The inheritance of chilling tolerance in tomato (Lycopersicon spp.)

During the past 25 years, chilling tolerance of the cultivated (chilling-sensitive) tomato Lycopersicon esculentum and its wild, chilling-tolerant relatives L. peruvianum and L. hirsutum (and, less intensively studied, L. chilense) has been the object of several investigations. The final aim of these studies can be seen in the increase in chilling tolerance of the cultivated genotypes. In this review, we will focus on low-temperature effects on photosynthesis and the inheritance of these traits to the offspring of various breeding attempts. While crossing L. peruvianum (male symbol) to L. esculentum (female symbol) so far has brought the most detailed insight with respect to physiological questions, for practical purposes, e.g., the readily cross ability, crossing programmes with L. hirsutum as pollen donor at present seem to be a promising way to achieve higher chilling-tolerant genotypes of the cultivated tomato. This perspective is due to the progress that has been made with respect to the genetic basis of chilling tolerance of Lycopersicon spp. over the past five years.     

Photosynthesis and non-photochemical excitation quenching components of chlorophyll excitation in maize and field bean during chilling at different photon flux density

The influence of chilling (8 °C, 5 d) at two photon flux densities [PFD, L = 200 and H = 500 μmol(photon) m⁻² s⁻¹] on the gas exchange and chlorophyll fluorescence was investigated in chilling-tolerant and chilling-sensitive maize hybrids (Zea mays L., K383×K130, K185×K217) and one cultivar of field bean (Vicia faba L. minor, cv. Nadwiślański). The net photosynthetic rate (P _N) for the both studied plant species was inhibited at 8 °C. P _N of both maize hybrids additionally decreased during chilling. Changes in the quantum efficiency of PS2 electron transport (Φ_PS2) as a response to chilling and PFD were similar to P _N. Measurements of Φ_PS2/Φ_CO2 ratio showed that in field bean seedlings strong alternative photochemical sinks of energy did not appear during chilling. However, the high increment in Φ_PS2/Φ_CO2 for maize hybrids can indicate reactions associated with chill damage generation. At 8 °C the non-photochemical quenching (NPQ) increased in all plants with chilling duration and PFD. The appearance of protective (q_I,p) and damage (q_I,d) components of q_I and a decrease in q_E (energy dependent quenching) took place. NPQ components of field bean and maize hybrids differed from each other. The amount of protective NPQ (q_E + q_I,p) components as part of total NPQ was higher in field bean than in maize hybrids at both PFD. On 5^th day of chilling, the sum of q_E and q_I,p was 26.7 % of NPQ in tolerant maize hybrids and 17.6 % of NPQ in the sensitive one (averages for both PFD). The increased PFD inhibited the ability of all plants to perform protective dissipation of absorbed energy. The understanding of the genotypic variation of NPQ components in maize may have implications for the future selection of plants with a high chilling tolerance.     

Photoinhibition, xanthophyll cycle and in vivo chlorophyll fluorescence quenching of chilling-tolerant Oxyria digyna and chilling-sensitive Zea mays

The relationship between susceptibility to photoinhibition, zeaxanthin formation and chlorophyll fluorescence quenching at suboptimal temperatures was studied in chilling-sensitive maize and in non-acclimated and cold-acclimated Oxyria digyna , a chilling-tolerant plant of arctic and alpine habitats. In maize, zeaxanthin formation was strongly suppressed by chilling. Zeaxanthin formed during preillumination at 20°C did not protect maize leaves from photoinhibition during a subsequent high-light, low-temperature treatment, as judged from the ratios of variable to maximal fluorescence, F_v/F_m. However, such preillumination significantly increased non-photochemical quenching (q_N) at low temperatures, mainly due to an enhancement of the fast-relaxing q_N component (i.e., of energy-dependent quenching. q_E). In O. digyna , cold-acclimation resulted in an increased zeaxanthin formation in the temperature range of 2.5–20°C. Cold-acclimation substantially decreased the susceptibility towards photoinhibition at 4°C, but q_N remained nearly unchanged between 2 and 38°C, as compared to control plants. Effects of cold acclimation on photosynthesis, photochemical quenching and quantum efficiency of photosystem II were small and indicated a slight amelioration only of the function of the photosynthetic apparatus at suboptimal temperatures (2–20°Ct. I) is concluded, that the xanthophyll cycle is strongly influenced by cold acclimation, while effects on the photosynthetic carbon assimilation only play a minor role in O. digyna.     

