Changes in Arabidopsis leaf ultrastructure, chlorophyll and carbohydrate content during spaceflight depend on ventilation

Leaf structure and function under spaceflight conditions have received little study despite their important implications for biological life support systems using plants. Previous reports described disruption of the membrane apparatus for photosynthesis and a general decrease in carbohydrate content in foliage. During a series of three short-duration experiments (Chromex-03, -04, -05) on the US space shuttle (STS-54, STS-51, STS-68), we examined Arabidopsis thaliana leaves. The plants were at the rosette stage at the time of loading onto the space shuttle, and received the same light, temperature, carbon dioxide and humidity regimes in the orbiter as in ground controls. The experiments differed according to the regime provided in the headspace around the plants: this was either sealed (on mission STS-54); sealed with high levels of carbon dioxide (on mission STS-51) or vented to the cabin air through a filtration system (on mission STS-68). Immediately post-flight, leaf materials were fixed for microscopy or frozen in liquid nitrogen for subsequent analyses of chlorophyll and foliar carbohydrates. At the ultrastructural level, no aberrations in membrane structure were observed in any of the experiments. When air-flow was provided, plastids developed large starch grains in both spaceflight and ground controls. In the experiments with sealed chambers, spaceflight plants differed from ground controls with regard to measured concentrations of carbohydrate and chlorophyll, but the addition of airflow eliminated these differences. The results point to the crucial importance of consideration of the foliage microenvironment when spaceflight effects on leaf structure and metabolism are studied.     

Growth and photosynthetic responses of wheat plants grown in space.

Growth and photosynthesis of wheat (Triticum aestivum L. cv Super Dwarf) plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O2 evolution/photosynthetic photon flux density response curves of leaf samples revealed that the CO2-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. The relative quantum yield of CO2-saturated photosynthetic O2 evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was due to an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H2O through photosystems II and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length, shoot length, total leaf area, number of inflorescence per plant, number of flower per inflorescence, whole plant fresh weight and whole plant dry weight. Photosynthetic characteristics were also analyzed based on the same experiment. For this, various photosynthetic pigment contents such as chlorophyll, carotenoid, anthocyanin and xanthophyll content were calculated. The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used. Root length increased due to growth regulator treatment, but shoot length decreased. Leaf area was decreased due to growth regulator treatment. The number of inflorescence increased in ABA treated plants, but it was decreased in PBZ treated plants. In ABA treated plants, the number of flowers per inflorescence was increased. In PBZ treated plants the number of inflorescence was reduced. The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants. There was an increase in chlorophyll content in growth regulator treated plants compared to control, and it was more in PBZ treated plants. The carotenoid content was also increased in ABA and PBZ treated plants.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length,shoot length,total leaf area,number of inflorescence per plant,number of flower per inflorescence,whole plant fresh weight and whole plant dry weight.Photosynthetic characteristics were also analyzed based on the same experiment.For this,various photosynthetic pigment contents such as chlorophyll,carotenoid,anthocyanin and xanthophyll content were calculated.The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used.Root length increased due to growth regulator treatment,but shoot length decreased.Leaf area was decreased due to growth regulator treatment.The number of inflorescence increased in ABA treated plants,but it was decreased in PBZ treated plants.In ABA treated plants,the number of flowers per inflorescence was increased.In PBZ treated plants the number of inflorescence was reduced.The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants.There was an increase in chlorophyll content in growth regulator treated plants compared to control,and it was more in PBZ treated plants.The carotenoid content was also increased in ABA and PBZ treated plants.     

Structure of potato tubers formed during spaceflight

Potato (Solanum tuberosum L. cv. Norland) explants, consisting of a leaf, axillary bud, and small stem segment, were used as a model system to study the influence of spaceflight on the formation of sessile tubers from axillary buds. The explants were flown on the space shuttle Columbia (STS-73, 20 October to 5 November 1995) in the ASTROCULTURE (TM) flight package, which provided a controlled environment for plant growth. Light and scanning electron microscopy were used to compare the precisely ordered tissues of tubers formed on Earth with those formed during spaceflight. The structure of tubers produced during spaceflight was similar to that of tubers produced in a control experiment. The size and shape of tubers, the geometry of tuber tissues, and the distribution of starch grains and proteinaceous crystals were comparable in tubers formed in both environments. The shape, surface texture, and size range of starch grains from both environments were similar, but a greater percentage of smaller starch grains formed in spaceflight than on Earth. Since explant leaves must be of given developmental age before tubers form, instructions regarding the regular shape and ordered tissue geometry of tubers may have been provided in the presence of gravity. Regardless of when the signalling occurred, gravity was not required to produce a tuber of typical structure.     

