Effect of cadmium on the growth and antioxidant enzymes in two varieties of Brassica juncea

Increasing contamination and higher enrichment ratio of non-essential heavy metal cadmium (Cd) induce various toxic responses in plants when accumulated above the threshold level. These effects and growth responses are genotype and Cd level dependent. An experiment was conducted to analyze the effect of Cd toxicity in Brassica juncea [L] Czern and Coss by selecting its two varieties Varuna and RH-30. Cadmium (0, 25, 50 or 100 mg CdCl₂ kg⁻¹ of soil) fed to soil decreased the values of growth characteristics, activity of nitrate reductase and leaf water potential, whereas activities of antioxidant enzymes and proline content increased with the increasing concentration of Cd, observed at 30 and 60 day stages of growth, in both the varieties. Moreover, Cd uptake by the roots was higher in RH-30 than Varuna. Also the activity of antioxidant enzymes and proline accumulation were higher in Varuna with increasing soil level of Cd. Out of the two varieties, Varuna was more tolerant than RH-30 to Cd stress.     

Response of two mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> L.) cultivars differing in photosynthetic capacity subjected to proline

The present paper deals with the effect of exogenous application of proline as a shotgun approach on growth, photosynthesis, and antioxidative system in 25-day-old plants of two different cultivars of Brassica juncea L. (Varuna and RH-30) under natural conditions. Exogenous application of proline significantly increased plant growth, photosynthetic rate, and the activities of antioxidant enzymes, compared with untreated seedlings. Pre-sowing seed soaking in 20 mM proline, for 8 h, proved best among all the other concentrations used.     

Salt-induced modulation in growth,photosynthesis and antioxidant system in two varieties of Brassica juncea

The present study was carried out to examine salt-induced modulation in growth, photosynthetic characteristics and antioxidant system in two cultivars of Brassica juncea Czern and Coss varieties (Varuna and RH-30). The surface sterilized seeds of these varieties were sown in the soil amended with different levels (2.8, 4.2 or 5.6 dsm⁻¹) of sodium chloride under a simple randomized block design. The salt treatment significantly decreased growth, net photosynthetic rate and its related attributes, chlorophyll fluorescence, SPAD value of chlorophyll, leaf carbonic anhydrase activity and leaf water potential, whereas electrolyte leakage, proline content, and activity of catalase, peroxidase and superoxide dismutase enzymes increased in both the varieties at 30 d stage of growth. The variety Varuna was found more resistant than RH-30 to the salt stress and possessed higher values for growth, photosynthetic attributes and antioxidant enzymes. Out of the graded concentrations (2.8, 4.2 or 5.6 dsm⁻¹) of sodium chloride, 2.8 sm⁻¹ was least toxic and 5.6 dsm⁻¹ was most harmful. The variation in the responses of these two varieties to salt stress is attributed to their differential photosynthetic traits, SPAD chlorophyll value and antioxidant capacity, which can be used as potential markers for screening mustard plants for salt tolerance.     

Photosynthesis and photoprotection in Nicotiana tabacum L. in vitro-grown plantlets

Nicotiana tabacum L. plantlets were cultured in vitro photoautotrophically (0% sucrose) and photomixotrophically (3% or 5% sucrose) at two irradiances (80 or 380 mumol m-2 s-1) with the aim of investigating the effect of these culture conditions on photosynthetic parameters and on protective systems against excess excitation energy. In plantlets grown photoautotrophically under higher irradiance photoinhibition was demonstrated. These plantlets had a decreased chlorophyll (Chl) a + b content and Chl a/b ratio, an increased content of xanthrophyll cycle pigments and a higher deepoxidation state, a decreased maximum photochemical efficiency of photosystem II (PS II) and actual photochemical efficiency of PS II, and an increased non-photochemical quenching. In the photoautotrophically grown plantlets and those photomixotrophically grown with 3% sucrose, the increase of growth irradiance from 80 to 380 mumol m-2 s-1 stimulated the activities of ascorbate-glutathione cycle enzymes with the exception of ascorbate peroxidase. Ascorbate peroxidase activity was not affected by the increase in growth irradiance but a significant decrease with increasing sucrose concentration was evident. The higher concentration of sucrose in the medium (5%) in combination with the higher irradiance inhibited photosynthesis (decrease in Chl a + b content and net photosynthetic rate) but no significant changes in activities of ascorbate-glutathione cycle enzymes were found. These results suggest that exogenous sucrose added to the medium improved high irradiance and oxidative stress resistance of the plantlets but the effect of sucrose is concentration dependent.     

