Gibberellin-regulated XET is differentially induced by auxin in rice leaf sheath bases during gravitropic bending

The asymmetric distribution of auxin plays a fundamental role in plant gravitropism, yet little is understood about how its lateral distribution stimulates growth. In the present work, the asymmetric distribution not only of auxin, but also that of gibberellins (GAs), was observed in rice leaf sheath bases following gravistimulation. Gravistimulation induced the transient accumulation of greater amounts of both IAA and GA in the lower halves of the leaf sheath bases of rice seedlings. OsGA3ox1, a gene of active GA synthesis, was differentially induced by gravistimulation. Furthermore, 2,3,5-tri-iodobenzoic acid (TIBA), an inhibitor of auxin transport, substantially decreased the asymmetric distribution of IAA and the gradient of OsGA3ox1 expression. Externally applied GA(3) restored the gravitropic curvature of rice leaf sheaths inhibited by either TIBA or by ancymidol, a GA synthesis inhibitor. The expression of XET (encoding xyloglucan endotransglycosylase) was differentially induced in the lower halves of gravistimulated leaf sheath bases and was also up-regulated by exogenous IAA and GA(3). Both ancymidol and TIBA decreased the gradient of XET expression. These data suggest that the asymmetric distribution of auxin effected by gravistimulation induced a gradient of GAs via asymmetric expression of OsGA3ox1 in rice leaf sheath bases, and hence caused the asymmetric expression of XET. Cell wall loosening in the curvature site of the leaf sheath triggered by the expression of XET would contribute to gravitropic growth.     

Gravistimulation leads to asymmetry of both auxin and gibberellin levels in barley pulvini

The auxin indole-3-acetic acid (IAA) is known to promote the biosynthesis of active gibberellins (GAs) in barley ( Hordeum vulgare ). We therefore investigated the possibility that this interaction might contribute to the gravitropic response of barley leaf sheath pulvini. Barley plants at the inflorescence stage were gravistimulated for varying times, and the pulvini were then separated into upper and lower halves for quantification of IAA and GAs by GC-MS. Consistent with the Cholodny–Went theory, the lower portion contained more IAA than did the upper portion. This difference was detected as early as 2.5 h after the start of gravistimulation, and bending was also observed at this stage. At later time points tested (6 h and 24 h), but not at 2.5 h or 3 h, the higher auxin content of the lower half was associated with a higher level of GA₁, the main bioactive GA in barley. Consistent with that result, the expression of Hv3ox2 , which encodes a key enzyme for the conversion of GA₂₀ to GA₁, was higher in the lower side than in the upper, after 6 h. It is suggested that in gravistimulated leaf sheath pulvini, auxin accumulates in the lower side, leading to a higher level of GA₁, which contributes to the bending response. Further evidence that GAs play a role in the gravitropic response was obtained from GA-related mutants, including the elongated sln1c mutant, in which GA signalling is constitutive. Pulvinar bending in the sln1c mutant was greater than in the wild-type. This result indicates that in the lower side of the gravistimulated pulvinus, the relatively high level of bioactive GA facilitates, but does not mediate, the bending response.     

Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin-insensitive genotype of wheat

Effect of gibberellic acid (GA₃) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)-insensitive (cv. Siete Cerros) genotype of wheat ( Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA₃ both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA₃ was additive, and there was no statistically signficant interaction between photoperiod and GA₃ concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA₃ under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.     

Distinct light responses of the adaxial and abaxial stomata in intact leaves of Helianthus annuus L

Using a laboratory-constructed system that can measure the gas exchange rates of two leaf surfaces separately, the light responses of the adaxial and abaxial stomata in intact leaves of sunflower ( Helianthus annuus L.) were investigated, keeping the intercellular CO₂ concentration ( C _i) at 300  µ L L⁻¹. When evenly illuminating both sides of the leaf, the stomatal conductance ( g _s) of the abaxial surface was higher than that of the adaxial surface at any light intensity. When each surface of the leaf was illuminated separately, both the adaxial and abaxial stomata were more sensitive to the light transmitted through the leaf (self-transmitted light) than to direct illumination. Relationships between the whole leaf photosynthetic rate ( A _n) and the g _s for each side highlighted a strong dependence of stomatal opening on mesophyll photosynthesis. Light transmitted through another leaf was more effective than the direct white light for the abaxial stomata, but not for the adaxial stomata. Moreover, green monochromatic light induced an opening of the abaxial stomata, but not of the adaxial stomata. As the proportion of blue light in the transmitted light is less than that in the white light, there may be some uncharacterized light responses, which are responsible for the opening of the abaxial stomata by the transmitted, green light.     

