Showing papers in "Plant Growth Regulation in 2003"

Salicylic acid induced physiological and biochemical changes in wheat seedlings under water stress

Abstract: Salicylic acid (SA) is an important signal molecule modulating plant responses to stress. It is recently reported to induce multiple stress tolerance in plants including drought. An experiment was, therefore, conducted to ascertain the effect of salicylic acid on the growth and metabolic profile of wheat seedlings under water stress. Irrespective of the SA concentration (1-3 mM) and water stress, SA treated plants showed, in general, a higher moisture content, dry mass, carboxylase activity of Rubisco, superoxide dismutase (SOD) activity and total chlorophyll compared to those of untreated seedlings. SA treatment, under water stress, protected nitrate reductase (NR) activity and maintained, especially at 3 mM SA concentration, the protein and nitrogen content of leaves compared to water sufficient seedlings. Results signify the role of SA in regulating the drought response of plants and suggest that SA could be used as a potential growth regulator, for improving plant growth under water stress.

Physiological responses of groundnut (Arachis hypogea L.) to drought stress and its amelioration: a critical review

Abstract: Groundnut (Arachis hypogea L.), is an important legume cash crop for the tropical farmers and its seeds contain high amounts of edible oil (43–55%) and protein (25–28%). Even though it is a fairly drought-tolerant, production fluctuates considerably as a result of rainfall variability. To develop a water stress response function in groundnut, research works have been done to improve the performance under varying degrees of stress at various physiological stages of crop growth. This review summarizes recent information on drought resistance characteristics of groundnut with a view toward developing appropriate genetic enhancement strategies for water-limited environments. It is suggested that there are considerable gains to be made in increasing yield and stabilizing the yield in environments characterized by terminal drought stress and by shortening crop duration. Many traits conferring dehydration avoidance and dehydration tolerance are available, but integrated traits, expressing at a high level of organization are suggested to be more useful in crop improvement programs. Possible genetic improvement strategies are outlined, ranging from empirical selection for yield in drought environments to a physiological–genetic approach. It was also suggested that in view of recent advances in understanding drought resistance mechanisms, the later strategy is becoming more feasible. It is summarized that application of knowledge into practice in a systematic manner can lead to significant gains in yield and yield stability of the world’s groundnuts production. Research is needed to develop transferable technology to help farmers of arid and semi-arid regions. Increasing soil moisture storage by soil profile management and nutrient management for quick recovery from drought are some of the areas that need to be explored further.

ABA effects on ethylene production, PAL activity, anthocyanin and phenolic contents of strawberry fruit

Abstract: Effects of exogenously applied abscisic acid (ABA) on ethylene production rate, phenylalanine ammonia-lyase ( PAL) enzyme activity, and anthocyanin and phenolic concentrations in harvested strawberry cv. Everest fruit were evaluated. Colouration and firmness were also assessed on fruit held for 3 days at 20 degreesC. ABA treatment accelerated fruit colour and softening. Treatment with 10(-5) or 10(-4) mol ABA l(-1) stimulated ethylene production. Anthocyanin and phenolic contents and PAL activity increased during storage, but more rapidly in ABA treated fruit. As a result, red colour development was accelerated. Endogenous ABA may play a role in strawberry fruit colour development during ripening through up-regulation of ethylene production and PAL activity.

Salt tolerant tomato plants show increased levels of jasmonic acid

Abstract: Tomato cultivars with different tolerance to NaCl were analysed for basal endogenous jasmonate (JAs) content, and its changes in response to salt-stress. Steady-state levels of JA and related compounds were higher in the salt-tolerant cv. Pera than in cv. Hellfrucht Fruhstamm (HF) and JA levels in both cultivars changed in response to salt-stress. A steady JA increase was observed in cv. HF from the beginning of salinisation, while in cv. Pera, JA level decreased after 24 h of salt treatment. These results support the hypothesis that changes in endogenous JA in response to stress are different in genotypes of contrasting salt tolerance. The effects of salinity were then studied on lipoxygenase (LOX) protein accumulation, transcripts of allene oxide synthase (AOS) and proteinase inhibitor II (Pin2), and activities of diacylglycerol kinase (DAG-k) and phosphatidate kinase (PA-k) (enzymes involved in the phosphatidic acid (PA) and diacylglycerol pyrophosphate (DGPP) metabolism). The accumulation of a high molecular weight LOX-like protein was more pronounced in salt treated-plants of cv. HF, although both cultivars responded to exogenous JA treatment by increasing LOX accumulation. AOS-mRNA and Pin2-mRNA had also accumulated after 6 h of NaCl and JA treatments. An increase in the phosphorylation of phospholipids PA and DGPP was evident in cv. Pera, indicating that DAG-k and PA-k were highly activated by salt treatment only in this cultivar. Thus, the difference in the lipid kinase activities between both cultivars may be related to the process of salt stress tolerance rather than to JA synthesis.

