Effects of light and spermine on senescence of hydrilla and spinach leaves

Light treatment markedly accelerated chlorophyll loss in Hydrilla (Hydrilla verticillata [L.f.] Royle) over dark treatment whereas such acceleration could not be observed in spinach (Spinacia oleracea L.) leaf segments. Spermine, a polyamine, retarded the loss of chlorophyll in the dark but markedly accelerated this loss in the light during senescence of Hydrilla leaves. However, such effect of spermine in the dark was not so pronounced in spinach. The loss of protein was slower in the light than in the dark in both the species. Spermine arrested the loss of protein (as in spinach) or even raised the protein level over initial (as in Hydrilla). Loss of both soluble and insoluble protein was slower in light than in darkness. Spermine treatment, either in light or darkness, markedly accelerated the loss of soluble protein but raised the level of insoluble protein over initial in both the species. The pattern of change in α-amino nitrogen in either species could be correlated well with that of protein level. In Hydrilla, light increased the soluble protein fraction over initial and this rise was prevented by cycloheximide and not by chloramphenicol. Also, spermine augmented the protease activity (both acid and neutral) while light retarded the rise in protease activity during senescence of either species. Although spermine treatment reduced the leaching of α-amino nitrogen and electrolytes in Hydrilla, it augmented the same in spinach.     

Experimental Feeding of Hydrilla verticillata Colonized by Stigonematales Cyanobacteria Induces Vacuolar Myelinopathy in Painted Turtles (Chrysemys picta)

Vacuolar myelinopathy (VM) is a neurologic disease primarily found in birds that occurs when wildlife ingest submerged aquatic vegetation colonized by an uncharacterized toxin-producing cyanobacterium (hereafter “UCB” for “uncharacterized cyanobacterium”). Turtles are among the closest extant relatives of birds and many species directly and/or indirectly consume aquatic vegetation. However, it is unknown whether turtles can develop VM. We conducted a feeding trial to determine whether painted turtles (Chrysemys picta) would develop VM after feeding on Hydrilla (Hydrilla verticillata), colonized by the UCB (Hydrilla is the most common “host” of UCB). We hypothesized turtles fed Hydrilla colonized by the UCB would exhibit neurologic impairment and vacuolation of nervous tissues, whereas turtles fed Hydrilla free of the UCB would not. The ability of Hydrilla colonized by the UCB to cause VM (hereafter, “toxicity”) was verified by feeding it to domestic chickens (Gallus gallus domesticus) or necropsy of field collected American coots (Fulica americana) captured at the site of Hydrilla collections. We randomly assigned ten wild-caught turtles into toxic or non-toxic Hydrilla feeding groups and delivered the diets for up to 97 days. Between days 82 and 89, all turtles fed toxic Hydrilla displayed physical and/or neurologic impairment. Histologic examination of the brain and spinal cord revealed vacuolations in all treatment turtles. None of the control turtles exhibited neurologic impairment or had detectable brain or spinal cord vacuolations. This is the first evidence that freshwater turtles can become neurologically impaired and develop vacuolations after consuming toxic Hydrilla colonized with the UCB. The southeastern United States, where outbreaks of VM occur regularly and where vegetation colonized by the UCB is common, is also a global hotspot of freshwater turtle diversity. Our results suggest that further investigations into the effect of the putative UCB toxin on wild turtles in situ are warranted.     

Effects of plant growth regulators on Hill activity of submerged aquatic plants during induced senescence