Leaf photosynthetic parameters of two maize (Zea mays) cultivars in response to various patterns of chilling temperatures and photon flux densities

Chilling‐induced photosynthetic impairment was examined in leaves of maize (Zea mays L.) seedlings of two cultivars, one adapted to western Europe and one adapted to Mexican highlands. Three experiments were performed in a controlled environment. The effects of chilling night temperatures, of chilling at high light intensity and of variable chilling day temperatures on photosynthetic parameters, were evaluated. Chilling in the dark period resulted in stomatal limitation of net photosynthesis. Chilling at moderate to high light intensities caused chilling‐dependent photoinhibition of CO₂ uptake. Photobleached maize leaves did not resume normal photosynthetic function. Maize cv. Batan 8686 from the highlands of Mexico was less susceptible to photosynthetic damage than maize cv. Bastion adapted for cultivation in W. Europe, when exposed to chilling night temperatures, or to mild chilling photoinhibitory conditions.     

遮荫下高原濒危药用植物川贝母(Fritillaria cirrhosa)光合作用和叶绿素荧光特征

测量了川贝母遮荫和全光下叶片光合生理参数和叶绿素荧光参数,探讨了其遮荫下生理生态学指标的变化和强光下的光适应机制,且对光合生理的测量过程给出了全面系统的介绍.川贝母日光合曲线呈双峰变化,遮荫后川贝母光合效率(Pmax)、细胞内CO2浓度(Ci)分别增加了31.1%、10%(p<0.01),有效光反应光强域值(PFD)增加了331.5 [μmol/(m2·s)],最大表观量子效率(AQY)和气孔导度(COND)也有所增加,暗呼吸速率(Rd)和叶片蒸汽压亏缺(Vpdl)明显降低,此均有利用光合产物的积累;F′v/F′m(光照下反应中心能量捕获效率)、qP(光化学淬灭)、ETR(电子传递效率)、Psips2(PSⅡ的效率)分别增加了14.7%(p<0.01)、8.8%(p<0.01)、10%(p<0.01)、24.2%(p>0.05),促进了川贝母叶片对光能的利用;Fv/Fm(光化学效率)变化不明显,说明"灯笼花"阶段,全光下川贝母没有受到到明显的胁迫,光合机构未遭到破坏.当自然光强超过光饱和点时,川贝母主要通过提高非化学淬灭,耗散过多吸收的热能以防止光合机构的破坏.当出现极端气候(高温干旱)时,川贝母繁育退化现象("树儿子"或"灯笼花"阶段退回到"一匹叶"生长阶段)可能是对环境适应的主要方式.另外川贝母叶片狭小、叶片倾角较大降低了强光辐射的有效面积,在形态结构上有利于避免过高光强对叶光合器官的损伤.     

Response of xanthophyll cycle and chloroplastic antioxidant enzymes to chilling stress in tomato over-expressing glycerol-3-phosphate acyltransferase gene

Over-expression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) increased unsaturated fatty acid contents in phosphatidylglycerol (PG) of thylakoid membrane in tomato. The effect of this increase on the xanthophyll cycle and chloroplast antioxidant enzymes was examined by comparing wild type (WT) tomato with the transgenic (TG) lines at chilling temperature (4 °C) under low irradiance (100 μmol m⁻² s⁻¹). Net photosynthetic rate and the maximal photochemical efficiency of photosystem (PS) 2 (F_v/F_m) in TG plants decreased more slowly during chilling stress and F_v/F_m recovered faster than that in WT plants under optimal conditions. The oxidizable P700 in both WT and TG plants decreased during chilling stress under low irradiance, but recovered faster in TG plants than in the WT ones. During chilling stress, non-photochemical quenching (NPQ) and the de-epoxidized ratio of xanthophyll cycle in WT plants were lower than those of TG tomatoes. The higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in TG plants resulted in the reduction of O₂ ^−· and H₂O₂ contents during chilling stress. Hence the increase in content of unsaturated fatty acids in PG by the over-expression of LeGPAT could alleviate photoinhibition of PS2 and PS1 by improving the de-epoxidized ratio of xanthophyll cycle and activities of SOD and APX in chloroplast.     

