Effects of geminivirus infection and growth irradiance on the vegetative growth and photosynthetic production of Eupatorium makinoi

Eupatorium makinoi plants with or without geminivirus infection were grown in shading frames with 70, 15 and 5.5% sunlight. Growth characteristics of these plants in the early vegetative phase were compared by means of growth analysis. We also measured leaf photosynthetic gas exchange rates and examined relationships between leaf photosynthesis and whole-plant growth. Relative growth rate (RGR=(1/W)×(dW/dt), where W is plant dry mass) of virus-infected plants was lower than that of uninfected plants under all three light conditions. The reduction of RGR by infection was increased with irradiance. The net assimilation rate (NAR=(1/A)×(dW/dt), where A is total leaf area of the plant) was also reduced both by infection and shading. NARs that were estimated from light-response curves of leaf photosynthesis, in situ measurements of irradiance, and respiration rates of leaves, stems and below-ground parts, agreed very well with the values obtained by conventional growth analysis techniques. Decreases in the estimated NAR value from infection and shading were mostly explained by the decreases in leaf photosynthesis. These results clearly showed that lowered RGR in virus-infected plants was attributed mainly to impaired photosynthesis in virus-infected leaves.     

Photosynthetic responses of <Emphasis Type="Italic">Chrysanthemum morifolium</Emphasis> to growth irradiance: morphology,anatomy and chloroplast ultrastructure

Seedlings of Chrysanthemum, cultivar ‘Puma Sunny’, were grown under a range of shading regimes (natural full sunlight, 55, 25, and 15% of full sunlight) for 18 days. Here, we characterized effects of varying light regimes on plant morphology, photosynthesis, chlorophyll fluorescence, anatomical traits, and chloroplast ultrastructure. We showed that leaf color was yellowish-green under full sunlight. Leaf area, internode length, and petiole length of plants were the largest under 15% irradiance. Net photosynthetic rate, water-use efficiency, PSII quantum efficiency, and starch grain were reduced with decreasing irradiance from 100 to 15%. Heavy shading resulted in the partial closure of PSII reaction centers and the CO₂ assimilation was restricted. The results showed the leaves of plants were thinner under 25 and 15% irradiance with loose palisade tissue and irregularly arranged spongy mesophyll cells, while the plants grown under full sunlight showed the most compact leaf palisade parenchyma. Irradiance lesser than 25% of full sunlight reduced carbon assimilation and led to limited plant growth. Approximately 55% irradiance was suggested to be the optimal for Chrysanthemum morifolium.     

不同光照条件下喜阴植物谢君魔芋对稳态和动态光源的响应特征

谢君魔芋(Amorphophallus xiei)是起源于云南西南地区热带雨林的典型喜阴植物,近年来得到了广泛种植和推广,在种植过程中,谢君魔芋需要采用遮荫栽培模式。为了揭示谢君魔芋对光照强度的适应策略,该研究探讨了生长在不同光照强度下(透光率为50%、29%、17%、7%)谢君魔芋叶片的光合作用特征、光合诱导特征、光合色素含量以及叶片氮素(N)含量和N分配。结果表明:随着生长环境光照强度的降低,单位叶面积和单位叶质量最大净光合速率、光合色素含量、最大羧化速率、最大电子传递速率及比叶面积均增大,而暗呼吸和光补偿点均减小。在光合诱导过程中,生长在透光率为17%光环境中的谢君魔芋完成50%光合诱导所需的时间最短,约为81.4 s;在光诱导进行10 min时,诱导状态最高,为87.3%。完成50%和90%光合诱导所需的时间与低光下初始气孔导度呈负相关关系。随着生长光照强度降低,叶片中的N分配到羧化组分和生物能转化组分中的比例先增大后减小,在透光率为17%的光环境下具有最大值;而叶片中的N分配到捕光色素组分中的比例随着生长环境光照强度降低而增加。该研究结果表明,喜阴植物谢君魔芋通过加强对低光和动态光源的利用能力及有效的N资源分配策略来适应低光照环境。     

The influence of the holoparasitic plant Cuscuta campestris on the growth and photosynthesis of its host Mikania micrantha

