Differences In Net Photosynthetic Rate Research Articles

Emmer wheat (Triticum dicoccum Schuebl.) favours high photosynthetic capacity adaptation to low nitrogen stress.

Although tetraploid wheat has rich genetic variability for cultivar improvement, its physiological mechanisms associated with photosynthetic productivity and resilience under nitrogen (N) deficit stress have not been investigated. In this study, we selected emmer wheat (Kronos, tetraploid), Yangmai 25 (YM25, hexaploid), and Chinese Spring (CS, hexaploid) as materials and investigated the differences in net photosynthetic rate (Pn), carboxylation capacity, electron transfer capacity, photosynthetic product output, and photosynthetic N allocation under normal N (CK) and low N (LN) through hydroponic experiments. Tetraploid emmer wheat (Kronos) had a stronger photosynthetic capacity than hexaploid wheat (YM25, CS) under low N stress, which mainly associated with the higher degree of PSII opening, electron transfer rate, Rubisco content and activity, ATP/ADP ratio, Rubisco activase (Rca) activity and Rubisco activation state, and more leaves N allocation to the photosynthetic apparatus, especially the proportion of N allocation to carboxylation under low N stress. Moreover, Kronos reduced the feedback inhibition of photosynthesis by sucrose accumulation through higher sucrose phosphate synthetase (SPS) activity and triose phosphate utilization rate (VTPU). Overall, Kronos could allocate more N to the photosynthetic components to improve Rubisco content and activity to maintain photosynthetic capacity under low N stress while enhancing triose phosphate output to reduce feedback inhibition of photosynthesis. This study reveals the physiological mechanisms of emmer wheat that maintain the photosynthetic capacity under low N stress, which will provide indispensable germplasm resources for elite low-N-tolerant wheat improvement and breeding.

Dynamic QTL mapping revealed primarily the genetic structure of photosynthetic traits in castor (Ricinus communis L.)

High photosynthetic efficiency is the basis of high biomass and high harvest index in castor (Ricinus communis L.). Understanding the genetic law of photosynthetic traits will facilitate the breeding for high photosynthetic efficiency. In this study, the dynamic QTL mapping was performed with the populations F2 and BC1 derived from 2 parents with significant difference in net photosynthetic rate (Pn) at 3 stages, in order to reveal the genetic structure of photosynthetic traits. In F2 population, 26 single-locus QTLs were identified, including 3/3/1 (the QTL number at stage I/II/III, the same below), 1/2/0, 1/2/2, 1/3/1, 0/1/1, and 1/1/2 QTLs conferring Pn, water use efficiency (Wue), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and chlorophyll content (Cc), with a phenotypic variation explained (PVE) of 8.40%/8.91%/6.17%, 5.36%/31.74%/0, 7.31%/12.80%/15.15%, 1.60%/6.44%/0.02%, 0/1.10%/0.70% and 2.77%/3.96%/6.50% respectively. And 53 epistatic QTLs (31 pairs) were identified, including 2/2/5, 5/6/3, 4/4/2, 6/3/2, 3/2/0 and 4/0/0 ones conferring the above 6 traits, with a PVE of 6.52%/6.47%/19.04%, 16.72%/15.67%/14.12%, 18.57%/15.58%/7.34%, 21.72%/8.52%/7.13%, 13.33%/4.94%/0 and 7.84%/0/0 respectively. The QTL mapping results in BC1 population were consistent with those in F2 population, except fewer QTLs detected. Most QTLs identified were minor-effect ones, only a few were main-effect ones (PVE > 10%), focused on 2 traits, Wue and Tr, such as qWue1.1, qWue1.2, FqTr1.1, FqTr6, BqWue1.1 and BqTr3; The epistatic effects, especially those related to the dominance effects were the main genetic component of photosynthetic traits, and all the epistatic QTLs had no single-locus effects except qPn1.2, FqGs1.2, FqCi1.2 and qCc3.2; The detected QTLs underlying each trait varied at different stages except stable QTLs qGs1.1, detected at 3 stages, qWue2, qTr1.2 and qCc3.2, detected at 2 stages; 6 co-located QTLs were identified, each of which conferring 2–5 different traits, demonstrated the gene pleiotropy between photosynthetic traits; 2 QTL clusters, located within the marker intervals RCM1842-RCM1335 and RCM523-RCM83, contained 15/5 (F2/BC1) and 4/4 (F2/BC1) QTLs conferring multiple traits, including co-located QTLs and main-effect QTLs. The above results provided new insights into the genetic structure of photosynthetic traits and important references for the high photosynthetic efficiency breeding in castor plant.

