Decline In Relative Growth Rate Research Articles

The genomic basis of nitrogen utilization efficiency and trait plasticity to improve nutrient stress tolerance in cultivated sunflower.

Maintaining crop productivity is challenging as population growth, climate change, and increasing fertilizer costs necessitate expanding crop production to poorer lands whilst reducing inputs. Enhancing crops' nutrient use efficiency is thus an important goal, but requires a better understanding of related traits and their genetic basis. We investigated variation in low nutrient stress tolerance in a diverse panel of cultivated sunflower genotypes grown under high and low nutrient conditions, assessing relative growth rate (RGR) as performance. We assessed variation in traits related to nitrogen utilization efficiency (NUtE), mass allocation, and leaf elemental content. Across genotypes, nutrient limitation generally reduced RGR. Moreover, there was a negative correlation between vigor (RGR in control) and decline in RGR in response to stress. Given this trade-off, we focused on nutrient stress tolerance independent of vigor. This tolerance metric correlated with the change in NUtE, plasticity for a suite of morphological traits, and leaf element content. Genome-wide associations revealed regions associated with variation and plasticity in multiple traits, including two regions with seemingly additive effects on NUtE change. Our results demonstrate potential avenues for improving sunflower nutrient stress tolerance independent of vigor, and highlight specific traits and genomic regions that could play a role in enhancing tolerance.

Obtaining Salt Stress-Tolerant Eggplant Somaclonal Variants from In Vitro Selection.

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208–305–370 µmol min−1 mg−1 FW) and catalase (CAT) (136–211–238 µmol min−1 mg−1 FW) activities compared to control plants (231 and 126 µmol min−1 mg−1 FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants.

Leaf silicification provides herbivore defence regardless of the extensive impacts of water stress

AbstractAltered precipitation patterns due to climate change are likely to impose water‐deficit stress in plants resulting in changes to specific leaf mass, leaf water content and chemical defences that may impact herbivorous arthropods. Grasses, in particular, accumulate large concentrations of silicon (Si) which provides physical defence against herbivores. Although Si uptake by plants may be affected by water availability, very few studies have investigated the combined effect of water‐deficit stress and Si on insect herbivore performance.We grew tall fescueFestuca arundinaceaSchreb. hydroponically, with and without Si, and half of the plants were treated with 20% polyethylene glycol (PEG) to impose osmotic stress. In all, 11 leaf traits (physiological, chemical and structural) were measured, silicified phytoliths on the leaf surface were visualised using scanning electron microscopy (SEM) in conjunction with X‐ray mapping, and plants were exposed to a chewing insect herbivore [Helicoverpa armigeraHübner (Lepidoptera: Noctuidae)].Although osmotic stress was associated with changes to leaf physiological and chemical traits, including increased specific leaf mass, decreased leaf relative water content and increased leaf nitrogen (N), there was no significant effect onH. armigerarelative growth rate (RGR). However, Si reduced RGR ofH. armigeraby 80%–98% while generating few changes to physiological and chemical leaf traits. Instead, the decline in RGR with Si was associated with changes to leaf structural traits, in particular, a greater density of silicified phytoliths on the leaf surface.Comparison of effect sizes indicated that leaf traits were primarily affected by osmotic stress but not Si, and that herbivore RGR was strongly negatively affected by Si but not osmotic stress. There was no interactive effect between the osmotic stress and Si treatments onH. armigeraRGR or plant traits except for leaf nitrogen and phenolic concentrations. This study provides further support that Si may prove to be beneficial to plants against chewing insect pests and remains robust regardless of water‐deficit stress conditions.A freePlain Language Summarycan be found within the Supporting Information of this article.

INFLUENCE OF THE INTENSITY OF FORMATION ON LIVE WEIGHT OF HEIFERS AND MILK PRODUCTIVITY OF COWS

INFLUENCE OF THE INTENSITY OF FORMATION ON LIVE WEIGHT OF HEIFERS AND MILK PRODUCTIVITY OF COWS

Combined effects of light reduction and ammonia nitrogen enrichment on the submerged macrophyte Vallisneria natans

