Journal of Experimental Botany, Vol. 52, No. 357, pp. 811-820,
April 15, 2001
© 2001 Oxford University Press
Original Papers |
Responses to bleaching herbicides by leaf chloroplasts of maize plants grown at different temperatures
1 Dipartimento di Biologia, Università di Padova, Via U. Bassi 56/B, I-35131, Padova, Italy
2 Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale ‘Amedeo Avogadro’, Corso Borsalino 54, I-15100, Alessandria, Italy
Received 19 July 2000; Accepted 10 October 2000
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Abstract |
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 Top Abstract IntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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The effects of growth temperature on chloroplast responses to norflurazon and amitrole, two herbicides inhibiting carotenogenesis, at phytoene desaturation and lycopene cyclization, respectively, were studied in leaves of maize plants grown at 20 °C and 30 °C in light. At the lower temperature both chemicals caused severe photo-oxidative damage to chloroplasts. In organelles of norflurazon-treated leaves neither carotenoids nor chlorophylls were detectable and the thylakoid system was dismantled. In organelles of amitrole-treated leaves lycopene was accumulated, but small quantities of ß-carotene and xanthophylls were also produced. Moreover, some chlorophyll and a few inner membranes still persisted, although these latter were disarranged, lacking essential protein components and devoid of photosynthetic function. The increase in plant growth temperature to 30 °C did not change the norflurazon effects on carotenoid synthesis and the photo-oxidative damage suffered by chloroplasts. By contrast, in organelles of amitrole-treated leaves a large increase in photoprotective carotenoid biosynthesis occurred, with a consequent recovery of chlorophyll content, ultrastructural organization and thylakoid composition and functionality. This suggests that thermo-modulated steps could exist in the carotenogenic pathway, between the points inhibited by the two herbicides. Moreover it shows that, unlike C3 species, C4 species, such as maize, can express a strong tolerance to herbicides like amitrole, when supplied to plants growing at their optimum temperature conditions.
Key words: Amitrole, carotenoid biosynthesis, chloroplast photo-oxidation, norflurazon, Zea mays.
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Introduction |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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Carotenoids are integral components of photosynthetic membranes, involved in different tasks required for plastid organization and function. They contribute, as antenna pigments, to light harvesting for photosynthesis (Young et al., 1998
), and recently it has been ascertained that carotenoids can also operate in thylakoid membranes as stabilizers of the lipidic phase (Havaux, 1998). However, the most important role of these pigments is the protective one against photo-oxidative damage of photosynthetic apparatus, played by quenching triplet chlorophyll and singlet oxygen (Young, 1991).
The necessity for carotenoid photoprotection is underlined by chlorophyll bleaching and photodamage suffered by membranes and other chloroplast components of light-grown seedlings when deprived of these pigments due to herbicide treatments (Feierabend et al., 1979; Sagar and Briggs, 1990) or mutations (Faludi-Daniel et al., 1968; Walles, 1972; Nielsen, 1974).
Despite the essential role of carotenoids in preserving an efficient photosynthetic apparatus, on which plant survival depends, the knowledge of their biosynthesis in leaf chloroplasts is still rather scarce, most information about the carotenogenic pathway coming from studies carried out on chromoplasts of ripening fruits. Very little is known, moreover, regarding mechanisms regulating carotenoid synthesis in chloroplasts, which might be different from those operating in chromoplasts (Fraser et al., 1994).
However, previous research carried out on leaves of the lycopenic tigrina 034 mutant of barley (Casadoro et al., 1983) and of barley plants treated with amitrole, a bleaching herbicide inhibiting lycopene cyclization (Agnolucci et al., 1996), suggested that temperature could be a factor affecting carotenoid biosynthesis. In both cases, in fact, chloroplasts of plants grown at 20 °C accumulated lycopene and produced very low quantities of protective carotenoids, suffering chlorophyll photo-oxidation and great damage of thylakoid membranes. By contrast, the organelles of plants grown at 30 °C showed a notable increase in carotenoid biosynthesis, with recovery of their structure and function.