English

Photosynthetic characteristics and expression patterns of the photosynthesis-related genes in the high-yield mulberry variety E’Sang 1 (E1) and normal mulberry variety Husang 32 (H32) were investigated in this study. The observation of daily variation of photosynthesis in E1 and H32 indicated that the peak of net photosynthetic rate(Pn)inE1 variety was significantly higher than that inH32 (P <0.05). Meanwhile, the Pn-PAR and Pn-Ci responses of E1 and H32 were evaluated, and the results showed that the carboxylation efficiency and compensation saturation point were much higher in E1 rather thanH32. Importantly, the photosystem II actual photochemical efficiency and photochemical quenching coefficient in the leaves of E1 were significantly higher than those in H32 (P<0.05). Also, the activity of RuBP in E1 was higher than that in H32 (P >0.05). Based on the RNA-seq data, a total of 3,356 differentially expressed genes (DEGs) were detected among different time points between E1 and H32. Of these, 1,136 DEGs were involved in the metabolic pathways, including three main photosynthesis-related metabolic pathways (i.e., carbon fixation in photosynthetic organisms, carbon metabolism, and porphyrin and chlorophyll metabolism). Meanwhile, 10 novel DEGs related to photosynthesis were detected, and four potential key genes of them could account for the differences in net photosynthetic rate and yield betweenH32 and E1.This study could provide important insights into the molecular breeding of mulberry varieties with high photosynthetic efficiency and contribute to understanding the genetic mechanism of photosynthesis.© 2021 Friends Science Publishers

Sex-specific responses of Populus deltoides to combined salinity and calcium under waterlogging conditions

In this study, we investigated the sex-specific ion uptake and physiological and biochemical responses to combined salinity and calcium treatments of male and female Populus deltoides under waterlogging conditions. Results indicate that both P. deltoides clones were sensitive to salinity and calcium. Under well-watered conditions, salinity stress could especially increase the Na content in female P. deltoides clones, whereas salinity and calcium could increase the K and Ca content in male clones. Waterlogging could evidently stimulate Na content in leaves under salinity, especially in female P. deltoides clones. However, waterlogging had no visible effects on the amount of Ca absorption between the two clones under abundant calcium conditions. The physiological and biochemical responses to combined salinity and calcium exceeded the effects of salinity or calcium individually. However, no significant difference was observed, hence indicating the similar responses of male and female P. deltoides clones. The lower Na content and Na:Ca ratio, and the higher K and Ca content in male clones suggest that the male clones could maintain ion homeostasis better than the female clones. The sex-specific differences in net photosynthetic rate, intercellular CO2 concentration, effective quantum yield of photosystem II, photochemical quenching coefficient, non-photochemical quenching coefficient, photosynthetic electron transport rate, content of superoxide anions, hydroxyl radicals, H2O2, soluble protein, and activities of superoxide dismutase under certain conditions suggest that female P. deltoides clones are more sensitive to salinity, calcium, and the combination of both than their male counterparts.

Effects of LED light quality on the growth of pepper seedling in plant factory

The extensive environment, especially low temperature and weak lighting in winter and spring, which limits the growth of pepper (Capicum annuum L.) seedlings, the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings. In this study, white LED lamps with R:B ratio of 0.7 (L0.7) and 1.5 (L1.5) and red-blue LED lamps with R:B ratio of 3.5 (L3.5) were used to cultivate seedlings of “CAU-24” pepper in the light intensity of 250 μmol/m2·s and photoperiod of 12 h/d, white fluorescent lamps with R:B ratio of 1.7 (F1.7) was used as control. The results showed that plant height, stem diameter, hypocotyl length, biomass accumulation, light energy use efficiency (LUE) and electric energy use efficiency (EUE) of pepper seedling under L1.5 were the highest. After 36 days of sowing, the dry weight of shoot reached 302.8±45.2 mg/plant. Leaf area reached maximum value of 153.5±22.0 cm2 under L0.7. The contents of chlorophyll a, chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7, but there was no significant difference in net photosynthetic rate. The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h) which was 1.5, 2, and 3 times greater than that of L3.5, L0.7, and F1.7, respectively. Therefore, compared with fluorescent lamp and other LED lamps, the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency, greater LUE and EUE. Keywords: pepper seedlings, LED light quality, R: B ratio, light energy use efficiency (LUE), electric energy use efficiency (EUE) DOI: 10.25165/j.ijabe.20191205.4847 Citation: Liu N, Ji F, Xu L J, He D X. Effects of LED light quality on the growth of pepper seedling in plant factory. Int J Agric & Biol Eng, 2019; 12(5): 44–50.

