Hydroponic treatment with salicylic acid decreases the effects of chilling injury in maize (Zea mays L.) plants

The addition of 0.5 mM salicylic acid (SA) to the hydroponic growth solution of young maize (Zea mays L.) plants under normal growth conditions provided protection against subsequent low-temperature stress. This observation was confirmed by chlorophyll fluorescence parameters and electrolyte leakage measurements. In addition, 1 d of 0.5 mM SA pre-treatment decreased net photosynthesis, stomatal conductivity and transpiration at the growth temperature (22/20 °C). Since there was only a slight decrease in the ratio of variable to maximal fluorescence (F_v/F_m) the decrease in photosynthetic activity is not due to a depression in photosystem II. The analysis of antioxidant enzymes showed that whereas SA treatment did not cause any change in ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) activities, there was a decrease in catalase (EC 1.11.1.6) activity, and an increase in guaiacol peroxidase (EC 1.11.1.7) and glutathione reductase (EC 1.6.4.2) activities after the 1-d SA treatment at 22/20 °C. In native polyacrylamide gels there was, among the peroxidase isoenzymes, a band which could be seen only in SA-treated plants. It is suggested that the pre-treatment of maize plants with SA at normal growth temperature may induce antioxidant enzymes which lead to increased chilling tolerance. Received: 4 June 1998 / Accepted: 23 November 1998     

ACC deaminase-containing Arthrobacter protophormiae induces NaCl stress tolerance through reduced ACC oxidase activity and ethylene production resulting in improved nodulation and mycorrhization in Pisum sativum

Induction of stress ethylene production in the plant system is one of the consequences of salt stress which apart from being toxic to the plant also inhibits mycorrhizal colonization and rhizobial nodulation by oxidative damage. Tolerance to salinity in pea plants was assessed by reducing stress ethylene levels through ACC deaminase-containing rhizobacteria Arthrobacter protophormiae (SA3) and promoting plant growth through improved colonization of beneficial microbes like Rhizobium leguminosarum (R) and Glomus mosseae (G). The experiment comprised of treatments with combinations of SA3, G, and R under varying levels of salinity. The drop in plant biomass associated with salinity stress was significantly lesser in SA3 treated plants compared to non-treated plants. The triple interaction of SA3 + G + R performed synergistically to induce protective mechanism against salt stress and showed a new perspective of plant-microorganism interaction. This tripartite collaboration increased plant weight by 53%, reduced proline content, lipid peroxidation and increased pigment content under 200 mM salt condition. We detected that decreased ACC oxidase (ACO) activity induced by SA3 and reduced ACC synthase (ACS) activity in AMF (an observation not reported earlier as per our knowledge) inoculated plants simultaneously reduced the ACC content by 60% (responsible for generation of stress ethylene) in SA3 + G + R treated plants as compared to uninoculated control plants under 200 mM salt treatment. The results indicated that ACC deaminase-containing SA3 brought a putative protection mechanism (decrease in ACC content) under salt stress, apart from alleviating ethylene-induced damage, by enhancing nodulation and AMF colonization in the plants resulting in improved nutrient uptake and plant growth.     

The subcellular localization of periwinkle farnesyl diphosphate synthase provides insight into the role of peroxisome in isoprenoid biosynthesis

Farnesyl diphosphate (FPP) synthase (FPS: EC.2.5.1.1, EC.2.5.1.10) catalyzes the formation of FPP from isopentenyl diphosphate and dimethylallyl diphosphate via two successive condensation reactions. A cDNA designated CrFPS, encoding a protein showing high similarities with trans-type short FPS isoforms, was isolated from the Madagascar periwinkle (Catharanthus roseus). This cDNA was shown to functionally complement the lethal FPS deletion mutant in the yeast Saccharomyces cerevisiae. At the subcellular level, while short FPS isoforms are usually described as cytosolic proteins, we showed, using transient transformations of C. roseus cells with yellow fluorescent protein-fused constructs, that CrFPS is targeted to peroxisomes. This finding is discussed in relation to the subcellular distribution of FPS isoforms in plants and animals and opens new perspectives towards the understanding of isoprenoid biosynthesis.     

