Stay-green in the post-anthesis period is thought to be an efficient drought-tolerance trait in crops, but its effectiveness in rice (Oryza sativa L.) is unknown. Our objectives were to determine whether the stay-green trait exists in rice cultivars in drought-prone areas. Twenty-four cultivars from Japan and Vietnam were grown in pots of 0.08 m in diameter and 1.00 m deep. At heading, irrigation was terminated in half of the pots and continued in the remaining pots. Every four days during the grain-filling period, we measured the leaf green color with a chlorophyll meter (SPAD), the green leaf area (GLA) and the fraction of transpirable soil water (FTSW). The capacity for maintenance of SPAD-value and GLA in desiccated soils was evaluated by determining the ratio of integrated SPAD-value and GLA in desiccated (D) plants to those in irrigated (I) plants (SPADD/I or GLAD/I, respectively). The SPADD/I and GLAD/I in 24 cultivars showed diverse frequency distributions. Cultivars belonging to higher ranges of the distribution in SPADD/I and GLAD/I tended to show higher ratios of plant dry weight at harvest in D to in I plants. SPADD/I and GLAD/I in the grain-filling period were poorly correlated with those in the seedling period in desiccated soils, and hence the capacity for maintenance of green leaves in the grain-filling period would differ from that in the seedling period. These results suggest that the stay-green trait exists as the capacity for maintaining green leaves and benefits dry matter production in desiccated soils in rice cultivars in drought-prone areas.
Understanding wheat (Triticum aestivum L.) response to high shoot/root temperature during the early growth stages is important for successful production in tropical and subtropical environments. This study examined the physiological response of wheat cultivars to high shoot and/or root temperatures during early growth stages. Three cultivars; Imam, Fang and Siete Cerros were grown in soil and hydroponically at three shoot/root temperatures (23/23, 23/35 and 35/35ºC for the soil experiment; and 22/22, 22/38 and 38/38ºC for the hydroponic experiment). Leaf dry weight and leaf area plant-1 were significantly decreased by high shoot/root temperature (HS/HR, 35/35 and 38/38ºC) but was not affected by a normal shoot/high root temperature (NS/HR, 23/35 and 22/38ºC). The NS/HR (22/38ºC) and HS/HR (38/38ºC) treatments in the hydroponic experiment significantly decreased photosystem II quantum yield (ΦPSII), photosynthetic rate (Pn) and specific leaf area (SLA) compared with the normal shoot/normal root (NS/NR, 22/22ºC) temperature treatment. Chlorophyll accumulation was significantly decreased by NS/HR, but increased significantly by HS/HR in most of the measuring dates. The heat-tolerant cultivar, Fang, always had the highest chlorophyll content, ΦPSII and Pn under all temperature treatments, while the heat-sensitive cultivar, Siete Cerros, always had the greatest reduction in these traits especially towards the end of the experiment. Imam and Fang responded to HS/HR in the hydroponic experiment by immediate and greater reductions in leaf dry weight, total leaf area and SLA during the first wk of the treatments compared with Siete Cerros. The response changed with the treatments duration such that Imam showed the least reduction and Siete Cerros was the most affected cultivar towards the end of the experiment. Thus, wheat cultivars differentially responded to high shoot/root temperature by reducing the leaf weight and area and hence accumulating more chlorophyll in the diminished leaves. The failure to undergo such changes led to significantly lower chlorophyll accumulation, ΦPSII and Pn under high root temperature.
Sugarcane (Saccharum spp.) is a major crop grown for sucrose production. In Japan, its sucrose concentration is highest in winter. We examined the effects of the temperature lowered in the daytime and night-time (LDT and LNT, respectively) on sugar assimilation. Since photosynthetic and respiration rates change with temperature, we assumed that plants under LNT (LNT plants) would have low respiration rates and thus high sugar yields, whereas those under LDT (LDT plants) would have low rates of photosynthesis and thus low sugar yields. However, because of their acclimatisation to the reduced temperatures, LNT and LDT plants had sugar yields that were similar, or superior, to those of control plants. Sugar yield depends on biomass and sugar concentration; the stems of LNT and LDT plants did not grow as tall as those of the controls, but the sucrose concentrations in their stems were higher than in the controls. 13C analysis revealed no difference in the partitioning of photosynthates to the soluble sugar fraction between control plants and those treated with low temperature. Control plants had higher glucose concentrations in the stem than treated plants, in which new photosynthates appeared to be partitioned preferentially into sucrose. Low temperature enhanced the sucrose concentration in the sugarcane stem not by improving the carbon budget, but by promoting the partitioning of carbon to stored sucrose.