Photoadaptation of two members of the Chlorophyta (Scenedesmus and Chlorella) in laboratory and outdoor cultures: changes in chlorophyll fluorescence quenching and the xanthophyll cycle

The role of the xanthophyll cycle in the adaptation of two chlorococcal algae Scenedesmus quadricauda and Chlorella sorokiniana to high irradiance was studied under laboratory and outdoor conditions. We wished to elucidate whether the xanthophyll cycle plays a key role in dissipating the excesses of absorbed light, as in higher plants, and to characterise the relationship between chlorophyll fluorescence parameters and the content of xanthophyll-cycle pigments. The xanthophyll cycle was found to be operative in both species; however, its contribution to overall non-photochemical quenching (NPQ) could only be distinguished in Scenedesmus (15–20% of total NPQ). The Scenedesmus cultures showed a larger pool of xanthophyll-cycle pigments than Chlorella, and lower sensitivity to photoinhibition as judged from the reduction of maximum quantum yield of photosystem II. In general, both algae had a larger xanthophyll-cycle pool when grown outdoors than in laboratory cultures. Comparing the two species, Scenedesmus exhibited a higher capacity to adapt to high irradiance, due to an effective quenching mechanism and high photosynthetic capacity; in contrast, Chlorella represents a species with a larger antennae system, less-efficient quenching and lower photosynthetic performance. Non-photochemical quenching (NPQ) induced through the xanthophyll cycle can, to a limited extent, represent a regulatory factor in diluted algal cultures grown in outdoor solar photobioreactors, as well as in natural algal phytoplankton populations exposed transiently to high irradiance. However, it does not play an appreciable role in dense, well-mixed microalgal suspensions. Received: 6 August 1998 / Accepted: 12 February 1999     

高温强光下水杨酸对黄瓜叶片叶绿素荧光和叶黄素循环的影响

在高温强光条件下,研究了外源水杨酸对黄瓜叶片叶绿素荧光参数和叶黄素循环的影响.结果表明,在高温强光胁迫前2 d用50～400 μmol·L^-1水杨酸处理叶片,抑制了高温强光下原初光能转换效率(F_v/F_m)、光合电子传递量子效率(ΦPSⅡ)、最大荧光(F_m)和光化学猝灭系数(qP)的下降,分别比对照提高了16.1%～30.2%、11.9%～33.0%、7.2%～41.0%和27.2%～160.8%,促进了非光化学猝灭系数(NPQ)的升高,比对照提高了13.1%～62.9%,而对初始荧光(F_o)影响不大.水杨酸处理可减小高温强光下叶黄素循环库的下降幅度,使(A+Z)/(V+A+Z)升高,分别比对照高29.5%和24.6%.这些结果说明,水杨酸可通过提高非辐射能量耗散,对高温强光引起的黄瓜叶片光合机构的破坏具有保护作用.     

Effects of elevated ozone on chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence in symptomatic and asymptomatic leaves of two tomato genotypes

Two different genotypes of Lycopersicon esculentum Mill. (cv. Cuor di Bue, O₃-sensitive and line 93.1033/1, O₃-resistant) were treated with a single dose of ozone (150 mm³ m⁻³ for 3 h). The PS 2 activity was examined by measurements of chlorophyll a fluorescence on symptomatic and asymptomatic leaves. Symptoms were evident on the 4^th leaves from the bottom, in both genotypes, while the 2^nd leaves of the line 93.1033/1 were asymptomatic. In these leaves, the net photosynthetic rate (P_N) did not change even if the F_v/F_m ratio significantly decreased. A strong reduction in P_N, mostly due to the stomatal closure, was observed in Cuor di Bue. The non photochemical quenching coefficient (q_NP) and the degree of PS 2 reaction centres closure (1-q_P) were higher, while the quantum efficiency of PS 2 photochemistry (Φ_PS2) and quantum efficiency of excitation energy capture (Φ_exc.) were lower in O₃ treated leaves of both genotypes. The limitation of photosynthesis was shown also by a decrease in the parameter %P, which diminished compared to controls in both genotypes. The response of the two genotypes for the energy fraction dissipated as thermal energy in the PS 2 antennae (%D) was similar. The fraction of %P remained lower during the recovery in symptomatic leaves of the resistant line as compared to the controls, whereas %X, which represents the amount of light energy that is not utilized in photochemistry or dissipated in the PS 2 antennae, significantly rose in the asymptomatic leaves of this line and in both the leaves of Cuor di Bue. From data obtained we concluded that ozone affected the plants independently on the appearance of visible symptoms of injury because the leaves without visible symptoms of both the genotypes were negatively influenced.     

