Consecutive Growth Cycles Research Articles

A study on genotype × environment interactions for the multiple traits of maize hybrids in China

AbstractThe correct interpretation of the adaptability and stability of maize (Zea mays L.) hybrids in different ecological environments is very important for plant breeders. Additive main effect and multiplicative interaction model and genotype main effects and genotype × environment interaction biplot are the two most popular methods in the analysis of genotype × environment interaction in multienvironment trials. We conducted an experiment designed to examine and evaluate the adaptability and stability of four agronomic traits of 19 tested maize genotypes in two consecutive growth cycles across seven provinces including 37 locations using a randomized completely block design with three replicates. The combined ANOVA for all traits showed that the effect of genotype, environment, and genotype × environment interaction were significant at 0.1% probability levels. In order to evaluate multiple agronomic traits more accurately, multitrait stability index (MTSI) as an emerging selection method based on mean performance and stability was adopted. Agronomic trait grain yield (GY) was positively correlated with grain weight per ear and growth period. In addition, it was also found that GY and bar tip length showed obvious negative correlation. The MTSI is very helpful for breeders who hope to select mean performance and stability based on a variety of agronomic traits because it provides a convenient selection process while taking into account the relevant results of the traits.

Combined environmental stresses induced by drip irrigation positively affect most solar greenhouse grown tomato fruit quality

To evaluate the potential for improvement of greenhouse grown tomato fruit quality under drip irrigation, this experiment was conducted in arid Northwest China for two consecutive growth cycles from 2017 to 2018 (summer and winter). Drip and furrow irrigation with different designed soil wetting proportions were employed in this study, and irrigation amounts were less in the drip than furrow irrigation. Results showed that the organoleptic quality, nutritional quality and antioxidant activity of tomato fruits generally improved under drip irrigation. However, compared with furrow irrigation, fruit fresh weight and size were significantly lower under drip irrigation in summer cycle, and the improvements in fruit quality attributes were relatively small in winter cycle. The combined environmental stresses, characterized by lower soil water content, higher air temperature, soil temperature and day and night temperature difference, were responsible for the improvements in fruit quality under drip irrigation. According to the correlation network analysis, firmness, b*, lycopene, β-carotene and total phenol were amongst the fruit quality parameters that essentially differed between drip and furrow irrigation. Furthermore, total phenol was important for the responses of tomato fruits to the combined environmental stresses under drip irrigation. In conclusion, drip irrigation in a naturally ventilated solar greenhouse could improve tomato fruit quality while achieving water-saving simultaneously.

Drip irrigation provides a trade-off between yield and nutritional quality of tomato in the solar greenhouse

To address the twin issues of food and nutrition security, the focus of agricultural production should be shifted from biomass productivity to nutritional gains. The objectives of this study were to evaluate the impact of conversion from furrow to drip irrigation on the yield components, water productivity (WP), nutritional yield (NY) and nutritional water productivity (NWP) of tomato during two consecutive growth cycles (2017–2018) in a greenhouse in the arid area of Northwest China. Results showed that the environment under drip irrigation was more beneficial to the accumulation of phytochemicals and the formation of total antioxidant activity in tomato fruits, which also significantly increased the NWP. However, the notable decline in single fruit fresh weight reducing the tomato yield significantly under drip irrigation in summer, while the WP and NY were similar to furrow irrigation. This indicated that the NY of tomato was mainly determined by the fruit yield, while the NWP was strongly affected by the mass concentration of nutrients. In contrast, no difference was found in the single fruit fresh weight and tomato yield between drip and furrow irrigation in winter, which related to the similar environmental conditions, while the WP and NY were significantly higher under drip irrigation. In summary, the potential and water use efficiency in nutrient production of tomato were enhanced under drip irrigation, and the improvement of fruit quality can offset the negative effect of yield reduction. Therefore, drip irrigation can achieve a good balance between the high yield and superior quality of tomato fruits, meanwhile reducing the pressure on the environment caused by horticultural production. We propose that the drip irrigation should be employed in the greenhouse in arid areas for tomato production, and the concepts of NY and NWP can be further applied to other horticultural crops with high nutritional value.

