枫香秋季变色期叶色变化及其生理基础

为探究秋季枫叶呈色的关键生理因素,该文以转色期叶色为绿色、黄色和红色的枫香单株为试材,研究了L^*、a^*、b^*值变化与叶片色素、可溶性糖及可溶性蛋白质含量变化的相关性。结果表明:(1)在变色期,3种色彩枫香叶片叶绿素a、叶绿素b、总叶绿素和类胡萝卜素均大量降解,花色素苷不同程度积累。(2)绿色叶单株叶绿素和类胡萝卜素始终保持较高含量,花色素苷含量上升4.2倍,叶片内色素含量比值始终保持稳定; 黄色叶单株叶绿素和类胡萝卜素含量最低,花色素苷含量上升4.4倍,b^*值与叶绿素含量极显著负相关,与类胡萝卜素含量显著负相关,与花色素苷/类胡萝卜素含量比值极显著正相关; 红色叶单株叶绿素和类胡萝卜素含量略高于黄色叶单株,花色素苷含量上升27.2倍,a^*值与叶绿素含量、类胡萝卜素含量极显著负相关,与花色素苷含量显著正相关,与色素含量比值无显著相关性。(3)红色叶单株具有较高的可溶性糖含量和可溶性蛋白质含量。因此,在枫香叶片变色期,保持较高的叶绿素和类胡萝卜素含量,维持色素含量比值稳定使叶片呈现绿色; 叶绿素和类胡萝卜素的大量降解,以及花色素苷/类胡萝卜素含量比值的升高使叶片呈现黄色; 叶绿素的降解和花色素苷的大量合成使叶片呈现红色。     

Carotenoid contents in leaves grown under various light intensities

The catotenoid content in the leaves of mosses, pteridophyt, gymnosperms and angiosperms (dicotyledons and monocotyledons0 growing in the sunlight and in the shade was studied. In the leaves of the plants growing in the shade the total carotenoid content and β-carotene increases as does chlorophyll. On the other hand, in the leaves of all plants a marked increase in lutein content was observed only in the leaves exposed to sunlight. The data indicates that carotenoids play a significant role, equal to that of chlorophyll, as ‘antennae’ absorbing light in the plants.     

光质和除草剂norflurazon对欧洲赤松子叶质体色素形成的影响

本文研究了不同光质和类胡萝卜素专一抑制剂 norflurazon 对欧洲赤松(Pinussylvestris)子叶叶绿体色素形成的影响,所得结果如下:1.在远红光下,类胡萝卜素相对合成速率大于叶绿素的合成速率,而在红光下恰恰相反。2.在白光下,当类胡萝卜素合成受抑制时,叶绿素的合成速率也有所降低。但是叶绿素相对积累量比类胡萝卜素大得多,叶绿素与类胡萝卜素的分子比增大到10:1,说明这两种色素的合成与积累有相当大的独立性。3.把连续在远红光下类胡萝卜素合成受抑制(含量为正常幼苗的30%)的松苗,移入强白光下4小时后,其总叶绿素和类胡萝卜素都有增加,表明只要有少量类胡萝卜素存在,光对色素合成的促进仍大于光氧化破坏。     

Consequences of chlorophyll deficiency for leaf carotenoid composition in tobacco synthesizing glutamate 1-semialdehyde aminotransferase antisense RNA: dependency on developmental age and growth light