Thus, it was deemed important to widen the research by studying the leaf behaviour of maize plants treated with amitrole and grown at 20 °C and 30 °C. This was in order to clarify whether, in a C4 species which requires growth temperatures (30–35 °C) higher than a C3 (20–25 °C), changes in carotenoid production would occur in the same range of temperature in which they were noticed in barley. Moreover, in addition to amitrole, norflurazon, which inhibits phytoene desaturation, was used in order to analyse if plant responses to this latter herbicide would also be affected by plant growth temperature. The plant supply with the two chemicals affecting different points of the carotenogenic pathway might be useful to provide some information on the location of eventual thermo-modulated steps.
Carotenoid content and composition, chlorophyll amounts and chloroplast membrane organization and functionality were analysed with biochemical, ultrastructural and immunological methods in leaves of maize plants treated with herbicides and grown at the two different temperatures.
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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Plant material
Grains of maize (Zea mays L. cv. Dekalb DK 300) were germinated and seedlings were grown at 20 °C or 30 °C in a growth chamber with a 12 h photoperiod, light of 200 µmol m-2 s-1 and relative humidity of 80%, on an inert substrate (vermiculite) moistened with water (control plants), 200 µM AM or 100 µM NF. A plant series was also grown in the same way and in the same chamber on water or on the two herbicide solutions for 5 d at 20 °C and then moved to 30 °C.
All the analyses were carried out on the second leaf of 9–10-d-old plants.
Total pigment analysis
Total chlorophylls and carotenoids from leaf tissues were analysed in a spectrophotometer (GBC UV/VIS 918) after extraction with N,N-dimethylformamide. The extinction coefficients proposed earlier (Lichtenthaler, 1989) were used to determine the pigment concentrations.
Reverse phase HPLC
One gram of fresh leaf tissue was ground in a mortar with liquid nitrogen and 200 mg of NaHCO3, in green safe light. The fine powder was transferred with 50 ml of acetone to a Buchner filter funnel and washed with 10 ml of ethyl acetate. After evaporation up to a final volume of 1 ml, 50 µl of the extract was injected into an Ultrasphere C18 reverse phase ion pair column (ODS 250x4.6 mm I.D., 5 µm) with a guard column. Elution was performed by using a concave gradient of 80% methanol to 100% ethyl acetate for 16 min. The gradient was generated by two pumps controlled by a system controller, with a flow rate of 0.750 ml min-1. The eluted pigments were detected at 430 nm and identified by comparing the obtained retention times with those of published chromatograms (Casadoro et al., 1983; Agnolucci et al., 1996).
Assay of leaf/environment oxygen exchanges
Oxygen release or uptake was measured with an oxygen electrode (YSI Model 53, Yellow Springs Instruments) on small pieces of leaf tissues (according to the method adopted by Ishii et al., 1977).
Electron microscopy
Samples from leaf tissues were fixed overnight at 4 °C in 3% glutaraldehyde in 0.1 M sodium cacodylate (pH 6.9) and then processed for the electron microscopy (Rascio et al., 1991).
Ultrathin sections, cut with an ultramicrotome (Ultracut, Reichert-Jung), were observed with a transmission electron microscope (TEM 300, Hitachi) operating at 75 kV.
All the observations were focused on chloroplasts of mesophyll cells, because in maize leaves only the organelles of these cells show an inner membrane system with grana and stroma thylakoids and contain photosystem II.
Isolation of thylakoid membranes
Thylakoids were isolated by grinding leaf tissues in ice-cold buffer containing 0.1 mol l-1 Tricine (pH 7.8), 5 mmol l-1 MgCl2, 15 mmol l-1 NaCl, and 0.33 mol l-1 sorbitol. After centrifugation at 10 000 g for 20 min, the pellet was resuspended in 50 mmol l-1 HEPES (pH 7.2), 5 mmol l-1 MgCl2 and centrifuged as before. Thylakoids were then resuspended in the same buffer containing 0.1 mol l-1 sorbitol, recentrifuged at 40 000 g for 10 min and finally resuspended in a solution containing 50 mmol l-1 NaHCO3, 50 mmol l-1 dithiothreitol and 20% sucrose.
