Measurement of summer dormancy in temperate perennial pasture grasses

The search to improve drought survival in temperate perennial grasses has led to a renewed interest in summer dormancy and how to quantify it. This endogenously controlled trait, found in some temperate perennial grasses, is associated with drought that normally occurs in summer. While cessation of leaf growth and senescence of herbage occurs in all grasses in response to drought, it is under summer irrigation that these same responses are observed only in summer-dormant germplasm and hence the trait can be identified in germplasm. Across the spectrum from completely summer-dormant to non-dormant, there is a range of expression. Our objective here is to highlight differences in characteristics of indices which measure summer dormancy and to identify aspects for incorporation into a superior index for use in measuring this trait. The experimental program comprised three field trials that compared 6 cultivars and a fourth that assessed a larger group of 12 cultivars of the same three species, cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), and phalaris (Phalaris aquatica L.). Seasonal herbage yield and foliage senescence were measured under three summer watering regimes: complete drought, mid-summer storm, and full irrigation at Mauguio, France. Different indices were calculated to compare against the approach which evaluates senescence under drought. The key outcomes are as follows. (1) The assessment of summer dormancy needs to be viewed as the plant response to a period of non-limiting water supply over summer. It makes little difference whether this is produced by full summer irrigation or a mid-summer simulated storm after a drought. Assessment of this trait under conditions of unbroken drought is discouraged because it can result in false scores. (2) The determination of summer dormancy intensity under full summer irrigation is most appropriate for the intensive study of the dynamics of dormancy expression over the entire summer. A simulated mid-summer storm within a drought gives an instantaneous view of dormancy intensity at a specific observation date and may be well adapted to the requirements of plant breeding. These methods are complementary. (3) Summer dormancy intensity can be assessed either by measuring herbage production or by a visual assessment of the level of herbage senescence. (4) An index of summer dormancy based on comparing irrigated summer herbage yield of any cultivar with that of a high, summer-yielding, non-dormant control cultivar was able to provide a reliable score of dormancy intensity. This index functions across a range of cultivars and species of perennial grasses. Further refinement of the index is needed to identify ‘standard’ high and low summer-dormant populations.

The significant influence of smoking status and gender on the clinical outcome in the patients with non-small cell lung cancer: The large cohort based study

7587

Background: To determine retrospectively whether smoking status and gender affect the treatment outcome and survival for the Japanese patients with non-small cell lung cancer. Methods: Using the database from the lung cancer registry of the National Hospital Study Group for Lung Cancer between 1987 and 2002, detailed demographic and survival information were obtained. A total of 18,346 (70%) documented smokers including the former and the current and 7,755 (30%) documented never smokers with non-small cell lung cancer were studied. A minimal follow-up period was two years. Among them, the 2,546 patients with stage IV lung adenocarcinoma were studied to examine the relationship between the smoking status or the gender and the chemotherapy effect. Multivariate analysis was performed using the Cox regression method. Results: There was an increased percentage of female subjects (72%) in the never smokers, and an increased percentage of male subjects (90%) in the smokers. The never smokers had lower performance status (PS) and lower clinical stage than the smokers (p<0.001). There was an increased percentage of adenocarcinoma (83%) in the never smokers. Multivariate analysis for all the patients demonstrated that the lower clinical stage, the lower PS, younger age, female and never smoking was an independent good prognostic factor The hazard ratio (HR) and its 95% CI was 3.73 (3.58–3.88), 2.69 (2.59–2.79), 1.21 (1.17–1.25), 1.15 (1.09–1.20), and 1.08 (1.04–1.14), respectively. Multivariate analysis for the stage IV adenocarcinoma also showed that the lower PS, female and never smoking was an independent good prognostic factor. The HR and its 95% CI was 2.37 (2.15–2.61), 1.35 (1.19–1.52) and 1.17 (1.04–1.32) respectively. In the treatment of chemotherapy for the stage IV adenocarcinoma patients, the never smokers had higher disease control rates (CR+PR+SD) than the smokers (p=0.08) and the females had higher response rates (CR+PR) than the males (p=0.02). Conclusions: The never smokers and females with non-small cell lung cancer were found to have a distinct and improved clinical outcome.