Pollen and ovule development in Arabidopsis thaliana under spaceflight conditions

The development of pollen and ovules in Arabidopsis thaliana on the space shuttle 'Endeavour' (STS-54) was investigated. Plants were grown on nutrient agar for 14 days prior to loading into closed plant growth chambers that received light and temperature control inside the Plant Growth Unit flight hardware on the shuttle middeck. After 6 days in spaceflight the plants were retrieved and immediately dissected and processed for light and electron microscope observation. Reproductive development aborted at an early stage. Pistils were collapsed and ovules inside were seen to he empty. No viable pollen was observed from STS-54 plants; young microspores were deformed and empty. At a late stage, the cytoplasm of the pollen contracted and became disorganized, but the pollen wall developed and the exine appeared normal. The tapetum in the flight flowers degenerated at early stages. Ovules from STS-54 flight plants stopped growing and the integuments and nucellus collapsed and degenerated. The megasporocytes appeared abnormal and rarely underwent meiosis. Apparently they enlarged, or occasionally produced a dyad or tetrad, to assume the form of a female gametophyte with the single nucleus located in an egglike cell that lacks a cell wall. Synergids, polar nuclei, and antipodals were not observed. The results demonstrate the types of lesions occurring in plant reproductive material under spaceflight conditions.     

Tolerance of mannitol-accumulating transgenic wheat to water stress and salinity

Previous work with model transgenic plants has demonstrated that cellular accumulation of mannitol can alleviate abiotic stress. Here, we show that ectopic expression of the mtlD gene for the biosynthesis of mannitol in wheat improves tolerance to water stress and salinity. Wheat (Triticum aestivum L. cv Bobwhite) was transformed with the mtlD gene of Escherichia coli. Tolerance to water stress and salinity was evaluated using calli and T(2) plants transformed with (+mtlD) or without (-mtlD) mtlD. Calli were exposed to -1.0 MPa of polyethylene glycol 8,000 or 100 mM NaCl. T(2) plants were stressed by withholding water or by adding 150 mM NaCl to the nutrient medium. Fresh weight of -mtlD calli was reduced by 40% in the presence of polyethylene glycol and 37% under NaCl stress. Growth of +mtlD calli was not affected by stress. In -mtlD plants, fresh weight, dry weight, plant height, and flag leaf length were reduced by 70%, 56%, 40%, and 45% compared with 40%, 8%, 18%, and 29%, respectively, in +mtlD plants. Salt stress reduced shoot fresh weight, dry weight, plant height, and flag leaf length by 77%, 73%, 25%, and 36% in -mtlD plants, respectively, compared with 50%, 30%, 12%, and 20% in +mtlD plants. However, the amount of mannitol accumulated in the callus and mature fifth leaf (1.7-3.7 micromol g(-1) fresh weight in the callus and 0.6-2.0 micromol g(-1) fresh weight in the leaf) was too small to protect against stress through osmotic adjustment. We conclude that the improved growth performance of mannitol-accumulating calli and mature leaves was due to other stress-protective functions of mannitol, although this study cannot rule out possible osmotic effects in growing regions of the plant.     

Gravitropic moss cells default to spiral growth on the clinostat and in microgravity during spaceflight

In addition to shoots and roots, the gravity (g)-vector orients the growth of specialized cells such as the apical cell of dark-grown moss protonemata. Each apical cell of the moss Ceratodon purpureus senses the g-vector and adjusts polar growth accordingly producing entire cultures of upright protonemata (negative gravitropism). The effect of withdrawing a constant gravity stimulus on moss growth was studied on two NASA Space Shuttle (STS) missions as well as during clinostat rotation on earth. Cultures grown in microgravity (spaceflight) on the STS-87 mission exhibited two successive phases of non-random growth and patterning, a radial outgrowth followed by the formation of net clockwise spiral growth. Also, cultures pre-aligned by unilateral light developed clockwise hooks during the subsequent dark period. The second spaceflight experiment flew on STS-107 which disintegrated during its descent on 1 February 2003. However, most of the moss experimental hardware was recovered on the ground, and most cultures, which had been chemically fixed during spaceflight, were retrieved. Almost all intact STS-107 cultures displayed strong spiral growth. Non-random culture growth including clockwise spiral growth was also observed after clinostat rotation. Together these data demonstrate the existence of default non-random growth patterns that develop at a population level in microgravity, a response that must normally be overridden and masked by a constant g-vector on earth.     

