Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Immediately after anthesis ears of spring wheat absorbed lessthan 0.5 mg CO₂, per hour in daylight and later evolved CO₂,in the light and in the dark. The rate of apparent photosynthesisof the combined flag-leaf lamina and sheath and peduncle (collectivelycalled flag leaf) of two spring wheat varieties, Atle and JufyI, was 3–4 mg per hour; the rates of the flag leaf andthe ear of two spring barleys, Plumage Archer and Proctor, wereeach about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergenceand maturity accounted for most of the final grain dry weight.The CO₂, fixed by the wheat ear was equivalent to between 17and 30 per cent of the grain weight, but more than this waslost by respiration, so assimilation in the flag leaf was equivalentto 110–20 per cent of the final grain weight. In barley,photosynthesis in the flag leaf and the net CO₂ uptake by theear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because oftheir greater surface, and flag leaves of wheat photosynthesizedmore than those of barley because they had more surface anda slightly greater rate of photosynthesis per dm².     

施氮量对超高产冬小麦灌浆期旗叶光响应曲线的影响

为冬小麦超高产栽培的氮肥管理提供技术支撑,在大田条件下研究了施氮量对超高产冬小麦灌浆期旗叶光响应曲线的影响.采用开放式气路测定了小麦旗叶的净光合速率、气孔导度、胞间二氧化碳浓度、蒸腾速率等相关指标,并运用"米式方程"对旗叶净光合速率进行了模拟,计算了光响应曲线的特征参数.结果表明,在0～300kg/hm2施氮范围内,随着光照强度的增加,各处理的旗叶净光合速率、气孔导度、蒸腾速率均随之增加,而胞间二氧化碳浓度却随之降低,但是在375kg/hm2施氮水平下旗叶的净光合速率、气孔导度、蒸腾速率的增加和胞间二氧化碳浓度的降低反而低于300kg/hm2施氮水平,表明合理的氮素水平对超高产小麦灌浆期旗叶的光响应曲线有明显的调节作用.在合理的施氮范围内,增施氮肥小麦旗叶在整个灌浆期内的最大净光合速率随之增加.在本试验条件下,超高产麦田的适宜施氮量为300kg/hm2.     

黑暗诱导衰老对不同年代冬小麦品种旗叶光系统Ⅱ功能的影响

小麦品种的更新换代是小麦产量不断提高的重要因素,阐明小麦品种演替过程中不同生理特性的变化对新品种选育具有重要参考价值.旗叶衰老速率快慢是影响小麦产量水平的关键因素,目前对于不同小麦品种衰老过程中旗叶光系统Ⅱ功能的变化规律尚不清楚.本试验选用1941-2014年间河南地区不同时期种植的31个品种,通过黑暗诱导离体叶片衰老,测定旗叶叶绿素荧光诱导动力学参数、叶绿素相对含量的变化,分析了光系统Ⅱ功能的变化规律.结果表明:品种演替过程中旗叶的叶绿素含量逐渐提高,衰老过程中近代品种叶绿素的降解速率低于较早年代品种;旗叶衰老过程中,近代品种荧光诱导动力学曲线的J点上升幅度小于I点;品种更替过程中光系统Ⅱ最大光化学效率和单位面积有活性反应中心数目逐渐增加,但是近代品种降低速率低于较早年代品种.叶绿素含量的变化与未衰老叶片中F_v/F_m没有显著相关性,但是随着衰老程度增加,相关性逐渐增大,且趋势线斜率逐渐提高;光系统Ⅱ单位面积有活性反应中心数目与品种育成时间呈显著正相关,且随着衰老程度增加,相关程度和趋势线斜率均显著提高.综上,小麦品种演替过程中,旗叶叶绿素含量逐渐升高,降解速率逐渐减缓,光合电子传递过程中Q_A到Q_B电子传递的抗衰老能力得到改善,从而减缓了衰老过程中光系统Ⅱ最大光化学效率和有活性反应中心的衰减速率,同时,叶绿素含量的提高和旗叶光系统Ⅱ抗衰老能力的增强也是品种更替过程中产量逐渐提高的重要因素.     