Effects of low concentrations of O3, leaf age and water stress on leaf diffusive conductance and water use efficiency in soybean

Ozone, leaf age and water stress each affected leaf conductance in soybean [ Glycine max (L.) Merr. Hodgson], but there were no interactions among these factors. Exposure to increased concentrations of O₃ (0.01, 0.05, 0.09. and 0.13 μl l⁻¹) resulted in linear declines in abaxial and adaxial conductances in leaves of all ages. There were no differences in relative response to O₃ between the two leaf surfaces. For well-watered plants, water use efficiency also decreased with exposure to increased O₃ concentrations (water-stressed plants were not tested). Abaxial conductance increased as leaves aged from 4 to 10 days and then declined with further aging. Adaxial conductance decreased with all increases in leaf age beyond 4 days, and the ratio of abaxial/adaxial conductance increased continuously throughout the leaf lifespan. During water-stress cycles (water withheld for 2–3 days) leaves of water-stressed plants had lower conductances than those from well-watered plants, and there was no difference in relative response between abaxial and adaxial stomata.     

Effects of catalase on the accumulation of H2O2 in rice cells inoculated with rice blast fungus, Magnaporthe oryzae

Roles of H₂O₂ in the infection process of Magnaporthe oryzae on rice were investigated. In a leaf sheath assay for up to 48 h post-inoculation, the absence or presence of catalase in the conidia suspension was correlated with the level of accumulated H₂O₂ in infected leaf cells, as observed by staining with 3',3-diaminobenzidine tetrahydrochloride. In the incompatible interaction, the appearance of autofluorescence or frequency of cell death characterized by granulation (symptoms characteristic of hypersensitive responses) was not significantly affected by the presence of catalase in the conidia suspension. In the leaf blade assay, inoculation of compatible conidia in the presence of catalase produced more severe symptoms than that of conidia in the absence of catalase at 6 days post-inoculation. These results suggest that, in this host–parasite interaction, the primary role of host-produced H₂O₂ is in limiting hyphal growth after penetration through toxic action. Furthermore, in incompatible interactions, H₂O₂ is implied not to be a major mediator of hypersensitive cell death.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

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.     

Growth and development of Brassica genotypes differing in endogenous gibberellin content. II. Gibberellin content, growth analyses and cell size

Three rapid cycling Brassica rapa genotypes were grown in greenhouse conditions to investigate the possible relationships between endogenous gibberellin (GA) content and shoot growth. Endogenous GA₁ GA₃ and GA₂₀ were extracted from stem samples harvested at 3 weekly intervals and analyzed by gas chromatography-mass spectrometry with selected ion monitoring, using [²H₂]-GA₁ and [²H₂]-GA₂₀ as quantitative internal standards. During the first 2 weeks, GA levels of the dwarf, rosette ( ros ), averaged 36% of levels in normal plants (on a per stem basis). Levels in the tall mutant, elongated internode (ein) , were consistently higher, averaging 305% of levels in normal plants.
Differences in shoot height across the genotypes resulted from varying internode length which resulted from epidermal cell length and number being increased in ein and decreased in ros relative to the normal genotype. The exogenous application of GA₃ to normal plants increased cell length while the application of paclobutrazol (PP333), a triazole plant growth retardant, reduced cell size. Thus, exogenous GA manipulations mimicked the influence of the mutant genes ros and ein. The dwarf, ros , had reduced shoot dry weights and relative growth rates compared to the other genotypes. Total dry weights were similar in ein and the normal genotype but stem weights were increased in ein , compensating for decreased leaf weights. Thus, the gibberellin-deficiency of ros resulted in generally reduced shoot growth. The overproduction of endogenous GA by ein did not result in enhanced shoot growth but rather a specific enhancement of internode elongation and stem growth at the expense of leaf size.     

Detection and identification of gibberellins in Douglas fir (Pseudotsuga menziesii) shoots

Extracts of Douglas fir ( Pseudotsuga menziesii [Mirb.] Franco) shoots were purified by reversed and normal phase HPLC; gibberellin (GA)-like compounds detected by radioimmunoassay with antibodies against GA₄ and the Tan-ginbozu dwarf rice micro-drop biossay were analyzed by GC-MS. Three major components were identified as GA₄, GA₇, and GA₉ while smaller amounts of GA¹, GA₃ and putative GA⁹-glucosyl ester were also present.     

Chromosome numbers of C3 and C4 variants within the species Alloteropsis sernialata (R.Br.) Hitchc. (Poaceae)

FREAN, M. L. & MARKS, E., 1988. Chromosome numbers of C₃ and C₄ variants within the species Alloteropais semialata (R.Br.) Hitch. (Poaceae). In a study of mid-lamina leaf sections, different variants of A. semialata were found to have C₃ or C₄ anatomy. The C₄ leaf showed a specialized photosynthetic vascular bundle sheath not present in the C₃ form. Chromosome counts made from pollen mother cell squashes showed that the C₃ form of A. semialata is a fertile diploid 2n = 2x = 18 and the C₄ form, a fertile allohexaploid 2n = 6x = 54. The cytological evidence suggests that the two forms should be considered as separate species.     