The decline of submerged plants resulting from low light and high ammonia nitrogen (ammonia-N) has become a serious problem worldwide. In the present study, three levels of ammonia-N concentrations (0, 3 and 6mgL–1) and four levels of light intensity (control, 15, 2.5 and 0.75% underwater light) were designed to investigate the combined effects of low light and high ammonia-N stress on the submerged plant Vallisneria natans. The effects of low light and ammonia-N were examined by measuring the relative growth rate (RGR), chlorophyll content and superoxide dismutase (SOD) and peroxidase (POD) activity in response to the stressors. The decline in RGR and increase in SOD and POD activity in high ammonia-N water were more significant than under low light conditions, indicating that the stress imposed on submerged plants due to ammonia-N enrichment is stronger. Moreover, the combination of ammonia-N enrichment and low light had a greater effect on submerged plants. This study indicates that V. natans were tolerant to ammonia-N concentrations <6mgL–1. Moreover, low light intensity (0.75% underwater light) amplified the toxic effects of ammonia-N, reducing ammonia-N tolerance from <6 to <3mgL–1.

Time indices of multiphasic development in genotypes of sweet cherry are similar from dormancy to cessation of pit growth.

The archetypical double sigmoid-shaped growth curve of the sweet cherry drupe (Prunus avium) does not address critical development from eco-dormancy to anthesis and has not been correlated to reproductive bud development. Accurate representation of the growth and development of post-anthesis ovaries is confounded by anthesis timing, fruiting-density and the presence of unfertilized and defective ovaries whose growth differs from those that persist to maturation. These factors were addressed to assess pre-anthesis and full-season growth and development of three sweet cherry cultivars, 'Chelan', 'Bing' and 'Sweetheart', differing primarily in seasonal duration and fruit size. Volume was calculated from photographic measurements of reproductive buds, ovaries and pits at all phases of development. A population of unfertilized ovaries was produced using bee-exclusion netting to enable a statistical comparison with an open pollinated population to detect differences in size and shape between successful and failing fruit growth. Anthesis timing and fruiting-density were manipulated by floral extinction at the spur and whole-tree scales. Developmental time indices were analysed using polynomial curve fitting of log-transformed data supported by Richards and logistic functions of asymptotic growth of the pit and maturing fruit, respectively. Pre-anthesis growth began at the completion of eco-dormancy. A slight decline in relative growth rate (RGR) was observed during bud scale separation approx. -16 d from anthesis (DFA) before resumption of exponential growth to a maximum about 14 DFA. After anthesis, reduced growth of unfertilized or defective ovaries was partly discriminated from successful fruit at 5 DFA and completely at 25 DFA. Time indices of RGR inflections were similar among cultivars when adjusted for anthesis date alone, until the end of pit growth. Asymptotic growth of the pit underpinned the declining growth rate of fruit at the end of the first exponential growth phase. Duration of the subsequent expansive growth phase accounted for genotypic differences in seasonal duration and final size. Pit size and final fruit size were inversely related to fruiting-density. Developmental differences among early, mid and late maturing cultivars were not detected until the final growth period.

Bio indices for 2,4-D sensitivity between two plant species: Azolla pinnata R.Br. and Vernonia cinerea L. with their cellular responses

In the present experiment a pteridophytic species Azolla and an angiospermic species Vernonia were evaluated on the basis of cellular reactivity for herbicidal action through ongoing concentrations. Initially, both the species recorded a significant activity of IAA-oxidase as mark of IAA metabolism with herbicidal sensitivity. Still, Vernonia species were more affected on 2,4-D mediated auxin catabolism. The loss of auxin concentrations on the tissues by 2,4-D reaction was also reflected on growth parameters including relative growth rate and chlorophyll biosynthesis. In a dose dependent manner Vernonia plants were more affected with loss of chlorophyll content and decline in relative growth rate. On the other hand, both those parameters were adjusted significantly with 2,4-D accumulation in Azolla. The stability of cellular metabolism was documented by significant down regulation of protein and lipid peroxidation with concomitant moderation to superoxide and hydrogen peroxide accumulation. The later two were more vulnerable to damage in the Vernonia plant with profuse accumulation of protein and lipid peroxidation products. Similarly, tissue specific reaction to superoxide and hydrogen peroxide accumulation were distinctly demarcated in two species significantly. As a whole, the cellular responses and metabolite distribution to 2,4-D sensitization are the features to describe bio-indices for aquatic fern species Azolla with comparison to angiospermic species Vernonia.

Coordination between water transport capacity, biomass growth, metabolic scaling and species stature in co-occurring shrub and tree species.

