Allelopathic effects ofEupatorium riparium on population regulation of two species ofGalinsoga and soil microbes

Summary Allelopathic effect ofEupatorium riparium Regel, a dominant ruderal weed at higher altitudes in Meghalaya state in north-eastern India, was studied on two common sympatric annual weeds,Galinsoga ciliata (Raf.) andG. parviflora Cav. and on soil microbes. Seed germination and radicle and plumule growth of both species ofGalinsoga were suppressed by the aqueous extract and leachate ofE. riparium. Although the leaf leachate, leaf and litter extracts and litter bed caused considerable reduction in leaf area and seed and dry matter production in both species ofGalinsoga, the effect was much more pronounced onG. parviflora. The inhibitory effect was directly correlated with the concentration of the extract and leachate. The soil microbial population and growth of theGalinsoga spp. declined considerably in the experimental pots where the soil had earlier received leachate of different plant parts ofE. riparium growing in it. The presence of the partly decomposed litter ofE. riparium in the pots reduced soil microbial population and growth of the two weeds much more strongly as compared to the litter in the advanced stages of decomposition. The study also revealed that the abundance and colony growth of the two test fungiviz. Trichoderma viride andAspergillus flavus were differentially affected by the allelopathy ofE. riparium; T. viride being favoured andA. flavus inhibited.     

Leaf architecture of some acanthaceae

Leaf architectural pattern has been studied in 27 genera and 35 species of the Acanthaceae. The major venation pattern conforms to pinnate camptodromous with eucamptodromous or festooned brochidodromous secondaries, pinnate craspedodromous inAcanthus ilicifolius and acrodromous inLepidagathis trinervis. Intersecondary veins are common. The marginal ultimate venation is looped. The areoles are variable in size. The vein endings are usually simple, linear or cuved or divide once or twice dichotomously. Isolated vein endings, tracheids, isolated free vein endings and extension cells are observed. Transfusion tracheids are seen inDicliptera verticillata. Miniature vessel elements with simple perforation plates are noticed lying free in the areole or at the end of tracheids inSeriocalyx scaber andThunbergia grandiflora.Elytraria acaulis, Nelsonia canescens andStaurogynae zeylanica exhibit venation pattern shown by majority of the taxa studied, of the Acanthaceae.     

The variations of NPK of cowpea (Vigna unguiculata (L) Walp) leaves with tillage,plant maturity and flooding on a clay soil

Summary The NPK concentrations in cowpea leaves (cv California Blackeye No. 5) with stage of plant development did not vary significantly with tillage treatment but several features of the concentration of these different ions with age, stage of plant development, incidence of flooding and soil water content are significant.In the major rainy season when soil water content was adequate and seldom above field capacity, there was an almost linear increase in the concentration of N and P in the leaves up to 56 days after planting which coincided with fruit development. This suggested that the accumulation of N and P do take place after flowering which occurred 39 days after planting. The pattern of accumulation of N and P in the minor rainy season suggested that flooding and the occurrence of prolonged soil moisture contents above field capacity suppressed the accumulation of these two nutrients. Potassium accumulation was high in the early stages of cowpea growth and declined with age of the crop. Flooding and high soil moisture contents seem to have had little or no effect on potassium accumulation in the leaves. The pattern of accumulation of N and P suggests that the supply of these nutrients to the cowpea plant must remain high up to fruit development and that additional N and P would need to be added to the soil after a flooding event or when the soil moisture content is above field capacity for prolonged periods.     

Changes in water status during water stress at different stages of development in wheat

The dynamics of stomatal resistance and osmotic adjustment in response to plant water deficits and stage of physiological development was studied in the leaves of spring wheat ( Triticum aestivum L., GWO 1809). Plants were germinated and grown in pots in a growth chamber at the Duke University Phytotron to four physiological stages of development (4th leaf, 7th leaf, anthesis, and soft dough), during which time stomatal resistance, total water potential and osmotic potential were measured on the last fully developed leaf of water stressed and non-stressed plants. Pressure potential was obtained by difference. Stomatal closure of the abaxial and adaxial surfaces were independent of each other, each having a different critical total water potential. The total water potential required to close the stomata on the last fully developed leaf were different at different stages of physiological development, decreasing as the plants grew older. The development of osmoregulation in wheat allows the closure of stomata during the vegetative stage at a high total water potential, but insures that stomata remain open from anthesis through the ear filling period to a lower total water potential.     

Photoperiodism and Crassulacean acid metabolism

Measurements of net CO₂ exchange, malate accumulation, properties and capacity of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in leaves of different ages of two short-day dependent Crassulacean acid metabolism (CAM) plants (Kalanchoe blossfeldiana v. Poelln. Tom thumb and K. velutina Welw.) show that, in both species: a) young leaves from plants grown under long days display a CO₂ exchange pattern typical of C₃ plants; b) leaf aging promotes CAM under long-day conditions; c) short-day treatment induces CAM in young leaves to a higher degree than aging under long days; d) at least in K. blossfeldiana, the PEPC form developed with leaf aging under long days and the enzyme form synthetized de novo in young leaves grown under short days were shown to have similar properties. Short days also promote CAM in older leaves though at a lesser extent than in young leaves: The result is that this photoperiodic treatment increases the general level of CAM performance by the whole plant. The physiological meaning of the control of PEPC capacity by photoperiodism could be to afford a precisely timed seasonal increase in CAM potentiality, enabling the plant to immediately optimize its response to the onset of drought periods.Abbreviations CAM Crassulacean acid metabolism - PEP phosphoenolpyruvate - PEPC phosphoenolpyruvate carboxylase (EC 4.1.1.31) - LD long day - SD short day     

Leaf vasculature in sugarcane (Saccharum officinarum L.)

