Floral Initiation Period Research Articles

Genetic mechanisms associated with floral initiation and the repressive effect of fruit on flowering in apple (Malus x domestica Borkh).

Many apple cultivars are subject to biennial fluctuations in flowering and fruiting. It is believed that this phenomenon is caused by a repressive effect of developing fruit on the initiation of flowers in the apex of proximal bourse shoots. However, the genetic pathways of floral initiation are incompletely described in apple, and the biological nature of floral repression by fruit is currently unknown. In this study, we characterized the transcriptional landscape of bourse shoot apices in the biennial cultivar, ’Honeycrisp’, during the period of floral initiation, in trees bearing a high fruit load and in trees without fruit. Trees with high fruit load produced almost exclusively vegetative growth in the subsequent year, whereas the trees without fruit produced flowers on the majority of the potential flowering nodes. Using RNA-based sequence data, we documented gene expression at high resolution, identifying >11,000 transcripts that had not been previously annotated, and characterized expression profiles associated with vegetative growth and flowering. We also conducted a census of genes related to known flowering genes, organized the phylogenetic and syntenic relationships of these genes, and compared expression among homeologs. Several genes closely related to AP1, FT, FUL, LFY, and SPLs were more strongly expressed in apices from non-bearing, floral-determined trees, consistent with their presumed floral-promotive roles. In contrast, a homolog of TFL1 exhibited strong and persistent up-regulation only in apices from bearing, vegetative-determined trees, suggesting a role in floral repression. Additionally, we identified four GIBBERELLIC ACID (GA) 2 OXIDASE genes that were expressed to relatively high levels in apices from bearing trees. These results define the flowering-related transcriptional landscape in apple, and strongly support previous studies implicating both gibberellins and TFL1 as key components in repression of flowering by fruit.

Cloning and Characterization of Two FLOWERING LOCUS T-like Genes from Rubber Tree (Hevea brasiliensis)

Two Flower locus T-like genes were isolated and characterized in rubber tree. Both of them were found to have conserved genomic characteristics of the phosphatidylethanolamine-binding protein family and their encoding proteins possess conserved key amino acid residues of FT. RT-qPCR results showed that HbFT1 was restricted in mature leaves, male and female flowers whereas HbFT2 showed the main expression in reproductive organs. Both of them can be induced by short-day conditions but with different expression patterns and regulated by temperature. Transgenic wild-type Arabidopsis can reduce the flowering time and change plant morphogenesis, with fewer rosette leaves and terminal inflorescence to some degrees, as well as the phenotype of ft-10 can also be successfully rescued by ectopic expressing each of them, respectively, suggesting that both of them can exert the function of AtFT. However, they displayed different seasonal-change expression patterns, with HbFT1 mainly accumulating in September for adult trees and in October for juvenile trees and HbFT2 transcript accumulating in March, which was the main floral initiation period, even though both of them showed higher transcript levels in adult trees than 2-year-old trees, implying their different biological functions during growth and development as well as flowering transition in rubber tree.

Modelling Soil Water Dynamics under Rainfed Agriculture to Mitigate Climate Change

The model performance to simulate soil water dynamics was evaluated by comparing the predicted soil water content values with calculated soil water at different phenological stages of wheat and total soil available water using neutron probe. The pre-sowing soil water (mm) in this study varied from 40 to 50 mm in loam and sandy clay soil of Islamabad and Chakwal, respectively. When soil water is >50 mm, its effect on crop establishment is dependent on amount and temporal distribution of rainfall. Plant available soil water seems to be the most important factor if rainfall occurs between sowing and floral initiation period as happened during 2008-09 in the present study. The dynamics of soil water from emergence to maturity represented here as total soil water that remained maximum at earlier plant stages especially when crop roots were established and utilized soil water effectively that resulted in the lowest level of water at maturity which can be due to the evapotranspiration. The results depicted that the soil water distribution pattern mainly depends on soil properties and if sowing methodologies are resilient with available soil water then crop stand will be good and crop uses water much effectively. The results also depicted that when soil water is at drain upper limit (DUL) and the crop sown at proper time along with least soil evaporation, the soil water can be more easily taken up by the plant roots. Furthermore, the simulated soil water by the model was in close agreement with actual data. The validation skill scores like R2 confirmed the actuality of the model, therefore, dynamic model like Agricultural Production System Simulator (APSIM) could be used to describe the distribution of rainwater into different components like infiltration, runoff and drainage, and it can be used as a decision support tool for accurate management of different cultural operations for sustainable atmosphere-soil-plant (ASP) system.