Compound leaves are associated with high hydraulic conductance and photosynthetic capacity: evidence from trees in Northeast China.

Characterizing differences in key functional traits between simple-leaved (SL) and compound-leaved (CL) tree species can contribute to a better understanding of the adaptive significance of compound leaf form. In particular, this information may provide a mechanistic explanation to the long-proposed fast-growth hypothesis of CL tree species. Here, using five SL and five CL tree species co-occurring in a typical temperate forest of Northeast China, we tested whether higher hydraulic efficiency underlies potentially high photosynthetic capacity in CL species. We found that the CL species had significantly higher hydraulic conductance at the whole-branch level than the SL species (0.52 ± 0.13 vs 0.15 ± 0.04 × 10-4 kg m-2 s-1 Pa-1, P = 0.029). No significant difference in net photosynthetic rate (14.7 ± 2.43 vs 12.5 ± 2.05 μmol m-2 s-1, P = 0.511) was detected between these two groups, but this was largely due to the existence of one outlier species in each of the two functional groups. Scrutinization of the intragroup variations in functional traits revealed that distinctions of the two outlier species in wood type (ring- vs diffuse-porous) from their respective functional groups have likely contributed to their aberrant physiological performances. The potentially high photosynthetic capacity of CL species seems to require ring-porous wood to achieve high hydraulic efficiency. Due to its limitation on leaf photosynthetic capacity, diffuse-porous wood with lower hydraulic conductivity largely precludes its combination with the 'throw-away' strategy (i.e., annually replacing the stem-like rachises) of compound-leaved tree species, which intrinsically requires high carbon assimilation rate to compensate for their extra carbon losses. Our results for the first time show clear differentiation in hydraulic architecture and CO2 assimilation between sympatric SL and CL species, which contributes to the probing of the underlying mechanism responsible for the potential fast growth of trees with compound leaves.

Seasonal effect on Moringa oleifera gaseous exchange and water use efficiency under diverse planting densities

The study on Moringa oleifera was conducted over twelve months during 2014-2015 to evaluate the impact of the growing season and varying planting densities on biomass yield and physiological at-tributes under dryland conditions. Trial was established at densities of 5000, 2500, 1667 and 1250 plants ha-1, with eight replicates. The increase in planting density led to an increase in biomass production. The monthly and seasonal data collected showed significant differences in net photosynthetic rate, transpiration, sub-stomatal CO2 and stomatal conductance. However, planting densities of M. oleifera had no significant effect on all the gaseous exchange parameters measured. The results further revealed that the amount of carbon dioxide assimilated by the tree is not attributable to photosynthetic and transpiration rates as well as stomatal conductance. Under water shortage condition and high temperature, M. oleifera used an adaptation strategy by reducing stomatal conductance and transpiration and hence increasing water use efficiency. Moringa oleifera thus has the ability to sequester carbon even under water stress conditions. The tree can therefore be recommended for planting at a relatively high density of 5000 plants ha-1 in many parts of Limpopo province where temperatures are favorable for improved farmers’ livelihoods as well as for climate change mitigation.