The influence of the holoparasite Cuscuta campestris Yuncker on the growth and photosynthesis of Mikania micrantha H.B.K. was studied. The results indicate that C. campestris infection significantly reduced the light use efficiency and light saturation point of the host. It significantly reduced the net photosynthetic rate (P(n)) of the 1st and 8th mature leaves of M. micrantha at light saturation point, the apparent quantum yield of the 1st mature leaves, the carboxylation efficiency and CO(2) saturated P(n) of the 8th mature leaves, but increased the light compensation point of the 1st mature leaves. Diurnally, it significantly reduced P(n) between 08.00 h and 16.00 h and stomatal conductance and transpiration from 10.00 h to 16.00 h for the 8th mature leaves. Moreover, the significantly adverse effects of C. campestris infection on P(n) were observed 18 d after parasitization (DAP) for the 4th, 8th and 12th, and 25 DAP for the 1st mature leaves of M. micrantha, and they became greater with infection time. The infection also significantly reduced the number of leaves, leaf area, stem length, and biomass, and prevented flowering of M. micrantha in the growing season, and caused almost complete death of the aerial parts of the host about 70 DAP, but the uninfected plants grew and developed normally. Furthermore, the total biomass of the infected host and the parasite was significantly less than that of the uninfected plants. Therefore, besides resource capture by C. campestris, the reduced growth of the infected plants must also be due to the negative effects of the parasite on host photosynthesis.     

Striga hermonthica reduces photosynthesis in sorghum: the importance of stomatal limitations and a potential role for ABA?

We report the effects of the root hemiparasite Striga hermonthica (Del.) Benth. on the growth and photosynthesis of two cultivars of sorghum: CSH-1, a susceptible variety, and Ochuti, which shows some tolerance to S. hermonthica in the field. Within 4 d of parasite attachment to the host roots, infected plants of both cultivars were significantly shorter than uninfected controls. At 55 d, infected plants of both cultivars had significantly less shoot and root biomass, and significantly smaller leaf areas than uninfected controls. The dry weight of S. hermonthica attached to host roots was insufficient at this stage to explain the decreased growth in terms of a competing sink for carbon and nitrogen. Leaf chlorophyll and nitrogen per unit area were greater in infected plants of both cultivars compared with control plants. However, whereas photosynthesis and transpiration in young leaves of infected CSH-1 plants declined with time when compared with controls, the rates in infected Ochuti plants were similar to those in uninfected controls throughout the time course of observation. In both cultivars, a strong correlation was observed between the rate of photosynthesis and stomatal conductance during photosynthetic induction, but infection resulted in a much slower induction than in controls. In CSH-1 plants, both steady-state photosynthesis and stomatal conductance were lower than in controls, whereas in leaves of Ochuti steady-state photosynthesis and stomatal conductance eventually reached the same values as in the control leaves. Results from AlC_i analysis and also from determination of ¹³C isotope discrimination were consistent with a stomatal limitation to photosynthesis in the leaves of Striga-infected plants. The concentration of the plant growth regulator abscisic acid (ABA) was measured in the xylem sap of infected CSH-1 plants only, and was found to be twice that of uninfected plants. A possible role of ABA in determining host response to infection by S. hermonthica is discussed.     

Mechanisms of photoinhibition induced by high light in Hosta grown outdoors

Aims It has long been recognized that photoinhibition of photosynthesis is induced by high light. However, our recent studies are not consistent with this traditional view. Therefore, the objective of this study is to explore the induction of photoinhibition and its mechanisms under full sunlight outdoors.
Methods Changes of leaf morphology, gas exchange, and chlorophyll a fluorescence were measured to investigate the induction and mechanisms of photoinhibition under high light in Hosta, which is a typical shade-tolerant plant.
Important findings Hosta plants grown under full sunlight (HT) and low light (LT) developed sun- and shade-type leaf morphological characteristics, respectively. Under a full sunlight, Hosta plants had lower photosynthetic rate and chlorophyll content than under the LT; whereas, there were only slight difference in the maximum quantum yield of photosystem II (F_v/F_m) between the two treatments, suggesting that Hosta plants could grow normally under full sunlight without severe photoinhibition. After transition from the low to a high light (LHT), the photosynthetic rate and maximum quantum yield of photosystem II decreased sharply, reflecting that the LHT treatment led to irreversibly inactivation of photosystem II. Additionally, the shape of chlorophyll a fluorescence transients also changed significantly; the relative fluorescence yield of the K and J steps were reduced by 24.3% and 34.2%, respectively, indicating that the acceptor side of photosystem II was damaged more severely than the donor side. Consequently, we postulate that photoinhibition in Hosta leaves is mainly induced by the sudden enhancement of light intensity outdoors. Hosta can acclimate to high irradiance through leaf development outdoors. Our finding is of great significance in understanding the acclimation of plants to high light and cultivation of shade-tolerant plants in field.     