Effects of cadmium stress upon activities of antioxidative enzymes, photosynthetic rate, and production of phytochelatins in leaves and chloroplasts of wheat cultivars differing in yield potential

We tested the mode of action of Cd on photosynthesis and activities of ATP-sulfurylase (ATP-S), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), and on contents of phytochelatins (PCs) and glutathione (GSH) in two cultivars of wheat (Triticum aestivum L.) PBW-343 and WH-542 differing in yield potential. Cd treatment increased Cd content and photosynthetic activity in PBW-343 more than in WH-542. The activities of APX, GR, ATP-S, and synthesis of PCs and GSH were also increased by Cd, but the CAT and SOD activities were inhibited in both the cultivars. The efficient functioning of antioxidative enzymes, production of PCs and GSH, helped in counteracting the effects of Cd namely in PBW-343, protected photosynthetic ability, and increased the tolerance to Cd.     

Increased activity of ATP-sulfurylase and increased contents of cysteine and glutathione reduce high cadmium-induced oxidative stress in mustard cultivar with high photosynthetic potential

Cadmium is known to reduce photosynthesis and overall growth of plants. Plants adopt several mechanisms of Cd detoxification, such as accumulation of sulfur-rich compounds, like glutathione (GSH) and its precursor cysteine. The accumulation of GSH is regulated by the activity of ATP-sulfurylase, a rate-limiting enzyme in sulfur assimilation. The carbon of Cys is provided through photosynthesis. Thus, a plant with the higher photosynthetic potential and ATP-sulfurylase activity may have the higher contents of Cys and GSH and therefore may provide for a greater tolerance to Cd stress. Mustard (Brassica juncea L. Czern and Coss.) cvs. Varuna (high photosynthetic potential) and RH30 (low photosynthetic potential) were subjected to 0 and 200 mg Cd/kg soil, and the activity of ATP-sulfurylase, the contents of Cys and GSH, oxidative stress, and activities of antioxidant enzymes were studied. Under 200 mg Cd/kg soil, cv. Varuna showed an increased ATP-sulfurylase activity, the higher contents of Cys and GSH, and the net photosynthetic rate than cv. RH30. In contrast, the activity of superoxide dismutase, the contents of thiobarbituric acid-reactive substances, and H₂O₂, and electrolyte leakage were found to be greater in cv. RH30 showing an increased oxidative stress than cv. Varuna. However, the activities of ascorbate peroxidase and glutathione reductase were greater in cv. Varuna than cv. RH30. The results show that a greater ATP-sulfurylase activity, an enhanced production of Cys and GSH, and an efficient antioxidant enzyme system in the high photosynthetic mustard cv. Varuna helped to the reduce the oxidative stress maintaing high photosynthesis.     

Physiological Responses and Tolerance Mechanisms to Cadmium in Conyza canadensis

Experiments were conducted to examine the effects of different concentrations of Cd on the performance of the Cd accumulator Conyza canadensis. Cd accumulation in roots and leaves (roots > leaves) increased with increasing Cd concentration in soil. High Cd concentration inhibited plant growth, increased the membrane permeability of leaves, and caused a significant decline in plant height and chlorophyll [chlorophyll (Chl) a, Chl b, and total Chl] content. Leaf ultrastructural analysis of spongy mesophyllic cells revealed that excessive Cd concentrations cause adverse effects on the chloroplast and mitochondrion ultrastructures of C. canadensis. However, the activities of antioxidant enzymes, such as superoxide dismutase, catalase, peroxidase, total non-protein SH compounds, glutathione, and phytochelatin (PC) concentrations, showed an overall increase. Specifically, the increase in enzyme activities demonstrated that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Cd in C. canadensis. Furthermore, results demonstrate that PC synthesis in plant cells is related to Cd concentration and that PC production levels in plants are related to the toxic effects caused by soil Cd level. These findings demonstrate the roles played by these compounds in supporting Cd tolerance in C. canadensis.     