MsPG3 polygalacturonase promoter elements necessary for expression during Sinorhizobium meliloti–Medicago truncatula interaction

We analyzed the changes in growth and cell wall properties of roots of rice (Oryza sativa L. cv. Koshihikari) grown for 68.5, 91.5, and 136 h during the Space Shuttle STS-95 mission. In space, most of rice roots elongated in a direction forming a constant mean angle of about 55° with the perpendicular base line away from the caryopsis in the early phase of growth, but later the roots grew in various directions, including away from the agar medium. In space, elongation growth of roots was stimulated. On the other hand, some of elasticity moduli and viscosity coefficients were higher in roots grown in space than on the ground, suggesting that the cell wall of space-grown roots has a lower capacity to expand than the controls. The levels of both cellulose and the matrix polysaccharides per unit length of roots decreased greatly, whereas the ratio of the high molecular mass polysaccharides in the hemicellulose fraction increased in space-grown roots. The prominent thinning of the cell wall could overwhelm the disadvantageous changes in the cell wall mechanical properties, leading to the stimulation of elongation growth in rice roots in space. Thus, growth and the cell wall properties of rice roots were strongly modified under microgravity conditions during spaceflight.     

Transgene expression patterns indicate that spaceflight affects stress signal perception and transduction in arabidopsis

The use of plants as integral components of life support systems remains a cornerstone of strategies for long-term human habitation of space and extraterrestrial colonization. Spaceflight experiments over the past few decades have refined the hardware required to grow plants in low-earth orbit and have illuminated fundamental issues regarding spaceflight effects on plant growth and development. Potential incipient hypoxia, resulting from the lack of convection-driven gas movement, has emerged as a possible major impact of microgravity. We developed transgenic Arabidopsis containing the alcohol dehydrogenase (Adh) gene promoter linked to the beta-glucuronidase (GUS) reporter gene to address specifically the possibility that spaceflight induces the plant hypoxia response and to assess whether any spaceflight response was similar to control terrestrial hypoxia-induced gene expression patterns. The staining patterns resulting from a 5-d mission on the orbiter Columbia during mission STS-93 indicate that the Adh/GUS reporter gene was activated in roots during the flight. However, the patterns of expression were not identical to terrestrial control inductions. Moreover, although terrestrial hypoxia induces Adh/GUS expression in the shoot apex, no apex staining was observed in the spaceflight plants. This indicates that either the normal hypoxia response signaling is impaired in spaceflight or that spaceflight inappropriately induces Adh/GUS activity for reasons other than hypoxia.     

The effects of (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4 triazol-1-yl) pentan-3-ol (Paclobutrazol:PP333) and root pruning on the growth,water use and response to drought of Colt Cherry rootstocks

The effect of (2RS, 3RS)-1-(4-Chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4 triazol-1-yl) pentan-3-ol (PP333) on the growth and transpiration of normal and root pruned colt rootstocks was measured. PP333 reduced plant height, stem diameter increment, leaf number, area and weight and stem weight. Root pruning reduced root, leaf and stem weight, and plant height in control plants. PP333 reduced both total water use and transpiration per unit leaf area and increased stomatal resistance. In control plants root pruning also reduced total water use and increased stomatal resistance. 15 days after the beginning of the experiment half the plants in all treatments were allowed to dry out. The effects of drought, i.e. reduced transpiration, growth and leaf water potentials, were smaller in PP333 treated than in control plants.     

Canopy and Seasonal Profiles of Nitrate Reductase in Soybeans (Glycine max L. Merr.)

Nitrate reductase activity of soybeans (Glycine max L. Merr.) was evaluated in soil plots and outdoor hydroponic gravel culture systems throughout the growing season. Nitrate reductase profiles within the plant canopy were also established. Mean activity per gram fresh weight per hour of the entire plant canopy was highest in the seedling stage while total activity (activity per gram fresh weight per hour times the total leaf weight) reached a maximum when plants were in the full bloom to midpod fill stage. Nitrate reductase activity per gram fresh weight per hour was highest in the uppermost leaf just prior to full expansion and declined with leaf position lower in the canopy. Total nitrate reductase activity per leaf was also highest in the upper-most fully expanded leaf during early growth stages. Maximum total activity shifted to leaf positions lower in the plant canopy with later growth stages.     

