Spatial distribution of growth rates and of epidermal cell lengths in the elongation zone during leaf development in Lolium perenne L.

Relative elemental growth rates (REGR) and lengths of epidermal cells along the elongation zone of Lolium perenne L. leaves were determined at four developmental stages ranging from shortly after emergence of the leaf tip to shortly before cessation of leaf growth. Plants were grown at constant light and temperature. At all developmental stages the length of epidermal cells in the elongation zone of both the blade and sheath increased from 12 m at the leaf base to about 550 m at the distal end of the elongation zone, whereas the length of epidermal cells within the joint region only increased from 12 to 40 m. Throughout the developmental stages elongation was confined to the basal 20 to 30 mm of the leaf with maximum REGR occurring near the center of the elongation zone. Leaf elongation rate (LER) and the spatial distributions of REGR and epidermal cell lengths were steady to a first approximation between emergence of the leaf tip and transition from blade to sheath growth. Elongation of epidermal cells in the sheath started immediately after the onset of elongation of the most proximal blade epidermal cells. During transition from blade to sheath growth the length of the blade and sheath portion of the elongation zone decreased and increased, respectively, with the total length of the elongation zone and the spatial distribution of REGR staying near constant, with exception of the joint region which elongated little during displacement through the elongation zone. Leaf elongation rate decreased rapidly during the phase when only the sheath was growing. This was associated with decreasing REGR and only a small decrease in the length of the elongation zone. Data on the spatial distributions of growth rates and of epidermal cell lengths during blade elongation were used to derive the temporal pattern of epidermal cell elongation. These data demonstrate that the elongation rate of an epidermal cell increased for days and that cessation of epidermal cell elongation was an abrupt event with cell elongation rate declining from maximum to zero within less than 10 h.Abbreviations LER leaf elongation rate - REGR relative elemental growth rates     

Senescence of leaf sheaths of ryegrass stubble: changes in enzyme activities related to H2O2 metabolism

Changes in the levels of reactive oxygen species (O2^.-, H₂O₂), and of activities of enzymes involved in their detoxification were investigated during senescence of leaf sheaths of ryegrass stubble. The accumulation of H₂O₂ in the medium leaf sheaths coincided with a drop in the levels of total glutathione, of pyridine nucleotides and of activities of monodehydroascorbate reductase and dehydroascorbate reductase. Conversely, a paradoxical increase in the ascorbate/ascorbate plus dehydroascorbate ratio was observed, which appears to be inconsistent with H₂O₂ accumulation. Our results suggest that oxalate might be an essential source of H₂O₂ in senescent leaf sheaths, and that oxalate oxidase might be involved in the defence of foliar tissue against pathogens during the progress of senescence. Moreover, it is assumed that glucid catabolism of the ryegrass stubble might be a starting point of a metabolic drain leading to ascorbate, then to oxalate during the late phase of leaf sheath senescence.     

Crocins transport in Crocus sativus: The long road from a senescent stigma to a newborn corm

Saffron, the desiccated stigmas of Crocus sativus, is highly appreciated by its peculiar colour, flavour and aroma. The main compounds that accumulated throughout stigma development in C. sativus are crocetin, its glucoside derivatives, crocins, and picrocrocin, all of which increased as stigmas reached a fully developed stage. After anthesis, and in the absence of fertilization, the flower enters in a senescence programme, which represents the ultimate stage of floral development and results in wilting of whole flower. The programmed senescence of flowers allows the removal of a metabolically active tissue. We studied the composition of saffron apocarotenoids during the senescence of C. sativus flowers, and observed that changes in crocins were due to their transport from the senescent stigma to the ovaries and the developing corm. Afterwards, deglucosylation of crocins in these tissues results in crocetin accumulation. This mobilization mimics the export to storage cells (resorbed) of different compounds during leaf senescence avoiding loss of nutrients in leaves that would otherwise be cycled back into the soil system through leaf litter decomposition. In C. sativus, the resorbed apocarotenoids are stored within the developing corm, where they are not further detected in the advanced stages of development, suggesting that they are metabolized during the early and active phases of corm development, where the glucose molecules from crocins might contribute to cell initiation and elongation.     