No significant financial relationships to disclose.

Phase II study of docetaxel and S-1 combination therapy in patients with previously treated non-small cell lung cancer

18122

Background: Docetaxel is active against chemotherapy-pretreated non-small-cell lung cancer (NSCLC). S-1 is a novel oral fluoropyrimidine, composed of tegafur, 5-chloro-2,4-dihydroxypyridine (dihydropyrimidinedehydrogenase inhibitor), and potassium oxonate (orotate phosphoribosyl transferase inhibitor). It has been commercially available and used for NSCLC in Japan. We conducted this study to evaluate the efficacy and safety of docetaxel combined with S-1 in NSCLC patients (pts) who were previously treated with one or more regimens. Methods: Eligible pts were required to have histologically or cytologically confirmed measurable or evaluable stage IIIB or IV NSCLC, age= 20 years, one or more previous chemotherapy, a performance status (PS) 0–1, and adequate organ function and bone marrow reserve. In this study, pts received S-1 (80 mg/m2 orally on days 1–14) and docetaxel (40mg/m2 IV on days 1). Treatment was repeated every 3 weeks. Results: Between January 2005 and May 2006, 30 pts were enrolled on this study. 29 pts were eligible and evaluable. Median age was 67 (48–79), male/female (23/6), PS 0/1 (9/20), stage IIIB/IV (7/22), and prior chemotherapy regimen 1/2/3 (23/4/2). 28 pts received a platinum-based chemotherapy. Response: PR=7(24%), SD=13, PD=7, NE=2. Median survival time was 10.2 months. Grade 3/4 toxicities (% of pts) were as follows: leukocytes 6/0 (20.6%), neutrophils 7/3 (34.4%), platelets 0/0, infection 0/1 (3.4%), fever 2/0 (6.9%), diarrhea 1/0 (3.4%), neurology 0/1 (3.4%), and mucositis 1/0 (3.4%). There were no treatment-related deaths. Conclusions: The combination of docetaxel and S-1 was effective with acceptable toxicity in pts with previously treated NSCLC. These results warrant further investigations of this regimen a randomized controlled trial as a second-line treatment for NSCLC.

No significant financial relationships to disclose.

[Extraabdominal desmoid tumor of the chest wall]

We report a rare case of desmoid tumor of the chest wall. A 75-year-old female visited our hospital due to a feeling of oppression in the left chest. A chest X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) revealed a large mass in the left thorax. Surgical resection of the tumor was performed under the left standard thoracotomy. The tumor was 90 x 80 x 75 mm in size and diagnosed pathologically as desmoid tumor which showed proliferation of spindle shape cells and collagen fibers. Immunohistochemistry revealed that the tumor cells were positive for vimentin, alpha-smooth muscle actin and negative for CD34. The patient has been well without recurrence for 2 years and 2 months after surgery.

Phase II study of UFT, vinorelbine and gemcitabine as first-line treatment in advanced non-small-cell lung cancer