Transgenic tobacco (Nicotiana tabacum), with a reduced chlorophyll content of up to less than 10% of the wild-type level due to a different expression of antisense RNA coding for glutamate 1-semialdehyde aminotransferase, were used to study the relationship between chlorophyll accumulation and changes in carotenoid composition in developing and mature leaves grown either under low (30 mol photons m^-2 s^-1) or high light (300 mol photons m^-2 s^-1). Regardless of the extent to which chlorophyll synthesis was reduced, under low light the ratios of total chlorophyll to carotenoids remained constant. In contrast, under high light the content of carotenoids was elevated relative to chlorophyll and increased further with progressive inhibition in chlorophyll synthesis. The xanthophyll-cycle pigment pool was most strongly increased (up to 18-fold) upon suppression of chlorophyll synthesis. Concurrently to the higher pool sizes a higher extent of violaxanthin was converted into antheraxanthin and zeaxanthin and this was found to be correlated with a decrease in the quantum yield of photosystem II photochemistry. While lutein increased (up to 3-fold) with decreasing chlorophyll contents in high light transformants, neoxanthin remained rather constant in all plants analysed. Based on the present results, two different levels for the regulation of carotenoid synthesis are proposed depending on (I) the chlorophyll synthesizing capacity, and (ii) the photosynthetic light utilization efficiency. The first point suggests a co-regulation between carotenoid and chlorophyll synthesis; the second emphasizes the special role of carotenoids for protection against light stress.     

Effects of Light Quality and Norflurazon on the Formation of Plastid Pigments in Cotyledons of Pinus sylvestris

The effects of different light qualities and a special inhibitor of carotenoid biosynthesis on formation of plastid pigments of cotyledons of Pinus sylvestris were studied. The experimental results indicate: 1. The rate of synthesis of carotenoids in far-red light is relatively higher than that of chlorophylls, on the contrary in red light the rate of chlorophyll synthesis is higher. 2. When biosynthesis of carotenoids is inhibited, in white light the rate of total chlorophyll synthesis reduced with similar proportion. Accumulation of chlorophyll, however, is relatively much more than that of carotenoids. The highest molar ratio of chlorophyll/carotenoids is approximately 10.0. This implicates that chlorophyll and carotenoid synthesis proceed with certain independence. 3. After 4h exposure of strong white light of 9 day-old pine seedlings grown with 10-5 mol 1-1 norflurazon in farred light, contents of carotenoids and total, chlorophyll of cotyledons increase. Chlorophyll a biosynthesis promoted by light is higher than photooxidation of the pigment.     

Eco-physiological studies on the response of taxodiaceous conifers to shading with special reference to the behavior of leaf pigments

The effects of light intensity on the content and composition of leaf pigments, especially of carotenoids, were studied with mature current-year leaves of Taxodiaceous saplings grown under different grades of shade in summer. Both chlorophyll and total carotenoid contents increased with decreasing light intensity, maintaining approximately linear relations between each other, over a range of relative solar radiation of 100% to 7% of full daylight. The regression of total chlorophyll content on mean solar radiation could be well approximated by Shinozaki-Kira's reciprocal equation. The ratio of chlorophyll a to chlorophyll b was smaller in the shade than in the sun. The percentage of α-carotene and violaxanthin in the total carotenoid content tended to increase with increasing degree of shade, while those of β-carotene and lutein were reduced. The eco-physiological meanings of the pigments were considered based on this evidence. The order of shade tolerance among the four species tested is also discussed taking the responses of leaf weight and chlorophyll content to incident light intensity into consideration.     

Relationships between carotenoid composition and growth habit in British plant species

The pigment composition of leaves from a number of different plant species collected from field sites in the region of Sheffield, UK, have been compared using high-performance liquid chromatography. Expression of pigment content per unit leaf area was dominated by variation in the total leaf chlorophyll. Neither chlorophyll per unit area nor the chlorophyll a/b ratio were found to be correlated with the habitat from which the plants originated. When the amounts of different carotenoids were expressed relative to the total carotenoid pool, it was found that whilst neither total carotene (α- +β-carotene) nor neoxanthin correlated with ability to grow in shade, the leaf content of both lutein and the total xanthophyll cycle carotenoids (zeaxanthin, anther-axanthin and violaxanthin) did, with lutein content being high in shade species and xanthophyll cycle intermediates low. There was a strong negative correlation between the relative amounts of each of these groups of carotenoids. The ratio of lutein to xanthophyll cycle carotenoids was strongly correlated to an index of shade tolerance.     