Effects of Tomatex /Triacontanol/ on chlorophyll fluorescence and tomato (Lycopersicon esculentum Mill.) yields

The influence of triacontanol in a form of Tomatex preparation on basic indices of chlorophyll fluorescence in tomato leaves (Delfina cv.), yield of fruits, and dry matter content in fruits was evaluated in a pot experiment situated in vegetation hall in 1999. Tomatex was applied into roots at seedling stage (6–7 leaves) or at the stage of seedling and flowering of the 2^nd inflorescence bunch. Plants were given by 0.3, 3.0, and 30 μg triacontanol per pot at a single dosage. Results obtained have shown that triacontanol regardless of the dose applied, significantly increased the maximal efficiency of PSII photochemistry in the dark (F_v/Fm), the efficiency of excitation capture by open PSII reaction centers (F_v’/F_m’), the actual quantum yield of PSII electron transport in the light-adapted state (Φ_PSII), the photochemical quenching coefficient (Q_p). However, nonphotochemical quenching coefficient (Q_n) and non-radiative dissipation (NPQ) were decreased. Plants treated with triacontanol at the doses of 0.3 and 3.0 μg had significantly higher yields of fruits than control. No differences were found between plants treated once and twice with the growth regulator. Triacontanol did not show univocal effects on dry matter content in fruits either.     

Photo-inhibition and seasonal photosynthetic performance of the seaweed Laminaria saccharina during a simulated tidal cycle: chlorophyll fluorescence measurements and pigment analysis

Laminaria saccharina (Lamouroux) form the largest, most abundant and conspicuous seaweed populations along the French coast of the eastern English Channel. As they are located in the intertidal zone, they are exposed to considerable irradiance variations, mainly related to tidal cycles. The response of these macro‐algae to light variations over a simulated daily tidal cycle was investigated in the laboratory during spring, autumn and winter using chlorophyll fluorescence and pigment analysis. The maximum quantum yield of photosystem II (PSII) photochemistry (F_v/F_m) and the operating PSII efficiency (Φ_PSII) showed clear daily cycles according to the irradiance variation throughout the 12 h simulated tidal cycle, whereas the pattern of the relative photosynthetic electron transport rate (rETR) was not so obvious. The algae reacted to the light increase by developing photoprotective mechanisms able to dissipate the excess energy reaching PSII by the de‐epoxidation of violaxanthin into zeaxanthin. Because of their better acclimation to strong irradiance, spring populations were less affected by this light treatment than were winter populations. In particular, L. saccharina showed more pigments of the xanthophyll cycle in spring to cope with strong irradiance exposure. Alternatively, they developed their antenna complexes in winter to harvest a maximum of light.     

Polyamine levels in pollinated and auxin-induced fruit of tomato (Lycopersicon esculentum) during development

The changes taking place during fruit development in the concentration of the 3 polyamine fractions, i.e. free, perchloric acid-soluble conjugates and perchloric acid-insoluble bound polyamines, were analyzed in tomato fruits ( Lycopersicon esculentum Mill, cv. F121) induced to set by either pollination or auxin application. Before the onset of cell division, total polyamines were 50% higher in auxin-treated fruits than in pollinated ones, most of the polyamines being found as perchloric acid-soluble conjugates in both fruit set treatments. At the onset the level of polyamines in both fruit types was 100 times higher than during cell expansion or ripening. The highest polyamine found during cell division was perchloric acid-soluble conjugated spermidine in both fruit set treatments. After cell division, polyamine concentration was similar in both fruit set treatments. The concentration of polyamines in the jelly was similar in pollinated and auxin-induced fruits during cell expansion but not during ripening. At the onset of ripening there was an increase of one order of magnitude in the concentration of perchloric acid-insoluble bound putrescine in the jelly of pollinated fruits. Polyamines were more than 5-fold higher in unpollinated ovaries than in fruits induced to set by either pollination or auxins. It is suggested that pollinated and parthenocarpic fruits differ in their polyamine metabolism during the initial stages of development, but not after cell division. It is also suggested that polyamines undergo rapid turnover during cell division. Perchloric acid-insoluble bound putrescine might play a role in seed formation in tomatoes.     

