Light-associated nitrogen distribution profile in flowering canopies of sunflower (Helianthus annuus L.) altered during grain growth

In vegetative canopies of many species, the vertical gradient of lamina nitrogen concentration (NW) parallels the profile of light distribution in such a way that the actual nitrogen partitioning approaches the optimum pattern for canopy photosynthesis. This paper evaluates the hypothesis that a strong sink for nitrogen, viz. growing grain, affects the pattern of lamina nitrogen distribution usually described for vegetative canopies. The light and NW profiles of sunflower (Helianthus annuus L.) crops were characterised from anthesis to physiological maturity. The factorial combination of two plant populations (2.4 and 4.8 plants m^–2) and two levels of nitrogen supply (0 and 5 g N m^–2) were the sources of variation for NW and light profiles. Before the onset of nitrogen accumulation in grain, the pattern of NW was similar to that described for other species and it was related to the distribution of light in the canopy. Important changes in the profile of NW occurred during grain filling that were unrelated to the light regime. Nitrogen was mobilised from leaves in all positions in the canopy and the rate of NW change was greater in leaves closer to the grain, which were also the leaves where nitrogen was more concentrated. It is concluded that the physiological mechanisms involved in determining the distribution of leaf nitrogen in vegetative canopies do not apply to sunflower during grain filling.     

Profiles of Leaf Nitrogen and Light in Reproductive Canopies of Cotton (Gossypium hirsutum)

During vegetative growth, the vertical profile of leaf nitrogen(N) often parallels the profile of light distribution withinthe canopy. This is more advantageous in terms of canopy photosynthesisthan a uniform distribution of leaf N. We investigated the influenceof both reproductive growth and N supply on the profiles ofN and light in canopies of irrigated cotton crops (Gossypiumhirsutum L.). Regular samplings were made from soon after theonset of reproductive growth until crop maturity. Every 2 weeks,a 1 m²sample of the canopy was cut in four successive verticallayers of equal thickness. Leaf area and N concentration (%)in each layer were measured. The vertical N gradient becamemore marked with ongoing reproductive development. It is hypothesizedthat because of the high rate of growth after the onset of reproductivedevelopment and the long duration of this phase compared toother species, the whole canopy photosynthetic benefit thatwould accrue from maintaining the N gradient is likely to beaccentuated. The rate of decline in leaf N concentration ina layer was not related to either the initial concentrationin the leaves nor the boll load within the layer.Copyright 2001Annals of Botany Company Gossypium hirsutum, leaf nitrogen, light profile, nitrogen, nitrogen distribution, remobilization, reproductive growth     

Planting density effects on assimilation and partitioning of photosynthates during grain filling in the late-sown wheat

Leaf blades of the late-sown winter wheat produced the major portion, i.e., more than 60 %, of the total ¹⁴C-photosynthates at grain filling, but ear (rachis and glumes) only about 15 %, sheaths about 11 %, and stem internodes about 11 %. The change of plant density in this experiment had little influence on the ¹⁴CO2-photoassimilation of the ear (rachis and glumes), flag leaf lamina, sheaths and stem internodes, but markedly affected photosynthesis of the second, the third and lower leaves. The photosynthetic rate [expressed as specific radioactivity, s-¹ kg-¹(d.m.)] and the amount of ¹⁴CO₂ photosynthates decreased significantly in the second, the third and other lower leaves at a high plant density. Upon grain-filling of the late-sown wheat, the grain was the major importer of photosynthates. Yet partitioning to the stem internodes depended on the plant density. Stem was the importer of photosynthates at a low plant density, but the exporter at a high plant density. In plants at a low plant density a fairly large proportion of photosynthates was distributed into the roots. The middle and lower above-ground parts of the late-sown wheat at a high plant density decreased or lost their function early. As a result, the plant senesced earlier. However, the grain setting, filling and yielding were restricted. An appropriately low plant density was suitable for prolonging the function of the middle and lower organs, delaying the senescence of plant, increasing the source supply for grain filling, and improving the grain yield. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Mechanical Significance of Clasping Leaf Sheaths in Grasses: Evidence from Two Cultivars of Avena sativa

