Dynamics of the Nuclear Complement of Giant Cells Induced by Meloidogyne incognita

The total numbers of nuclei in giant cells induced by Meloidogyne incognita in pea, lettuce, tomato, and broad bean were determined. Mature giant cells from pea had the most nuclei per giant cell with a mean of 59 ± 23, lettuce had the fewest with 26 ± 16, and tomato and broad bean were intermediate. The rate of increase in numbers of nuclei for all plant species was greatest during the first 7 days after inoculation. No mitotic activity was observed in giant cells associated with adult nematodes. Number of nuclei per giant cell doubled each day during the period of greatest mitotic activity, but number of total chromosomes per giant cell increased 20-fold per day at the same time. The hypothesis is presented that factor(s) responsible for the polyploid, mulfinucleate condition characteristic of giant cells may be different from factor(s) responsible for aneuploid numbers of chromosome per nucleus or for nuclear aberrations such as the presence of linked nuclei.     

Increased activity of aminopeptidase in the cotyledons of red light-promoted lettuce seeds is controlled by the axis

The first major reserves to be mobilized following germination of light-promoted lettuce seeds ( Lactuca saliva L. cv. Grand Rapids) are the carbohydrates, largely mannans, located within the cell walls of the endosperm. When these have been depleted, the cotyledonary reserves are hydrolysed; the first of these to decline is protein. Water-, salt- and ethanol-soluble proteins are mobilized simultaneously, and coincident with their loss from the cotyledons there is an increase in aminopeptidase activity. The level of enzyme activity increases appreciably in irradiated seeds after about 30 h from the start of imbibition. Essential for this increase, at least initially, is the presence of the axis - first to perceive the light stimulus, and then to produce and/or release a chemical promoter which diffuses into the cotyledons and effects the rise in enzyme activity. Protein synthesis in the cotyledons is a prerequisite for both development and maintenance of the increased aminopeptidase activity.     

Plant growth retardant activity of 4-homoisotwistane derivatives

A variety of simple derivatives of 3-substituted 4-homoisotwistane derivatives were prepared, and their effect on the growth of cucumber seedlings in complete darkness was investigated. The 3-hydroxy derivative was found to show a strong inhibitory activity at 50 μg/ml, so a series of other hydroxy derivatives of 4-homoisotwistane, endo-2-, exo-2-, and 5-hydroxy- and exo-2,3-dihydroxy-4-homoisotwistane were prepared in order to obtain information on structure-activity relationships. The endo-2-hydroxy derivative inhibited the growth of cucumber and the germination of lettuce seed at 12.5 μg/ml. All the hydroxy derivatives tested increased the number of adventitious roots in hypocotyls of kidney bean at 100 μg/ml, but they inhibited root formation at the lowest part of the cuttings, and the effect was again exhibited most strongly by the endo-2-hydroxy compound. It is suggested that the 2- and 3-hydroxy derivatives possess a potent activity as plant growth retardants.     

Pathogenicity of Meloidogyne hapla to Lettuce as Affected by Inoculum Level, Plant Age at Inoculation and Temperature

Pathogenicity of Meloidogyne hapla to lettuce was influenced by inoculum level, age of plant at inoculation and temperature. Top weight of ''Minetto'' lettuce was reduced 32% when 2-week-old lettuce plants were each inoculated with five egg masses. Higher inoculum levels did not further decrease top weight significantly. Inoculation at seeding reduced top growth more than inoculation of 1-, 2- or 3-week-old seedlings. M. hapla reduced growth more at the intermediate (21.1 C night and 26.7 C day), than at the low (15.5 C night and 21.1 C day) or high (26.7 C night and 32.2 C day), temperature regimes.     

Effect of leaf surface extraction on palatability of romaine lettuce to Diabrotica balteata

Abstract The leaf surface of a plant, especially its chemical components, constitutes the first line of resistance to herbivores and other pests. Our previous research indicated that ‘Valmaine’ (Val) romaine lettuce, Lactuca sativa L., was highly resistant to feeding by adult banded cucumber beetle, Diabrotica balteata LeConte, while ‘Tall Guzmaine’ (TG) was highly susceptible. We investigated the leaf surface chemistry of these two cultivars for its possible role in their resistance to D. balteata. Three solvents with different polarity (hexane, methylene chloride, and methanol) were tested to remove leaf surface chemicals, but only methylene chloride and methanol extracts were used in feeding bioassays. Adult D. balteata consumed much more of the leaf tissue of Val and TG when their surface chemicals were removed with methylene chloride, but not methanol, compared to nonextracted leaf tissue, leading us to hypothesize that methylene‐chloride extractable leaf surface chemicals may have a role in the expression of lettuce resistance. However, leaf surface chemicals extracted from Val with methylene chloride were not a deterrent to adult D. balteata when applied to palatable lima bean leaf surfaces at various concentrations in dual‐choice tests. Furthermore, the application of surface extracts from TG did not stimulate beetle feeding in similar choice tests. In a no‐choice feeding test, there was no significant difference in leaf area consumption on lima bean leaves sprayed with extracts of Val or TG. These results suggest that leaf surface chemicals in romaine lettuce do not explain the resistance of Val to adult D. balteata, and that factors inside the leaf may play a role in resistance. We discuss the possibility that the solvent may have increased the palatability of lettuce leaves to D. balteata by causing enzymatic browning and cellular damage, which is likely to have degraded internal feeding deterrents and impaired the plant's ability to emit latex.     