Effect of plant variety, plant age and photoperiod on glandular pubescence and host-plant resistance to potato moth (Phthorimaea operculella) in Lycopersicon spp.

The effect of plant age and daylength on glandular pubescence was determined for two lines of tomato derived from Lycopersicon hirsutum (BTN 979 and LA 1777A) and a variety of L. esculentum (N 91‐1‐1‐1‐1). Densities of type I, IV, VI and VII glandular trichomes were lowest in N 91‐1‐1‐1‐1 and, over all varieties, were more dense on plants aged greater than 6 wk. Daylength interacted with variety to significantly affect densities of type VII trichomes only. Host‐plant resistance to Phthorimaea operculella was determined in preliminary tests using insects cultured from founders from a potato crop and in confirmatory tests using (less readily available) insects recovered from foliage of a tomato crop. Mortality of ex‐potato neonates on LA 1777 A and BTN 979 foliage was higher 18 h after placement than for N 91‐1‐1‐1‐1, with no effect of day length or plant age. Mortality for ex‐tomato neonates followed a similar trend. Ten days later, two‐thirds of ex‐tomato larvae had established mines on N 91‐1‐1‐1‐1 but fewer (16.7%) were live on other varieties. Stepwise multiple regression using variety as the sole factor was significant (P<0.001) in accounting for 61.4% of the variation in ex‐tomato larval survival but addition of other factors to the regression model was not significant. BTN 979 supported fewer, smaller adults to develop than did N 91‐1‐1‐1‐1, whilst no adults developed on LA 1777 A. In a non‐choice test using ex‐potato adults, significantly more eggs were laid on N 91‐1‐1‐1‐1 than on L. hirsutum varieties and 9‐wk‐old plants were preferred over plants three weeks older or younger. The same variety and plant age trends were evident in a free‐choice test using ex‐tomato adults.     

遮荫对濒危植物崖柏光合作用和叶绿素荧光参数的影响

崖柏(Thuja sutchuenensis)是我国特有的极度濒危植物。目前尚缺乏从光合生理角度对其濒危机制开展讨论与研究。光是影响植物生存和生长发育最重要的环境因子之一,且有可能成为植物种群自然更新的主要限制因子。因此,通过人工遮荫方式,探讨了3种光环境下(L0全光,L1-50%全光,L2-25%全光)崖柏幼苗的光合能力及叶绿素荧光参数的差异。结果表明,遮荫导致了叶片表观量子效率和最大净光合速率增加。随着生长光强的降低,崖柏幼苗的暗呼吸速率、光补偿点和光饱和点均有所下降。叶绿素荧光参数方面,遮荫导致了PSⅡ原初光能转换效率(Fv/Fm)、PSⅡ潜在活性(Fv/Fo)、PSⅡ有效光量子产量(Fv'/Fm')和非光化学猝灭系数(NPQ)增加;但随着生长光强减弱,崖柏幼苗叶片的光化学猝灭系数(PQ)和电子传递速率(ETR)逐渐降低。同时,遮荫也造成了叶片叶绿素含量(Chla+Chlb)的显著增加。结果表明,崖柏对光具有较强的耐受范围(尤其是低光)和内在调节机制,初步判定崖柏林下光照的不足不会成为崖柏自然更新的决定性限制因子。     

Relationships among violaxanthin deepoxidation,thylakoid membrane conformation,and nonphotochemical chlorophyll fluorescence quenching in leaves of cotton (Gossypium hirsutum L.)

