Rice chaff, a major by-product of rice cultivation, is generally known for its high content of Si. Pot and small field plot (concrete plot) experiments were conducted to ascertain the effects of rice chaff in powdered form (Cp) and normal rice chaff (Ch) with or without bio-decomposer application on lodging resistance, yield, Si and N absorption of rice (Oryza sativa L. cv. Hatsushimo). The results showed that the absorption of Si by plants could be promoted by Cp supplied together with a bio-decomposer, although the N content in plants was not increased. In the concrete plot experiment, lodging resistance was improved by Cp applied under a lightly-fertilized condition due to the high breaking strength and strong bending stress caused by the high Si content in the plants. Cp application tended to increase under a lightly-fertilized condition, but decreased the yield under a heavily-fertilized condition. It was suggested hat Cp application is effective on rice growth under a lightly-fertilized condition, and that Cp may be useful as an alternative of inorganic Si fertilizer and contribute to a sustainable Si recycle system in rice cultivation.
Epibrassinolide (EBR, 24-epibrassinolide), one of the brassinosteroids (BRs), promotes elongation and sugar accumulation in the epicotyl of cucumber (Cucumis sativus L.) seedlings. In the seedlings with the primary leaf removed, such effects of EBR were not observed. On the other hand, in the seedlings with cotyledons removed, EBR promoted epicotyl elongation as in intact seedlings, and also promoted sugar accumulation in the epicotyl although the promotion was weaker than in intact seedlings. To examine the sugar transport to the epicotyl from the primary leaf, cotyledon, and hypocotyl, we applied [14C]-labeled sucrose to each organ, and examined the distribution of radioactivity 18 hr later. Allocation to the epicotyl of [14C]-sucrose applied to the primary leaf was enhanced by EBR, but that of [14C]-sucrose applied to the cotyledon or hypocotyl was not. This suggests that EBR specifically promotes the transport of sugar from the primary leaf to the epicotyl, and enhances sugar accumulation in the epicotyl.
We obtained transgenic rice (Oryza sativa L. cv. Nipponbare) plants with the gene for maize sucrose-phosphate synthase (EC 126.96.36.199, SPS). Some of the transgenic plants over-expressed maize SPS (over-expressing plants) and some had reduced levels of native SPS protein (co-suppressed plants). There was a positive correlation between the amounts of maize SPS protein and SPS activities. However, apparent Km values for uridine diphosphoglucose (UDPG) were higher in over-expressing plants than in control rice plants. These results suggest that over-produced maize SPS protein was not fully activated. The sucrose contents did not differ significantly between control and over-expressing rice plants, but they were lower in co-suppressed plants than in control plants. The starch contents were negatively and the sucrose/starch ratios were positively correlated with SPS activities. Thus, carbon partitioning in the transgenic rice was changed, even though rice is predominantly a sucrose-former.
Leaf sheaths of rice plants are known to temporarily accumulate starch prior to heading, which is subsequently remobilized and transported into the panicle after heading. We investigated the time course for both carbohydrate content and steady state mRNA levels of enzymes related to starch and sucrose metabolism in the rice leaf sheath (Oryza sativa L. cv. Nipponbare). Leaf sheaths from the second leaf below the flag leaf accumulated high levels of starch before heading but they rapidly decreased after heading. In contrast, the flag leaf sheath did not accumulate as much starch. In the second leaf sheath, the mRNA levels of enzymes involved in starch synthesis, ADP glucose pyrophosphorylase (EC 2. 7. 7. 27), soluble starch synthase (EC 2. 4. 1.21) and branching enzyme (EC 2.4. 1. 18) were high before heading, which coincided with rapid accumulation of starch. The mRNA levels of sucrose synthesis enzymes, cytosolic FBPase (EC 3. 1. 3. 11) and sucrose phosphate synthase (EC 2. 4. 1. 14), and the sucrose transporter (OsSUT1) increased at the time of heading, which was largely coincident with a decrease in the mRNA levels of starch synthesis enzymes. In the flag leaf sheaths, changes in mRNA levels of starch synthesis enzymes were not pronounced, however mRNA levels of sucrose synthesis enzymes and the sucrose transporter showed a clear increase throughout the heading period. The different characteristics observed between the two leaf sheaths will be discussed in relation to the sink to source transition.
Cassava (Manihot esculenta Crantz) can produce a high crop yield even in an environment with irregular rains. This is mainly attributed to its abilities to maintain leaf area under drought conditions and rapidly regrow after rain. In this study, we investigated the mechanism of leaf maintenance under water deficits through measurement of photosynthetic rate and water potential changes in leaves. The cassava plants were grown in pots and exposed to water deficits, and the diurnal changes in water potentials, rates of photosynthesis and transpiration and stomatal conductance were measured. The relationship between leaf water potential (ψw) and photosynthetic rate with decreasing soil water, and osmotic adjustment were also investigated. With respect to water supply in leaves, the movement of water in plants was measured using stem heat balance. Under water deficits, photosynthesis occurred only in the early morning. The water loss was reduced by stomatal closure in the mid-day. This was attributed to the complete closure of the stomata during the decrease in ψw to a range between - 1.0 and - 1.4 MPa. Furthermore, the firm stomatal closure is caused by the consistency of osmotic potential under decreases in soil water, i.e., to a lack of osmotic adjustment. Water stored in the pith parenchyma of stem flowed into leaves in the morning. From these results, we conclude that cassava can consistently maintain an adequate water level in leaves via water storage and the sensitivity of stomata to water deficits, thereby avoiding leaf dehydration.