Inhibition of catalase activity by oxidative stress and its relationship to salicylic acid accumulation in plants

Abstract: The decrease in catalase activity and its relationship to change in salicylic acid content were investigated in rice, wheat, and cucumber seedlings exposed to oxidative stresses A decrease in chlorophyll fluorescence (ΔF/Fm′), measured as an indicator of the oxidative stress, and a drop in catalase activity were observed following treatment with NaCl in all plant seedlings tested Furthermore, such decreases in ΔF/Fm′ and catalase activity were also observed under low temperature conditions in both rice cultivars, whereas the degrees of decrease were dependent on their low temperature tolerance Although the content of salicylic acid increased in rice seedlings stressed by NaCl treatment, it was inversely correlated with the decrease in the catalase activity Such a relationship between the decrease in catalase activity and increase in salicylic acid content was confirmed with paraquat treatment of the rice seedlings These results suggested that the fall in catalase activity is a phenomenon occurring in many plant species under oxidative stress and is related to the accumulation of salicylic acid in oxidatively-stressed plants

Cytokinins in macroalgae

Abstract: Thirty-one seaweeds were collected from the warmer KwaZulu-Natal coast and the cooler Cape waters (South Africa). Plant material was extracted with 70% ethanol supplemented with deuterium labelled standards of all known isoprenoid cytokinins. The samples were then centrifuged and purified by combined DEAE-Sephadex×octadecylsilica column and immunoaffinity chromatography and finally analysed for cytokinins by HPLC-linked mass spectrometry and a photodiode array detector. The cytokinin profiles were similar in all the macroalgae regardless of their taxonomy and growing locality. The main type of isoprenoid cytokinins present were zeatins with cis forms being more common than trans forms and isopentenyladenine (iP) derivatives. Only a few dihydrozeatin-type cytokinins were detected at very low levels in only nine species. Aromatic cytokinins were also present but at lower levels and were represented by benzyladenine (BA) and ortho- and meta-topolin derivatives. The topolins were present in greater diversity and concentrations than BA. For all the cytokinin types, the free bases, O-glucosides and nucleotides were the most common with no N-glucosides being detected and ribosides present at very low levels. The results suggest that different pathways for regulating cytokinin concentrations operate in macroalgae than in higher plants.

Effects of salicylic acid and cold on freezing tolerance in winter wheat leaves

Abstract: The effects of salicylic acid (SA) (0.01, 0.1 and 1 mM) and cold on freezing tolerance (freezing injury and ice nucleation activity) were investigated in winter wheat (Triticum aestivum cv. Dogu-88) grown under control (20/18 °C for 15, 30 and 45-day) and cold (15/10 °C for 15-day, 10/5 °C for 30-day and 5/3 °C for 45-day) conditions. Cold acclimatisation caused a decrease of injury to leaf segments removed from the plants and subjected to freezing conditions. Exogenous SA also decreased freezing injury in the leaves grown under cold (15/10 °C) and control (15 and 30-day) conditions. Cold conditions (10/5 and 5/3 °C) caused an increase in ice nucleation activity by apoplastic proteins, which were isolated from the leaves. For the first time, it was shown that exogenous SA caused an increase in ice nucleation activity under cold (15/10 and 10/5 °C) and control conditions. These results show that salicylic acid can increase freezing tolerance in winter wheat leaves by affecting apoplastic proteins.