The vascular system of the leaves of Saccharum officinarum L. is composed in part of a system of longitudinal strands that in any given transverse section may be divided into three types of bundle according to size and structure: small, intermediate, and large. Virtually all of the longitudinal strands intergrade, however, from one type bundle to another. For example, virutually all of the strands having large bundle anatomy appear distally in the blade as small bundles, which intergrade into intermediates and then large bundles as they descend the leaf. These large bundles, together with the intermediates that arise midway between them, extend basipetally into the sheath and stem. Most of the remaining longitudinal strands of the blade do not enter the sheath but fuse with other strands above and in the region of the blade joint. Despite the marked decrease in number of bundles at the base of the blade, both the total and mean cross-sectional areas (measured with a digitizer from electron micrographs) of sieve tubes and tracheary elements increase as the bundles continuing into the sheath increase in size. Linear relationships exist between leaf width and total bundle number, and between cross-sectional area of vascular bundles and both total and mean cross-sectional areas of sieve tubes and tracheary elements.     

Mechanism of effect of aging on membrane transport in leaf strips of Centranthus ruber: Possible ethylene involvement in cutting shock

Cerulenin has been used to investigate the mechanism by which leaf strips of Centranthus ruber (L.) Lam et D.C. increase their capacity for solute uptake during a period of incubation in CaSO₄ (aging). -Aminoisobutyric acid was used to assess uptake capability. The leaf strips developed their uptake capacity for at least 8–10 h after excision. Cerulenin, if added to the aging medium immediately after cutting or at any time during the aging process, almost completely halted this development, but did not bring about loss of the uptake capacity already achieved. That cerulenin was specifically interfering with fatty-acid biosynthesis was indicated by the fact that it drastically depressed incorporation of labelled acetate into the lipid fraction but did not affect the incorporation of labelled alanine. Cycloheximide strongly inhibited the development of uptake capacity, but sensitivity to actinomycin D was not evident for at least 2 h. The results are consistent with the concept that slicing leads to immediate damage to tissue membranes and that aging is a process of membrane repair, involving renewed synthesis of membrane lipids and membrane proteins.The damage to membranes associated with cutting may involve wound ethylene. This is indicated by the following findings: Treatment of aged leaf strips with Ethrel (2-chloroethylphosphonic acid) resulted in drastic loss of their acquired uptake capacity. The strips recovered from such Ethrel-induced loss of uptake capacity while aging in CaSO₄ as they can after cutting. Cerulenin halted recovery of uptake capacity after ethrel treatment just as it did after cutting. Treatment of leaves before cutting with amino-ethoxyvinylglycine somewhat improved the uptake performance of leaf strips immediately after excision.     

Intercellular strands associated with stomata: Stomatal pectic strands

Summary Pectic strands are shown to connect the lower stomatal ledges and to develop across the posterior chamber of a number of plant species. Similar strands are formed between guard cells and subsidiary cells, and between epidermal cells.     

Pattern of dry-matter accumulation,and nitrogen concentration and uptake as influenced by levels and methods of nitrogen application in rainfed-upland rice

Summary Dry-matter accumulation, and concentration and uptake of nitrogen increased with increasing level of nitrogen at all the stages of crop growth. The differences in nitrogen concentration due to nitrogen levels were greatest at panicle initiation stage and started becoming narrower with the advancement in crop age. Split application of nitrogen with its heavier fractions at tillering and panicle initiation stages either through soil alone or soil+foliage (1/3+1/3+1/3) resulted in higher dry-matter accumulation, and higher nitrogen concentration and uptake than other methods. The crop, on an average, removed 61 kg N/ha. Plants accumulated nearly 15% of the total absorbed nitrogen, up to tillering, 50% up to panicle initiation and 85–90% up to heading. Proportionately lesser nitrogen uptake and dry-matter accumulation at post-heading stage is an indicative of a major constraint for production efficiency of rainfed-upland rice culture.     

Nodulation,nitrogen fixation,leaf area,and sugars content inLablab purpureus as affected by sulfur nutrition

Summary In order to explore interrelations between S nutrition, soluble sugars, leaf area, nodulation and N₂ fixation, greenhouse experiments were done with several levels of S added to perlite-sand cultures or to a moderately S-deficient soil. Sulfur had indirect effects on nodulation and N₂ fixation, possibly by improving sugars supply and N metabolism.In perlite-sand culture, leaf area increased with concentrations of supplied S up to 50 and 200 M for symbiotic and N-treated plants respectively, then decreased at higher concentrations. Plant yield and total sugars content (mg per plant) for the N-treated plants behaved similar to leaf area in response to added S but in the symbiotic plants maximum values were obtained at 100 M S. In soil, Mo had no effect on growth but interacted significantly with S in affecting total sugars content. High levels of S depressed sugars content at low Mo but raised it at high Mo.Sulfur increased the N content of soil-grown plants. It increased the N content of plants grown in perlite-sand culture except at very high levels of S. There was little effect on concentration of N in the shoots. Nitrogen content correlated significantly with leaf area and sugar content, and highly significantly with S concentration in the shoots.