Functional significance of triazine-herbicide resistance in defence of Senecio vulgaris against a rust fungus

We investigated the functional significance of plant performance (dry mass, photosynthesis) in plant defence (resistance and tolerance) against pathogen infection, and potential negative cross-resistance between herbicide resistance and plant defence against disease. We compared isonuclear triazine-herbicide-resistant (TR) and -susceptible (TS) biotypes of Senecio vulgaris, in the presence and absence of infection by the rust Puccinia lagenophorae. In a growth chamber study with two reduced irradiance levels, rust infection had a severe effect on plant performance with infected plants having 55% less dry mass and 54% reduced whole-plant photosynthesis than non-infected plants. The TR biotype was more susceptible (reduced resistance) to the pathogen, but the biotypes did not differ in their ability to compensate for rust infection (tolerance). TR plants were less productive than TS plants when grown non-shaded (ca. 10% full sunlight) but not when shaded (ca. 5% full sunlight). This is especially important for situations, where S. vulgaris grows under the crop canopy (e.g. in maize). Here, very low light levels might contribute to a numerical increase of TR relative to TS plants even when only occasionally treated with triazine. Whole-plant photosynthesis was reduced by 21% in TR plants as compared to the TS biotype, and by 59% in plants grown in the shaded as compared to the non-shaded treatment. When whole-plant photosynthesis values were corrected for the estimated leaf area of plants, we found no significant variation between biotypes, shade treatments or rust treatments. In experimental mixed TR:TS field populations, the proportion of TR plants decreased more rapidly in rust-infected populations than uninfected. This finding, together with the lower resistance in the TR than the TS biotype to the rust fungus observed in the growth chamber experiment, may indicate negative cross-resistance, which is a potential tool in the management of herbicide-resistant weeds.     

Photosynthetic acclimation to variability in the light environment of early and late successional plants

Summary Fourteen plant species from early-, mid-, and late-successional habitats were grown for a period of 25 to 50 days in each of two light environments, i.e. full sunlight and in deep shade. The rate of photosynthesis for newly formed leaves was measured as a function of light intensity for plants from each light environment. Photosynthetic flexibility, measured as the difference in response between sun- and shade-grown plants, was determined for each of 5 parameters including dark respiration, quantum yield, light compensation, half-saturating irradiance for photosynthesis, and the photosynthetic rate at 1,400 E m^-2 s^-1. We found photosynthetic flexibility to be high for early successional annuals, intermediate for midsuccessional species, and low for late successional species.     

Photosynthetic acclimation of Tradescantia albiflora to growth irradiance: morphological, ultrastructural and growth responses

Tradescantia albiflora (Kunth), a trailing ground species naturally occurring in deep shade in rainforests, has an unusual photosynthetic acclimation profile for growth irradiance. Although capable of increasing its capacity for electron transport, photophosphorylation and carbon fixation when grown in full sunlight, Tradescantia has constant chlorophyll alb ratios, photosystem reaction centre stoichiometry and pigment-protein composition at all growth irradiances (Chow et al. 1991. Physiol. Plant. 81: 175–182). To gain an insight into the compensatory strategies which allow Tradescantia to grow in both high and low lights, plants were grown under shade cloth (100 to 1.4% relative growth irradiance) and leaf and chloroplast attributes were compared. While shade Tradescantia chloroplasts had three times more chlorophyll per chloroplast and twice the length of thylakoid membranes compared to plants grown in full sunlight, the ratios of appressed to nonappressed thylakoid membranes were constant. The average net surface charge density of destacked thylakoids was the same for plants grown at moderate and low-irradiance, consistent with their similar stacking profiles. Tradescantia plants grown in direct sunlight had 10-times more fresh and dry weight per plant compared to plants grown in shade, despite a lower photosynthetic capacity on a leaf area basis with partial photoinhibition. We conclude that having a light-harvesting apparatus permanently locked into the "shade-plant mode " does not necessarily prevent a plant from thriving in high light. Analyses of leaf growth at different irradiances provide a partial explanation of the manner in which Tradescantia compensates for very low photosynthetic capacity per unit leaf in sunlight.     