We studied the effects of different ear removal treatments on the senescence order of functional leaves and the effects of removal of 3/4 ear on the chlorophyll content, net photosynthetic rate, transpiration rate, stomata conductance, malonaldehyde content and catalase activity in the functional leaves in wheat. The results showed that different ear removal resulted in different frequency of plants with leaf-color inversion (i.e., the green color of both the 2nd and 3rd leaf from the top or only the 2nd leaf was deeper than that of the flag leaf). Removal of 3/4 ear or whole ear, obviously increased the frequency of plants with leaf-color inversion. The chlorophyll content, photosynthetic rate, transpiration rate, stomata conductance and catalase activity in the flag leaf of plants with leaf-color inversion were mostly lower than those in the 2nd and 3rd leaf from the top, but the malonaldehyde content of flag leaf was obviously higher than that of the 2nd and 3rd leaf from the top. The experiments demonstrated that removal of 3/4 ear accelerated the senescence of flag leaf, delayed the senescence of the 2nd and the 3rd leaf from the top and altered the senescence order of wheat functional leaves.
The productivity of sweet potato is governed by both the rate of cell division and sink activity of its tuberous root. The aim of this study was to reveal the mechanisms that regulate cell division activity and sink activity during tuberous root formation. As an indicator of the cell division activity, we used the transcript level of two D3-type cyclins, which regulate cell cycle progression through the formation of the regulatory subunit of the cyclin-dependent kinase complex. As an indicator of photosynthetic product sink activity, we used the gene expression of ADP-glucose pyrophosphorylase (AGPase), one of the key enzymes of starch synthesis. During tuberous root formation, the expression of D3 cyclin genes increased to the maximal levels and then decreased. In contrast, the expression of the AGPase gene increased continuously. Sucrose enhanced the expression of D3 cyclin and AGPase genes, but a high concentration of sucrose repressed the expression of a D3 cyclin gene. In the presence of sucrose, cytokinin increased the expression of D3 cyclins, but abscisic acid (ABA) did not. However, cytokinin and ABA repressed the induction of AGPase gene expression by sucrose. These results suggested that sugars, cytokinin and ABA regulate the cell division activity and the sink activity in sweet potato.
We investigated the effects of combined soil physical stresses of compaction and drought on the production of fully hydrated mucilage (mucilage) and root border cells (RBCs) in maize. The exudation of carbon and water were also estimated using stable isotopes of 13C and deuterated water (D2O) under same soil conditions. As plant age progressed during seedling stage, mucilage production increased, however, RBCs release did not. Soil compaction increased the release of D2O, RBCs, and production of mucilage which implies the function of roots to reduce mechanical impedance during root penetration. Drying stress increased only carbon release, but reduced the others. This indicates that RBCs adhere more strongly to the root cap due to drying of mucilage, and water release may be reduced to save the water loss. The highest rhizodeposition of mucilage, RBCs and D2O were occurred under wet compact soil condition, however, that of carbon occurred under dry compact soil condition.
Most studies on non-structural carbohydrate (NSC) are concentrated on the leaf and tuber, and little is known about NSC in the stem and its function. To test the hypothesis that NSC stored in stem contributes to stable tuber bulking under stress conditions, we grew plants in pots in a greenhouse under drought and shading conditions for 17 d during tuber bulking. Compared with the control, drought and shading significantly reduced leaf and stem dry weights (DW) and total NSC concentration in the main stem base. However, tuber DW increased by 77% in drought and by 46% in shading conditions relative to the control. The contributions of NSC loss in the stem to tuber DW increase in drought and shading conditions were 37% and 54%, respectively. This study suggests that NSC stored in the stem base is supplied to tuber under stress conditions to support tuber bulking.