Bioavailability of soil Cu, Fe, Mn and Zn from soil fractions

Cationic micronutrients bioavailability depends on the chemical characteristics of soil fractions. Fourteen soils received individual doses of five micronutrients (Cu, Fe, Mn, Zn, B) arranged in seven treatments set according a Baconian Matrix. The soils incubated with treatments during 15 days had corn cultivated in greenhouse for 30 days, in three consecutive growth cycles. The cationic micronutrients were determined in the corn shoots after each growth cycle. Soil samples collected before the first and after each growth cycle had the available concentrations of Cu, Fe, Mn and Zn determined by single extractions (Mehlich-1 and DTPA-pH 7.3) and by sequential extraction. Correlation analysis was performed for the Cu, Fe, Mn and Zn concentrations determined in the corn shoots, the available concentrations of Cu, Fe, Mn and Zn in the soils (Mehlich-1 and DTPA) and the concentrations of Cu, Fe, Mn and Zn in the soil fractions (sequential extraction). The distribution of available metals forms in fractions reflected their affinity with soil components. Soil available Cu correlated with Cu bound to organic matter. The exchangeable fraction was the main source of soil available Mn and Zn. The Fe availability related mainly to the Mn oxides, Fe oxides, and exchangeable fractions. The plants absorbed Cu mainly from the Mn-oxides and organic matter fractions. Manganese absorbed by plants originated from the exchangeable and Mn-oxides fractions. The Zn absorbed by plants originated mainly from the exchangeable fraction. Correlations of single metal extractions (Mehlich-1 and DTPA) with Cu, Mn and Zn contents in plants were positive.

Nutrient content of solvent-extracted castor meal separated in granulometric fractions by dry sieving and applied as organic fertilizer

Castor meal is the main by-product of the industrial oil extraction of castor seed (Ricinus communis L.). It was observed that castor meal could be separated by sieving into apparently distinct fractions. This study measured the relative weight and the nutrient content of six granulometric fractions of castor meal separated by sieving and tested the hypothesis that the fractions with lower N content have a longer residual effect when used as organic fertilizer. Samples of solvent-extracted castor meal were sieved in meshes with openings varying from 9.5 to 0.11 mm. The relative weight of each fraction was measured and calculated, and the nutrient content was determined. In another experiment, the meal was sieved into only three fractions for being tested as organic fertilizer for cotton (Gossypium hirsutum L.) plants for two consecutive growth cycles without additional organic fertilization. The finest fraction (particles < 0.11 mm) had a relative weight of 3.53 %, and the highest relative weight (32.85 %) was found in the fraction with particles between 1.0 and 2.0 mm. The finer were the particles, the higher was the content of N, P, K, Mg, and S, and the lower was the content of Ca. All the castor meal fractions were effective as organic fertilizer for cotton plants. The only difference among fractions was the nutrient content. The evolution of CO2 by microbial respiration confirmed that all the three fractions of castor meal were completely mineralized within one month. Castor meal fractions had no residual effect for supplying N to cotton plants cultivated in the same soil for the second cycle without additional organic fertilization.