Changes in germination, growth and soluble sugar contents of Sorghum bicolor (L.) Moench seeds under various abiotic stresses

Abstract: The effect of various abiotic stresses on germination rate, growth and soluble sugar content in Sorghum bicolor (L.) Moench cv. CSH 6 seed embryos and endosperm during early germination was investigated. Under stress conditions germination, water potential and tissue water content decreased markedly. Subsequently, this reduction resulted in marked decreases in fresh weight both in embryos and endosperm. Conversely, a substantial increase in dry weight was observed. Furthermore, a considerable increase in the sugar contents in both embryo and endosperm was detected. The fructose level was always higher than glucose and sucrose in response to various stresses. However, as compared to the control the level of glucose and sucrose was higher in embryos and endosperm after stress treatments. Based upon these results a possible physiological role of sugars in the germination of sorghum seeds is discussed.

Hormones in the grains in relation to sink strength and postanthesis development of spikelets in rice

Abstract: Inferior spikelets usually exhibit a slower grain filling rate and lower grain weight than superior spikelets in a rice (Oryza sativa L.) panicle. This study investigated whether the variations in grain filling between the two kinds of spikelets were attributed to their sink strength and whether the sink strength was regulated by the hormonal levels in the grains. Using two field-grown rice genotypes, the division rate of endosperm cells, hormonal levels in the grains, and grain weight of both superior and inferior spikelets were determined during the grain filling period. The results showed that superior spikelets had dominance over inferior spikelets in endosperm cell division rate and cell number, grain filling and grain weight. Changes in zeatin (Z) and zeatin riboside (ZR) contents paralleled and were very significantly correlated with the cell division rate and cell number. Cell division rate and the content of indole-3-acetic acid (IAA) in the grains were also significantly correlated. Gibberellin (GAs; GA1+ GA4) content of the grains was high but ABA levels were low at the early grain filling stage. ABA increased substantially during the linear phase of grain growth and was very significantly correlated with grain dry weight during this period. Application of kinetin at 2 through 6 days post anthesis (DPA) significantly increased cell number, while spraying ABA at 11 through 15 DPA significantly increased the grain filling rate. The results suggest that differences in sink strength are responsible for variations in grain filling between superior and inferior spikelets. Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.

Water stress effects on photosynthesis in different mulberry cultivars

Abstract: The effect of water stress on photosynthesis was determined in five mulberry cultivars (Morus alba L. cv. K-2, MR-2, BC2-59, S-13 and TR-10). Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5 -MPa to 2.0 -MPa. Photosynthetic rates, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, photosystem II activity and chlorophyll content were used as key parameters to assess photosynthetic performance. There was a marked variation in the photosynthetic rates and ribulose-1,5-bisphosphate carboxylase activity among the five mulberry cultivars subjected to water stress. Photosystem II (PSII) and sucrose phosphate synthase activities were also severely reduced as measured by drought conditions. Of the five mulberry cultivars, S-13 and BC2-59 showed higher photosynthetic rates, ribulose-1,5-bisphosphate carboxylase activity, high sucrose phosphate synthase activity and photochemical efficiency of PSII compared to the other varieties.

Application of brassinosteroids to rice seeds (Oryza sativa L.) reduced the impact of salt stress on growth, prevented photosynthetic pigment loss and increased nitrate reductase activity

Abstract: The effect of applying brassinosteroids to seeds on growth, pigment levels and nitrate reductase activity of rice (Oryza sativa L) plants grown on saline substratum was investigated Brassinosteroids reduced the impact of salt stress on growth, considerably restored pigment levels and increased of nitrate reductase activity

Amelioration of osmotic stress by brassinosteroids on seed germination and seedling growth of three varieties of sorghum

Abstract: The effect of 28-homobrassinolide and 24-epibrassinolide on the germination and seedling growth of three varieties of sorghum, viz CSH-14 and ICSV-745 (susceptible to water stress) and M-35-1 (resistant to water stress), under osmotic stress conditions was studied Both the brassinosteroids were very effective in increasing the percentage of germination and seedling growth of all the three varieties of sorghum under osmotic stress, the growth promotion being associated with enhanced levels of soluble proteins and free proline Brassinosteroid treatment enhanced the activity of catalase and reduced the activities of peroxidase and ascorbic acid oxidase

Growth promotion of bean ( Phaseolus vulgaris L.) by a polyamine-producing isolate of Streptomyces griseoluteus

