Changes In Relative Growth Rate Research Articles

Removal of mercury by silica-supported ionic liquids: Efficiency and ecotoxicological assessment

Anthropogenic impacts have affected the coastal environment and contributed to its contamination. Mercury (Hg) is widespread in nature and has been shown to be toxic in even the smallest amounts, negatively affecting not only the marine ecosystem but also the entire trophic chain due to its biomagnification. Mercury ranks third on the Agency for Toxic Substances and Diseases Registry (ATSDR) priority list and it is therefore imperative to develop more effective methods than those currently available to avoid the persistence of this contaminant in aquatic ecosystems. The present study aimed to evaluate the effectiveness of six different silica-supported ionic liquids (SIL) in removing Hg from contaminated saline water, under realistic conditions ([Hg] = 50 µg/L), and to ecotoxicologically evaluate the safety of the SIL-remedied water, using as test model the marine macroalga Ulva lactuca. The results revealed that SIL [Si][C3C1im][SCN] (250 mg/L) was the most effective in removing Hg from solution, with a efficiency up to 99 % in just 6 h, that enable to obtain < 1 µg/L Hg (European guideline in drinking water). U. lactuca exposed to either the SIL and/or the remedied water showed no significant changes in relative growth rate and chlorophyll a and b levels, compared to the control condition. Biomarker analysis (LPO, GSH, GSSG, SOD, GPx, CAT and GRed) also showed no significant changes in the biochemical performance of U. lactuca. Therefore, it could be assumed that water treatment with SIL or its presence in an aqueous environment does not pose toxicity levels that could inhibit the metabolism or cause cell damage to U. lactuca.

Are small trees more responsive to nutrient addition than large trees in an evergreen broadleaved forest?

Nitrogen (N) and phosphorus (P) availability exert a profound influence on forest productivity and function. However, forecasting tree responses is still challenging because trait plasticity among different size classes and tree species remains largely unclear.We conducted a field experiment in an evergreen broadleaved forest fertilized with four treatments: +N (100 kg N ha−1 yr−1), +P (50 kg P ha−1 yr−1), N+P (100 kg N ha−1 yr−1 + 50 kg P ha−1 yr−1), and a control. We selected four species across size classes (small trees, DBH < 15 cm; large trees, DBH ≥ 15 cm) to quantify the relative growth rate (RGR) and functional traits related to the leaf economic spectrum (LES).+P increased the RGR in small trees rather than in large trees, and its effect on RGR varied with tree species in small trees. In contrast, +N and N+P did not affect the RGR in small or large trees. Small trees exhibited greater trait plasticity in light-saturated photosynthetic rate (Pmax) and photosynthetic N and P use efficiencies (PNUE and PPUE) than large trees under P addition. In contrast, nutrient addition did not change LES traits in large trees. Most notably, treatment-induced changes in RGR were significantly correlated with changes in Pmax and PNUE in small trees and with leaf mass per area (LMA) in large trees in this subtropical forest, suggesting that trait plasticity drives tree growth responses.Our results highlight that small subtropical trees have a greater capacity to respond to nutrient alterations and have the potential to change species abundance under future N and P deposition.

Growth analysis of the everbearing strawberry ‘Delizzimo’ under controlled temperature and photoperiod conditions