The elastic (Young's) modulus and flexural rigidity of internodeswith and without their clasping leaf sheaths were determinedfor culms from two cultivars (‘Astro’) and (‘Garry’)of Avena sativa L. Data indicate that early in the developmentof culms, leaf sheaths can have a higher elastic modulus thanthe internodes they envelope, and by virtue of their location,leaf sheaths contribute significantly to the flexural rigidity(hence, resistance to bending) of internodal segments. As culmsmature, the elastic modulus of leaf sheath and internodal tissuesreach parity. However, because of the acropetal pattern by whichnew internodes are produced by shoot apices, sheaths continueto provide mechanical support to distal internodes, particularlythe peduncle. Data for the two cultivars indicate that the elasticmodulus and flexural rigidity of culms can vary significantlywithin the species. Comparisons between the flexural rigidityof the two cultures and the resistance of stems to lodging indicatethat flexural rigidity is not significant to lodging. The engineeringprinciples relevant to the mechanical advantages conferred byclasping leaf sheaths are discussed within the context of grassshoot morphology. Biomechanics, leaf sheath, Avena, elastic modulus     

Dynamics of Vertical Leaf Nitrogen Distribution in a Vegetative Wheat Canopy. Impact on Canopy Photosynthesis

The development of vertical canopy gradients of leaf N has beenregarded as an adaptation to the light gradient that helps tomaximize canopy photosynthesis. In this study we report thedynamics of vertical leaf N distribution during vegetative growthof wheat in response to changes in N availability and sowingdensity. The question of to what extent the observed verticalleaf N distribution maximized canopy photosynthesis was addressedwith a leaf layer model of canopy photosynthesis that integratesN-dependent leaf photosynthesis according to the canopy lightand leaf N distribution. Plants were grown hydroponically attwo amounts of N, supplied in proportion to calculated growthrates. Photosynthesis at light saturation correlated with leafN. The vertical leaf N distribution was associated with thegradient of absorbed light. The leaf N profile changed duringcrop development and was responsive to N availability. At highN supply, the leaf N profiles were constant during crop development.At low N supply, the leaf N profiles fluctuated between moreuniform and steep distributions. These changes were associatedwith reduced leaf area expansion and increasing N remobilizationfrom lower leaf layers. The distribution of leaf N with respectto the gradient of absorbed irradiance was close to the theoreticaloptimum maximizing canopy photosynthesis. Sensitivity analysisof the photosynthesis model suggested that plants maintain anoptimal vertical leaf N distribution by balancing the capacityfor photosynthesis at high and low light. Copyright 2000 Annalsof Botany Company Canopy photosynthesis, leaf nitrogen distribution, nitrogen, Triticum aestivum L, wheat     

Mineral Depletion and Leaf Senescence in Soya Bean as Influenced by Foliar Nutrient Application During Seed Filling

Senescence, as judged by the time courses of leaf lamina photosynthesis,soluble protein and chlorophyll contents, was studied in relationto mineral redistribution in field-grown soya beans [Glycinemax (L.) Merr] to investigate the hypothesis that the depletionof nutrients m the leaves by the developing seeds is the causeof soya bean senescence. A mineral nutrient solution was appliedto the canopy during the seed-filling period, and the effectson senescence and mineral depletion of the leaves were determinedin three cultivars, at two leaf positions, weekly from beginningof seed filling through physiological maturity. The onset of senescence occurred shortly after the beginningof rapid seed filling Photosynthetic rate declined about 60per cent within 3 weeks. Protein dropped by 52 per cent andchlorophyll by 48 per cent over the same period. Foliar nutrient application, at a rate previously shown to givesignificant yield increases in soya beans, increased the concentrationsof N, P and K in the leaf laminae, but tended only to delaytheir decline and failed to either delay the onset or alterthe course of senescence. The results of this experiment seem to indicate that, undernormal growth conditions, the events of senescence in the soyabean are not causally related to the N, P or K concentrationsof the leaf laminae Glycme max (L.) Merr., soya bean, nitrogen, phosphorus, potassium, leaf protein, chlorophyll, photosynthesis, foliar nutrient application, mineral depletion, leaf senescence     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

