Influence of gibberellic acid and different salt concentrations on germination percentage and physiological parameters of oat cultivars

Gibberellic acid (GA₃) is one of the plant growth regulators which improve salt tolerance and mitigate the salt stress impact on plants. The extant analysis was carried out to study the effect of GA₃ and different salt concentrations on seed germination and physiological parameters of oat cultivars. Oats is substantially less tolerant to salt than wheat and barley. Experimentation was conducted as factorial with Completely Randomized Block Design with three replicates. Different concentration of NaCl salt ((25, 50, 75 and 100 mM) were used in test control group and 100 and 150 ppm of GA₃ were used in two group by pre-treated (after 24 h of the seed soaking) and plants were analyzed on 15th day. Results indicate that increasing salinity would decrease the germination percentage and growth parameter in three oat cultivars. Quotes data indicating a 13%, 19.9% and 32.48% in cultivars NDO-2, UPO-212 and UPO-94 germination reduction when soil salinity reaches 50 mM. A 36.02%, 47.33% and 56.365 reduction in germination is likely when soil salinity reaches 100 mM respectively same cultivars. Seeds treated with GA₃ significantly promoted the percentage of germination, shoot and root length, total fresh and dry weight of seedling, tissue water content and seedling vigor index by NDO-2 and UPO-212 under different saline concentration. The maximum average of germination and growth parameters were observed from 150 ppm GA₃ treated seeds. But this concentration was significantly inhibited root length in sensitive cultivar UPO-94 at 75 and 100 mM salt as compared to 100 ppm. We observed that, the high concentration of GA₃ was not suitable for sensitive oat cultivars. Because the plant root are the real workforce behind any plants success. Thus, it may be concluding that, GA₃ treatment could curtail the toxic effect of salinity by increasing germination percentage and shoot and root length, total fresh and dry weight, tissue water content and seedling vigor index in tolerant cultivar.     

Influence of Azospirillum inoculation on the mineral uptake and growth of rice under hydroponic conditions

Seedlings of rice (Oryza sativa L. var. IR42) were inoculated with nitrogen-fixingAzospirillum lipoferum (strain 34H) by immersing the roots in the inoculum for 6 h. The plants were grown in the prescence of NH₄ ⁺-N for 47 days in a hydroponic system under greenhouse conditions. Inoculation significantly enhanced PO₄-ion uptake of the plants in 4 of the 7 samplings tested while the uptake of NH₄-ion was significantly increased in two samplings and was decreased in one sampling. Inoculation reduced root length significantly and caused significant increases in shoot fresh and dry weights. Root surface area was not affected by inoculation. Bacterial population counts suggested thatA. lipoferum survived on the roots till the end of the experiment.     

Nitrogen nutrition of rice plants under salinity

Two rice (Oryza sativa L.) cultivars, Koshihikari and Pokkali, were grown in solution culture at three concentrations of NaCl or Na₂SO₄ [0 (S0), 50 (S1), and 100 (S2) mmol dm^–3] and three N contents [0.7 (N1), 7 (N2) and 14 (N3) mmol dm^–3]. Salinity significantly decreased dry matter of both cultivars. Pokkali had better growth than Koshihikari under both saline and non-saline conditions. Applications of N enhanced development of shoot dry mass under S0 and S1 treatments up to N2. Under S2, N application had no effect on shoot dry mass of both cultivars. Root dry mass of both cultivars decreased with increasing N application at S1 and S2. Shoot and root NO₃-N content in both rice cultivars increased with increasing N concentration in the nutrient solutions. The absorption of NO₃-N was less in Koshihikari than Pokkali plants, and also was much less in Cl^– than SO₄ ^2– salinity suggesting the antagonism between Cl^– and NO₃ ^–. In addition a significant negative correlation between concentrations of NO₃-N and Cl^– in the shoots or roots was observed in both cultivars     