BackgroundThere is limited information on the effect of environment on vegetative growth in everbearing (EB) strawberry (Fragaria x ananassa Duch.) and its comparison with the situation in seasonal flowering types.MethodsWe investigated the effects of photoperiod (daylengths of 10 and 20 h) and temperature (12, 19 and 26 ℃) on leaf growth, dry matter production and partitioning, concentrations of soluble sugars, starch, and chlorophyll in the F1 hybrid ‘Delizzimo’ grown in a single experiment in daylight phytotron compartments in Norway.ResultsPlants grown in the long photoperiod (LD) and higher temperatures had greater leaf growth and higher dry matter production than those under short day (SD) and low temperature conditions. Growth decreased over the 39 days of the experiment. The changes in growth in the different environments were associated with changes in relative growth rate (RGR) and these were driven by changes in net assimilation rate (NAR) and leaf area ratio (LAR). The plants directed more dry matter to the leaves and crowns under LD and high temperature conditions and less dry matter to the roots, thus increasing the plant’s shoot to root ratio. Long days decreased the concentrations of sugars and starch in most of the tissues, while the effect of temperature was more complex. Higher temperatures increased the concentrations of sugars in the leaves in LD, while starch accumulated in the roots under SD and low temperature conditions. Sucrose accumulated temporarily in the crowns at the time of flower bud formation in LD and higher temperatures.ConclusionsThe results of the experiment demonstrate that the effects of photoperiod and temperature on the vegetative growth of everbearing strawberry are similar to those reported for seasonal-flowering strawberry. Increases in temperature and photoperiod and the resulting enhancement of the RGR was associated with accumulation of soluble sugars (sucrose, glucose and fructose) in the above-ground parts of the plant, whereas low temperature and SD resulted in accumulation of starch in the roots.

Impact of Temperature, Low pH and NH4+ Enrichment on Ecophysiological Responses of a Green Tide Species Ulva australis Areschoug

Ulva are ubiquitous and opportunistic green algae species that easily adapt to various environmental conditions. These algae are responsible for the green tides that cause many environmental and ecological problems in coastal waters. We investigated the physiological responses of Ulva australis under warming, acidification, and eutrophication conditions. The physiological changes in the algae were observed under various combinations of temperature, pH, and NH4+ levels. Combinations of three temperatures (10°C, 20°C, and 30°C), two pH levels (7.80 and 8.20), and two NH4+ concentrations (4 μM and 120 μM) were considered under laboratory conditions. Temperature, NH4+, and pH had significant impact on the photosynthetic and nutrient uptake rates. However, the 12 h observation could not stimulate the seaweed to change the pH in the cultured media. Changes in relative growth rates, photosynthetic efficiency, and variations in tissue C and N were not affected by the interactions between temperature, pH level, and nutrient concentration. It is probable that, due to global warming, the bloom of Ulva australis may continue in warm, acidic, coastal waters with high nutrient levels.

Comparison of plasma membrane H+-ATPase response to acid rain stress between rice and soybean.

Acid rain is a global environmental issue due to inhibiting severely plant growth and productivity. To discover the tolerant mechanism in plants under acid rain stress, we studied the difference in response of two crops (rice and soybean) to simulated acid rain (pH5.0 ~ 2.5) at growth and physiological, biochemical and molecular levels during exposure and recovery periods by hydroponics. By analyzing the change in relative growth rate, chlorophyll content and plasma permeability in rice and soybean, we found that rice could tolerate acid rain above pH3.0 whereas soybean could tolerate acid rain above pH4.5. By RT-PCR analyses, immunoprecipitation and enzyme kinetics study, we observed that pH4.5 acid rain promoted the transcriptional expression of H+-ATPase genes and the phosphorylation of H+-ATPase and increased H+-ATPase activity in the two crops for resisting acid stress. The increased degree in soybean was larger than that in rice. Acid rain at pH3.0 still promoted the transcription regulation to maintain H+-ATPase activity higher in rice for resisting stress but caused irreversible inhibition on express of H+-ATPase and decreased H+-ATPase activity in soybean. All results suggest that the different tolerance in rice and soybean to acid rain stress could be associated with difference in plasma membrane H+-ATPase at transcriptional regulation, post-translational modification and the substrate affinity.

Function of Sitka spruce stone cells as a physical defence against white pine weevil.