The kinetics and temperature dependencies of development and relaxation of light-induced absorbance changes caused by deepoxidation of violaxanthin to antheraxanthin and zeaxanthin (Z; peak at 506 nm) and by light scattering (S; peak around 540 nm) as well as of nonphotochemical quenching of chlorophyll fluorescence (NPQ) were followed in cotton leaves. Measurements were made in the absence and the presence of dithiothreitol (DTT), an inhibitor of violaxanthin deepoxidase. The amount of NPQ was calculated from the Stern-Volmer equation. A procedure was developed to correct gross AS (S_g) for absorbance changes around 540 nm that are due to a spectral overlap with Z. This protocol isolated the component which is caused by light-scattering changes alone (S_n). In control leaves, the kinetics and temperature dependence of the initial rate of rise in S_n that takes place upon illumination, closely matched that of Z. Application of DTT to leaves, containing little zeaxanthin or antheraxanthin, strongly inhibited both S_n and NPQ, but DTT had no inhibitory effect in leaves in which these xanthophylls had already been preformed, showing that the effect of DTT on A_n and NPQ results solely from the inhibition of violaxanthin deepoxidation. The rates and maximum extents of S_n and NPQ therefore depend on the amount of zeaxanthin (and/or antheraxanthin) present in the leaf. In contrast to the situation during induction, relaxation of Z upon darkening was much slower than the relaxation of S_n and NPQ. The relaxation of S_n and NPQ showed quantitatively similar kinetics and temperature dependencies (Q₁₀=2.4). These results are consistent with the following hypotheses: The increase in lumen-proton concentration resulting from thylakoid membrane energization causes deepoxidation of violaxanthin to antheraxanthin and zeaxanthin. The presence of these xanthophylls is not sufficient to cause S_n or NPQ but, together with an increased lumen-proton concentration, these xanthophylls cause a conformational change, reflected by S_n. The conformational change facilititates nonradiative energy dissipation, thereby causing NPQ. Membrane energization is prerequisite to conformational changes in the thylakoid membrane and resultant nonradiative energy dissipation but the capacity for such changes in intact leaves is quite limited unless zeaxanthin (and/or antheraxanthin) is present in the membrane. The sustained S_n and NPQ levels that remain after darkening may be attributable to a sustained high lumen-proton concentration.Abbreviations A antheraxanthin - DTT dithiothreitol - F, F_m chlorophyll fluorescence yield at actual, full closure of the PSII centers - NPQ nonphotochemical chlorophyll fluorescence quenching - PFD photon flux density - PSII photosystem II - V violaxanthin - Z zeaxanthin - S_n, Z spectral absorbance change caused by light-scattering, violaxanthin deepoxidation We thank Connie Shih for skillful assistance in growing the plants, and for conducting HPLC analyses. A Carnegie Institution Fellowship and a Feodor-Lynen-Fellowship by the Alexander von Humboldt-Foundation to W. B. is gratefully acknowledged. This work was supported in part by Grant No. 89-37-280-4902 of the Competitive Grants Program of the U.S. Department of Agriculture to O.B. This is C. I. W. — D. P. B. Publication No. 1094.     

外源NO与蔗糖对盐胁迫下番茄(Lycopersicon esculentum Mill)幼苗氧化损伤的保护效应

选取长至6～8片真叶的健康番茄(Lycopersicon esculentum Mill)幼苗,分别进行蔗糖、硝普钠(sodium nitropresside, SNP, 作为外源NO供体)及其体积比例组合(1:1)处理;36h后施以NaCl胁迫,并分别于0h(胁迫前)、24h、48h和72h 取样,进行相关生理生化指标测定.具体5个实验处理如下:A. 蒸馏水(CK); B. 100 mmol/L NaCl;C. 0.1 mmol/L SNP 100 mmol/L NaCl;D. 0.1 mmol/L SNP 1.0mmol/L蔗糖 100 mmol/L NaCl; E. 1.0 mmol/L蔗糖 100 mmol/L NaCl.结果表明:与SNP和蔗糖单独处理相比,二者组合处理对缓解盐胁迫下番茄幼苗的氧化损伤存在正协同效应,主要表现在进一步增强了番茄幼苗超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)的活性;提高了脯氨酸(Pro)的含量,同时膜脂过氧化产物丙二醛(MDA)含量显著降低(P＜0.05).采用聚丙烯酰胺浓度梯度凝胶电泳对盐胁迫24 h和48 h材料的POD同功酶检测表明,当NaCl单独处理时,番茄幼苗叶片POD同功酶第V条带缺失,其它谱带酶量减少,抑制了POD同功酶的表达;SNP和蔗糖单独处理能够保护盐胁迫(24、48h)所导致的POD同功酶条带的完整;而组合处理既保证了POD同功酶条带的完整,又加强了酶量的表达.随着盐胁迫时间的延长,其氧化损伤程度愈烈,SNP和蔗糖组合处理能够更有效地缓解盐胁迫对番茄幼苗植株造成的氧化损伤.     