The impacts of AMPEP K+ (Ascophyllum marine plant extract, enhanced with potassium) on the growth rate, carrageenan quality, and percentage incidence of the damaging epiphyte Neosiphonia apiculata on four strains of the commercially important carrageenophyte Kappaphycus, as developed by micropropagation techniques

Four strains of Kappaphycus spp. (viz. K. alvarezii—tambalang brown and green, K. striatus—sacol green) and K. malesianus (aring-aring) were grown in Semporna, Sabah, for three consecutive growth cycles from August 2018 to January 2019, each for a duration of 45 days. The study was established in order to determine the impacts of a commercially produced phyco-stimulant: Ascophyllum marine plant extract powder, enhanced with potassium (i.e., AMPEP K+) on micropropagated Kappaphycus strains on the mean daily growth rate (DGR), quality characteristics of extracted, refined carrageenan from the harvested biomass (i.e., yield, viscosity, and gel strength), and the percentage incidence of the damaging, endophytic Neosiphonia apiculata, while in open water cultivation. Results showed that the AMPEP K+-treated thalli were significantly different (P < 0.01), in terms of the three major assessment criteria used in this study. Amongst the four cultivars, and under the conditions tested, K. striatus was the most resistant to the incidence of N. apiculata, particularly when treated with AMPEP K+. The use of the brown seaweed-derived extract, as a phyco-stimulant, applied to a commercially cultivated, red seaweed for the promotion of thallus growth, reduction of biotic stress caused by endophytes, and important improvements to commercially valuable traits, such as carrageenan quality, are encouraging. It is recommended that these protocols should be adopted in crop management to assist the Malaysian seaweed industry.

Analysis of capsaicinoid biosynthesis pathway genes expression in callus cultures of Capsicum chinense Jacq. cv. ‘Umorok’

The placental tissue of the highly pungent chilli cultivar, Capsicum chinense Jacq. cv. ‘Umorok’, is used as explants for callus induction. Callus cultures were subcultured after every 32 days and growth curves for a period of six consecutive growth cycles were studied till a stable capsaicinoids producing callus cultures were obtained. The capsaicinoids content in placental tissue explants decreased gradually during the first 2 months of culture as the explants dedifferentiated to form friable callus while the biomass and capsaicinoid content did not show much change in the subsequent growth cycles. The maximum callus biomass of 7.8 g freshweight (FW) or 0.56 g dry weight (DW) per culture were obtained on the 24th day of every growth cycle and the maximum average capsaicinoids content (1.6 mg g−1 FW capsaicin and 0.78 mg g−1 FW dihydrocapsaicin) were obtained on the 20th day of every growth cycle. To investigate the underlying dynamics for capsaicinoid biosynthesis during callus formation, comparative gene expression analysis of the genes involved in capsaicinoid biosynthesis pathway were also studied by qRT-PCR analysis. When compared with placental tissue, all the studied genes showed reduced expression during callus formation, especially putative aminotransferase (pAMT) and pungent gene 1 (Pun1), which were extensively down regulated from the 3rd month onwards in the callus cultures. Therefore, the present study revealed that the down-regulated expression of mainly two putative genes in capsaicinoid biosynthetic pathway (pAMT and Pun1) resulted in lower accumulation of capsaicinoids in callus cultures compared to placental tissues of fruits. The present study reports the gene expression analysis of the genes involved in capsaicinoid biosynthesis pathway during callus formation from placental tissue explants of Capsicum chinense Jacq.

Impacts of Ascophyllum marine plant extract powder (AMPEP) on the growth, incidence of the endophyte Neosiphonia apiculata and associated carrageenan quality of three commercial cultivars of Kappaphycus

Three commercial cultivars of Kappaphycus (e.g., K. alvarezii—Crocodile and Giant) and K. striatus (Sacol) were grown in Semporna, Sabah, for three consecutive growth cycles, each for a duration of 45 days. The study intended to determine the impacts of Ascophyllum marine plant extract powder (AMPEP) on the daily growth rates (DGR), percentage incidence of endophytic Neosiphonia apiculata, and the commercial, quality characteristics of extracted carrageenan from the harvested biomass (i.e., yield, viscosity, and gel strength). Results showed that the performances of AMPEP-treated thalli were significantly different (P < 0.01), in terms of the three major assessment criteria used in this study. Amongst the three cultivars and under the conditions tested, K. striatus was the most resistant to the incidence of N. apiculata, especially when treated with AMPEP. The use of AMPEP as a red seaweed biostimulant for the promotion of thallus growth rate, reduction of biotic stress caused by endophytes, and important improvements to commercially valuable traits, such as carrageenan quality, are encouraging and could be adopted in crop management protocols to assist the industry.

