In sweet sorghum, which is a potential biomass crop, the diameter of internode is an important component of stem yield. However, the thickening of successive internodes is poorly understood. The objective of this study was to clarify the relationship between the thickening of successive internodes using the age indicated by the leaf number on the main stem (AL) as a time scale. Furthermore, the relationship between the elongating and thickening period of successive internodes along the stem was analyzed. Internodes were collected from AL3, when the 3rd leaf had just expanded above the 2nd leaf sheath, to AL17, and at 9 weeks after heading as final harvest. Although the internode thickening patterns based on AL could not be combined into one or a few patterns, a significant correlation (P<0.001) was found between internode position and AL at which the internodes were thickening, suggesting that a regularity of internode thickening existed among successive internodes. The higher the internode position, the longer the first half of the thickening period (from 15% to 50% of thickening), whereas the period of the second half (50%–85% thickening) was constant irrespective of internode position. These results suggest that the degree of the elongation and thickening of successive internodes can be estimated by using AL.
Root traits that can contribute to drought resistance have not been clearly indentified. We examined the role of root system development in enhancing water uptake and contribution to dry matter production by using the root box-pinboard method, with which quantitative assessment of root system development and the water uptake of root are possible. Chromosome segment substitution lines CSSL45 and CSSL50, and the recurrent parent Nipponbare were grown under continuously waterlogged conditions (control), and various intensities of water deficit in root boxes. There was no significant difference among the genotypes in shoot growth and root development, while CSSL45 and CSSL50 showed greater shoot dry weight than Nipponbare under water deficit conditions. This was due to their abilities to promote root system development as compared with Nipponbare, which facilitated greater water extraction than Nipponbare, especially under the mild water deficit condition of 20–25% w/w soil moisture contents. Furthermore, the increased root length density did not exceed the estimated critical value for water uptake, which indicates that plastic root system development was functionally effective and efficient for the enhancement of water uptake under mild water deficit conditions.
In order to identify β-amylase isoforms acting inside plastids in rice (Oryza sativa L.), in the rice genome database we searched the genes predicted to encode β-amylase-like proteins, and designated them OsBAM1−9. OsBAM1, OsBAM7, andOsBAM9 genes were mainly expressed in germinating seeds and developing caryopses. In contrast, the transcripts of OsBAM2, OsBAM3, OsBAM4 and OsBAM5,which have a putative chloroplast transit peptide in their N-terminal regions, were mainly detected in leaf blades, leaf sheaths and internodes after heading. Soluble protein fractions prepared from Escherichia coli containing recombinant OsBAM2 and OsBAM3 proteins had significant β-amylase activity. Furthermore, OsBAM2-GFP and OsBAM3-GFP fusion proteins introduced into epidermis of Allium cepa scaly bulb were localized to the plastids. These results strongly suggest that OsBAM2 and OsBAM3 are plastid-targeted active β-amylase.
The root and coleoptile growth of aerobically germinated rice (Oryza sativaL.) seedlings was suppressed by anoxic stress, but the suppression was more conspicuous in roots than in coleoptiles. In this study, the physiological and metabolic responses of roots to anoxia were compared with those of coleoptiles in aerobically germinated rice seedlings. ATP concentration in the coleoptiles was higher than that in the roots under anoxia. Alcohol dehydrogenase activity and ethanol concentration in the coleoptiles were also higher than in the roots under anoxia, which suggest that ethanolic fermentation may be more active in the coleoptiles than in the roots where glycolysis and ethanolic fermentation are the main source of ATP production. Activity of α-amylase, which mobilized reserved starch in the seeds, was not detected in the roots and coleoptiles of rice seedlings either under aerobic or anoxic conditions. However, α-amylase activity was found in endosperms of the rice seedlings even under anoxia. The α-amylase activity in anoxic endosperms was 64% of that in aerobic endosperms. Sugar concentration in the anoxic coleoptiles was higher than that in the anoxic roots. ATP and ethanol concentrations in the roots and coleoptiles of rice seedlings were correlated well with sugar concentrations in the roots and coleoptiles, which also showed a good correlation with anoxia tolerance of roots and coleoptiles with respect to elongation. These results suggest that the sugar level may be important for the anoxia tolerance of the roots and coleoptiles since the availability of sugar is essential for the operation of ethanolic fermentation leading to ATP production under anoxia, and it may serve to distinguish the anoxia tolerance of the roots and coleoptiles of the rice seedlings.
Super hybrid rice Liangyoupeijiu was grown by transplanting (TP) at a spacing of 20 cm×20 cm with one seedling per hill and by direct-seeding (DS) at a seeding rate of 22.5 kg ha-1 (about 120 seeds m-2) in Changsha, Hunan Province, China in 2004 – 2010. Grain yield and yield components were measured each year, and some physiological factors were determined in 2009. There was no significant difference in mean grain yield across years between DS and TP. DS produced more panicles per m2 but less spikelets per panicle than TP. The differences in number of spikelets per m2, spikelet filling percentage and grain weight between DS and TP were not significant. A large number of panicles per m2 in DS was derived from the increased number of tillers per m2 rather than increased rate of panicle-bearing tillers, and the number of tillers per m2 was mainly determined by the number of hills per m2 because the number of tillers per hill was small in DS plants. Tillering rate, tillering duration as well as carbohydrate and nitrogen metabolism were critical to the reduced number of tillers per hill in DS. In DS plants with fewer spikelets per panicle, the numbers of primary branches and secondary branches per panicle, spikelets per primary and secondary branches, and also panicle length and spikelets per unit panicle length were smaller. These differences were attributed to the smaller source leaf size as well as lower root activity and the nutritional status at panicle initiation.