A comparison of flowering behaviour of sugarcane clones in two different locations

Flowering is highly variable and erratic in tropical environments in recent years. Due to changing weather conditions, the flowering intensity varied in two different locations with contrasting conditions. Flowering occurred in both the environments but the percentage of varieties flowered and the flowering intensity differed widely between the two locations. The environmental factors viz., temperature, and rainfall data of both the locations in the 2004 season were analyzed. The day time temperature of >31°C during the sensitive floral induction and initiation period occurred for more number of days in traditional breeding plot, where the flowering intensity was very much reduced. However, there were no appreciable differences in minimum temperature for flower initiation and development. The reduction in flowering ability of clones in the traditional breeding plots could be due to high temperature prevailing prior to and during the floral initiation period and deficient rainfall.

A comparison of IAA and ABA levels in leaves and roots of two citrus cultivars with different degrees of alternate bearing

SummaryThe IAA and ABA contents in the leaves and roots in alternate-bearing citrus were compared in defruited and non-defruited (control) trees. Two satsuma mandarin cultivars, ‘Aoshima’, a highly alternate bearer and ‘Miyagawa’, a slightly alternate bearer, were used. Defruiting increased the IAA content in roots, but not in leaves, and increased the ABA contents in leaves of ‘Aoshima’, but not in roots. The IAA content in the roots of the control trees was lower from September to November (‘Aoshima’) and October to November (‘Miyagawa’), including the floral initiation period (from early-September to early-December). The ABA content in the leaves of the defruited trees of ‘Aoshima’ was higher than that in the control trees from September to December excluding October. There was no difference in the ABA content in the leaves of ‘Miyagawa’ between the defruited and control trees. From the comparison of the ratio of sprouting nodes and the type of shoots ‘generative, mixed or vegetative’ between cultivars, it is concluded that the high degree of alternate bearing in ‘Aoshima’ is due to the low ratio of sprouting nodes, and high ratio of vegetative shoots. The above results suggest that the ABA content in leaves may be related to sprouting and floral initiation, which determines the degree of alternate bearing.

Analysis of Spike Development of Three Spring Wheat Genotypes under Various Cultural Conditions

The spike development in three spring wheat genotypes was studied under various cultural conditions. Two genotypes weakly responsive to cultural conditions in spikelet number per spike (T1 from Nepal and Haruyutaka from Japan) and one weakly responsive to cultural conditions in spike length (U6 from Xinjiang Uygur district of China) were grown under three cultural conditions with different seeding density and fertilization levels : 680 seeds m−2 without fertilizer (unfavorable), 340 seeds m−2 with common fertilizer (common) and 170 seeds m−1 with double fertilizer (favorable). The durations of the vegetative phase, spikelet phase and the spike elongation phase were scarcely influenced by these cultural conditions, although the leaf number was influenced. The development of spikelets seemed to be determined by several factors other than those affecting the developmental processes of the spike. In U6, the increase in shoot apex length during the floral initiation period under the favorable condition was accompanied with an increase in double ridge number and spikelet number per spike, but such a relationship was not observed in T1 and Haruyutaka. T1 and Haruyutaka had a higher rate of spikelet formation under the favorable condition than under the unfavorable condition, but U6 showed a rather lower rate of spikelet formation under the favorable condition. Thus, the effects of the cultural conditions on the spikelet number per spike differed with genotype. At the time of terminal spikelet formation, U6 tended to have a longer spike than T1 and Haruyutaka. However, since the rate of spike elongation was higher in T1 and Haruyutaka than in U6, the spike length at anthesis was shorter in U6.