Stone cells are a physical defence of conifers against stem feeding insects such as weevils and bark beetles. In Sitka spruce, abundance of stone cells in the cortex of apical shoot tips is associated with resistance to white pine weevil. However, the mode of action by which stone cells interfere with growth and development of weevil larvae is unknown. We developed a bioassay system for testing potential effects of stone cells, which were isolated from resistant trees, on weevil larvae. Bioassays using artificial diet and controlled amounts of stone cells focused on physical defence. We evaluated the effects of stone cells on establishment of neonate larvae, mandible wear and changes in relative growth rates of third instar larvae. Establishment of neonates and relative growth rates of third instars were significantly reduced by stone cells. Stone cells appeared to be indigestible by weevil larvae. Our results suggest that stone cells affect weevil establishment and development by forming a physical feeding barrier against neonate larvae at the site of oviposition, and by reducing access to nutrients in the cortex of resistant trees, which contain an abundance of stone cells in place of a more nutrient rich tissue in susceptible trees.

Growth Analysis of Irrigated ‘Tifton 85’ and Jiggs Bermudagrasses as Affected by Harvest Management

Growth analysis of forage crops allows integration of photosynthesis, respiration, and allocation of photosynthate from estimates of physiological and morphological indices. These measurements help explain differences in growth potential between plants across seasons and in response to harvest management. The objective was to describe and explain patterns of growth of ‘Tifton 85’ (Cynodon spp.) and Jiggs [C. dactylon (L.) Pers.] bermudagrasses to three harvest frequencies (14, 28, and 42 d) during 2 yr. Grasses showed different growth patterns during the cool and warm seasons. Crop growth rate (CGR) was similar during the warm season (69 kg ha–1 d–1), but Jiggs had greater relative growth rate (RGR) and lesser stubble mass and residual leaf mass. Jiggs had greater net assimilation rate (NAR) than Tifton 85 during the warm (14.2 vs. 11.4 kg dry matter [DM] m–2 d–1, respectively) and cool seasons (6.9 vs. 2.5 kg DM m–2 d–1, respectively). Tifton 85 partitioned more biomass to leaf than Jiggs (leaf weight ratio [LWR] of 0.35 vs. 0.28 kg kg–1). The 14‐d harvest frequency reduced CGR, RGR, and NAR of both grasses. Small changes in RGR occurred beyond 28 d of regrowth, but leaf area ratio (LAR) and LWR decreased, suggesting that grasses should be harvested ∼ every 28 d during the warm season. Longer regrowth periods during the cool season increased both CGR and RGR. Harvest management affects differently the growth and morphological components of Jiggs and Tifton 85 in this environment.

Ecotypic variation in growth responses to simulated herbivory: trade-off between maximum relative growth rate and tolerance to defoliation in an annual plant.

It has been hypothesized that slow-growing plants are more likely to maximize above-ground biomass and fitness when defoliated by herbivores than those with an already high relative growth rate (RGR). Some populations of the annual herb Datura stramonium L. can tolerate foliar damage better than others. The physiological basis of this difference is examined here in a comparative study of two ecotypes that differ in tolerance and maximum growth rate, using a growth analytical approach. One hundred and fifty-four plants of each ecotype grown under controlled conditions were suddenly defoliated (35 % of total leaf area removed) and a similar sample size of plants remained undefoliated (control). Ontogenetic plastic changes in RGR and its growth components [net assimilation rate (NAR), specific leaf area and leaf weight ratio (LWR)] after defoliation were measured to determine whether these plastic changes maximize plant growth and fitness. Different ontogenetic phases of the response were discerned and increased RGR of defoliated plants was detected at the end of the experimental period, but brought about by a different growth component (NAR or LWR) in each ecotype. These changes in RGR are putatively related to increases in fitness in defoliated environments. At the intra-specific scale, data showed a trade-off between the ability to grow under benign environmental conditions and the ability to tolerate resource limitation due to defoliation.

Re-analysis of plant CO2 responses during the exponential growth phase: interactions with light, temperature, nutrients and water availability.

