-6.25 g(Cu) m"^]. Shoot contents of Cu, Mn and Fe were measured as well as the concentrations of plastocyanin (PC), plastoquinone (PQ) and cytochromes (cyt) f, 6553, 6-559up, and b- 559hp. While Cu concentration increased wilh increasing levels of metal in the solutíon, Mn and Fe concentrations progressively decreased after Cu treatments higher than 0.05 g m‘3. On a chlorophyll basis, the contents of PC and cyt/decreased after the 0.01 g(Cu) m'^ Cu treatonent, while the contents of cyt f>-559Lp and b- 559hp did not show any apparent conelatíon, and the PQ concentration sharply increased with increasing Cu toxicity. Membrane permeability and acid RNAse activity were enhanced with increasing Cu concentration.
Fluorescence excitation spectra of different protochlorophyll(ide) (PChlide) a forms in intact etiolated cucumber cotyledons showed a pronounced increase in intensity of the 390 nm band in comparison with spectra of the pigment in Solutions. The native PChlide F657 also had an additional band at 360 nm in its excitation spectra, which disappeared after leaf homogenization and was restored by addition of dithionite. The restoration correlated with changes around 340 nm in the excitation spectrum of blue-green fluorescence. In consideration of this fact, the 360 nm band seems to correspond to energy transfer from NADPH to PChlide a. After the onset of irradiation a new band appeared at 380 nm in the excitation spectrum of the main pigment fluorescence, which was very similar to that found in the absorption spectinm of isolated Chl a. Moreover, in the Soret region the excitation spectrum had a double band splitting which disappeared only after the Shibata shift, simultaneously with the disappearance of the 360 nm band. Besides the well-known PChl(ide) F633, F642, and F657 forms, etiolated cucumber cotyledons háve emission at 673 nm. Its excitation spectrum was hardly distinguishable from the PChlide F657 fluorescence excitation spectrum in etiolated samples. In the irradiated plants this band had excitation spectrum of monomeric Chl a. The intensity of band at 673 run decreased and transiently increased after PChlide photoconversion. The dynamics of these fluorescence intensity changes under inadiation showed positive correlation both with PChlide F657 and with PChl(ide) F642, indicating the short wavelength Chl a preexistence in etiolated plants and its additional formation after the onset of irradiation.
Chloroplast polypeptide composition of rice plants {Oryza sativa L. cv. Safari) exposed for 30 d to increasing Cu ion concentrations in a hydroponie growth medium was analyised. The conventional discontinuous SDS-aerylamide gel electrophoretic systém, the SDS PhastGel (Pharmacia Fine Chemicals) gradient 10-15 and tíie 5-8 pH range polyaciylamide isoelectric focusing of the PhastSystem separation and development technique were ušed. With Cu levels greater than 0.25 g m'^ die polypeptide bands with apparent molecular masses of 42/41, 33/32, 21/20 and 19/18 kDa deereased in the PhastSystem separation and development systém, whereas with the conventional discontinuous SDS buffer systém gel electrophoresis all these bands disappeared except the 33/32 kDa band. Also, under the latter systém excess Cu deereased the 56/55, 55/54, 26 and 22 kDa bands which was not shown by the PhastSystem separation and development technique. Furthermore, in the discontinuous SDS-PAGE high Cu levels induced the disappearance of the 16.5, 14.5 and 12 kDa bands, which were again not shown by the PhastSystem separation and development technique; yet the opposite oceurred with the 49 kDa band of the gel profiles. Polyacrylamide isoelectric focusing of thyiakoid membranes showed in all Cu treatments two major bands at pl 7.7 and <5 and a minor one at pl 6.48. At Cu concentrations lower than 1.25 g m'^ two additional smáli bands appeared (pl 5.5 and 5.18); and at Cu concentrations greater than 0.25 g m'^ these smáli bands were replaced by four different ones (pl 6.7, 6.05, 5.35, 5.25).
Chlorophyll (Chl) fluorescence technique was ušed to monitor Cu damage in photosynthetic process in intact leaves of a Cu-tolerant {Silene conipacla) and a non- Cu-tolerant {Thlaspi ochroleucum) species. The initial fluorescence level (Fq) increased whereas the variable fluorescence (Fy) decreased in T. ochroleucum under low and high Cu-dose, suggesting injuries both in reaction centie level and in photooxidizing side of photosystem 2 (PS2). The photochemistiy activity of PS2, Fy/Fp, revealed a slight increase under 8 pM Cu in both species, while at 160 pM of Cu a strong inhibition in T. ochroleucum was observed. The Fp/F() ratio appeared to increase under low Cu dose, however the high Cu dose in nutrient solution resulted in damage to the thylakoid structure affecting the PS2 donor and acceptor side, mainly in T. ochroleucum. The slow part of the Chl fluorescence induction cuiwe was affected more by Cu stress, than the fast one. At low Cu concentration the Rfd value increased in S. compacla but decreased in T. ochroleucum. Fligh Cu dose induced an almost complete inhibition of this parameter, that was more severe in the non-tolerant plants. Yet, low Cu dose enhanced the Chl content in S. compacla but on exposure to 160 pM Cu the symptoms of chlorosis were more visible in T. ochroleucum. Thus, excess of Cu has direct negative effects on the photosynthetic electron transport that may be accounted for by the destruction of the photosynthetic pigments.
Following treatment with 5-aminolevulinic acid the activity of iS-adenosyl-L- methionineimagnesium protoporphyrin IX methyltransferase (EC 2.1.1.11) in wheat leaves decreased, whereas monomethyl ester magnesium protoporphyrin IX and protochlorophyllide accumulated. The inactivation of the enzyme was the result of a cessation of the enzyme-product complex dissociation because of the limited number of porphyrin-binding sites on the structural carrier.