Systemic acquired resistance in Cavendish banana induced by infection with an incompatible strain of Fusarium oxysporum f. sp. cubense

Fusarium wilt of banana is caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). The fact that there are no economically viable biological, chemical, or cultural measures of controlling the disease in an infected field leads to search for alternative strategies involving activation of the plant's innate defense system. The mechanisms underlying systemic acquired resistance (SAR) are much less understood in monocots than in dicots. Since systemic protection of plants by attenuated or avirulent pathogens is a typical SAR response, the establishment of a biologically induced SAR model in banana is helpful to investigate the mechanism of SAR to Fusarium wilt. This paper described one such model using incompatible Foc race 1 to induce resistance against Foc tropical race 4 in an in vitro pathosystem. Consistent with the observation that the SAR provided the highest level of protection when the time interval between primary infection and challenge inoculation was 10 d, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL, EC 4.3.1.5), peroxidase (POD, EC 1.11.1.7), polyphenol oxidase (PPO, EC 1.14.18.1), and superoxide dismutase (SOD, EC 1.15.1.1) in systemic tissues also reached the maximum level and were 2.00–2.43 times higher than that of the corresponding controls on the tenth day. The total salicylic acid (SA) content in roots of banana plantlets increased from about 1 to more than 5 μg g⁻¹ FW after the second leaf being inoculated with Foc race 1. The systemic up-regulation of MaNPR1A and MaNPR1B was followed by the second up-regulation of PR-1 and PR-3. Although SA and jasmonic acid (JA)/ethylene (ET) signaling are mostly antagonistic, systemic expression of PR genes regulated by different signaling pathways were simultaneously up-regulated after primary infection, indicating that both pathways are involved in the activation of the SAR.     

Treatment with salicylic acid decreases the effect of cadmium on photosynthesis in maize plants

The present study investigated the possible mediatory role of salicylic acid (SA) in protecting photosynthesis from cadmium (Cd) toxicity. Seeds of maize (Zea mays L., hybrid Norma) were sterilized and divided into two groups. Half of the seeds were presoaked in 500muM SA solution for only 6h, after which both groups were allowed to germinate for 3d and were then grown for 14d in Hoagland solution at 22/18 degrees C in a 16/8-h light/dark period and 120mumolm(-2)s(-1) PAR. All seedlings (without H(2)O and SA controls) were transferred to Cd-containing solutions (10, 15, and 25muM) and grown for 14d. The rate of CO(2) fixation and the activity of ribulose 1,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were measured. Changes in the levels of several important parameters associated with oxidative stress, namely H(2)O(2) and proline production, lipid peroxidation, electrolyte leakage, and the activities of antioxidative enzymes (superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, EC 1.11.1.6), and guaiacol peroxidase (POD, EC 1.11.1.7)) were measured. Exposure of the plants to Cd caused a gradual decrease in the shoot and root dry weight accumulation, with the effect being most pronounced at 25muM Cd. Seed pretreatment with SA alleviated the negative effect of Cd on plant growth parameters. The same tendency was observed for the chlorophyll level. The rate of CO(2) fixation was lower in Cd-treated plants, and the inhibition was partially overcome in SA-pretreated plants. A drop in the activities of RuBPC and PEPC was observed for Cd-treated plants. Pretreatment with SA alleviated the inhibitory effect of Cd on enzyme activity. Proline production and the rates of lipid peroxidation and electrolyte leakage increased in Cd-treated plants, whereas the values of these parameters were much lower in SA-pretreated plants. Treatment of plants with Cd decreased APX activity, but more than doubled SOD activity. Pretreatment with SA caused an increase in both APX and SOD activity, but caused a strong reduction in CAT activity. The data suggest that SA may protect cells against oxidative damage and photosynthesis against Cd toxicity.     