SDS-PAGE and immunoblotting
Gel electrophoresis in the presence of 0.1% SDS and 6 mol l-1 urea was carried out as described earlier (Laemmli, 1970), with modifications (Gounaris et al., 1988), using a 12–18% linear acrylamide gradient. Forty micrograms of protein per line were loaded. Protein concentration was measured using the Bio-Rad Protein Assay method (Bio-Rad) (Bradford, 1976). Proteins were electroblotted onto a nitrocellulose column (Sartorius, 0.45 µm) (Dunn, 1986). Before immunodetection, proteins were visualized by staining the filters with 0.2% Ponceau S in 3% trichloracetic acid. Filters, blocked with 10% skimmed milk in TBS, were incubated with rabbit primary antibody and biotinylated goat-antirabbit IgG and then with streptavidin alkaline phosphatase-conjugated (Sigma). Coloured bands were observed upon the addition of nitroblue tetrazolium and 4-chloro-5-bromo-p-indolylphosphate.
Polyclonal antibodies against some polypeptides of PSII were used in this study: anti D1 (Barbato et al., 1991) and anti D2 (Barbato et al., 1992a) of the reaction centre, anti CP43 and anti CP47 of the inner antennae (Barbato et al., 1992b), anti LHCII (Barbato et al., 1992b) and anti 22 kDa (Barbato et al., 1995). Antibody against cyt f belonging to the cyt b6/f complex, was also used. This last antibody was a gift of Dr E Bergantino (Department of Biology, University of Padova).
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Results and discussion |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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Plants grown at 20 °C
Phenotypes:
Maize plants submitted to the distinct experimental treatments showed very different phenotypes (Fig. 1
). Compared to the green control plants, the leaves of plants supplied with AM were pale yellow, whereas the NF-treated ones exhibited completely white leaves. Moreover, plants treated with both herbicides were shorter than the control ones.
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This reduced growth could be explained by curtailed availability of organic nutrients due to lack of green photosynthetic tissues. However, it could also depend on an abscisic acid (ABA) deficiency, related to inhibited carotenogenesis (Gamble and Mullet, 1986
; Neill et al., 1986; Zeevaart and Creelman, 1988), xanthophylls being involved in ABA biosynthetic pathway (Liotenberg et al., 1999; Cutler and Krochko, 1999). A slower growth rate has also been noticed in plants of ABA-deficient ‘wilty’ mutant of pea (De Bruijn et al., 1993) and ascribed to the disturbed water relations caused by the diminished hormone production.
Photosynthetic pigments:
The pigment analyses (Fig. 2a) and their identification by HPLC (Fig. 2b), showed the presence of some coloured carotenoids and chlorophylls in organelles of AM-treated leaves, although very reduced with respect to those of the control ones (Fig. 2a). Moreover, the HPLC analyses revealed a peculiar carotenoid spectrum where, besides small quantities of main xanthophylls and ß-carotene, the lycopene peak was also recognizable (Fig. 2b).
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In maize chloroplasts, as already shown in barley ones (Agnolucci et al., 1996
), the AM-treatment, inhibiting lycopene cyclization, still permitted the synthesis of detectable carotenoid amounts, and this could account for some chlorophyll photoprotection. Interestingly, in organelles of barley lycopenic mutants a comparable situation, with lycopene accumulation and the presence of small quantities of photoprotective carotenoids and chlorophylls was noticed (Casadoro et al., 1983).
Differently, the absence of any coloured carotenoids and chlorophylls was noticed in leaf plastids of NF-treated plants (Fig. 1a
, b), thus showing that inhibition of phytoene desaturase and interruption of photoprotective pigment biosynthesis brought about the complete photo-oxidation and disappearance of chlorophylls.
Chloroplast ultrastructure:
In the mesophyll cells of control leaves the mature chloroplasts showed an abundant and well organized inner membrane system and a ribosome-rich stroma (Fig. 3a), while in the corresponding tissues of AM-treated leaves severe damage was suffered by chloroplasts (Fig. 3b), in which loss of part of the ribosomes and reduction and alteration of the thylakoid system occurred. This latter consisted of a few membranes irregularly distributed in the stroma or tightly pressed to form very electron-dense stacks. These ultrastructural features, seem to be characteristic of lycopene-accumulating organelles which have been described by other authors in damaged chloroplasts from maize (Hudák, 1998) and barley (Nielsen, 1974; Casadoro et al., 1983) lycopenic mutants, and also noticed in organelles of AM-treated barley plants (Agnolucci et al., 1996). Thus, in chloroplasts of AM-treated plants, the maintained ability to synthesize small quantities of photoprotective carotenoids led to the preservation of some chlorophyll, as well as a certain number of inner membranes.