The grain-shattering habit was compared among diploid and autotetraploid cultivars of common buckwheat (Fagopyrum esculentum Moench.). In the first experiment, one diploid and one autotetraploid cultivar were grown in the field, and the number of grains shed naturally by wind or rain, and the number of grains detached by threshing the plants (by dropping from 1 m height onto a concrete floor, five times) were measured to evaluate grain shattering. The number of the naturally shed grains in the field was higher in the diploid than in the autotetraploid cultivar, although the number of grains detached by threshing was not different between the two cultivars. In another set of experiments, breaking bending strength and breaking tensile strength of pedicels were measured as indices of grain-shattering habit to examine the difference in shattering among two autotetraploid and four diploid cultivars (two summer types and two autumn types). They were grown in summer and autumn seasons to examine the environmental effect on grain shattering. Both breaking strengths were about two times higher in the autotetraploid cultivars than in the diploid cultivars. The breaking strength was well correlated with the diameter of pedicels. The values of grain-shattering resistance traits obtained in the autumn cropping season were higher than those obtained in the summer cropping season.
The changes in pollen grain diameter were examined in relation to the floret opening and anther dehiscence in rice (Oryza sativa L.). In the first experiment, the florets were artificially opened by excising the top of the glumes at various times before the expected natural flowering time. Pollen diameter increased rapidly in the artificially opened florets, but slowly in the controls in which the glumes were left intact. The time of anther dehiscence coincided well with the time when pollen grains reached their maximum diameter. In addition, the pollen grain diameter was significantly correlated with the percentage of dehisced anthers in the florets artificially opened at various times. These results indicate that floret opening induces the swelling of pollen grains and that the swelling is an important event for anther dehiscence. In the second experiment, anther segments with pollen left remaining intact and those with pollen removed were immersed in water. The septa in the anther segments without pollen failed to rupture in water, whereas 70% of the septa in the anther segments with pollen left remaining ruptured, indicating that the septa can be ruptured by the swelling pressure of pollen grains resulting in unfolding of anther locules. From these findings, we infer that the rapid swelling of pollen grains in response to floret opening is a driving force to rupture the septum and unfold the locules.
The tillering, lodging and yield of two types of direct-seeded rice (dry and water seeding), under deep water (DW) and ordinary water treatment (OW), were compared in 1994 and 1995. The percentage of productive tillers to maximum tiller number under DW was 85% for transplanted, 60% for water-seeded and 84% for dry-seeded rice (mean 76%), while that under OW was 59, 50 and 74% (mean 61%), respectively, in both years. By DW, longer culm length and fresh weight tended to be increased, thus elevating bending moment, but the culm diameter and culm-breaking weight were increased showing the lower lodging index. In water-seeded rice, the suppression of the development of non-productive tillers by DW was relatively weak compared to that in dry-seeded or transplanted rice. Although the number of panicles was similar under DW and OW, 1000-grain weight and percentage of grain filling were significantly improved by DW. The grain yield was higher under DW, and the mean grain yields of the two years were 4.82 t ha-1 under DW and 4.48 t ha-1 under OW.
Epidermal cell wall biogenesis with emphasis on cuticular layer formation during direct somatic embryogenesis in rice was examined by transmission electron microscopy. The first phenomenon noticed in the early globular stage of somatic embryos was a high activity of cell wall formation. In this stage, many endoplasmic reticula, Golgi bodies and their vesicles were present and epidermal cells were covered by fibrillar material. Cutin was initially deposited on the epidermal cell wall of late globular or early elongate stage embryos. In the late elongate stage, a lamellated cuticular layer formed, and in the late scutellar stage, a more homogenous continuous cuticular layer formed. The cuticular layer disappeared gradually from the scutellum cell wall as the somatic embryo germinated. The disappearance of the cuticular layer was similar to that of the zygotic embryo. There is no cuticular layer on the scutellar epithelial cell wall of the immature zygotic embryo 5 days after germination. Our observations lead to the conclusion that one of the structural and physiological markers of direct somatic embryogenesis is the transformation of fibrillar material into the cuticular layer.
The mesophyll gland in patchouli (Pogostemon patchouli) was composed of secretory materials covered with a cuticle, a secretory head cell, a stalk cell and a basal cell. A large number of polysomes, mitochondria and smooth-appearing endoplasmic reticula showing a contracted figure were observed in the secretory head cells. Some endoplasmic reticula were sometimes observed in ramiform profiles. The aromatic cyclic sesquiterpenes were assumed to secrete into a subcuticular space through the thick cell wall from the peripheral area of the secretory head cell. Some cytoplasmic inclusions were localized in the secretory head cells and were considered to have been caused by a viral infection. On the basis of the ultrastructural details of the mesophyll glands, we discuss the secretory machinery by which the cyclic sesquiterpenes are produced and the possibility of the disturbance by viruses of the production of aromatic substances.