Acyl-CoA elongase expression during seed development in Brassica napus

The Bn-FAE1.1 and Bn-FAE1.2 genes encode the 3-ketoacyl-CoA synthase, a component of the elongation complex responsible for the synthesis of very long chain monounsaturated fatty acids (VLCMFA) in the seeds of Brassica napus. Bn-FAE1 gene expression was studied during seed development using two different cultivars: Gaspard, a high erucic acid rapeseed (HEAR), and ISLR4, a low erucic acid rapeseed (LEAR). The mRNA developmental profiles were similar for the two cultivars, the maximal expression levels being measured at 8 weeks after pollination (WAP) in HEAR and at 9 WAP in LEAR. Differential expression of Bn-FAE1.1 and Bn-FAE1.2 genes was also studied. In each cultivar the same expression profile was observed for both genes, but Bn-FAE1.2 was expressed at a lower level than Bn-FAE1.1. Secondly, VLCMFA synthesis was measured using particulate fractions prepared from maturating seeds harvested weekly after pollination. The oleoyl-CoA and ATP-dependent elongase activities increased from the 4th WAP in HEAR and reached the maximal level at 8 WAP, whereas both activities were absent in LEAR. In contrast, the 3-hydroxy dehydratase, a subunit of the elongase complex, had a similar activity in both cultivars and reached a maximum from 7 to 9 WAP. Finally, antibodies against the 3-ketoacyl-CoA synthase revealed a protein of 57 kDa present only in HEAR. Our results show: (i) that both genes are transcribed in HEAR and LEAR cultivars; (ii) that they are coordinately regulated; (iii) that Bn-FAE1.1 is quantitatively the major isoform expressed in seeds; (iv) that the Bn-FAE1 gene encodes a protein of 57 kDa responsible for the 3-ketoacyl-CoA synthase activity.     

Control of Pratylenchus penetrans and Meloidogyne hapla and Yield Response of Alfalfa Due to Oxamyl Seed Treatments

Alfalfa (Medicago sativa L. cv. Saranac) seed were soaked for 20 minutes in water, acetone, or methanol containing 10 or 50 mg/ml of oxamyl (Vydate L) or coated with a 2% aqueous cellulose solution containing the same amounts of oxamyl. Seed were analyzed for oxamyl by HPLC immediately after treatment and after 9 and 26 months of storage. Oxamyl content of alfalfa seed did not decline after 26 months of storage. The effects of seed treatment on growth of alfalfa and nematode control were examined using soils infested with Pratylenchus penetrans and Meloidogyne hapla. Germination was not affected by any of the seed treatments. Twenty-one days after sowing, the total growth of alfalfa seedlings grown from seed treated with 50 mg/ml of oxamyl in P. penetrans-infested soils had increased by 62% over controls. Nodulation per pot increased by as much as 267%, and the densities of P. penetrans per gram of root were reduced by as much as 73% compared to control plants. In M. hapla-infested soils, increases in plant growth (32%) and nodulation (71%) also occurred with oxamyl-treated seeds. Root gall reduction (86%) was also substantial due to oxamyl seed treatment.     

The salicylic acid analog 2,6-dichloroisonicotinic acid has specific impact on the response of the halophyte plant species <Emphasis Type="Italic">Solanum chilense</Emphasis> to salinity

