Distribution patterns of assimilated 14C in vegetative and reproductive shoots of Lolium perenne and L. temulentum

The movement of ¹⁴C-labelled assimilate to the terminal meristem, stem, mature leaves, tillers and roots was measured in Loliurn perenn and Lolium temulentum after exposure to ¹⁴C0₂ of the youngest fully-expanded leaf and, on fewer occasions, the oldest healthy leaf on the main shoot. During early vegetative growth, the terminal meristem, tillers and roots received most of the ¹⁴C exported from the youngest leaf. As the shoot aged, more ¹⁴C was exported to the terminal meristem and tillers and less to roots. When the stem became a sizeable sink for ¹⁴C at the six-leaf (L. temulentum) or eleven-leaf (L. perenne) stage, less ¹⁴C moved to tillers and much less to roots. The terminal meristem continued to receive ¹⁴ at a steady rate throughout late vegetative growth. The transition from vegetative to reproductive growth in both species was marked by an abrupt increase in the export of ¹⁴C to stem from the upper leaf, but there was little change in the proportion of ¹⁴C which moved to the developing leaves and incipient inflorescence at the terminal meristem. At the same time, less ¹⁴C moved to tillers and much less to roots. Immediately before ear emergence, the export of ¹⁴C from the upper leaf (flag leaf) to the stem declined and the proportion moving to the ear increased, reaching a maximum of 55–75% as the ear emerged. The relative patterns of export of upper and lower leaves showed that while some ¹⁴ moved from each leaf to all meristems, the proximity of actively growing meristems appeared to be the main factor which determined the destination of most exported ¹⁴C. The distribution of ¹⁴C from upper and lower leaves was most alike in young vegetative plants of L. perenne. At later stages of development of both species, the terminal meristem and stem received most 14¹⁴C from the upper leaf, while roots and tillers received mos 14¹⁴C from the oldest leaf at the base of the shoot.     

EFFECTS OF SEEDING DENSITY AND BASIC MANURE ON THE GROWTH OF DRY NURSERY SEEDLINGS IN LATE DOUBLE CROPPING RICE IN SOUTH CHINA

During the period of dry nursery seedling raising of late double cropping indica rice in South China, both chemical fertilizer and farmyard manure did not show obvious effect on the growth of shoot and root in young seedlings at 4-leaf stage (18-day-old seedling), but had significant effects on root growth in old seedlings with 6-7 leaves (27-day-old seedling) at suitable seeding densities (65-125g m~(-2)). There were satistically significant differences (at 0.01 or 0.05 levels)between treatments in root number and rooting ability of root-pruned seedlings.     

Relative importance of Na+, Cl−, and abscisic acid in NaCl induced inhibition of root growth of rice seedlings

The relative importance of endogenous abscisic acid (ABA), as well as Na⁺ and Cl^– in NaCl-induced responses related to growth in roots of rice seedlings were investigated. The increase in ammonium, proline and H₂O₂ levels, and cell wall peroxidase (POD) activity has been shown to be related to NaCl-inhibited root growth of rice seedlings. Increasing concentrations of NaCl from 50 to 150 mM progressively decreased root growth and increased both Na⁺ and Cl^–. Treatment with NaCl in the presence of 4,4-diisothiocyano-2,2-disulfonic acid (DIDS, a nonpermeating amino-reactive disulfonic acid known to inhibit the uptake of Cl^–) had less Cl^– level in roots than that in the absence of DIDS, but did not affect the levels of Na⁺, and responses related to growth in roots. Treatment with 50 mM Na-gluconate (the anion of which is not permeable to membrane) had similar Na⁺ level in roots as that with 100 mM NaCl. It was found that treatment with 50 mM Na-gluconate effected growth reduction and growth-related responses in roots in the same way as 100 mM NaCl. All these results suggest that Cl^– is not required for NaCl-induced responses in root of rice seedlings. Endogenous ABA level showed no increase in roots of rice seedlings exposed to 150 mM NaCl. It is unlikely that ABA is associated with NaCl-inhibited root growth of rice seedlings.     