Systemic regulation of leaf anatomical structure, photosynthetic performance, and high-light tolerance in sorghum

Leaf anatomy of C3 plants is mainly regulated by a systemic irradiance signal. Since the anatomical features of C4 plants are different from that of C3 plants, we investigated whether the systemic irradiance signal regulates leaf anatomical structure and photosynthetic performance in sorghum (Sorghum bicolor), a C4 plant. Compared with growth under ambient conditions (A), no significant changes in anatomical structure were observed in newly developed leaves by shading young leaves alone (YS). Shading mature leaves (MS) or whole plants (S), on the other hand, caused shade-leaf anatomy in newly developed leaves. By contrast, chloroplast ultrastructure in developing leaves depended only on their local light conditions. Functionally, shading young leaves alone had little effect on their net photosynthetic capacity and stomatal conductance, but shading mature leaves or whole plants significantly decreased these two parameters in newly developed leaves. Specifically, the net photosynthetic rate in newly developed leaves exhibited a positive linear correlation with that of mature leaves, as did stomatal conductance. In MS and S treatments, newly developed leaves exhibited severe photoinhibition under high light. By contrast, newly developed leaves in A and YS treatments were more resistant to high light relative to those in MS- and S-treated seedlings. We suggest that (1) leaf anatomical structure, photosynthetic capacity, and high-light tolerance in newly developed sorghum leaves were regulated by a systemic irradiance signal from mature leaves; and (2) chloroplast ultrastructure only weakly influenced the development of photosynthetic capacity and high-light tolerance. The potential significance of the regulation by a systemic irradiance signal is discussed.     

Photosynthetic Characteristics of Eastern Dwarf Mistletoe (Arceuthobium pusillum Peck) and its Effects on the Needles of Host White Spruce (Picea glauca [Moench] Voss)

Abstract: We studied the biochemical composition and photosynthetic characteristics of the aerial parasite eastern dwarf mistletoe (Arceuthobium pusillum) and the effect of infection on the needles of host white spruce (Picea glauca) in a coastal forest stand in Maine, USA. Eastern dwarf mistletoe was capable of photosynthetic oxygen evolution; however, rates were low and were exceeded by respiratory oxygen consumption at all light intensities through full sunlight. Therefore, eastern dwarf mistletoe acts as a net sink for host photosynthate. Relative to those of uninfected trees, needles from infected branches of white spruce were significantly smaller in terms of length, fresh weight, maximum cross section and the diameter of the vascular cylinder. Needles of uninfected and infected trees did not differ in terms of fresh weight to dry weight ratio, nor in nitrogen, soluble sugar or starch content. Needles of infected trees possessed significantly less α-carotene and neoxanthin, but did not otherwise differ from uninfected needles in terms of chlorophyll and carotenoid composition. Since specific physiological roles for α-carotene and neoxanthin have not been described, the functional significance of the decreases in their content is not known. Photosynthetic capacities of needles from infected and uninfected white spruce did not differ significantly, as measured by oxygen evolution. These findings suggest that dwarf mistletoe infection does not substantially perturb host white spruce source-sink balance at the end of the growing season and that carbon exchange dynamics between the host and parasite are unlikely to fully explain the detrimental effects of infection on white spruce.     