CO2 浓度升高对两种沈阳城市森林树种光合特性的影响

利用开顶式气室, 研究了CO2浓度升高条件下城市森林主要树种油松(Pinus tabulaefomis)和银杏(Ginkgo biloba)主要光合特性的变化。结果表明, 整个生长季, CO2浓度升高(700 mmol.mol-1)条件下2树种叶片的净光合速率、可溶性糖、淀粉和可溶性蛋白含量均接近或高于相应对照(自然CO2浓度)值, 但不同树种增加的幅度不同; 而2树种的叶绿素含量和Chl a/Chl b值对CO2浓度升高反应不一, 表现为CO2浓度升高条件下油松的叶绿素含量较对照值高, Chl a/Chl b值降低, 银杏的叶绿素含量为前期升高, 后期降低, Chl a/Chl b值变化与之正好相反, 说明城市森林组成树种对CO2浓度升高的响应具有复杂性。CO2浓度升高条件下, 两树种均未发生光合适应现象。     

Responses of photosynthetic characteristics and antioxidative metabolism in winter wheat to post-anthesis shading

In a field experiment, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Jinan 17 (a multiple-spike cultivar), were treated with 78% (S1), 50% (S2), and 10% (S3) of full sunshine (S0, control) from anthesis to maturity to determine the responses of photosynthetic characteristics and antioxidative enzyme activities in a flag leaf. Compared with S0 treatment, the chlorophyll (Chl) content and maximal efficiency of photosystem II (PSII) photochemistry (F_v/F_m) of flag leaves were enhanced in treatments S1 and S2. From 0 to 7 d post flowering, the Chl content and F_v/F_m in S3 were also higher than those in S0, but significantly lower than those in controls, respectively. With the increase of shading intensity, the effective quantum yield of PSII (Φ_PSII) was promoted; whereas, the ratio of Chl a/b declined. Compared with S0, treatments S2 and S3 significantly suppressed the activities of superoxide dismutase (SOD) and peroxidase (POD), net photosynthetic rate (P _N), and contents of total soluble sugar, nevertheless, S1 treatment showed positive effects on the above parameters. Under the same shading condition, Jinan 17 had larger Chl content and higher activities of PSII and antioxidative enzymes, but lower malondialdehyde (MDA) content than Tainong 18. The results indicated that multiple-spike cultivar was more advantageous for the Huang-Huai-Hai Plain, where shading problem occurs later during the growth period, than the large-spike cultivar, because of the lesser damage in a flag leaf and better photosynthetic function of the former one. Wheat plants under S1 shading condition had relatively high activities of antioxidative enzymes and a low degree of membrane lipid peroxidation, which was in favor of stress resistance, maintaining high P _N duration, and accumulation of photosynthates in wheat plants.     

Physiological and Biochemical Changes during Seed Filling in Relation to Leaf Senescence in Soybean

Field experiments with Glycine max (L.) Merr. cv. Ludou 11 and Ludou 4 were conducted to evaluate changes in photosynthetic rate, antioxidative enzyme activity, soluble protein, chlorophyll (Chl) and carotenoid (Car) contents in relation to leaf senescence during seed filling period. Photosynthetic rate, soluble protein content, catalase and peroxidase activities were the highest at 25 days after flowering (DAF). Chl a, Chl b and Car contents reached the maximum at 15 DAF and rapidly decreased after 33 DAF.     

Age-dependent response of maize leaf segments to cadmium treatment: effect on chlorophyll fluorescence and phytochelatin accumulation

The relationship between the age of leaf tissue and response of the photosynthetic apparatus and phytochelatin accumulation to Cd treatment was studied. Studies were carried out with seedlings of Zea mays L. cv. Hidosil grown in the presence of 100-200 mumol/L Cd for 14 days under low light conditions. The third leaf was divided into 3 segments of equal length differing in the stage of tissue maturity and used for measurements of chlorophyll content, chlorophyll fluorescence, glutathione and phytochelatin content and Cd accumulation. A close relationship between the age of leaf tissue and response of the photosynthetic apparatus to Cd was shown. Cadmium (200 mumol/L) reduced photochemical processes more in older than younger leaf segments as seen in the Chl fluorescence parameters Fv/F0, and t1/2, while the chlorophyll fluorescence decrease ratio (Rfd) was inhibited more strongly in younger ones. Fv/Fm was slightly affected. Cd-induced enhancement of GSH content was correlated with higher phytochelatin accumulation to a greater extent in younger than in older leaf segments. Phytochelatin level corresponded to changes of photochemical processes in older leaves. The peptide thiol:Cd molar ratio for the phytochelatins varied depending on Cd concentration and age of leaf segments. The protective role of phytochelatins for the photosynthetic apparatus is discussed.     