17100

Background: Vinorelbine (VNR)/gemcitabine (GEM) is active and well tolerated chemotherapy regimens for the treatment of patients (pts) with advanced non-small-cell lung cancer (NSCLC). UFT is composed of uracil and tegafur in a molar ratio of 4:1, and tegafur is a prodrug of 5-FU. Sequential exposure to 5-FU followed by GEM has been reported to give additive effects in vitro. For these reasons, we conducted a phase II study of triple treatment with these 3 drugs for advanced NSCLC. The objectives were to determine the tumor response rate, survival, safety and toxicity of this combination chemotherapy. Methods: Eligible pts were required to have histologically or cytologically comfirmed measurable or evaluable stage IIIB or IV NSCLC, age <75 years, no previous chemotherapy, a Karnofsky performance status (PS) 0–1, and adequate organ function and bone marrow reserve. In this study, pts received UFT (300 mg/m2 orally on days 1-5, 8–12) plus VNR (25 mg/m2 IV on days 6 and 13) and GEM (1000 mg/m2 IV on days 6 and 13). Treatment was repeated every 3 weeks. Results: Between September 2002 and November 2004, 32 pts were enrolled on this study. Characteristics of this study were as follows: male/female = 20/12; median age = 65 years (range 46–74); PS 0/1 = 11/21; stage IIIB/IV = 5/27. Median # of cycles = 2 (range 1–10). Response: PR = 7 (21.9%), SD = 14, PD = 10, NE = 1. Median survival time was 13.9 mos. 1-year survival rate was 56.7% (95% confidence interval, 38.9–74.4%). Gr 3/4 toxicity (% of pts) was as follows: leukocytes 40.6%, neutrophils 56.3%, platelets 3.1%, infection 9.4%, hypoxia 6.3%, dyspnea 3.1% and ALT/AST 3.1%. There were no treatment-related deaths. Conclusions: The combination of UFT, VNR and GEM appears effective with acceptable toxicity.

No significant financial relationships to disclose.

Minimising cold damage during reproductive development among temperate rice genotypes. II. Genotypic variation and flowering traits related to cold tolerance screening

Low temperature during microspore development increases spikelet sterility and reduces grain yield in rice (Oryza sativa L.). The objectives of this study were to determine genotypic variation in spikelet sterility in the field in response to low temperature and then to examine the use of physio-morphological traits at flowering to screen for cold tolerance. Multiple-sown field experiments were conducted over 4 consecutive years in the rice-growing region of Australia to increase the likelihood of encountering low temperature during microspore development. More than 50 cultivars of various origins were evaluated, with 7 cultivars common to all 4 years. The average minimum temperature for 9 days during microspore development was used as a covariate in the analysis to compare cultivars at a similar temperature. The low-temperature conditions in Year 4 identified cold-tolerant cultivars such as Hayayuki and HSC55 and susceptible cultivars such as Sasanishiki and Doongara. After low temperature conditions, spikelet sterility was negatively correlated with the number of engorged pollen grains, anther length, anther area, anther width, and stigma area. The number of engorged pollen grains and anther length were found to be facultative traits as their relationships with spikelet sterility were identified only after cold water exposure and did not exist under non-stressed conditions.

Minimising cold damage during reproductive development among temperate rice genotypes. I. Avoiding low temperature with the use of appropriate sowing time and photoperiod-sensitive varieties

Multiple-sown field trials in 4 consecutive years in the Riverina region of south-eastern Australia provided 24 different combinations of temperature and day length, which enabled the development of crop phenology models. A crop model was developed for 7 cultivars from diverse origins to identify if photoperiod sensitivity is involved in determining phenological development, and if that is advantageous in avoiding low-temperature damage. Cultivars that were mildly photoperiod-sensitive were identified from sowing to flowering and from panicle initiation to flowering. The crop models were run for 47 years of temperature data to quantify the risk of encountering low temperature during the critical young microspore stage for 5 different sowing dates. Cultivars that were mildly photoperiod-sensitive, such as Amaroo, had a reduced likelihood of encountering low temperature for a wider range of sowing dates compared with photoperiod-insensitive cultivars. The benefits of increased photoperiod sensitivity include greater sowing flexibility and reduced water use as growth duration is shortened when sowing is delayed. Determining the optimal sowing date also requires other considerations, e.g. the risk of cold damage at other sensitive stages such as flowering and the response of yield to a delay in flowering under non-limiting conditions. It was concluded that appropriate sowing time and the use of photoperiod-sensitive cultivars can be advantageous in the Riverina region in avoiding low temperature damage during reproductive development.

