Leaf Growth Rate Research Articles

Early response to salt ions in maize (Zea mays L.)

Abscisic acid (ABA) regulates leaf growth and transpiration rate of plants exposed to salt stress. Despite the known fact that cell dehydration is instrumental for the modulation of ABA concentrations when NaCl is high in the external environment, it was never tested as to whether sodium (Na) or chlorine (Cl) also modulate ABA concentrations. To answer this question, a hydroponic study on maize (Zea mays) was established, by exposing plants to 50mM of sodium glucosamide or glucosamine chloride. The effect of both ions on ABA was investigated in an early stage before (i) the salt ions accumulated to toxic tissue concentrations and before (ii) cells dehydrated. This allowed studying early responses to Na and Cl separately, well before plants were stressed by these ions. Gas chromatography–mass spectrometry analysis was used to quantify ABA concentrations in roots and in leaves after a period of 2h after ion application. The transcript abundance of the key regulatory enzyme of the biosynthesis of ABA in maize, the 9-cis-epoxycarotenoid dioxygenase gene viviparous 14, was quantified via real-time quantitative-reverse-transcriptase-polymerase-chain-reaction. The results reveal that Cl and Na induce the increase of leaf tissue ABA concentrations at two hours after plants were exposed to 50mM of the ions. Surprisingly, this effect was more pronounced in response to the Cl component. The increase in the guard-cell regulating ABA concentration correlated with a reduced transpiration. Mainly because of this result we suggest that the early accumulation of ABA is useful in maintaining cell turgor.

Comparative systemic analysis of the cellular growth of leaves and roots in controlled conditions

The comparative cytological analysis of the leaf/root growth of Lolium multiflorum has been performed. It revealed differences of the mentioned above/under-ground organs that express the whole plant’s polarity. To perform accurate and simultaneous growth comparison a climatic-hydroponics system has been implemented. A sharp increase in the epidermis cell length of the leaf meristem has been detected for the first time. It allows the proposal of a new way to demarcate the boundary of the meristem and suggests a lengthed leaf meristem, that is 4 times longer than the root meristem. As the cell cycle duration in leaves and roots is similar, the prolonged leaf meristem and a higher leaf growth rate could be determined by the longer life span of cells in meristem, resulting in more cell cycles. The prolonged meristem provides a significantly higher leaf growth rate, ensuring a functional balance with roots. The elongation zone of the roots is significantly shorter than in leaves, which is caused by the larger relative root elongation rate and the slower meristemic root growth rate. The novelty formulated, i.e., the prolonged leaf meristem, opens theoretical perspectives in longitudinal zonation, in finding molecular markers and provides practical significance for the biology of productivity.

Experimental evidence of warming-induced flowering in the Mediterranean seagrass Posidonia oceanica

Sexual reproduction in predominantly clonal marine plants increases recombination favoring adaptation and enhancing species resilience to environmental change. Recent studies of the seagrass Posidonia oceanica suggest that flowering intensity and frequency are correlated with warming events associated with global climate change, but these studies have been observational without direct experimental support. We used controlled experiments to test if warming can effectively trigger flowering in P. oceanica. A six-week heat wave was simulated under laboratory mesocosm conditions. Heating negatively impacted leaf growth rates, but by the end of the experiment most of the heated plants flowered, while controls plants did not. Heated and control plants were not genetically distinct and flowering intensity was significantly correlated with allelic richness and heterozygosity. This is an unprecedented finding, showing that the response of seagrasses to warming will be more plastic, more complex and potentially more resilient than previously imagined.

Overexpression of Arabidopsis thaliana brassinosteroid-related acyltransferase 1 gene induces brassinosteroid-deficient phenotypes in creeping bentgrass.