Salicylic acid (SA) is involved in the salt-resistance of the halophyte plant species Solanum chilense. The SA analog 2,6-dichloroisonicotinc acid (INA) is commonly used to elicit SA signal transduction in response to biotic stress and is frequently used to confirm the SA involvement in plant response to pathogens. Data are lacking concerning its impact on plant response to salinity, especially in the halophyte species. Solanum chilense was cultivated in the absence or presence of 125 mM NaCl in nutrient solution and exposed to 0.01 mM exogenous SA or sprayed with 0.5 mM INA. Exogenous SA increased the shoot dry weight while INA did not. Exogenous INA, in contrast to SA, increased the shoot Na⁺ concentration in NaCl-treated plants and decreased the root K⁺ concentration. In the absence of salt, both SA and INA induced an increase in H₂O₂ which was not due to ascorbate peroxidase (EC 1.11.1.11) inhibition. In salt-treated plants, SA stimulated the ascorbate peroxidase activity while INA did not. Exogenous SA increased the root putrescine and spermidine concentrations while INA significantly decreased the concentration of these protecting compounds. It is concluded that exogenous SA and INA do not have similar impacts on the plant behavior and that the difference between these compounds may be influenced by NaCl. The use of INA as a reliable SA analog should therefore be considered with caution in halophyte plant species.     

Role of salicylic acid in regulating ultraviolet radiation-induced oxidative stress in pepper leaves

The effect of salicylic acid (SA) counteracting the UV-A, UV-B, and UV-C-induced action on pepper (Capsicum annuum L.) plants was studied. For this purpose, the activities of antioxidant enzymes (peroxidase, polyphenol oxidase, ascorbate peroxidase, catalase, and glutathione reductase) were measured. Plants were sprayed with SA and treated with UV-A (320–390 nm), UV-B (312 nm), and UV-C (254 nm) radiation with a density of 6.1, 5.8, and 5.7 W/m². The activities of antioxidant enzymes were enhanced in leaves in response to UV-B and UV-C radiation. SA treatment moderated an increase in the activities of some antioxidant enzymes (peroxidase, ascorbate peroxidase, catalase, and glutathione reductase) in plants that were treated with UV radiation. The activity of antioxidant enzyme polyphenol oxidase in plants that were treated with UV-B, UV-C, and SA was significantly increased. The aim of the present study was to investigate the possible protective effect of SA treatment on UV-A, UV-B, and UV-C stress.     

Salicylic Acid Enhances Resistance to Fusarium oxysporum f. sp. phaseoli in Common Beans (Phaseolus vulgaris L.)

Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli (Fop) is one of the most serious diseases of common bean (Phaseolus vulgaris L.) and is especially prevalent in China. In this study, we demonstrated that exogenous application of 2 mM salicylic acid (SA) by leaf spraying could induce resistance against Fop in common beans. Accumulation of free and conjugated SA in roots was detected by HPLC analysis and compared. After 168 h of daily SA treatment, the free SA level in roots was eight times higher than in control plants. However, the conjugated SA level reached a peak at 72 h of SA treatment, which was nine times higher than in control plants, and then sharply declined at 168 h. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidases (POX, EC 1.11.1.7) in roots were 9.4 and 6.3 times higher than in control plants after 168 h of SA treatment, respectively. H₂O₂ and O₂ ^? levels reached 2.6 and 13.6 times higher, respectively, than in the control plants at 168 h after SA treatment. Host reactions of SA-treated plant roots infected by Fop observed in microscopy included the deposition of electron-dense materials along the secondary walls. However, untreated inoculated plants showed marked cell wall degradation and total cytoplasm disorganization of root cells. These results indicated that SA applied to foliar tissue is capable of enhancing the systemic acquired resistance of common bean roots to infection by Fop.     

Salicylic acid-altering Arabidopsis mutants response to salt stress

Aims

The role of salicylic acid (SA) in plant responses to salinity is still a matter of controversy. To address the effect of endogenous SA variation in level and signaling on plant responses to salinity, biochemical and physiological analyses were performed on SA-altering Arabidopsis mutants including snc1 with high level of SA, transgenic line nahG with low SA, npr1-1 with SA signaling blockage, snc1/nahG plants (expression of nahG in the snc1 background), as well as wild type plants.

