Auxin transport capacity in relation to the dwarfing effect of apple rootstocks

SUMMARY

Basipetal auxin transport in shoots obtained from dwarfing (M.9) and less-dwarfing (MM.Ill) apple rootstocks was compared by measuring the distribution of ¹⁴C-[carboxy]-labelled indole 3-acetic acid supplied to the ends of shoot segments. Auxin was transported at a greater velocity in MM.111 than in M.9 in both woody and non-woody segments, and was effectively blocked by 2,3,5-triiodobenzoic acid. The velocities of transport were approximately 8 mmh-¹ in M.9,and 13 mmh-¹ MM.111. There was relatively little transport in the acropetal direction, and there were no significant differences between the two rootstocks in total auxin uptake. Chromatographic analysis suggested that the metabolismof the auxin supplied followed similar patterns in both rootstocks. It is proposed that the slower auxin transport in M.9 results from a lower capacity for auxin efflux from transporting cells. A limiting auxin transport capacity could explain the reduced cambial activity and subsequent xylem formation in the dwarfing M.9 rootstock, and thus make an important contribution to the dwarfing effect.     

Increasing fruit set in Vitis vinifera

Girdling, growth retardant succinic acid 2-2-dimethyl hydrazide (Alar), 2-naphthoxyacetic acid (NOA), and Gibberellic acid (GA₃) were tested as a fruit-setting agent in 1975 for ‘Yaghooti’, a stenospermocarpic cultivar of Vitis vinifera grape. Bloom Alar spray at 7500 p.p.m. increased the number of berries per cluster and the cluster weight. Bloom auxin spray did not effectively increase fruit set, while gibberellin had a depressing effect. Girdling also increased fruit set and a combination of Alar and girdling had the most pronounced effect on fruit set. None of the treatments significantly altered soluble solids and/or vitamin C content of the berries.     

Application of 2,4-dichlorophenoxypropionic acid 2-ethylhexyl ester reduces mature fruit abscission in Citrus navel cultivars

Summary

2,4-dichlorophenoxyacetic acid (2,4-D) isopropyl ester has been used extensively, since the 1950’s, to reduce mature fruit abscission in Citrus navel cultivars. However, this synthetic auxin is no longer registered for this purpose in the European Union (EU). 2,4-dichlorophenoxypropionic acid (2,4-DP) 2-ethylhexyl ester has been registered in the EU for use in citrus growing and can be an effective replacement for 2,4-D to reduce pre-harvest fruit abscission. Use of the 2-ethylhexyl ester of 2,4-DP sprayed before mature fruit abscission significantly reduced fruit drop in sweet orange (Citrus sinensis L. Osbeck) ‘Washington navel’ and ‘Navelate’. The magnitude of the response depended on the concentration applied. At 15 mg l^–1, the percentage of abscised fruit was reduced by 50–75% compared to untreated trees, depending on the variety and the orchard. Increasing the concentration applied to 50 mg l^–1 did not improve this response. The response to this auxin was as effective as that obtained with 2,4-D applied on the same day at the same concentration (15 mg l^–1). 2, 4-DP treatment had no effect on skin colour or on the internal and external characteristics of the fruit at harvest.     

Effect of IAA gradient between the peduncle and branch on physiological drop of citrus fruit (Kiyomi tangor)

Summary

Changes in indole acetic acid (IAA) concentrations of the peduncle, branch and abscission zone were examined during the physiological fruit-drop period, to investigate the role of endogenous auxin in the peduncle and branch on the physiological drop of the fruit. The effects of 2,3,5-triiodebenzoic-acid (TIBA), applied to the peduncle or branch, on the IAA concentration in each organ and the drop ratio were also investigated. The fruit-drop ratio increased when TIBA was applied to the peduncle (TIBA-P application), whereas it decreased when the application was to the branch (TIBA-B application). Prior to fruit drop, marked IAA accumulation occurred in the abscission zone in the control and after TIBA-P application. An IAA gradient from the branch to the peduncle was found for TIBA-P applications, but a reverse gradient for TIBA-B applications. These results suggest that the reduction of IAA polar transport above the abscission zone is necessary to promote abscission and that both IAA accumulation in the abscission zone and the IAA gradient between the peduncle and branch are involved in abscission.     

