The distributions of Na and chlorophyll in the leaves of rice (Oryza sativa L.) seedlings grown under a saline condition were examined in relation to the anatomical changes caused by salinity. In salt-treated plants, the Na content was higher in older leaves and basal part of the leaf. In the 4th leaf of salt-treated plants, Na content was the highest in the middle part of the leaf sheath and decreased toward the tip of the leaf blade. The chlorophyll content in the 4th leaf was decreased by salt treatment at the tip and middle parts of the leaf blade, whereas it was unaffected in the leaf sheath and at the base of the leaf blade. Electron microscopic studies revealed that salt-treatment caused plasmolysis, vesiculation of cellular membranes and degradation of cytoplasm at the tip of the leaf blade, but scarcely caused such alterations at the base of the leaf blade. The present study suggests that the damage by salinity correlates more strongly with the age of the tissue than the Na content of the tissue.
The effects of flag leaves and panicles on canopy photosynthesis in a leading cultivar (Nipponbare) and two high-yielding rice cultivars (Takanari and Chugoku 117) bred in Japan were compared. The total dry matter production was in the order of Takanari > Chugoku 117 > Nipponbare. Canopy photosynthesis was highest in Takanari throughout the growth season, and was higher in Chugoku 117 than in Nipponbare during the ripening period. The photosynthetic rate in the flag leaf was in the order of Nipponbare > Takanari > Chugoku 117. The light extinction coefficient of canopy was higher in Takanari than in the others. At the middle ripening stage, canopy photosynthesis increased 35 and 17% in Nipponbare and Takanari, respectively, by the removal of panicles and decreased 37 and 48%, respectively, by the removal of flag leaves. In Chugoku 117, canopy photosynthesis was hardly influenced by these treatments. Clearly, the panicles intercept more radiation at the upper layer of the canopy in Nipponbare than in Takanari and flag leaves contribute more to canopy photosynthesis in Takanari than in Nipponbare. However, these effects were small in Chugoku 117. In conclusion, Takanari produces more dry matter than the others due to larger, wider, longer and more erect 1st (flag) and 2nd leaves above the panicles, which intercept more radiation. Chugoku 117 had erect panicles which allowed more radiation to penetrate into the deeper layer of the canopy, resulting in a high dry matter production. The lower panicle height relative to leaf layer and erect panicles are important characteristics for higher yield in rice.
Two cultivars of spinach and one cultivar of komatsuna were sand cultured using a nutrient solution with Na and K in various combinations. The growth (fresh weight of shoot) of spinach cv. Atlas was significantly increased when 1.4 mM KCl of the 7 mM KCl was replaced with 1.4 mM NaCl, although the growth was reduced when more KCl was replaced with NaCl. In another spinach cv. All Right, however, NaCl substituting for 20% of KCl showed no significant effects. In komatsuna, Na used in place of K at any ratio reduced the growth. The growth of spinach cv. Atlas was increased by applying 20 mM NaCl, irrespective of K dose (480-2400 mg K2O per 1/2000 a Wagner pot). The growth of spinach cv. All Right was also increased by 20 mM NaCl when K was at a deficient level (480-960 mg K2O per pot), but was not when K was at an excessive level (1920-2400 mg K2O per pot). In komatsuna, 20 mM NaCl reduced the growth. In spinach, Na prevented the decrease of the photosynthetic rate and stomatal conductance caused by K deficiency.
The growth directions and elongation rates of axile roots that compose the framework of an upland rice root system are quite varied. The objective of this study was to elucidate the direction of growth of the axile roots relative to their root diameter and the structural characteristics of their root caps. The relationships of photosynthate translocation to either the growth direction or the elongation rate of the axile roots were also examined using a stable isotope 13C. The growth direction of the axile roots significantly correlated with their diameter. The axile roots with a relatively large diameter tended to elongate vertically in the vegetative stage, though the regression coefficients varied according to phyllochrons. The roots that emerged at the reproductive stage elongated horizontally relative to the large diameter. In the roots that emerged at the same phyllochrons, the prophyll roots elongated more vertically than the proximal roots did. The axile roots that elongated vertically formed wide columellae and large amyloplasts in the cap cells. The highest 13C abundance in the axile root tip zone was found at 21 hrs after feeding 13CO2. The length of the apical unbranched zone behind the axile root tip positively correlated with the 13C abundance in the root apical zones during the first 21 hrs after feeding, indicating that the roots that elongated fast would be superior in photosynthate intake in the apical zone. The axile roots that elongated vertically took in more photosynthate in their apical zones, however, the relationship was not particularly close.