Methods

Plants were cultured in 1?×?Hoagland solution under controlled conditions. For salt exposure, NaCl at final concentrations of 100?mM, 200?mM, and 300?mM, respectively, was added to the culture solution after 25?d of seed germination. Except where mentioned, plant leaves were harvested after 14?d of salt stress, and used for physiological and chemical analyses.

Results

Salt stress caused all plants growth retardation with a dose-effect relationship relative to control. However, compared to wild type plants, a greater growth inhibition occurred in snc1, while a less inhibition was observed in nahG and npr1-1 plants, and a comparable extent was detected in snc1/nahG plants in which the SA level was near to that in wild type plants. The snc1 plants had lower net photosynthetic rate, variable to maximum fluorescence ratio, quantum efficiency of photosystem 2, reduced glutathione/oxidized glutathione ratio, proline levels, and higher malondiadehyde levels and electrolyte leakage rates as compared to wild type plants under salt stress. These values were effectively reversed by the expression of nahG gene in snc1 plants. The nahG and npr1-1 plants always exhibited more tolerance to salinity in above-mentioned indices than wild type plants. However, higher activities of superoxide dismutase and peroxidase in snc1 plants did not contribute to salt tolerance.

Conclusions

These data showed that SA deficit or signaling blockage in Arabidopsis plants was favorable to salt adaptation, while a high accumulation of SA potentiated salt-induced damage to Arabidopsis plants.     

Salicylic acid increases tolerance to oxidative stress induced by hydrogen peroxide accumulation in leaves of cadmium-exposed flax (Linum usitatissimum L.)

The aim of this study is to investigate the impacts of exogenous salicylic acid (SA) pretreatments on hydrogen peroxide (H₂O₂) accumulation, protein oxidation, and H₂O₂-scavenging enzymes in leaves of Cd-treated flax seedlings. Cd-enhanced H₂O₂ levels were related to increased activities of guaiacol peroxidase (POX, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11), and were independent of changes in catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) activities. In control flax seedlings, exogenous SA pretreatments inhibited the activity of CAT, resulted in an enhanced production of H₂O₂ suggesting that SA requires H₂O₂ to initiate an oxidative stress. However, although leaves of Cd-free flax seedlings pretreated with SA accumulated in vivo H₂O₂ by 1.2-fold compared with leaves of Cd-only exposed ones; the damage to growth and proteins after the exposure to Cd was significantly less, indicating that SA can regulate the Cd-induced oxidative stress. Moreover, the Cd-treated seedlings primed with SA exhibited a higher level of total antioxidant capacities and increased activities of H₂O₂-detoxifying enzymes.     

Role of exogenous salicylic acid in alleviating cadmium-induced toxicity in Kentucky bluegrass

To understand the role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity in Kentucky bluegrass (Poa pratensis L.), we investigated the changes of biochemical and physiological indexes in five-week-old Kentucky bluegrass seedlings exposed to 0, 5, 10 or 50 μM Cd with or without 500 μM SA for 7 d. Results showed that, compared to the Cd treatment applied alone, 500 μM SA pretreatment significantly decreased Cd accumulations and increased the chlorophyll level, growth and nutrient elements content (K, Ca, Mg and Fe) in plants, accompanying with the reduction in malondialdehyde and hydrogen peroxide contents. Furthermore, SA pretreatment enhanced remarkably the superoxide dismutase, ascorbate peroxidase and peroxidase activity in the Cd-stressed plants, but decreased catalase activity. Overall, SA might regulate the antioxidant defense activities, reduce Cd uptake and stimulate nutrient elements absorption in Cd-treated with Kentucky bluegrass, thereby improving its resistance to Cd stress.     