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In the mesophyll cells of NF-supplied leaves, the plastids looked impressively damaged. They were almost devoid of thylakoids and with few ribosomes recognizable in a rather empty stroma (Fig. 3c
). Thus, the total carotenoid-deficiency gave rise to photo-oxidative events which, besides chlorophyll degradation, brought about dismantling of thylakoids and demolition of most 70S ribosomes.
Thylakoid membrane composition:
The analysis of thylakoid composition, carried out on chloroplasts of control and AM-treated plants showed that, besides organization, thylakoid composition was also dramatically altered in the organelles of the herbicide-supplied leaves. Western analysis, accomplished with antibodies against essential components of PSII, particularly sensitive to photo-oxidative damage (Aro et al., 1993), revealed that these membranes lacked chlorophyll a-binding polypeptides encoded by the organelle DNA, such as D1 and D2 of the reaction centre and the inner antennae CP43 and CP47 apoprotein (Fig. 4a). However, in the altered thylakoids the same analysis showed a certain amount, although reduced with respect to that of control chloroplasts, of the cyt f apoprotein (Fig. 4c), which is also encoded by the plastid DNA.
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The finding of this latter polypeptide showed that, in contrast to the assumption by Feierabend et al., ribosomes still present in damaged organelles were functional and able to sustain a certain, though limited, protein synthesis (Feierabend et al., 1979
). This suggested that the total lack of chlorophyll a-binding polypeptides could be due to degradation of their newly-synthesized molecules, as a consequence of chlorophyll photo-oxidation, preventing the pigment–protein cotraductional linkage, necessary for apoprotein stabilization (Mullet et al., 1990).
PSII polypeptides encoded by nuclear DNA, such as 22 kDa, and the chlorophyll a/b-binding apoproteins of LHCII were found in the anomalous membranes (Fig. 4b). Their quantities were also lower than those of control chloroplasts. However, it has to be considered that in the photo-oxidized organelles the protein insertion and/or stability in the impaired membranes might be negatively affected. As regards the LHCII proteins, their stabilization in altered thylakoids might plausibly depend on the ability to bind the limited but available quantities of chlorophylls, maintained by pigment turnover. In fact, even though chlorophylls are photo-oxidized afterward, their biosynthesis still occurs in carotenoid-deficient plastids (Frosch et al., 1979).
Leaf/environment oxygen exchanges:
As expected, no emission, but only oxygen absorption occurred in leaf tissues of both AM- and NF-treated plants (Fig. 5). Moreover, the values of oxygen uptake were similar when measured in light or in darkness and comparable with the respiratory consumption of control leaves. This indicated that leaf tissues supplied with herbicides lacked any trace of photosynthetic activity.
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The specific targets of bleaching herbicides are indeed chloroplasts, while it is generally assumed that they do not affect the structure and functionality of other cellular components, such as mitochondria (Feierabend and Shubert, 1978
; Feierabend et al., 1979; Taylor, 1989; Sagar and Briggs, 1990; Zito et al., 1995; Agnolucci et al., 1996). However, it has been noticed that some of these chemicals, including amitrole, can also inhibit the activity of the peroxisomal catalase (Feierabend and Shubert, 1978; Feierabend et al., 1979)
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Plant grown at 30 °C |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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Phenotypes:
The increase in growth temperature led, in AM-treated plants, to an astonishing recovery of leaf pigmentation as well as of growth rate, both of which now approached those of control plants (Fig. 1b
). In contrast, it did not lead to a change in the appearance of NF-treated plants, which were reduced in height and with totally white leaves (Fig. 1b).