遮荫和全光下生长的棉花光合作用和叶绿素荧光特征

 遮荫条件下（遮荫下光强相当于自然光强的40％左右）棉花(Gossypium hirsutum)叶片光合速率明显降低,仅为自然光强下生长叶片的30%～40％,叶片中RuBP羧化酶活性降低,而表观量子效率(AQY)较高。不同光照条件下生长的棉花叶片对短时间持续光强的光合诱导过程有明显的差异,由弱光转到强光下,自然光强下生长的叶片的Pn、Gs、ΦPSⅡ及非光化学猝灭系数(NPQ)都能在较短的时间内达到最大值,而遮荫叶片需要的时间较长;遮荫下生长的棉花叶片的实际光化学效率,随光强的增加下降幅度较大,而自然光照下生长的叶片下降幅度较小;自然光照下生长的叶片的NPQ随光强的升高达到较高水平,而遮荫叶片在较低的光强下即达到最大值,此时NPQ较低,遮荫叶片依赖于叶黄素循环的能量耗散水平较低。遮荫叶片较低的光合速率以及过剩光能耗散能力是其转入自然强光后光抑制严重的主要原因。     

Induction characteristics and response of photosynthetic quantum conversion to changes in irradiance in mulberry plants

A study was conducted, using rapid time course of chlorophyll (Chl) fluorescence parameters, and light-response curves of Chl fluorescence parameters, to determine the induction requirements and response of photosystem II (PSII) photochemistry and non-photochemical reactions after changes in irradiance in greenhouse mulberry plants. The induction of PSII photochemistry rapidly approached to steady state after leaves were treated from darkness to low irradiance (LI). When irradiance of leaves changed from darkness to high irradiance (HI), a biphasic induction was observed. A slight photoinhibition occurred in the leaves exposed to sunlight coming to the greenhouse, whereas a chronic photoinhibition occurred in the leaves fully exposed to sunlight outside the greenhouse. The chronic photoinhibition was demonstrated by sustained reduction of maximal quantum yield of PSII photochemistry (Fv/Fm). Moreover, the leaves of mulberry plants in greenhouse were sensitive to abrupt changes in irradiance and the sensitivity of leaves suffered in a short-term (1h) high light treatment was reduced, based on the changes in photosynthetic quantum conversion. These results demonstrated an inducible response of photosynthetic quantum conversion to changes in irradiance in mulberry.     

The effect of shading on photosynthesis,growth, and regrowth following defoliation for Bromus tectorum

Summary The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects.     

Photosynthetic Characteristics of Rice Leaves Aged under Different Irradiances from Full Expansion through Senescence

Effects of irradiance on photosynthetic characteristics were examined in senescent leaves of rice (Oryza sativa L.). Two irradiance treatments (100 and 20% natural sunlight) were imposed after the full expansion of the 13th leaf through senescence. The photosynthetic rate was measured as a function of intercellular CO₂ pressure with a gas-exchange system. The amounts of cytochrome f, coupling factor 1, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and chlorophyll were determined. The coupling factor 1 and cytochrome f contents decreased rapidly during senescence, and their rates of decrease were much faster from the 20% sunlight treatment than from the full sunlight treatment. These changes were well correlated with those in the photosynthetic rate at CO₂ pressure = 600 microbars, but not with those under the ambient air condition (350 microbars CO₂) and 200 microbars CO₂. This suggested that the amounts of coupling factor 1 and cytochrome f from the full sunlight treatment cannot be limiting factors for the photosynthetic rate at ambient air conditions. The Rubisco content also decreased during senescence, but its decrease from the 20% sunlight treatment was appreciably retarded. However, this difference was not reflected in the photosynthetic rates at the ambient and 200 microbars CO₂. This implied that in vivo Rubisco activity may be regulated in the senescent leaves from the 20% sunlight treatment. The chlorophyll content decreased most slowly. In the 20% sunlight treatment, it remained apparently constant with a decline in chlorophyll a/b ratio. These photosynthetic characteristics of the senescent rice leaves under low irradiance were discussed in relation to acclimation of shade plants.     