Speciation and dynamics of phosphorus in some organically amended soils of southwestern Nigeria

Availability of soil phosphorus (P) is a function of its dynamics and can be improved by using organic amendments. Experiments were carried out to determine the effect of poultry manure (PM) on soil P fractions and bioavailability to soybean (Glycine max). Soils from ten farmers’ fields in Southwest Nigeria, were used for incubation and pot experiments. Treatments were five rates of PM (0, 2.5, 5.0, 7.5 and 10 t ha−1). Triplicate units in incubation and pot experiments were arranged in Completely Randomised Design. Soybean was grown for three consecutive growth cycles of seven weeks each and soil samples were analysed for Saloid P, Al-P, Fe-P, Ca-P, occluded P, reductant soluble P, and residual P. Results indicated that Fe-P was the dominant active inorganic P in the soils while residual P was the dominant inactive inorganic-P in most of the soils. In the pot experiment, application of poultry manure significantly increased organic P in the soils in the first growth cycle, but decreased slightly in second growth cycle. Highest and lowest (P ≤ 0.05) organic P values were observed in soil samples from Ayetoro and Odeda, respectively. In the pot experiment, application of PM reduced P fixation and occluded P fraction in the soils. There was general increase in available P in most of the soils considered despite increase or decrease in other forms of P. Poultry manure reduced the fixation of P and release of occluded phosphorus. Generally, Poultry manure significantly improved soil P fractions and plant P tissue concentrations.

Cultivation study of the marine microalga Picochlorum oculatum and outdoor deployment in a novel bioreactor for high-density production of algal cell mass

Microalgae are considered a promising source of renewable diesel and jet fuel. Currently, large-scale microalgae cultivations are performed in open ponds because of their low capital and operating costs, but they generally suffer from low cell mass yield and high risk of contamination. A novel, cost-effective, and modular horizontal bioreactor (HBR) for algae cultivation was developed, as described in the present study. The HBR was designed to keep costs low and was engineered to minimize water and energy use while enhancing CO2 and nutrient uptake. The selected marine microalgal strain, Picochlorum oculatum (Nannochloris oculata), has shown potential for biofuel production. A series of controlled indoor growth experiments was first performed to identify the appropriate P. oculatum growth conditions before demonstrating the HBR performance. Supplying CO2 continuously or by pH-control (pulsed) did not affect culture progression. Growth on urea and nitrate yielded comparable results, while ammonium was less effective. Varying inoculum size from 10% to 15% or 20% had no significant effect on lag time and final cell concentration and comparable growth was measured in the 7–8 pH range. The 150-L HBR's performance was successfully demonstrated outdoors by growing P. oculatum at the identified growth conditions selected to reduce operating costs (pH-controlled CO2, pH 7.5, 10% inoculum, and nitrate). High-density growth was achieved without any contamination issues in outdoor HBR cultivations over 68 days in central Florida during two consecutive growth cycles.

Biofortified maize (Zea mays L.) provides more bioavailable iron than standard maize: Studies in poultry (Gallus gallus) and an in vitro digestion/Caco‐2 model