Effects of plant growth regulators on Hill activity during induced senescence of leaves of three submerged aquatic plants Vallisneria spiralis L., Hydrilla verticillata (L.f.) Royle and Potamogeton pectinatus L., and a terrestrial plant Spinacia oleracea L. were studied. Hill activity was reduced by 39.3, 42.7, 45.2 and 245.1 μmol DCIP (2,6-dichloroindophenol) (mg chl)^?1h^?1 in Vallisneria, Hydrilla, Potamogeton and Spinacia, respectively. During induced senescence of isolated mature leaves, Hill activity declined with increasing incubation time in all species. Kinetin (0.23 mM) treatment reduced the loss of Hill activity; while both 0.69 mM ehthrel and 0.075 mM ABA treatments decreased it in each species. The effect of kinetin was greatest in Spinacia, followed by Potamogeton, Hydrilla and Vallisneria, while the effect of either ethrel or ABA or both was greatest in Potamogeton, followed by Spinacia, Vallisneria and Hydrilla. Kinetin pre-treatment for an optimal period (12 h) followed by treatment with either ethrel or ABA partially removed the inhibitory effect of the latter on Hill activity. Pre-treatment of tissues with either ethrel or ABA solution, restricted to 12 h, followed by kinetin treatment markedly reduced the promotive effect of kinetin on the Hill activity of these species.     

Environment of planktic crustaceans as changed by hornwort: Effect on abundance of Daphnia

The effect of submersed hydrophyte Ceratophyllum demersum L. on the abundance of Daphnia longispina O.F. Müller has been studied. The experiments demonstrated that the hydrochemical characteristics in overgrowths of Ceratophyllum are within the limits of tolerance for D. longispina. The concentrations of waterborne phosphates, chlorophyll a, and bacterial biomass increase in the presence of hornwort. In plant overgrowths, Daphnia is suppressed due to the restriction of its movement. In a medium containing only metabolites of Ceratophyllum, the abundance of Daphnia longispina increases due to the enrichment of food resources.     

A comparative study on isoenzyme patterns in Hydrilla verticillata (L.F.) royle from Ireland and North Eastern Poland

In Europe, Hydrilla verticillata (L.f.) Royle (Family: Hydrocharitaceae) is a relatively rare plant which occurs in one lake in Ireland and at a few sites in Poland and the Soviet Union. Isoenzyme studies in Hydrilla plants from Ireland and Poland yielded patterns which were nearly identical, suggesting a close genetic relationship. It has been hypothesized that Hydrilla was more widespread in Europe in the past and that the Irish site represents a relict area.     

Bacterial community structure in freshwater springs infested with the invasive plant species Hydrilla verticillata

The phylogenetic composition and physiological profiles of bacterial communities in freshwater springs were evaluated during the blooming and non-blooming stages of the invasive plant species, Hydrilla verticillata. Community-level physiological profiles (CLPPs) and pyrosequencing of 16S rRNA gene amplicons were used to study potential Hydrilla mediated shifts in the physiological potential and phylogenetic composition of the bacterial community in infested systems. The results of CLPP revealed that the microbes in the Hydrilla invaded sites utilized less substrates during blooming periods than during non-blooming periods of the plant. Spearman’s rank correlation analysis showed some relationships between the relative abundances of bacterial taxa and the Biolog substrate utilization pattern. The relative abundance of the identified taxa showed some striking differences based on the blooming status of Hydrilla and to a lesser extent on site variation. The relative abundance of Actinobacteria, Bacteriodetes, and Verrucomicrobia was generally higher during Hydrilla blooms, while Deltaproteobacteria was generally higher during non-blooming stages of Hydrilla. The detected genera also varied based on the blooming stages of the plant. Based on the findings, it appears that Hydrilla alters the phylogenetic composition and structure of the bacterial community during the blooming stage.     

Two photosynthetic mechanisms mediating the low photorespiratory state in submersed aquatic angiosperms

The submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal exhibited different photosynthetic pulse-chase labeling patterns. In Hydrilla, over 50% of the ¹⁴C was initially in malate and aspartate, but the fate of the malate depended upon the photorespiratory state of the plant. In low photorespiration Hydrilla, malate label decreased rapidly during an unlabeled chase, whereas labeling of sucrose and starch increased. In contrast, for high photorespiration Hydrilla, malate labeling continued to increase during a 2-hour chase. Thus, malate formation occurs in both photorespiratory states, but reduced photorespiration results when this malate is utilized in the light. Unlike Hydrilla, in low photorespiration Myriophyllum, ¹⁴C incorporation was via the Calvin cycle, and less than 10% was in C₄ acids.