入侵植物喜旱莲子草和本地种接骨草光合生理特征对增温响应的差异

PDF HTML阅读 XML下载 导出引用 引用提醒 入侵植物喜旱莲子草和本地种接骨草光合生理特征对增温响应的差异 DOI: 10.5846/stxb201509021817 作者: 作者单位: 西华师范大学西南野生动植物资源保护省部共建教育部重点实验室,西华师范大学环境科学与工程学院,西华师范大学生命科学学院,西华师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 四川省教育厅自然科学重点项目（14ZA0122）；西华师范大学博士科研启动基金项目（13E001） Distinctive responses of photosynthetic characteristics to warming of invasive Alternanthera philoxeroides and native Sambucus chinensis Author: Affiliation: Key Laboratory of Southwest China Wildlife Resources Conservation Ministry of Education,China West Normal University,College of Environmental Science and Engineering,China West Normal University,College of Life Science,China West Normal University,College of Life Science,China West Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用红外加热器模拟增温，比较入侵植物喜旱莲子草和本地种接骨草的光合特性对增温响应的差异，以预测气候变暖背景下入侵植物的入侵潜力，并为筛选替代控制植物提供依据。结果表明：增温导致喜旱莲子草和接骨草的叶绿素a/b值分别比对照显著提高6.21%和降低5.55%。无论增温与否，接骨草的叶绿素b含量显著高于喜旱莲子草，而叶绿素a/b值则相反。增温导致喜旱莲子草净光合速率显著提高9.23%，由于气孔导度增大引起蒸腾速率大幅度增加，使得其水分利用效率比对照显著降低10.64%。增温仅导致接骨草的气孔导度显著增加10.95%，而对其他气体交换特征无显著影响。对照条件下，尽管接骨草的气孔导度和胞间CO2浓度分别显著低于喜旱莲子草7.03%和4.57%，但是前者的净光合速率和水分利用效率分别显著高于后者10.30%和11.92%。增温条件下，两种植物的净光合速率和气孔导度无显著差异，由于接骨草的蒸腾速率显著低于喜旱莲子草18.02%，故其水分利用效率显著高于后者26.45%。增温、物种及其两者的交互作用对光补偿点、光饱和点、最大净光合速率、暗呼吸速率和初始量子效率等光响应参数影响均不显著。总之，对照条件下，接骨草凭借较高的叶绿素b含量、净光合速率和水分利用效率，比喜旱莲子草具有更强的光合能力。但增温后，接骨草的光合优势被削弱。研究从光合生理角度证明接骨草有望作为喜旱莲子草的替代控制植物，但是未来气候变化背景下喜旱莲子草的入侵潜力可能增强。 Abstract:Global climate change could exacerbate biological invasions by changing competitive interactions, and hence, threaten ecosystem biodiversity and stability. Replacement control, which relies on the growth advantage of native plants, is one of the most effective methods to suppress invasion. In the present study, distinctive photosynthetic responses to warming of invasive (Alternanthera philoxeroides) and native (Sambucus chinensis) plants were compared to determine the invasive potential of alien plants, and to screen native species for replacement control under climate change scenarios. Plants were grown in two different air temperatures (unwarmed or ambient temperature and warmed at (0.76±0.10)℃ by using an infrared heater) for a 5-month short-term period, and photosynthetic pigment concentrations and gas exchange characteristics were determined. The results showed that warming significantly and positively improved the chlorophyll a/b ratio by 6.21% in A. philoxeroides(P < 0.01), but negatively by 5.55% in S. chinensis(P < 0.05). Meanwhile, chlorophyll b, rather than both chlorophyll a and carotenoid, was significantly higher in S. chinensis than in A. philoxeroides, at ambient (P < 0.001) and increased temperatures (P < 0.05). Increased temperatures significantly increased the net photosynthetic rate by 9.23% in A. philoxeroides(P < 0.01), but decreased the water use efficiency by 10.64% (P < 0.01) due to a respective increase in stomatal conductance by 11.10% (P < 0.05) and transpiration rate by 21.46% (P < 0.001). In contrast, increased temperatures significantly enhanced stomatal conductance by 10.95% in S. chinensis(P < 0.001), but had no effect on other gas exchange traits. Under the control conditions, the stomatal conductance and intercellular CO2 concentration were 7.03% (P < 0.05) and 4.57% (P < 0.001) higher, but the net photosynthetic rate and water use efficiency were 10.30% (P < 0.001) and 11.92% (P < 0.05) lower in A. philoxeroides than in S. chinensis, respectively. However, under increased temperatures no significant differences in net photosynthetic rate and stomatal conductance were observed between the two plant species. In contrast, under increased temperatures, water use efficiency was 26.45% higher in S. chinensis than in A. philoxeroides(P < 0.001), possibly because of lower transpiration rates in S. chinensis. Increased temperatures, species, and their interactions did not have significant effects on photosynthetic-light curve parameters. In general, S. chinensis had a stronger photosynthetic capacity than the invasive A. philoxeroides in terms of chlorophyll b content, net photosynthetic rate, and water use efficiency, especially in control conditions. However, the photosynthetic advantage of S. chinensis was eliminated with increased temperatures. Collectively, our results suggested that S. chinensis could potentially be used in ecological restoration to replace A. philoxeroides in invaded habitats. 参考文献 相似文献 引证文献