Iron biofortification is a strategy that alleviates Fe deficiency by improving staple crops, such as maize. Previously, we demonstrated that by using a Caco2 cell model, two maize varieties were developed for high and low Fe bioavailability, yet with similar Fe concentrations. In vitro and in vivo assessments of Fe bioavailability in these lines showed an advantage to the high Fe variety. In the current study, we tested bioavailable Fe in the consecutive growth cycles of these maize lines, in addition we compared the Fe bioavailability between cooked and raw maize +/− added Fe in the maize based diets. Diets were made with 75% w/w maize of either the low (“Low”) or high (“High”) Fe bioavailability maize. Chicks (n=10) were fed the maize diets for 7 weeks. Hemoglobin (Hb), body weight, feed consumption, liver ferritin and gene expression were measured. Duodenal DMT1, Dcytb and ferroportin were higher (P&lt;0.05) in the “Low” groups vs. the “High” groups, indicating adaptation to the “Low” diets. Hb concentrations, Hb‐maintenance efficiency, Hb‐Fe and liver ferritin were higher in the “High“ groups vs. the “Low” groups (P&lt;0.05), indicating greater Fe absorption from the diet and improved Fe status. We conclude that the “High” variety contains more bioavailable Fe than the ”Low” and that maize shows promise for Fe biofortification. Also, the increased Fe bioavailability quality is kept in the biofortified maize daughter lines.

Estimating genetic effects in maternal and paternal half-sibs from tetraploid-diploid crosses in Musa spp.

Ploidy manipulations and interspecific crosses have allowed considerable genetic progress in Musa breeding, but estimation of genetic parameters for parental selection remains a major challenge. This study aimed to determine the components of genetic variance and the relative contribution of genetic effects to phenotypic variation of yield and phenological traits in secondary triploid hybrids from tetraploid–diploid crosses. The hybrids were evaluated in two consecutive growth cycles on a tropical forest site. Non-genetic effects accounted for a large fraction of the variation observed for most traits, except bunch weight. Partitioning of genetic variance into additive and dominance components confirmed the predominant role of additive genetic effects on the expression of bunch weight, fruit filling time, fruit length, plant height, and number of leaves while primarily non-additive effects accounted for suckering behavior and fruit circumference. Maternal general combining ability (GCA) effects accounted for the additive genetic variation in plant height and number of leaves, suggesting that selection for these traits should be carried out in tetraploid clones. Conversely, paternal GCA effects were the primary causes of genetic variation for fruit filling time, bunch weight, and fruit length, suggesting that these characters should be selected for in diploid clones. Specific combining ability (SCA) effects were observed for all traits, except fruit filling time, suggesting that additional genetic gain could be achieved through recombinative heterosis for these traits.

Wood formation in Abies balsamea seedlings subjected to artificial defoliation

We determined the cambial sensitivity and quantified the anatomical differences in xylem of Abies balsamea (L.) Mill. seedlings subjected to artificial defoliation to simulate spruce budworm feeding. Defoliation was performed by removing two-thirds of needles of all current-year shoots for up to four consecutive growth cycles to account for inter- and intra-annual xylem formation. In Experiment 1, xylem development was studied from May to October 2005 in seedlings defoliated at the end of June. In Experiment 2, anatomical features of the xylem were measured along the tree rings formed in 2005 and 2006 during the four cycles of growth and defoliation. Control and defoliated seedlings showed similar patterns of cambial activity and timing of xylem differentiation, although fewer enlarging cells were observed in August to September in defoliated seedlings. Tree-ring widths were similar in control and defoliated seedlings, with thinner rings produced in the greenhouse in winter. No effect of defoliation on cell lumen area was observed, and effects on radial cell diameter and wall thickness were found only occasionally. The results indicate that the A. balsamea seedlings produced all the resources required to maintain stem growth during the four cycles of defoliation.