Ethoxyzolamide, a carbonic anhydrase inhibitor and a repressor of the low photorespiratory state, increased the label in glycolate, glycine, and serine of Myriophyllum. Isonicotinic acid hydrazide increased glycine labeling of low photorespiration Myriophyllum from 14 to 25%, and from 12 to 48% with high photorespiration plants. Similar trends were observed with Hydrilla. Increasing O₂ increased the per cent [¹⁴C]glycine and the O₂ inhibition of photosynthesis in Myriophyllum. In low photorespiration Myriophyllum, glycine labeling and O₂ inhibition of photosynthesis were independent of the CO₂ level, but in high photorespiration plants the O₂ inhibition was competitively decreased by CO₂. Thus, in low but not high photorespiration plants, glycine labeling and O₂ inhibition appeared to be uncoupled from the external [O₂]/[CO₂] ratio.

These data indicate that the low photorespiratory states of Hydrilla and Myriophyllum are mediated by different mechanisms, the former being C₄-like, while the latter resembles that of low CO₂-grown algae. Both may require carbonic anhydrase to enhance the use of inorganic carbon for reducing photorespiration.

     

Oxygen regime in a fishpond with duckweeds (lemnaceae) and Ceratophyllum

The depth of oxygen and the daily changes in oxygen concentration were assessed by in situ measurements in stands of (1) Lemnaceae; (2) Ceratophyllum; (3) Lemnaceae + Ceratophyllum; and (4) phytoplankton at the peak of the vegetation season. With the aim of excluding the influence of phytoplankton on the diurnal oxygen course, oxygen concentrations were measured in near-natural conditions below both the dense and the loose covers of Lemnaceae, placed in nutrient solution. The duckweeds Lemna minor L. and Spirodela polyrhiza (L.) Schleid. did not release any oxygen into the nutrient solution, despite the fact that their biomass increased by 7 and 4 gm^?2 dry matter per 12 h in the loose and the dense stand, respectively. The oxygen uptake by the bottom sediments reduced the oxygen concentration by up to 2 mg1^?1.     

Zooplankton densities in a Hydrilla infested lake

The number of individuals and species of zooplankton were sampled concurrently with Hydrilla biomass and water quality for one year in a small, eutrophic central Florida lake. Throughout the study, rotifer species and individuals dominated the zooplankton. The abundance of the zooplankton tended to remain high when Hydrilla biomass was at its seasonal low during late winter and early spring. When hydrilla growth increased in the late spring and summer months causing a decrease in total alkalinity, specific conductivity, water color, turbidity, orthophosphate and chlorophyll a concentrations; the abundance of the zooplankton declined. During this time, there was a shift from limnetic to littoral species, principally rotifers. Hydrilla growth did not affect the mean number of cladoceran or copepod species, but may have led to an increase in rotifer species.     

Propagule type influences competition between two submersed aquatic macrophytes

Summary Glasshouse competition experiments with Hydrilla verticillata (L.f.) Royle indicate that plants grown from turions are weaker competitors than those grown from tubers, when compared to the widely distributed macrophyte, Potamogeton pectinatus L. These results support an earlier hypothesis about the importance of propagule size for predicting the outcome of plant competition (Grace 1985; Schaffer and Gadgil 1980). Results of outdoor growth experiments indicate that even though Hydrilla plants from turions are relatively weaker competitors, they are able to grow succesfully in an existing macrophyte bed composed of either, P. pectinatus or P. gramineus. During the early stages of Hydrilla invasion into an area of existing macrophytes, native plants may coexist with Hydrilla. However, once the abundance of Hydrilla tubers in the sediment increases, Hydrilla may displace existing plants.     