Effects of carotenoid sequestration on a caterpillar's cryptic coloration and susceptibility to predation

Carotenoids are used for many functions by animals, including combining with other pigments to produce aposematic and cryptic coloration. Carotenoids in combination with blue pigments are responsible for green coloration in many caterpillars, and thus carotenoid sequestration may reduce their contrast against a green foliage background. We tested the hypothesis that carotenoid sequestration reduces contrast and enhances survival by rearing Trichoplusia ni Hübner (Lepidoptera: Noctuidae) on Brassica oleracea L. var. Acephala (Brassicaceae) leaves and exposing them to predators. We found that carotenoids derived from the host plant are partially excreted, along with chlorophyll, but also sequestered in hemolymph. Larvae that were given plants that provided carotenoids showed less contrast against their host plants within 1 day compared to larvae that were not provided with carotenoids. Last, both short‐term field observations and laboratory trials of larvae caged with predatory Podisus maculiventris Say (Hemiptera: Pentatomidae) nymphs showed that survival of carotenoid‐sequestering larvae was higher compared to larvae that did not sequester. These results suggest that carotenoid sequestration may be an important adaptive strategy that reduces susceptibility to natural enemies that hunt by sight. Further research that examines the mechanisms by which carotenoids are absorbed and modified will lend insights into the evolution of carotenoids functioning as passive defensive compounds.     

Responses of Chlorophyll Fluorescence and Carotenoids Biosynthesis to High Light Stress in Rice Seedling Leaves at Different Leaf Position

In the present study, we investigated the changes of photosynthesis, chlorophyll fluorescence and the content of carotenoid pigments in rice ( Oryza sativa L.) seedling leaves and their responses to high light. The results showed that the rate of photosynthesis, the contents of individual and total carotenoids and the pool size of xanthophyll cycle decreased with age increasing of the leaf. When the leaves were exposed to high light for 2 h, the qN of mature leaf (5th leaf) increased more significantly than that of younger (6th leaf) and older leaves (3rd and 4th leaf). Comparing with the leaves before exposure to high light, the excitation pressure on PSⅡ (1-qP) increased by 44%, 57%, 19% and 45% in the 3rd, 4th, 5th and 6th leaf under high light, respectively. The highest content of carotenoids and the greatest conversion of violaxanthin to zeaxanthin were found in the 5th leaf, and it was consistent with the 5th leaf exhibiting the strongest resistance to high light. Our results suggested that the ability of rice leaf to resist photoinhibition is related to the level of carotenoids and the ability of carotenoids biosynthesis.      

Changes in the chlorophyll and carotenoid contents in the leaves of steppe plants along a latitudinal gradient in South Ural

We studied the content of chlorophylls and carotenoids in the leaves of steppe plants of South Ural growing along a latitudinal gradient from southern steppe to forest-steppe. The content of chlorophylls (a + b) was 5–6 mg per 1 g of the leaf dry weight and did not depend on the latitude, whereas the content of carotenoids in the leaves increased northward from 1.0 to 1.5 mg/g dry wt. At the same time, the greatest changes occurred in the ratios between the forms of pigments: the chlorophyll a/b ratio increased from 1.8 to 2.8, and the chlorophyll/carotenoid ratio decreased from 5.6 to 3.5. The obtained results indicate that adaptation of the pigment apparatus of steppe plants growing along the latitudinal gradient occurs due to the transformation of the light-harvesting complex.     

Carbon Fixation Gradients across Spinach Leaves Do Not Follow Internal Light Gradients

In situ measurements of 14C-CO2 incorporation into 40-[mu]m paradermal leaf sections of sun- and shade-grown spinach leaves were determined. Chlorophyll, carotenoid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content in similar 40-[mu]m paradermal leaf sections was also measured. The carbon fixation gradient did not follow the leaf internal light gradient, which decreases exponentially across the leaf. Instead, the 14C-CO2 fixation was higher in the middle of the leaf. Contrary to expectations, the distribution of carbon fixation across the leaf showed that the spongy mesophyll contributes significantly to the total carbon reduced. Approximately 60% of the carboxylation occurred in the palisade mesophyll and 40% occurred in the spongy mesophyll. Carbon reduction correlated well with Rubisco content, and no correlation between chlorophyll and carotenoid content and Rubisco was observed in sun plants. The correlation among chlorophyll, carotenoids, Rubisco, and carbon fixation was higher in shade leaves than in sun leaves. The results are discussed in relation to leaf photosynthetic and biochemical measurements that generally consider the leaf as a single homogeneous unit.     