Abstract: Of seventy-five actinomycetes isolated from a bean rhizosphere in the United Arab Emirates, an isolate of Streptomyces griseoluteus (WT) was found to be capable of producing relatively high levels of putrescine on decarboxylase agar medium and to produce putrescine, spermidine and spermine in liquid decarboxylase medium. In the glasshouse, the application of the WT strain to soil amended with arginine (as a precursor for putrescine) significantly (P 0.05) differences between the levels of polyamines, endogenous PGRs, chlorophylls (a, b), and carotenoids between plants that were not exposed to either of the strain (control) and those grown in soil with the PNPM strain. Both WT and PNPM strains were incapable of producing in vitro detectable levels of PGRs, indole-acetic acid, indole-pyruvic acid, gibberellic acid, isopentenyl adenine and zeatin in the culture filtrates. This study is the first to demonstrate the potential of a polyamine-producing actinomycete to promote plant growth. In addition, it is also the first published report of the production of polyamines by streptomycete actinomycetes.

Behaviour of antioxidant defense system in the adaptive response to salt stress in Helianthus annuus L. cells

Abstract: A relationship between the antioxidant defense system and salt tolerance in two types of sunflower calli differing in salt sensitivity was studied. No reduction in growth occurred in the NaCl-salt-adapted cell line (T) when grown on 175 mM NaCl but growth of the salt-stressed cell line (S) was reduced by 83%. Lipid peroxidation and protein oxidation increased during acute stress of salt stressed cells at 14 and 28 d of the experiment, while salt-adapted calli (T) remained similar to non-shocked (C) values. The antioxidant defense system of callus adapted to growth under NaCl responded differently to 175 mM of salt compared with the corresponding controls under shock treatment. Salt-adapted and salt-stressed calli showed a similar pattern in GSH content at day 14 but at day 28 in S calli, GSH content was increased 100% over the non-shocked calli, while T calli returned to the initial values. In the salt-stressed calli, a general decrease in all the antioxidant enzymes studied (except for glutathione reductase and dehydroascorbate reductase activities) was observed at day 28. Except for catalase, the antioxidant enzymes were elevated constitutively in adapted calli as compared to stressed cells, when both were grown in the absence of NaCl (time 0), and remained unaltered until 28 d after the beginning of the experiment. These results suggest the involvement of an enzymatic antioxidant defense system in the adaptive response to salt stress in Helianthus annuus L. cells.

Benzoic acid may act as the functional group in salicylic acid and derivatives in the induction of multiple stress tolerance in plants

Abstract: Benzoic acid, sulfosalicylic acid and methyl salicylic acid wereevaluated for their regulatory role in inducing multiple stress tolerance inbean (Phaseolus vulgaris cv Brown Beauty) and tomato(Lycopersicum esculentum cv Romano) plants. All threemolecules were effective in inducing tolerance to heat, drought and chillingstress similar to that reported previously for salicylic and acetylsalicylicacids. Benzoic acid is effective at lower concentrations than salicylic acid orits derivatives. The benzoic acid structural portion is common to all fivemolecules and is the most likely basic functional molecular structure impartingstress tolerance in plants.

Relationships of endogenous plant hormones to accumulation of grain protein and starch in winter wheat under different post-anthesis soil water statusses

Abstract: Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought or waterlogging, endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, four winter wheat (Triticum aestivum L.) varieties differing in grain protein content, Heimai 76, Wanmai 38, Yangmai 10 and Yangmai 9, were subjected to drought (SRWC = 45∼50%, DR), waterlogging (WL) and moderate water supply (SRWC = 75∼80%, CK), beginning from 4 days post-anthesis (DPA) to maturity. On the 10 (grain enlargement stage) and 20 (grain filling stage) DPA, endogenous abscisic acid (ABA), gibberellins (GA1+3), indole-3-acetic acid (IAA) and zeatin riboside (ZR) were determined in sink and source organs of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in four varieties. The ABA levels were much higher under DR and WL than under CK. Compared with CK, GA1+3 levels in whole-plant under DR and WL changed a little at 10 DPA, but markedly decreased under DR and WL at 20 DPA. Changes of endogenous IAA level under DR and WL exhibited a complicated pattern, depending on organs and growth stages. Particularly at the 20 DPA, the mean levels of IAA in roots, leaves and grains decreased significantly under DR and WL. In comparison with CK, ZR levels in all organs significantly decreased under DR and WL at both stages. The correlation analyses between yields and contents of starch and protein in grains and levels and ratios of four hormones in source and sink organs indicated that the changes in yield and content of grain starch and protein under DR and WL were associated with the reduced IAA, ZR and GA1+3 levels and elevated ABA level in plants, especially in grains. It was proposed that the changed levels of endogenous hormones under post-anthesis DR and WL might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.