Effects of awns on the photosynthesis and yield of wheat, Triticum aestivum

Two pairs of awned and awnless near-isogenic lines of winter wheat were used in a field study in which canopy enclosure apparatus and carbon-14 dosing were employed to assess the contribution of the awns to photosynthesis and grain yield. Awns contributed an average of 12-2% to canopy gross photosynthesis but did not increase the net photosynthesis of the complete canopy. The presence of awns decreased photosynthesis in the remaining ear structures and in the flag and penultimate leaf laminae. Seven days after dosing during the phase of rapid grain filling, 80% of the carbon recovered was located in the grains. The awns intercepted 9% of the incident visible radiation when fully green, and senesced at similar rates as the ears and flag leaves. In a second experiment the effect of awns on grain yield and its components was investigated in crosses segregating for height and presence of awns. Awns did not increase grain yields in either experiment. It appears that for British conditions in the absence of severe drought there is little advantage to be gained at present by breeding awned varieties of wheat.     

Photosynthetic capacity of field-grown durum wheat under different N availabilities: A comparative study from leaf to canopy

The effect of N availability on photosynthetic capacity, growth parameters and yield was studied in field-grown durum-wheat plants at both the leaf and canopy levels. Two contrasting nitrogen levels (120 and 0 kg ha^?1) were assayed in a randomised block design with nine replicates each. Total biomass was measured at anthesis and yield and its agronomical components at maturity. Photosynthetic measurements were performed 2 weeks after anthesis in two plots of each N treatment. Flag leaves were measured, using a LI-COR 6400 combined with the chlorophyll fluorescence meter, and the whole canopy by measuring CO₂ and H₂O fluxes in an innovative canopy-chamber system. We showed a clear increase in photosynthetic gas exchange and chlorophyll contents with N fertilisation at both canopy and leaf levels. As a consequence the increase in yield as response to N fertilisation seems the result of a larger green leaf area combined with a higher photosynthetic capacity of the leaves attributable to an increase in the maximum carboxylation velocity of Rubisco. Moreover gas-exchange measurements of the flag leaf during grain filling seem to provide a realistic characterisation, not just of the photosynthetic performance of the crop, but also about the impact of N availability on yield. Thus, measurements performed on the flag leaf matched those at the canopy level, with proportional increases in terms of gas exchange and chlorophyll content, providing a fast, cheap and reliable estimation of canopy photosynthesis and the grain yield attained by the crop.     

冷型小麦旗叶衰老和活性氧代谢特性研究

以典型的冷型小麦和暖型小麦为试验材料,研究了同一环境背景下不同温度型小麦开花后的旗叶衰老和活性氧代谢特性。结果表明,与暖型小麦相比,冷型小麦籽料灌浆期旗叶叶绿素和可溶性蛋白质含量下降缓慢、含量高,整个业粒形成和灌浆期ＭＤＡ积累速度慢、含量低,籽粒灌浆期防御活性氧伤害的关键性保护酶（ＳＯＤ、ＣＡＴ和ＰＯＤ）活性下隆幅度小,灌浆中后期活性水平高。由此认为,小麦旗叶衰老和活性氧代谢特性与其温度型的归属关     

潘庆民1,于振文2,王月福2

采用盆栽和水泥池栽研究了追氮时期对小麦光合作用、14C同化物运转分配和硝酸还原酶(NR)活性的影响.结果表明,拔节(雌雄蕊原基形成)期较起身(二棱)期追施氮肥,显著提高了小麦开花后的旗叶叶绿素含量和单叶光合速率;灌浆期旗叶14C同化物向籽粒转移比例显著提高,而在营养器官的滞留比例显著降低;旗叶和根系中硝酸还原酶(NR)活性亦显著提高.小麦穗粒数、粒重和产量增加,蛋白质含量提高.     