Effect of imazaquin on absorption,translocation, and pattern of distribution of chlormequat chloride in winter wheat

The role of imazaquin in the absorption, translocation, and distribution of chlormequat chloride in CYCOCEL^* CL has been studied in winter wheat. Three treatments were applied to the 5th leaf of the main stem at growth stage 5 (Feekes Large scale): (1)¹⁴C-chlormequat chloride, (2) CYCOCEL^* CL containing¹⁴C-chlormequat chloride, and (3) CYCOCEL^* CL containing¹⁴C-imazaquin. Tracing of the radioactivity was followed in the treated leaf, main stem, tillers, and roots. Results showed that more than 85% of the radioactivity absorbed remained in the treated leaf. Ten days after the application of chlormequat chloride alone, 94.4% of the¹⁴C-chlormequat was found in the treated leaf, 2.9% in the main stem, 1.2% in the tillers, and 1.4% in the root system versus 88.2, 8.2, 2.1, and 1.4%, respectively, for the chlormequat chloride plus imazaquin treatment. It was concluded that imazaquin increases the mobility and the pattern of distribution of chlormequat chloride in the plant.     

Effect of imazaquin on absorption, translocation, and pattern of distribution of chlormequat chloride in winter wheat

The role of imazaquin in the absorption, translocation, and distribution of chlormequat chloride in CYCOCEL^* CL has been studied in winter wheat. Three treatments were applied to the 5th leaf of the main stem at growth stage 5 (Feekes Large scale): (1)¹⁴C-chlormequat chloride, (2) CYCOCEL^* CL containing¹⁴C-chlormequat chloride, and (3) CYCOCEL^* CL containing¹⁴C-imazaquin. Tracing of the radioactivity was followed in the treated leaf, main stem, tillers, and roots. Results showed that more than 85% of the radioactivity absorbed remained in the treated leaf. Ten days after the application of chlormequat chloride alone, 94.4% of the¹⁴C-chlormequat was found in the treated leaf, 2.9% in the main stem, 1.2% in the tillers, and 1.4% in the root system versus 88.2, 8.2, 2.1, and 1.4%, respectively, for the chlormequat chloride plus imazaquin treatment. It was concluded that imazaquin increases the mobility and the pattern of distribution of chlormequat chloride in the plant.     

Evaluation of Pseudomonas fluorescens for Suppression of Sheath Rot Disease and for Enhancement of Grain Yields in Rice (Oryza sativa L.)

Pseudomonas fluorescens strains antagonistic to Sarocladium oryzae, the sheath rot (Sh-R) pathogen of rice (Oryza sativa L.), were evaluated in greenhouse and field tests for suppression of Sh-R severity and enhancement of grain yields of rice. Imprints of rice seedlings and a direct-observation technique of staining roots with fluorochromes confirmed the association of P. fluorescens with roots and the ability of the strain to move along shoot tips. In greenhouse tests, P. fluorescens-treated rice plants (cv. IR 20) showed a 54% reduction in the length of Sh-R lesions. In three field tests, treatment with P. fluorescens reduced the severity of Sh-R by 20 to 42% in five rice cultivars. Bacterization of rice cultivars with P. fluorescens enhanced plant height, number of tillers, and grain yields from 3 to 160%.     