Light‐induced pigment degradation in leaves and ripening fruits studied in situ with reflectance spectroscopy

Pigment breakdown mediated by activated oxygen species is a consequence and a general symptom of oxidative stress and injury to plants. We have attempted to estimate the patterns of pigment bleaching and follow pigment susceptibility to irradiation as related to the process of senescence/ripening. Light‐induced pigment breakdown was studied in situ in the leaves of a shade‐requiring plant, wax flower ( Hoya carnosa R. Br.), as well as in apple ( Malus domestica Borlh. cv. Zhigulevskoe) and lemon ( Citrus limon Burm. cv. Pavlovsky) fruits, using reflectance spectroscopy. It was found that the sensitivity of plant pigments to photobleaching increases as ripening progresses in lemon fruit. Kinetic analysis showed that in all systems a rapid breakdown of the pigment occurs after a lag‐phase. The signature analysis revealed a common pattern of chlorophyll and carotenoid changes, but degradation of the individual pigments was found to be inhomogeneous. Both in lemon and apple fruits a decrease in reflectance in the band of carotenoid absorption preceded pigment photodestruction. In the fruits, the bulk of chlorophyll b and the long‐wavelength chlorophyll a forms were degraded at early stages of the process whereas the breakdown of both chlorophylls in H. carnosa leaves was more synchronous. Prolonged irradiation induced bleaching of the main chlorophyll a band with maximum at 678 nm in the difference spectra, as well as carotenoids. Some features of reflectance spectra in the bands of chlorophyll and carotenoid absorption were found to be suitable for the differentiation of photo‐induced pigment breakdown from the transformation of the pigments taking place during senescence.     

CO2浓度倍增对谷子拔节期和灌浆期光合色素含量和PSⅡ功能的影响

研究了CO_2浓度倍增对谷子(Setaria italica (L.)Beauv.)叶片单位鲜重和单位叶面积叶绿素(Chl)和类胡萝卜素(Car)的含量以及PSⅡ功能的影响。结果表明,CO_2浓度倍增能提高拔节期成熟叶片和灌浆期成熟旗叶的Chl和Car的含量,并且能提高这两种叶片PSⅡ反应中心开放部分的比例。然而拔节期叶片和灌浆期旗叶的qN值和PSⅡ总的光化学量子产量,以及 F_v/F_o、F_v/F_m和F_d/F_s的值对CO_2浓度倍增的响应不同,表明CO_2浓度倍增对拔节期叶片光合功能的改善优于灌浆期的旗叶。     

Chloroplast protection in greening leaves

Changes in photosynthetic activity, leaf pigments and the activities of enzymes that scavenge damaging oxygen species in chloroplasts were followed during the greening of 8-day-old etiolated pea (Pisum sativum L. cv. Meteor) seedlings. Accumulation of chlorophyll and carotenoids was accompanied by development of photosynthetic activity. Carotenoids present in etiolated leaves, and the high ratio of carotenoid to chlorophyll detected during the early hours of greening are suggested to provide important protection against singlet oxygen. Superoxide dismutase, ascor-bate peroxidase and glutathione reductase, which scavenge superoxide and hydrogen peroxide in chloroplasts, are present at high activities in etiolated leaves and throughout greening. The mechanisms by which developing chloroplasts may generate damaging oxygen species, and the role of these scavengers during greening is discussed.     

Responses to bleaching herbicides by leaf chloroplasts of maize plants grown at different temperatures.

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 degrees C and 30 degrees 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 beta-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 degrees 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 C(3) species, C(4) species, such as maize, can express a strong tolerance to herbicides like amitrole, when supplied to plants growing at their optimum temperature conditions.     