Relationships between grain yield and morphological characters in the winter wheat genotypes of the Belgian national list

Yield per shoot and to a much lesser extend yield per unit area were related to morphological characters. The flag sheath was better related to shoot yield than were any of the three uppermost leaf laminae. Among these the areas of the two lower leaves showed a better relationship to the yield than did the flag leaf lamina. Variation in main shoot yield was associated mainly with variation in grain number. More attention should be given to morphological character related to spike development before anthesis.     

Pressure gradients along whole culms and leaf sheaths, and other aspects of humidity-induced gas transport in Phragmites australis

Emergent aquatic macrophytes growing in waterlogged anaerobic sediments overlain by deep water require particularly efficient ventilating systems. In Phragmites australis (Cav.) Trin. ex Steud, pressurized gas flows, generated by humidity-induced diffusion of air into leaf sheaths, enhance oxygen transport to below-ground parts and aid in the removal of respiratory CO2 and sediment-generated CO2 and methane. Although modelling and flow measurements have pointed to the probable involvement of all leaf sheaths in the flow process and the development of pressure gradients along the whole lengths of living culm and leaf sheaths, direct measurements of pressure gradients have never been reported. The aim of this study was to search for pressure gradient development in Phragmites culms and leaf sheaths and to determine their magnitudes and distribution. In addition, dynamic (with gas flow) and static pressures (no flow condition) and their relationship to flows, leaf sheath areas, and living-to-dead culm ratios were further investigated. Dynamic pressures (DeltaPd) recorded in the pith cavities of intact (non-excised) leafy culms, pneumatically isolated from the below-ground parts and venting through an artificial bore-hole near the base, revealed a curvilinear gradient of pressure 'asymptoting' towards the tips of the culms. Similarly, DeltaPd in upper and lower parts of leaf sheaths increased with distance from the base of the culm, with values in the upper parts always being greater. Curvilinear gradients of pressure were also found along pneumatically isolated individual leaf sheaths, but radial channels linking the leaf sheath aerenchyma with the pith cavity of the culm appeared to offer little resistance to flow. In keeping with predictions, static pressure differentials (DeltaPs) achieved in intact and excised culms and single leaf sheaths on intact culms proved to be relatively independent of leaf sheath area, whereas the potential for developing convective flows (pressure-driven flows) increased with increasing leaf sheath area. As measured by the ventilating coefficient [1-(DeltaPd/(DeltaPs)] the old dead (efflux) to living (influx) culm ratio of 1:12 compared with 1:25 raised ventilating efficiency from 31% to 71%, giving flows per tall culm into the rhizome system of c. 2.8 cm3 and 6.5 cm3 min-1, respectively. It was concluded that dynamic pressure gradients probably extend along the whole length of the leafy culms and leaf sheaths of Phragmites and that all leaf sheaths and all exposed points along the leaf sheaths can contribute convective gas-flow to the rhizome system.     

Leaf contents differ depending on the position in a rice leaf sheath during sink-source transition.