Effect of 24-epibrassinolide on growth, protein content and antioxidative defense system of Brassica juncea L. subjected to cobalt ion toxicity

Brassica juncea L. plants were subjected to cobalt (Co) ion (0, 5?×?10^?4, 10^?3, 1.5?×?10^?3 and 2?×?10^?3?M) toxicity and were sprayed with different concentrations of 24-epibrassinolide (24-EBL) (0, 10^?10, 10^?8 and 10^?6?M) at 15-day stage after sowing. They were sampled at 30 and 60?days after sowing and analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 1.15.1.1) catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APOX) (EC 1.11.1.11), guaiacol peroxidase (POD) (EC 1.11.1.7) glutathione reductase (GR) (EC 1.6.4.2), monodehydroascorbate reductase (MDHAR) (EC 1.1.5.4) and dehydroascorbate reductase (DHAR) (EC 1.8.5.1)) were analyzed. The plants exposed to cobalt ion exhibited a significant decline in growth in terms of shoot length and number of leaves. However, foliar spray treatment with 24-EBL was able to alleviate the stress generated by cobalt ion and significantly improved the above parameters. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX, MDHAR and DHAR) and protein content were also regulated considerably in leaves of plants treated with 24-EBL alone, 10^?8?M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application of cobalt ion to soil and consequently sprayed with 24-EBL. Similarly, the protein content was also regulated in leaves of B. juncea plants treated with 24-EBL as compared to untreated control plants, thereby revealing stress-protective properties of 24-EBL.     

Effects of salicylic acid on paraquat tolerance in<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> plants

Foliar spraying ofArabidopsis thaliana (Columbia ecotype) plants with a 1.0-mM salicylic acid (SA) solution significantly improved their tolerance to subsequent paraquat (PQ)-induced oxidative damage. Leaf injuries, including losses of chlorophyll, protein, and fresh weight, were reduced. Our analysis of antioxidant enzymes in the leaves showed that SA pre-treatment effectively retarded rapid decreases in the activities of Superoxide dismutase (SOD), catalase, and ascorbate peroxidase that are normally associated with PQ exposure. In addition, guaiacol peroxidase activity was remarkably increased. In a native gel assay of peroxidase (POD) isozymes, staining activity of the POD1 isozyme, which disappeared in plants exposed only to 10 μM PQ, was significantly recovered by the 1.0-mM SA pre-treatment POD2 isozyme activity was also pronounced in all SA-treated plants compared with the control. A 12-h SA pre-treatment, without subsequent PQ stress, also caused a small increase in the endogenous H₂O₂ content that accompanies the symptoms of mild leaf injuries. This enhanced level occurred in parallel with a slight SOD increase and a catalase decrease. From our results, it can be assumed that, due to the small increase in SOD as well as catalase inactivation via SA pre-treatment, a moderate increase in H₂O₂ levels may occur. In turn, a large induction of guaiacol peroxidase leads to enhanced PQ tolerance inA. thaliana plants.     

Effect of root length on epicotyl dormancy release in seeds of Paeonia ludlowii,Tibetan peony

Background and Aims

Epicotyl dormancy break in seeds that have deep simple epicotyl morphophysiological dormancy (MPD) requires radicle emergence and even a certain root length in some species. However, the mechanisms by which root length affects epicotyl dormancy break are not clear at present. This study aims to explore the relationship between root length and epicotyl dormancy release in radicle-emerged seeds of Tibetan peony, Paeonia ludlowii, with discussion of the possible mechanisms.

Methods

Radicle-emerged seeds (radicle length 1·5, 3·0, 4·5 and 6·0 cm) were incubated at 5, 10 and 15 °C. During the stratification, some seeds were transferred to 15 °C and monitored for epicotyl–plumule growth. Hormone content was determined by ELISA, and the role of hormones in epicotyl dormancy release was tested by exogenous hormone and embryo culture.

