The aim of this investigation was to comparatively examine the physio-biochemical responses of oil palm seedlings to mannitol- and PEG-induced iso-osmotic stresses. The water content of osmotically stressed oil palm seedlings decreased, but the proline content and the electrolyte leakage of the seedlings increased with decreasing water potential (Ψw). However, the responses varied with the strength of osmotic stress and type of osmotic agent. Relative electrolyte leakage (REL) was negatively correlated to chlorophyll content in the osmotically stressed leaves. Chlorophyll a (Chla), chlorophyll b (Chlb), total carotenoids (Cx+c) and total chlorophyll (TC) in the seedlings were significantly reduced by osmotic stress, subsequently reducing maximum quantum yield of PSII (Fv/Fm) and photon yield of PSII (ΦPSII), thereby lowering net-photosynthetic rate (Pn) and inhibiting growth. Physio-biochemical parameters, including REL, Fv/Fm, and ΦPSII in oil palm seedlings were reduced more greatly by PEG-induced osmotic stress than by mannitol-induced stress. A deterioration in morphological characters, including leaf chlorosis, leaf burn, and green leaf area reduction were demonstrated in oil palm seedlings under osmotic stress induced by either mannitol or PEG. However, the toxic symptoms in oil palm seedlings under PEG-induced stress were severer than in those under mannitol-induced iso-osmotic stress, especially under severe osmotic stress.
The viability of the estrogen-receptor (ER)-based chemically inducible gene expression system LexA-VP16-ER (XVE) in combination with the site-specific DNA recombination Cre/loxP system in rice was examined using transgenic plants introduced with a plasmid vector pUH-GFP2 that controls the expression of a green fluorescent protein (GFP) gene. β-estradiol applied to the germinating seeds of the transgenic plants, successfully induced the mRNA expression of the GFP gene. Inducible gene suppression was also tested by replacing the GFP gene by an RNAi cassette; this cassette targeted OsSPS1, a gene encoding sucrose phosphate synthase. When the RNAi plants were treated with the inducer, the transcript levels of OsSPS1 decreased. Concomitantly, the plant length became shorter or the sucrose/starch molar ratio in the leaf blades decreased, suggesting the successful suppression of the target gene. Finally, the utility and remaining problems of this inducible expression system are discussed.
The application of synthetic cytokinin (6-benzylaminopurine, BA) to racemes of soybean genotype IX93-100 at 7 days after anthesis (DAA) enhanced pod-set percentage of the florets at the 5th position and above (numbered from the base on rachis). The endogenous cytokinin (trans-zeatin riboside) content of individual florets was measured at the 1, 3, 5, 7th position every 3 days after anthesis. Cytokinin was detected only from the florets at 9 DAA, and the content was higher in the more proximal florets while it became negligible in the 7th floret. These results suggest that an increase in the amount of cytokinin in individual florets might enhance the pod setting of the florets positioned at the middle or distal part within the raceme.
Genetic improvement in water uptake ability and/or water use efficiency (WUE) of rice cultivars is one option to enhance productivity under water-limited conditions. We examined the genotypic variation in biomass production among 70 rice cultivars (69 cultivars of NIAS global rice core collection and Azucena) under different soil moisture conditions, and to identify whether water uptake ability or WUE is responsible for the variation, if any. Two-week-old seedlings were transplanted into pots and grown for three weeks in an environmentally-regulated growth chamber under three soil moisture regimes: flooded (−0.02 MPa soil water potential) and two unflooded (−0.10 and −0.52 MPa) conditions. Substantial genotypic variations in total dry weight (TDW) were observed under all three regimes. Among all the cultivars tested, TDW was significantly correlated with water uptake ability, but not with WUE. However, several cultivars exhibited comparably higher WUE while showing superior biomass production under the −0.52 MPa regime. The amount of water uptake was significantly correlated with root dry weight among cultivars regardless of moisture regimes, while substantial genotypic difference in the amount of water uptake per unit root dry weight was observed. These results indicate that a marked genotypic difference exists in biomass production at the early vegetative growth under water-deficient conditions, and that this difference appears to be ascribed primarily to greater water uptake capacity, and additionally to higher WUE in drought-tolerant cultivars.