Chilli rhizosphere fungus Aspergillus spp. PPA1 promotes vegetative growth of cucumber (Cucumis sativus) plants upon root colonisation

A rhizosphere fungus was isolated from roots of chilli plants and identified as Aspergillus spp. PPA1. The fungus was tested for its ability to promote the growth of cucumber plants in a pot experiment. Cucumber seeds were sown in sterilised field soil amended with wheat grain inoculum (WGI) of PPA 1 at the rate of 0.5, 1 and 1.5% w/w, and plants were grown for 21 days in a net house. The treatment with PPA1 significantly increased shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, root dry weight, plant length, leaf area and leaf chlorophyll content of cucumber plants compared to non-treated control. The growth promotion rate increased with the increasing concentration of inoculum of PPA1 applied to the soil. The fungus was re-isolated from the roots of cucumber plants at higher frequencies. These results suggest that Aspergillus spp. PPA1 is a root colonising plant-growth promoting fungus for cucumber.     

Biomass Partitioning in Tomato Plants Infected with Meloidogyne incognita

Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1, 10, 50, 100, and 200 (x 1,000) eggs per plant and maintained in a growth chamber for 40 days. Total fresh biomass (roots + shoots) at harvest was unchanged by nematode inoculation with Pi of 1 x 10⁵ eggs or less. Reductions in fresh shoot weight with increasing Pi coincided with increases in root weight. Total fresh biomass declined with Pi above 1 x 10⁵ eggs, whereas total dry biomass declined at Pi above 1 x 10⁴ eggs. The greatest reduction percentages in fresh shoot biomass induced by root-knot nematodes occurred in the stem tissue, followed by the petiole + rachis; the least weight loss occurred in the leaflets. Although biomass varied among shoot tissues, the relationship between biomass of various shoot tissues and Pi was described by quadratic equations. The linear and quadratic coefficients of the equations (stem, petiole + rachis, or leaflets on Pi) did not differ among tissues when calculations were based on standardized values. Meloidogyne incognita-infected plants had thinner leaves (leaf area/leaf weight) than did uninfected plants. Reductions in leaf weight and leaf area with nematode inoculation occurred at nodes 5-15 and 4, 6-14, respectively. Losses in plant height and mass due to nematodes reflected shorter internodes with less plant mass at each node.     

Ultrastructure of potato tubers formed in microgravity under controlled environmental conditions

Previous spaceflight reports attribute changes in plant ultrastructure to microgravity, but it was thought that the changes might result from growth in uncontrolled environments during spaceflight. To test this possibility, potato explants were examined (a leaf, axillary bud, and small stem segment) grown in the ASTROCULTURETM plant growth unit, which provided a controlled environment. During the 16 d flight of space shuttle Columbia (STS-73), the axillary bud of each explant developed into a mature tuber. Upon return to Earth, tuber slices were examined by transmission electron microscopy. Results showed that the cell ultrastructure of flight-grown tubers could not be distinguished from that of tuber cells grown in the same growth unit on the ground. No differences were observed in cellular features such as protein crystals, plastids with starch grains, mitochondria, rough ER, or plasmodesmata. Cell wall structure, including underlying microtubules, was typical of ground-grown plants. Because cell walls of tubers formed in space were not required to provide support against the force due to gravity, it was hypothesized that these walls might exhibit differences in wall components as compared with walls formed in Earth-grown tubers. Wall components were immunolocalized at the TEM level using monoclonal antibodies JIM 5 and JIM 7, which recognize epitopes of pectins, molecules thought to contribute to wall rigidity and cell adhesion. No difference in presence, abundance or distribution of these pectin epitopes was seen between space- and Earth-grown tubers. This evidence indicates that for the parameters studied, microgravity does not affect the cellular structure of plants grown under controlled environmental conditions.     