Effects of Proline and Glycinebetaine on Vicia Faba Responses to Salt Stress

Plants of bean (Vicia faba L. cv. Calvor 103) were salt-stressed with NaCl and CaCl₂ in concentrations inducing soil osmotic potentials (ψ_soil) from 0 to -1.2 MPa and were sprayed with proline (8.7 μM) and glycinebetaine (8.5 μM) solutions. Bean plants respond to increasing soil salinity by decreased leaf relative water content and osmotic potential. Salinity decreased the contents of dry mass, chlorophyll, soluble and hydrolysable sugars, soluble proteins and enhanced content of total free amino acids, Na⁺, Ca²⁺ and Cl^-. The ratio of K⁺/Na⁺ was decreased on salinization. The membranes of leaf discs from salt-stressed plants appeared to be less stable under heat stress (51 °C) than that of unstressed plants. The reverse was true for discs placed under dehydration stress (40 % polyethylene glycol 6000). Proline and glycinebetaine application reduced membrane injury, improved K⁺ uptake and growth. Also both solutes increased chlorophyll contents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of inoculation ofPoa pratensis andTriticum aestivum with root-associated,N2-fixing Klebsiella,Enterobacter and Azospirillum

Strains ofKlebsiella pneumoniae, Klebsiella terrigena, Enterobacter agglomerans andAzospirillum lipoferum were compared as diazotrophic inoculants in association withPoa pratensis andTriticum aestivum. Each strain colonized both plants in numbers ranging from 10⁴ to 10⁷ bacteria per root, and electron microscopy and immunofluorescence staining of inoculated roots revealed bacteria mainly on root hairs. Indirect immunofluorescence with specific antifimbriae antibodies showed that the enteric bacteria expressed their fimbria in both associations. All associations were positive in an acetylene reduction test but only in half of them was atmospheric nitrogen transferred to the plant. In the inoculated plants, variable effects in the dry matter and N yields in both hosts were observed and no correlation was found between dry matter, nitrogen content or the amount of fixed nitrogen. In infected plants, the number of root hairs and lateral roots increased and the length of the zone of elongation decreased. The changes in root morphology were more evident in associations with enteric bacteria than with Azospirillum. The results give further evidence on the importance of bacterial adhesion in associative N₂ fixation and suggest that bacteria-induced physiological changes in plant roots may be more important than the amount of nitrogen transferred to the plant.     

The effect of aluminium on phosphate uptake by three isolated ectomycorrhizal fungi

Three wheat cultivars with different tolerances against free aluminium were grown monoxenically in association with Azospirillum brasilense. In situ nitrogen fixation, measured with the acetylene reduction assay, was higher by the aluminium-tolerant cultivars than by the sensitive cultivar. The transfer of fixed nitrogen to the host plant, determined by the ¹⁵N dilution technique, was also significantly higher in the aluminium-resistant wheat plants. The total accumulation of fixed nitrogen in the host plants due to an A. brasilense inoculation varied from approximately 13% to 17% of the total nitrogen in the root and 2.9% to 3.9% of the nitrogen in the shoot.The quantity and quality of exudates released in liquid nutrient solution were analysed separately for two of the wheat cultivars, one aluminium-tolerant and one aluminium-sensitive. After 29 days of growth the aluminium-tolerant plants exudated significantly higher total amounts of carbon than aluminium-sensitive plants. No differences between the two cultivars existed in the carbon exudation rate per gram dry root.Much higher concentrations of low molecular dicarboxylic acids i.e. succinic, malic and oxalic acid, were found in the exudates of aluminium-tolerant plants. Dicarboxylic acids are potential chelating compounds for positively charged metals such as aluminium and they may play an important role in protecting the plant against aluminium incorporation. They are also very suitable substrates for Azospirillum spp. It is therefore suggested that these factors may be causing the higher associative nitrogen fixation rates which was found in the aluminium-tolerant wheat cultivars.     

Interaction between barley and mixed cultures of nitrogen fixing and phosphate-solubilizing bacteria