Interactions between hormonal and developmental signalling in the prevention of side-shoots in rose (Rosa hybrida L.)

Summary

This study investigated the effects of auxin sprays on the development of side-shoots in rose (Rosa hybrida L.). The rationale was to prevent or to minimise side-shoot development in a commercially acceptable rose cultivar. Equallyspaced doses (at 0, 15, 30, 45 or 60 mg l^–1) of -naphthaleneacetic acid (NAA) were applied at the equivalent of 100 l ha^–1 to roses grown on an inert substrate in a commercial greenhouse, via repeated foliar sprays at 2, 4, or 8 d intervals over 7 weeks. Unattended or hand-pinched plants were used as negative or positive controls, respectively.The interaction between auxin dose and spray interval had a significant (P ≤ 0.001) influence on the number and growth rate of side-shoots on a stem. All auxin doses tested completely prevented side-shoot development on rose stems at a 2 d spray interval. This high efficacy was attributed to prevention of the irreversible phase-change in the regulation of apical dominance. However, the interaction between auxin dose and spray interval significantly (P ≤ 0.001) influenced the occurrence of leaf epinasty, a physiological condition with a negative impact on cut-shoot quality. Bullheads, another undesirable physiological condition, was significantly (P ≤ 0.001) influenced by auxin dose. This novel technology is expected to lower rose production costs. The data obtained in this study demonstrate the interaction between hormonal and developmental signalling in apical dominance. Possible modes of action are discussed.     

Effect of Ethephon (2-Chioroethyl Phosphonic Acid) on Endogenous Levels of Auxins,Inhibitors and Cytokinins in Relation to Senescence and Abscission in Vicia Faba L.

Treating three cultivars of Vicia faba L. with ethephon led to reduced vegetative growth and enhanced abscission of leaves, flowers and immature pods. No clear pattern emerges of changes in the levels of endogenous auxin and inhibitors as a result of treatment with the growth regulator. Cytokinin levels in leaves of treated plants were much higher than in the controls but no changes occurred in stem tissue. The results are discussed in relation to senescence, abscission and flowering.     

The effect of sucrose on the expression of the VvTFL1 and VFL genes during flower development in the “Xiangfei” grapevine

VFL and VvTFL1 genes expression patterns and the effects of sucrose on the expression of VFL and VvTFL1 genes in different organs of the “Xiangfei” grapevine (Vitis vinifera L.) were investigated. VvTFL1 gene expression was detected in the meristem of the apical bud and lateral bud, but was not detected during inflorescence differentiation and flower organ development. After sucrose treatment, VvTFL1 gene expression increased in the apical bud, but decreased in the lateral bud. These results suggested that the VvTFL1 gene might be mainly involved in the apical growth process of shoots, and exogenous sucrose had an effect on the VvTFL1 gene by increasing shoot apical meristem initiation of apical buds. The VFL gene was expressed primarily during inflorescence differentiation and early flower organ development, but it gradually reduced in later flower development. After sucrose treatment, VFL gene expression increased in the inflorescence and small or middle flower, but a little change was seen in the large flower. These results suggested that the VFL gene plays important roles in the initiation of inflorescence meristems and the morphological formation of flower organs. Exogenous sucrose had an effect on VFL gene expression at the early stage of flower development.     

Some factors affecting the response of grapevines to ethephon

Factors influencing the effects of ethephon on fruit abscission and leaf senescence in several Vitis vinifera L. cultivars were studied under field conditions in a series of exploratory experiments. Cultivars appeared to vary greatly in their response to treatment. Ethephon concentration, surfactant concentration, fruit maturity, application conditions and degree of foliage wetting all influenced the degree of response.The experiments were not conducted on a common cultivar, thus limiting the conclusions which can be drawn. It is apparent from the results that a complexity of plant, environmental and application factors affect the response of grapevines to ethephon.     