Susceptibility of Tobacco Leaves to Photoinhibition following Infection with Two Strains of Tobacco Mosaic Virus under Different Light and Nitrogen Nutrition Regimes

Sensitivity to photoinhibition under high light stress (2000 [mu]mol photons m-2 s-1 for 2 h in air) and recovery from this stress were examined in leaves of control, uninfected tobacco (Nicotiana tabacum cv Xanthi) leaves and in leaves in tobacco plants infected with tobacco mosaic virus (TMV) when grown under low light (150-200 [mu]mol photons m-2 s-1) or high light (1200 [mu]mol photons m-2 s-1) with high (8.0 mM) or low (0.5 mM) nitrate supply. Photoinhibition was monitored using the dark-adapted fluorescence parameters variable fluorescence/maximum fluorescence, an indicator of photosynthetic efficiency that correlated well with the quantum yield of photosynthetic oxygen evolution, and initial fluorescence, potentially an indicator of photoinhibitory damage. Susceptibility to photoinhibition was greater in low light- and low nitrogen-grown control plants than in high light- or high nitrogen-treated plants. Compared with uninfected controls, infection with the masked strain PV42 increased susceptibility to photoinhibition only in plants grown under low light/low nitrogen conditions. In expanding leaves, infection with severe strain TMV PV230 markedly accelerated photoinhibition under these conditions and under high light/low nitrogen conditions, even before visible symptoms were evident. High nitrogen levels during growth protected against this accelerated photoinhibitory response to virus infection during light stress and generally promoted recovery, at least prior to symptom development. As symptoms developed, the yellow regions provided evidence for chronic photoinhibitory damage, prior to and during the stress treatment, irrespective of growth conditions. Green regions of leaves showing visible symptoms were generally indistinguishable from control, uninfected plants during photoinhibitory stress and recovery. In developed leaves that remained free of visible symptoms during the experiments, in spite of the accumulation of about the same amounts of virus protein (S. Balachandran, C.B. Osmond, A. Makino [1994] Plant Physiol 104: 1043-1050) infection led to an acceleration of photoinhibition during stress treatments, especially in low light/low nitrogen treatments, in which chronic photoinhibitory damage was evident. These studies suggest a role for photoinhibitory damage in the acceleration of visible symptom development following TMV PV230 infection of expanding leaves, as well as in acceleration of senescence in developed leaves without visible symptoms.     

Physiological responses and photo-protective mechanisms of two Rhododendron plants to natural sunlight after long term shading

AimsResponses of plants to increased irradiance are governed by two strategies: an increase in the utilization of absorbed light and photo-protective mechanisms. Varied physiological responses to increased irradiance were observed in plant species with differing adaptabilities to light regimes. This research aims to explore the physiological responses and photo-protective mechanisms of two Rhododendron plants to changes in light regimes. MethodsChlorophyll fluorescence parameters and rapid light curves were measured for leaves of R. hybrida (a shade-tolerant species) and R. simsii (a light-loving and shade-tolerant species) following exposure to sunlight for five days after growing in the shade for one year.Important findings Natural sunlight decreased the efficiency of photochemical reaction by reducing the fraction of incident light in photochemical energy utilization and decreased thermal dissipation through regulating energy dissipation in photosystem II (PSII) in the leaves of R. hybrida. As a result, natural sunlight induced the accumulation of excess excitation energy in PSII, and caused photo-inhibition and even photodamage in the leaves of R. hybrida, which was suddenly transferred from long-term shading to sun exposures. The acclimation capacity to changes of growth light regimes was stronger in R. simsii than in R. hybrida, due to a higher capability for photochemical reaction, thermal dissipation and cyclic electron flows around photosystem I in the leaves of R. simsii. Rhododendron simsii could utilize a high fraction of incident light in photochemistry and regulate energy dissipation in PSII to protect the photosynthetic apparatus under both shading and natural sunlight condition. Therefore, high light intensity under natural sunlight did not cause photo-inhibition in R. simsii.     