Effects of NaCl on the growth, ion content, root cap structure and Casparian band development were examined in four rice (Oryza sativa L.) cultivars with different salt resistance (salt-sensitive indica-type IR 24 and japonica-type Nipponbare and salt-resistant indica-type Nona Bokra and Pokkali). Experiments were conducted to find the differences in salinity resistance during early seedling and developed seedling stages among the cultivars. For salinity treatment, sodium chloride (NaCl) was added to nutrient solution at concentrations of 0, 25 and 50 mM for 7 days from germination to the 7th day (early seedling stage) or from the 7th day to 14th day (developed seedling stage). Growth inhibition by salinity was more prominent in the early seedling stage than in the developed seedling stage. Based on the growth, the order of the sensitivity was IR24>Nipponbare>Nona Bokra>Pokkali. The growth of NaCl-treated rice cultivars relative to control was significantly and negatively correlated with the Na+ content and Na+/K+ ratio in roots and shoots in both stages. Scanning electron microscopic observation revealed that the root cap tissues proliferated and extended to the basal part of the root tip by salinity. The length of root cap was, however, reduced by 50 mM NaCl in sensitive cultivars due to peeling off. An endodermal Casparian band was formed in the basal region of the root tip. Development of the Casparian band was more prominent in sensitive cultivars than in tolerant cultivars. Root cap proliferation might be related to NaCl resistance in rice seedlings, but the Casparian band may not function efficiently in Na+ exclusion. Essentially the present results suggest that exclusion of Na+ from roots plays a critical role in expression of Na+ resistance in rice seedlings and the root cap is important for Na+ exclusion.
Soil moisture condition is a major factor that affects root system development and thus, crop production. This study aimed to evaluate genotypic variations of cassava in root system structures and their responses to different soil moisture conditions by examining various root traits including production and elongation of adventitious roots and their laterals. Four pot experiments were conducted and different genotypes of various backgrounds were grown under well-watered, droughted, droughted to rewatered conditions. One field experiment was also conducted with selected genotypes till maturity. Results showed that substantial genotypic variations exist in root system structure, and the effects of the soil moistures were significant for most of the root traits. The principal component analysis (PCA) showed that the lateral root development mainly accounted for the variations in root system structure regardless of soil moisture conditions. The PCA on the differences between droughted and well-watered control, and droughted-rewatered and the control further indicated that the branching ability of adventitious roots was mainly responsible for the root system responses to drought as well as rewatering. Genotypic ranking in root system responses to drought was almost consistent among the pots and field experiments. Genotypic variations in rooting depth were relatively small while those in horizontal spread were apparent in the field experiment. The ability to maintain adventitious root elongation under drought, resulting in relatively large horizontal spread of root system and to recover sharply from drought by lateral root branching may be related to good growth and yield performance under field.
Buckwheat contains fagopyrin, which induces photosensitization in light-skinned livestock when exposed to sunlight. Here, we developed a high-performance liquid chromatography (HPLC) method to measure the fagopyrin content of buckwheat. The HPLC profile of the fagopyrin extract purified from Tartary buckwheat ‘Rotundatum’ had 3 apparent peaks. The ultraviolet-visible (UV-vis) absorption spectrum of each peak yielded absorbance maxima (λmax) at 547 nm and 591 nm, indicating that these peaks corresponded to fagopyrin and unidentified fagopyrin derivatives. We considered the total content reflected by the 3 peaks to be the fagopyrin content of buckwheat. We determined the fagopyrin content in the leaves of Tartary buckwheat ‘Rotundatum’ and common buckwheat ‘Miyazakiootsubu’ both by UV-vis photometric analysis and the newly developed HPLC method. The fagopyrin content is overestimated by UV-vis photometry because the extracts contain a considerable amount of chlorophyll. Thus, HPLC analysis is more efficacious for fagopyrin-content measurements than UV-vis photometric analysis. The HPLC analysis of fagopyrin is easy, quick and efficacious for screening buckwheat varieties with trace or no fagopyrin. There are only a few reports on the accumulation sites of fagopyrin in buckwheat. We revealed that in Tartary and common buckwheat, fagopyrin is present mainly in the leaves and flowers and slightly in the stems, hulls, and groats. The fagopyrin contents of the leaves and flowers of Rotundatum were approximately 2.6 and 2.8 times higher than those in Miyazakiootsubu, respectively.