Leaf contents differ depending on the position in a rice leaf sheath during sink-source transition.

Carbohydrate contents varied with position in a leaf sheath, and differed between the flag leaf sheath and the second leaf sheath below the flag leaf (-2 leaf sheath) in rice (Oryza sativa L.). In the -2 leaf sheath before heading, light microscopy revealed differences in the distribution of starch granules depending on position. Leaf sheaths were divided into several parts, and the contents of carbohydrates (starch, sucrose, and hexoses) were measured in each part. Before heading, the content of accumulated starch increased linearly from the top to the bottom in -2 leaf sheaths (r2=0.99, P<0.001), as did the contents of accumulated sucrose and hexoses in flag leaf sheaths (r2=0.94, P<0.01). In flag leaf sheaths, the relative content of sucrose synthase (SuS), which plays a central role in the degradation of sucrose into hexoses, increased from the top to the bottom, consistent with hexose contents. After heading, the accumulated carbohydrates were dramatically decreased. In -2 leaf sheaths, the activity of alpha-amylase (EC 3.2.1.1), the rate-limiting step in starch degradation, was consistent with the degree of starch degradation, but in flag leaf sheaths with little starch before heading. These results show that carbohydrate contents differ, depending on the position in a leaf sheath. In addition, there were big differences in leaf contents between flag leaf sheaths and -2 leaf sheaths.     

Mechanism of resistance to the spotted stalk borer,Chilo sacchariphagus,in the sugarcane cultivar R570

Resistance in sugarcane [Saccharum spec. (Poaceae)] to the spotted stalk borer, Chilo sacchariphagus (Bojer) (Lepidoptera: Pyralidae), was studied by comparing feeding behaviour on resistant cv. R570 and susceptible cv. R579. In a field survey, the feeding behaviour of C. sacchariphagus larvae was described to identify their feeding sites on the plant. In a greenhouse artificial infestation study, we compared the establishment of larvae on potted plants. In laboratory choice and no‐choice experiments, we studied the establishment of larvae on plant organs (stalk, sheath, leaf spindle). Study of the feeding behaviour showed that: (1) first to fourth instars are able to feed on stalk, sheath, and leaf spindle, (2) boring into the stalk occurs mostly in the four uppermost internodes, and (3) most young larvae bore through the abaxial surface of leaf sheaths to reach the stalk. In greenhouse experiments, we observed an early two‐fold reduction of the number of larvae on R570 plants within the first 48 h after infestation. In laboratory experiments, larval antixenosis was demonstrated at the abaxial surface of R570 leaf sheath, but was observed neither in the leaf spindle nor in the stalk. First, second, and third instars were susceptible to this antixenosis. We hypothesize that the main resistance mechanism in R570 is an early reduction of larval establishment on plants, due to antixenosis located at the abaxial surface of leaf sheaths.     

Identification of Nitrogen,Phosphorus, and Potassium Deficiencies in Rice Based on Static Scanning Technology and Hierarchical Identification Method

Establishing an accurate, fast, and operable method for diagnosing crop nutrition is very important for crop nutrient management. In this study, static scanning technology was used to collect images of a rice sample''s fully expanded top three leaves and corresponding sheathes. From these images, 32 spectral and shape characteristic parameters were extracted using an RGB mean value function and using the Regionprops function in MATLAB. Hierarchical identification was used to identify NPK deficiencies. First, the normal samples and non-normal (NPK deficiencies) samples were identified. Then, N deficiency and PK deficiencies were identified. Finally, P deficiency and K deficiency were identified. In the identification of every hierarchy, SVFS was used to select the optimal characteristic set for different deficiencies in a targeted manner, and Fisher discriminant analysis was used to build the diagnosis model. In the first hierarchy, the selected characteristics were the leaf sheath R, leaf sheath G, leaf sheath B, leaf sheath length, leaf tip R, leaf tip G, leaf area and leaf G. In the second hierarchy, the selected characteristics were the leaf sheath G, leaf sheath B, white region of the leaf sheath, leaf B, and leaf G. In the third hierarchy the selected characteristics were the leaf G, leaf sheath length, leaf area/leaf length, leaf tip G, difference between the 2^nd and 3^rd leaf lengths, leaf sheath G, and leaf lightness. The results showed that the overall identification accuracies of NPK deficiencies were 86.15, 87.69, 90.00 and 89.23% for the four growth stages. Data from multiple years were used for validation, and the identification accuracies were 83.08, 83.08, 89.23 and 90.77%.     