两种杜鹃花属植物对长期遮阴后全光照环境的生理响应及其光保护机制

植物通过提高光能利用能力和光保护途径以响应环境光强的增加, 但不同植物对环境光强增加的生理响应存在差异, 从而导致植物对光环境的适应性不一致。为探讨植物对光环境变化的生理响应及其适应机制, 该文以遮阴条件下培养1年的2种杜鹃属(Rhododendron)植物比利时杜鹃(R. hybrida)和杜鹃(R. simsii)为材料, 对其由遮阴后转入全光照下培养5天时的叶片叶绿素荧光参数及其快速光曲线变化进行了比较研究, 以期从叶片吸收光能分配和光保护机制的角度探讨这2种植物对光环境变化的适应机制。结果表明: 全光照降低了喜阴植物比利时杜鹃叶片的光化学反应和热耗散能力, 且其吸收光能分配于光化学反应和调节性能量耗散部分的比例减少, 导致光系统II反应中心过量激发能积累, 造成了叶片光抑制甚至光破坏。杜鹃作为耐阴喜光植物对光环境变化具有较强的适应性, 具有较高的光化学反应、热耗散和环式电子传递能力等内在生理特性; 在遮阴和全光照两种光环境下均能维持较高的吸收光能在光化学反应和调节性能量耗散部分的分配比例, 从而保护了光合机构的正常运行, 是其全光照强光未造成叶片光抑制的原因。     

Effects of light availability on host plant chemistry and the consequences for behavior and growth of an insect herbivore

We examined how light availability influenced the defensive chemistry of tomato (Lycopersicon esculentum: Solanaceae). Tomato plants were grown either in full sunlight or under shade cloth rated at 73%. Leaves from plants grown in full sunlight were tougher, had higher concentrations of allelochemicals (chlorogenic acid, rutin and tomatine), and had less protein than leaves from plants grown in shade. We determined how these differences in host plant quality due to light availability affected the behavior and growth of a Solanaceae specialist, Manduca sexta. Both in the greenhouse and in the field, caterpillars on shade-grown plants grew heavier in a shorter amount of time than those on plants that had previously been grown in full sunlight. In contrast, the effects of previous light availability to plants on caterpillar behavior appeared to be minor.To further investigate how light availability to plants influenced herbivore growth, we examined the effects of leaf-powder diets made from tomato leaves of different ages (new, intermediate, or mature) grown in full sunlight or shade on caterpillar performance. Caterpillars fed diets made from plants grown in shade consumed less but grew faster than larvae fed diets made from tomato plants grown in full sunlight. Caterpillars fed diets made from new leaves grew larger in less time than caterpillars fed diets made from intermediate aged leaves. Caterpillars did not survive on the mature leaf powder diets. There were plant-light treatment by larval thermal regime interactions. For example, at 26:15 °C , plant-light treatment had no effect on stadium duration, but at 21:10 °C, stadium duration was prolonged with the full sunlight-new leaf diet compared with the shaded-new leaf diet. In a second diet experiment, we examined the interactive effects of protein and some tomato allelochemicals (rutin, chlorogenic acid and tomatine) on the performance of caterpillars. There were food quality by thermal regime interactions. For instance, at 26:15 °C , neither protein nor allelochemical concentration influenced stadium duration, whereas at 21:10 °C, stadium duration was prolonged with the low protein-high allelochemical diet, which simulated full sunlight leaves. In sum, light availability to plants affected defensive chemistry and protein concentration. The difference in food quality was great enough to influence the growth of a specialist insect herbivore, but the effects were temperature-dependent.     

不同传播方式的内生真菌感染对羽茅的生理生态影响北大核心CSCD

通过田间试验,研究了垂直传播的Neotyphodium属内生真菌和水平传播的Epichloё属内生真菌对羽茅(Achnatherum sibiricum)生理生态的影响。结果表明:Neotyphodium属内生真菌感染对羽茅的株高和叶长有显著的正效应,而Epichloё属内生真菌感染对羽茅株高和叶长的增益作用较少。感染Neotyphodium属内生真菌的羽茅最大净光合速率显著高于感染Epichloё属内生真菌的羽茅,Neotyphodium属内生真菌显著提升了羽茅的气孔限制值和水分利用效率,而实验测定的第一年结果显示:Epichloё属内生真菌对羽茅的各个光合指标具有明显的负效应(胞间CO2浓度除外)。Neotyphodium属内生真菌感染使得宿主植物积累的可溶性糖含量显著高于感染Epichloё属内生真菌的羽茅和不染菌的羽茅植株。感染Epichloё属内生真菌的羽茅中氮含量显著高于感染Neotyphodium属内生真菌的羽茅。总之,内生真菌的传播方式是影响羽茅生理生态学特性的一个因素,并且垂直传播的内生真菌对羽茅生长和生理特性的益处高于水平传播的内生真菌。