Hydrilla verticillata (Hydrocharitaceae), a recent invader threatening Brazil’s freshwater environments: a review of the extent of the problem

Hydrilla verticillata (Hydrocharitaceae) is a highly prolific, rooted submerged macrophyte native to Asia that has invaded aquatic systems worldwide, causing many ecological and human-related problems. Hydrilla recently invaded the Paraná River basin in Brazil, making other ecologically and socially important Brazilian watersheds more susceptible to invasion by this plant. Here, I summarize the relevant information about Hydrilla, focusing on its biotic attributes, abiotic tolerance and effects on ecosystems. The aim of this review is to provide background information to assist with planning for the potential impacts of this species in the Neotropical region (particularly in Brazil) and the development of research, monitoring and management strategies. A wide ecological amplitude, resistance organs, and high growth rates and dispersion ability provide Hydrilla with great potential to invade and infest a variety of habitats, often resulting in important physico-chemical and biotic effects on the environment. Hydrilla is similar in its morphological and ecological aspects to Egeria najas and Egeria densa (South American Hydrocharitaceae), but this non-native species is a superior competitor and can be expected to exert significant pressure in habitats colonized by these native Hydrocharitaceae. Socially important rivers (such as the S?o Francisco River) have a high risk of being infested with Hydrilla, especially in stretches affected by dams, which could prejudice important human activities like hydropower generation. Important wetlands for biodiversity conservation (such as the Pantanal) may also be invaded, but they seem to be more resistant to infestations as long as their natural hydrologies are preserved. Before investing substantial effort to control Hydrilla, managers should weigh the potential costs and benefits of available techniques and consider the potential benefits of Hydrilla in providing ecosystem services.     

Possible mechanisms of light-induced chlorophyll degradation in senescing leaves of Hydrilla verticillata

Light treatment markedly accelerated the chlorophyll loss in senescing leaves of Hydrilla verticillata [(L.f.) Royle] as compared to dark treatment, whereas such acceleration could not be observed in senescing spinach (Spinacia oleracea L.) leaves. The light-induced cholorophyll loss in Hydrilla was retarded slightly by chloramphenicol and markedly by cycloheximide. Catalase (EC 1.11.1.6) activity did not change appreciably in Hydrilla leaves either in light or in darkness, while in spinach it declined markedly in the dark, and light retarded such decline. Peroxidase activity in Hydrilla showed faster increase in light than in darkness, while in spinach it increased only in light during senescence. The activity of phenol(pyrogallol)-specific peroxidase increased markedly in light, and that of ascorbate-specific peroxidase decreased slightly both in light and darkness during senescence of Hydrilla leaves. This rise in phenolspecific peroxidase activity was prevented by cycloheximide treatment. Pretreatment of Hydrilla leaves with monophenol (2,4-dichlorophenol) and o-diphenol (hydroquinone) accelerated and retarded, respectively, the light-induced cholorophyll loss. Pretreatment of Hydrilla leaves with H₂O₂ augmented the chlorophyll loss more markedly in light than in darkness. The endogenous level of H₂O₂ increased more in light than in dark during senescence of Hydrilla leaves. Treatment of Hydrilla leaves with 3-(3.4-dichlorophenyl)-l,l-dimethylurea. a photosystem II inhibitor, prevented both light-induced rise in H₂O: level and chlorophyll loss, but it was without effect in the dark. Retardation of light-induced chlorophyll loss occurred during senescence of Hydrilla leaves when light was given in different photoperiods in a 24-h daily cycle for 6 days instead of as continuous irradiance. There was a negative correlation between the length of the photoperiod and the extent of cholorophyll loss.     