Hg2+和Cd2+胁迫对满江红生理和细胞超微结构的影响

研究了在梯度浓度Hg2+和Cd2+胁迫下,满江红(Azolla imbricata (Roxb.) Nakai)的叶绿素含量、叶绿素a/b比值、光合放氧速率、呼吸速率、抗氧化酶系(超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD))和细胞超微结构受Hg2+和Cd2+的毒害影响.结果显示:随着胁迫程度的增大,叶绿素含量、叶绿素a/b比值、光合放氧速率明显下降,呼吸速率均在2 mg/L浓度下达到峰值,尔后下降; SOD、CAT、POD的活性均出现不同程度的应激性升高(除POD在Cd2+处理时下降),尔后下降.电镜观察发现,随着污染物浓度的增加和胁迫时间的延长,叶绿体出现膨大、破损和解体;线粒体嵴突膨胀和线粒体变形及空泡化;核染色质凝集,核仁消失,核膜破裂.实验结果表明: Hg2+和Cd2+污染不仅损害植物的生理活性,而且也破坏细胞的超微结构,最终导致植物死亡;随着Hg2+和Cd2+胁迫的增大,细胞超微结构的损伤程度和植物的生理变化是同步的;植物受毒害的程度表现出明显的剂量效应关系;在同一处理时间和浓度下,Cd2+对满江红的毒性大于Hg2+.Hg2+对满江红的致死浓度为3.5～4.0 mg/L,Cd2+为3.0～3.5 mg/L.对满江红鱼腥藻(Anabaena azollae Strasburger)细胞的超微结构变化观察表明,满江红鱼腥藻对Hg2+和Cd2+的耐受性明显高于满江红.     

Hg^2＋和Cd^2＋胁迫对满江红生理和细胞超微结构的影响

研究了在梯度浓度Hg^2 和Cd^2 胁迫下,满江红（Azolla imbricata(Roxb.)Nakai)的叶绿素含量,叶绿素a/b比值,光合放氧速率,呼吸速率,抗氧化酶系（超氧化物歧化酶（SOD）,过氧化氢酶（CAT）,过氧化物酶（POD）和细胞超微结构受He^2 和Cd^2 的毒害影响。结果显示：随着胁迫程度的增大,叶绿素含量,叶绿素a/b比值,光合放氧速率明显下降,呼吸速率均在2mg/L浓度下达到峰值,尔后下降;SOD,CAT,POD的活性均出现不同程度的应激性升高（除POD在Cd^2 处理时下降）,尔后下降,电镜观察发现,随着污染物浓度的增加和胁迫时间的延长,叶绿体出现膨大,破损和解体;线粒体嵴突膨胀和线粒体变形及空泡化;核染色质凝集,核仁消失。核膜破裂,实验结果表明：Hg^2 和Cd^2 污染不仅损害植物的生理活性,而且也破坏细胞的超微结构,最终导致植物死亡,随着Hg^2 和Cd^2 为3.0-3.5mg/L。对满江红鱼腥藻（Anabaena azollae Strasburger)细胞的超微结构变化观察表明,满江红鱼腥藻对Hg^2 和Cd^2 的耐受性明显高于满江红。     

Activity of Photosystem 2, Lipid Peroxidation,and the Enzymatic Antioxidant Protective System in Heat Shocked Barley Seedlings