Variations in the dorso-ventral organization of leaf structure and Kranz anatomy coordinate the control of photosynthesis and associated signalling at the whole leaf level in monocotyledonous species

Photosynthesis and associated signalling are influenced by the dorso-ventral properties of leaves. The degree of adaxial/abaxial symmetry in stomatal numbers, photosynthetic regulation with respect to light orientation and the total section areas of the bundle sheath (BS) cells and the surrounding mesophyll (M) cells on the adaxial and abaxial sides of the vascular bundles were compared in two C₄[ Zea mays (maize) and Paspalum dilatatum ] and one C₃[ Triticum turgidum (Durum wheat)] monocotyledonous species. The C₃ leaves had a higher degree of dorso-ventral symmetry than the C₄ leaves. Photosynthetic regulation was the same on each side of the wheat leaves, as were stomatal numbers and the section area of the BS relative to that of the M cells (BS/M section area ratio). In contrast, photosynthetic regulation in maize and P. dilatatum leaves showed a marked surface-specific response to light orientation. Compared to the adaxial sides of the C₄ monocotyledonous leaves, the abaxial surfaces had more stomata and the BS/M section area ratio was significantly higher. Differences in dorso-ventral structure, particularly in Kranz anatomy, serve not only to maximize photosynthetic capacity with respect light orientation in C₄ monocotyledonous leaves but also allow adaxial and abaxial-specific signalling from the respective M cells.     

Internode length in Lathyrus odoratus. Effects of mutants l and lb on gibberellin metabolism and levels

After the application of [¹³C³H]-gibberellin A₂₀ to wild-type (tall) sweet peas ( Lathyrus odoratus L.) labelled gibberellin A₁ (GA₁), GA₈, GA₂₉ and 2-epiGA₂₉ were identified as major metabolities by gas chromatography-mass spectrometry after high performance liquid chromatography. By contrast in genetically comparable dwarf ( II ) plants only labelled GA₂₉ and 2-epiGA₂₉ were produced in significant amounts, although evidence was obtained for trace amounts of labelled GA₁ and GA₈. The apical portions of dwarf plants contained 8–10 times less GA₁ than those of tall plants but at least as much GA₂₀ (measured using di-deuterated internal standards). In conjunction with previous data these results strongly indicate that in genotype ll internode length is reduced and leaf growth altered by a reduction in GA1 levels attributable to a partial block in the 3β-hydroxylation of GA₂₀ to GA₁.
In contrast to dwarf plants, semidwarf plants (genotype lblb ) contained more GA₁ in the apical portion than wild-type counterparts. This is consistent with the suggestion that lb alters some aspect of GA sensitivity.     

Molecular weight distribution of hemicellulosic polysaccharides of the cell wall of tall and dwarf rice cultivars, and the effect of GA3

Growth rate, osmotic potential of the cell, cell wall mechanical properties, sugar composition and molecular weight (MW) distribution of water-soluble hemicellulosic polysaccharides of the second leaf sheath of one tall ( Oryza sativa L. cv. Nihonbare) and two dwarf ( Oryza sativa L. cvs. Tan-ginbozu and Waito C) cultivars of rice were compared. The effect of gibberellic acid (GA₃) on the above-mentioned parameters was also studied using the tall (Nihonbare) and one of the dwarf (Waito C) cultivar. The minimum stress-relaxation time (T₀) was higher in the cell wall from the two dwarfs than in the tall cultivar. Furthermore, in the water-soluble hemicellulosic polysaccharides the mass-average MW of β -glucan was higher and that of arabinoxylan was lower in the tall cultivar than in the dwarf ones. Thus, dwarfism of cvs Tan-ginbnozu and Waito C might be correlated with the different MW distributions of β -glucan and arabinoxylan. GA₃ induces growth in the dwarf Waito C cultivar, decreases the T₀ value of the cell wall, and also decreases the average MW of water-soluble hemicelluloses. Changes in β (1–3)(1–4)glucan or arabinoxylan or in both are proposed as part of the cell wall loosening mechanism induced by gibberellin.     

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.     