Biomechanics and development of the climbing habit in two species of the South American palm genus Desmoncus (Arecaceae)

Mechanical properties are investigated in Desmoncus orthacanthos and D. polyacanthos from French Guiana, South America. Differences in size and axis stiffness are related to different trellis requirements and habitats. The leaf sheath surrounds the stem, increasing stiffness of young self-supporting stages and apical parts of older climbing plants. Senescence of the leaf sheath reduces stiffness of older climbing axes of both species. Its eventual loss in D. orthacanthos facilitates deformation into coils and loops when plants slip from their supports following senescence of leaves bearing attachment organs. In smaller climbing axes of D. polyacanthos, the senescent leaf sheath remains attached and axes rarely form loops and coils below attachment. An increase in stiff mechanical properties toward the base of both species is radically different from that of many dicotyledonous lianas. Besides the presence of attachment organs, stem mechanical properties of Desmoncus are similar to those of erect though not fully self-supporting stems of Bactris major, a sympatric species of the sister group genus to Desmoncus. The climbing habit in Desmoncus may have evolved via (1) heterochronic processes including early elongation of internodes relative to increase in stem diameter (reduction of the establishment phase) and (2) increased persistence of leaf sheaths.     

Morphogenesis of galls induced by Baccharopelma dracunculifoliae (Hemiptera: Psyllidae) on Baccharis dracunculifolia (Asteraceae) leaves.

The commonest insect gall on Baccharis dracunculifolia (Asteraceae) leaves is induced by Baccharopelma dracunculifoliae (Hemiptera, Psyllidae). The gall-inducing insect attacks young leaves in both the unfolded and the fully expanded stages. Four developmental phases were observed in this type of gall: 1) A folding phase, during which the leaf lamina folded upward alongside the midrib and the edges of the upper portion of the leaf approached each other, forming a longitudinal slit. A single chamber was formed on the adaxial surface of the leaf; 2) A swelling phase, in which the folded leaf tissues thickened and the edges of the leaf drew closer together, narrowing the slit. In this phase the gall matured, turning succulent, fusiform and pale green. The single nymphal chamber was lined with white wax and was able to house from one to several nymphs; 3) A dehiscence phase, characterized by the opening of the slit to release inducers; and 4) A senescence phase, when the gall turned dark and dry. The dermal system of the mature gall was composed of a single-layered epidermis. The mesophyll was swollen, and the swelling was due mainly to hyperplasia of the parenchyma. The vascular tissues along the midrib vein were conspicuous and the perivascular fibers resembled parenchymal cells. The hypertrophied secretory cavities contained low lipophylic content. This gall does not form nutritive tissue, but salivary sheaths left by the inducers were observed near the parenchyma, vascular bundles and secretory cavities. This study complements our current knowledge of gall biology and sheds further light on the plasticity of plant tissues stimulated by biotic factors.     

STRUCTURE OF THE SHOOT APEX IN LACTUCA SATIVA

Histological observations of the leaf lettuce ‘Black Seeded Simpson’ showed the dormant embryo to possess two visible leaves and a flkat to slightly depressed plumular apex. Observations conducted over a 12-day period of germination and growth showed the development of L₁ and L₂, emergence of L₃ and L₄, and periodic changes in size of the apex which were associated with leaf emergence. Thus the dormant embryo of Lactuca appears to be considerably more advanced in development than was previously believed. The shoot apex appeared flat to slightly depressed at all developmental stages studied.     