The impact of heat shock on minimising the activity of photosystem 2 (PS2) initiating high lipid peroxidation (POL) level and consequently changes in the enzymatic-antioxidant protective system was studied in seedlings of two Egyptian cultivars of barley (Giza 124 and 125). Heat doses (35 and 45 °C for 2, 4, 6, and 8 h) decreased chlorophyll (Chl) contents coupled with an increase in Chl a/b ratio, diminished Hill reaction activity, and quenched Chl a fluorescence emission spectra. These parameters reflect the disturbance of the structure, composition, and function of the photosynthetic apparatus as well as the activity of PS2. POL level, as dependent on the balance between pro- and anti-oxidant systems, was directly correlated with temperature, exposure time, and their interaction. Heat shock caused an increase in the electric conductivity of cell membrane, and malonyldialdehyde content (a peroxidation product) coupled with the disappearance of the polyunsaturated linolenic acid (C_18:3), reflecting the peroxidation of membrane lipids which led to the loss of membrane selective permeability. Moreover, it induced distinct and significant changes in activities of antioxidant enzymes. Superoxide dismutase and peroxidase activities have been progressively enhanced by moderate and elevated heat doses, but the most elevated one (45 °C for 8 h) showed a decrease in activities of both enzymes. In contrast, catalase activity was reduced with all heat shocks.     

空间搭载后的蜀葵幼苗叶中光合色素含量及抗氧化酶活性变化

蜀葵种子经返回式卫星搭载后,其幼苗叶中光合色素(叶绿素a、b,胡萝卜素)总量低于地面未经搭载的.叶绿素a b含量明显降低, 叶绿素b的下降幅度远大于叶绿素a,因而Chla/b值增高.经空间搭载后萌发12 d的幼苗体内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性均低于地面未经搭载的,而丙二醛(MDA)含量则明显升高.     

Photosynthetic pigments content, <Emphasis Type="Italic">δ</Emphasis>-aminolevulinic acid dehydratase and acid phosphatase activities and mineral nutrients concentration in cadmium-exposed <Emphasis Type="Italic">Cucumis sativus</Emphasis> L.

In this study, the effects of cadmium chloride (CdCl₂) on plant growth, histology of roots, photosynthetic pigments content, δ-aminolevulinic acid dehydratase (ALA-D; E.C. 4.2.1.24) and acid phosphatase activities (AP; E.C. 3.1.3.2), soluble phosphorus (Pi) measurement and mineral nutrients content in cucumber seedlings (Cucumis sativus L.) were investigated. Cucumber seedlings were grown in vitro in an agar-solidified substrate containing four CdCl₂ treatments (0, 100, 400, and 1000 μM) for ten days. Cd was readily absorbed by seedlings and its content was greater in the roots than in the shoot. Cd reduced shoot and root length, and fresh and dry biomass of seedlings. Inhibition of root cell elongation in Cd-treated seedlings was observed by the increase of the mean radial size of cells belonging to three zones of the root tip. The highest level of Cd reduced in a similar manner chlorophyll a, chlorophyll b and total chlorophyll contents. Increasing concentrations of Cd resulted in a linear decrease in carotenoids levels of cotyledons. Interestingly, the ALA-D activity in cotyledons was inhibited only at the highest level of Cd. Root and shoot AP activities were, respectively, activated and inhibited at all CdCl₂ concentrations. Root Pi concentration was increased in all Cd treatments and it was not altered in the shoot tissues. Moreover, in general, the nutrient contents were increased in the root and decreased in the shoot. Therefore, we suggest that Cd affects negatively growth, photosynthetic pigments, ALA-D and AP activities and partition of mineral nutrients in cucumber seedlings.     

硅对连作黄瓜幼苗光合特性和抗氧化酶活性的影响

以‘津研四号’黄瓜品种为试材,研究了叶面喷施不同浓度硅(Si)(0、1、2、3、4、5 mmol·L^-1)对连作黄瓜幼苗生长、光合特性和抗氧化酶活性的影响.结果表明: 在一定浓度(1～3 mmol·L^-1 Si)范围内,施Si可降低幼苗叶片电解质渗漏率(EL)和丙二醛(MDA)含量;提高叶绿素a(Chl a)、叶绿素b(Chl b)、类胡萝卜素(Car)和总叶绿素含量,叶片净光合速率(P_n)升高;超氧化物歧化酶(SOD)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)和过氧化氢酶(CAT)活性均有所提高;黄瓜幼苗株高、茎粗、叶面积及干物质积累量增加.随施Si浓度的进一步增加(4～5 mmol·L^-1),叶片中EL和MDA含量升高,但仍低于对照;抗氧化酶活性和光合作用下降,幼苗生长受到显著抑制.说明外源Si可通过提高黄瓜幼苗叶片抗氧化酶活性来降低膜脂过氧化,通过增加光合作用来提高黄瓜幼苗长势,进而增强对连作障碍的抗性.以2 mmol·L^-1Si处理效果最好.     