The lignans, e.g., sesamin and sesamolin, are components of the functional food sesame (Sesamum indicum L.) seed. This study aims to clarify the effects of environmental factors during ripening on the concentrations of these lignans to produce lignan-rich seeds. Here, we examined the effects of 4 factors (seeding time, day length, air and soil temperatures). The concentrations of sesamin and sesamolin in the seed from the capsule at different nodes on the stem were monitored using the high performance liquid chromatography (HPLC). A low air-temperature (22/15ºC) during ripening increased the concentrations in the seed at the full-ripe stage of individual capsules compared with a high air-temperature (30/23ºC). A short day-length (10-hr) and high soil-temperature did not affect the concentrations. The concentrations showed a tendency to increase with delay of seeding time. Under natural air-temperature conditions, the concentrations in the seeds from the capsules at a higher position on the stem were higher than those at a lower position, mainly due to the air temperature during ripening. The contents per seed were affected by the environmental factors through the difference in seed weight. The concentrations increased with the increase in seed dry weight and decreased with the desiccation of seeds during maturity. Under a low air-temperature condition, the rate of decrease in sesamin concentration was low, the accumulation period was longer and the maximum concentration of sesamolin was higher, resulting in higher contents of these lignans.
The firmness of buckwheat noodles plays an important role in its palatability. We investigated the effects of artificial sprouting after harvest and preharvest sprouting in the field of buckwheat grains on the firmness of cooked buckwheat noodles by measuring the force required to compress the cooked noodles. Sprouting significantly decreased the peak force and peak strain to compress cooked noodles, suggesting that sprouting lowers the palatability of cooked buckwheat noodles. Sprouting significantly decreased the force needed to compress cooked noodles largely, suggesting that the cooked noodles made from sprouting grains lead to the perception of less resistance to completely cut off by mastication.
In most southern parts of Iran, wheat (Triticum aestivum L.) residues have been traditionally burned or removed; that is often criticized for soil organic and nutrient losses, reducing soil microbial activity and increasing CO2 emission. A 2-years (2005−2007) field study was carried out at the College of Agriculture, Shiraz University, Shiraz, Iran, to evaluate the influence of crop residues management and nitrogen (N) rates on dryland wheat. The experiment was conducted as strip split plot with four replications. Horizontal plots were three crop residues rates (0, 500 and 1000 kg ha-1), vertical plots consisted of two dryland current wheat cultivars (CVs) (Azar 2 and Nicknejad), and sub-plots were three N rates (0, 35, and 70 kg N ha-1). Increasing crop residue rates increased soil organic carbon. Number of spike per plant, grains per spike, grains per plant and 1000-grain weight of both CVs significantly increased with increased N and residue rates in both years. The lowest grain yield was obtained from 1000 kg ha-1 residue incorporation without N application showing the soil N imbalance. The optimum crop growth and the highest grain yield was achieved from the highest crop residues and N rates, indicating that the most reliable system for dryland wheat production in the region is complete residues incorporation into the soil following disking, seeding with chisel seeder and application of 70 kg N ha-1.
