Effect of paclobutrazol on cell wall polysaccharide composition of the apple tree

The effect of paclobutrazol, a gibberellin biosynthesis inhibitor, on cell wall carbohydrate composition of apple shoots was determined. Inhibition of apple shoot extension corresponded to a change in wall composition. Paclobutrazol did not inhibit shoot growth during the first year (1983) after the treatment. There was also no significant difference in cell wall carbohydrate composition between control and paclobutrazol treated shoots. In the second year (1984), however, paclobutrazol altered the composition of cell wall polysaccharides and inhibited shoot extension. Paclobutrazol treatment increased rhamnose, arabinose and galacturonic acid but decreased cellulose. The ratio of xylem to phloem was also reduced by paclobutrazol treatment.     

Translocation of carbon in powdery mildewed barley

This paper compares translocation in healthy and powdery mildew (Erysiphe graminis f. sp. hordei, race CR3) infected barley (Hordeum vulgare, variety Manchuria). The sink-like properties of the powdery mildew infection were used to determine what effect imposing a sink in the midst of normal source tissue (mature primary leaf) had on the translocation process. The pattern of translocation was determined by monitoring the movement of ¹⁴C which was photosynthetically incorporated from ¹⁴C either by the primary or second leaf. In the healthy primary leaf of barley, ¹⁴C fixed in the tip section of the blade was preferentially translocated to the root, whereas ¹⁴C fixed in the basal section was primarily translocated to the shoot. When a sporulating powdery mildew infection was present in the mid-section of the primary leaf, ¹⁴C fixed in that section or in the acropetal healthy tip section readily accumulated in the infection area. Labeled carbon fixed in the healthy basal section was translocated into the other parts of the plant with only a small fraction moving acropetally into the infected mid-section. The ¹⁴C fixed by the second leaf was translocated to the root and younger shoot with very little entering the primary leaf. The presence of the mildew infection did not alter this pattern.     

Effects of shoot bending of apple trees on accumulation and translocation of14C-labelled assimilates

The translocation of¹⁴C-labelled assimilates from a single leaf in bent and intact apple shoots was studied in varying stages of shoot development. In actively growing shoots¹⁴C-labelled assimilates translocated from the treated leaf and accumulated mainly in the shoot apex. In moderately growing apple shoots radioactive assimilates were translocated from the treated leaf in both directions towards and down the shoot. In apple shoots showing only slight growth activity the¹⁴C-labelled assimilates were transported from the treated leaf mainly to the base of the shoot, stem and roots. Bending shoots changed the pattern of distribution of radioactive assimilates. Bending actively and moderately growing shoots resulted in higher concentration of 14-carbon in the shoot apex than in controls. In slowly growing and non-growing apple shoots bending caused a higher accumulation of radioactive assimilates in the bent section than in an equal section of control shoots.     

Translocation of some assimilates from the sink to the donor in apple tree

The shoot apex or fruitlets of Jonathan apple trees grafted on M IX rootstock and grown in pots in a greenhouse were exposed to¹⁴CO₂ in an assimilation chamber. The translocation of¹⁴C-labelled assimilates from treated organs to other parts of the plant was studied. It was found that a very small amount of¹⁴C-labelled compounds was translocated from the shoot apex and very young fruitlets to the shoot stem. Preliminary chromatographic studies show that the chemical composition of the labelled substances detected below assimilation chamber differs profoundly from that of those remaining in the supplied leaves. The results support the view that there exists a translocation of some substances, possibly regulators from the sink to the donor.     

The absorption, translocation and distribution of the herbicide glyphosate in maize expressing the CP-4 transgene