The significance of xylem function and metabolic scaling theory begins from the idea that water transport is strongly coupled to growth rate. At the same time, coordination of water transport and growth seemingly should differ between plant functional types. We evaluated the relationships between water transport, growth and species stature in six species of co-occurring trees and shrubs. Within species, a strong proportionality between plant hydraulic conductance (K), sap flow (Q) and shoot biomass growth (G) was generally supported. Across species, however, trees grew more for a given K or Q than shrubs, indicating greater growth-based water-use efficiency (WUE) in trees. Trees also showed slower decline in relative growth rate (RGR) than shrubs, equivalent to a steeper G by mass (M) scaling exponent in trees (0.77-0.98). The K and Q by M scaling exponents were common across all species (0.80, 0.82), suggesting that the steeper G scaling in trees reflects a size-dependent increase in their growth-based WUE. The common K and Q by M exponents were statistically consistent with the 0.75 of ideal scaling theory. A model based upon xylem anatomy and branching architecture consistently predicted the observed K by M scaling exponents but only when deviations from ideal symmetric branching were incorporated.

Modulation of osmotic adjustment and antioxidant status in salt-stressed leaves of Thermopsis turcica

Thermopsis turcica is distributed naturally in saline soils. Interestingly, how T. turcica can live in harsh salt conditions is unknown. To study its defense responses under salinity, T. turcica was grown in a medium containing 100 and 200 mM NaCl for 7 and 14 days. Physiological parameters, ion contents, reactive oxygen species accumulation, activities of antioxidant enzymes/isozymes, NADPH oxidase enzyme/isozyme, lipid peroxidation (TBARS) and osmolyte contents were investigated. Stress caused a rapid decline in relative growth rate, relative water content and chlorophyll fluorescence (Fv/Fm) under both NaCl treatments. These traits were more suppressed at 200 mM NaCl. The decline in osmotic potential (ΨΠ) with salinity increased the gradient for water flux into the cell and assisted in turgor maintenance. The increased membrane permeability under stress caused the entrance of excess Na+ and K+ into the cell. Stress decreased superoxide dismutase, catalase and peroxidase after 14 days of growth in 200 mM NaCl, whereas glutathione reductase (GR) increased throughout the experiment. While ascorbate peroxidase (APX) increased by 44 % at 7 days, it decreased after 14 days exposure to 200 mM NaCl. 200 mM NaCl caused the highest increase in TBARS at 14 days, indicating a decrease in OH· scavenging activity. Increasing concentrations of salinity caused an increase in glycine betaine (GB) and choline (Cho), though an increase in proline was only observed at 200 mM NaCl for 14 days. Briefly, H2O2 was more efficiently eliminated in 100 mM-treated plants by the ascorbate–glutathione cycle in which APX acts a strong catalyst together with GR. Also, Cho and GB help to maintain osmotic adjustment and cytoplasmic function.

Decline in relative growth rate of 3 juvenile radiata pine clones subjected to varying competition levels in Canterbury, New Zealand

Le taux de croissance relative (RGR) est le rapport entre la croissance et la taille en debut de periode de croissance. L'hypothese selon laquelle RGR serait constant a ete l'objet depuis longtemps de debats dans divers endroits. Dans cette etude, on a quantifie, pendant 3 annees consecutives, les variations de RGR moyen (RGR ) de 3 clones de Pinus radiata D. Don soumis a divers niveaux de competition (desherbage complet, desherbage d'un cercle de 2 m de diametre, desherbage de 1 m de diametre, pas de desherbage). RGR a ete calcule, chaque hiver, a partir de caracteristiques morphologiques et physiologiques de l'evolution du RGR, qui ont ete quantifiees comme suit : formula math. LA = surface foliaire totale du plant, Lw = biomasse foliaire totale du plant, W = biomasse totale du plant, SLA = surface foliaire specifique, c'est-a-dire rapport entre la surface et la biomasse des feuilles, LWR = rapport de biomasse foliaire, c'est-a-dire rapport entre la biomasse foliaire totale du plant et la biomasse totale du plant, T = âge, ULR = efficience folaire unitaire, c'est-a-dire accroissement en biomasse totale du plant rapporte a la surface foliaire. Les resultats obtenus montrent que le RGR est le moins eleve en valeur absolue pour le traitement temoin sans desherbage. RGR diminue dans le temps et avec la hauteur des arbres dans tous les traitements avec desherbage alors qu'il augmente pour le temoin. L'hypothese d'un RGR constant (RGR = k modele) est mise en defaut car il varie dans le temps et avec la hauteur des arbres. L'evolution de RGR pendant la periode en cause est mieux decrite par une fonction exponentielle decroissante: RGR = a + b × exp(-cW). On a mis en evidence des differences d'evolution de RGR selon les clones, le clone 3 presentant un RGR inferieur a celui des deux autres. Ceci est du a une valeur superieure de LWR et de LAR (SLA x LWR) de ce clone. Les principales raisons de la baisse du RGR moyen sont: (1) decroissance de ULR avec l'âge et la taille des plants, (2) changements allometriques, (3) vieillissement physiologique pouvant accentuer les effets d'auto-ombrage. La taille des arbres joue un role plus important que l'âge sur les changements de RGR. Cette etude contribue a supprimer la notion d'un RGR constant tout en fournissant les raisons expliquant la baisse de ce parametre chez les jeunes arbres.