Irrigation scheduling of plastic greenhouse vegetable crops based on historical weather data

Irrigation scheduling based on the daily historical crop evapotranspiration (ETh) data was theoretically and experimentally assessed for the major soil-grown greenhouse horticultural crops on the Almeria coast in order to improve irrigation efficiency. Overall, the simulated seasonal ETh values for different crop cycles from 41 greenhouses were not significantly different from the corresponding values of real-time crop evapotranspiration (ETc). Additionally, for the main greenhouse crops on the Almeria coast, the simulated values of the maximum cumulative soil water deficit in each of the 15 consecutive growth cycles (1988–2002) were determined using simple soil-water balances comparing daily ETh and ETc values to schedule irrigation. In most cases, no soil-water deficits affecting greenhouse crop productivity were detected, but the few cases found led us to also assess experimentally the use of ETh for irrigation scheduling of greenhouse horticultural crops. The response of five greenhouse crops to water applications scheduled with daily estimates of ETh and ETc was evaluated in a typical enarenado soil. In tomato, fruit yield did not differ statistically between irrigation treatments, but the spring green bean irrigated using the ETh data presented lower yield than that irrigated using the ETc data. In the remaining experiments, the irrigation-management method based on ETh data was modified to consider the standard deviation of the inter-annual greenhouse reference ET. No differences between irrigation treatments were found for productivity of pepper, zucchini and melon crops.

Multivariate analyses of Burkholderia species in soil: effect of crop and land use history.

The assessment of Burkholderia diversity in agricultural areas is important considering the potential use of this genus for agronomic and environmental applications. Therefore, the aim of this work was to ascertain how plant species and land use management drive the diversity of the genus Burkholderia. In a greenhouse experiment, different crops, i.e., maize, oat, barley, and grass, were planted in pots containing soils with different land use histories, i.e., maize monoculture, crop rotation, and permanent grassland, for three consecutive growth cycles. The diversity of Burkholderia spp. in the rhizosphere soil was assessed by genus-specific PCR-denaturing gradient gel electrophoresis (DGGE) and analyzed by canonical correspondence analysis (CCA). CCA ordination plots showed that previous land use was the main factor affecting the composition of the Burkholderia community. Although most variation in the Burkholderia community structure was observed between the permanent grassland and agricultural areas, differences between the crop rotation and maize monoculture groups were also observed. Plant species affected Burkholderia community structure to a lesser extent than did land use history. Similarities were observed between Burkholderia populations associated with maize and grass, on the one hand, and between those associated with barley and oat, on the other hand. Additionally, CCA ordination plots demonstrated that these two groups (maize/grass versus barley/oat) had a negative correlation. The identification of bands from the DGGE patterns demonstrated that the species correlated with the environmental variables were mainly affiliated with Burkholderia species that are commonly isolated from soil, in particular Burkholderia glathei, B. caledonica, B. hospita, and B. caribiensis.

Two separate growth phases during the development of Leishmania in sand flies: implications for understanding the life cycle

The life cycle of Leishmania alternates between two main morphological forms: intracellular amastigotes in the mammalian host and motile promastigotes in the sand fly vector. Several different forms of promastigote have been described in sandfly infections, the best known of these being metacyclic promastigotes, the mammal-infective stages. Here we provide evidence that for Leishmania ( Leishmania) mexicana and Leishmania ( Leishmania) infantum (syn. chagasi) there are two separate, consecutive growth cycles during development in Lutzomyia longipalpis sand flies involving four distinct life cycle stages. The first growth cycle is initiated by procyclic promastigotes, which divide in the bloodmeal in the abdominal midgut and subsequently give rise to non-dividing nectomonad promastigotes. Nectomonad forms are responsible for anterior migration of the infection and in turn transform into leptomonad promastigotes that initiate a second growth cycle in the anterior midgut. Subsequently, leptomonad promastigotes differentiate into non-dividing metacyclic promastigotes in preparation for transmission to a mammalian host. Differences in timing, prevalence and persistence of the four promastigote stages were observed between L. mexicana and L. infantum in vivo, which were reproduced in cultures initiated with lesion amastigotes, indicating that development is to some extent governed by a programmed series of events. A new scheme for the life cycle in the subgenus Leishmania ( Leishmania) is proposed that incorporates these findings.