Maize (Zea mays L. var. Bonnie) transformed with a gene encoding a 5-enolpyruvylshikimate 3-phosphate synthase with altered sensitivity showed over 100-fold greater resistance to the herbicide glyphosate (N-[phosphonomethyl]glycine) in comparison with its non-transformed progenitor (parental control) at the third-leaf stage. Studies with [¹⁴C]-glyphosate at a dosage lethal to the parental control, but sublethal to the transgenic, revealed that a maximum of 45-65% of the applied dose was absorbed, with greater absorption occurring in transgenic plants. Translocation of glyphosate was closely related to its absorption (r value 0.956) with approximately 15% more of the applied dose being mobilized in transgenic plants than the parental controls. Analysis of electronic autoradiograms along the treated leaf lamina found discrete internal regions of glyphosate accumulation closely associated with the site of application. These regions contained lower amounts of glyphosate present in the treated leaf lamina was almost completely translocated in transgenic plants, while in the parental controls more remained and the leaf became necrotic. In both types of maize there was a small accumulation of herbicide in the tip region of the leaf which was not mobilized. Younger shoot tissues and roots were major sinks for translocated glyphosate accumulating approximately 25-40% of the applied dose depending upon treatment. In the parental control, equal amounts of glyphosate were found distributed between young shoot tissues and roots; while in transgenic plants, the young shoot tissue accumulated around three times more glyphosate than the roots. In both plant types, glyphosate was localized in the meristems and young, actively growing leaves. Specific glyphosate activity (the amount of glyphosate per unit dry weight of tissue) in the major sinks of the transgenic declined towards the end of the treatment period but remained relatively constant in the parental control. In conclusion, enhancing glyphosate resistance by genetic transformation influenced the absorption, translocation and distribution of this herbicide in whole plants.Keywords: Zea mays, glyphosate (N-[phosphonomethyl]-glycine), transgenic, absorption, translocation, source-sink.      

Distribution of labelled assimilates within a young apple tree after supplying14CO2to a leaf or shoot

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography. The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf. The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots. After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Translocation of paclobutrazol and gibberellic acid in Sturt's Desert Pea (Swainsona formosa)

The translocation patterns of paclobutrazol and gibberellic acid were studied by applying these plant growth regulators locally to the main or lateral shoots of Sturt's Desert Pea. Paclobutrazol only reduced the growth of shoots to which it was directly applied indicating that it was readily translocated acropetally within a shoot (via xylem) but not basipetally (via phloem), although some phloem translocation has been reported. Gibberellic acid elongated the main shoot and enhanced apical dominance irrespective of the place of application suggesting it is readily translocated both through xylem and phloem. The translocation patterns did not vary between the main or lateral shoots.     

LEAF DEVELOPMENT,PHOTOSYNTHESIS, AND C14 DISTRIBUTION IN POPULUS DELTOIDES SEEDLINGS

Rates of net photosynthesis and dark respiration and distribution of C¹⁴ from selected leaves were determined for young cottonwood (Populus deltoides) trees at different stages of development. Four series of five trees—one series for each of four treated leaf positions—were included in the study. Maximum C¹⁴ export occurred when a leaf had just attained maximum size. Lower stem leaves reached maturity quickly and began exporting photosynthate when demands of the young seedling were high. Leaves at higher stem positions matured more slowly, but senescence was also delayed so their effective export life was prolonged. Translocation from a newly exporting leaf was primarily upward to developing leaves and the apex. As a leaf at any one position aged, the translocation pattern gradually shifted from upward to bi-directional and finally to a predominantly downward direction. Photosynthate translocated downward was incorporated into stem wood and roots. Maximum photosynthetic efficiency coincided with the downward shift of C¹⁴ export. Thereafter, net photosynthesis began to decline, at first slowly and then more rapidly. The patterns of photosynthesis, respiration, and C¹⁴ export associated with leaf age all varied according to leaf position on the stem.     

Translocation and degradation of injected uniconazole in apple during a 4-month growing period

One-year-old ‘Golden Delicious’ apple trees grafted onto MM 106 rootstocks were injected in the rootstock stem (shank) with¹⁴C-uniconazole to determine the extent to which uniconazole is translocated and degraded over the length of an average growing season. In 4 months, 16% of recovered¹⁴C-activity was translocated to the new shoots. Most of the¹⁴C-activity remained in the rootstock. Chromatographic evaluation of shoot extracts demonstrated that the¹⁴C-activity associated with uniconazole decreased 49% in 4 months. However, shoot growth was still inhibited which suggests that the amount of uniconazole that was degraded did not interfere with the inhibition of gibberellin biosynthesis, probably due to the continuous translocation of uniconazole that occurred.     