Composition of leaf surface waxes of Triticum species: Variation with age and tissue

The composition of cuticular wax from plants of spring wheat (varieties Selkirk and Manitou) and of durum wheat (variety Stewart 63) at various stages of growth, and of wax from different parts of the plants varies considerably. Wax was analysed, without preliminary separation, by GLC using Dexsil 300 as liquid phase. Alcohols are major components of wax from leaf blades and β-diketones are major components of wax from leaf sheaths, especially the flag leaf sheath. Glaucousness of the leaf sheath is due to the high β-diketone content. In the first 50 days after germination, before sheaths and flag leaf are completely developed, the major component is octacosanol (> 50%). At 66 days, when sheath development is complete, β-diketone content is greatest. Hydrocarbon composition differs for wax from leaf blade and leaf sheath and also for different leaf blades and between adaxial and abaxial sides of the flag leaf. From 66 to 100 days ester content of wax increases, especially in Selkirk wheat, apparently due to formation of wax containing high proportions of esters of trans-α,β-unsaturated C₂₂ and C₂₄ acids. The content of these acids in the free fatty acids and of diesters based on these acids also increases during this period.     

A combined 15N tracing/proteomics study in Brassica napus reveals the chronology of proteomics events associated with N remobilisation during leaf senescence induced by nitrate limitation or starvation

Our goal was to identify the leaf proteomic changes which appeared during N remobilisation that were associated or not associated with senescence of oilseed rape in response to contrasting nitrate availability. Remobilisation of N and leaf senescence status were followed using ¹⁵N tracing, patterns of chlorophyll level, total protein content and a molecular indicator based on expression of senescence‐associated gene 12/Cab genes. Three phases associated with N remobilisation were distinguished. Proteomics revealed that 55 proteins involved in metabolism, energy, detoxification, stress response, proteolysis and protein folding, were significantly induced during N remobilisation. Four proteases were specifically identified. FtsH, a chloroplastic protease, was induced transiently during the early stages of N remobilisation. Considering the dynamics of N remobilisation, chlorophyll and protein content, the pattern of FtsH expression indicated that this protease could be involved in the degradation of chloroplastic proteins. Aspartic protease increased at the beginning of senescence and was maintained at a high level, implicating this protease in proteolysis during the course of leaf senescence. Two proteases, proteasome beta subunit A1 and senescence‐associated gene 12, were induced and continued to increase during the later phase of senescence, suggesting that these proteases are more specifically involved in the proteolysis processes occurring at the final stages of leaf senescence.     

The Genetic Reprogramming of Polyamine Homeostasis During the Functional Assembly,Maturation, and Senescence-Specific Decline of the Photosynthetic Apparatus in Hordeum vulgare

Polyamines (PAs) are ubiquitous aliphatic amines important and, in many cases, essential for plant growth, abiotic stress response, and tolerance. Here we provide evidence for genetic reprogramming of PA homeostasis that occurs during the de-etiolation, maturation, and senescence of the primary leaf in Hordeum vulgare (barley). We analyzed expression levels of key genes in the anabolic and catabolic branches of PA metabolism throughout the life cycle of etioplasts, at all steps of the functional assembly of the photosynthetic apparatus, and during leaf senescence. The changes in the total PAs titer of the leaf were followed throughout the different developmental stages. Furthermore, we align all three stages of the photosynthetic performance (rapid light-dependent de-etiolation, phase of optimal efficiency, and senescence-induced deterioration) with the changes in PA homeostasis. Finally, we focus on two phases during aging (early and late senescence) and we present their bioenergetic (for example, PSII maximal efficiency, ATPase conductivity) and genetic profiles, with emphasis on sensitive parameters that describe this process for the photosynthetic apparatus and PA metabolism, respectively. In conclusion, the fine tuning of PA homeostasis is regulated by the simultaneous genetic reprogramming of the anabolic and catabolic branches of PA metabolism and adjusts all the developmental changes from de-etiolation to maturation and senescence.     