Constraints to growth of annual nettle (Urtica urens) in an elevated CO2atmosphere: Decreased leaf area ratio and tissue N cannot be explained by ontogenetic drift or mineral N supply

The current literature indicates that the stimulation of relative growth rate (RGR) by an elevated atmospheric CO2concentration is transient.Urtica urensL. was exposed to an elevated atmospheric CO2concentration for 26 days to better understand the factors involved in this constraint to growth. Plants were grown hydroponically without nutrient limitation in controlled‐environment cabinets. Consistent with studies of other C3 species, the initial CO2stimulation of RGR ofU. urenswas not sustained and declined in the early stages of exposure. Whilst the decline in RGR was most strongly linked to a reduction in the CO2stimulation of net assimilation rate (NAR), its initial increase was constrained by an early and persistent reduction in leaf area ratio (LAR) due to a decreased specific leaf area (SLA). The decline in NAR could not be linked to any down‐regulation of photosynthetic capacity of individual leaves, despite an accumulation of soluble sugars in them. The reductions in LAR and SLA reflected an accumulation of structural weight in addition to an accumulation of total non‐structural carbohydrate (TNC). To account for the impact of ontogenetic drift on the partitioning of weight and leaf area, this study extends the usual allometric approach to include an analysis of effects on the vertical placement of regression lines (i.e. their elevations). Using this approach, we argue that CO2‐induced reductions in LAR and SLA cannot be explained by ontogenetic drift. By monitoring the tissue N concentration, external N supply was shown unambiguously to be non‐limiting for growth at any plant size. Nevertheless, tissue N was consistently lower in elevated CO2, independent of both ontogeny and TNC accumulation, raising the possibility that the reductions in NAR, LAR and SLA are related to some internal constraint on N utilization.

A Mechanistic Theory for the Relationship between Growth Rate and the Concentration of Nitrate-N or Organic-N in Young Plants derived from Nutrient Interruption Experiments

A simple assumption about nitrate assimilation (incorporating a single parameter to represent the conversion of nitrate into organic-N) has been used to derive mechanistic equations to describe the interrelationships between the concentrations of nitrate-N and organic-N, and dry weight for both the whole plant and its shoot in nutrient interruption experiments. These equations have been combined with a logistic growth model, which was derived from initial assumptions about the way in which plants use stored N under these conditions (Burns, 1994), to quantify effects of nitrate-N and organic-N concentrations on relative growth rate. The models were tested by fitting equations for the predicted relationships to data for young cabbage and lettuce plants, from which estimates of the N assimilation parameter were obtained. The tests showed that predictions of relative growth rate were generally in good agreement with the data over the whole range, as were those for the corresponding relationships between dry weight and either nitrate-N or organic N- concentration, and for the interrelationships between the two forms of N. The most reliable estimates of the N assimilation parameter were obtained from relationships where nitrate-N concentration was the explanatory (independent) variable, because the fits of the corresponding relationships with organic-N were relatively insensitive to large changes in its values. The results showed no evidence of any consistent variation in the size of this N assimilation parameter with the nitrate status of the plant. However, small between-crop differences in its value suggest that shoot nitrate may have been assimilated slightly more efficiently in cabbage than in lettuce.The new model predicts that dry matter production is restricted as soon as the external N supply is withheld (irrespective of the plant nitrate status), producing a slow but consistent decline in relative growth rate which is maintained until nitrate is almost depleted, whereupon it falls rapidly. This implies that the rate of chemical reduction of stored nitrate was not sufficient to maintain an adequate supply of organic-N for the production of new dry matter (even when its concentration in the plants is still high). The results show that nitrate concentrations in excess of 0·1 mmol g-1 are required in plants to avoid serious reductions in growth rate when N is in short supply.