The interaction of nitrogen application and temperature during reproductive stage on spikelet sterility in field-grown rice

Increased grain yield in response to high rates of application of nitrogen (N) fertiliser is often limited by increased spikelet sterility, particularly under low temperature conditions in the New South Wales (NSW) rice industry. In 3 field experiments, different N rates were applied for different sowing dates to investigate the interaction between N rate and temperature during microspore development on spikelet sterility and grain yield. In one experiment the effect of water depth on spikelet sterility was also investigated. Engorged pollen production, spikelet sterility, and yield and its components were recorded. Application of N affected a few different processes that lead into spikelet sterility. Application of N at both pre-flood (PF) and panicle initiation (PI) significantly reduced the number of engorged pollen grains per anther, which was negatively correlated with spikelet sterility. Application of N and low temperature during microspore development with the absence of deep water also decreased pollen engorgement efficiency (the percentage of pollen grains that were engorged). Application of N further increased spikelet density, which, in turn, increased both spikelet sterility and grain yield. The combined effect of spikelet density and low temperature during microspore development explained the 44% of variation in the number of engorged pollen grains per anther. Grain yield was decreased by low temperature during microspore development in the shallow water when N was applied. Spikelet sterility as a result of late sowing was strongly correlated with minimum temperature during flowering. It is concluded that N application reduced pollen number per anther as a result of increased spikelet density, and this made the spikelets more susceptible to low temperature, causing increased spikelet sterility.

[An operative approach of extrapleural pneumonectomy]

We present a case of breast cancer with pleural metastasis and empyema treated with extrapleural pneumonectomy. We showed the some of technically important points for this operation. The careful preparation was needed to prevent hemorrhage from such as great vessels, bronchial arteries and intercostal arteries. Especially in this surgical procedure, we should select the best approach method to have enough surgical field for complete tumor resection. We suggest that we should make additional thoracotomy and skin incision immediately when we feel the surgical field is not wide enough during the operation. The extrapleural pneumonectomy is one of the most highly invasive operation in general thoracic surgery, so careful perioperative managements should be required.

Low temperature induced spikelet sterility in rice. I. Nitrogen fertilisation and sensitive reproductive period

Low temperature during panicle development in rice increases spikelet sterility. This effect is exacerbated by high rates of nitrogen (N) application in the field. Spikelet sterility induced by low temperature and N fertilisation was examined in glasshouse experiments to clarify the mechanisms involved. In two glasshouse experiments, 12-h periods of low (18/13�C) and high (28/23�C) day/night temperatures were imposed over periods of 5–7 days during panicle development, to determine the effects of low temperature and N fertilisation on spikelet sterility. In one experiment, 50% sunlight was imposed together with low temperature to investigate the additive effects of reduced solar radiation and low temperature. The effect of increased tillering due to N fertilisation was examined by a tiller removal treatment in the same experiment. Pollen grain number and spikelet sterility were recorded at heading and harvest, respectively. Although there was no significant effect of low temperature on spikelet sterility in the absence of applied N, low temperature greatly increased spikelet sterility as a result of a reduction in the number of engorged pollen grains per anther in the presence of applied N. Spikelet sterility was strongly correlated with the number of engorged pollen grains per anther. Low temperature during very early (late stage of spikelet differentiation–pollen mother cell stage) and peak (second meiotic division stage–early stage of extine formation) microspore development caused a severe reduction in engorged pollen production mainly as a result of reduced total pollen production. Unlike low temperature, the effect of shading was rather small. The increased tillering due to application of high rates of N, increased both spikelet number per plant and spikelet sterility under low temperature conditions. The removal of tillers as they appeared reduced the number of total spikelets per plant and maintained a large number of engorged pollen grains per anther which, in turn, reduced spikelet sterility. The number of engorged pollen grains per anther determined the numbers of intercepted and germinated pollen grains on the stigma. It is concluded that N increased tillering and spikelet number per plant and this, in turn, reduced the number of engorged pollen grains per anther, leading into increased spikelet sterility under low temperature condition.