Brassinosteroids (BRs) are naturally occurring steroidal hormones that play diverse roles in various processes during plant growth and development. Thus, genetic manipulation of endogenous BR levels might offer a way of improving the agronomic traits of crops, including plant architecture and stress tolerance. In this study, we produced transgenic creeping bentgrass (Agrostis stolonifera L.) overexpressing a BR-inactivating enzyme, Arabidopsis thaliana BR-related acyltransferase 1 (AtBAT1), which is known to catalyze the conversion of BR intermediates to inactive acylated conjugates. After putative transgenic plants were selected using herbicide resistance assay, genomic integration of the AtBAT1 gene was confirmed by genomic PCR and Southern blot analysis, and transgene expression was validated by northern blot analysis. The transgenic creeping bentgrass plants exhibited BR-deficient phenotypes, including reduced plant height with shortened internodes (i.e., semi-dwarf), reduced leaf growth rates with short, wide, and thick architecture, high chlorophyll contents, decreased numbers of vascular bundles, and large lamina joint bending angles (i.e., erect leaves). Subsequent analyses showed that the transgenic plants had significantly reduced amounts of endogenous BR intermediates, including typhasterol, 6-deoxocastasterone, and castasterone. Moreover, the AtBAT1 transgenic plants displayed drought tolerance as well as delayed senescence. Therefore, the results of the present study demonstrate that overexpression of an Arabidopsis BR-inactivating enzyme can reduce the endogenous levels of BRs in creeping bentgrass resulting in BR-deficient phenotypes, indicating that the AtBAT1 gene from a dicot plant is also functional in the monocot crop.

Quantitative Effects of Phosphorus on Maize Canopy Photosynthesis and Biomass

The objective of this study was to quantify the response of maize (Zea mays L.) canopy photosynthesis, development and biomass to P under controlled conditions. Maize was grown in Soil‐Plant‐Atmosphere Research (SPAR) chambers in Beltsville, MD, with four levels of P (0 [L], 0.01 [Ml], 0.05 [M2], and 0.2 [H] mmol P L−1) and three levels of N (2, 5, and 12 mmol L−1). Five destructive harvests for biomass were taken. There was no significant N effect, so only the P effects were analyzed, and chambers were pooled over P treatments. Maximum net canopy carbon assimilation in the two lowest P rates was 0.4 g C plant−1 d−1. Carbon assimilation for the M2 rate was half that of the control (1.3 vs. 2.5 g C plant−1 d−1). End of season biomass was decreased relative to the control by 57% in M2 and 79% in L and M1. Leaf appearance rate and area decreased with increasing P deficiency. Differences in tissue P concentrations varied over a narrow range in the P deficiency treatments, suggesting that continued availability of P to maintain growth was important. Decreases in biomass were due to P‐deficiency‐related decreases in leaf growth and photosynthetic rate. Light interception in the low P treatments was near 90%, suggesting that decreases in photosynthesis and leaf growth were due to P effects on metabolic factors rather than reduction in light interception.

Impact of polyethylene microbeads on the floating freshwater plant duckweed Lemna minor

Microplastics (MP), small plastic particles below 5 mm, have become one of the central concerns of environmental risk assessment. Microplastics are continuously being released into the aquatic environment either directly through consumer products or indirectly through fragmentation of larger plastic materials. The aim of our study was to investigate the effect of polyethylene microbeads from cosmetic products on duckweed (Lemna minor), a freshwater floating plant. The effects of microbeads from two exfoliating products on the specific leaf growth rate, the chlorophyll a and b content in the leaves, root number, root length and root cell viability were assessed. At the same time, water leachates from microbeads were also prepared to exclude the contribution of cosmetic ingredients on the measured impacts. Specific leaf growth rate and content of photosynthetic pigments in duckweed leaves were not affected by polyethylene microbeads, but these microbeads significantly affected the root growth by mechanical blocking. Sharp particles also reduced the viability of root cells, while the impact of microbeads with a smooth surface was neglected. It was concluded that microbeads from cosmetic products can also have negative impacts on floating plants in freshwater ecosystems.