Many short-term experiments have been conducted under increasing CO2 but results have been varied and have not yet led to a conclusive quantitative understanding of the CO2 response of plant growth. This may have been partly due to a lack of explicit consideration of the positive feedback inherent in plant growth during periods of exponential growth. This feedback can increase an initial physiological enhancement of relative growth rate (RGR) into a much larger biomass enhancement. To overcome this problem, we re-analysed existing experimental data from 78 publications. We calculated the RGRs of C3 plants and their relative enhancement under elevated CO2 and derived response indices that were independent of the duration of experiments and the RGR at normal atmospheric CO2. The RGR of unstressed plants increased by 14±2% under doubled CO2, with observed RGR enhancement linearly correlated with calculated photosynthetic enhancements (based on the Farquhar-von Caemmerer-Berry photosynthesis model), but at only half their numeric values. Calculated RGR enhancements did not change significantly for temperatures from 12 to 40°C, but were reduced under nutrient limitation, and were increased under water stress or low irradiance. We concluded that short-term experiments can offer simple and cost-effective insights into plant CO2 responses, provided they are analysed by calculating relative changes in RGR during the strictly exponential initial growth phase.

Induced overexpression of cytochrome P450 sterol 14α-demethylase gene (CYP51) correlates with sensitivity to demethylation inhibitors (DMIs) inSclerotinia homoeocarpa

The fungus Sclerotinia homoeocarpa causes dollar spot, the most important turfgrass disease worldwide. Demethylation inhibitor (DMI) fungicides have been relied upon heavily to manage this disease. Presently, populations of S. homoeocarpa with reduced sensitivity or resistance to DMIs are widespread in the United States. Cytochrome P450 sterol 14α-demethylase (ShCYP51) and its flanking regions were identified and sequenced in 29 isolates of S. homoeocarpa with a range of DMI sensitivities. No modifications were found in the gene coding and upstream regions that were consistently related to DMI sensitivity. In the absence of propiconazole, ShCYP51 was expressed at a similar low level among DMI baseline and resistant isolates. In the presence of propiconazole, DMI-resistant isolates were induced to express ShCYP51 at significantly higher levels than baseline isolates by propiconazole at 5 mg L(-1) for 5 h or at 0.5 mg L(-1) for 72 h. The ShCYP51 expression level after 72 h exposure to 0.5 mg L(-1) of propiconazole was linearly related to EC50 values and ΔRG (the change in relative growth rate over time), with R(2) values equal to 83.7 and 90.0% respectively. Induced overexpression of ShCYP51 in resistant isolates following DMI exposure is an important factor determining DMI sensitivity in S. homoeocarpa.