Low temperature induced spikelet sterility in rice. II. Effects of panicle and root temperatures

Low temperatures impose restrictions on rice (Oryza sativa L.) production at high latitudes. This study is related to low temperature damage that can arise mid-season during the panicle development phase. The objective of this study was to determine whether low temperature experienced by the root, panicle, or foliage is responsible for increased spikelet sterility. In temperature-controlled glasshouse experiments, water depth, and water and air temperatures, were changed independently to investigate the effects of low temperature in the root, panicle, and foliage during microspore development on spikelet sterility. The total number of pollen and number of engorged pollen grains per anther, and the number of intercepted and germinated pollen grains per stigma, were measured. Spikelet sterility was then analysed in relation to the total number of pollen grains per spikelet and the efficiency with which these pollen grains became engorged, were intercepted by the stigma, germinated, and were involved in fertilisation. There was a significant combined effect of average minimum panicle and root temperatures on spikelet sterility that accounted for 86% of the variation in spikelet sterility. Total number of pollen grains per anther was reduced by low panicle temperature, but not by low root temperature. Whereas engorgement efficiency (the percentage of pollen grains that were engorged) was determined by both root and panicle temperature, germination efficiency (the percentage of germinated pollen grains relative to the number of engorged pollen grains intercepted by the stigma) was determined only by root temperature. Interception efficiency (i.e. percentage of engorged pollen grains intercepted by the stigma), however, was not affected by either root or panicle temperature. Engorgement efficiency was the dominant factor explaining the variation in spikelet sterility. It is concluded that both panicle and root temperature affect spikelet sterility in rice when the plant encounters low temperatures during the microspore development stage.

Crystal structure of human AUH protein, a single-stranded RNA binding homolog of enoyl-CoA hydratase

BACKGROUND

The AU binding homolog of enoyl-CoA hydratase (AUH) is a bifunctional protein that has two distinct activities: AUH binds to RNA and weakly catalyzes the hydration of 2-trans-enoyl-coenzyme A (enoyl-CoA). AUH has no sequence similarity with other known RNA binding proteins, but it has considerable sequence similarity with enoyl-CoA hydratase. A segment of AUH, named the R peptide, binds to RNA. However, the mechanism of the RNA binding activity of AUH remains to be elucidated.

RESULTS

We determined the crystal structure of human AUH at 2.2 A resolution. AUH adopts the typical fold of the enoyl-CoA hydratase/isomerase superfamily and forms a hexamer as a dimer of trimers. Interestingly, the surface of the AUH hexamer is positively charged, in striking contrast to the negatively charged surfaces of the other members of the superfamily. Furthermore, wide clefts are uniquely formed between the two trimers of AUH and are highly positively charged with the Lys residues in alpha helix H1, which is located on the edge of the cleft and contains the majority of the R peptide. A mutational analysis showed that the lysine residues in alpha helix H1 are essential to the RNA binding activity of AUH.

CONCLUSIONS

Alpha helix H1 exposes a row of Lys residues on the solvent-accessible surface. These characteristic Lys residues are named the "lysine comb." The distances between these Lys residues are similar to those between the RNA phosphate groups, suggesting that the lysine comb may continuously bind to a single-stranded RNA. The clefts between the trimers may provide spaces sufficient to accommodate the RNA bases.

[Examination of eye position after strabismus surgery in Kawasaki Medical School Hospital]

PURPOSE

To examine the factors which affect changes in the position of the eyes following the strabismus surgery.

METHODS

The postoperative position of 240 eyes with concomitant strabismus was examined. The factors which seemed to have an effect on the position of the eyes were enumerated, and a logistic regression analysis of the results was done.