New insights into an RNAi approach for plant defence against piercing‐sucking and stem‐borer insect pests

Insect double‐stranded (ds)RNA expression in transgenic crops can increase plant resistance to biotic stress; however, creating transgenic crops to defend against every insect pest is impractical. Arabidopsis Mob1A is required for organ growth and reproduction. When Arabidopsis roots were soaked in dsMob1A, the root lengths and numbers were significantly suppressed and plants could not bolt or flower. Twenty‐four hours after rice roots were immersed in fluorescent‐labelled dsEYFP (enhanced yellow fluorescent protein), fluorescence was observed in the rice sheath and stem and in planthoppers feeding on the rice. The expression levels of Ago and Dicer in rice and planthoppers were induced by dsEYFP. When rice roots were soaked in dsActin, their growth was also significantly suppressed. When planthoppers or Asian corn borers fed on rice or maize that had been irrigated with a solution containing the dsRNA of an insect target gene, the insect's mortality rate increased significantly. Our results demonstrate that dsRNAs can be absorbed by crop roots, trigger plant and insect RNAi and enhance piercing‐sucking and stem‐borer insect mortality rates. We also confirmed that dsRNA was stable under outdoor conditions. These results indicate that the root dsRNA soaking can be used as a bioinsecticide strategy during crop irrigation.     

The Export and Distribution of 14C-labelled Assimilates from each Leaf on the Shoot of Lolium temulentum during Reproductive and Vegetative Growth

In both reproductive and vegetative plants of Lolium temulentumL., the export of ¹⁴C-labelled assimilates from each healthyleaf on the main shoot to terminal meristem, stem, tillers,and roots was measured each time a new leaf was expanded, fora period of 5 to 6 weeks. Some labelled assimilates moved fromeach leaf on the main shoot to every meristem in the same shoot,as well as to the tops and roots of adjacent organically attachedtillers. The terminal meristem of the reproductive shoot, which includedthe developing inflorescence, received 70–80 per centof the carbon assimilated by the emerged portion of the growingleaf, 15–25 per cent of the carbon assimilated by thetwo youngest expanded leaves, and 5–10 per cent of thatfrom each of the older leaves. A similar pattern of carbon supplyto the terminal meristem was found in vegetative shoots, exceptthat older leaves on young vegetative shoots supplied even lessof their carbon to the terminal meristem. The general conclusionis that developing leaves at the tip of the shoot receive aboutthe same proportion of carbon from each leaf as does a developinginflorescence. Young expanded leaves provided most labelled assimilates forstem growth; during both reproductive and vegetative growth,expanded leaves increased their export of labelled carbon tostem, and exported less of their ¹⁴C to roots and sometimesto tillers. In these reproductive and vegetative shoots, grown in a constantexternal environment, the major changes in the pattern of distributionof labelled assimilates appeared to be the result of increasedmeristematic activity in stem internodes; the development ofan inflorescence had no obvious direct effect on the carboneconomy of shoots.     

Effect of decapitation on absorption,translocation, and phytotoxicity of imazamethabenz in wild oat (Avena fatua L.)

The release of apical dominance by the physical destruction in situ of the apical meristem and associated leaf primordia (decapitation) promoted the growth of tillers in non-herbicide-treated wild oat plants, as indicated by increased tiller lengths and fresh weights. At 96 h after [¹⁴C] herbicide treatment following decapitation, the absorption of [¹⁴C]imazamethabenz and total translocation of radioactivity were respectively increased by 28% and 49%. By 96 h after [¹⁴C]imazamethabenz application, the radioactivity detected in the roots of decapitated plants was 45% higher than that in the roots of nondecapitated plants while the radioactivity in tillers of decapitated plants was 2.6-fold that in tillers of intact plants. Decapitation together with foliar spraying of imazamethabenz at 200 g ha^–1 further reduced tiller fresh weight, greatly decreased the total tiller number, and thereafter significantly increased overall phytotoxicity by 32% as measured by total shoot fresh weight. The results of this study support the hypothesis that main shoot apical dominance limits translocation of applied imazamethabenz to lateral shoots, rendering tillers less susceptible to growth inhibition by the herbicide.     