镉胁迫对不同甘蓝基因型光合特性和养分吸收的影响

以2个耐镉(Cd)性不同的甘蓝品种为材料,研究了不同Cd浓度(0、20、50、100μmol.L-1)对甘蓝植株生长、叶片光合特性和养分吸收的影响.结果表明:Cd敏感品种在低浓度Cd(20μmol.L-1)处理下生长受到明显抑制,叶片净光合速率(Pn)、气孔导度(Gs)、PSⅡ光化学效率(Fv/Fm)、PSⅡ光合电子传递量子效率(ΦPSⅡ)及地上部、根系干质量显著降低;Cd耐性品种在高浓度Cd(50和100μmol.L-1)处理下生长和光合特性受到显著影响;Cd胁迫降低了甘蓝叶片叶绿素a和b含量,尤其对叶绿素a的影响较大,进而抑制了叶片光合能力.Cd胁迫显著降低了植株对Mn的吸收,抑制了Mg和Fe从根部向地上部的转运,且Cd敏感品种受抑制幅度更大;Cd胁迫促进了Cd耐性品种对P和S的吸收,而Cd敏感品种相反.因此,Cd胁迫下甘蓝敏感品种叶片Mn、Fe、Mg、S和P含量的降低是影响其叶片光合作用,进而抑制植株生长的重要生理原因.     

Biochemical Changes that Occur during Senescence of Wheat Leaves : I. Basis for the Reduction of Photosynthesis

Changes in activities of photosynthetic enzymes and photochemical processes were followed with aging of vegetative and flag leaves of wheat (Triticum aestivum L. cv Roy). Activities of stromal enzymes began to decline prior to photochemical activities. In general, total soluble protein and the activities of ribulose-1,5-bisphosphate carboxylase and NADP-triose-phosphate dehydrogenase declined in parallel and at an earlier age than leaf chlorophyll (Chl), leaf photosynthesis, and photosynthetic electron transport activity. Leaves appeared to lose whole chloroplasts as opposed to a general degradation of all chloroplasts based on three lines of evidence: (a) electron transport activity calculated on an area basis declined much earlier than the same data expressed on a Chl basis; (b) Chl content per chloroplast was similar for mature and senescent tissue; and (c) the absorbance at 550 nanometers (light scattering) per unit of Chl remained essentially constant until the end of senescence. Chloroplasts did, however, undergo some modifications before they were lost (e.g. loss of stromal enzyme activities), but the reduction in leaf photosynthesis was apparently caused by a loss of whole chloroplasts.     

竹柏2种颜色叶片的光合特性研究

为了解竹柏(Podocarpus nagi)的光合特性,以3 a生全绿叶和花叶竹柏为材料,测定其光合色素含量和气体交换参数。结果表明,全绿叶竹柏叶片的叶绿素a、叶绿素b、类胡萝卜素、叶绿素a+b、叶绿素a/b和叶绿素a+b/类胡萝卜素均显著高于花叶竹柏;全绿叶竹柏叶片的初始量子效率、最大光合速率和暗呼吸速率均显著高于花叶,而光饱和点和光补偿点均显著低于花叶;全绿叶竹柏叶片的初始羧化效率、光合速率、CO2饱和点和光呼吸速率均高于花叶,而CO2补偿点低于花叶。2种颜色叶片的气孔导度、蒸腾速率和水分利用效率均随着光合有效辐射的增大而增大,且均表现为全绿叶花叶,而胞间CO2浓度则相反,表现为花叶全绿叶。因此,全绿叶竹柏利用弱光的能力强于花叶竹柏,而花叶竹柏利用强光的能力更强,在园林绿化配置中,可根据2种颜色叶片的光合特性合理配置。