Pot experiments were carried out to investigate the effect of inoculation with pure and mixed cultures of nitrogen fixers Azospirillum lipoferum 137, Arthrobacter mysorens 7 and the phosphate-solubilizing strain Agrobacterium radiobacter 10 on growth and mineral nutrition of two barley cultivars. A significant positive effect on grain yield both of the studied barley cultivars was obtained after inoculation with mixtures of A. lipoferum 137 + A. radiobacter 10 and A. lipoferum 137 + A. mysorens 7 only. The acetylene reduction activity on roots or in batch culture was significantly higher when A. lipoferum 137 and A. radiobacter 10 were combined. Using ¹⁵N isotope dilution technique it was established that these mixed cultures significantly increased the accumulation of nitrogen fertilizer in the plants. The strain A. radiobacter 10 promoted a better accumulation of phosphorus fertilizer by plants and A. mysorens 7 increased the total phosphorus content in plant tissues. The maximum positive effect of joint inoculation on plant development was observed when the combined nitrogen in soil was in short supply. It was concluded that inoculation with bacterial mixtures provided a more balanced nutrition for the plants and the improvement in root uptake of nitrogen and phosphorus was the major mechanism of interaction between plants and bacteria. The introduced bacteria were able to colonize actively the rhizoplane of barley. No interspecific competition or antagonism were established between components of the bacterial mixtures in the rhizoplane. The strains A. mysorens 7 and A. radiobacter 10 improved viability of A. lipoferum 137 when the plants were grown in acid soil. Field experiments carried out on 3 barley cultivars confirmed the assertion that inoculation with mixed cultures significantly increases the grain yield and nitrogenous nutrition of plants as compared with single cultures.     

Light intensity, gibberellin content and the resolution of shoot growth in Brassica

The role of gibberellins (GAs) in the regulation of shoot elongation is well established but the phytohormonal control of dry-matter production is poorly understood. In the present study, shoot elongation and dry-matter production were resolved by growing Brassica napus L. seedlings under five light intensities (photon flux densities) ranging from 25 to 500 μmol m⁻² s⁻¹. Under low light, plants were tall but produced little dry weight; as light intensity was increased, plants were progressively shorter but had increasing dry weights. Endogenous GAs in stems of 16- and 17-d-old plants were analyzed by gas chromatography-selected ion monitoring with [²H₂] internal standards. The contents of GAs increased dramatically with decreasing light intensity: GA₁, GA₃, GA₈ and GA₂₀ were 62, 15, 16 and 32 times higher, respectively, under the lowest versus highest light intensities. Gibberellin A₁₉ was not measured at 25 μmol m⁻² s⁻¹ but was 9␣times greater in the 75 compared to 500 μmol m⁻² s⁻¹ treatment. Shoot and hypocotyl lengths were closely positively correlated with (log) GA concentration (for example: r ² = 0.93 for GA₁ and hypocotyl length) but shoot dry matter was negatively correlated with GA concentration. The application of gibberellic acid (GA₃) produced elongation of plants grown under high light, indication that their low level of endogenous GA was limiting shoot elongation. Although endogenous GA₂₀ showed the greatest influence of light treatment, metabolism of [³H]GA₂₀ and of [³H]GA₁ was only slightly influenced by light intensity, suggesting that neither 2β- nor 3β-hydroxylation were points of metabolic regulation. The results of this study indicate that GAs control shoot elongation but are not directly involved in the regulation of shoot dry weight in Brassica. The study also suggests a role of GAs in photomorphogenesis, serving as an intermediate between light condition and shoot elongation response. Received: 18 June 1998 / Accepted: 29 July 1998     

Growth and solute accumulation in 3-week-old seedlings of Agropyron elongatiun stressed with sodium and potassium salts