감나무 정단신초의 초기생장에 대한 분석

감나무(Diospyros kaki) 신초의 초기생장을 이해하기 위하여 발아 후 두 달 동안 정단신초의 생장을 성목 '부유'와 '서촌조생'을 대상으로 3년간 경남의 두 지역에서 조사하였다. 정단신초의 신장은 전엽 후 10일 무렵인 4월 하순부터 5월 상순에 가장 왕성하였고 이후 5월 하순까지는 완만하였다. 단위 엽면적은 5월 하순에도 지속적으로 증가하였다. 개화 전 꽃봉오리의 단위 생체중은 5월 상순까지 완만하게 증가하였다가 5월 하순의 개화 후에는 급속하게 증가하였다. 신초신장은 5월 하순까지 대부분 정지되었지만 신초건물중은 5월 동안 직선적으로 증가하였는데, 줄기의 비대 및 잎과 과실의 생장이 계속되기 때문이었다. 5월 하순에 잎이 신초 건물중의 60% 이상, 줄기 건물중은 20% 이하를 차지하였고, 과실의 비율은 7-17%로 높아졌다. 신초의 상대생장률(RGR)은 4월 하순에 하루 <TEX>$213mg{\cdot}g^{-1}$</TEX> 이상이었다가 5월 하순에는 <TEX>$63mg{\cdot}g^{-1}$</TEX> 이하로 감소하였다. 신초의 순동화율(NAR) 변화도 RGR과 비슷하여 4월 하순에 하루 <TEX>$1.9-2mg{\cdot}cm^{-2}$</TEX>에서 5월 하순에는 <TEX>$0.5-0.8mg{\cdot}cm^{-2}$</TEX>로 낮아졌다. 신초생장의 RGR과 NAR 모두 품종 간 차이는 뚜렷하지 않았다. 결론적으로 신초의 초기생장은 저장양분 분배와 재배환경의 영향이 큰 것으로 판단되었다. The growth of terminal shoots of persimmon (Diospyros kaki) was analyzed during the first two months from the time of bud sprout to understand the dynamics of their early growth. Field-grown, mature 'Fuyu' and 'Nishimurawase' trees were used in a three-year study at two locations in Gyeongnam province. The growth of terminal shoots was most active from late April, about 10 days after foliation, to early May, followed by a gradual decline by late May. The increase in leaf area continued unabated throughout May. The weight of a flower bud increased slowly until early May and rapidly after flowering. Although its extension growth had been ceased by late May, dry weight (DW) of a terminal shoot continued to increase almost linearly throughout May due to shoot thickening and continued growth of leaves and fruits. In late May, the leaves and the stem accounted for more than 60% and less than 20% of total DW of a shoot respectively; fruit proportion increased to 7 to 17% by then. Relative growth rate (RGR) of the terminal shoot was higher than 213 <TEX>$mg{\cdot}g^{-1}{\cdot}d^{-1}$</TEX> in late April, but declined to less than 63 <TEX>$mg{\cdot}g^{-1}{\cdot}d^{-1}$</TEX> in late May. Like the pattern of seasonal changes in RGR, net assimilation rate (NAR) of the shoots decreased from 1.9 to 2 <TEX>$mg{\cdot}cm^{-2}{\cdot}d^{-1}$</TEX> to 0.5 to 0.8 <TEX>$mg{\cdot}cm^{-2}{\cdot}d^{-1}$</TEX>. An early-season 'Nishimurawase' did not differ from a late-season 'Fuyu' in RGR and NAR during the first two months of growth. The early growth of the shoots was affected mainly by the reserves redistributed from permanent organs, however, environmental conditions at the time was also involved.

Effect of Coronatine on Antioxidant Enzyme Response of Chickpea Roots to Combination of PEG-Induced Osmotic Stress and Heat Stress

Abiotic stresses, such as high temperature and drought, are major limiting factors of crop production and growth. Coronatine (COR), a structural and functional analog of jasmonates, is suggested to have a role in abiotic stress tolerance. The aim of our study was to examine whether pretreatment with COR enhances the tolerance of chickpea (Cicer arietinum L. cv ICC 4958) roots to PEG-induced osmotic stress, heat stress, and their combination. Therefore, seedlings raised hydroponically in a growth chamber for 15 days were pretreated with or without COR at 0.01 μM for 24 h and then exposed to 6 % PEG 6000-induced osmotic stress or heat (starting at 35 °C and then gradually increased 1 °C every 15 min and kept at 44 °C for 1 h) stress for 3 days. After different treatment periods, the changes in relative growth rate (RGR); malondialdehyde (MDA), proline (Pro), and hydrogen peroxide (H2O2) contents; and the activities of antioxidant enzymes/isoenzymes in roots of chickpea seedlings with or without 0.01 μM COR application were studied. RGR in roots was increased by COR application. Under all stress conditions, H2O2, MDA, and Pro levels increased sharply, but pretreatment with COR significantly reduced them. Moreover, COR increased the activities of H2O2 scavenger enzymes such as catalase (CAT) under heat stress, ascorbate peroxidase (POX) under PEG stress, and CAT and POX under combined stresses. Therefore, COR might alleviate adverse effects of PEG stress and heat stress and combined stresses on roots of chickpea by reduction of H2O2 production, enhancing or keeping the existent activity of antioxidant enzymes, thereby preventing membrane peroxidation.