Using two rice cultivars, the effect of severe, mild and no water stress, W3, W2 and W1, respectively, on flag leaf physiology, the ecological characteristics of canopy and organ temperatures were studied in 2008 and 2009. The grain yield was reduced under W3 due to decreased seed setting rate and 1000 grain weight but not under W2. Water stress had a significant effect on the flag leaf physiological characteristics along with the soluble sugar and amino proline content. Catalase and peroxidase activities, photosynthetic and transpiration rates, and stomatal conductance in W2 were significantly higher than in W3 and similar to those in W1. The organ and canopy temperatures were significantly higher in W3 than in either W1 or W2, and there was no significant difference between W1 and W2. This study clearly showed that water stress had a significant effect on leaf physiology, temperature of organs and canopy. Mild water stress (soil water potential maintained at -15- -20 kPa) could construct a population that is water-saving and resistant to heat stress. This facilitates access to a high yield as well.
Transgene escape mediated by pollen dispersal is one of the preeminent concerns about genetically modified crops, including rice. In this study, the rice pollen donor of non-glutinous Oryza sativa ssp. japonica cv. ‘Tainung 67’ [TNG 67] had a greater potential of pollen flow, which was shown by the greater quantity, germination rate, and viability of pollen, than the other rice pollen donor of transgenic AAN. The pollen-mediated gene flow was detected by the frequency of outcrossed seeds in a “checker-board pattern” and alternating row arrangement of rice pollen donor (TNG 67 or AAN) and pollen recipient (glutinous rice ‘TNG 73’) in the fields. We conducted field experiments to assess rice pollen dispersal with or without a “green” fence of Chinese hibiscus, Hibiscus rosa-sinensis L., of approximately 2 m in height and 0.6 m in thickness. Without a green fence, the outcrossing rate of TNG 73 seeds decreased with increasing distance from the pollen donor, from 1.68% at 1 m to 0.01% at 35 m, with no outcrossing beyond 40 m. The outcrossing rate varied with the direction of pollen donor, from 0.05% in the northeastern direction to 0.78% in the southern direction, which was caused by prevailing wind direction. With the green fence, no seeds of TNG 73 were outcrossed. Since a buffer zone of at least 40 m is needed to prevent outcrossing of rice by pollen dispersal in an open field, planting of Chinese hibiscus around the rice field as a green fence would be an effective measure for preventing transgene escape mediated by pollen flow.
With the renewed interest in mixed cropping and the increasing awareness of environmental degradation arising from high chemical inputs, this experiment was conducted to assess the effect of supplementing inorganic with an organic fertilizer on the growth and yield of rice and cowpea under the mixed cropping system. Treatments comprised six sole crops and three mixed crops, each under 100% NPK (C), 50%NPK+ 50% cow dung (CCD) and cow dung alone (CD). The fertilizer treatments did not significantly affect cowpea performance. However, the number of panicles per hill and the number of spikelets per panicle of rice were higher under mixed cropping than under sole cropping. On the average, rice grain yield was significantly lower under the mixed cropping than under the sole cropping. The land equivalent ratios increased under all the fertilizer treatments indicating the efficiency of the mixed-cropping system. The results of the experiment suggest that rice– cowpea mixed cropping under CCD and CD is a viable production option.
To determine the effects of CO2 under different atmospheric pressures, we assessed the effects of elevated CO2 on the growth of spring wheat (Triticum aestivum L.) in a field experiment in Lhasa (3688 m above sea level), the Tibet Plateau, China, and in a growth chamber (GC) experiment in Sapporo (15 m above sea level), Japan. Open-top chambers (OTCs) were installed at Lhasa and spring wheat was grown under CO2 at a partial pressure of 23.4 Pa (ambient CO2) and 38.5 Pa (elevated CO2, equivalent to a 200 µmol mol-1 increase). In the OTC experiments, CO2 was elevated with gas-firing equipment and a blower, so that the air temperature inside the OTC for elevated CO2 was raised 0.8ºC. In the GC experiment in Sapporo, we used three CO2 partial pressure levels; 24.8, 39.8 and 59.3 Pa and two air temperature regimes, 11/19ºC and 11/21ºC (night/day). In the OTC experiment, dry weight at harvest was lower in the elevated CO2 than in the ambient CO2. In the GC experiment, the effect of the elevation of CO2 from 24.8 to 39.8 Pa on biomass was greater than that from 39.8 to 59.3 Pa. A 2ºC increase in temperature reduced dry weight at all CO2 levels and offset the positive effect of CO2 increase from 39.8 to 59.3 Pa. The difference between the results obtained in the experiments in OTC and GC was not clear and might have involved artifacts such as blower and/or ethylene effects.