Effect of water stress on growth, Na+ and K+ accumulation and water use efficiency in relation to osmotic adjustment in two populations of Atriplex halimus L.

Abstract: The effect of water stress on growth, Na+ and K+ accumulation and water utilization was investigated in plants of two populations of Atriplex halimus L. originating from Kairouan (Tunisia) and Tensift (Morocco). Water deficit was applied by withholding water for 22 days. All plants remained alive until the end of the treatment although growth was strongly reduced in both populations. Water stress decreased CO2 assimilation in saturating conditions, mainly in the population obtained from Kairouan, suggesting an impact of drought on the dark phase of photosynthesis, beside a decrease in stomatal conductance which was recorded mainly in the population obtained from Tensift. The two studied populations did not differ in their water consumption, as indicated by similar soil gravimetric water content and plant transpiration. However, water use efficiency increased under stress conditions in the population from Tensift but not in the population from Kairouan. The latter population displayed a larger capacity for osmotic adjustment. A drought-induced specific increase in Na+ concentration was also reported in both populations. It is concluded that in A. halimus, water stress resistance estimated in terms of biomass production, could be associated with higher WUE rather than with with a greater osmotic adjustment and that sodium may assume a specific physiological function in this xerohalophytic C-4 species.

Amelioration of chilling stress by triadimefon in cucumber seedlings

Abstract: Cucumber (Cucumis satvus L.) seeds were imbibed in distilled water (control) and 10 mg l−1 triadimefon (TDM) for 10 h and then grown in a plant growth chamber with a light/dark temperature of 28/20 °C and a photoperiod of 14 h with a light intensity of 60 µmol m−2 s−1. 14-day-old seedlings were exposed to chilling stress with a light/dark temperature of 6/3 °C for 4 d. TDM improved the growth rate of cucumber seedling subjected to chilling stress and increased photosynthetic pigments contents and relative water content compared with the control at the end of chilling stress. Chilling stress decreased protein content and the activities of SOD, CAT and POD, but it increased proline, H2O2 and MDA accumulation, and relative electrical conductivity. TDM ameliorated the injury caused by chilling stress by preventing decreases in protein content and the activities of SOD, CAT and POD and by inhibiting increases in proline, H2O2 and MDA contents, and relative electrical conductivity, which suggested that TDM ameliorated the negative effect of chilling stress.

Differential effect of sorbitol and polyethylene glycol on antioxidant enzymes in rice leaves

Abstract: Polyethylene glycol (PEG) and sorbitol (ST) have each been used in osmotically induced water stress studies in plants, however, these osmotica may not have equivalent effects in plants. The present study was designed to examine whether antioxidant enzyme responses in rice leaves are different for PEG and ST of osmotic potential -1.5 MPa. As judged by relative water content, PEG treatment resulted in a higher degree of water stress in rice leaves than ST treatment. PEG treatment markedly increased lipid peroxidation, judged by malondialdehyde content, in rice leaves. However, ST treatment had no effect on lipid peroxidation. An increase in peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities was observed in rice leaves treated with ST. PEG treatment had no effect on POX and APX activities and decreased GR activity in rice leaves. The decrease in superoxide dismutase activity induced by PEG was more pronounced than by ST. Cycloheximide blocked the enhanced activities of POX, APX and GR by ST, indicating de novo synthesis of the enzymes. Results suggest that ST but not PEG treatment can up-regulate antioxidant system in rice leaves.