In Abashiri in eastern Hokkaido, Japan, grain yields of winter wheat (Triticum aestivum L. cv. Hokushin) in the western area, with umbric andosol or dystric cambisol soil types, are lower and unstable compared to those in the eastern area, with mostly haplic andosol soil type. The aim of this study was to evaluate yield differences between the eastern and western areas. The vertical root distribution of wheat plants was examined over two seasons in farmers’ fields in both areas by a wall profile method. Plants grown in the western area had shallower root systems than those grown in the eastern area. Poor soil porosity and high soil penetration resistance suppressed the vertical distribution of root systems in umbric andosol and dystric cambisol. Grain yields were not always correlated with the amount and distribution of the root system. Grain yield in the 2004/2005 season was not correlated with root depth index, whereas it was positively correlated in the 2005/2006 season. During the period from heading to maturity (mid June to late July) over the two seasons, grain yield was associated with precipitation more than with temperature and total solar radiation. In the 2005/2006 season, during the late growing stage of wheat, precipitation was extremely low and soils were very dry. The difference in grain yield between the eastern and western areas was significant and negatively related to precipitation during the period from heading to maturity. Significant correlations of yield with sunshine duration and solar radiation from the heading stage to maturity were observed only on haplic andosol. The results suggest that the major factor controlling yearly changes in the difference in grain yield of winter wheat between the eastern and western areas is the difference in photosynthetic ability, which is based on rooting depth and water supply in response to solar radiation during the late growing stage.
We evaluated the genotypic differences in growth, grain yield, and water productivity of six rice (Oryza sativa L.) cultivars from different agricultural ecotypes under four cultivation conditions: continuously flooded paddy (CF), alternate wetting and drying system (AWD) in paddy field, and aerobic rice systems in which irrigation water was applied when soil moisture tension at 15 cm depth reached −15 kPa (A15) and −30 kPa (A30). In three of the six cultivars, we also measured bleeding rate and predawn leaf water potential (LWP) to determine root activity and plant water status. Soil water potential (SWP) in the root zone averaged −1.3 kPa at 15 cm in AWD, -5.5 and -6.6 kPa at 15 and 35 cm, respectively, in A15, and −9.1 and −7.6 kPa at 15 and 35 cm, respectively, in A30. The improved lowland cultivar, Nipponbare gave the highest yield in CF and AWD. The improved upland cultivar, UPLRi-7, and the traditional upland cultivar, Sensho gave the highest yield in A15 and A30, respectively. The yields of traditional upland cultivars, Sensho and Beodien in A30 were not lower than the yields in CF. However, the yields of the improved lowland cultivars, Koshihikari and Nipponbare, were markedly lower in A15 and A30. Total water input was 2145 mm in CF, 1706 mm in AWD, 804 mm in A15, and 627 mm in A30. The water productivity of upland rice cultivars in aerobic plots was 2.2 to 3.6 times higher than that in CF, while those of lowland cultivars in aerobic plots were lower than those in CF. The bleeding rate of Koshihikari was lower in A15 and A30 than in CF and AWD, and its LWP was significantly lower in A15 and A30 than in CF and AWD, but Sensho and Beodien showed no differences among the four cultivation conditions. We conclude that aerobic rice systems are promising technologies for farmers who lack access to enough water to grow flooded lowland rice. However, lowland cultivars showed severe growth and yield reductions under aerobic soil conditions. This might result from poor root systems and poor root function, which limits water absorption and thus decreases LWP. More research on the morphological and physiological traits under aerobic rice systems is needed.
Daytime temperature during seed filling is a crucial determinant of grain yield in pulse crops. Although there is much research about the effect of daytime temperature during seed filling on soybean yield in temperature-controlled chambers, the effect in the field has been little explored. Long-term manipulative field experiments are important tools to provide accurate information for revealing the impacts of climate change on crop yields. Using the field records of a long-term fertilization experiment conducted in Northeast China, we analyzed the response of soybean yields to mean daily maximum temperature during seed filling over the period 1987−2007. The results showed that there was a clear positive response of soybean yields to increased mean daily maximum temperature during seed filling ranged from 20 to 24ºC. When compared with the average soybean yields over the last two decades, grain yields increased by 6−10% for each 1ºC increase in mean daily maximum temperature during seed filling and more than 22% of yield trends can be explained. These findings provide a direct evidence for the response of soybean yield to climate change in the field study.
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