Agropyron elongatum [Host. (Beauv.)] [^cv. Arizona Glendale, was grown in liquid medium salinized with either NaCl, KCI, or a 50:50 mixture of these two salts at osmotic potentials ranging from 0 to –1.6 MPa. The amount of growth in 21 days was measured, and extracts were made of the shoots at this time. The extracts were assayed for low-molecular-weight organic compounds (glucose, fructose, sucrose, be-taine, proline) and inorganic solutes (Na⁺, K⁺, Cl^?, P.). The purpose was to determine if there was any correlation between the harmful effect of salinity on growth and the concentrations of solutes in tissues. Growth inhibition of A. elongatum was roughly proportional to the osmotic potential of the growth medium and was independent of the ionic composition of the salinizing salts. Total monovalent cation (the sum of Na⁺ and K⁺) concentrations and the ratio of these two cations in leaves were mainly a function of the ionic compostion of the salt in growth media, and, to a lesser degree, of osmotic potentials. F At an osmotic potential of –0.2 MPa, total monovalent cation in leaves was the same as in non-stressed plants. However, if the salinizing salt contained NaCl, there was an increase in foliar Na⁺ with a balancing decrease in K⁺. At stress levels between –0.4 and –1,6 MPa, and, if the media were salinized with either 100% NaCl or a 50:50 mixture of NaCl and KCI, total monovalent cation concentrations remained constant at a value that was twice that in non-stressed plants. Although total monovalent cation concentrations were equal in plants grown under these two salinity conditions, the K⁺/Na⁺ ratios shifted from a value of 1:2 in plants grown in 100% NaCl to 3:1 in plants subjected to the 50:50 mixture. If 100% KCI was used to salinize media, total monovalent cation was 80% of its concentration in NaCl-treated plants in the range of –0.4 to -1.2 MPa. At –1.6 MPa due to 100% KCI, total monovalent cation was double that in plants subjected to -0.4 MPa. In the range of osmotic potentials from–0.2 to –1.2 MPa, the chloride:cation ratio was 1:2. At –1.6 MPa the ratio changed to 3:4. Proline started accumulating in leaves of A. elongatum when the tissue concentration of total monovalent cation exceeded 200 μ (g fresh weight)^?1. Above this threshold value of total monovalent cation, the proline concentration of leaves was 6% of the amount of total monovalent cation that exceeded 200 umol (g fresh weight)¹.     

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na⁺ and Cl⁻ in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ_w) decreased from an average value of approximately −1.0 MPa, measured on control plants and S10, to −1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g⁻¹ fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.     

Effects of Temperature, Nitrogen Fertilization, and Plant Age on Nitrogen Fixation by Setaria italica Inoculated with Azospirillum brasilense (strain cd)

The association between the nitrogen-fixing bacterium Azospirillum brasilense (strain cd) and the grass Setaria italica was studied under different environmental and soil conditions. Highest acetylene reduction rates in intact plants were observed at the booting stage of Setaria (2350 nmol ethylene produced hour⁻¹ plant⁻¹) at 27 C. Higher temperatures, up to 32 C, enhanced ethylene reduction. Significant increases in shoot dry weight, panicle weight, and length were obtained in inoculated plants fertilized with suboptimal NH₄NO₃ levels. The increase in nitrogen content of plants inoculated with A. brasilense was shown to be due to N₂ fixation. This was demonstrated by growing plants in washed quartz sand with no combined nitrogen. The bacteria also increased branching and development of roots. It was concluded that inoculation of Setaria with A. brasilense may lead both to increases in plant yield and saving of nitrogen fertilizer.     

Effects of root-zone solutes on Eucalyptus camaldulensis and Eucalyptus bicostata seedlings: Responses to Na+, Mg2+ and Cl-

Specific-ion effects in salt-treated eucalypts were examined with two species known to differ in salt tolerance viz. E. camaldulensis (more tolerant) and E. bicostata (less tolerant). Sand-cultured plants were irrigated with different nutrient solutions designed to impose either osmotic stress (concentrated macronutrients with balanced cations and anions) or specific ion stress from either NaCl or MgCl₂, or from nutrient solutions rich in particular ions viz. Na⁺, Mg²⁺ and Cl^- (balancing counter ions were provided in all cases). Half-strength Hoagland nutrient solution served as control. All treatments were applied at osmotic pressures of approximately 0.52 MPa by appropriate concentrations of each solution. In general, salt-induced growth reductions were greater for E. camaldulensis than for E. bicostata, although E. camaldulensis showed strongest exclusion of Na⁺, Mg²⁺ and Cl^- from shoots. Application of NaCl and concentrated macronutrients resulted in similar growth reductions. E. bicostata seedlings exposed to high Cl^- concentrations in the presence of Mg²⁺ and concentrated cations suffered significantly more shoot and root reduction than those exposed to other salts. Treatment with solution rich in Cl^- resulted in extensive leaf damage, which suggested that Cl^- may have exerted a specific effect. No specific Na⁺ effect was observed for either species, even though shoot Na⁺ concentrations were considerably higher for E. bicostata than for E. camaldulensis. Root growth was considerably less for plants treated with Mg²⁺ salts and this effect was associated with low root Ca²⁺ concentrations.     