The effects of gibberellic acid and nutrient sprays on growth and yield of brussels sprout

Young plants of brussels sprout, cv. Cambridge Special, growing in pots in a glasshouse, were sprayed on ten occasions with gibberellic acid (GA) at 0, 25, 100 and 400 p.p.m. and ammonium nitrate (NH₄NO₃) at 0, 0·0125, 0·025 and 0·05 M concentrations in all combinations. In 24 days both GA and NH₄NO₃ increased leaf area, leaf number, dry weights of leaf, stem and root, and fresh weights of leaf and stem. GA increased stem height and decreased fresh weight/unit leaf area (leaf thickness), whereas NH₄NO₃ did not affect stem height and increased leaf thickness. Of the GA treatments, 100 p.p.m. gave the largest plants as judged by fresh weight of the whole plant and leaf area, and of the N treatments 0·05 M NH₄NO₃ increased growth most. The best treatment combination was 0·05 M NH₄NO₃ with 100 p.p.m. GA, which gave the greatest fresh and dry weights of the whole plant, leaf area and leaf dry weight as well as increasing leaf thickness. Significant interactions were found between GA and N for dry weight of leaf, fresh and dry weight of root, and leaf thickness but not for leaf area or stem growth (fresh weight, dry weight, height). The combination of levels of GA and N that can be expected to increase leaf area, leaf dry weight and leaf thickness simultaneously, may lie within narrow limits for a particular crop. In a second experiment plants were sprayed with all combinations of GA (0 and 100 p.p.m.) seven times under glass in pots and ten times in the field, and three levels of KH₂PO₄ on twelve occasions in the field. Sprouts (axillary buds) were harvested in October and February. At the first harvest GA did not affect fresh weight or number, but increased both the total number of sprouts picked (with GA = 80·7; without GA = 69·8 per plant) and the total fresh weight of saleable sprouts (with GA = 2·59; without GA = 2·33 lb/plant). KH₂PO₄ also increased the weight and number of sprouts at the final harvest and the number of small sprouts at the first. There were interactions between GA and KH₂PO₄ (P= < 0·001) for both tota weight and number of saleable sprouts.     

基于器官生物量构建植株形态的玉米虚拟模型

探讨了基于玉米器官生物量模拟其形态的方法,并应用2000年田间试验数据提取了玉米节间、叶鞘和叶片的形态构建参数。基于玉米虚拟模型生物量分配模块模拟的器官生物量积累和建立的形态构建方法与提取的参数,模拟了2001年玉米不同生长阶段的器官形态,模拟结果与田间试验数据吻合较好。应用本模型实现了玉米生长过程中植株各个器官形态变化以及植株高度、叶面积动态的模拟,并实现了植株形态的可视化。     

EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL-290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38–48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased.     

长期弱光对苦草幼苗生长发育的影响

用遮光法研究弱光(5%、1%、0.5%、0.1%全光照)对苦草幼苗生长发育的影响,统计了苦草的生物学参数,测定了叶片叶绿素荧光参数。结果表明:1)0.1%组无新株萌发,随着实验时间的延长其余组新株萌发逐渐被抑制。2)随着实验时间增加和光照强度降低,老株叶片形成受到的抑制程度呈增大趋势;前20d时新株叶片形成未被抑制,但随着实验时间延长显著被抑制。3)老株、新株的叶宽均受到显著抑制。4)老株叶片的伸长显著被抑制,且随着光强降低叶片伸长的幅度呈显著降低趋势;前20天时新株叶长被促进,随着实验时间延长叶片伸长显著被抑制。5)随实验天数的增加,老株叶片光化学最大量子产量(Fv/Fm)呈显著降低趋势,第80天时相对电子传递速率(rETR)和非光化学淬灭(NPQ)显著降低。6)新、老植株根、茎、叶的鲜重均显著低于对照,且随着光照强度降低老株的茎重/株重和根重/株重呈增加趋势,而叶重/株重呈显著的降低趋势。第80天时苦草植株仍具有一定的光合能力,地下茎的生物量比例较高,因此,≤1%全光照下苦草植株具有较强的耐受能力。     

植物生长调节剂对西南桦苗木生长的影响

用 ABT6 和 GA3对西南桦苗木进行叶面喷施试验。试验结果表明 ,GA3的 3种浓度即 2 0× 10 - 6 m g/L、50× 10 - 6 m g/L、80× 10 - 6 m g/L在苗木高生长、地径大小、苗木干鲜重及苗木根系生长发育方面都比清水对照( CK)有明显地提高。ABT6 各浓度特别是 50× 10 - 6 m g/L处理的在苗木分枝数、单株叶面积、苗木干鲜重及苗木根系生长发育方面也比对照有显著的提高。综合各指标 ,用 A BT6 生长调节剂的 50× 10 - 6 mg/L比 2 0× 10 - 6mg/L、80× 10 - 6 mg/L处理及 GA3生长调节剂各浓度处理在生产实践上更适宜用于培育西南桦苗木。