THERMOMORPHOGENESIS IN LILIUM LONGIFLORUM

Stem elongation and leaf orientation in Lilium longiflorum Thunb. were influenced more by the difference (DIF) between day temperature (DT) and night temperature (NT) than absolute DT or NT from 14 to 30 C. Plant height and internode length increased 129 and 382%, respectively, as DIF (DT-NT) increased from –16 to 16 C as compared to only 15 and 58% when either DT or NT was increased from 14 to 30 C, respectively. Leaf orientation, defined as the angle between a line perpendicular to the stem and the line from the leaf base to the leaf tip, increased 43° (leaves became more upright) as DIF increased from –16 to 16 C. In contrast to plant height, internode length, and leaf orientation, leaf and flower length were influenced more by absolute temperature than DIF. Leaf and flower length decreased 32 and 14%, respectively, as NT increased from 14 to 30 C. DT had little effect on either leaf or flower length. The influence of DIF on stem elongation suggested that thermomorphogenesis was not a function of total plant carbohydrate or carbohydrate translocation. Instead, DIF appeared to influence the endogenous gibberellin content or the response of plant tissue to gibberellin. Similarities between thermomorphogenic plant responses and photomorphogenic plant responses suggested that these two processes may be related with respect to their perception and/or transduction.     

UV-B-induced Inhibition of Stem Elongation and Leaf Expansion in Pea Depends on Modulation of Gibberellin Metabolism and Intact Gibberellin Signalling

Information on the involvement of elongation-controlling hormones, particularly gibberellin (GA), in UV-B modulation of stem elongation and leaf growth, is limited. We aimed to study the effect of UV-B on levels of GA and indole-3-acetic acid (IAA) as well as involvement of GA in UV-B inhibition of stem elongation and leaf expansion in pea. Reduced shoot elongation (13%) and leaf area (37%) in pea in response to a 6-h daily UV-B (0.45 W m^?2) exposure in the middle of the light period for 10 days were associated with decreased levels of the bioactive GA₁ in apical stem tissue (59%) and young leaves (69%). UV-B also reduced the content of IAA in young leaves (35%). The importance of modulation of GA metabolism for inhibition of stem elongation in pea by UV-B was confirmed by the lack of effect of UV-B in the le GA biosynthesis mutant. No UV-B effect on stem elongation in the la cry-s (della) pea mutant demonstrates that intact GA signalling is required. In conclusion, UV-B inhibition of shoot elongation and leaf expansion in pea depends on UV-B modulation of GA metabolism in shoot apices and young leaves and GA signalling through DELLA proteins. UV-B also affects the IAA content in pea leaves.     

14CO2 Fixation, Translocation, and Carbon Metabolism in Rapidly Expanding Leaves ofPopulus deltoides

To examine ¹⁴CO₂ fixation, potential translocation, and carbonflow among leaf chemical fractions of young developing leaves,the shoot tip of 24-leaf cottonwood (Populus deltoides Bartr.ex. Marsh) plants were cut off under water, placed in artificialxylem sap, and treated with ¹⁴CO₂ in continuous and pulse-chaseexperiments. Additional leaves on whole plants were spot treatedon the lamina tip to follow export from the tip only. The analysedleaves ranged in age from leaf plastochron index(LPI) –5to 3, the spot treated leaves from LPI 2 to 5. After 30 minfixation, the specific activity in the lamina tip increasedlinearly with leaf age from LPI –5 to 1 (0.5 to 4.5 kBqmg^–1). Specific activity in the lower lamina increasedslowly with leaf age and did not reach 500 kBq mg^–1 untilLPI –1. Total ¹⁴CO₂ fixed in the lower lamina exceededthat fixed in the tip by LPI –2 because of the large amountof tissue present in the lower lamina. Although the lamina tipfixed high levels of ¹⁴CO₂, pulse-chase studies coupled withautoradiography indicated no vein loading or translocation fromthe tip until about LPI 4 or 5. The ¹⁴C fixed in both tip andlower lamina was incorporated at the site of fixation and wasnot distributed to younger tissue or translocated from the lamina.Although the percentage distribution (¹⁴C in each chemical fractioncompared with the total in all fractions) of ¹⁴C among certainchemical fractions, e.g. sugars, amino acids and proteins, indicatedthat the mesophyll of the tip was more mature than the lowerlamina, physiologically both leaf sectors were immature basedon the expected ¹⁴C distribution in mature tissue. Informationfrom this and other studies indicates that the extreme tip ofa developing cottonwood leaf first begins to export photosynthateabout LPI 4 or 5 on a 24-leaf plant. The first photosynthatetranslocated may be incorporated into the vascular tissues andmesophyll directly below the tip. However, as the tip continuesto mature photosynthate is translocated past the immature lowerlamina into the petiole and out of the leaf. Populus deltoides Bartr. ex. Marsh, eastern cottonwood, translocation, leaf development, ¹⁴C fixation, carbon metabolism     