Morphological and Physiological Responses of Nine Ornamental Species to Saline Irrigation Water

To provide more species for landscapes where poor-quality irrigation water is used, salt tolerance of commonly used landscape plants should be characterized. Nine ornamental species, including six herbaceous and three woody, were irrigated with nutrient solution at electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solution at EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) for 8 weeks and their growth and physiological responses were determined. Although growth was reduced in orange peel jessamine (Cestrum ‘Orange Peel’) and mexican hummingbird bush (Dicliptera suberecta) as salinity increased, no obvious signs of stress or injury were observed, indicating that orange peel jessamine and mexican hummingbird bush were the most salt tolerant. Flame acanthus (Anisacanthus quadrifidus var. wrightii), rock rose (Pavonia lasiopetala), and ‘Dark knight’ bluebeard (Caryopteris ×clandonensis ‘Dark Knight’) had more growth reduction than that of orange peel jessamine and mexican hummingbird bush with minimal or no foliar damage in EC 5 and slight foliar damage in EC 10. Cardinal flower (Lobelia cardinalis) and mexican false heather (Cuphea hyssopifolia) exhibited mortality rates of 30% and 20%, severe foliar damage, and greater than 70% reduction in leaf area and dry weight in EC 10 compared with their respective controls. Although the growth reductions in butterfly blue (Scabiosa columbaria) were not as great as cardinal flower and mexican false heather, 40% of butterfly blue plants were dead with moderate foliar damage in EC 10. Therefore, cardinal flower, mexican false heather, and butterfly blue plants were considered as moderately salt sensitive. Eastern red columbine (Aquilegia canadensis) was the most salt sensitive among the species investigated with moderate foliar damage in EC 5 and all plants died in EC 10. Four out of the nine species tested had significant differences in net photosynthetic rate (Pn), stomatal conductance (gs), and/or relative chlorophyll content between the control and EC 10, and the difference varied with species. Shoot ion concentrations of the nine ornamentals were also affected by salinity levels and varied among species.

Growth, photosynthesis and haustorial development of semiparasitic Santalum album L. penetrating into roots of three hosts: a comparative study

Photosynthetic and morphological differences between suitable ( Dalbergia sissoo, Lonicera japonica ) and unsuitable ( Aquilaria sinensis ) hosts in their semiparasitic associations with Santalum album were assessed. Santalum album L. is an important semiparasitic tree whose roots join to host roots, through haustoria, to acquire water and nutrients. Yet little is known how different hosts affect S. album growth, photosynthetic performance and haustorial development. In this study, Dalbergia sissoo Roxb., a leguminous tree, and Lonicera japonica Thunb., a non-leguminous vine, were suitable hosts while Aquilaria sinensis (Lour.) Gilg, a non-leguminous tree, was not. The three host plants were cultivated with sandalwood seedlings for 1 year, inducing significant differences in net photosynthetic rate, stomatal conductance and transpiration rate, plant height, haustorial size and number of haustoria. S. album growth was strongly related to net photosynthetic rate, stomatal conductance and transpiration rate. Well-formed and frequently replaced haustoria in the good host D. sissoo likely enhanced metabolism and nutrient transport. Ultrastructural observations showed differences in the interfacial region and internal structure between finger parenchymal cells and host root cells, vascular tissue, the reaction of host root cells and penetration modes. Among them, the finger parenchymal cells in the haustoria that connected with hosts D. sissoo and L. japonica roots were rich in organelles, including mitochondria, endoplasmic reticulum and lysosomes. Numerous small vacuoles accumulated inside membranes of the host root cells and finger parenchymal cells. Many lysosomes were present at the interfacial region where large-scale digestion of the host root cells in D. sissoo and L. japonica occurred. In contrast, in the finger parenchymal cells of the haustoria that joined to A. sinensis roots, organelles were not that obvious and black-stained material at the interfacial regions was indistinct. The modes of invasion were also different. The finger parenchymal cells penetrated into the roots of hosts D. sissoo and L. japonica by cell membrane fusion, pressure and degrading enzymes while in A. sinensis, host root cells were surrounded by the finger parenchymal cells and were self-digested. Even though mature haustoria could penetrate into the root xylem of hosts D. sissoo and A. sinensis, the haustoria that connected with D. sissoo had a mature xylem while A. sinensis had not yet formed any vessel elements. In all S. album haustoria connected to the three host roots, the vascular system developed some xylem but no phloem was observed.

