Effect of the Rht3 dwarfing gene on dynamics of cell extension in wheat leaves, and its modification by gibberellic acid and paclobutrazol

The second leaf of wheat was used as a model system to examinethe effects of the Rht3 dwarfing gene on leaf growth. Comparedto the rht3 wild type, the Rht3allele decreased final leaf length,surface area and dry mass by reducing the maximum growth rates,but without affecting growth duration. Gibberellic acid (GA₃)increased final leaf length and maximum growth rate in the rht3wild type, but was without effect on the Rht3 mutant, whichis generally regarded as being non-responsive to gibberellin(GA). Paclobutrazol, an inhibitor of GA biosynthesis, decreasedfinal leaf length and maximum growth rate in the rht3 wild typeto values similar to those in the untreated Rht3 mutant. NeitherGA₃ nor paclobutrazol affected the duration of leaf growth.The decrease in leaf length was produced by reduction of celllength rather than cell number. The maximum relative elementalgrowth rate (REGR) for cell extension was essentially the samein all treatments, as was the time between the cells leavingthe meristem and achieving maximum extension rate. The differencesbetween the genotypes and treatments were all almost entirelydue to differences in the time taken from the attainment ofmaximum REGR of cell extension to the cessation of extension.This was reflected in the length of the extension zone, whichwas approximately 6–8 per cent of final leaf length. Theeffects of the Rht3 allele, GA₃ and paclobutrazol all appearto be on the processes which promote the cessation of cell elongation. Key words: Cell extension, gibberellin, leaf growth, Rht3 gene, Triticum, wheat     

Effect of Temperature on Gibberellin (GA) Responsiveness and on Endogenous GA(1) Content of Tall and Dwarf Wheat Genotypes

Near-isogenic wheat (Triticum aestivum L.) lines differing in height-reducing (Rht) alleles were used to investigate the effects of temperature on endogenous gibberellin (GA) levels and seedling growth response to applied GA₃. Sheath and lamina lengths of the first leaf were measured in GA treated and control seedlings, grown at 11, 18, and 25°C, of six Rht genotypes in each of two varietal backgrounds, cv Maris Huntsman and cv April Bearded. Endogenous GA₁ levels in the leaf extension zone of untreated seedlings were determined by gas chromatography-mass spectrometry with a deuterated internal standard in the six Maris Huntsman Rht lines grown at 10 and 25°C. Higher temperature increased leaf length considerably in the tall genotype, less so in the Rht1 and Rht2 genotypes, and had no consistent effect on the Rht1+2, Rht3 and Rht2+3 genotypes. In all genotypes, endogenous GA₁ was higher at 25°C than at 10°C. At 10°C the endogenous GA₁ was at a similar level in all the genotypes (except Rht2+3). At 25°C it increased 1.6-fold in the tall genotype, 3-fold in Rht1 and Rht2, 6-fold in Rht3, and 9-fold in Rht1+2. Likewise, the genotypic differences in leaf length were very conspicuous at 25°C, but were only slight and often unsignificant at 11°C. The response of leaf length to applied GA₃ in the Rht1, Rht2, and Rht1+2 genotypes increased significantly with lowering of temperature. These results suggest the possibility that the temperature effect on leaf elongation is mediated through its effect on the level of endogenous GA₁ and that leaf elongation response to endogenous or applied GAs is restricted by the upper limits set by the different Rht alleles.     

Effects of NORIN 10 and Tom Thumb Dwarfing Genes on Morphology, Physiology and Abscisic Acid Production in Wheat

The pleiotropic effects of three genetically related dwarfinggenes were investigated in near-isogenic lines of wheat. TheNORIN 10 semi-dwarfing alleles, Rht 1 and Rht 2, and the TomThumb allele, Rht 3, were assessed for effects on some vegetativemorphological and physiological characters. The Rht allelesaffected leaf size with a resultant decrease in leaf area ofthe whole plant. Rht 3, which had the most marked effects, reducedleaf area in young plants by as much as 30 per cent. Althoughflag leaf dimensions and stomatal distributions of the flagleaf were altered, the gene had no effect on its area, stomatalconductance or net CO₂ exchange rate. Comparisons of Rht andtall plants revealed no differences in the abscisic acid (ABA)levels of either turgid or partially dehydrated leaves. Triticum aestivum L., wheat, dwarfing genes, leaf structure, abscisic acid, stomatal conductance, CO₂, exchange, relative growth rate     

The regulation of leaf elongation and xyloglucan endotransglycosylase by gibberellin in 'Himalaya' barley (Hordeum vulgare L.)