Effects of Fruit Removal on Photosynthesis, Stomatal Conductance and ABA Level in the Leaves of Vegetative Shoots in Relation to Flowering of Satsuma Mandarin.

Photosynthetic rate (Pr) and stomatal conductance (Sc) in the leaves of satsuma man-darin cv. Aoshima were measured from July to November on 1) vegetative shoots of intact (control) bearing branch unit (BBU) consistisng of two fruit bearing shoots and a vegetative one, and 2) those of BBU from which fruits were removed in June or September. The data between the bearing and non-bearing vegetative shoots are discussed in re-lation to the flowering potential for the following spring.Pr in the leaves of the fruit-removed BBU increased by 24% in September, whereas it increased to 41% by October by fruit removal in June. Pr increased only 30% by November when fruits were removed in September. Sc in leaves of fruit-removed BBU in-creased by 18% in September; but to 46% by October through fruit removal in June; and 114% by November when fruit removal occured in September.In relation to stomatal aperture, ABA concentration in the leaves was measured from September to November during which floral initiation of satsuma mandarin is believed to occur. Leaves of BBU had significantly high ABA concentration in September in the case that the fruits were still remained on the unit, but it was much lower in BBU where fruits were removed in June, and even lower when the fruis were removed in September.These results indicate a possible contribution of Pr increase during the floral initiation period to the vegetative shoots as well as an involvement of ABA through a regulation of stomatal aperture in the leaves during the period. Conclusively fruit removal could enhance flowering rather effectively.

The Influence of Temperature Upon Physiological Processes in Early-Flowering and Late-Flowering Strains of Thlaspi arvense L.

This study was initiated to determine net photosynthesis, respiration, and stomatal conductance for early-flowering (EF) and late-flowering (LF) strains of Thiaspi arvense L., and to determine the relative impact of temperature on these processes in the two strains. The strains have been shown to differ by a single gene. Vernalized EF and LF plants were grown under controlled environments at day temperatures of 1 50C, 200C, and 250C (1 6-h photoperiod) each, with 1 50C nights. During the period of floral initiation for the EF strain, net photosynthesis, respiration, and stomatal conductance were determined in both strains. Plants of the LF strain had higher net photosynthesis rates and lower respiration rates. Net photosynthesis was most efficient at 200C days, while respiration rates increased with increasing temperature. Stomatal conductance was greater in the EF strain, which also had larger stomata than plants of the LF strain. Generally, EF plants grew more quickly in terms of shoot dry weight than LF plants. However, at 250C, the LF plants had significantly more shoot dry weight. We suggest that differential net photosynthesis and respiration rates of the EF and LF strains of T. arvense may influence the relative amounts of carbohydrates and nitrogen available to the shoot apices and therefore affect the time to floral transition.

Synchronization of anthesis and enhancement of vegetative growth in coffee (Coffea arabicaL.) following water stress during floral initiation

SUMMARYThe possibility of using water stress during floral initiation and development, to synchronize flowering in potted coffee trees of cvs Catuai Rojo and Mundo Novo was investigated. Moderate and severe cyclic and constant water stress had little effect on vegetative growth during floral initiation. However, upon rewatering, shoot growth was significantly greater in plants where leaf water potential [¨,] had declined to -2.5 MPa compared with plants where ¨, was maintained above -0.5 MPa. The period of floral initiation was not influenced by water stress and occurred only under short days (<12 h). In contrast, a y, of -2.5 MPa significantly reduced the number of inflorescences compared with plants maintained at a ¨| of -0.5 or -1.5 MPa. This reduction was associated with leaf drop in stressed plants. Therefore, regular irrigation during the period of floral initiation is recommended. Water stress (¨, of -1.5 or -2.5 MPa compared with -0.5 MPa) accelerated floral development with no deleterious effects...