Photosynthetic pigments:
Pigment analyses (Fig. 6a) and chromatograms obtained by HPLC (Fig. 6b) showed that in AM-treated leaves both carotenoid and chlorophyll amounts (Fig. 6a) underwent a great improvement, reaching values approaching those of control leaves. Moreover, HPLC chromatograms (Fig. 6b) showed a normalization of the carotenoid spectrum, with the disappearance of lycopene and an increase of the ß-carotene and xanthophyll peaks. In this case, the rise in plant growth temperature drastically reduced the inhibitory effects of herbicide on carotenogenesis, leading to a substantial recovery of pigment biosynthesis and to a consequent chlorophyll protection against photo-oxidation.
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These events, occurring in maize plants at 30 °C, confirmed what had already been noticed, at the same temperature, in barley plants treated with amitrole (Zito et al., 1995
; Agnolucci et al., 1996) as well as in barley lycopenic mutant tigrina 034 (Casadoro et al., 1983), which did not undergo treatment with exogenous herbicide.
In contrast, the complete absence of carotenoids and chlorophylls in NF-treated leaves (Fig. 6a, b) demonstrated that the rise in growth temperature did not interfere with the inhibitory effect of herbicide on photoprotective pigment biosynthesis.
Plastid ultrastructure:
The large increase in carotenoid biosynthesis gave rise to a good recovery of plastid ultrastructure in AM-treated leaves. As in the well organized chloroplasts of control leaves (not shown), the organelles of mesophyll cells (Fig. 7a) exhibited a rather abundant membrane system with grana and stroma thylakoids regularly distributed in a rather ribosome-rich stroma. By contrast, the total lack of photoprotective pigments was responsible for the dramatic damage still suffered by plastids of NF-treated leaves, where, in the stroma devoid of most ribosomes, vesicles and membrane profiles could occasionally be found (Fig. 7b).
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Thylakoid membrane composition:
The achievement of the correct thylakoid organization was paralleled, in AM-treated chloroplasts, by normalization of their protein composition. The immunoblotting analyses (Fig. 8) revealed comparable amounts of all the polypeptides tested, encoded by both nucleus (Fig. 8b) and plastid (Fig. 8a, c) DNA, in membranes of control and herbicide-supplied organelles, including the chlorophyll a-binding proteins of the PSII core, not found in the altered thylakoids of AM-treated plants grown at 20 °C.
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Leaf/environment oxygen exchanges:
Likewise, the increase in plant growth temperature led to a substantial recovery of photosynthetic activity in AM-treated leaves, which, evaluated as oxygen emission in light, exceeded 80% of that of control plants (Fig. 9). By contrast, only oxygen uptake was still recorded in NF-treated leaves.
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Plants grown at 20–30 °C |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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In a further experiment, plants grown for 5 d at 20 °C were moved to 30 °C. As shown in Fig. 1c
, tissues of AM-treated leaves differentiated from the basal meristem at the two temperatures exhibited a very different pigmentation. The older leaf regions, which had grown at 20 °C and contained damaged carotenoid-deficient plastids, were pale yellow, whereas the younger leaf regions, grown at 30 °C, looked green, due to the greatly improved carotenoid biosynthesis and the previously described normalization of the other chloroplast parameters. Moreover, the persistence of pale yellow leaf tissues at 30 °C revealed that photodamage suffered by chloroplasts at 20 °C was irreversible and did not permit organelle recovery with the rise in plant growth temperature. On the other hand, the ability of the leaf to produce green tissues at the higher temperature showed that herbicide-damaging effects at 20 °C did not affect the proplastids of meristematic cells. These organelles, still devoid of chlorophylls, did not undergo photo-oxidative damage due to carotenoid-deficiency and could give rise to green chloroplasts when the temperature rise led to improved carotenoid biosynthesis.
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Conclusions |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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The experimental results show that at the lower plant growth temperature, both amitrole and norflurazon cause dramatic damage to maize leaf chloroplasts, due to their inhibitory effects on carotenoid production. The NF-treatment, which interrupts the biosynthetic pathway at the level of phytoene desaturation, brings about a complete chlorophyll photo-oxidation and photosynthetic membrane demolition. The treatment with amitrole, hampering lycopene cyclization, still permits reduced production of photoprotective pigments, with preservation of small chlorophyll quantities as well as of some inner membranes. These latter, however, are greatly altered and totally deprived of photosynthetic activity due to the photo-oxidative degradation of essential components of the electron transport chain.