Penetration into rice tissues by brown planthopper and fine structure of the salivary sheaths

The fine structure of the salivary sheaths in plant tissues can provide important information on homopteran probing and ingestion behaviors. Salivary sheaths secreted by the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and their tissue pathway were investigated using light, scanning electron, and transmission electron microscopy. About half of the salivary flanges on the surface of the food substrate were connected with internal salivary sheaths. Only 43% of the salivary sheaths showed side branches. Many sculpture‐like protuberances and small cavities had been formed on the outer surface of the salivary sheath, but the sheath lumen circumferences were sealed. Brown planthoppers showed a preference for probing and leaving salivary sheaths in the susceptible rice variety TN1 rather than in the resistant variety B5 during the first 2 days of the experiments. The salivary sheaths in rice tissues reached the inner tissue layer of the leaf sheaths and stems, but were mostly observed to end in the first and second layer of the leaf sheaths. Brown planthoppers also preferred to probe into the thick segment of the outer leaf sheath. After ingestion by the insect, the cytoplasm in both phloem and companion cells degraded and the main organelles were lost. Numerous small vesicles were found in most of the phloem cells, but cell walls remained intact. Large numbers of symbiont‐like structures were observed inside the salivary sheath lumen. These results indicated that BPH has complicated feeding behaviors, which warrants further investigation.     

Cuticular wax deposition in growing barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis>) leaves commences in relation to the point of emergence of epidermal cells from the sheaths of older leaves

In grasses, leaf cells divide and expand within the sheaths of older leaves, where the micro-environment differs from the open atmosphere. By the time epidermal cells are displaced into the atmosphere, they must have a functional cuticle to minimize uncontrolled water loss. In the present study, gas chromatography and scanning electron microscopy were used to follow cuticular wax deposition along the growing leaf three of barley (Hordeum vulgare L.). 1-Hexacosanol (C₂₆ alcohol) comprised more than 75% of extractable cuticular wax and was used as a marker for wax deposition. There was no detectable wax along the first 20 mm from the point of leaf insertion. Deposition started within the distal portion of the elongation zone (23–45 mm) and continued beyond the point of leaf emergence from the sheath of leaf two. The region where wax deposition commenced shifted towards more proximal (basal) positions when the point of leaf emergence was lowered by stripping back part of the sheath. When relative humidity in the shoot environment was elevated from 70% (standard growth conditions) to 92–96% for up to 4 days prior to analysis, wax deposition did not change significantly. The results show that cuticular waxes are deposited along the growing grass leaf independent of cell age or developmental stage. Instead, the reference point for wax deposition appears to be the point of emergence of cells into the atmosphere. The possibility of changes in relative humidity between enclosed and emerged leaf regions triggering wax deposition is discussed.     

Rice Resistance to Sheath Blight Mediated by Potassium

This study investigated the effect of potassium (K) on sheath blight (Rhizoctonia solani) development on rice plants from cultivars BR‐IRGA 409 and Labelle grown in nutrient solution containing 0, 50 and 100 mm of K. Sheath blight progress on inoculated sheaths was evaluated by measuring the relative lesion length at 48, 72, 96 and 120 h after inoculation (hai). Data were used to calculate the area under relative lesion length progress curve (AURLLPC). The foliar K concentration on leaf sheaths tissue increased by 61.48 and 116.05% to cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates increased from 0 to 100 mm . A linear model best described the relationship between the AURLLPC and the K rates. The AURLLPC decreased by 29.2 and 21.3% for cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates in the nutrient solution increased. It can be concluded that high K concentration on leaf sheaths tissue was important to decrease sheath blight symptoms on rice leaf sheaths.     

芋侧球茎发生发育的形态学机理

观察了魁芋和多子芋腋芽、侧球茎发生发育的形态学变化规律,分析了主球茎顶芽和不同发育期腋芽中蛋白质的组成。结果表明,魁芋每一叶轮上腋芽数目为１;多子芋为３或３个以上,其中一个体积较大。魁芋侧球茎发育初期伸长的速度大于增粗,首先形成圆柱型,然后顶端膨大形成体积很小的侧球茎。多子芽腋芽伸的同时茎部明显变粗,首先形成圆锥型,然后发育成品种特有的形状。根据发育进程将腋芽发育分成ＡＢ１－ＡＢ９个时期,将主球茎     

Characterization of a histidine- and alanine-rich protein showing interaction with calreticulin in rice