Inter-genotypic differences in drought tolerance of maritime pine are modified by elevated [CO2

Despite the importance of growth [CO 2 ] and water availability for tree growth and survival, little information is available on how the interplay of these two factors can shape intraspecific patterns of functional variation in tree species, particularly for conifers. The main objective of the study was to test whether the range of realized drought tolerance within the species can be affected by elevated [CO 2 ]. Intraspecific variability in leaf gas exchange, growth rate and other leaf functional traits were studied in clones of maritime pine. A factorial experiment including water availability, growth [CO 2 ] and four different genotypes was conducted in growth rooms. A 'water deficit' treatment was imposed by applying a cycle of progressive soil water depletion and recovery at two levels of growth [CO 2 ]: 'ambient [CO 2 ]' (aCO 2 400 μmol mol -1 ) and 'elevated [CO 2 ]' (eCO 2 800 μmol mol -1 ). eCO2 had a neutral effect on the impact of drought on growth and leaf gas exchange of the most drought-sensitive genotypes while it aggravated the impact of drought on the most drought-tolerant genotypes at aCO2. Thus, eCO2 attenuated genotypic differences in drought tolerance as compared with those observed at aCO2. Genotypic variation at both levels of growth [CO2] was found in specific leaf area and leaf nitrogen content but not in other physiological leaf traits such as intrinsic water use efficiency and leaf osmotic potential. eCO2 increased Δ 13 C but had no significant effect on δ 18 O. This effect did not interact with the impact of drought, which increased δ 18 O and decreased Δ 13 C. Nevertheless, correlations between Δ 13 C and δ 18 O indicated the non-stomatal component of water use efficiency in this species can be particularly sensitive to drought. Evidence from this study suggests elevated [CO 2 ] can modify current ranges of drought tolerance within tree species.

Effects of Mowing Height of Cut and Nitrogen on FAO‐56 PM Crop Coefficients for Recreational Turf in the Cool‐Humid Region

Irrigating recreational turf requires ET (evapotranspiration) replacement for water conservation and to sustain optimal leaf growth and turf function under traffic stress. Lysimeter measured actual ET (ETa) can be estimated using a reference crop ET (ETo) from meteorological data adjusted using a crop coefficient (Kc, ETa/ETo) to correct for cultural affects on ETa. Previous studies have not fully investigated the effects of turf culture on Kc. The objective of this research was to develop reliable Kc when ETo is computed using the FAO‐56 Penman‐Monteith equation, with Kc adjusted according to the effects on ETa of two mowing heights of cut (HOC), two N rates, and three species. Creeping bentgrass (CB) as golf turf and Kentucky bluegrass (KB) and perennial ryegrass (PR) as sports‐lawn turf were planted in South Deerfield, MA. Species and two N rates (98 and 196 kg N ha–1 yr–1) were arranged as main plots (3.12 by 1.56 m). Main plots were split according to HOC, with KB and PR mowed at 3.125 and 6.25 cm and CB mowed at 0.3125 and 0.9375 cm. Crop coefficients were calculated as ETa:ETo ratio and using linear regression (slope) estimates during July and August from 2011 to 2013. Results were similar between the two Kc methods. Adjustments to Kc values are necessary to account for variations in leaf growth rates (r = 0.66, n = 48, P ≤ 0.001) caused principally by HOC, with N having some influence on PR. Golf HOC (CB) ranged from 0.90 to 1.00 in Kc while sports‐lawn turf HOC (KB and PR) ranged from 1.15 to 1.25.

A foliar disease simulation model to assist the design of new control methods against black leaf streak disease of banana