Three photosynthetic patterns characterized by cluster analysis of gas exchange data in two rice populations

Plant photosynthetic rate is affected by stomatal status and internal CO2 carboxylation. Understanding which process determines photosynthetic rate is essential for developing strategies for breeding crops with high photosynthetic efficiency. In this study, we identified different physiological patterns of photosynthetic rate in two different rice populations. Photosynthetic gas exchange parameters were measured during the flowering stage in two rice populations. Clustering and correlation analyses were performed on the resulting data. Five or six groups were defined by K-means clustering according to differences in net photosynthetic rates (Pn). According to differences in stomatal conductance (gs) and carboxylation efficiency (CE), each group was clustered into three subgroups characterized by physiological patterns stomatal pattern, carboxylation pattern, and intermediate pattern. Pn was significantly correlated with gs (r=0.810) and CE (r=0.531). Pn was also significantly correlated with gs and CE in the three physiological patterns. The correlation coefficients were highest in the stomatal pattern (0.905 and 0.957) and lowest in the carboxylation pattern (0.825 and 0.859). Higher correlation coefficients between Pn and gs or CE in the three physiological patterns indicate that clustering is very important for understanding factors limiting rice photosynthesis.

Effects of an exogenous xylanase gene expression on the growth of transgenic rice and the expression level of endogenous xylanase inhibitor gene RIXI

Xylanases have attracted considerable interest in recent years owing to their various applications in industry and agriculture. The use of transgenic plants to produce xylanases is a less expensive alternative to biotechnological programmes. The aim of this study was to elucidate whether introducing a foreign xylanase gene ATX into rice had any adverse effect on plant growth and development. A recombinant xylanase gene ATX was introduced into rice variety Zhonghua 11 through Agrobacterium-mediated transformation. The T₂ generation of transgenic rice was compared with the control (non-transgenic plants). Exogenous xylanase gene ATX was expressed in rice, and all examined transgenic lines exhibited xylanase activity. The transgenic lines (T₂, 'X1-3' and 'X2-5') appeared to grow and develop normally. There were no differences in net photosynthetic rate between transgenic rice lines ('X1-3' and 'X2-5') and wild type (WT) rice plants at the heading/flowering stage. Xylanases are key enzymes in the degradation of plant cell walls. Cell wall composition analysis showed that that there were no changes in cell wall polysaccharides in the root apex but some alterations in leaves in transgenic rice plants. The results also showed that the expression of exogenous xylanase gene ATX in rice would increase the expression of endogenous xylanase inhibitor gene RIXI, which could play a role in plant defence. Thus the stress resistance of transgenic rice plants might be improved. Exogenous xylanase gene ATX could be successfully expressed in rice, and the exogenous protein had no apparent harmful effects on growth and development in transgenic rice plants.

Brassica napus Growth is Promoted by Ascophyllum nodosum (L.) Le Jol. Seaweed Extract: Microarray Analysis and Physiological Characterization of N, C, and S Metabolisms