Effects of nitrogen dioxide on biochemical and physiological characteristics of soybean.

One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).

PREWEANING PATTERNS OF GROWTH IN THREE BREED GROUPS OF ANGE BEEF CALVES

Preweaning weight records of 2856 spring-born calves raised at the University of Alberta cattle ranch during a 15-yr period were used in this study. Calving occurred mainly in April and May every year. Calves from three breed groups: Hereford (HE), Beef Synthetic (SY) and Beef Crossbred (XB) were weighed at birth, and in late June, July and August and at weaning in mid-October. They were classified as early, mid-season and late-born according to their birth dates. Average daily gain (ADG) between two consecutive weighings and relative growth rate (RGR) at each interval were analyzed by the least squares method and the adjusted means were plotted against the mean ages of the calves classified at 2-wk intervals to determine the pattern of changes in ADG and RGR with the increase in age of the calf. The SY calves had the highest ADG and RGR followed by the XB and HE (P < 0.05). Bull calves exhibited significantly higher (P < 0.05) absolute growth rate than heifer calves but the sexes were not different in RGR. Preweaning ADG reached a peak when calves were between 110 and 120 d old and declined thereafter. The decline in RGR was linear during the preweaning period. The mean growth rates of the early and mid-season calves were significantly (P < 0.05) higher than that of the late-born calves, and early-born calves showed more consistent gain than the mid-season and late-born calves. A pronounced decline in gain was observed for mid-season and late-born calves in late summer when pasture condition deteriorated indicating that early weaning and supplementation of calves' diet at that stage might be beneficial in sustaining growth rate of the calves. Key words: Cattle (beef), preweaning growth, calf (beef)

Growth, photosynthesis and assimilate partitioning in Lolium temulentum exposed to chilling temperatures

Vegetative plants of Lolium temulentum L, grown at 20°C with an 8 h photoperiod were transferred to either 5 or 2°C (8 h photoperiod) at 4th leaf maturity. Measurement of dry weight gain indicated a marked decline in relative growth rate below 5°C, with growth being reduced as much between 5 and 2°C as between 20 and 5°C. This reduction was not associated with increased mortality and was reversible if plants were returned to 20°C. Tissue explants from cold‐treated plants retained the ability to extend if returned to 20°C Rates of extension in explants were less temperature sensitive than the relative growth rates observed in intact plants. Measurements of photosynthetic capacity, and of the patterns of accumulation of reserve carbohydrate in plants exposed to different temperatures, suggested that the inhibition of growth caused by chilling is not caused by an inability of the plants to fix sufficient carbon.

Effects of Chronic Ozone Exposure on the Growth of Trifolium subterraneum and Trifolium repens

Plants of Trifolium subterraneum and T. repens were exposed to 9 parts per hundred million ozone for 4 h per day, 5 days per week for 5 weeks. Leaf necrosis was apparent after the first week of exposure and this was followed by the death of some leaves and stems. At the end of the exposure, significant reductions were found in total dry weight (30-40%), plant part dry weight and leaf area (ͭ6 30%). Ozone caused a rapid decline in relative growth rate which was related to a reduction in net assimilation rate.

Growth correlations in shoot apices ofBrassica campestris L. during transition to flowering

Growth correlations in the shoot apical meristem during transition to flowering were studied in a quantitative long day plant,Brassica campestris L. cv. Ceres, requiring only one long day for floral initiation. During photo-inductive exposure of the plants, an overall increase in cell number could be observed at the shoot apex concomitant with promotion of leaf initiation. Release from apical dominance and decline in relative growth rate of leaf primordia are reported as early effects of photo-induction. With the onset of floral differentiation, production of new leaf primordia had stopped altogether. Maximum increase in RNA concentration could be noticed in axillary meristems following photoperiodic treatment, whereas in vegetative plants the highest RNA concentration was found in leaf primordia. The significance of these changes occurring during transition to flowering is discussed.