Carbohydrate contents varied with position in a leaf sheath, and differed between the flag leaf sheath and the second leaf sheath below the flag leaf (-2 leaf sheath) in rice (Oryza sativa L.). In the -2 leaf sheath before heading, light microscopy revealed differences in the distribution of starch granules depending on position. Leaf sheaths were divided into several parts, and the contents of carbohydrates (starch, sucrose, and hexoses) were measured in each part. Before heading, the content of accumulated starch increased linearly from the top to the bottom in -2 leaf sheaths (r2=0.99, P<0.001), as did the contents of accumulated sucrose and hexoses in flag leaf sheaths (r2=0.94, P<0.01). In flag leaf sheaths, the relative content of sucrose synthase (SuS), which plays a central role in the degradation of sucrose into hexoses, increased from the top to the bottom, consistent with hexose contents. After heading, the accumulated carbohydrates were dramatically decreased. In -2 leaf sheaths, the activity of alpha-amylase (EC 3.2.1.1), the rate-limiting step in starch degradation, was consistent with the degree of starch degradation, but in flag leaf sheaths with little starch before heading. These results show that carbohydrate contents differ, depending on the position in a leaf sheath. In addition, there were big differences in leaf contents between flag leaf sheaths and -2 leaf sheaths.     

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.     

Stay‐green: A consequence of the balance between supply and demand for nitrogen during grain filling?

Retention of green leaf area in grain sorghum under post‐anthesis drought, known as stay‐green, is associated with greater biomass production, lodging resistance and yield. The stay‐green phenomenon can be examined at a cell, leaf, or whole plant level. At a cell level, the retention of chloroplast proteins such as LHCP2, OEC33 and Rubisco until late in senescence has been reported in sorghum containing the KS19 source of stay‐green, indicating that photosynthesis may be maintained for longer during senescence in these genotypes. At a leaf level, longevity of photosynthetic apparatus is intimately related to nitrogen (N) status. At a whole plant level, stay‐green can be viewed as a consequence of the balance between N demand by the grain and N supply during grain filling. To examine some of these concepts, nine hybrids varying in the B35 and KS19 sources of stay‐green were grown under a post‐anthesis water deficit. Genotypic variation in delayed onset and reduced rate of leaf senescence were explained by differences in specific leaf nitrogen (SLN) and N uptake during grain filling. Matching N supply from age‐related senescence and N uptake during grain filling with grain N demand found that the shortfall in N supply for grain filling was greater in the senescent than stay‐green hybrids, resulting in more accelerated leaf senescence in the former. We hypothesise that increased N uptake by stay‐green hybrids is a result of greater biomass accumulation during grain filling in response to increased sink demand (higher grain numbers) which, in turn, is the result of increased radiation use efficiency and transpiration efficiency due to higher SLN. Delayed leaf senescence resulting from higher SLN should, in turn, allow more carbon and nitrogen to be allocated to the roots of stay‐green hybrids during grain filling, thereby maintaining a greater capacity to extract N from the soil compared with senescent hybrids.     

Sequential and non-sequential pattern of monocarpic senescence in two rice cultivars

Two rice ( Oryza sativa L.) cultivars viz. Ratna (dwarf, photoperiod insensitive) and Masuri (tall, photoperiod sensitive) were selected to analyse their mode of senescence. At the vegetative stage, leaf senescence, expressed as the loss of chlorophyll and protein and a decline in the activities of catalase and alkaline pyrophosphatase, was found to be a function of chronological age (sequential) in both cultivars. With advancing reproductive development, cultivar Masuri retained this sequential mode but cultivar Ratna showed a non-sequential mode of senescence where the flag leaf senesced earlier than the older second leaf, unlike that observed at the vegetative stage. Masuri showed a more rapid senescence than Ratna. In both cultivars, excision of any leaf during anthesis initially retarded the senescence of the remaining leaves on the defoliated plants but soon after, at the grain maturation stage, the leaf senescence started at a higher rate compared with that of the intact control plant. In Ratna, when either the second or the third leaf was removed, the flag leaf senesced faster than that of the unexcised control plant. In Masuri, when either the flag or the third leaf was removed, the second leaf senesced earlier than that of the intact control. In both cultivars, excision of the third leaf showed the least detrimental effect on yield. The greatest detrimental effect on grain yield per plant was observed in Ratna when the flag leaf was removed and in Masuri when the second leaf was removed. Mobilization of metabolites from the source leaf to the sink and the consequent depletion in the leaf as the cause of senescence is discussed.     