Influence of nicotianamine and iron supply on formation and elongation of adventitious roots in hypocotyl cuttings of the tomato mutant 'chloronerva' (Lycopersicon esculentum)

The influence of nicotianamine (NA) on formation and elongation of adventitious roots in hypocotyls of de-rooted NA-less mutant seedlings of Lycopersicon esculentum Mill, was examined in relation to the iron supply [ferric N-N'-ethylenediaminedi-(2-hydroxyphenylacetate) (FEDDHA), ferric ethylenediaminetetracetate (FeEDTA), ferric N-(2-hydroxyethyl)-ethylenediaminetriacetate (FeHEDTA, Fe-citrate and FeCl₃] in the nutrient solution. The initiation of root primordia in hypocotyl cuttings was independent of NA and occurred with about the same frequency in both, mutant and wild-type. In the mutant the development of primordia to adventitious roots was blocked at all iron sources used, except FeEDTA. Addition of NA (5x 10⁻⁶ to 2 × 10⁻⁵ M ) to the rooting medium resulted in a fast growth of adventitious roots in mutant cuttings with all iron sources tested. Rooting of wild-type cuttings was independent from NA application and iron sources. We suppose that NA is involved in the intracellular transport of iron. Its function is possibly linked with chelation of ferrous iron in the cell.     

Photoinhibition at chilling temperatures and effects of freezing stress on cold acclimated spinach leaves in the field. A fluorescence study

The role of high light stress in a natural environment was studied on spinach plants ( Spinacia oleracea L. cv. Wolter) grown in the field during the winter season. Fluorescence induction (at 293 K and 77 K) of leaves was used to characterize the stress effects. Night frost with minimum temperatures between – 1.5°C and –7.5°C (i.e. above the'frost killing point'at ca. –11.5°C) led to impaired photosynthesis. This was seen as increased initial fluorescence (F_o), decreased ratio of variable to maximum fluorescence (F_V/F_M) and lowered rates of O₂ evolution. The freezing injury was reversible within several frostless days. Exposure to high light (about 900 mol m_–2 s_–1) at chilling temperatures in the field caused photoinhibition, manifested as decreased variable fluorescence (F_V) and F_V/F_M ratio without changes in F_O. The photoinhibitory fluorescence quenching was not stronger after frost than after frostless nights; synergism between light stress and preceding freezing stress was not observed. Fluorescence induction signals at 77 K showed that F_V of photosystems I and II decreased to the same extent, indicating increased thermal deactivation of excited chlorophyll. Photoinhibition was fully reversible at +4°C within 1 h in low light, but only partially in moderate light. Preceding night frosts did not affect the recovery. The photoinhibition observed here is regarded as a protective system of thermal dissipation of excess light energy.     

Adaptability of tomato and pepper leaves to changes in photoperiod: Effects on the composition and function of the thylakoid membrane

The adaptability of the thylakoid membrane to extended photoperiod (from natural to 24 h) was studied using a photoperiod-sensitive species ( Lycopersicon esculentum Mill. cv. Trend) and a non-photoperiod-sensitive species ( Capsicum annuum L. cv. Delphin). Our results have shown that thylakoid membranes of both species adapt to an extended photoperiod by increasing their photosystem II to photosystem I ratio (PSII/PSI) in order to provide a more balanced energy distribution between both photosystems to improve quantum yield. In tomato plants, these results correspond with a lower chlorophyll (Chl) a/b ratio, a decrease in Chl associated with PSI light-harvesting chlorophyll a/b protein complexes and with an increase in Chl associated with PSII light-harvesting chlorophyll a/b protein complexes. In spite of these changes, the electron transport capacity through PSII and PSI per unit of Chl and the light saturation point of PSII remained unchanged. The inability of tomato plants to use supplemental light for an extended photoperiod is not the result of photoinhibitory conditions. In pepper plants a significant increase in electron transport capacity and in the light saturation point of PSII was found. There was a significant increase in CO₂ assimilation when the light period was increased from 12 to 24 h. In contrast to tomato, pepper plants adapt to a 24-h photoperiod by increasing their carboxylation capacity which is accompanied by an increase in electron transport capacity and the light saturation point.