Micropropagation of photinia employing rhizobacteria to promote root development

An alternative protocol was developed for in vitro propagation of photinia (Photinia × fraseri Dress), an ornamental shrub, using the plant growth-promoting rhizobacteria (PGPR) Azospirillum brasilense and Azotobacter chroococcum during rhizogenesis. Shoot tips from four-year-old mature plants, cut in spring and summer, were used as initial explants. They were cultured on Murashige–Skoog (MS) medium with Gamborg’s vitamins, N⁶-benzyladenine (BA: 11.1 μM) and gibberellic acid (GA₃: 1.3 μM), obtaining 63% of established explants. The highest shoot length (22.9 mm) and multiplication rate (4.3) was achieved by cultivating for four weeks in the same basal medium supplemented with 4.4 μM BA. Both auxin induction and bacterial inoculation were used for rooting. Elongated shoots were treated with two concentrations of indole-3-butyric acid (IBA: 4.9 or 49.2 μM) during 6 days for auxin induction. Then, the shoots were transferred to an auxin-free medium and inoculated with A. brasilense Cd, Sp7 or A. chroococcum (local strain). Bacterial inoculation induced earlier rooting of photinia shoots. A. brasilense Cd with 49.2 μM IBA pulse showed a significant increase (P ≤ 0.05) in root fresh and dry weight (105%, 137%), root surface area (65%) and shoot fresh and dry weight (32%, 62%). A. brasilense Sp7 enhanced the root fresh weight (34%) and root surface area (41%) while no significant differences with A. chroococcum inoculation were detected. The PGPR inoculated micro-cuttings in combination with auxin induction pulses may play a useful role in root organogenesis of micropropagated plants.     

Abscisic acid, temperature and salinity interactions on growth and some mineral elements in Carthamus plants

Growth and contents of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), chloride (Cl), phosphorus (P) and sulphur (S) in shoot and root tissues of Carthamus tinctorius plants were measured at combinations of four nutrient solution osmotic potentials (_s=0, -0.3, -0.6 and -0.9 MPa) induced by NaCl and CaCl treatments, three constant temperatures (T) ranging from 15 to 35°C and four abscisic acid (ABA) concentrations (0,10,50 and 100 mg L^–1). Unstressed and stressed plants grown in optimal temperature conditions (25°C) maintained higher growth rates (dry mass production) than plants grown under low and high temperatures (15 and 35°C respectively). Shoot and root growth (dry mass production) were largely inhibited by salinity but the magnitude of growth inhibition was temperature dependent. Safflower plants respond to salinity stress by increases in Ca, Cl and to a lesser extent Na in their shoots and roots and by a decrease in the ratio of fresh to dry weight. The ratio of K/Na was decreased progressively on salinization. With stressed plants, ABA application reduced the toxicity of salt treatment, improved K uptake under salinity, effectively increased K/Na ratio and helped the plants to avoid Na toxicity and sometimes enhanced growth. The effect of ABA on the growth was more pronounced at optimum temperature (25°C). The association between the internal mineral element concentrations was largely affected by ABA application and temperature change but a wide fluctuation in response was noticed. The effects of single factors (_s, T and ABA) on the growth and mineral contents were statistically significant. Also, bifactorial (_s× T, _s × ABA and T × ABA) and three factorial (_s × T × ABA) interactions significantly affected the parameters. Further statistical treatment of the data (coefficient of determination ²) led to four important findings: (1) Salinity (_s) was dominant in affecting Ca and Cl contents in both shoot and root as well as root Na content. (2) Temperature (T) had a dominant effect on growth, shoot K, Mg, P, S and root P, and S contents (3) The share of _s × T × ABA interaction was dominant for root Na and Mg contents. (4) The single factors and their interactions had a dual role in their subsidiary effects.Abbreviations ABA abscisic acid - _s osmotic potential - ² coefficient of determination - F.wt fresh weight - d.m. dry matter - T temperature - MPa mega pascal - SAR sodium adsorption ratio - P phosphorus - S sulphur     