TEMPERATURE IS A KEY REGULATOR OF GROWTH AND FLOWERING IN PROTEA NERIIFOLIA AND PROTEA CYNAROIDES

The strategy of this study was to determine the period of floral initiation for both species and then to determine the critical regulator(s) of flower initiation and floral development. Plants grown under different temperature regimes gave best shoot extension and flower initiation at temperatures with 10°C night and 15 to 25°C day. Field data from four locations showed a correlation of time of flower initiation and temperatures over the same range. Temperature is an important determinant of the vegetative flush period of both species. The stem diameter of all shoots is a consequence of the vegetative flush growth and in turn is well correlated with flower initiation. Plants given day temperatures of 20°C or above remain in the vegetative phase. Flower abortions in Protea neriifolia and reversions from floral to vegetative shoots in Protea cynaroidesresult from high day temperatures. Daylength was not found to be critical for flower initiation. A cool temperature period acts as a control to change shoots from the vegetative to reproductive phase.

Irrigation-Depressing Effect on Floral Initiation of Cabernet Sauvignon Grapevines in Bordeaux Area

An irrigation experiment is described in combination with a training-systems trial, conducted on Cabernet Sauvignon grapevines in the Bordeaux area from 1975 to 1977. The physiological development of vegetative parts was normal, but was increased along with two kinds of strong depressing effects on floral initiation: 1) a general depression, probably due to a decline in capture of solar energy at the renewal-area level: and 2) a specific depression, mostly on primary buds, which could be inhibited during the floral-initiation period by too great a water flow in the tissues. The influence of the level and rhythm of water provision is discussed. Some implications for field practices are indicated, particularly in regard to wine quality.

Photoperiod and temperature effects on the flowering of Stylosanthes guyanensis

Selections of Stylosanthes guyanensis were grown in controlled environment cabinets at 27� and 20�C and exposed to differing photoperiods. All selections showed a short-day flowering response, the apparent critical photoperiod varying from about 13 hours in CPI 40255 to about 11.5 hours in cv. Schofield. The 20� treatment promoted flowering in longer photoperiods in CPI 40255 and cv. Schofield and almost prevented flowering in CPI 34906 and cv. Cook. CPI 33706 did not flower at 27�C. Flowering response was not related simply to latitude or altitude of selection origin. Removal of mature leaves hastened flowering. The same selections grown in the field at Mt. Cotton, south-east Queensland (lat. 27�37'S) reached floral initiation at dates varying from February 5 to April 20. The duration of the period of floral initiation to flower appearance was negatively associated with daily maximum temperature. The range of first flowering dates within a selection varied from 8 to 78 days.

Sugarcane Flower-Control Studies With Paraquat, Gibberellic Acid, and Sodium Meta-Silicate

Sugarcane flower control studies were conducted with Paraquat, gibberellic acid (GA) and sodium meta-silicate (Si) applied as foliar sprays just prior to the period of floral initiation. The test clone, C.P. 52-43, blooms heavily in southern Puerto Rico and initiates flower primordia about September 10. The primary objective was to determine whether flowering could be prevented by physiologically removing the apical meristem, with a growth stimulant such as GA, rather than by destruction of the green top, as by treatment with a desiccant such as Paraquat. Secondary objectives included comparisons of growth and sugar responses to GA and Paraquat, and to determine whether Si, believed to act as a buffer against physiological extremes, possessed anti-flowering activity. Two experiments were conducted simultaneously in a field of 7-months old, first-ratoon cane at Central Mercedita, Ponce. Each experiment was given identical spray applications of GA and Si; in addition, one experiment received Paraquat superimposed over all plots shortly after the GA and Si applications were complete. Aqueous GA, 0.01 percent active material, was applied with knapsack sprayers to 1/1000-acre plots in volumes equal to 300 gallons per acre. Si was similarly applied at the level of 500 p.p.m. Treatments also included GA and Si combined in one solution. Paraquat was applied by aircraft at the rate of 0.5 pint per acre in 8 gallons of water per acre. GA and Si treatments were given on August 22 and repeated on August 29. Paraquat was applied once on September 1. The following results were obtained: 1. Flower counts taken on December 27 showed that GA given alone was the most effective treatment, reducing flowering rates to 0.02 percent. Paraquat reduced flowering to about one-third of control levels. Si had no effect by itself, but reduced the effectiveness of GA when the two agents were combined. 2. Total green weights, stalk weights, and internode lengths were increased by GA. Each parameter was decreased by Paraquat. Si given alone appeared to increase total green weight and stalk weight but the responses were not statistically significant. The primary effect of Si in combination with GA and Paraquat was to reduce the degree of growth stimulation by the hormone, and to lessen the growth suppression by the desiccant. 3. Sugar production was increased by GA and decreased by Paraquat. Paraquat also lessened the degree and duration of positive GA effects. Si had little effect on sugar as a lone entity but produced a buffering effect against relative sugar extremes as it did for growth extremes. 4. Early Paraquat injury to leaves, and hence to sugar-forming mechanisms, appeared to be more than compensated after about 2 months. Tonnage losses due to the foliar injury appeared to be permanent. 5. GA growth stimulation was followed by a reversion to less than normal growth. This growth reversion detracted from the total growth increases that otherwise might have been achieved. It was proposed that growth decline could be lessened with Si given as a delayed or follow-up treatment after GA. 6. Present evidence is consistent with the view that sugarcane flowering can be prevented more effectively by stimulating the apical meristem, at the critical period of flower initiation, than by destroying foliate essential for maximum growth and sugar production.