Effects of applied gibberellic acid and paclobutrazol on leaf expansion and biomass allocation in two Aegilops species with contrasting leaf elongation rates

The role of gibberellin (GA) in leaf elongation has long been known, however, its involvement in whole shoot growth and biomass allocation is much less clear. We studied the effects of exogenously supplied GA₃ and paclobutrazol, an inhibitor of GA biosynthesis, on these processes in Aegilops caudata and Aegilops tauschii , species with contrasting leaf growth characteristics. In both species, addition of GA₃ increased leaf elongation rate (LER) through its promoting effect on both cell size and cell number, while paclobutrazol decreased it. Similarly, GA₃ increased biomass allocation to the leaves, mainly leaf sheaths, at the cost of allocation to the roots, whereas paclobutrazol had the opposite effect in both species. Despite the increase in LER and biomass allocation to the shoot upon GA₃ application, the relative growth rate (RGR) remained constant. Specific leaf area (SLA) was only temporarily affected by GA₃ addition. Our results show that the inherent differences in LER and biomass allocation between the slow-elongating A. caudata and the fast-elongating A. tauschii are considerably reduced by the exogenous supply of GA₃ to the slow-elongating species, or paclobutrazol to the fast-elongating one. This suggests a role for gibberellins in explaining inherent differences in leaf area expansion and biomass allocation between the two species in this study.     

MODIFICATION OF THE VEGETATIVE DEVELOPMENT OF PHASEOLUS VULGARIS WITH N,N-DIMETHYLAMINOMALEAMIC ACID

Bean plants treated with N, N-dimethylaminomaleamic acid (DMAM) were characterized by a reduction in plant height, dark-green foliage, short, thick internodes, restricted petiole extension, and, at high concentrations, a slight reduction in leaflet expansion and dry matter accumulation. DMAM specifically affects internodal and petiolar tissues. The inhibitory stimulus of DMAM is readily translocated following application to a single leaf and the subsequent suppression of stem elongation increased with increasing dose. The failure of the rachises of the trifoliate leaves to fully extend resulted in an overlapping of the bases of the lamellae of the individual leaflets. The inhibitory effects of DMAM on stem elongation can be completely reversed with gibberellin A₃ (10 or 100 ppm). This might suggest, that DMAM may be interfering with the natural synthesis of gibberellin in the plant.     

Transitory growth control of apple seedlings with less persistent triazole derivatives

Paclobutrazol, triapenthenol (RSW0411), and BAS111 were applied to 4-week-old Delicious apple seedlings (Malus domestica Borkh.) as a root drench at 0.1, 1.0, and 10.0 mg per plant. Paclobutrazol eliminated shoot extension growth for 8 weeks at all three rates. RSW0411 controlled shoot elongation only at the highest rate. BAS111 produced the widest response, with shoot growth ranging from 38% to 93% of controls for the highest and lowest rates, respectively. Generally, leaf area decreased and leaf density increased with increasing rates of all chemicals. Root weight of plants treated with paclobutrazol nearly doubled but increased only slightly with RSW0411 and BAS111. Chemical analysis of the leaf tissue 8 weeks after treatment showed paclobutrazol levels highest, followed by RSW0411 and BAS111. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Visualizing real time [11C]methionine translocation in Fe-sufficient and Fe-deficient barley using a Positron Emitting Tracer Imaging System (PETIS)