Activities of key enzymes for starch synthesis in relation to growth of superior and inferior grains on winter wheat (Triticum aestivum L.) spike

Abstract: Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to be closely associated with starch synthesis in grains. The present study was undertaken to determine if the enzymes involved in starch synthesis cause the differences in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Triticum aestivum L.) varieties differing in grain weight and three nitrogen rates for one variety, the contents of amylose and amylopectin, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire period of grain filling. Superior grains showed generally higher starch accumulation rates and activities of enzymes including SS (sucrose synthase), UDPGPPase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-glucose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weight than inferior grains. Nitrogen increased enzyme activities and starch accumulation rates, and thus improved individual grain weight, especially for inferior grains. The SS, ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were significantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starch synthase play key roles in regulating starch accumulation and grain weight in superior and inferior grains on a wheat spike.

Water relations and xylem transport of nutrients in pepper plants grown under two different salts stress regimes

Abstract: Two iso-osmotic concentrations of NaCl and Na2SO4 were used for discriminating between the effects of specific ion toxicities of salt stress on pepper plants (Capsicum annuum L.) grown in hydroponic conditions, in a controlled-environment greenhouse. The two salts were applied to plants at different electrical conductivities, and leaf water relations, osmotic adjustment and root hydraulic conductance were measured. Leaf water potential (Ψw), leaf osmotic potential (Ψo) and leaf turgor potential (Ψp) decreased significantly when EC increased, but the decrease was less for NaCl- than for Na2SO4-treated plants. The reduction in stomatal conductance was higher for NaCl-treated plants. There were no differences in the effect of both treatments on the osmotic adjustment, and a reduction in root hydraulic conductance and the flux of solutes into the xylem was observed, except for the saline ions (Na+, Cl− and SO4 2−). Therefore, pepper growth decreased with increasing salinity because the plants were unable to adjust osmotically or because of the toxic effects of Cl−, SO4 2− and/or Na+. However, turgor of NaCl-treated plants was maintained at low EC (3 and 4 dS m−1) probably due to the maintenance of water transport into the plant (decrease of stomatal conductance), which, together with the lower concentration of Na+ in the plant tissues compared with the Na2SO4 treatment, could be the cause of the smaller decrease in growth.

Accumulation of some nitrogen compounds in response to salt stress and their relationships with salt tolerance in rice (Oryza sativa L.) seedlings

Abstract: The salt-induced accumulation of some nitrogen compounds (free amino acids, ammonium and urea) in shoots of eight rice cultivars differing in salt tolerance was investigated. Salt treatment (100 mM, 6 days) significantly increased the proline content of shoots but this appeared to be a reaction to stress damage and not associated with salt tolerance, because proline contents were higher in the more sensitive cultivars. Besides proline, some other free amino acids also accumulated leading to a significant increase in the total amino acid content of the stressed seedlings. High levels of free ammonium also accumulated under conditions of stress; this was highly correlated with the accumulation of Na+ in the shoots and negatively correlated with salt tolerance. The accumulation of ammonium was positively correlated with the accumulation of many free amino acids, and also associated with the production of urea in the stressed seedlings. Results from the present investigations suggest that an increase in the concentration of some free amino acids including proline, may be a result of the reassimilation of the stress-induced ammonium. A high capacity to assimilate ammonium may be an important factor in alleviating the consequence of stress because ammonium can be toxic at high concentrations.

Expression and activities of ethylene biosynthesis enzymes during ripening of banana fruits and effect of 1-MCP treatment

Abstract: The respiratory climacteric, ethylene evolution and activities and expression of ethylene biosynthesis enzymes show a characteristic pattern in banana during ethylene induced ripening A unique biphasic respiratory climacteric with a 10 and 6 fold increment in respiration rates on days 2 and 6 respectively after ethylene treatment is preceded by ethylene evolution on days 1 and 4 with 83 and 693 fold increments respectively This represents a unique feature of ripening in banana While ACC synthase transcript accumulation matched the respiratory climacteric, the ACC synthase activity and ACC oxidase transcript accumulation showed a different pattern The most significant observation was the effect of 1-MCP on ACC content and in vitro ACC oxidase activity Though 1-MCP treated fruit did not show any respiratory climacteric or burst in ethylene production, it did not inhibit completely ACC accumulation and in vitro ACC oxidase activity No transcript accumulation of ACC synthase was observed at any time in 1-MCP treated fruits, whereas a basal level of ACC oxidase transcript was detected throughout It is concluded that ethylene induced ripening of banana is characteristically different from that of other climacteric fruits and that ethylene biosynthesis may have more than one mechanisms operating during ripening which are tightly controlled at various levels