RESULTS

In comparison with esotropia, in exotropia the eyes showed a tendency to return gradually to a normal position. There was no remarkable improvement in stereoscopic vision following strabismus surgery. Based on the standards of the Japanese Association of Strabismus and Amblyopia [the cure standard for strabismus], the results of strabismus surgery were as follows: Grade 1(cosmetically satisfactory) was mainly observed for esotropia, and Grade 3(good) for exotropia. The factors which had a significant effect on the postoperative position of the eyes were as follows: esotropia amblyopia, muscle movement, and operative methods; exotropia: retinal correspondence, operative methods, and the necessity of inferior oblique muscle surgery.

CONCLUSIONS

There was little correction of the position of the eyes. In individual cases, the factors which affect position of eyes were examined, and it was considered necessary to increase the amount of correction. Age is a factor which has an effect, but the effect on esotropia and exotropia is small.

Structural basis for double-sieve discrimination of L-valine from L-isoleucine and L-threonine by the complex of tRNA(Val) and valyl-tRNA synthetase

Valyl-tRNA synthetase (ValRS) strictly discriminates the cognate L-valine from the larger L-isoleucine and the isosteric L-threonine by the tRNA-dependent "double sieve" mechanism. In this study, we determined the 2.9 A crystal structure of a complex of Thermus thermophilus ValRS, tRNA(Val), and an analog of the Val-adenylate intermediate. The analog is bound in a pocket, where Pro(41) allows accommodation of the Val and Thr moieties but precludes the Ile moiety (the first sieve), on the aminoacylation domain. The editing domain, which hydrolyzes incorrectly synthesized Thr-tRNA(Val), is bound to the 3' adenosine of tRNA(Val). A contiguous pocket was found to accommodate the Thr moiety, but not the Val moiety (the second sieve). Furthermore, another Thr binding pocket for Thr-adenylate hydrolysis was suggested on the editing domain.

[Effectiveness of docetaxel plus cisplatin in large cell lung cancer showing little response to prior chemotherapy with MVP]

The present patient was a 53-year-old male who had large cell lung cancer of c-T4N1M0. We administered multi-drug regimen including mitomycin C, vindesine and cisplatin (CDDP) because of cancer invasion into the great vessels seen on a chest CT. After 3 courses, the cancer showed no change in size. Therefore, we adopted chemotherapy of docetaxel (Taxotere: TXT) and CDDP. After 4 courses, the size of the mass had decreased (partial response). The only major toxic defect was grade 3 neutropenia. A good response to TXT and CDDP could lead to complete resection of lung cancer. It is suggested that TXT is effective in the treatment of large cell lung cancer.

[Preoperative evaluation of cardiac disease for patients with lung cancer: usefulness of treadmill exercise electrocardiogram]

118 patients with lung cancer who underwent treadmill exercise electrography (ECG) as part of their preoperative evaluation, were investigated for postoperative events. On the treadmill exercise ECG 27 patients were positive and 91 were negative. The more elderly patients tended to reveal ischemic findings in treadmill exercise ECG. Of the 71 patients with normal of result by ECG at rest, 15 patients (21.1%) had postoperative ischemic change on ECG. As a result, it was considered that this examination was insufficient to detect latent ischemic heart disease. The patients who had a discontinued at stage 2 or less of the Bruce protocol and had a negative result by treadmill exercise ECG, were classified as insufficient group and separated from the others. (27/118 patients). This group consisted of advanced age (p < 0.05) who tended to experience postoperative events. In the sufficient group, patients showed ischemic events predominantly on ECG at postoperative period (p < 0.01). We concluded that as preoperative screening of heart disease prior to lung cancer surgery ECG at rest was not adequate while treadmill exercise ECG was useful.