Black leaf streak disease (BLSD), caused by the fungal pathogen Mycosphaerella fijiensis, is considered as the most destructive foliar disease of banana. To advance our knowledge of the dynamics of the disease at plant scale as well as of the components of varietal resistance, we designed, calibrated and evaluated a mechanistic model to simulate the disease on a banana plant. The model runs in discrete time at plant scale and describes plant growth and pathogen dynamics under optimal epidemiological conditions. The model is divided into two modules: a deterministic plant sub-model that simulates the simplified architecture and growth of the banana, and a pathogen sub-model that simulates the detailed life cycle of the pathogen including infection, lesion growth, asexual and sexual sporulation, and the dispersal of spores on the plant. The three most influential epidemiological parameters identified by sensitivity analysis of the model (lesion growth rate, infection efficiency, and incubation period) were estimated in a Bayesian framework using Markov chain Monte Carlo methods and acquired data on the dynamics of leaf lesions under natural conditions. The posterior densities provided precise knowledge on pathogen life history traits. The evaluation of the model using an independent data set confirmed the good quality of the predictions. Simulations allowed us to evaluate the impact of host resistance components, auto-infection at plant scale, and of the leaf emergence rate, which is linked with cropping practices, on the severity of BLSD. This foliar disease simulation model will help design new methods of controlling BLSD.

Response of the eelgrass (Zostera marina L.) to the combined effects of high temperatures and the herbicide, atrazine

High temperatures, especially in the summer or during local heat waves, often coincide with high concentrations of herbicides in some estuarine areas during flood plumes. The combined effects of thermal stress (at 26–32°C) and the herbicide atrazine (at concentrations of 0, 3 and 10μgL−1) on eelgrass (Zostera marina L.) were studied in a 7-day exposure experiment. The results showed that both atrazine and temperatures above 30°C inhibited the photosynthetic efficiency and energy conversion potential of the photosystem II (PsiI) as indicated by the effective quantum yield (ΔF/F’m) and the maximum yield (Fv/Fm), respectively. High temperatures (31°C and 32°C) decreased the Chl a content and stopped the leaf growth of eelgrass. Atrazine concentration had no effect on the photosynthetic pigments at all temperatures; however, decreased leaf growth rate was detected at 30°C. A high level of agreement between the observed and predicted inhibition of photosynthesis by an Independent Action (IA) model demonstrates that the combined effects of high temperature and atrazine are more harmful to eelgrass than is a single pressure. The present study adds further evidence for seagrass protection and environmental management under the hypothesis that thermal stress combined with herbicides pose a greater threat to seagrasses.

Population-Level Differentiation in Growth Rates and Leaf Traits in Seedlings of the Neotropical Live Oak Quercus oleoides Grown under Natural and Manipulated Precipitation Regimes.

Widely distributed species are normally subjected to spatial heterogeneity in environmental conditions. In sessile organisms like plants, adaptive evolution and phenotypic plasticity of key functional traits are the main mechanisms through which species can respond to environmental heterogeneity and climate change. While extended research has been carried out in temperate species in this regard, there is still limited knowledge as to how species from seasonally-dry tropical climates respond to spatial and temporal variation in environmental conditions. In fact, studies of intraspecific genetically-based differences in functional traits are still largely unknown and studies in these ecosystems have largely focused on in situ comparisons where environmental and genetic effects cannot be differentiated. In this study, we tested for ecotypic differentiation and phenotypic plasticity in leaf economics spectrum (LES) traits, water use efficiency and growth rates under natural and manipulated precipitation regimes in a common garden experiment where seedlings of eight populations of the neotropical live oak Quercus oleoides were established. We also examined the extent to which intraspecific trait variation was associated with plant performance under different water availability. Similar to interspecific patterns among seasonally-dry tropical tree species, live oak populations with long and severe dry seasons had higher leaf nitrogen content and growth rates than mesic populations, which is consistent with a “fast” resource-acquisition strategy aimed to maximize carbon uptake during the wet season. Specific leaf area (SLA) was the best predictor of plant performance, but contrary to expectations, it was negatively associated with relative and absolute growth rates. This observation was partially explained by the negative association between SLA and area-based photosynthetic rates, which is contrary to LES expectations but similar to other recent intraspecific studies on evergreen oaks. Overall, our study shows strong intraspecific differences in functional traits in a tropical oak, Quercus oleoides, and suggests that precipitation regime has played an important role in driving adaptive divergence in this widespread species.