Nitrate uptake kinetics of grapevine under root restriction

To examine the effect of root restriction on the nitrate uptake and the nitrate transport system activity, 2-year old “Fenghou” grapevines (Vitis Vinifera × V. Labrasca) were planted in pots with volume 2 L and 12 L served as root restriction and the control, respectively. The pots were filled with perlite and watered with rainwater and nutrient solution. Vine growth and kinetics of nitrate uptake in vine roots were evaluated. The results showed that root restriction significantly inhibited the shoots and roots growth, enhanced the nitrate uptake rate, decreased the kinetics parameter K_m value and increased V_max value, that is to say, root restriction depressed the affinity of nitrate high-affinity transport system (HATS) and improved the nitrate uptake rates of both high (HATS) and low-affinity transport system (LATS). However, root restriction significantly decreased the amount of net nitrate uptake, which led to the low nitrate concentration in leaves and roots.     

Shedding of the upper parts of grapevine shoots

Shedding of the upper parts of unlignified grapevine (Vitis vinifera L.) canes is frequent during autumn. Stress conditions during the growing-season lead to similar shedding of shoot tips. The separation process occurs above a node in the boundary area between the distal part of the diaphragm and the pith.Ethephon (2-chloroethyl-phosphonic acid) sprays, at 750 or 1500 mg l^?1, induced separation of the shoot tips of ‘Perlette’ and ‘Queen of the Vineyards’. Ethylene (C₂H₄) 200 vpm and ethephon at 10, 100 and 1000 mg l^?1 enhanced separation in shoot explants, whereas 2,4,5-TP (2,4,5-trichlorophenoxy-propionic acid) at concentrations above 1 mg l^?1 arrested it.This phenomenon may be regarded as a shoot abscission process which may represent adaptation of self-pruning of the grapevine.     

High-frequency somatic embryo production from unfertilized ovules of grapes

Somatic embryos were produced in large numbers from cultured, unfertilized ovules of Vitis vinifera, cultivars ‘Cabernet Sauvignon’ and ‘Grenache’, and of the hybrid grape ‘Gloryvine’ (V. vinifera × V. rupestris). Callus of nucellar origin was produced by culturing the ovule explants initially in Nitsch medium containing 5 μM 2,4-dichlorophenoxy acetic acid (2,4-D) or 5 μM β-naphthoxyacetic acid (NOA) plus 1 μM benzyladenine (BA), and then in a medium supplemented with NOA (10 μM) plus BA (1 μM). Embryos were produced when callus was transferred to basal medium containing no auxin or cytokinin. Secondary and tertiary embryos were formed by budding of primary somatic embryos. Prolonged culture of ovular callus in NOA (10 μM) plus BA (1 μM) gave rise to cell aggregates which developed into free-floating roots when transferred to basal medium.     

Levels of extractable para-coumaric acid in the exomesocarp and seed of persisting and abscising peach fruit

Besides ABA, another inhibitor, para-coumaric acid (PCA), was isolated in peach fruit (Prunus persica Batsch cultivar ‘Andross’). The nature of this inhibitor was established by combined gas chromatography—mass spectrometry. Its level was determined spectrophotometrically and confirmed by wheat coleoptile and cress seed assay on mesocarp and seed of fruits classified as to abscission potential on the basis of their growth rate during Stage I. Levels of inhibitors were parallel in exo-mesocarp and seed. Extracts from fruit with high abscission potential contained a significantly higher amount of free PCA than did those with low or intermediate potential. The bound PCA was higher in fruit with high or intermediate abscission potential and its level seems related to the pit hardening, since the highest concentrations were found during Stage II of fruit development.     