盐胁迫下不同基因型冬小麦渗透及离子的毒害效应

以4种不同基因型冬小麦为试验材料,利用分根法研究了盐胁迫对小麦的渗透胁迫和离子毒害的效应。结果表明,在盐胁迫下,小麦既受渗透胁迫,也受盐离子胁迫。渗透胁迫效应比较快,大约在处理后1-2d内发生;离子毒害效应比较缓慢,大约需3-4d时间。在一半盐胁迫(200mmol/L NaCl)和一半非盐胁迫的分根条件下,小麦没有明显的渗透胁迫效应,小麦植株地上部Na⁺ 累积到毒性水平之前盐处理对小麦生长无抑制效应。小麦具有将Na⁺ 从盐胁迫一侧转移非盐一侧的能力,说明小麦吸收的Na⁺ 有一部分可以从地上部回流到根系中,回流率可达76%-89%。无水分胁迫(不加入PEG)的回流率大于水分胁迫(加入PEG)的回流率。不同基因型小麦在盐分吸收累积和回流,及渗透和离子胁迫的速度和程度等方面具有明显差异。NR 9405和小偃6号的Na⁺ 累积速度要少于陕229和RB 6;NR 9405根系排Na⁺ 能力强于陕229和RB 6。因此,NR 9405和小偃6号的耐盐性高于陕229和RB 6。     

Exogenous application of gibberellic acid and silicon to promote salinity tolerance in pea (Pisum sativum L.) through Na+ exclusion

Salinity is a worldwide problem limiting the plant growth and risking food security. This study was conducted to examine exogenous application of silicon (Si), gibberellic acid (GA₃) upon the ion transport, growth, yield, and antioxidant enzymes activities of pea plant in saline conditions. Two pea varieties Meteor-FSD and Samrina Zard were pre-treated with GA₃ (10^-4 M) for 12 h. Plants were allowed to grow with or without silicon in washed silica sand. Ten days old seedlings were shifted in pots with 10 kg soil. Twenty-five days old plants were exposed to 0 and 5 dS m^?1 sodium stress. Results showed that exogenous application of GA₃ + Si was the best treatment for increasing plant biomass and yield in the presence and absence of NaCl. Furthermore, application of Si or GA₃ enhanced chlorophyll content in the leaves, thereby increasing the net assimilation rate of pea varieties under NaCl stress by increasing the antioxidant enzyme activity. Treatment of Si alone or in combination with GA₃ significantly reduced Na⁺ movement in both pea varieties. Results showed that Si has more prominent role than GA₃ alone to build-up high plant biomass, yield, soluble protein content and reduction of Na⁺ transport. Samrina Zard variety showed higher yield, shoot and root dry weight as compared to Meteor-FSD variety in presence and absence of salt. It was concluded that Si can be used as a nutrient for pea under saline or non-saline conditions. Moreover, application of GA₃ has a potential role for increasing salinity tolerance, mostly in sensitive pea varieties.     

Involvement of endogenous gibberellins in the regulation of increased tomato shoot growth in solarized soil

Environmental factors often affect plant growth bymodifying the levels of endogenous gibberellins (GAs).In this study, the involvement of GAs in theregulation of enhanced shoot growth in tomato (Lycopersicon esculentum Mill.) plants grown in soiltreated by solarization (a soil disinfestation method)was investigated. Seedlings at the cotyledonary stagewere transplanted into either solarized or untreatedcontrol soil. Plants in both soils grew free of anydisease symptoms. As soon as four days after planting,seedlings in solarized soil had a higher dry weightcompared to the control. Throughout most of theexperimental period of 18 days, leaf weight ratio washigher in the solarized vs. the control soil. Treatingshoot tips of control plants with 0.1 mg^.L^-1GA₃ resulted in enhanced leaf and stem growth,thus reaching values similar to those of plants grownin solarized soil. The opposite effect was obtained bytreating plants grown in solarized soil with1 mg^.L^-1 uniconazole, a GA biosynthesisinhibitor. Quantitative GC-MS analyses revealed thatGA₁ content in one and two-weeks old transplantsgrown in various solarized soils was up to 1.8 fold,and that GA₃ content in two-weeks old plants wasup to five fold the values in the control. Theseincreases were linearly correlated with the increasein leaf dry weight. It was concluded that theincreased quantities of GA₁, and eventuallyGA₃, play a role in the increased growth oftomato shoots in solarized soil as early as seven daysafter transplanting.deceased     

Growth and pigment content of wheat as influenced by the combined effects of salinity and growth regulators