Calreticulin (CRT) is a major calcium-sequestering protein in the endoplasmic reticulum and has been implicated in a variety of cellular functions. To analyze the function of CRT in rice, a yeast two-hybrid protein interaction assay was used for identifying interacting proteins. Fourteen of 17 interacting cDNA clones found coded for a novel histidine- and alanine-rich protein (OsHARP) of 342 amino acid residues. The mRNA expression level of OsHARP was up-regulated in rice seedlings treated with gibberellin (GA), but not ABA and showed a similar pattern as OsCRT mRNA. Rice plants transformed with the OsHARP promoter-GUS construct showed GUS staining in the basal parts of leaf sheaths, and although GUS activity increased when treated with GA₃, it was not as high an increase as when mRNA was analyzed. To elucidate the role of OsHARP in leaf sheath elongation, antisense OsHARP transgenic rice lines were constructed. The antisense OsHARP transgenic rice plants were consistently shorter than the vector control under normal conditions. To examine whether OsHARP expression would affect other proteins, basal leaf sheaths from antisense OsHARP transgenic rice plants were analyzed using proteomic techniques. In antisense transgenic-rice OsHARP plants, OsCRT was down-regulated and the levels of 20 other proteins were changed compared to the pattern of the vector control. These results signify an important role of HARP in rice leaf sheath cell division or elongation and suggest that CRT may interact with HARP during certain stages of development.     

Observations on penetration of Barley leaves by the aphidRhopalosiphum maidis (Fitch)

Summary Penetration of leaves of barley,Hordeum vulgare L., by the corn leaf aphid,Rhopalosiphum maidis (Fitch), was studied with light, phase, and electron microscopes. Penetration of epidermis and mesophyll was largely intercellular, that of vascular bundles or veins largely intracellular. Like other aphids,R. maidis secretes a salivary sheath which surrounds the stylets. When mesophyll cells and parenchymatous elements of the veins were penetrated by stylets, their protoplasts were pushed to one side by intruding sheath material; hence, the protoplasts were not punctured by the stylets, although sometimes the plasmalemma of penetrated cells was ruptured by sheath material. The salivary sheaths ended more or less abruptly outside the walls of sieve elements being fed upon, the maxillary stylets projecting beyond the sheaths and into the sieve elements. Before penetrating a functional sieve element the aphid apparently flushes its stylets in order to clear them for ingestion of food. Salivary and food canals merge near the tips of the maxillary stylets to form a single canal, which ends short of the tips.This research was supported by the U.S. National Science Foundation (GB-8330).     

COMPARATIVE BUNDLE SHEATH AND MESOPHYLL DIFFERENTIATION IN THE LEAVES OF THE C4 GRASSES PANICUM EFFUSUM AND P. BULBOSUM

The two C₄ Panicum species examined differ in C₄ acid decarboxylation type and in developmental origin of bundle sheaths in major veins of their leaf blades. In Panicum effusum R.Br. (NAD-malic enzyme type) both mesophyll (PCA) and chlorenchymatous bundle sheath (PCR) cells are derived from ground meristem. In contrast, in Panicum bulbosum H.B.K. (NADP-malic enzyme type), bundle sheath cells are derived from procambium, while mesophyll develops from ground meristem. To test the hypothesis that the developmental divergence of bundle sheath and mesophyll cells would occur earlier when these two tissues had different ontogenetic origins (in P. bulbosum) than when these tissues had the same origin (in P. effusum), the development of major veins in each species was investigated. We measured cell length and cross sectional area, plastid and mitochondrial number, plastid area, vacuole area fraction, wall thickness and fraction adjacent to intercellular space using direct and digitizer measurements of transmission electron micrographs of leaf cross sections of successive developmental stages. Many of the statistically significant changes in the structural parameters measured occurred late in development of both species. The magnitude of developmental change in P. effusum PCR cells was sometimes more dramatic, viz. changes in cell and PCR plastid area, and in mitochondrion number per cell. However, earlier divergence of PCR and PCA length and volume, and wall fraction adjacent to intercellular space in P. bulbosum than in P. effusum indicates that ontogenetic origin of PCR cells from procambium could determine the timing of at least some developmental events.