Non-structural carbohydrate status and CO2 exchange rate of apple fruitlets at the time of abscission influenced by shade,NAA or BA

Four days of 90% shading at the time of fruit setting (1–5 days after petal fall, DAPF) of mature ‘Jonagold’/M.9 apple trees was combined with the application of thinning agents to establish the possible interaction of both main treatments on fruit retention, and the effects of the main treatments on fruitlets CO₂ exchange and their carbohydrate concentration. Shading alone reduced yield by up to 35%. When shading was followed by the application of 15 ppm 1-naphthaleneacetic acid (NAA) or 50 ppm 6-benzyladenine (BA), the interaction between shading and chemical thinners was on the border of significance. Following the assumption that abscission was induced by shading before the application of chemical thinning agents, the same process of diminished dark respiration rate (R_d) was found on fruitlets sampled 3 days after the end of shading and 7 days after NAA and BA spraying, i.e. in the fruitlets that were considered prone to drop. A week after the end of shading the abscission of fruitlets due to shading was completed and on the remaining fruitlets that were not prone to abscission any more, larger negative net CO₂ assimilation rates (A) and enhanced R_d were recorded. Fruitlets prone to abscission sampled 2 days after the end of shading showed a lower concentration of glucose and ascorbic acid and a higher concentration of starch. Eight days after the end of shading, the fruitlets from shaded trees that were not prone to abscission any more contained less fructose while the fruitlets from NAA and BA sprayed trees had a higher concentration of fructose a week after application. The results do not support the hypothesis that a good assimilate supply is needed for the retention of apple fruitlets, because the fruitlets retained on trees expressed even stronger CO₂ loss and because the concentration of non-structural carbohydrates did not decrease in fruitlets prone to drop with the exception of glucose.     

Inflorescence development of flowering and blasted gladiolus plants in relation to development of other plant parts

Flower differentiation in Gladiolus × grandiflorus takes place immediately after initation of all the leaves. The prefloral stage was observed in shoots 3–4 mm long and the shoot apex was floral when the first foliage leaf was half extended.Initiation of individual florets continued up to the 7-leaf stage. Flower development is acropetal and continued up to anthesis of each individual floret.Flower blasting generally starts at the tip of the inflorescence and advances towards the base of the flower stalk. Blasting starts as a stoppage in the growth of the inflorescence, the flower stalk and the leaves on the stalk. Later these organs shrivel. Daughter corms fill early as a consequence of blasting.     

High frequency multiplication of Phalaenopsis gigantea using trimmed bases protocorms technique

This study was conducted to determine the effects of coconut water (CW) and activated charcoal (AC) on multiplication of Phalaenopsis gigantea protocorms. The protocorms used for this study were obtained by germinating seeds in vitro. Protocorms with trimmed and untrimmed bases were cultured on XER basal medium containing 0, 10, 15 or 20% (v/v) CW; and 0, 1, 2 or 2.5 g AC l⁻¹. Trimmed protocorms exhibited the highest percentage of proliferation on a medium containing 15% (v/v) CW and 2.5 g AC l⁻¹ (56.82 ± 38.86%) with an average of 4.24 ± 2.89 protocorms formed per protocorm. Untrimmed protocorms cultured on a medium containing 20% (v/v) CW without AC produced the highest percentage of new protocorms (6.93 ± 6.28%) with an average of 0.72 ± 0.57 per protocorm. When CW was added to a medium singly, 10% (v/v) CW induced a higher degree of proliferation on trimmed protocorms (5.68 ± 10.14%) with an average 0.50 ± 0.84 new protocorms per protocorm. Untrimmed protocorms proliferate to a much lower extent (2.57 ± 2.74%) with an average of 0.72 ± 0.57 protocorms per protocorm when cultured on a similar medium. A high concentration of CW enhanced proliferation on untrimmed protocorms, but increased mortality of trimmed protocorms. The addition of CW with AC to media increased protocorm proliferation and survival of both trimmed and untrimmed protocorms. When cultured on all media, trimmed protocorms produced a higher number of new protocorms (an average 0.5–7.0) as compared to untrimmed protocorms (0.3–1.9). Comparative studies showed that trimmed protocorms produced up to 10 times more new protocorms than untrimmed ones. Altogether this study showed that trimmed protocorms cultured on a medium containing CW and AC can be used for high-frequency multiplication of P. gigantea seedlings.     