The potential role of xyloglucan endotransglycosylase (XET)in GA-stimulated cell elongation was investigated during leafexpansion in barley (Hordeum vulgare L.). XET activity in aqueousextracts of leaves was detected in all segments along the elongatingblade of leaf 1 of seedlings, but was at highest levels in basalsegments. Leaf 1 elongation rates of gibberellin (GA)-responsivedwarf mutants were lower than the wild type, and accompaniedby reduced levels of XET activity. Leaf elongation rates ofthe dwarfs increased following treatment with gibberellic acid(GA₃) associated with higher levels of XET activity. The slendermutant, crossed into a dwarfing background, exhibited high ratesof leaf 1 elongation and high levels of XET activity withoutadded GA₃. The elongation of leaf 3 in a GA-responsive dwarfmutant was also studied. Treatment with GA₃ resulted in bladeand sheath lengths being 5-fold and 7-fold (respectively) thelengths of controls, and again there were increases in bladeand sheath XET activities. To investigate the basis for changesin XET activity levels two XET-related cDNA clones were isolated.RNAs detected by the two clones occurred at the highest levelsin basal segments of rapidly elongating leaves, but they haddifferent distribution patterns along the leaf. Overall, thedata indicate that an XET-like activity is detectable in barleyleaves, that the activity level and related. Key words: Gibberellin (GA), leaf elongation, Hordeum vulgare, xyloglucan endotransglycosylase (XET)     

Exogenous GA3 Application Can Compensate the Morphogenetic Effects of the GA-Responsive Dwarfing Gene Rht12 in Bread Wheat

The most common dwarfing genes in wheat, Rht-B1b and Rht-D1b, classified as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA, have been verified as encoding negative regulators of gibberellin signaling. In contrast, the response of gibberellin-responsive (GAR) dwarfing genes, such as Rht12, to exogenous GA is still unclear and the role of them, if any, in GA biosynthesis or signaling is unknown. The responses of Rht12 to exogenous GA₃ were investigated on seedling vigour, spike phenological development, plant height and other agronomic traits, using F_2∶3 and F_3∶4 lines derived from a cross between Ningchun45 and Karcagi-12 in three experiments. The application of exogenous GA₃ significantly increased coleoptile length and seedling leaf 1 length and area. While there was no significant difference between the dwarf and the tall lines at the seedling stage in the responsiveness to GA₃, plant height was significantly increased, by 41 cm (53%) averaged across the three experiments, in the GA₃-treated Rht12 dwarf lines. Plant height of the tall lines was not affected significantly by GA₃ treatment (<10 cm increased). Plant biomass and seed size of the GA₃-treated dwarf lines was significantly increased compared with untreated dwarf plants while there was no such difference in the tall lines. GA₃-treated Rht12 dwarf plants with the dominant Vrn-B1 developed faster than untreated plants and reached double ridge stage 57 days, 11 days and 50 days earlier and finally flowered earlier by almost 7 days while the GA₃-treated tall lines flowering only 1–2 days earlier than the untreated tall lines. Thus, it is clear that exogenous GA₃ can break the masking effect of Rht12 on Vrn-B1 and also restore other characters of Rht12 to normal. It suggested that Rht12 mutants may be deficient in GA biosynthesis rather than in GA signal transduction like the GA-insensitive dwarfs.     

Effects of Gibberellin on Shoot Development in the dgt Mutant of Tomato

The morphological effects of gibberellin A₃ (GA₃) on the dgtmutant of tomato were investigated. The mutant effectively showedthe normal range of responses, including a promotion of stemlength due to an increased number of longer internodes, a dramaticincrease in apical dominance, and effects on leaf shape andcolour. In the case of stem elongation, the quantitative responseof the mutant was greater than normal. The morphological abnormalitiescharacteristic of the dgt mutant, such as horizontal growth,a thin stem and hyponastic leaves, were not normalized by GA₃. It is concluded that the demonstrated lack of response to auxinof the dgt mutant does not impair its gibberellin responses. Tomato, gibberellin, auxin, mutant, shoot development     

The Effect of (2-chloroethyl)-trimethylammonium Chloride on the Growth of Barley

Barley (Hordeum vulgare L. C.I.666) was shown to be susceptibleto the growth retardant (2-chloroethyl)-trimethylammonium chloride(CCC). The estimation of cell number in the dwarfed third leafblade indicated that a decrease in mitotic activity had occurredin treated plants. There was also a decrease in cell size intreated plants. The dwarfing action of CCC was reversed by exogenousgibberellic acid (GA₃) but this was shown to be the result ofincreased cell elongation only. GA₃ did not promote cell divisionin healthy or CCC-treated plants. Assay of endogenous gibberellinsshowed a significant reduction in the level of a substance correspondingto GA₃ in CCC-treated plants. It is suggested that CCC-induceddwarfing of barley is largely the result of a reduction in meristematicactivity. This may be related to an effect on gibberellin biosynthesisbut is not reversed by the application of exogenous GA ₃.     