Plant Spacing Implications for Grafted Grapevine II Soil Water, Plant Water Relations, Canopy Physiology, Vegetative and Reproductive Characteristics, Grape Composition, Wine Quality and Labour Requirements

Vitis vinifera L. cv. Pinot noir vines grafted onto rootstock 99 Richter and grown under six plant spacings (3 x 3 m; 3 x 1,5 m; 2 x 2 m; 2 x 1 m; 1 x 1 m; 1 x 0,5 m) were investigated in terms of canopy dimension and microclimate, soil conditions, canopy physiology, vegetative and reproductive growth characteristics, grape composition, wine quality and labour input. Vines were pruned to six buds/m2 soil surface and supplementary irrigated just after pea berry size and veraison stages. The number of leaf layers, light intensity and air flow generally decreased with closer spacing, whereas relative humidity increased. In contrast to the virtually stable, albeit lower, soil water content of closer-spaced vines, that of wider spacings noticeably decreased from veraison to ripeness. This may be ascribed to the almost continuous seasonal shading of the soil in the case of the narrower spacings, and the generally higher soil temperatures found for the wider spacings. Leaf and bunch water potentials of both wider- and closer-spaced vines decreased during the ripening period. Bunches were more sensitive to water stress. Leaf and bunch water potential coincided with soil water content. The lower photosynthetic activity of closely spaced vines was accompanied by increased transpirational water loss and is mainly ascribed to less favourable canopy microclimate. Despite the supplementary irrigation and slight differences in leaf water potential between spacings, wider-spaced vines apparently grew under less water stress during the ripening period. This was also evident from leaf xylem sap abscisic acid levels at ripeness. Shoot, leaf and berry growth rates apparently increased with narrower spacing, whereas total leaf area per vine decreased. Fresh berry mass of narrow-spaced vines was, however, slightly lower at ripeness. Budding of narrow spacings increased, whereas fertility and bunch mass were reduced, resulting in decreased yield per vine. Optimum berry set and yield per hectare occurred for medium-spaced vines (2 x 2 m, 2 x 1 m); this was also evident on a m2 soil surface basis. Leaf area per fresh mass of widely spaced vines ( 3 x 3 m, 3 x 1,5 m) was much lower than the generally required 10 - 12 cm2 and points to overcropping. Musts of widely spaced vines had less soluble solids and titratable acidity, whereas must pH increased progressively from widely to closely spaced vines. It would seem that widely spaced vines were overcropped due to low cultivar vigour and/or low yielding capacity of the soil, eventually affecting ripening. Grapes from medium-spaced vines had higher anthocyanin levels in the skin. Sensorially, wines made from closer spacings (2 x 2 m, 2 x 1 m, 1 x 1 m, 1 x 0,5 m) scored distincly higher than those from widely spaced vines. Although yield per hectare was higher, closely spaced vines (1 x 1 m, 1 x 0,5 m) needed significantly higher inputs for canopy management, harvesting and pruning. Considering land utilisation, vine performance, wine quality as well as labour input, medium-spaced vines (2 x 2 m; 2 x 1 m) performed optimally.

少分けつ性水稲品種「合川1号」の出葉速度

少分けつ性水稲品種「合川1号」の出葉速度

Improving \u201ccolor rendering\u201d of LED lighting for the growth of lettuce

Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve “color rendering” of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 μmol·m−2·s−1 for a 16 hd−1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the “color rendering” of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2–3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth.

Microvine : A New Model to Study Grapevine Growth and Developmental Patterns and their Responses to Elevated Temperature