Endogenous gibberellins in young seedlings of wheat (Triticum aestivum) cultivars

Gibberellins A₁, A₃, A₄ and A₇ were identified by combined gas chromatography mass spectrometry (GC-MS) in leaf and stem tissues of 17-day-old seedlings of wheat ( Triticum aestivum L. ), cvs Siete Cerros (semi-dwarf, Rht1) and Møystad (tall), of F₁, hybrids from the cross Møystad × Siete Cerros and of 2 selected lines from the cross Møystad x Sonora 64 (Rht1 and Rht2). GA, and GA, were identified by full scan mass spectra separately in all 5 extracts, GA₄ and GA₇, were identified by selected ion monitoring in a bulked fraction. About 90% of the biological activity (Tan-ginbozu dwarf rice bioassay) in all 5 extracts was due to the GA₁/GA₃-fraction.     

Epidermal focussing and effects upon photosynthetic light-harvesting in leaves of Oxalis

Abstract. In Oxalis , epidermal cells on both the adaxial and abaxial surface of the leaf concentrated light within the leaf by a lens mechanism. Focal lengths of epidermal cells were estimated using two methods: they were calculated from radius of curvature measurements taken from individual epidermal cells, and were measured directly in agarose replicas of the leaf surface. In the three species of Oxalis examined, light that was incident upon the adaxial leaf surface was concentrated within the palisade, whereas light that was incident upon the abaxial leaf surface was concentrated within the spongy mesophyll. Using sensiometric analysis, theoretically maximal focal intesifications were measured in leaf replicas at the focal maximum and at intermediate positions corresponding to the mid-region of the palisade and spongy mesophyll tissues. Focal intensifications ranged from 2.2 to 10.4 times incident light at the focal maximum, and 1.3 to 4.5 in the palisade or spongy mesophyll layers. Elimination of epidermal focussing, by covering the leaf surface with a thin layer of mineral oil, strongly affected chlorophyll fluorescence induction curves resulting in a decrease of 10–40% in the initial (F₀) and variable fluorescence (F_v). These results are consistent with the interpretation that the chloroplasts were adapted to their light microenvironment within the leaf and that focussing by the epidermis channelled light to a population of chloroplasts that were adapted to high light.     

Light dependent activation of CO2 assimilation and the ratio of Rubisco activase to Rubisco during leaf aging of rice (Oryza sativa)

The effects of the ratio of Rubisco activase to Rubisco (activase/Rubisco ratio) on light dependent activation of CO₂ assimilation were investigated during leaf aging of rice. Changes of photosynthetic CO₂ gas exchange rates in relation to step increases of light intensity from two photon flux densities of 60 µmol m⁻² s⁻¹ (low initial PFD) and 500 µmol m⁻² s⁻¹ (high initial PFD) to saturated PFD of 1 800 µmol m⁻² s⁻¹ were measured. These photosynthetic activation processes were considered to be limited by the Rubisco activation rate when analyzed by the relaxation method. The relaxation time of low initial PFD gradually declined from 3 to 33 days after leaf emergence and showed high and negative correlation to the activase/Rubisco ratio. The initial rate of Rubisco activation under low initial PFD linearly correlated to the amounts of Rubisco activase, whereas these were almost constant from 3 to 23 days after leaf emergence. But these correlations could not be recognized in the case of high initial PFD. Moreover, the relaxation times were more sensitive to intercellular CO₂ concentration (C_i) under high initial PFD than under low initial PFD, especially, at C_i below 300 µl l⁻¹. These results suggest the involvement of the activase/Rubisco ratio in the photosynthetic activation under relatively low initial PFD, and the limitation of photosynthetic activation under relatively high initial PFD by Rubisco carbamylation during leaf aging of rice.     

Expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in maize tissues

The activity of the enzyme 3-hydroxy-3-methlglutaryl-coenzyme A reductase (HMGR, EC 1.1.1.34) is highly expressed in 4-day-old etiolated seedlings of normal (cv. DeKalb XL72AA), dwarf ( d ₅) and albino ( lw ₃) maize ( Zea mays L.). HMGR activity of maize seedlings appeared to be exclusively associated with the microsomal rather than the plastidic fraction of maize cells. Maize tissues with high meristematic activity such as germinating seeds, leaf bases, root tips and the site of origin of lateral roots contained high levels of microsomal HMGR activity. The activity of HMGR extracted from leaf tips of normal, dwarf and albino maize seedlings is regulated by light. Microsomal HMGR activity from leaf tips of 4-day-old maize seedlings was inhibited significantly following exposure to strong light (600 μmol m⁻² s⁻¹) for more than 10 h. By comparison, microsomal HMGR activity from leaf bases and root tips of maize was not inhibited by exposure to strong light. These results suggest that the microsomal HMGR which is highly expressed in maize may be related to sterol biosynthesis and membrane biogenesis rather than plastidic-associated isoprenoid synthesis and that light may regulate HMGR activity indirectly by increasing cell differentiation.