Gibberellins and leaf expansion in near-isogenic wheat lines containing Rht1 and Rht3 dwarfing alleles

In near-isogenic lines of winter wheat (Triticum aestivum L. cv. Maris Huntsman) grown at 20° C under long days the reduced-height genes, Rht1 (semi-dwarf) and Rht3 (dwarf) reduced the rate of extension of leaf 2 by 12% and 52%, respectively, compared with corresponding rht (tall) lines. Lowering the growing temperature from 20° to 10° C reduced the rate of linear extension of leaf 2 by 2.5-fold (60% reduction) in the rht3 line but by only 1.6-fold (36% reduction) in the Rht3 line. For both genotypes, the duration of leaf expansion was greater at the lower temperature so that final leaf length was reduced by only 35% in the rht3 line and was similar in the Rht3 line at both temperatures. Seedlings of the rht3 (tall) line growing at 20° C responded positively to root-applied gibberellin A₁ (GA₁) in the range 1–10 μM GA₁; there was a linear increase in sheath length of leaf 1 whereas the Rht3 (dwarf) line remained unresponsive. Gibberellins A_{1, 3, 4, 8, 19, 20, 29, 34, 44} and ₅₃ were identified by full-scan gas chromatography-mass spectrometry in aseptically grown 4-d-old shoots of the Rht3 line. In 12-d-old seedlings grown at 20° C, there were fourfold and 24-fold increases in the concentration of GA₁ in the leaf expansion zone of Rht1 and Rht3 lines, respectively, compared with corresponding rht lines. Although GA₃ was present at a similar level to GA₁ in the rht3 (tall) line it accumulated only fivefold in the Rht3 (dwarf) line. The steady-state pool sizes of endogenous GAs were GA₁₉ ? GA₂₀ = GA₁ in the GA-responsive rht3 line whereas in the GA non-responsive Rht3 line the content of GA₁₉≈ GA₂₀ ? GA₁. It is proposed that one of the consequences of GA₁ action is suppression of GA₁₉-oxidase activity such that the conversion of GA₁₉ to GA₂₀ becomes a rate-limiting step on the pathway to GA₁ in GA-responsive lines. In the GA-non-responsive Rht lines it is suggested that GA₁₉ oxidase is not downregulated to the same extent and GA₁ accumulates before the next rate-limiting step on the pathway, its 2β-hydroxylation to GA₈. The steady-state pool sizes of GA_{19, 20, 1, 3} and ₈ were similar in developmentally equivalent tissues of the rht3 (tall) line growing at 10° C and 20° C despite a 2.5-fold difference in the rate of leaf expansion. In contrast, in the Rht3 (dwarf) line, the extent of accumulation of GA₁ reflected the severity of the phenotype at the two temperatures with slower growing tissues accumulating less, not more, GA₁. These results are interpreted as supporting the proposed model of regulation of the GA-biosynthetic pathway rather than previous suggestions that GA₁ accumulates in GA-insensitive dwarfs as a consequence of reduced growth rates.     

Effects of Interactions between Low-temperature Treatments, Gibberellin (GA3) and Photoperiod on Flowering and Stem Height of Spring Rape (Brassica napus var. annua)

Exogenous gibberellin A₃(GA₃) reduced the number of leaf nodesat flowering and time to flowering and increased the stem heightat flowering in three genotypes of spring rape (Brassica napusvar.annua L.). The responses to GA₃were similar to those forlong days (LD) and low-temperature treatments, suggesting thatthe effect of photoperiod and the vernalization response areprobably mediated through gibberellins. The response to exogenousGA₃was greatest in non-cold-treated plants in short days (SD)suggesting that endogenous GAs are limiting in these conditions.CCC, an inhibitor of gibberellin biosynthesis, caused a smallincrease in the number of leaf nodes at flowering and time toflowering and a small decrease in the stem height at flowering,but unexpectedly, its effect was hardly influenced by the applicationof exogenous GA₃. Genotypes that showed the clearest responsesto the treatments with regard to the number of leaf nodes atflowering and time to flowering did not show the clearest responseswith regard to the stem height at flowering; the pattern ofresponses of the number of leaf nodes at flowering and timeto flowering was distinct from that of stem height at flowering.This indicates that flower formation and stem elongation areseparable developmental processes which may be controlled bydifferent endogenous gibberellins, different levels of a specificendogenous gibberellin, or different responses to gibberellin.Copyright 1999 Annals of Botany Company Brassica napus var. annua, gibberellin, photoperiod, spring rape, vernalization.     