Evaluation of cadmium genotoxicity in Lactuca sativa L. using nuclear microsatellites

Cadmium (Cd) is a non-essential element and is a widespread environmental pollutant. Exposure to cadmium can result in cytotoxic, carcinogenic and mutagenic effects. Mutagenesis is indicative of genetic instability and can be assayed using microsatellites. Microsatellites or simple sequence repeats (SSRs) are composed of tandem repeats of short sequence motifs (1–6 bp) that are polymorphic, mainly in the number of tandem repeated units. Therefore, chromosomic mutations like inversion, deletion or translocation and point mutations can be detected by this type of molecular marker. In this study we have evaluated the mutagenic/genotoxic effects of cadmium in lettuce (Lactuca sativa L.). Five-week-old lettuce plants grown in a modified Hoagland's medium were exposed for a further 14 days to a medium containing 100 μM Cd(NO₃)₂. Genomic DNA was extracted from lettuce leaves and roots, harvested at days 0, 1, 3, 7 and 14, and nine SSRs were tested, amplified and analysed to evaluate microsatellite instability (MSI). Mutagenic effects of cadmium on microsatellite DNA loci were assessed and no MSI was observed in the used markers.     

A computer-controlled multi-titration system to study transpiration, OH− efflux and nitrate uptake by intact lettuce plants (Lactuca sativa L.) under different environmental conditions

Abstract An apparatus is described in which water and nutrient uptake (NO^?₃) and pH were measured and controlled by a microcomputer. Measurements were made twice hourly using appropriate electrodes, both in the nutrient solutions in which the plants were grown and in standard reference solutions. The signals from the electrodes were amplified to a range of 0–10 V and were fed to an A/D converter activated by the computer. The needs for water, NO^?₃, H⁺ and OH^? were then calculated and the necessary adjustments were made to the solutions by automatic injection of the correct amounts to each container in turn. These amounts were records of water and nitrate uptake and pH shift and were saved on disc. The plants were arranged on a turntable which gave additional benefit by smoothing out variations in light intensity. The system allowed a different solution to be maintained for each plant if required.     

纳米二氧化钛对生菜的生长效应分析

为了阐明纳米二氧化钛颗粒(TiO₂NPs)对生菜(Lactuca sativa)生长的影响，采用自行设计的水培装置探究不同浓度TiO₂NPs (300~1 200 mg/L)下，生菜生长和生理生化指标的变化。结果表明，300 mg/L TiO₂NPs能促进生菜幼苗的根长、茎长、叶表面积、鲜重和干重；随着TiO₂ NPs浓度增大，生菜的生长指标呈现下降趋势，但仍优于对照组。生菜体内的抗氧化酶(SOD、POD)在低TiO₂ NPs浓度(300 mg/L)时，活性明显下降；随着TiO₂ NPs浓度增大，这两种抗氧化酶活性逐渐增强。因此，生菜对TiO₂NPs胁迫具有浓度依赖性，表现为“低促高抑”，且能够通过抗氧化酶系统来减轻TiO₂NPs伤害。     

Photoperceptive Site of the Photoinduction of Root Hairs in Lettuce (Lactuca sativa L. cv. Grand Rapids) Seedlings Under Low pH Conditions

Lactuca sativa L. cv. Grand Rapids) seedlings under acidic conditions by a phytochrome-mediated response. Microbeam irradiation of 1 mm root segments with the first (100 Jm⁻²) and second (1,000 Jm⁻²) maxima of the fluence response curve for red light induction of root hair initiation indicated that the ca. 5 mm apical portion of 12 mm long roots was the site of photoperception. The root hair-forming portion of the root was situated at a distance of 1.7 mm from the root tip at the time of red light irradiation and extended (at most 1.5 mm) towards the basal end at a later stage of development, irrespective of which portion of the root was irradiated with red light. Received 13 August 1999/ Accepted in revised form 22 December 1999