Floral Initiation, Development, and Associated Phenomena of Dianthus caryophyllus L. Part I - Effect of Photoperiod1

Abstract Dianthus caryophyllus L., a quantitative long day plant, was used for studies of the effect of photoperiod on the different stages of plant development. The anatomical structure of the vegetative shoot apex and the changes during floral transformation are described. These stages were not affected by the various photoperiod lengths, i.e., 9, 13, and 18 hr. The developmental cycle of D. caryophyllus may be divided into 3 stages: vegetative, floral initiation, and floral development. The influence of photoperiod on the duration of each of the 3 stages was different. The length of the vegetative stage was inversely related to the length of the photoperiod (the longer the photoperiod, the shorter the vegetative stage). Daylength had no effect on the period of floral initiation, but did affect the period of floral development (i.e., the longer the photoperiod, the longer the developmental stage). The rate of stem elongation under all treatments increased exponentially until the floral initiation state, and then the plants grown under photoperiods of 13 hr or longer elongated significantly faster than those under the 9-hr photoperiod. After flower initiation was completed, the rate of stem elongation suddenly increased linearly until the flower opened. In contrast to the vegetative shoot, the rate of stem elongation of flowering plants was completely independent of photoperiod, and the rate was the same in the 9, 13, and 18 hr photoperiods.

Change in Carbohydrates in Alfalfa (Medicago sativa L.) Roots During the Period of Floral Initiation and Seed Development1

Alfalfa plants grown under field conditions at Tucson, Arizona, were used to investigate the change in acidhydrolyzable carbohydrates, glucose, fructose, sucrose, and starch stored in the roots during the time of floral initiation and seed development at three different seasons of the year.Acid‐hydrolyzable carbohydrates and starch reached their lowest level in the roots more rapidly in plants that were cut in June and August as compared with plants that were cut in April to begin growth for seed production. Floral initiation and development also occurred earlier during the June and August growth periods. This early reduction in stored reserves coincided with early floral initiation and development. The concentration of glucose, fructose, and sucrose was quite low in alfalfa roots during all growth periods. Positive and significant association existed between the concentration of specific carbohydrate fractions in alfalfa roots during the first three weeks after forage removal and seed production, number of pods per stem, number of seeds per pod, and percentage pod set.

Reducing Inflorescence Formation by Shading Individual Sultana Buds

For four seasons, individual buds developing on sultana vines in the field were shaded with a number of materials during the period of floral initiation. Heavy shading up to complete darkening consistently reduced the number and size of inflorescence primordia. This reduced fruitfulness could not be related to changes in the spectral quality of the light, which might have upset the phytochrome system, nor to changes in temperature of the buds.