Soybean (Glyrine max (L.) Merr.) is considered to be susceptible to flooding, a major agronomic problem in the world, and nitrogenase activity rapidly declines due to oxygen deficiency in root nodules. We investigated nodule acclimation to flooding at the morphological level using a soybean cultivar possessing the ability to form secondary aerenchyma. After 1 week of treatment, lenticels were formed on the surface of the root nodules, and secondary aerenchyma were observed through the lenticels under both irrigated and flooded conditions. As the plant grew, the nodule epidermis came off, and well-developed secondary aerenchyma covered the nodule surface. The secondary aerenchyma originated from the secondary meristem (phellogen) girdling the sclerenchyma, and the degree of development was greater in flooded nodules than in irrigated ones. Although root nodulation and total nitrogenase activity (TNA) decreased under flooded conditions, there were no differences in shoot N concentration, specific nitrogenase activity (SNA) and relative ureide-N in the xylem bleeding sap between plants in the irrigated and flooded conditions. Under flooded conditions, however, when the entry of oxygen into the secondary aerenchyma formed in the hypocotyl was inhibited by vaseline treatment (pasting on the surface of the hypocotyl), the shoot N concentration, TNA, SNA, the ureide-N concentration and the relative ureide-N in the sap declined remarkably. These results suggested that secondary aerenchyma formation in soybean plants is a morphological acclimation response to flooding stress, and that one of the functions is to supply atmospheric oxygen to root nodules, which consequently enables nodule activity to be maintained.
In Crotalaria juncea L., adventitious buds were formed in cotyledonary explants cultured on 0.8% agar-solidified 1/2 MS basal medium containing B5 vitamins, 1.0 or 0.5 mg L-1 NAA, 5.0 or 10.0 mg L-1 BA and 3% sucrose. The frequency of adventitious bud formation was 30-45% in all combinations of NAA and BA. In histological observations, prominent mitotic figures were observed in several cells of the subepidermal palisade layers on the adaxial side of the explants in contact with medium after 3 days of culture. Calli were formed within 6 days of culture. After 10 days of culture, numerous mature tracheary elements were produced at random in the proliferated regions, and cell divisions at the superficial region led to the formation of the meristematic structure. The shoot apex of the seedling produced numerous trichomes from superficial cells, but the adventitious bud formed on the cotyledon produced no trichomes. Initiation of the meristematic region in the explant could be used as a target site for gene transfer experiments.
The physiological responses of wild Oryza species (Oryza latifolia Desv., a salt-tolerant species and O. rufipogon Griff., a salt-susceptible species) to salinity stress were investigated by comparing with check varieties of cultivated rice (O. sativa L.), SR26B (salt-tolerant) and IR28 (salt-susceptible). As the Nacl concentration of water culture solution was raised to 12 dS m-1 (about 113mM), leaf Na+ content per dry matter in wild Oryza species increased from 4 to 17 times as compared with the control (no NaCl treatment), whereas the accumulation was lower in cultivated rice varieties. The increased concentration of leaf Na+ resulted in the decrease in leaf water potential (Ψw) in all rice species, although the degree of decline in photosynthetic rate was different among the varieties. It was notable that the photosynthetic rate was almost constant in O. latifolia though Ψw decreased to - 2.0 MPa with the increased NaCl concentration in the water culture solution. A significant negative correlation between free-proline content and osmotic potential (Ψs) of leaf blade was found in both salt tolerant entries, SR26B and O. latifolia. In spite of higher leaf Na+ storage, the survival rate of O. latifolia was higher than that of SR26B, indicating that the mechanism of salt tolerance in O. latifolia may be different from that in SR26B.
A spectropolarimeter equipped with eight spectral bands in the visible, near- and short-wave infrared ranges (490-2200 nm) as well as a rotary film polarizer has been developed for measuring the reflectance and degree of polarization of light reflected from field crop canopies. This paper describes the design and specification of the instrument and the results of preliminary field experiments. Solar and view zenith angles and view azimuth direction relative to the solar position had a much greater influence on polarization than reflectance. For fully developed sweet potato and soybean canopies, the degree of polarization was a better discriminator of the canopy than each single band reflectance and a reflectance-based vegetation index such as normalized difference vegetation index (NDVI).
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