不同秧苗素质和移栽密度条件下臭氧胁迫对水稻光合作用、物质生产和产量的影响

近地层臭氧浓度升高使水稻生长受抑进而使产量下降,但这种影响是否因不同栽培条件而异尚不清楚。2011年依托先进的稻田臭氧FACE(Free Air gas Concentration Enrichment)技术平台,以汕优63为供试材料,臭氧设置大气臭氧浓度(Ambient)和高臭氧浓度(比Ambient高50%),秧苗素质设置弱苗(移栽时无分蘖)和壮苗(移栽时带两个分蘖),移栽密度设置低密度(16穴/m2)、中密度(24穴/m2)和高密度(32穴/m2),研究不同秧苗素质和移栽密度条件下臭氧胁迫对水稻生长和产量的影响。结果表明:高浓度臭氧使水稻结实期叶片SPAD值、净光合速率、气孔导度和蒸腾速率明显下降,但胞间CO2浓度和叶温无显著变化。高浓度臭氧对水稻拔节前物质生产量没有影响,但使拔节至抽穗期、抽穗至成熟期物质生产量平均分别降低13%和29%,进而使成熟期生物产量和籽粒产量均显著下降。方差分析表明,臭氧与秧苗素质间没有互作效应,但臭氧与移栽密度的互作对最终产量的影响达显著水平。以上结果表明,臭氧胁迫使水稻生长后期光合受阻,导致物质生产和产量显著下降;适当增加移栽密度可能会减少臭氧胁迫下水稻产量的损失。     

Nickel and Al-excess inhibit nitrate reductase but upregulate activities of aminating glutamate dehydrogenase and aminotransferases in growing rice seedlings

The present study was undertaken to examine the influence of toxic levels of Ni and Al, on the activities of key nitrogen assimilatory enzymes in roots and shoots of growing rice seedlings. When seedlings of two inbred rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12, sensitive to both Ni and Al, were raised in sand cultures containing 200 and 400 μM NiSO₄ or 80 and 160 μM Al₂(SO₄)₃, a marked inhibition in the activities of NO₃ ⁻ assimilatory enzymes NR and GS was observed in roots as well as shoots during a 5–20 day growth period. Both Ni and Al treatments, in growth medium, stimulated the activity of aminating glutamate dehydrogenase (NADH-GDH) whereas the activity of deaminating GDH (NAD⁺-GDH) decreased under metal toxicities. The activities of the aminotransferases studied; alanine aminotransferase (AlaAT) and aspartate amino transferase (AspAT) increased due to Ni and Al treatments. Results suggest that both Ni and Al treatments impair N assimilation in rice seedlings by inhibiting the activities of NR and GS and that GDH appears to play a role in assimilation of NH₄ ⁺ in metal stress conditions. Further, higher activity of aminotransferases in metal stressed seedlings might be helpful in meeting higher demand of amino acids under stressed conditions.     

两个特用稻的营养供应水平与32P、14C分布和谷产量的关系

香稻(竹香粘)的分蘖数多,其分蘖期根系吸收³²P和³²P分布到分蘖,以高、中肥和高N,高K肥处理的为高;¹⁴C-葡萄糖同化物分布在分蘖比黑米稻(黑优粘)和常规稻“双桂36”的高,但灌浆期和黄熟期¹⁴C分布在稻穗较少.低肥处理的稻谷产量较高.而在高、中肥条件下结实率降低,实粒数减少,成穗率稍低,谷产量也比“黑优粘”和“双桂36”低. “黑优粘”在高肥、高N条件下的分蘖多,成穗率高、结实粒数也较多,稻谷产量比“竹香粘”高,在高、中肥、高 N高 P条件下,³²P分布于分蘖多,分蘖的¹⁴C分布则以高 N,高 K肥条件下的多;开花和灌浆用稻穗的¹⁴C分布皆以高 K肥水平的为高。“黑优粘”是耐肥和需钾肥品种,高肥、高K可提高其稻谷产量,但仍比“双桂36”低.     