The Spatial Distribution of Growth in the Extension Zone of Seedling Wheat Leaves

Two models of the distribution of relative elemental rates ofelongation (RELEL) were tested for the extension zone (EZ) ofthe first foliage leaf of seedling wheat plants, by comparisonto patterns of separation of rings and gyres in the walls ofprotoxylem vessels. One model, containing a defined growth maximumin the basal half of the EZ, is favoured in the literature andwas derived from data published for perennial ryegrass. Theother, containing a flat, broad maximum throughout the regionof the EZ with stomates, was constructed from regressions ofinterstomatal distance against distance along the EZ in thefirst foliage leaf of wheat seedlings. The test strongly favouredthe model with the flat maximum. Although the gibberellic acid(GA) insensitivity alleles Rht1 and Rht2 reduce length of extensionzone (LEZ), leaf extension rate (LER) and final cell and leaflengths, they had no effect on maximum RELEL. Results with aninhibitor of GA synthesis indicated that control of leaf elongationby the control of LEZ may be generalizable as a mechanism bywhich GA controls LER in the grass leaf. Extension zone, elongation, gibberellic acid, Rht, wheat, Triticum aestvum L.     

Influence of Gibberellic Acid and the Rht3 Gene on Choline and Phospholipid Metabolism in Wheat Aleurone Tissue

The effect of gibberellic acid (GA3) on phospholipid metabolismand -amylase production was studied in aleurone tissue of twonear-isogenic lines of wheat (Triticum aesuvum L.). Incubationof embryoectomized seeds from a GA-responsive line (rht3, tall)with GA₃ caused the induction of -amylase activity after a lagphase of 30 h. In the case of embryoectomized seeds from a ‘GA-insensitive’line (Rh13, dwarf), however, the lag phase was extended up to50 h. During the first 14 h following imbibition, GA₃ inhibitedcholine uptake and its subsequent incorporation into phosphatidylcholine in the Rhr3 line but not in the rht3 line. GA₃ promotedphospholipid breakdown in both the lines during this period,however. GA₃ also terminated independent turnover of the cholineN-methyl groups in phosphatidyl choline and promoted turnoverof the whole choline headgroup. These results are discussedin relation to the possibility that phosphatidyl choline turnoveris an integral part of the GA₃ signal-transduction mechanismin aleurone tissue. Key words: GA3, Rht3 gene, choline, phospholipid     

Regulation of Leaf Shape in the Solanifolia Mutant of Tomato (Lycopersicon esculentum) by Plant Growth Substances

The solanifolia mutant (sf/sf) of tomato (Lycopersicon esculentum)produces leaves consisting of leaflets with entire margins,unlike the lobed leaflets of normal plants. Normal plants treatedwith gibberellic acid (GA₃) produced leaves with entire marginswhereas mutant plants exposed to 2-chloroethyl-trimethyl ammoniumchloride (CCC)—an inhibitor of gibberellin biosynthesis—producedlobing of leaflets. The leaf area of the mutant was significantlygreater than that of the normal, but was not significantly differentfrom GA₃-treated normal leaves. Similarly, in CCC-treated mutantleaves the leaf area was not different from that of normal untreatedleaves. These observations suggest that the sf/sf mutation affectsthe leaf shape through its effect on endogenous gibberellinsand/or inhibitory substances. Leaf shape, Lycopersicon esculentum, plant growth substances, tomato     

Quantitative Analysis of Endogenous Gibberellins in Normal and Dwarf Cultivars of Rice