Effects of putrescine and ethephon on some oxidative stress enzyme activities and proline content in salt stressed spinach leaves

Abstract: The effects of putrescine and ethephon on peroxidase (POD; EC 1.11.1.7), polyphenol oxidase (PPO; EC 1.14.18.1), catalase (CAT; EC 1.11.1.6) activities and proline content in spinach leaves under saline stress were investigated. In control conditions, putrescine increased PPO and CAT activities and proline content, but decreased POD activity. Ethephon increased these three enzyme activities but did not affect proline content. In saline conditions, putrescine increased POD and CAT activities and proline content, while it decreased PPO activity. Ethephon increased both PPO and CAT activities and proline content, but decreased POD activity. Putrescine and ethephon have opposite effects on the enzyme activities and proline accumulation because they acts as antagonists.

Effect of ethylene and 1-methylcyclopropene on chlorophyll catabolism of broccoli florets

Abstract: Branchlets of broccoli (Brassica oleracea L) were used to examine ethylene-stimulated chlorophyll catabolism Branchlets treated with: 1) air (CK); 2) 1 µL·L−1 1-methylcyclopropene (1-MCP) for 14 hr at 20 °C; 3) 1000 µL·L−1 ethylene (C2H4) for 5 hr at 20 °C; or 4) 1-MCP then C2H4, were stored in the dark at 20 °C for up to 3 d Chlorophyll (Chl) content and branchlet hue angle decreased during the storage period and 1-MCP treatment delayed this change Chl degradation in broccoli was accelerated by exposure to C2H4, especially for Chl a Prior treatment with 1-MCP prevented degreening stimulated by C2H4 Lipoxygenase activity was not altered by any of the treatments, however, 1-MCP with or without ethylene resulted in reduced activity of chlorophyllase (Chlase) and peroxidase (POD) Exposure to C2H4 stimulated Chlase activity and extended the duration of high POD activity Treatment with 1-MCP followed by C2H4 resulted in reduced POD activity and delayed the increase in Chlase activity The results suggest chlorophyll in broccoli can be degraded via the POD – hydrogen peroxide system Exposure to C2H4 enhances activity of Chlase and extends the duration of high POD activity, and these responses may accelerate degreening Treatment with 1-MCP delays yellowing of broccoli, an effect that may be due to the 1-MCP-induced reduction in POD and Chlase activities

1-substituted cyclopropenes: Effective blocking agents for ethylene action in plants

Abstract: A series of 1-alkane substituted cyclopropenes has been prepared and tested as ethylene antagonists using banana fruits as an assay system. 1-Methyl-, 1-ethyl-, 1-propyl-, 1-butyl-, 1-pentyl-, 1-hexyl-, 1-heptyl-, 1-octyl-, 1-nonyl-, and 1-decylcyclopropene were all very active compounds. 1-Methylcyclopropene protected bananas from ethylene with a minimum concentration of 0.7 nl.l−1 after a 24 h exposure. As the carbon chain length was extended the minimum requirement increased some, but starting with 1-butylcyclopropene, the minimum concentration requirement declined and many cyclopropenes were required in lower concentrations than 1-methylcyclopropene. The time of protection at ambient temperature (22–23 °C) was 12 d for 1-methyl-, 1-ethyl-, 1-propyl-, and 1-butylcyclopropene. 1-Pentylcyclopropene protected bananas for 14 d, 1-hexylcyclopropene for 20 d, 1-heptylcyclopropene for 21 d, 1-octylcyclopropene for 25 d, 1-nonylcyclopropene for 35 d, and 1-decylcyclopropene for 36 d.

Effect of low temperature on dormancy breaking and growth after planting in lily bulblets regenerated in vitro