Toward an understanding of disequilibrium dihedral angles in mafic rocks

The median dihedral angle at clinopyroxene‐plagioclase‐plagioclase junctions in mafic rocks, Θcpp, is generally lower than equilibrium (109° ± 2°). Observation of a wide range of mafic bodies demonstrates that previous work on systematic variations of Θcpp is incorrect in several important respects. First, the spatial distribution of plagioclase compositional zoning demonstrates that the final geometry of three‐grain junctions, and hence Θcpp, is formed during solidification (the igneous process): sub‐solidus textural modification in most dolerites and gabbros, previously thought to be the dominant control on Θcpp, is insignificant. Θcpp is governed by mass transport constraints, the inhibiting effects of small pore size on crystallization, and variation in relative growth rates of pyroxene and plagioclase. During rapid cooling, pyroxene preferentially fills wider pores while the narrower pores remain melt‐filled, resulting in an initial value of Θcpp of 78°, rather than 60° which would be expected if all melt‐filled pores were filled with pyroxene. Lower cooling rates create a higher initial Θcpp due to changes in relative growth rates of the two minerals at the nascent three‐grain junction. Low Θcpp (associated with cuspate clinopyroxene grains at triple junctions) can also be diagnostic of infiltration of previously melt‐free rocks by late‐stage evolved liquids (the metasomatic process). Modification of Θcpp by sub‐solidus textural equilibration (the metamorphic process) is only important for fine‐grained mafic rocks such as chilled margins and intraplutonic chill zones. In coarse‐grained gabbros from shallow crustal intrusions the metamorphic process occurs only in the centers of oikocrysts, associated with rounding of chadacrysts.

Ghrelin effects on the activities of digestive enzymes and growth of Lymantria dispar L.

Ghrelin, along with several other hormones, has significant effects on appetite and growth in humans and animals. The aim of our study was to examine changes in relative growth rates, ?- and ?-glucosidase activities and endocrine cell size in the midgut of 4th instar caterpillars of the pest insect Lymantria dispar L. after ghrelin treatment. Four subpicomolar injections of ghrelin (0.3 pmol) or physiological saline were applied every 24 h to two separate groups of fifteen caterpillars. Repeated administration of ghrelin in subpicomolar doses elevated the relative growth rate, induced ?- and ?-glucosidase activities and increased the size of endocrine cells. The results are the first data about ghrelin effects on relative growth rate, digestive enzyme activities and midgut endocrine cells in insects. This information supports the use of this relatively simple model system in future studies of mechanisms underlying digestion in complex organisms.

Differences in morpho-physiological leaf traits reflect the response of growth to drought in a seeder but not in a resprouter Mediterranean species.

Understanding the mechanisms underlying the response of different plant functional types to current and projected changes in rainfall is particularly important in drought-prone areas like the Mediterranean. Here, we report the responses of two species with contrasting leaf characteristics and post-fire regeneration strategies (Cistus ladanifer L., malacophyllous, seeder; Erica arborea L., sclerophyllous, resprouter) to a manipulative field experiment that simulated a severe drought (45% reduction of historical average rainfall). We measured monthly changes in relative growth rate (RGR), specific leaf area (SLA), bulk leaf carbon isotope composition (δ13C), predawn water potential (Ψpd), photosynthetic gas exchange, bulk modulus of elasticity and osmotic potential at maximum turgor (π). Temporal (monthly) changes in RGR of C. ladanifer were correlated with all measured leaf traits (except π) and followed Ψpd variation. However, the temporal pattern of RGR in E. arborea was largely unrelated to water availability. SLA monthly variation reflected RGR variation reasonably well in C. ladanifer, but not in E. arborea, in which shoot growth and δ13C increased at the time of maximum water stress in late summer. The relationship between water availability, and RGR and carbon assimilation in C. ladanifer, and the lack of any relationship in E. arborea suggest that the former has an enhanced capacity to harness unpredictable rainfall pulses compared with the latter. These contrasting responses to water availability indicate that the projected changes in rainfall with global warming could alter the competitive ability of these two species, and contribute to changes in plant dominance in Mediterranean shrublands.