Endogenous levels of gibberellins in shoots and ears of twodwarf rice (Oryza sativa L.) cultivars, Tan-ginbozu (dx mutant)and Waito-C (dy mutant), were analyzed and compared with thoseof normal rice cultivar, Nihonbare. The endogenous levels of13-hydroxylated gibberellins in Tan-ginbozu were much lowerthan those in Nihonbare. In Waito-C, the levels of GA₁₉ andGA₂₀ in the shoots were higher but that of GA₁ was lower thanthe levels of these gibberellins in Nihonbare. These resultssupport the hypothesis that the dy gene controls the 3ß-hydroxylationof GA₂₀ to GA₁ while the dx gene controls a much earlier stepin the gibberellin biosynthesis. Our results indicate that GA₁is the active gibberellin that regulates the vegetative growthof rice. The endogenous levels of GA₄ in the ears of the twodwarf cultivars of rice were higher than the level of GA₄ inthe ears of the normal cultivar, Nihonbare suggesting that thebiosynthesis of gibberellin is not blocked in the anthers ofthe dwarf rice. (Received April 27, 1989; Accepted July 12, 1989)     

Effect of GA3 on the Molecular Mass of Polyuronides in the Cell Walls of Alaska Pea Roots

The role of cell wall matrix polysaccharides in gibberellin-regulatedroot growth is unknown. We examined pectic polysaccharides frompea roots treated with or without gibberellin A₃ (GA₃) in thepresence of ancymidol, an inhibitor of gibberellin biosynthesis.Pectic polymers solubilized by CDTA (trans-l,2-cyclohexanediamine-N,N,N',N'-tetraaceticacid) at 23°C and subjected to gel permeation analysis exhibitedhigh polydispersity with a molecular mass in excess of 500 kDa.Subsequent extraction of cell walls with CDTA at 100°C solubilizedpolymers with an average mol mass of 10 to 40 kDa. Subjectingthe high molecular mass pectic polymers extracted at 23°Cto 70–100°C for 2h generated 10 to 40 kDa fragments,similar in size distribution to those solubilized directly fromcell walls by CDTA solutions at 100°C. Pectic polymers from(GA₃+Anc)-treated roots were of higher average mol mass thanthose from Anc-treated roots in both the elongation zone andin the basal maturation zone. Since (GA₃+Anc)-treated rootselongate more quickly than Anc-treated roots [Tanimoto (1994)Plant Cell Physiol. 35:1019], the slender, GA₃-treated rootsmay produce and deposit highly integrated pectins more rapidlythan the thicker, Anc-treated roots in the elongating or elongatedcell walls. ²Present address: Horticultural Sciences Department, POB 110690IFAS, University of Florida, Gainesville, FL 32611-0690 U.S.A.     

Effects of Repetitive Acid Immersion, Red Light, and Gibberellin A3 Treatments on Phytochrome-mediated Germination Control in Skotodormant Lettuce Seeds

Dry lettuce seeds (Lactuca sativa L. cv. Grand Rapids), whichreceived 5 min far-red light (FR) 0.5 h after the onset of waterimbibition, showed 17% and 50% germination without and withacid immersion treatment (pH 0.1) for 1 h and rinsing with water,respectively. The acid treatment caused only 6% germinationor less in FR-treated seeds held for 10 to 30 d in dark storage.The 10 to 30 d skotodormant seeds did not respond to red light(R) or gibberellin A₃ (GA₃) singly, but showed 84% or higherpercentage germination if 1 h acid immersion was given beforeR or GA₃. The 20 d skotodormant seeds, which received R treatmentat day 10 but remained dormant showed 89% germination with onlyacid treatment. Similar values were obtained with 30 d skotodormantseeds which received one or two R treatments at day 10 or 20,i.e. the only requirement for these R-treated dormant seedswas an acid immersion. This releases the skotodormancy and rendersthe seeds more sensitive to R or GA₃, but the skotodormancywas initiated again if no light or hormone treatments were givenimmediately. The repetitive R or GA₃ treatments, which did notcause skotodormant seeds to germinate, lessened the degree ofskotodormancy. The germination of these skotodormant seeds canonly be induced by the synergistic action of R and GA₃. In thisstudy, GA₃ caused higher germination percentages in R-treatedskotodormant seeds than R stimulated in GA3-treated seeds. Itis suggested that (i) repetitive R or Ga₃ treatments maintaina high endogenous level of the far-red-absorbing form of phytochrome(P_fr) and GA activity, respectively, (ii) the accumulated stableintermediates of phytochrome persist in fully-imbibed skotodormantseeds for up to 20 d, without phytochrome expressing its functionuntil the seeds are acidified and (iii) a model is formulatedto interpret the results of acidification, growth promotersand R effects on germination of light-sensitive lettuce seeds. Key words: Phytochrome, Latuca saliva, seed germination, dark reversion of phytochrome, gibberellin A₃, acidification, skotodormancy     