不同发育时期追施氮肥对冬小麦旗叶中光合酶活性的影响

小麦开花后,随着旗叶的衰老,旗叶中1,5-二磷酸核酮糖羧化酶（RuBPC）、磷酸烯醇式丙酮酸羧化酶（PEPC）和乙醇酸氧化酶（GO）活性呈下降趋势。随着追施氮肥时期的推迟,光合酶活性呈增加趋势,这意味着氮肥追施时间后移有利于提高小麦光合速率。在旗叶衰老后期,大穗型品种小麦旗叶中光合酶活性略高于多穗型品种小麦。     

Trehalose metabolism in root nodules of the model legume Lotus japonicus in response to salt stress

In wheat ( Triticum aestivum L), the leaves particularly flag leaves have been considered to be the key organs contributing to higher yields, whereas awns have been considered subsidiary organs. Compared with extensive investigations on the assimilation contribution of leaves, the photosynthetic characteristics of awns have not been well studied. In this study, we investigated the ultrastructure of chloroplasts, oxygen evolution, and phosphoenolpyruvate carboxylase [phosphoenolpyruvate carboxylase (PEPCase) EC 4.1.1.31)] activity in both flag leaves and awns during the ontogenesis of wheat. Transmission electron microscope observations showed initial increases in the sizes of grana and the degree of granum stacks from the florescence-emergence stage both in flag leaves and in awns, followed by the breakdown of membrane systems after the milk-development stage. The results of oxygen evolution assays revealed that in both organs, the rate of photosynthesis increased in the first few stages and then decreased, but the decrease occurred much earlier in flag leaves than in awns. A PEPCase activity assay demonstrated that the activity of PEPCase was much higher in awns than in flag leaves throughout ontogeny; the value was particularly high at the late stages of grain filling. Our results suggest that awns play a dominant role in contributing to large grains and a high grain yield in awned wheat cultivars, particularly during the grain-filling stages.     

Monocarpic senescence in wheat: Influence of sterile glumes and ear

The senescence of sterile glumes, flag leaf and the other two leaves below the ear of wheat ( Triticum aestivum L. cv. Sonalika) was studied in relation to grain development and surgical manipulation. The senescence of sterile glumes was faster than that of the leaves in terms of chlorophyll and protein degradation. The flag leaf senesced later than the other two leaves below it. Removal of sterile glumes markedly reduced the harvest index (crop: straw ratio) and average dry weight per grain as compared to removal of the flag leaf. Maximum grain weight was achieved after the glumes had senesced completely. Removal of the ear delayed senescence of all the three leaves. It is concluded that sterile glumes are important suppliers of assimilate for grain filling and that nutrient drainage is the primary cause of the monocarpic senescence in wheat.     

钾对小麦旗叶蔗糖和籽粒淀粉积累的影响

 利用冬小麦品种‘鲁麦22’(Triticum aestivum cv. `Lumai 22’)在大田条件下研究了钾素对小麦旗叶蔗糖和籽粒淀粉积累及其有关酶活性的影响。结果表明,钾素有利于提高旗叶光合速率,增强开花后旗叶磷酸蔗糖合成酶活性,提高旗叶中蔗糖的含量;从而提高了灌浆期间籽粒中蔗糖的供应,增强了籽粒中蔗糖合成酶和腺苷二磷酸葡萄糖焦磷酸化酶的活性,加速了淀粉积累速率,提高了粒重和产量。     

NAT对植物生长及生理活性调控作用的初步研究

以新合成的 N- (1-萘乙酰基 ) - N′- (4 -氨替吡啉基 )硫脲 (NAT)配制成不同浓度 (10、2 0、50mg.L-1)的水溶液 ,对大田扬花期小麦进行叶面喷洒和蜀葵叶片扦插基部的浸泡处理 ,并在分别含有 0 .1mg.L-1NAT与 NAA的培养基中对护颖分化期的小麦幼穗进行离体培养。测定了处理后小麦灌浆后期旗叶的生理指标 ,统计测量了扦插生根的效果 ,并观察记录了幼穗培养再分化的情况。结果表明 ,NAT可有效的延缓小麦旗叶的衰老 ,促进蜀葵叶柄的扦插生根和促进小麦幼穗离体培养的再分化作用。其效果比 NAA更为明显。     

Distribution of photosynthate produced before and after anthesis in tall and semi-dwarf winter wheat, as affected by nitrogen fertiliser