Changes in the Activities of Ribulose 1,5-Bisphosphate and Phosphoenolpyruvate Carboxylases in Submersed Aquatic Angiosperms during Aging

Changes in the activities of ribulose-1,5-bisphosphate carboxylase (RuBPcase) and phosphoenolpyruvate carboxylase (PEPcase) during aging and senescence of leaves of submersed aquatic angiosperms, Potamogeton pectinatus L., Vallisneria spiralis L., and Hydrilla verticillata (L.f.) Royle were studied. The activity of RuBPcase decreased with both aging and senescence in three species. PEPcase activity increased from young to mature leaves in all three plants and also in old leaves of Hydrilla. The ratio of RuBPcase to PEPcase activity was lowest in mature and highest in old leaves, and increased with aging of isolated mature leaves in Potamogeton and Vallisneria, but decreased markedly in Hydrilla with aging and senescence. Kinetin treatment (0.23 mm) increased RuBPcase activity in three species and PEPcase activity in Potamogeton and Vallisneria, but decreased PEPcase activity in Hydrilla. Treatments with 2-chloroethylphosphonic acid (Ethrel, 0.69 mm) and abscisic acid (ABA, 0.075 mm) showed almost an opposite trend.     

Growth and carbon utilization by sprouted propagules of two species of submersed rooted aquatic plants grown in darkness

Hydrilla verticillata (L. f.) Royle tubers from monoecious plants andPotamogeton gramineus L. winter buds were sprouted and allowed to grow in the dark for 120 days. We measured plant length and counted the number of leaves at 2–3 day intervals.Hydrilla grew most rapidly during the first 16–17 days andPotamogeton grew most rapidly during the first 16–25 days. Measurement of propagule carbon content over time indicated that cessation of rapid growth coincided with depletion of tuber carbon by one-half forHydrilla. ForPotamogeton, growth was reduced after 16 to 25 days while the winter bud C half-life was 37 days. Calculations indicated thatHydrilla mobilized 49% andPotamogeton 39% of the initial propagule carbon to support growth. In a second experiment, in which plants were grown in substrate the plants grew taller and produced slightly more leaves per plant.Potamogeton removed from darkness after specified time periods, and allowed to grow for 21 days in a greenhouse recovered from 20–30 days in the dark. Similarly treatedHydrilla plants recovered from up to 80 days in the dark.Potamogeton had mobilized 79% of initial C by the time it was unable to recover from the dark treatment. Combined results for both species indicate that the majority of propagule C was utilized in the first 16 to 30 days following sprouting. In conjunction with an understanding propagule sprouting requirements, this information will be useful in the timing of application for management techniques. The U.S. Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged. The U.S. Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Nutrient content of the aquatic macrophytesElodea canadensis andCeratophyllum in the course of the year

Summary In Lake Vechten, a sandpit near the city of Utrecht (The Netherlands), the submerged macrophyte vegetation is dominated by two species, namelyCeratophyllum demersum andElodea canadensis. In the course of the year both species are able to develop two distinct forms: the normal vegetative form in summer, the dormant form in winter.Elodea is anchored to the substrate by roots,Ceratophyllum by modified leaves, called rhizoids by GLÜCK (1906, 1911). Both species form distinct zones. The depth at which the plants occur abundantly is 0 to 3 m in the case ofElodea and from 3 to 5 forCeratophyllum.     

FOSSIL CERATOPHYLLUM (CERATOPHYLLACEAE) FROM THE TERTIARY OF NORTH AMERICA

Fossil fruits and a vegetative axis assignable to the extant genus Ceratophyllum are described from four North American Tertiary localities. Fossil fruits assignable to the extant species C. muricatum and C. echinatum are reported from the Eocene Green River and Claiborne formations, and the Miocene Esmerelda Formation, respectively. An extinct species, C. furcatispinum, is described from the Paleocene Fort Union Formation and represents the oldest published report of Ceratophyllum in the fossil record. The existence of extant angiosperm species in the Eocene is very unusual and may be attributable in this case to slow evolutionary rates and unusual evolutionary properties associated with hydrophily in the genus Ceratophyllum.     