Individual and combined effects of shading and thinning chemicals on abscission and dry-matter accumulation of ‘Royal Gala’ apple fruit

Summary

Shade and chemical thinning treatments were applied to mature ‘Royal Gala’/M.26 apple trees either alone or in combination to study their effects on the pattern of abscission and growth of spur fruit. Natural fruit drop occurred in two distinct waves in both years; the first wave peaked 20 d after bloom (DAB) at a weekly abscission rate of c 15% in both years. The second wave of fruit drop in 2001 occurred earlier and was more intense than in the previous season. Application of NAA as a bloom thinner increased the maximum weekly abscission rate during the first wave of fruit drop in both years. Chemical fruit thinning treatments (Carbaryl in 2000, BA or delayed lime sulphur in 2001) had no effect on abscission or growth of spur fruit. Covering trees with 80% shade cloth for 3 d (2000) or 5 d (2001) stimulated a wave of fruit abscission that peaked c 10–15 d after removal of the cloth. Shade during the period from 20–25 DAB stimulated more fruit drop than earlier shade treatments, resulting in weekly abscission rates as high as 70%.There were no additive effects of combining thinning chemicals and shade treatments on abscission of fruit from spurs. However, additive effects of shade and thinning treatments were observed when measured as whole-tree crop density values, indicating that abscission of fruit from one-year wood was stimulated when low light conditions preceded application of (fruit) thinning chemicals. Shading trees from 34–39 DAB in 2000 resulted in a transient reduction and subsequent increase in the rate of dry-matter accumulation in fruit that were retained. Considerable challenges lie ahead in developing models of fruit growth that can account for the inter-dependent effects of light and crop load on fruit abscission and development that exist within an orchard environment.     

Sensitivity of Geraldton waxflower to ethylene-induced flower abscission is reduced at low temperature

Summary

Exposure to ethylene gas elicits flower abscission from cut stems of Geraldton waxflower (Chamelaucium uncinatum Schauer). Ethylene response rates in plants are mediated by temperature. At 20°C, flower abscission from waxflower ‘Purple Pride’ occurred upon 12 h exposure to 1 µ11^–1 ethylene. This ethylene treatment did not cause flower abscission at either 10 or 2°C. Moreover, flowers held at 2°C were insensitive to 48 h exposure to 1, 10 and 100 µ11^–1 ethylene. However, increasing the duration of treatment with 1 µ11^–1 ethylene at 10 and 2°C to 48 and 144 h, respectively, induced flower abscission. When flowers were held at 20°C in air without exogenous ethylene following continuous exposure to 1 µ11^–1 ethylene at 2°C, the duration required to elicit flower abscission was reduced from 144 to 72 h. Collectively, these responses show that maintaining harvested waxflower at low temperature (e.g. 2°C) is an effective means to minimise ethylene-mediated flower abscission.     

Effects of ozone and sulfur dioxide on grapevines

Greenhouse-grown ‘Ives’ and ‘Delaware’ grapevines (Vitis labruscana, Bailey) were fumigated for 4-hours with ozone (O₃) and/or sulfur dioxide (SO₂) at 0.40 and 0.80 mg l^?1. Fumigations were performed in a plexiglass chamber situated within a controlled environment walk-in growth chamber. When applied separately, both gases induced characteristic foliar injury. ‘Ives’ grapevines were much more sensitive to $\text{O}{}_3\text{SO}{}_2$ fumigations than were ‘Delaware’ grapevines. Within each cultivar, leaf necrosis and shoot growth reduction were greatest following fumigation with 0.80 mg l^?1 O₃ plus 0.80 mg l^?1 SO₂. Leaf abscission occurred only on ‘Ives’ and was related to foliar necrosis. Shoot growth following fumigation was less on vines having most foliar necrosis. Yet, ‘Delaware’ vines showing less than 1% leaf area necrosis still had significant reductions in shoot growth. All O₃ and SO₂ fumigations resulted in stomatal opening.