Key Results

Cold stratification did not break the epicotyl dormancy until the root length was ≥6 cm. The indole-3-actic acid (IAA) and GA₃ contents of seeds having 6 cm roots were significantly higher than those of seeds with other root lengths, but the abscisic acid (ABA) content was lowest among radicle-emerged seeds. GA₃ (400 mg L⁻¹) could break epicotyl dormancy of all radicle-emerged seeds, while IAA (200 mg L⁻¹) had little or no effect. When grown on MS medium, radicles of naked embryos grew and cotyledons turned green, but epicotyls did not elongate. Naked embryos developed into seedlings on a mixed medium of MS + 100 mg L⁻¹ GA₃.

Conclusions

A root length of ≥6·0 cm is necessary for epicotyl dormancy release by cold stratification. The underlying reason for root length affecting epicotyl dormancy release is a difference in the GA₃/ABA ratio in the epicotyl within radicle-emerged seeds, which is mainly as a result of a difference in ABA accumulation before cold stratification.     

Cadmium-induced oxidative damage in mustard [Brassica juncea (L.) Czern. & Coss.] plants can be alleviated by salicylic acid

The present study was carried out to examine the effects of salicylic acid (SA) on growth, activities of antioxidant enzymes and some physio-biochemical attributes in mustard [Brassica juncea (L.) Czern. & Coss.] plants exposed to cadmium (Cd) stress. Increasing concentrations of Cd led to decreased growth, shoot biomass, relative water content (RWC) and rate of photosynthesis (A). SA allayed the adverse effects of Cd on growth, RWC, and A, but the inhibitory effect of Cd on stomatal conductance (g_s) and transpiration rate (E) was further promoted due to SA treatment. Cadmium-induced oxidative stress increased proline, lipid peroxidation and electrolyte leakage, but on exposure to SA, these parameters showed a marked decrease. Lower concentrations of Cd caused enhanced Cd transport into the plant. Cadmium suppressed the uptake of macro- and micro-nutrients, but exogenous application of SA restored the capability of plants to accumulate essential elements. SA mitigated the Cd-induced inhibition in the growth of mustard plants. Cadmium-induced increase in the activities of some key antioxidant enzymes, superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR) was reduced by the exogenous application of SA. This reflects that SA might have acted as one of the potential antioxidants in mustard plants under Cd stress.     

Deep simple epicotyl morphophysiological dormancy in seeds of two Viburnum species, with special reference to shoot growth and development inside the seed

Background and Aims

In seeds with deep simple epicotyl morphophysiological dormancy, warm and cold stratification are required to break dormancy of the radicle and shoot, respectively. Although the shoot remains inside the seed all winter, little is known about its growth and morphological development prior to emergence in spring. The aims of the present study were to determine the temperature requirements for radicle and shoot emergence in seeds of Viburnum betulifolium and V. parvifolium and to monitor growth of the epicotyl, plumule and cotyledons in root-emerged seeds.

Methods

Fresh and pre-treated seeds of V. betulifolium and V. parvifolium were incubated under various temperature regimes and monitored for radicle and shoot emergence. Growth of the epicotyl and cotyledons at different stages was observed with dissecting and scanning electron microscopes.

Key Results

The optimum temperature for radicle emergence of seeds of both species, either kept continuously at a single regime or exposed to a sequence of regimes, was 20/10 °C. GA₃ had no effect on radicle emergence. Cold stratification (5 °C) was required for shoot emergence. The shoot apical meristem in fresh seeds did not form a bulge until the embryo had grown to the critical length for radicle emergence. After radicle emergence, the epicotyl–plumule and cotyledons grew slowly at 5 and 20/10 °C, and the first pair of true leaves was initiated. However, the shoot emerged only from seeds that received cold stratification.

Conclusions

Seeds of V. betulifolium and V. parvifolium have deep simple epicotyl morphophysiological dormancy, C_1bB (root)–C₃ (epicotyl). Warm stratification was required to break the first part of physiological dormancy (PD), thereby allowing embryo growth and subsequently radicle emergence. Although cold stratification was not required for differentiation of the epicotyl–plumule, it was required to break the second part of PD, thereby allowing the shoot to emerge in spring.