Abstract: Lilies regenerating on scale segments may develop dormancy in vitro depending on the culture conditions. The dormancy is broken by storage for several weeks at a low temperature (5 °C). The effect of the low temperature on sprouting, time of leaf emergence and further bulb growth was studied. Dormant and non-dormant bulblets were regenerated in vitro on bulb scale segments cultured at 20 °C or 15 °C, respectively. The low temperature not only affected the number of sprouted bulblets but also the time of emergence. The longer the cold storage, the faster and more uniform leaf emergence occurred. Both dormant and non-dormant bulblets grew faster after a low temperature treatment of six weeks. Thus, during dormancy breaking the tissue is prepared not only for sprouting but also for subsequent bulb growth. These processes are rather independent as low temperature stimulates growth in non-dormant bulblets whereas these bulblets sprout also without treatment at low temperature. Moreover, the hormone gibberellin induces rapid sprouting but has no influence on further bulb growth. Good growth in bulblets exposed to the low temperature coincided with production of an increased leaf weight. However, the relationship is not absolute as bulblets that were cold-treated for six weeks grew larger than bulblets cold-treated for four weeks but the formation of leaf biomass was similar. During storage at low temperature starch was hydrolyzed in the bulb scales and sugars accumulated. This indicates that during this period, preparation for later bulb growth involves mobilization of carbohydrate reserves which play a role in leaf growth and development of the photosynthetic apparatus. Starch hydrolysis proceeded in the outer scales after planting. Approximately six weeks later, the switch from source to sink took place in the bulblet, which became visible as a deposition of starch in the middle scales.

A regulatory role for proline metabolism in stimulating Arabidopsis thaliana seed germination

Abstract: Analysis of the rate-limiting dehydrogenases of the oxidative pentosephosphate pathway (OPPP), as well as changes in the contributions of14C1- and 14C6-labelled glucose torespired CO2 during germination, indicated activation of the OPPPduring Arabidopsis seed germination An approximatelyfour-fold increase in free proline (Pro) was also observed prior to radicleemergence in most seeds Delayed radicle emergence in transgenicArabidopsis seeds which expressed an antisense copy of thegene encoding the Pro biosynthetic enzymeδ1-pyrroline-5-carboxylate synthetase correlated with anapproximately 35% reduction in the maximal concentration of Pro accumulated bythe antisense lines during germination A dose-dependent inhibition ofArabidopsis seed germination by millimolar concentrationsof Pro capable of feedback inhibition of Pro synthesis reinforced the role ofPro synthesis in promoting germination The ability of the artificial oxidantsmethylene blue and phenazine ethosulphate to overcome the inhibitory effects ofPro suggests a functional link between elevated Pro synthesis and increasedOPPPactivity and the importance of coupling of both pathways in stimulatinggermination

The effects of auxin on lateral root initiation and root gravitropism in a lateral rootless mutant Lrt1 of rice ( Oryza sativa L.)

Abstract: Auxins control growth and development in plants, including lateral rootinitiation and root gravity response. However, how endogenous auxin regulatesthese processes is poorly understood. In this study, the effects of auxins onlateral root initiation and root gravity response in rice were investigatedusing a lateral rootless mutant Lrt1, which fails to formlateral roots and shows a reduced root gravity response. Exogenous applicationof IBA to the Lrt1 mutant restored both lateral rootinitiation and root gravitropism. However, application of IAA, a major form ofnatural auxin, restored only root gravitropic response but not lateral rootinitiation. These results suggest that IBA is more effective than IAA in lateralroot formation and that IBA also plays an important role in root gravitropicresponse in rice. The application of NAA restored lateral root initiation, butdid not completely restore root gravitropism. Root elongation assays ofLrt1 displayed resistance to 2,4-D, NAA, IBA, and IAA.This result suggests that the reduced sensitivity to exogenous auxins may be due tothe altered auxin activity in the root, thereby affecting root morphology inLrt1.

Changes in protein and amino acid contents in two cultivars of rice seedlings with different apparent tolerance to cadmium

Abstract: Changes in protein and amino acid contents in Cd-treated rice (Oryza sativa L.) seedlings of two cultivars were investigated. By assessing the decrease in chlorophyll content in the second leaves as an indicator of Cd toxicity, it was seen that cv. Tainung 67 (TNG 67) seedlings were apparently more tolerant to Cd than cv. Taichung Native 1 (TN 1). Following treatment with CdCl2, protein content decreased with a progressive and substantial increase of protease activity and total amino acids in TN 1, but not in TNG 67. The patterns of individual amino acids in Cd-treated leaves of both cultivars were examined and, only in cv. TN 1 a substantial increase in the content of all amino acids analysed, except for methione, was recorded. The role of these changes in endogenous amino acids in Cd toxicity of TN 1 leaves is discussed.