Long-term acclimation of mesophyll conductance, carbon isotope discrimination and growth in two contrasting Picea asperata populations exposed to drought and enhanced UV-B radiation for three years

Two Picea asperata Mast. populations originating from wet and dry climate regions of China were subjected to enhanced UV-B radiation, drought and their combination in a greenhouse for 3 years. Drought treatment caused a significant decrease in photosynthesis, mesophyll conductance ( g m), carbon isotope discrimination ( Δ) and growth characteristics when compared with well-watered treatment. In contrast to the great effects of drought stress, enhanced UV-B radiation showed some but not as substantial negative effects on these parameters. Little interaction effect between drought and UV-B radiation was detected, and the drought effect in combination with enhanced UV-B was not more pronounced than with no enhanced UV-B radiation. These results suggest that enhanced UV-B radiation does not aggravate the drought effect on P. asperata seedlings. The results also showed that the proportional role of the intercellular CO 2 ( C i) decreased, while the role of chloroplastic concentration ( C c) became increasingly important in explaining the high values of carbon isotope composition ( δ 13C), when the water stress progressed in time. In addition, multivariate causal models proposed that there is a direct causal relationship between specific leaf area (SLA) and g m, which is not mediated by leaf N. Besides, there are functional links between g m and photosynthetic capacity ( V cmax). On the other hand, the study showed that net assimilation rate (NAR) is the main driving force for changes in relative growth rate (RGR), especially in low-water environments, and the degree of acclimation of respiration in the light ( R L) is of central importance to the greater role played by NAR in determining variation in RGR.

Salt Tolerance is Associated with Differences in Ion Accumulation, Biomass Allocation and Photosynthesis in Cowpea Cultivars

AbstractCowpea is widely cultivated in arid and semi‐arid regions of the world where salinity is a major environmental stress that limits crop productivity. The effects of moderate salinity on growth and photosynthesis were examined during the vegetative phase of two cowpea cultivars previously classified as salt‐tolerant (Pitiúba) and salt‐sensitive (TVu). Two salt treatments (0 and 75 mm NaCl) were applied to 10‐day‐old plants grown in nutrient solution for 24 days. Salt stress caused decreases (59 % in Pitiúba and 72 % in TVu) in biomass accumulation at the end of the experiment. Photosynthetic rates per unit leaf mass, but not per unit leaf area, were remarkably impaired, particularly in TVu. This response was unlikely to have resulted from stomatal or photochemical constraints. Differences in salt tolerance between cultivars were unrelated to (i) variant patterns of Cl− and K+ tissue concentration, (ii) contrasting leaf water relations, or (iii) changes in relative growth rate and net assimilation rate. The relative advantage of Pitiúba over TVu under salt stress was primarily associated with (i) restricted Na+ accumulation in leaves paralleling an absolute increase in Na+ concentration in roots at early stages of salt treatment and (ii) improved leaf area (resulting from a larger leaf area ratio coupled with a larger leaf mass fraction and larger specific leaf area) and photosynthetic rates per unit leaf mass. Overall, these responses would allow greater whole‐plant carbon gain, thus contributing to a better agronomic performance of salt‐tolerant cowpea cultivars in salinity‐prone regions.

Ontogenetic shift in the scaling of dark respiration with whole‐plant mass in seven shrub species