Organ-specific analysis of the anaerobic primary metabolism in rice and wheat seedlings. I: Dark ethanol production is dominated by the shoots

During anaerobiosis in darkness the main route for ATP production in plants is through glycolysis in combination with fermentation. We compared the organ-specific anaerobic fermentation of flooding-tolerant rice (Oryza sativa) and sensitive wheat (Triticum aestivum) seedlings. A sensitive laser-based photoacoustic trace gas detection system was used to monitor emission of ethanol and acetaldehyde by roots and shoots of intact seedlings. Dark-incubated rice seedlings released 3 times more acetaldehyde and 14 times more ethanol than wheat seedlings during anaerobiosis. Ninety percent of acetaldehyde originated from shoots of both species. In comparison to wheat shoots, the high ethanol production of rice shoots correlated with larger amounts of soluble carbohydrates, and higher activities of fermentative enzymes. After 24 h of anaerobiosis in darkness rice shoots still contained 30% of aerated ATP level, which enabled seedlings to survive this period. In contrast, ATP content declined almost to zero in wheat shoots and roots, which were irreversibly damaged after a 24-h anaerobic period. When plants were anaerobically and dark incubated for 4 h and subsequently transferred back to aeration, shoots showed a transient peak of acetaldehyde release indicating prompt re-oxidation of ethanol. Post-anoxic acetaldehyde production was lower in rice seedlings than in wheat. This observation accounts for a more effective acetaldehyde detoxification system in rice. Compared to wheat the greater tolerance of rice seedlings to transient anaerobic periods is explained by a faster fermentation rate of their shoots allowing a sufficient ATP production and an efficient suppression of toxic acetaldehyde formation in the early re-aeration period.Angelika Mustroph and Elena I. Boamfa contributed equally to the paper.     

Infection process of Gaeumannomyces graminis var. graminis on the roots and culms of rice

Crown sheath rot, caused by the ascomycete Gaeumannomyces graminis var. graminis that infects the root and the base of the culm of rice, causes early grains maturation, tiller death and reduced yield. As a paucity of information exists in the literature on the rice‐G. graminis var. graminis interaction at the microscopic level, this study aimed to gain novel insights into the infection process of this pathogen in the root and culm of rice using both light and scanning electron microscopy. In the roots, the fungus initially colonized the epidermal, exodermal and sclerenchyma cells. At 15 days after inoculation (dai), fungal hyphae colonized the cortex and clusters of perithecia were observed in the roots. At 20 dai, the fungus reached the central cylinder, and an intense fungal colonization at the base of the culm was observed that resulted in the formation of a mycelial mat on both adaxial and abaxial surfaces of the leaf sheaths. At 25 dai, fungal growth was noticed in the parenchyma cells, vascular bundles and airspaces. Perithecia emerged through the base of prophyllum and from the first leaf sheath at 30 dai. The results of this study provide new insights into the infection process of G. graminis var. graminis in rice and may help to find better control measures in reducing crown sheath rot development.     

Characterization of transgenic rice plants that express rgp1, the gene for a small GTP-binding protein from rice

 The rgp1 gene, which encodes a small GTP-binding protein from rice, was introduced into rice protoplasts by electroporation. Transformed protoplasts were cultured on liquid protoplast-culture medium for 1 month, and then cells that had proliferated were transferred to a selection medium that contained 50 mg/l hygromycin B. Among 50 colonies that were selected and transferred to regeneration medium, 3 colonies generated shoots. However, two of the three shoots failed to form roots and ceased growing. A single regenerated shoot that formed roots was planted in soil and transferred to a greenhouse. Southern hybridization showed that the regenerated plant harbored a single copy of the introduced gene. The transformant (T₀) plant was shorter than the controls, it developed three times as many tillers as controls, it developed three times as many tillers as control plants but it produced mostly sterile seeds. In a test of hygromycin resistances, viable seeds segregated into resistant and sensitive seedings at a ratio of approximately 1 : 3. The progeny (T₁) plants were short with many tillers, and some produced seeds normally. The T₂ seedlings grew more rapidly than control seedlings for the first 28 days after germination, but control plants subsequently outgrew the T₂ plants. Northern blotting analysis revealed that the rgp1 gene in T₂ plants was expressed consitutively throughout all developmental stages. The results suggest that the observed phenotypic changes were due to expression of the exogenous rgp1 gene. Received: 21 September 1997/Accepted: 31 March 1998     