In 2 years the distribution of radioactivity recovered in entire shoots of field-grown winter wheat was determined at various times after exposing the top two leaves (flag leaf or second leaf) to ¹⁴CO₂ for 30 s. In 1976 when ¹⁴C was supplied to either leaf 14 days before anthesis, 30% was in the ear at anthesis. Less than 5% was in the leaf exposed to ^I4CO₂. The remainder was equally divided between the stem above and below the flag-leaf node when the flag leaf had been exposed, and was mainly in the lower part of the stem when the second leaf had been exposed. By maturity the proportion in the stem had decreased; 20% of the total activity was in the grain and 30% was still in the ear structures. When ¹⁴C was supplied 10 days after anthesis, the proportion in the ear 24 h later ranged from 42 to 69% of that in the whole shoot when the flag leaf was exposed, and from 6 to 28% when the second leaf was exposed. At maturity these proportions increased to 92 and 85% when the ¹⁴C had been supplied to flag leaves and second leaves respectively. When ¹⁴C was supplied 25 days after anthesis to either flag leaves or second leaves, more than 90% of the activity was in the mature ears. Less than 5% of the ¹⁴C remaining at maturity from any treatment was still in the leaf exposed to ¹⁴CO₂. Between 2 and 6% of ¹⁴C supplied after anthesis was in the non-grain parts of the ear. The proportion of the ¹⁴C in the ear was greatest for the semi-dwarf varieties Maris Fundin and Hobbit, less for Maris Huntsman, and least for Cappelle-Desprez. These varietal differences were large 24 h after exposure to ¹⁴CO₂, especially in 1976. They were small and rarely significant at maturity. Nitrogen fertiliser up to 210 kg N ha^-1 had negligible effects on the distribution of ¹⁴C, although it greatly increased growth and yield, especially in 1975.     

Comparison of the photosynthetic characteristics in the pericarp and flag leaves during wheat (Triticum aestivum L.) caryopsis development

The pericarp of cereal crops is considered a photosynthetically active tissue. Although extensive studies have been performed on green leaves, the photosynthetic role of the pericarp in cereal caryopsis development has not been well investigated. In the present study, we investigated the anatomy, ultrastructure, chlorophyll (Chl) fluorescence, and oxygen evolution of the pericarp during caryopsis ontogenesis in field wheat (Triticum aestivum L.). The results showed that wheat pericarp cross-cells contained Chl; the grana stacks and thylakoid membranes in the cross-cells were more distinct in the pericarp than those in the flag leaves as shown by transmission electron microscopy. Chl fluorescence revealed that the photosynthetic efficiency, which was indicated by values of maximum efficiency of PSII photochemistry and effective PSII quantum yield, was lower in the pericarp compared to that of the flag leaf eight days after anthesis (DAA), whereas similar values were subsequently observed. The nonphotochemical quenching values were lower from 8–16 DAA but significantly increased in the pericarp from 24–32 DAA compared to the flag leaf. The oxygen evolution rate of the flag leaves was consistently higher than that of pericarp; notably, isolated pericarps released more oxygen than intact pericarps during caryopsis development. These results suggest that the pericarp plays a key role in caryopsis development by performing photosynthesis as well as by supplying oxygen to the endosperm and dissipating excessive energy during the grain-filling stages.     

Dry Matter Production,Photosynthesis of Flag Leaves and Water Use in Winter Wheat Are Affected by Supplemental Irrigation in the Huang-Huai-Hai Plain of China

Winter wheat is threatened by drought in the Huang-Huai-Hai Plain of China, thus, effective water-saving irrigation practices are urgently required to maintain its high winter wheat production. This study was conducted from 2012 to 2014 to determine how supplemental irrigation (SI) affected soil moisture, photosynthesis, and dry matter (DM) production of winter wheat by measuring the moisture in 0–20 cm (W2), 0–40 cm (W3), and 0–60 cm (W4) soil profiles. Rainfed (W0) and local SI practice (W1, irrigation with 60 mm each at jointing and anthesis) treatments were designed as controls. The irrigation amount for W3 was significantly lower than that for W1 and W4 but higher than that for W2. The soil relative water content (SRWC) in 0–40 cm soil profiles at jointing after SI for W3 was significantly lower than that for W1 and W4 but higher than that for W2. W3 exhibited lower SRWC in 100–140 and 60–140 cm soil profiles at anthesis after SI and at maturity, respectively, but higher root length density in 60–100 cm soil profiles than W1, W2 and W4. Compared with W1, W2 and W4, photosynthetic and transpiration rates and stomatal conductance of flag leaves for W3 were significantly greater during grain filling, particularly at the mid and later stages. The total DM at maturity, DM in grain and leaves, post-anthesis DM accumulation and its contribution to grain and grain filling duration were higher for W3. The 1000-grain weight, grain yield and water use efficiency for W3 were the highest. Therefore, treatment of increasing SRWC in the 0–40 cm soil profiles to 65% and 70% field capacities at jointing and anthesis (W3), respectively, created a suitable soil moisture environment for winter wheat production, which could be considered as a high yield and water-saving treatment in Huang-Huai-Hai Plain, China.     