Grain nitrogen concentration differences among three sorghum hybrids with similar grain yield

The differences in grain nitrogen (N) concentration among 3 sorghum (Sorghum bicolor (L.) Moench) hybrids with similar grain yield were examined under N-limiting conditions in relation to the availability of assimilate and N to grain. Several manipulation treatments [N fertiliser application, lower leaves shading, thinning (reduced plant population), whole canopy shading, canopy opening, spikelet removal] were imposed to alter the relative N and assimilate availability to grain under full irrigation supply. Grain N concentration increased by either increased grain N availability or yield reduction while maintaining N uptake. Grain N concentration, however, did not decrease in the treatments where relative abundance of N compared with assimilate was intended to be reduced. The minimum levels of grain N concentration differed from 0.95% (ATx623/RTx430) to 1.14% (DK55plus) in these treatments. Regardless of the extent of variation in assimilate and N supply to grain, the ranking of hybrids on grain N concentration was consistent across the manipulation treatments. For the 3 hybrids examined, higher grain N concentration was associated with higher N uptake during grain filling and, to a lesser extent, with higher N mobilisation. Hybrids with larger grain N accumulation had a larger number of grains. There was no tradeoff between grain N concentration and yield, suggesting that grain protein concentration can be improved without sacrificing yield potential.

Enzyme structure with two catalytic sites for double-sieve selection of substrate

High-fidelity transfers of genetic information in the central dogma can be achieved by a reaction called editing. The crystal structure of an enzyme with editing activity in translation is presented here at 2.5 angstroms resolution. The enzyme, isoleucyl-transfer RNA synthetase, activates not only the cognate substrate L-isoleucine but also the minimally distinct L-valine in the first, aminoacylation step. Then, in a second, "editing" step, the synthetase itself rapidly hydrolyzes only the valylated products. For this two-step substrate selection, a "double-sieve" mechanism has already been proposed. The present crystal structures of the synthetase in complexes with L-isoleucine and L-valine demonstrate that the first sieve is on the aminoacylation domain containing the Rossmann fold, whereas the second, editing sieve exists on a globular beta-barrel domain that protrudes from the aminoacylation domain.

Barley yield and grain protein concentration as affected by assimilate and nitrogen availability

Two types of experiments were conducted with the malting barley cv. Grimmett to examine how assimilate and nitrogen (N) availability at different growth stages determined yield and grain protein concentration (GPC) in south-east Queensland. In one series of experiments, plants were sown in April, June, and August so that they would experience different growing conditions, and responses to N application rate were examined. Another experiment examined response of growth, yield, and GPC to variation of assimilate production pre and post anthesis, caused by the canopy manipulation treatments of opening, closure, and 50% shading at 3 different growth stages. Without N application all 3 sowings produced similar yields (1·9-2·3 t/ha), but when N was applied, yield was higher and responded more to applied N in the June sowing than in the other sowings.The different responses of grain yield to N application rate among the 3 sowing dates were not due to differences in N uptake but to the efficiency of N use; with favourable temperatures throughout crop growth, the crop sown in June utilised N most eciently to develop a large number of grainsand to produce sufficient as similates to fill these grains. When yield had a positive response to low N application rates, then there was generally no response of GPC, whereas when there was no response of grain yield to further rate of N application then GPC increased. The results of the second experiment show that N uptake depended on plant N demand at early stages of growth when N was still available in the soil, but total N content of tops at maturity was similar among canopy manipulation treatments. Canopy opening at any stage of growth tended to increase tiller number, leaf area index, and above-ground dry matter, but the effect was greater attillering stage which produced the highest yield because of the greatest number of heads. Shading reduced yield at all stages, but particularly at pre-anthesis. Shading and canopy closure during grain filling reduced grain yield, but with similar N uptake these treatments significantly increased GPC .These results indicate that GPC depends on both assimilate and N availability to grain, and GPC can increase sharply when grain yield is reduced with low assimilate availability as a result of adverse growing conditions. Responses of grain yield to applied N depended on environmental conditions, particularly the patterns of air temperature during growth, and the crop utilised N more efficiently to produce higher yield when it was not exposed to extreme temperatures during the latter stages of growth.