Double-low rapeseed cultivars that produce no erucic acid and have only a small amount of glucosinolates are widely used. However, the roots in mature plant residue and leaves and roots of these seedlings still contain a large amount of biologically active glucosinolates, and it is important to clarify the effect of rapeseed cultivation on the subsequent crops. We analyzed the biological activities of the tissues of double-low cultivar at harvest. The laboratory bioassays revealed that the seeds and roots of mature rapeseed plants contained some autotoxic components that were volatile and water-soluble. We also analyzed the effects of root exudates from growing rapeseed plants on rapeseed germination and growth using the stair-step method and found that the root exudates were autotoxic. In the field, we investigated the allelopathic effects of rapeseed plants on the growth, yield, and quality of the subsequent sunflower plant in the same field. The growth, yield and thousand kernel weight of sunflower were reduced by the preceding cultivation of rapeseed. There were many spontaneously germinated juvenile rapeseed plants in the sunflower field preceded by rapeseed cultivation. Analysis of the plant and soil nitrogen (N) indicated that the growth reduction of sunflower was not caused by the competition for N with the spontaneously germinated juvenile rapeseed plants. The main factors responsible for poor sunflower growth under field after the cultivation of rapeseed were suggested to be some non-volatile, water-soluble components produced by the roots of the spontaneously germinated juvenile rapeseed.
Short-term waterlogging often occurs in upland fields converted from paddies in Japan, since paddy fields have poor surface drainage and a high water table. The objective of this study was to clarify the effects of different durations of waterlogging (W) and waterlogging with soil reduction (WR) on soybean nitrogen fixation at different soil temperatures. Acetylene reduction activity (ARA) was reduced by W treatment for 3, 5 and 7 days (d), ARA was restored to the same level as in the control (C) at 3 days after the end of the treatment (DAT). However, ARA reduced by the WR treatment for 3, 5 and 7 d in a greenhouse was not restored. In the experiments under three soil temperature conditions (lower than 30ºC, around 34ºC and higher than 36ºC) and with two waterlogging durations (3 and 5d) in the growth chamber, ARA reduced by the W treatment was restored after the treatment irrespective of soil temperature and waterlogging duration whereas ARA reduced by WR was restored only after the short-term waterlogging at a low soil temperature. The nodule dry weight and respiration rate of the root system significantly decreased when ARA was greatly reduced. In addition, ARA at 3 DAT was positively correlated with stomatal conductance (SC) at 4 DAT. We concluded that the recovery of nodule nitrogen fixation from the reduction by waterlogging is strongly affected by the oxidation-reduction potential and temperature of the soil, and the nodule damage could be evaluated by SC.
Our objective was to clarify whether rice cultivars with a higher grain dry-matter increase rate (GIR) under elevated temperature condition show a higher percentage of milky white rice kernels (MWK). The rate of MWK judged using a rice-quality selector significantly varied with the cultivar and experimental year. The spikes of the cultivars detached 5–7 days after heading were solution-cultured with an adequate nutrient supply for one week at 25, 28 and 33ºC. GIR was overall the highest at 28ºC, and GIR at this temperature was considered to reflect the potential GIR in all the grains tested. There was a close correlation between the rate of MWK and the GIR at 28ºC under field conditions when temperatures during the grain-filling period were approximately over 25ºC. It was suggested that cultivars with a higher potential GIR under elevated temperature conditions have a higher risk of the formation of MWK.
A weatherproof digital imaging system for the near infrared band (NIR, 820–900 nm) was positioned 12 m above a 600-m2 rice field. During the 2008 and 2009 paddy rice seasons, the system automatically logged images at 10-min intervals throughout the day. Radiometric corrections for the NIR images utilized a solar irradiance sensor and prior calibrations to calculate 0900–1500 JST daily-averaged reflectance factors (DARF). Prior to heading, empirically derived equations for predicting leaf area index (LAI) using the 2008 DARF values in NIR, the cosines of angles between the view and the planting row directions, and between the view and the meridian directions were verified with the 2009 data set. Transformation of a model variable by arcsine square root function improved the performance of the LAI prediction by reducing the errors and bias at low LAI values. Adding variables to incorporate lateral angular components to the horizontal viewing angular parameters hardly affected the overall performance of the models and did not reduce variation. This was probably because the height and position of the camera system were the same in successive years. In-plot means of two or four predicted values in each plot reduced the root-mean square error 30%. These results indicate that radiometric NIR images derived using a fixed-point observation system can accurately predict LAI and the simple multiple linear regression equations developed for a given year can be used the following year without in-situ recalibration.
The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.
Here we describe the configuration and operation of a field-use digital imaging system (multi-band spectrum camera, MBSC) that captures images in two spectral bands in the visible and near infrared wavelength ranges, and automatically converts and stores data as reflectance factor (RF) images. The instrument consists of a weatherproof camera unit, a skylight sensor and a PC and hard disc for a control unit. The camera unit has two industrial use digital camera boards attached with interference band-pass filters and objective lenses. The skylight sensor has light detectors equipped with band-pass filters identical to those used in the camera unit. The system is designed to collect images in each band and convert data into RF using the skylight intensity at prescheduled times. The MBSC has potential to automatically monitor agronomic variables in fields up to several hundred square meters.
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