Environmental conditions and phosphorus removal in Florida lakes and wetlands inhabited by Hydrilla verticillata (Royle): implications for invasive species management

Hydrilla verticillata is considered the most problematic aquatic plant in the United States. In south Florida, Hydrilla dominance has also been documented in treatment wetlands. This paper characterizes (1) environmental conditions which favor Hydrilla growth and (2) understand its nutrient removal capability. Despite its occurrence over a wide range of environmental conditions, Hydrilla abundance increased with increasing pH, alkalinity, total P and total N, and decreased with water depth in selected Florida lakes. No relationship was found between color, Secchi depth and Hydrilla abundance. In several Hydrilla-dominated lakes, mean total P concentration (126 μg/l) at inflow was reduced to 106 μg/l at outflow. The maximum inflow total P concentration in a lake with positive nutrient reduction was 148 μg/l. Total P removal efficiency by Hydrilla-dominated lakes and wetlands was comparable to or higher than systems dominated by emergent and other submerged plants. Mean total P settling rates for lakes and a constructed wetland dominated by Hydrilla were estimated at 19 and 34 m/year, respectively, which were higher than or comparable to similar systems dominated by other aquatic plants. Results from this study suggest that reduction of Hydrilla from constructed wetlands will not likely improve nutrient removal performance.     

32P uptake in three submerged aquatic plant species

Summary Highest uptake of³²P by young shoots of three plant species was observed and lowest by old ones. The uptake of³²P was highest inHydrilla shoots, followed byVallisneria andPotamogeton.Kinetin (0.23 mM) pretreatment (24 h) increased the uptake of³²P, while 0.69 mM ethrel or 0.075 mM ABA decreased it in all species.³²P was transported to the largest extent to the young shoots of the submerged plants and to the smallest extent to the old ones by kinetin pretreatment. Kinetin enhanced the uptake of³²P most inHydrilla shoots, followed byVallisneria andPotamogeton. Ethrel diminished³²P uptake most inPotamogeton shoots and to the smallest extent inHydrilla, while ABA lowered it most inHydrilla shoots and to the smallest extent inPotamogeton. Kinetin, ethrel and ABA can modify the uptake of³²P of these aquatic plants.     

Charophyte occurrence in Ceratophyllum demersum stands

The hornwort Ceratophyllum demersum is a loosely attached to the bottom or free-floating vascular macrophyte, which builds dense stands in nutrient-rich waters. The hornwort stands are usually monospecific communities with a negligible contribution of other aquatic plants. However, some published literature data and our own observations evidenced the co-occurrence of densely growing Ceratophyllum and other macrophytes, including charophytes, which by contrast to hornwort are indicative of clear and less productive waters. Thus, the aim of this study was to identify the charophyte species growing in C. demersum stands and to define the environmental conditions promoting this co-occurrence. In 18 natural lakes of Western Poland, 60 stands of Ceratophyllum demersum were studied in the years 2001–2005. A total of 25 species built the studied stands. As many as eight charophyte species, 13 vascular plants, two moss species and one filamentous alga co-occurred with C. demersum. Among charophytes rare to Poland Chara polyacantha and Nitella gracilis were identified. Nitellopsis obtusa and Chara globularis revealed the highest frequencies along with Myriophyllum spicatum. Morphology of lakes combined with water quality, particularly transparency, appeared to regulate the coexistence of charophytes and C. demersum, macrophytes usually competing with each other.     

GENETIC DIVERSITY IN THE MONOECIOUS HYDROPHILE CERATOPHYLLUM (CERATOPHYLLACEAE)

This study surveys genetic variation in two clonal, monoecious, water-pollinated species that differ in their extent of sexuality and distributional range. Electrophoresis was used to quantify allozyme variability in 12 Wisconsin populations of the widespread Ceratophyllum demersum and the rare C. echinatum. Electrophoretic data indicate that populations of both species have low levels of sexual recombination, low levels of variation, and are structured genetically like inbreeding terrestrial plants. Ceratophyllum populations differ from “typical” clonal terrestrial plants by lower genetic diversity, lower proportions of multiclonal populations, and fewer genotypes per population. In two populations where sexual recombination is documented, heterozygosity is low with significant deficiencies. Monoecy in Ceratophyllum may be related to historical evolutionary factors, whereas vegetative reproduction has a greater influence on the genetic population structure of extant populations. The low genetic identity between C. demersum and C. echinatum supports their recognition as distinct species.