Growing standardized plant material in controlled environment can facilitate the disentangling of the many impacts of climate change on grapevine production and quality. Microvine is a natural gibberellic acid insensitive mutant showing dwarfism, early and continuous flowering along the vegetative axes. It was initially proposed as a model for genetics. In this study, we questioned its suitability to facilitate and hasten the characterization of grapevine vegetative and reproductive growth and development patterns as wells as their responses to temperature elevation. A series of experiments were performed in the greenhouse and in growth chambers under either ‘standard’ (25/15°C days/night) or contrasted (from 22/12°C up to 30/25°C) thermal treatments for several weeks. Under ‘standard’ thermal condition, measured temporal patterns of leaf and berry growth were similar among several phytomers along the main axis allowing us to estimate temporal growth patterns from spatial distribution of organ size. These patterns were stable between independent experiments under similar thermal and irradiance conditions. When plants were exposed to contrasted thermal treatments, leaf emergence rate was found linearly related to average daily temperature allowing us to derive a thermal time based model of development. Under cool thermal conditions (22/12°C), the temporal evolution of biochemical parameters was similar to that classically found for grapevine. However, exposing plants to a + 8°C thermal treatment for 450 °Cd revealed strong alterations of the thermal time based developmental program with either acceleration (leaf and internode growth) or delay (flowering, sugar accumulation in berries), as well as major uncoupling between growth and storage in internodes. These results reveal the potential of Microvine to study grapevine responses to the many facets of climate change.

RosettR: protocol and software for seedling area and growth analysis

BackgroundGrowth is an important parameter to consider when studying the impact of treatments or mutations on plant physiology. Leaf area and growth rates can be estimated efficiently from images of plants, but the experiment setup, image analysis, and statistical evaluation can be laborious, often requiring substantial manual effort and programming skills.ResultsHere we present rosettR, a non-destructive and high-throughput phenotyping protocol for the measurement of total rosette area of seedlings grown in plates in sterile conditions. We demonstrate that our protocol can be used to accurately detect growth differences among different genotypes and in response to light regimes and osmotic stress. rosettR is implemented as a package for the statistical computing software R and provides easy to use functions to design an experiment, analyze the images, and generate reports on quality control as well as a final comparison across genotypes and applied treatments. Experiment procedures are included as part of the package documentation.ConclusionsUsing rosettR it is straight-forward to perform accurate, reproducible measurements of rosette area and relative growth rate with high-throughput using inexpensive equipment. Suitable applications include screening mutant populations for growth phenotypes visible at early growth stages and profiling different genotypes in a wide variety of treatments.

Physiological determinants of storage root yield in three cassava genotypes under different nitrogen supply

SUMMARYPhysiological traits can be used to improve the efficiency of selecting suitable genotypes to grow under nitrogen (N) limitation. The objective of the current study was to investigate the relationship between physiological characteristics and storage root yield of three cassava genotypes under three rates of N fertilizer. The experiments were conducted from 2014 to 2016 at farm fields in Thailand. A split-plot randomized complete block design with four replications was used. Three different rates of N fertilizer, i.e., 46·9, 90·0 and 133·2 kg N/ha and three cassava genotypes, Rayong 9, Rayong 11 and Kasetsart 50, were used. Kasetsart 50 had the highest mean performance for most crop traits. Growth rate of stem (SGR), storage root (SRGR) and crop (CGR) during 180–210 days after planting (DAP) and leaf area index (LAI) at 120 DAP were related to storage root dry weight for all three rates of N fertilizer. Storage root growth during 90–120 DAP, CGR during 180–210 DAP and specific leaf area (SLA) at 210 DAP contributed most to storage root dry weight of the three genotypes grown at 46·9 kg N/ha, while the combination of SRGR during 90–120 DAP, SRGR during 180–210 DAP, LAI at 210 DAP and SLA at 210 DAP was best for N fertilizer at 90·0 kg N/ha and the combination of leaf growth rate (LGR) during 180–210 DAP and LAI at 210 DAP was best for N fertilizer at 133·2 kg N/ha.

Genetic Diversity of Salt Tolerance in Miscanthus.