A field experiment was conducted to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in different levels of salinity (33 or 66 mM) and in growth regulators (indolyl-3-acetic acid, IAA at SO g m^-3, gibberellic acid, GA₃ at 100 g m^-3, or kinetin at 100 g m_-3) on the shoot growth and pigment content of the developing wheat flag leaf. Salinity at 33 or 66 mM led to an insignificant increase in the fresh and dry masses as well as in the shoot diameter and shoot length, but it attenuated the flag leaf area. In the majority of cases, salinity increased the chlorophyll (Chla, Chlb) and carotenoid contents as well as the number of chloroplasts per a mesophyll cell. The growth in the wheat shoot of the saline-treated plants was, in general, stimulated in response to presoaking the grains in kinetin or GA₃. On the other hand, IAA + salinity led to a negligible effect on the growth in the wheat plants particularly at the early stages of growth. The presoaking of grains in NaCl at 33 mM + IAA or 66 mM + kinetin induced a marked increase in the pigment content of the wheat flag leaf particularly at the early stages of growth. The interaction between salinity and phytohormones increased the number of chloroplasts; kinetin was the most effective.     

Heterosis and the metabolism of gibberellin A20 in sorghum

The correlation between gibberellin (GA) metabolism and growth rate was investigated using two Sorghum bicolor inbred lines, Hegari and AT×623, and their heterotic F₁ hybrid. Previous studies have demonstrated that this hybrid is taller and has substantially greater shoot dry weights and leaf areas than either parental inbred. [³H]GA₂₀ was applied to the leaf whorl of seedlings and after 24 hours, plants were harvested and separated into roots, shoot cylinders containing the apical meristems, and leaf blades. Chromatographic analyses of metabolites indicated the conversions of [³H]GA₂₀ to [³H]GA_{1,8 and 29}. The conversion of [²H]GA₂₀ to [²H]GA₁ was demonstrated by gas chromatography-selected ion monitoring (GC-SIM). Putative glucosyl conjugates of all of the [³H]GAs were also produced and GA₈ was identified by GC-SIM following enzymic cleavage of the putative [³H]GA₈ glucosyl conjugate fraction. Comparing the genotypes, [³H]GA₂₀ metabolism was more rapid in the shoot cylinders of the hybrid than in the shoot cylinders from inbreds. In the hybrid samples, there was a three-fold increase in the putative conjugate(s) of [³H]GA₁ which was the principal metabolite, and increased production of [³H]GA₈ and the putative conjugates of [³H]GA₂₉ and [³H]GA₈. Conversely, levels of the remaining precursor, [³H]GA₂₀, and its putative conjugate(s) were reduced in the hybrid. The rate of GA₂₀ metabolism was thus positively correlated with growth rate across these sorghum genotypes. This correlation supports a promotive role of GA in the regulation of shoot growth and in the expression of heterosis (hybrid vigor) in sorghum.     

Photoperiod-induced changes in gibberellin metabolism in relation to apical growth and senescence in genetic lines of peas (Pisum sativum L.)

In an early-flowering line of pea (G2) apical senescence occurs only in long days (LD), while growth in short days (SD) is indeterminate. In SD, G2 plants are known to produce a graft-transmissible substance which delays apical senescence in related lines that are photoperiod-insensitive with regard to apical senescence. Gibberellic acid (GA₃) applied to the apical bud of G2 plants in LD delayed apical senescence indefinitely, while N⁶-benzyladenine and -naphthaleneacetic acid were ineffective. Of the gibberellins native to pea, GA₉ had no effect whereas GA₂₀ had a moderate senescence-delaying effect. [³H]GA₉ metabolism in intact leaves of G2 plants was inhibited by LD and was restored by placing the plants back in SD. Leaves of photoperiod-insensitive lines (I-types) metabolized GA₉ readily regardless of photoperiod, but the metabolites differed qualitatively from those in G2 leaves. A polar GA₉ metabolite, GA_E, was found only in G2 plants in SD. The level of GA-like substances in methanol extracts from G2 plants dropped about 10-fold after the plants were moved from SD to LD; it was restored by transferring the plants back to SD. A polar zone of these GA-like materials co-chromatographed with GA_E. It is suggested that a polar gibberellin is synthesized by G2 plants in SD; this gibberellin promotes shoot growth and meristematic activity in the shoot apex, preventing senescence.Abbreviations GA gibberellin - GA₃ gibberellic acid - SD short days - LD long days