A mutant of the red microalga Porphyridium sp. (Rhodophyceae) resistant to DCMU and atrazine

A mutant (DC-2) of the unicellular red alga Porphyridium sp. (UTEX 637) resistant to the herbicide diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea, DCMU] was isolated after induced mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine (NNG) at a frequency of 2.1 × 10−5. The minimal concentration of DCMU that completely inhibited growth of the wild type was fiftyfold lower than that required for complete inhibition of the mutant's growth. The mutant was found to be stable over several consecutive growth cycles in the absence of DCMU. When the wild type was exposed to a sub-lethal concentration of DCMU (0.2 μM),its photosynthesis was reduced by up to 72%, while the mutant was not affected by this concentration. In the presence of up to 5.0 μM DCMU the Pmax of the mutant was slightly reduced. However, these concentrations completely inhibited photosynthesis in the wild type. DCMU at a concentration of 0.2 μM decreased the cellular level of phycobiliproteins (phycoerythrin and phycocyanin) but not of chlorophyll a, while no change was recorded in the level of these pigments in the mutant culture grown with 2.5 μM DCMU. Sulphated polysaccharides responded in the opposite way to phycobiliproteins: their total content did not change at 0.2 μM DCMU in the wild type, while that of DC-2 was reduced by 38%. DC-2 mutant proved to be resistant to another photosystem II-inhibiting herbicide, 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine). It grew in a medium containing up to 100-μM atrazine, whereas growth of the wild type was completely inhibited at 5.0 μM.

Production of iridoid glucosides in cell suspension cultures of Penstemon serrulatus: effects of nutritional factors

The cell growth and iridoid production were studied in suspension cultures derived from anther-callus of Penstemon serrulatus. Penstemide and serrulatoloside were major iridoids produced by the cell cultures. Cells (14 days old) produced up to 7.8% of dry weight of penstemide and 5.1% of serrulatoloside. However, formation of both iridoids gradually decreased during consecutive growth cycles. It was possible to improve the quantity of penstemide and serrulatoloside in cell cultures by altering the concentrations of some nutritional factors in the medium. The best results were obtained by increasing the concentration of sucrose (to 5% or 7%); the contents of penstemide and serrulatoloside were 4-fold higher than those obtained in the presence of 3% sucrose. Sucrose concentration from 5% to 7% improved not only the content of iridoids, but also cell growth. Further stimulation of iridoid production was achieved by the selection of high iridoid-producing cell line and transferring the cells to optimized medium.

The role of hydroplasmic pressure in stolonic growth movements in the hydroid, Bougainvillia

AbstractThe effects of intrastolonic pressure on growth activity of the stolon have been ascertained by simultaneously observing the direction of hydroplasmic flow and movements of the stolon tip at close time intervals over many consecutive growth cycles. During each growth cycle (4.4–5.8 minutes long) the tip passes through three distinct stages of inherent retractile potential and associated responsiveness to hydroplasmic pressure. (1) Beginning abruptly at the crest, it displays a strong retractile propensity: low pressure (from proximal flow) elicits a retraction of up to 5.5 μ per 0.2 minute, until the onset of distal flow (increasing pressure) causes it to immediately re‐extend. Thus the depth of retraction is directly determined by the degree and duration of low pressure following the crest. (2) After 1.8–2.0 minutes this retractile tendency becomes suddenly diminished. The tip, if still retracted, now re‐extends regardless of the intrastolonic pressure, and proximal flow during the middle third of the cycle causes only a delayed and shallow retraction to define an intermediate peak. (3) During the final third of the cycle the tip is nonresponsive to hydroplasmic pressure: even under circumstances of lowest pressure, it extends forward to a new crest. It is suggested that this varying retractile capacity may be associated with the pattern of changing thickness of the epidermal layer at the stolon tip.Certain features of the hydroplasmic flow and stolon growth cycles appear to be interrelated, most notably the consistent cessation of proximal flow in relation to a crest or trough. Thus some degree of control seems likely between the stolon tip and the contractile zone responsible for flow.