Despite its high capacity to take up nitrate from soil, winter rapeseed (Brassica napus) is characterized by a low N recovery in seeds. Thus, to maintain yield, rapeseed requires a high fertilization rate. Increasing nutrient use efficiency in rapeseed by addition of a biostimulant could help improve its agroenvironmental balance. The effects of marine brown seaweed Ascophyllum nodosum on plant growth have been well described physiologically. However, to our knowledge, no study has focused on transcriptomic analyses to determine metabolic targets of these extracts. A preliminary screening of different extracts revealed a significant effect of one of them (AZAL5) on rapeseed root (+102 %) and shoot (+23 %) growth. Microarray analysis was then used on AZAL5-treated or nontreated plants to characterize changes in gene expression that were further supported by physiological evidence. Stimulation of nitrogen uptake (+21 and +115 % in shoots and roots, respectively) and assimilation was increased in a similar manner to growth, whereas sulfate content (+63 and +133 % in shoots and roots, respectively) was more strongly stimulated leading to sulfate accumulation. Among the identified genes whose expression was affected by AZAL5, MinE, a plastid division regulator, was the most strongly affected. Its effect was supported by microscopic analysis showing an enhancement of chloroplast number per cell and starch content but without a significant difference in net photosynthetic rate. In conclusion, it is suggested that AZAL5, which promotes plant growth and nutrient uptake, could be used as a supplementary tool to improve rapeseed agroenvironmental balance.

Responses of Transgenic Tobacco Plants with Increased Proline Content to Drought and/or Heat Stress

Transgenic tobacco plants (M51-1) constitutively over-expressing a modified gene for the proline biosynthetic enzyme △2-pyrroline-5-carboxylate synthetase (P5CSF129A) and the corresponding wild-type plants (WT) were compared during drought or heat stress and under combination of both stresses. The proline content in M51-1 was several times higher than in WT plants. Under optimal conditions, the transpiration rate and stomatal conductance of M51-1 plants were lower than those in WT plants. The differences in net photosynthetic rate were not significant and water use efficiency and contents of chlorophyll and xanthophyll cycle pigments were higher in M51-1 than in WT plants. Drought induced by cessation of watering for 7 d resulted in decrease of all gas exchange parameters and chlorophyll content, but in an increase of the content of xanthophyll cycle pigments and degree of their de-epoxidation. After application of heat stress (40°C/60 min) to control or water-stressed plants the gas exchange parameters decreased considerably. Short-term heat stress alone, however, did not affect pigment contents. The responses of M51-1 and WT plants to the tested stresses did not differ significantly. Therefore, a decisive contribution of elevated proline content to drought or heat stress tolerance of tobacco was not proved.

Effects of Preconditioning on Photosynthesis of Rice Seedlings under Water Stress

Abstract Rice seedlings (Oryza sativa L.) were grown in a controlled environment and divided into control seedlings (CK1: 80% field capacity was always held), preconditioned seedlings (PT, 6 days mild drought for preconditioning–3 days re-watering–intermediate drought stress) and non-preconditioned seedlings (CK2, 9 days 80% field capacity and immediately followed by intermediate drought). Photosynthetic CO 2 exchange, photosynthetic pigment content were measured in CK1 and PT after preconditioning and re-watering as well as CK1, PT and CK2 after intermediate drought. After exposure to 6 days mild drought preconditioning, stomatal conductance (gs), transpiration rate (E) and chlorophyll content were lower, while Car content and Car/Chl ratio were higher in PT than those in CK1. PT had no significant differences in net photosynthetic rate (Pn) compared to CK1. After re-watering, Chla content was higher but Car/Chl ratio was lower in PT than those in CK1, and other parameters of PT were similar to CK1. After exposure to intermediate drought stress for 6 days, PT showed high water use efficiency (WUE) after intermediate drought stress. CK2 suffered more serious injuries than PT as indicated by lower Pn and pigment content, suggesting that the differences in response to intermediate drought stress in CK2 and PT seedlings are closely related to the effect of mild drought preconditioning. It may be concluded that preconditioning made rice seedlings modulate their metabolism such that they could acclimatize more successfully to the fluctuating water stress environment.

Effect of Altitude on the Response of Net Photosynthetic Rate to Carbon Dioxide Increase by Spring Wheat

: The partial pressure of CO2 in air decreases with the increase in altitude. Therefore, increase in molar concentration of CO2 is smaller at higher altitudes than at lower altitudes for increases in molar fraction of CO2. This study aimed to predict the effect of global CO2 increase on net photosynthetic rateof spring wheat (Triticum aestivum L.) at high altitudes. The net photosynthetic rate of spring wheat grown in Lhasa (3688 m above sea level), China, was compared with that of the same cultivar grown in Sapporo (15 m above sea level), Japan. At the current level of CO2, it was significantly lower in Lhasa than in Sapporo, and stomatal conductance, chlorophyll content (SPAD value) and apparent quantum yield were similar in both locations. The interaction ofCO2 level and altitude was suggested; the amount of increase in net photosynthetic rate caused by increase in CO2 was smaller at high altitudes than at low altitudes. Lower CO2 partial pressure at higher altitude could explain the difference in net photosynthetic rate between altitudes, and the interaction of CO2 level and altitude.