[¹¹C]methionine was supplied to Fe-deficient and Fe-sufficient barley plants through a single leaf, and real time ¹¹C movement was monitored using a Positron Emitting Tracer Imaging System (PETIS). In Fe-deficient plants, [¹¹C]methionine was translocated from the tip of the absorbing leaf to the 'discrimination centre' located at the base of the shoot, and then retranslocated to all the chlorotic leaves within 60 min, while a negligible amount was retranslocated to the roots. In Fe-sufficient plants, methionine was translocated to the discrimination centre and then only to the newest leaf on the main shoot within 60 min. A negligible amount was also retranslocated to the roots. In conclusion, methionine from the above-ground parts of a plant is not a precursor of mugineic acid under Fe-deficiency. The discrimination centre is suggested to play a vital role in the distribution of mineral elements and metabolites in graminaceous monocots.Keywords: [¹¹C]methionine, discrimination centre, Fe deficiency, mugineic acid, PETIS.      

Studies of the response of peach and nectarine plants to gibberellin biosynthesis inhibitors in a hydroponic system

In small rooted peach and nectarine plants grown in a hydroponic system, low paclobutrazol (PBZ) levels applied to the roots suppressed shoot and root development, but to a different degree. A much stronger retarding effect was observed on the shoot, with a very limited effect on roots, resulting in a reduced shoot:root ratio. The effect of the inhibitor on the roots was a rapid increase in root diameter, with increased root branching upon recovery from the inhibiting effect. Root thickening, a typical response to PBZ, was detected also in nectarines when only the top was treated with the inhibitor, indicating a basal movement of PBZ, thus contradicting the accepted notion that its translocation is only acropetal. Root thickening was the earliest detected morphological response to PBZ, being observed already 3 days after exposure to the retardant. The return to a normal diameter was abrupt. Uniconazol (UNI) had a much stronger retarding effect on peach plants than did similar concentrations of PBZ. Reduced top growth resulted in a reduction in water consumption.Abbreviations PBZ paclobutrazol - UNI uniconazol - GA Gibberellin - GBI gibberellin biosynthesis inhibitor - ABA abscisic acid This research was supported by Grant no. 1-779-84 from the US-Israel Binational Agricultural Research and Development Fund (BARD).Contribution from the Agricultural research organization, The Volcani Center, Bet Dagan, Israel. No. 1506-E, 1994 series.     

An Anatomical Study of Rhizome Bud Formation Induced by Paclobutrazol and Adventitious Root Formation in In Vitro Cultures of Lapageria rosea (Ruiz et Pav.)

An anatomical study was made of bud dimorphism in in vitro shootcultures of Lapageria rosea cv. Nashcourt, utilizing the presenceand absence of the gibberellin-biosynthesis inhibitor paclobutrazol(10 µM) in the medium to control the development of axillarybuds. Patterns of axillary bud development differed betweenthe aerial pattern of shoot extension (in the absence of paclobutrazol)and rhizome bud formation (in the presence of paclobutrazol),with respect to planes of cell division, cell expansion andthe formation of adventitious root primordia. These differencesare examined and discussed. Lapageria rosea cv. Nashcourt, Chilean Bellflower, rhizome bud, paclobutrazol, gibberellin biosynthesis inhibitor, micropropagation     

Controlling plant growth via the gibberellin biosynthesis system – I. Growth parameter alterations in apple seedlings

'York Imperial' apple seedlings ( Malus domestica Borkh.) were continuously supplied via the roots with paclobutrazol [(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol)], a triazole GA biosynthesis inhibitor, at 0.68 μ M in a nutrient solution. In comparison to controls, seedlings treated with paclobutrazol for 66 days showed a 91% reduction in shoot length, a 66% reduction in leaf area but only a 17% reduction in leaf number. This effect could be reversed by GA₃ applied to the foliage at 71.4 μ M 0, 19 or 35 days after paclobutrazol was initially supplied and leaf area values for paclobutrazol-treated seedlings given both treatments did not differ significantly from controls. Plots of growth data indicate linearity of shoot longitudinal growth of GA₃-treated seedlings. Leaf area increase was non-linear after GA₃ treatment up to approximately 30 days, when the rate dropped. On a per shoot basis, leaf weight closely followed leaf area but on a per unit area basis, paclobutrazol-treated leaves were heavier than controls; GA₃ applications temporarily reversed this trend.