Dynamic change in photosynthetic pigments and chlorophyll degradation elicited by cereal aphid feeding

The concentration of photosynthetic pigments (i.e., chlorophylls a and b, and carotenoids) and chlorophyll degradation enzyme (i.e., chlorophyllase, oxidative bleaching, and Mg-dechelatase) activities on aphid-damaged and non-damaged regions of the infested leaves were determined with two infestation periods (6 and 12 days). Russian wheat aphid [Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae)] feeding caused significant losses of chlorophylls a and b and carotenoids in the damaged regions. However, bird cherry-oat aphid [Rhopalosiphum padi (L.) (Hemiptera: Aphididae)] feeding did not, except a significantly lower level of carotenoids was observed in the damaged regions from the short-infestation (6-day) samples. Interestingly, the non-damaged regions of D. noxia-infested leaves on both sampling dates had a significant increase of chlorophylls a and b and carotenoid concentrations when compared with the uninfested leaves. Although D. noxia feeding did not cause any changes in either chlorophyll a/b or chlorophyll (a+b)/carotenoid ratio between the damaged and non-damaged leaf regions on short-infestation (6-day) samples, a significantly lower chlorophyll a/b ratio was detected in long-infestation (12-day) samples. The assays of chlorophyllase and oxidative bleaching activities showed no significant differences between the damaged and non-damaged regions of the infested leaves on either sampling date. Mg-dechelatase activity, however, was significantly higher in D. noxia-damaged than non-damaged leaf regions from the short-infestation samples, while no differences were detected from the long-infestation samples. Furthermore, the long-infestation samples showed that Mg-dechelatase activity from both D. noxia-damaged and non-damaged regions increased significantly in comparison with the respective regions of either uninfested or R. padi-infested leaves. We infer that non-damaged regions of D. noxia-infested leaves compensate for the pigment losses in the damaged regions, and that Mg-dechelatase activity changed dynamically from a localized response to a systemic response as infestation duration extends. The findings from this study on cereal aphid-elicited chlorosis (or desistance) would help us to elucidate plant resistance mechanisms, in particular plant tolerance to non-defoliating herbivory.     

CHLOROPHYLL AND CAROTENOID ACCUMULATION IN THREE CHLOROPHYLLOUS CALLUS PHENOTYPES OF GLYCINE MAX

Effects of exogenous carbohydrates and various medium supplements on chlorophyll and carotenoid accumulation in three chlorophyllous callus phenotypes of Glycine max (L.) Merrill were studied. Glucose (filtered), at 3%, supported the highest level of chlorophyll and carotenoids in the NG and Y phenotypes, while only moderate levels of chlorophyll accumulated in the LG phenotype. Sucrose (filtered and autoclaved), at 3%, supported phenotypical levels of chlorophyll and carotenoids for all phenotypes. Ascorbic acid, at 75 mg/l, stimulated chlorophyll-carotenoid accumulation for all phenotypes, while δ-aminolevulinic acid was slightly toxic for pigment biosynthesis in the NG and LG phenotypes. In contrast, δ-aminolevulinic acid supported chlorophyll-carotenoid accumulation in the Y phenotype. A negative correlation (r_XY) was evident between chlorophyll formation and callus growth for all phenotypes. Light intensity of 3,000 lux suppressed chlorophyll accumulation in the Y callus phenotype while an increase in pigment formation occurred in the NG and LG callus phenotypes. In comparison, light intensity of 700 lux supported chlorophyll accumulation in the Y callus phenotype. Carotenoid accumulation appeared to be coupled with chlorophyll formation in all callus phenotypes except for the Y callus phenotype when grown under the higher light intensity. All phenotypes accumulated chlorophylls a and b, α- and β-carotene, lutein plus zeaxanthin, violaxanthin and neoxanthin as indicated by their respective absorption maxima. Under cultural conditions, the genetic mutation (yll) in these soybean callus phenotypes appeared to regulate carotenoid formation which in turn influenced chlorophyll stability.