Carbon Dioxide Enhancement Effects in Container‐ versus Ground‐Grown Soybean at Equal Planting Densities

Prior work showed that CO2 enhancement ratios (ER) were similar for plants grown in open‐top chambers (OTCs) whether grown in the ground or in insulated containers aboveground. Per plant comparisons were suspect since the ground‐grown plants were cultivated in rows at normal densities making it difficult to separate the effects of plant competition from the variables of interest. Soybean [Glycine max (L.) Merr. cv. Essex] was grown in the ground and in aboveground containers in OTCs in ambient and elevated CO2 at equal planting densities. The hypothesis was that at equal densities, container‐ and ground‐grown plants would exhibit both equivalent ERs and equivalent per plant yields. Although the only differences in net photosynthetic rate (An:μmol m−2 s−1) and conductance to water vapor (gs:mol m−2 s−1) were due to CO2 and container‐ and ground‐grown plants had similar ERs (mean = 20%), per plant yields were still less in the container‐grown plants at both levels of CO2 (mean = −17%). Reproductive measures, except mass per seed, as well as total stem biomass were significantly reduced in the containers. High CO2 increased seed oil concentration and the level of fatty acid saturation. The only observed environmental difference was higher daytime root zone temperatures in containers (2–6°C). The robust ERs suggest that neither above‐ nor below‐ground resource limitations was the cause of the yield discrepancies.

Assessments of CO2 Assimilation on a Per-leaf-area Basis are Related to Total Leaf Area

Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO2 assimilation as μmol·m−2·s−1). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO2 assimilation expressed on a leaf-area basis (μmol·m−2·s−1) will be independent of leaf area only when total net CO2 assimilation (leaf CO2 assimilation as μmol·s−1) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates of CO2 assimilation were often misleading. When CO2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.

Structural and biochemical mechanism responsible for the stay-green phenotype in common wheat

In order to increase the supply of assimilated carbon to grain, a new stay-green wheat cultivar, Chuannong17 (CN17), with delayed leaf senescence, carrying wheat-rye 1RS.1BL translocated chromosome was developed. CN17 exhibited distinct differences in net photosynthetic rate (Pn), chlorophyll (Chl) content, malondialdehyde (MDA) content, activity of both superoxide dismutase (SOD) and catalase (CAT) during the grain filling stage, and flag leaf senescence compared with the control. The new cultivar maintained longer and higher photosynthetic competence compared with the control, and this aspect correlated with the difference in chloroplast development. Moreover, the stay-green phenotype of CN17 was also observed under natural growth conditions. Consequently, the coordination of the physiological, biochemical, and structural aspects in the stay-green cultivar produced higher seed weights and per-plant yield compared with the control cultivar.

Effects of Reflective Sheet Mulching on Net Photosynthesis, Leaf Character and Fruit Quality of Cherry and Pear

To clarify the effect of reflective sheet mulching on photosynthesis of fruit tree canopies, we investigated, in sweet cherry and pear orchards, the photosynthetic photon flux density (PPFD) reflected from sheet-covered ground, the difference in net photosynthetic rate (Pn) between sheeted and unsheeted (control) plots, and the effects of long-term mulching on leaf character and fruit quality. In complementary greenhouse experiments, we investigated thePn of leaves illuminated by various combinations of a range of artificial PPFDs at the abaxial and abaxial surfaces. Though the maximum reflected PPFDs from the control plots distributed below 10μmol m-2s-1in the cherry and 20μmol m-2s-1in the pear, those from the sheeted plots were around 200 μmol m-2s-1. Combining these results with those obtained in the greenhouse experiments led us to estimate that the mean increment ofPnprovided by mulching would be about 2.1 μmol CO2m-2s-1for cherry and about 3.2 μmol CO2m-2s-1for pear. The observed increments ofPnin the lower leaf layers of mulched trees were discussed. Long-term mulching resulted in leaves with sun leaf character and improved the coloring of cherry fruit, though there was no difference in fruit size between the mulched and unmulched plots for either cherry or pear.