Some treatments affecting growth substances in developing wheat ears

Cytokinin, auxin and gibberellin-like substances were bio-assayed in extracts from developing ears of wheat plants grown in various conditions. Changes in cytokinin activity along the ears may be related to the earlier flowering in the middle of the ear. Ears on the main stems of plants from which all the tillers had been removed contained less cytokinin than the main-stem ears of normal tillered plants. When grain development was stopped by preventing fertilization of the ovules the ear contained more cytokinin than normal ears. With de-tillered plants, removing flag leaves before anthesis increased cytokinin, gibberellin and auxin in the ears; later removal of flag leaves did not affect cytokinin but decreased gibberellin in the ears. Conversely, removing ears before anthesis did not affect cytokinin or auxin in the flag leaves, but their gibberellin was less than that of flag leaves on intact plants. Treatment of wheat ears with zeatin did not affect grain weight or number per ear which supports the conclusion that the growth substances in the ear may be adequate for normal grain growth.     

小麦开花后旗叶中蔗糖合成与籽粒中蔗糖降解

在小麦开花后,旗叶中蔗糖磷酸合成酶（SPS）活性在开花后14d内一直维持较高水平,蔗糖合成酶（SS）的活性在开花后14-28d较高,蔗糖的含量与SPS活性呈显著正相关,籽粒中蔗糖合成酶（SS）在开花后28d内一直维持较高的活性;与此相对应,籽粒蔗糖的含量在开花后28d内呈明显的下降趋势。而旗叶和籽粒中SS活性均与籽粒淀粉的积累速率呈极显著正相关。     

Differences in Sugar Accumulation and Mobilization between Sequential and Non-Sequential Senescence Wheat Cultivars under Natural and Drought Conditions

Wheat leaf non-sequential senescence at the late grain-filling stage involves the early senescence of younger flag leaves compared to that observed in older second leaves. On the other hand, sequential senescence involves leaf senescence that follows an age-related pattern, in which flag leaves are the latest to undergo senescence. The characteristics of sugar metabolism in two sequential senescence cultivars and two non-sequential senescence cultivars under both natural and drought conditions were studied to elucidate the underlying mechanism of drought tolerance in two different senescence modes. The results showed that compared to sequential senescence wheat cultivars, under natural and drought conditions, non-sequential senescence wheat cultivars showed a higher leaf net photosynthetic rate, higher soluble sugar levels in leaves, leaf sheaths, and internodes, higher leaf sucrose synthase (SS) and sucrose phosphate synthase (SPS) activity, and higher grain SS activity, thereby suggesting that non-sequential senescence wheat cultivars had stronger source activity. Spike weight, grain weight per spike, and 100-grain weight of non-sequential senescence cultivars at maturity were significantly higher than those of sequential senescence cultivars under both natural and drought conditions. These findings indicate that the higher rate of accumulation and the higher mobilization of soluble sugar in the leaves, leaf sheaths and internodes of non-sequential senescence cultivars improve grain weight and drought tolerance. At the late grain-filling stage, drought conditions adversely affected leaf chlorophyll content, net photosynthetic rate, soluble sugar and sucrose content, SS and SPS activity, gain SS activity, and weight. This study showed that higher rates of soluble sugar accumulation in the source was one of the reasons of triggering leaf non-sequential senescence, and higher rates of soluble sugar mobilization during leaf non-sequential senescence promoted high and stable wheat yield and drought tolerance.     

Genotypic and nutrition-dependent variation in water use efficiency and photosynthetic activity of leaves in winter wheat (Triticum aestivum L.)

Effects of high and reduced NPK nutrition on the genetic variation of components of water use efficiency at the leaf and whole-plant levels were examined in pot-grown old and modern cultivars of winter wheat (Triticum aestivum L.). At the subsequent growth stages, the photosynthetic rate (A), transpiration rate (E), leaf area (LA) and gas exchange efficiency (A/E) were measured on fully developed 4th, 5th, penultimate and flag leaves. At the plant canopy level, the total amount of water transpired was recorded during the whole life cycle to determine the efficiency of water use in the vegetative (WUEveg) and grain (WUEgen) matter formation. Considerable genotypic differences were found for the characters studied. The limited NPK supply caused a decrease in LA, A and A/E, but contributed to an increase in WUEgen. Examined cultivars (C) did not interact with nutrition levels (N) for these characteristics. However, the position of leaves (L) and the C x L and N x L interactions significantly affected the variance in leaf photosynthetic characteristics. A and A/E were negatively correlated with LA, and the flag leaves were photosynthetically less active and less efficient per unit area than the lower leaves. The whole-plant components of WUE were found to be more genetically stable than the photosynthetic leaf characteristics. Some modern cultivars tended to form leaves of higher A and A/E than the older ones, and this corresponds with a more efficient use of water in grain formation (WUEgen) of the former. Stay-green duration of flag leaves and harvest index showed positive correlations with WUEgen. However, no close associations were noticed between WUE components and stress tolerance, and the modern cultivars were usually less tolerant to NPK shortage.     