The Role of Gibberellins in Early Growth and Development of Sugar Beet

Two gibberellin(GA)-like compounds were found in both rootsand shoots of sugar beet plants using the barley endosperm bioassay.One had chromatographic properties similar to GA₃ and GA₁; theother was highly non-polar, relatively inactive in the endospermassay, and may be a new gibberellin. Presence of the GA_3/1-likecompound was confirmed with the dwarf rice bio-assay. The quantityof this GA was relatively high in the root compared with theshoot at the 3–4 leaf stage when the first supernumerarycambia are being formed in the root. As plants developed throughthe 8–9 leaf stage and the 15–16 leaf stage thequantity of GA per unit fresh weight of material decreased. Application of gibberellic acid (GA₃) to the roots of youngsugar beet plants caused a significant increase in root dryweight shortly after treatment and the rate at which supernumerarycambia were produced was increased. Application of GA₃ to asingle petiole caused a significant increase in both root andshoot dry weight. GA₃ applied to either root or shoot causeda reduction in the rate of leaf formation although total leafarea per plant and shoot dry weight were unaffected. The probablerole of GA-like substances in controlling the growth and developmentof young sugar beet plants is discussed.     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Distribution of Radioactivity from Exogenously Supplied [1-14C]Indol-3-yl-acetic Acid and [3, 4-3H (N)] Gibberellin A, in Geotropically-stimulated Picea abies (L.) Karst. Roots

The distribution of exogenously-supplied radioactive labelledindol-3-yl-acetic acid (IAA) and gibberellin A₁ (GA₁) in geotropicallystimulated roots of Norway spruce (Picea abies (L.) Karst.)has been demonstrated. Seedlings were positioned with theirroot tips in 2.1 x 10^–6 M [¹⁴C]IAA or 1.3 x 10^–8m ³H-GA₁ for 4 and 20 h, respectively. After geotropic stimulationfor 90 min in the horizontal position the root tips were cutlongitudinally in 50 µm thick sections, using a freeze-microtome.The radioactivity in the ¹⁴C-IAA treated roots occurred in higherconcentration in the lower than in the upper halves (ratio 1.25:1). A similar trend was observed in the [³H]GA₁-treated rootswhere the ratio lower: upper halves was 2.04: 1. The ratio ofradioactivity in right and left halves of vertical roots wasapproximately the same in roots supplied with [¹⁴C]IAA and [³H]GA₁(1.09: 1). The supplied radioactive compounds were analysed chromatographicallyafter extraction in methanol of 6 mm apical root segments. Onlya small fraction (7–8 per cent) of the supplied [¹⁴C]IAAwas revealed unchanged in the segments. The major part of thechromatographed, labelled compound has not been identified,but on basis of its R_F value it is suggested that it may beindol-3-acetyl-aspartic acid (IAAasp). The chromatographic analysis of the [³H]GA,-treated segmentsshowed that only small fractions of this gibberellin has beenconverted to other compounds. These results have been discussed and correlated with knowledgeof plant growth regulators and their participation in root geotropism. Picea abies, spruce, geotropism, gibberellin A₁, indol-3-yl-acetic acid, growth regulators, redistribution in roots     

Gibberellic Acid Sensitivity Determines the Length of the Extension Zone in Wheat Leaves

To test the hypothesis that gibberellic acid (GA) sensitivityaffects the length of the extension zone (LEZ) of leaf No. 1of wheat seedlings, we performed a gene dosage experiment usingRht dwarfing genes that condition GA insensitivity. We utilizednearly isogenic lines, at Rht-dosage levels of 0, 2 and 4 alleles.Anatomical markers (distances between successive stomates) wereused to infer the distribution of growth along the axis of theleaf. Interstomatal distance (ISD) and LEZ were inverse linearfunctions of Rht-dosage. The number of stomates matured perhour was independent of Rht-dosage. The relationship betweenISD and distance along the axis within the extension zone (EZ)was indistinguishable from linear. Rht-dosage did not affectthe slope of the regression of ISD against distance along theEZ. A-REST (AR; ancymidol, a potent GA synthesis inhibitor)reduced LEZ. Wild type was more sensitive to AR than doubledwarf. AR affected growth of leaf No. 1 more than length ofthe coleoptile, regardless of Rht-dosage. AR-dosage affectedcell division, whereas Rht-dosage did not. Extension zone, elongation, gibberellic acid, Rht, wheat, Triticum aesiivum L.