Effects of ethanol on growth of rice seedlings

Effects of ethanol, the end product of ethanolic fermentation, on the growth of rice (Oryza sativa L.) seedlings were determined as a means of evaluating growth responses under anoxia. The ethanol concentrations in roots and coleoptiles of the seedlings subjected to 48 h-anoxia, and in their culture medium were 23 and 32 µmol g^–1 fresh weight, and 19 µmol ml^–1, respectively. The growth of the roots and coleoptiles of the seedlings was restricted by exogenous ethanol at concentrations above 50 mM and 100 mM, respectively, suggesting that the roots are more sensitive to ethanol than the coleoptiles.     

Potassium influx and efflux of 2,4-D- and MCPA-treated rice plants

Summary A study was made of the effects of the herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methyl-phenoxyacetic acid) on ion uptake, leakage and growth of rice seedlings. Using isotopically-labelled solutions containing different concentrations of 2,4-D or MCPA, it was established that 10^–4 M 2,4-D or MCPA effectively inhibited potassium ion uptake, while K-ion leakage from the roots occurred only at 10^–3 M. The growth of the rice seedlings was markedly retarded even at low (10^–6 M) concentrations, and the roots and shoots showed different tolerances to the herbicide. At 10^–8 M herbicide, the effects were not injurious, but rather favourable. Reduction in root length by herbicides was not in accordance with dry-matter production.     

Tiller dynamics and assimilate partitioning in Lolium perenne with particular reference to flowering

The fate of 100 seedling plants of Lolium perenne L. was studied over a period of 2 years in a field plot. The birth and death of tillers and the production of inflorescences was followed, and the components of seed yield were recorded in detail in the first year. The pattern of distribution of ¹⁴CO₂ assimilated by the main shoot was examined at monthly intervals and during the first flowering season the distribution of ¹⁴C-assimilate from individual leaves and from the inflorescence was also studied. The capacity of individual tillers to assimilate ¹⁴CO₂ prior to flowering and the re-distribution of previously accumulated assimilate during seed growth were also assessed. Plants died at a more or less constant rate with time and only 54 survived to the end of the 2–yr period. First year mortality was associated with severe grazing or cutting but in the second year the death of ungrazed plants was observed. There was great variability in the production of tillers by surviving plants. In both years the number of live tillers per plant increased from July to the end of April with particularly rapid tillering in March and April establishing the maximum value for each year. There was a similar phase of rapid tillering after flowering in July. The number of live tillers per plant declined by 50% during stem elongation and inflorescence emergence and the majority of dead tillers were young secondary (in the first year) and tertiary (in the second year) tillers with a mean age of 40 days. Such tillers had poor assimilatory capacity prior to the onset of death and were not supplied with assimilate from the main shoot. Most of the plants surviving at the end of the experiment flowered in both years and one quarter of the maximum number of live tillers per plant recorded in April of each year produced inflorescences. The earlier a tiller was produced the greater was its chance of flowering and the greater its production of seed. The greater weight of seed produced was associated with the development of more seed-bearing florets per spikelet. There was relatively little export of “C-assimilate from the flowering main shoot, and the lower internodes formed the major sink for post-anthesis assimilate. The growth of seeds appeared to be relatively independent of the leaves for current assimilate. There was some evidence that assimilate accumulated in lower internodes was remobilised and utilised in the growth of seeds and new tillers. Overall, the results confirm the view that the grass plant is a dynamic population of short-lived tillers and indicate that increasing competition for assimilate at flowering exerts a major influence on the production and survival of tillers.     

Fungal endophyte infection changes growth attributes in Lolium multiflorum Lam

Abstract Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non‐competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.