Summary 1. Recent evidence suggests that metabolic scaling exponents should shift from ≈ 1 to ∼¾ as plants grow from seedlings to mature trees. This study examines whether there is an ontogenetic shift in the scaling exponent of dark respiration with whole‐plant biomass and whether the allometry of dark respiration vs. plant total nitrogen content is consistent with these metabolic scaling relationships. 2. We examined seedling mass, dark respiration, biomass allocation, water and nitrogen contents, and relative growth rates for 351 seedlings of seven shrub species that span three orders of magnitude in total plant mass (i.e. &lt;1 mg to &gt;1 g). 3. Dark respiration increased with increasing seedling mass in each of three growth stages for each species. The scaling exponents for dark respiration vs. plant mass were c. 1·0 during the earliest stage of seedling development (&lt;60 days after germination) but declined in the later two growth stages (&gt;90 and &lt;120 days after seed germination) for five of the seven species studied. However, the metabolic scaling relationship was isometric when the data were pooled for each species across all size classes. 4. With increasing plant size, the biomass allocated by each species to the metabolically active organ (leaf) generally scaled against whole plant biomass with a slope smaller than 1·0 but significantly larger than ¾. 5. Water and nitrogen contents declined with increasing seedling mass and whole plant dark respiration increased disproportionally (i.e. scaling slope &gt;1) with increasing total plant water or nitrogen content, possibly because small seedlings have a lower water and nutrient‐use efficiency compared to larger ones in water‐ and nutrient‐ unlimited habitats. 6. The change in relative growth rate paralleled the ontogenetic shift in the dark respiration vs. mass relationship, which may explain the isometric metabolic scaling relationship if growth efficiency is inversely proportional to seedling mass. 7. We therefore demonstrate an ontogenetic shift in the metabolic scaling during plant ontogeny. Although the proximate mechanisms underlying the shift are not fully understood, we speculate that a contributing factor is the accrual of less metabolically active tissues or organs with increasing total body mass in the form of secondary tissues with high cell wall volume fractions (e.g. wood and phellum).

Regulation of cell shape, wing hair initiation and the actin cytoskeleton by Trc/Fry and Wts/Mats complexes

The two NDR kinase family genes in Drosophila are tricornered ( trc) and warts ( wts). Previous studies on trc have focused on its role in the morphogenesis of extensions of epidermal cells and in dendrite branching and tiling. Studies on wts have focused on its roles as a tumor suppressor, in controlling photoreceptor type and in the maintenance of dendrites. Here we examine and compare the function of these genes in wing cells prior to their terminal differentiation. Mutations in these genes lead to changes in cell shape, cellular levels of F-actin, the timing of differentiation, and the expression of multiple wing hairs and DE-Cadherin. We showed that the effects of wts on all of these processes appear to be mediated by its regulation of the Yorkie transcription factor. We also provide evidence that trc regulates the expression of DE-cadherin and mwh. In addition, we showed that the effects on cell shape and the timing of differentiation appear to be not linked to changes in relative growth rate of cells compared to their neighbors.

Can CO2 enrichment modify the effect of water and high light stress on biomass allocation and relative growth rate of cork oak seedlings?

To test whether the impact of an enriched-CO2 environment on the growth and biomass allocation of first-season Quercus suber L. seedlings can modify the drought response under shade or sun conditions, seedlings were grown in pots at two CO2 concentrations × two watering regimes × two irradiances. Compared to CO2, light and water treatment had greater effects on all morphological traits measured (height, stem diameter, number of leaves, leaf area, biomass fractions). Cork oak showed particularly large increases in biomass in response to elevated CO2 under low-watered (W−) and high-illuminated conditions (L+). Allocation shifted from shoot to root under increasing irradiance (L+), but was not affected by CO2. Changes in allocation related to water limitation were only modest, and changed over time. Relative growth rate (RGR) and net assimilation rate (NAR) were significantly greatest in the L+/W+ treatment for both CO2 concentrations. Changes in RGR were mainly due to NAR. Growth responses to increased light, water or CO2 were strongest with light, medium with water availability and smallest for CO2, in terms of RGR. The rise in NAR for light and water treatments was counterbalanced by a decrease in SLA (specific leaf area) and LMF (leaf mass fraction). Results suggest that elevated CO2 caused cork oak seedlings to improve their performance in dry and high light environments to a greater extent than in well-irrigated and low light ones, thus ameliorating the effects of soil water stress and high light loads on growth.