As far as the responses to herbicides are concerned, plant behaviour drastically changes with the rise in growth temperature. At 30 °C the NF-treatment still causes the chloroplast damage noticed at 20 °C, with total carotenoid and chlorophyll loss and thylakoid dismantling. By contrast, in organelles of AM-treated leaves the damage found at 20 °C is quite subdued. Carotenoid synthesis is greatly improved and quite normalized, with the disappearance of lycopene and the production of ß-carotene and xanthophyll amounts near to those of control plants. Consequently, the chlorophyll content, the correct thylakoid organization and composition and the photosynthetic functionality are all recovered.
The essential event, occurring with the increase of plant growth temperature and accounting for normalization of chloroplast parameters is the regained ability of AM-treated organelles to carry out carotenoid synthesis, as also shown by plant leaves grown first at 20 °C and then at 30 °C.
The hypothesis that this event might be due to a herbicide thermo-instability, with its faster degradation at the higher temperature was excluded by previous analyses on barley, which showed comparable AM quantities in leaves grown at 20 °C or 30 °C (Zito et al., 1995; Agnolucci et al., 1996). Moreover, the same temperature effect on carotenogenesis occurred in barley lycopenic mutant tigrina 034 (Casadoro et al., 1983), where the lycopene cyclization was inhibited by mutation and not by herbicide supply.
Thus, in maize, as already found in barley, the carotenoid biosynthetic pathway seems to be sensitive to temperature. This might be due to the existence of thermo-modulable step(s) in which some changes in membrane environment, such as increased fluidity or modified interaction between lipidic components and enzymatic proteins, as well as conformational changes of these latter might play a role. The plant responses to herbicides suggest that this thermo-modulability might involve reactions between the NF-inhibited step, not affected by temperature increase, and the AM-inhibited one.
Recently, ß-carotene and xanthophyll synthesis through an alternative way, bypassing the lycopene cyclization, has been proposed for tomato chromoplasts (Pecker et al., 1996) and for Arabidopsis chloroplasts (Cunningham et al., 1996). Thus the possibility might be considered that this way is common in leaf chloroplasts and that its activity and rate depends on plant growth temperature.
Information worthy of note emerging from this experimental work is that in maize chloroplasts the temperature range, in which most of the amitrole inhibitory effect on carotenogenesis occurs, is the same as that noted in barley. This is of particular interest, considering that barley is a C3 plant growing well at 20 °C, whereas maize, as a C4, prefers higher growth temperatures of 30–35 °C.
This means that plants such as barley, or other C3 species with the same temperature requirements, are sensitive to amitrole-damaging effects and cannot survive its supply at their usual growth temperature. By contrast, plants such as maize or other C4 species can express a strong tolerance to the same herbicide, and probably to other chemicals operating in the same way, when supplied to the plants growing at their best temperature conditions.
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Acknowledgments |
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The authors are grateful to Dr Elisabetta Bergantino for the gift of the antibody against cyt f. This research was supported by grants from National Research Council of Italy and from MURST.
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Notes |
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3 To whom correspondence should be addressed. Fax: +39 49 8276280. E-mail: rascio{at}civ.bio.unipd.it
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Abbreviations |
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AM, amitrole; amitrole, (2-amino-1,2,4-triazole); BSA, bovine serum albumin; CP43, chlorophyll-protein 43; CP47, chlorophyll-protein 47; cyt, cytochrome; HEPES, N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid; HPLC, high performance liquid chromatography; LHCII, light harvesting chlorophyll a/b-protein complex of PSII; NF, norflurazon (4-chloro-5-(methylamino)-2-(
,,-trifluoro-m-tolyl)-3-(2H)-pyridazinone); PBS, phosphate buffer saline; PSII, photosystem II; PAGE, polyacrylamide gel electrophoresis; SDS, sodium dodecyl sulphate; TBS, TRIS buffer saline; TRIS, (hydroxymethyl); aminomethane buffer saline; Tricine, N-(tris-hydroxymethyl)glycine. |
References |
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TopAbstractIntroductionMaterials and methodsResults and discussionPlant grown at 30...Plants grown at 20-30...ConclusionsReferences |
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