除草剂对冬小麦光合特性、籽粒产量及品质的调控效应

通过田间试验研究了4种除草剂(2,4-D丁酯、‘巨星’、‘世玛’和‘骠马’)对2个小麦品种(‘临优145’和‘临汾138’)光合特性、籽粒产量和品质的影响。结果表明:2,4-D丁酯使小麦灌浆期间旗叶的叶绿素相对含量(SPAD值)和净光合速率(Pn)一直较低,千粒重和籽粒产量显著低于对照;‘巨星’使灌浆前期的SPAD值和Pn较高而中后期快速下降,灌浆持续时间缩短,产量与对照相近;‘世玛’使灌浆前中期SPAD值和Pn较低但后期下降缓慢,灌浆持续时间延长,千粒重和籽粒产量显著高于对照和其它处理;‘骠马’对光合特性和产量影响较小。2,4-D丁酯和‘骠马’使籽粒的蛋白质含量、湿面筋含量、沉降值、吸水率、评价值显著或极显著提高,稳定时间延长,而形成时间与对照相近;‘巨星’和‘世玛’处理的品质指标大多低于或接近对照。研究发现,除草剂通过调控小麦旗叶光合特性和灌浆进程来影响其千粒重和籽粒产量,且除草剂和品种间存在差异;2,4-D丁酯虽能明显改善小麦品质但却显著降低籽粒产量,‘骠马’使小麦品质特性改善的同时也使籽粒产量有所提高,‘世玛’虽能显著提高籽粒产量却使品质特性变差。     

Sink-limitation to yield and biomass: a summary of some investigations in spring wheat

Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m‐2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag‐leaf photosynthetic rate during grain‐filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post‐anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain‐filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag‐leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi‐ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.     

杂交小麦不同发育时期叶绿素蛋白复合体的变化

杂交小麦“９０１”在不同发育时期及不同叶位,叶片色素蛋白复合体含量均高于对照品种陕２２９,尤其表现在“９０１”的旗叶,而陕２２９的倒二叶在籽粒形成后期、灌浆期,略高于“９０１”,倒三叶在籽粒发育后期至成熟期“９０１”的含量要高于陕２２９。叶绿素蛋白复合体分析结果说明,在不同发育时期、不同叶位,“９０１”叶片色素蛋白复合体中含有较高的叶绿素b,尤其表现在籽粒形成后期的旗叶上。２个品种在不同发育时期,不同时叶位之间,色素蛋白复合体组分上没有差异。仅表现在成熟期,陕２２９的倒三叶各色素带含量减少,并且消失１条叶绿素蛋白复合体带,初步认为此带是ＬＨＣＰ的寡聚体之一,而“９０１”比陕２２９晚７d倒二叶上表现出样的现象,表明“９０１”叶片色素蛋白复合体抗衰老能力很强。     

The Influence of Leaf Removal upon the Development of the Grain of Winter Wheat

The paper describes the effects on grain development of theremoval of half the flag leaf, the entire flag leaf and allthe leaves from selected main shoots of a field crop of wheat,cultivar Maris Ranger, 7 days after anthesis. None of the treatmentsreduced grain weights in the 14 days following defoliation.Even in the next 14 days only the more severe defoliations reducedgrain weight, with the most severe treatment causing the greatestreduction. Ultimately the rate of grain growth in plants onwhich only a half of the flag leaf had been removed also fellbehind that of the controls. Final grain yields were in theorder, control plants, > plants with half the flag leaf removed,> the entire flag leaf removed, > all the leaves removed.The significance of these results in interpreting the factorslimiting grain growth in wheat is discussed.     

不同栽培模式下小麦灌浆期蛋白质周转研究

通过田间试验研究5种栽培模式对小麦灌浆期蛋白质周转的影响。5种栽培模式分别为常规栽培、秸秆覆盖、地膜覆盖、垄沟种植和补灌栽培,施氮量为120kg／hm^2。结果表明：不同栽培模式下小麦灌浆期蛋白质周转变化基本一致,覆膜栽培模式旗叶可溶性蛋白含量和蛋白水解酶活性较高,旗叶蛋白水解酶和籽粒蛋白积累能力大于其它栽培模式;垄沟栽培模式的旗叶各指标含量较高,但其蛋白质周转效率低,导致贪青晚熟不利于蛋白质周转,从而影响产量的形成。