Miscanthus is a woody rhizomatous C4 grass that can be used as a CO2 neutral biofuel resource. It has potential to grow in marginal areas such as saline soils, avoiding competition for arable lands with food crops. This study explored genetic diversity for salt tolerance in Miscanthus and discovered mechanisms and traits that can be used to improve the yield under salt stress. Seventy genotypes of Miscanthus (including 57 M. sinensis, 5 M. sacchariflorus, and 8 hybrids) were evaluated for salt tolerance under saline (150 mM NaCl) and normal growing conditions using a hydroponic system. Analyses of shoot growth traits and ion concentrations revealed the existence of large variation for salt tolerance in the genotypes. We identified genotypes with potential for high biomass production both under control and saline conditions that may be utilized for growth under marginal, saline conditions. Several relatively salt tolerant genotypes had clearly lower Na+ concentrations and showed relatively high K+/Na+ ratios in the shoots under salt stress, indicating that a Na+ exclusion mechanism was utilized to prevent Na+ accumulation in the leaves. Other genotypes showed limited reduction in leaf expansion and growth rate under saline conditions, which may be indicative of osmotic stress tolerance. The genotypes demonstrating potentially different salt tolerance mechanisms can serve as starting material for breeding programs aimed at improving salinity tolerance of Miscanthus.

Protein Degradation Rate in Arabidopsis thaliana Leaf Growth and Development.

We applied 15N labeling approaches to leaves of the Arabidopsis thaliana rosette to characterize their protein degradation rate and understand its determinants. The progressive labeling of new peptides with 15N and measuring the decrease in the abundance of >60,000 existing peptides over time allowed us to define the degradation rate of 1228 proteins in vivo. We show that Arabidopsis protein half-lives vary from several hours to several months based on the exponential constant of the decay rate for each protein. This rate was calculated from the relative isotope abundance of each peptide and the fold change in protein abundance during growth. Protein complex membership and specific protein domains were found to be strong predictors of degradation rate, while N-end amino acid, hydrophobicity, or aggregation propensity of proteins were not. We discovered rapidly degrading subunits in a variety of protein complexes in plastids and identified the set of plant proteins whose degradation rate changed in different leaves of the rosette and correlated with leaf growth rate. From this information, we have calculated the protein turnover energy costs in different leaves and their key determinants within the proteome.

Ecotoxicological assessments show sucralose and fluoxetine affect the aquatic plant, Lemna minor

Pharmaceuticals and personal care products (PPCP) are prevalent in aquatic systems, yet the fate and impacts on aquatic plants needs quantification for many compounds. We measured and detected sucralose (an artificial sweetener), fluoxetine (an antidepressant), and other PPCP in the Portneuf River in Idaho, USA, where Lemna minor (an aquatic plant in the environment and used in ecotoxicology studies) naturally occurs. Sucralose was hypothesized to negatively affect photosynthesis and growth of L. minor because sucralose is a chlorinated molecule that may be toxic or unusable for plant metabolism. A priori hypotheses were not created for fluoxetine due to lack of previous studies examining its impacts on plants. We conducted laboratory ecotoxicological assessments for a large range of concentrations of sucralose and fluoxetine on L. minor physiology and photosynthetic function. Frond green leaf area, root length, growth rate, photosynthetic capacity, and plant carbon isotopic composition (discrimination relative to a standard; δ13C) were measured among treatments ranging from 0 to 15000nmol/L-sucralose and 0–323nmol/L-fluoxetine. Contrary to our predictions, sucralose significantly increased green leaf area, photosynthetic capacity, and δ 13C of L. minor at environmentally relevant concentrations. The increase of δ 13C from sucralose amendments and an isotope-mixing model indicated substantial sucralose uptake and assimilation within the plant. Unlike humans who cannot break down and utilize sucralose, we documented that L. minor—a mixotrophic plant—can use sucralose as a sugar substitute to increase its green leaf area and photosynthetic capacity. Fluoxetine significantly decreased L. minor root growth, daily growth rate, and asexual reproduction at 323nmol/L-fluoxetine; however, ambiguity remains regarding the mechanisms responsible and the applicability of these extreme concentrations unprecedented in the natural environment. To our knowledge, this was the first study to show aquatic plants can uptake and metabolize sucralose as a carbon source. This study further supports the common notion that L. minor can be useful in bioremediation of PPCP from wastewaters.