Maximum likelihood inference and bootstrap methods for plant organ growth via multi-phase kinetic models and their application to maize

* BACKGROUND AND AIMS: Fitting the parameters of models of plant organ growth is a means to investigate how environmental conditions affect plant architecture. The aim of this article is to evaluate some non-linear methods for fitting the parameters of multi-phase models of the kinetics of extension of plant organs such as laminae, sheaths and internodes. * METHODS: A set of computational procedures was developed allowing parameter-fitting of multi-phase models, using the maximum likelihood criterion, in which phases are identified with reference to ontogenic processes. Two bootstrap methods were compared to assess the precision of the estimates of fitted parameters, and of functions of these parameters such as the final leaf length, and the duration and rate of the rapid extension phase. Methods were applied to an experimental dataset, representing the kinetics of laminae, sheaths and internodes along the maize shoot, for two contrasting densities. * KEY RESULTS: A set of multi-phase models was proposed to describe the extension of laminae, sheaths and internodes along the shoot. The distinguishable phases differed between laminae, sheaths and internodes. For sheaths and laminae, but not for internodes, the same model could be fitted to all phytomers along the shoot. The variation of parameters along the shoot and between density treatments, as well as derived functions such as the durations of the phases of extension, are presented for laminae. It was the duration of the fast extension period, rather than its rate, which determined the difference in final length between treatments. * CONCLUSIONS: Such methods permit a large degree of objectivity and facilitate the analysis of such rather complicated but co-ordinated datasets. The work also illustrates some natural limitations of maximum likelihood methods, and viable ways of overcoming them by including a priori knowledge in the model fitting method are discussed.     

Some effects of leaf posture on photosynthesis and yield in wheat

Canopy enclosures were used to study the photosynthesis of two winter wheat genotypes with contrasting leaf posture (E, erect; L, lax). Over the grain filling period, the net carbon dioxide fixation during the daytime was nearly always greater in E than in L. In general, a greater proportion of the fixation took place in the lower leaves of E than L. Because of the slower senescence of its lower leaves, the leaf area index of E was slightly but consistently higher than that of L and this appeared to account, in part, for the difference between the genotypes in canopy photosynthesis. However, during June and early July, when the leaf area indices were above three, the more uniform distribution of light in the canopy of E than in that of L appeared to be a cause of its higher rate of photosynthesis. Over the grain filling period, more dry matter was lost from the stems of L than from those of E. It is suggested that the shortfall of assimilate for grain filling was met, at least in part, by translocation of materials from the stems and that their greater depletion in L made up for the lower contribution from current assimilation in this genotype.     

Photosynthesis of the flag leaf blade and its sheath in high-yielding hybrid rice 'Liangyoupeijiu'.

Using high-yielding hybrid rice 'Liangyoupeijiu' (LYP9) and hybrid rice 'Shanyou 63' (SY63) as the experimental materials and using (14)C radio-autography, the photosynthetic capacities and distribution of photosynthates in flag leaf blades and sheaths of LYP9 were studied. The results showed that net photosynthetic rates (Pn) of the flag leaf blades and sheaths of LYP9 were much higher than those of SY63; the light transmissivity rates (LT) measured at the medium height of the flag leaf sheaths and the penultimate leaf sheaths were also significantly higher than those of SY63. The incipient activities, total activities and activation percentages of Rubisco in the flag leaf blade and sheath of LYP9 were all higher than those of SY63. The photosynthate transport rate in the sheaths of LYP9, and the quantity of photosynthate transported to the spikes and transformed to economic yield of LYP9 were all higher than those of SY63. The photosynthates produced by the sheaths were mainly transported to spike to make a certain contribution (about 15%) to yield.