The dry matter production, photosynthetic characteristics and nutrient concentrations in the plant tissues of sago palm seedlings cultured for 4.5 months in a hydroponic system at pH 5.7, 4.5, and 3.6 were examined. Plant growth in weekly increment of length, leaf emergence, leaf senescence, and total leaflet area was similar at all pHs. There was no significant effect of pH on the dry matter weight, although it tended to be lighter at pH 3.6 than at pH 5.7. Similarly, the photosynthetic rate and its related parameter were not significantly affected by the pH. However, the photosynthetic rate at pH 3.6 tended to be lower than that at pH 5.7, which was attributed to a decrease in the stomatal conductance. The effect of the low pH on the nutrient concentration in plant tissues was not distinct. We concluded that sago palm seedlings could maintain leaf morphogenesis and nutrient uptake in growth media at a pH ranging from 5.7 to 3.6 for 4.5 months, which led to a high growth rate and maintenance of dry matter production even at pH 3.6.
We evaluated the effects of the water table controlled by a water table controlling system, farm-oriented enhancing aquatic system (FOEAS), on soybean productivity. FOEAS was constructed in a heavy soil paddy field; we made plots with water tables maintained at −32 (water table depth [WTD]32) and −20 cm (WTD20) from the soil surface and, as a control, an open-ditch drained plot (ODD). Soybean cultivar “Tachinagaha” and non-nodulating cultivar “En1282” were cultivated in 2006 and 2007. The moisture of the topsoil in the water table-controlled plots showed less fluctuation owing to rainfall. The roots and nodules were distributed only in the upper soil layer in ODD, but more were distributed in deeper soil layers in WTD32 and WTD20. In Tachinagaha, the SPAD value and stomatal conductance were higher in WTD32 and WTD20 than in ODD, resulting in a higher apparent photosynthetic rate. The aboveground total dry weight and nitrogen accumulation of Tachinagaha were higher in the water table-controlled plots than in ODD; in En1282, this difference was insignificant. The relative ureide value which is an index of nodule activity, in ODD was depressed by both excess and deficit soil moisture; however, that in WTD32 remained relatively high during the growing stage. Tachinagaha showed higher yield in FOEAS plots, especially in WTD32 than in ODD in both years. The results indicate that control of water table by FOEAS increases nitrogen fixation, photosynthesis, and yield of soybeans in upland fields converted from paddy fields.
To examine the effect of the size of the potato microtuber (MT) produced in vitro on the posterior field performance, we examined the growth and yield of the late maturity cultivar Norin 1 using four sizes of MT: 0.3–0.5 g, 0.5–1 g, 1–3 g and 3–5 g, and conventional seed tubers (CT) (approximately 50 g). The experiment was conducted at Hokkaido University, Sapporo Japan in 1998 and 1999. The tubers were planted in May of each year, in a randomized block design with three replications. Plants from MT lighter than 0.5 g showed a slower initial leaf and tuber growth than heavier MT, but around the full flowering stage there was no significant difference with the MT size in leaf or tuber growth. CT plants showed higher initial leaf and tuber growth compared with MT plants, especially in 1999. No differences in growing period, number of tubers, and tuber fresh and dry yield were observed with the MT size. However, in 1999, the growing period was longer and tuber fresh and dry yields at harvest were higher in CT plants. MT of all sizes used in the study can be used for direct field planting, but more studies are needed to increase the yield stability of MT plants.