Dune reed (DR) and swamp reed (SR) are two ecotypes of reed (Phragmites communis Trin.) that displayed differences in stress tolerance. To uncover the molecular basis for such difference, the effects of heat stress were studied using the calli derived from the two ecotypes. Heat stress caused increased ion leakage, inhibited growth, decreased cell viability, and elevated hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents in the calli of both ecotypes, but DR callus showed better heat tolerance than SR callus. In DR callus, heat stress caused significant increase in the endogenous ABA content but not in SR callus. Application of fluridone (an ABA synthesis inhibitor) aggravated the heat stress damages on the DR callus whereas it had only minimal impact on the SR callus. Exogenous application of ABA alleviated the heat stress symptoms in the calli of both ecotypes. ABA treatment increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase, and also decreased H₂O₂ and MDA contents. These results indicate that the ability of ABA synthesis under heat stress is a key factor attributing to the higher heat tolerance of DR than SR.

Primary leaf explants of aseptically grown seedlings of moth bean [Vigna aconitifolia (Jacq.) Marechal] immersed in water or not were treated in microwave oven (2450 MHz, 800 W cm^-2) for 1, 3, 5 and 7 s before culturing. Callusing and shoot emergence from these explants were enhanced up to microwave exposure lasted 5 s while longer treatment of water-immersed explants delayed callusing. One polypeptide (26.6 kD) was up regulated in the callus derived from microwave treatment in water-immersed explants. RAPD analysis detected alteration in DNA sequences due to microwave treatment in water-immersed explants for 7 s. The frequency of mutation was 1.6 % (4 bands out of 248) over all the cultures analyzed and the same was 13 % (4 bands out of 31), if amplicons generated at 7 s treatment alone were considered.

A protocol for somatic embryogenesis in Azadirachta indica A Juss. has been standardized using in vivo leaflets. Experiments were carried out to examine the effect of various auxins, cytokinins, sucrose, inorganic and organic salts on subsequent somatic embryo induction and maturation. Embryogenic calli were induced on Murashige and Skoog (MS) medium supplemented with 1.5 mg dm^-3 kinetin and 1.5 mg dm^-3 indole-3-acetic acid and subsequently all the stages of somatic embryo development (globular, cordate, torpedo and cotyledonary) were observed. Maturation of these embryos was accomplished with the same growth regulators after three subcultures. The histological study of somatic embryos showed resembles to zygotic embryos. The matured somatic embryos were transferred onto half strength MS-medium devoid of growth regulators for their germination (82 %). Plantlets were acclimatized in the field with a survival rate of 80-83.5 %.

Extracellular proteins and glycoproteins secreted by ammonium- or auxin-induced somatic embryogenic cultures of pumpkin were analyzed. Despite an overall similarity in developmental characteristics between these embryogenic cultures, distinct expression patterns of extracellular proteins and glycoproteins were observed. Ammonium, when supplied as the sole source of nitrogen, caused acidification of the culture medium and significantly reduced protein secretion. Buffering pH in the ammonium-containing medium restored extracellular protein secretion and glycosylation and an enhanced cell aggregation but not the development of later embryo stages. As revealed by Concavalin A (Con A) immunodetection, extracellular glycoproteins containing α-D-mannose and α-D-glucose were most abundant in proembryogenic cultures grown in a buffered ammonium-containing medium and in a medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D). We assume that extracellular proteins (Mr 28, 31, and 44 kDa) and Con Abinding glycoproteins (Mr 26, 30, 40, 53, and 100 kDa) found in both proembryogenic cultures may have a role during somatic embryogenesis induction. The glycan components of proteins were further characterized by affinity blotting with different lectins. Binding patterns of mannose-specific lectin from Galanthus nivalis partially correlated with those detected with Con A, whereas no signal was observed with lectins from Datura stramonium and Arachis hypogea regardless of the treatment applied. Results indicate that complex N- or O-glycans are not typical for early phases of pumpkin embryo development. The accumulation of extracellular glycoproteins with high-mannose-type glycans from 30 to 34 kDa, observed after the transfer from the ammonium- or 2,4-D-containing media into a maturation medium, appeared to be associated with development of later embryo stages. This study also revealed the presence of EP-3-like endochitinases in pumpkin embryogenic cultures, particularly in cultures grown in the buffered ammonium-containing medium, however, these proteins should be examined further.

We have earlier reported that the endophyte infection can enhance photosynthetic capacity and antioxidant enzyme activities in rice exposed to salinity stress. Now, the changes in primary photochemistry of photosystem (PS) II induced by Na₂CO₃ stress in endophyte-infected (E+) and endophyte-uninfected (E-) rice seedlings were studied using chlorophyll a fluorescence (OJIP-test). Performance indices (PI_ABS and PI_Total) of E- and E+ rice seedlings revealed the inhibitory effects of Na₂CO₃ on PS II connectivity (occurrence of an L-band), oxygen evolving complex (occurrence of a K-band), and on the J step of the induction curves, associated with an inhibition of electron transport from plastoquinone A (Q_A) to plastoquinone B (Q_B). In E+ seedlings, Na₂CO₃ effects on L and K bands were much smaller, or even negligible, and also there was no pronounced effect on the J step. Furthermore, the OJIP parameters indicated that 20 mM Na₂CO₃ had a greater influence on the photosystem (PS) II electron transport chain than did the 10 mM Na₂CO₃, and that changes were greater in E- than in E+. Endophyte infection was therefore deemed to enhance the photosynthetic mechanism of Oryza sativa exposed to salinity stress.

Exposure to low temperatures is one of the most important factors that generate abiotic stress in plants, and the rapid accumulation of soluble sugars belongs to significant metabolic responses to cold stress. The accumulation of soluble sugars may be at least partially triggered by an increased rate of starch degradation. The analysis of transcript profiles and starch degrading enzyme activities in leaves of two potato cultivars was performed during a 12-h exposure to 2 °C. An induction of β-amylase expression and activity as well as an accumulation of reducing sugars were observed in cv. Desiree. No accumulation of reducing sugars and no significant changes in the β-amylase activity were initially observed in cv. Russet Burbank. Surprisingly, an increased α-amylase activity was observed in the last hours of the experiment, which was accompanied by an increased amount of reducing sugars. The results indicate that the leaves of Desiree and Russet Burbank potatoes growing under cold stress may degrade starch via different pathways.

Hypocotyls of cotton (Gossypium hirsutum L.) cultivars cv. YZ-1, Coker 312 and Coker 201 were inoculated on Murashige and Skoog callus induction medium. YZ-1 exhibited a very high regeneration potential, with 81.9 % of the explants inoculated differentiated into embryogenic callus within 8-10 weeks. During the process of callus maintenance (subculture for 1 to 3 years), the total embryos number in Coker 312 and Coker 201 calli dropped sharply, and the percentage of embryo germination decreased. On the contrary, the callus of YZ-1 consistently maintains a high frequency of plant regeneration after long-time subculture. Transgenic kanamycin-resistant calli of Coker 201 partially lost the ability of somatic embryogenesis and plant regeneration. The stress produced by the transformation procedure slightly affected somatic embryogenesis and plant regeneration of YZ-1, which showed minimum loss of plant regeneration ability.

A highly efficient protocol for plant regeneration from cotyledonary node of two chickpea (Cicer arietinum L.) cultivars ICCV-10 and Annigeri used phenylacetic acid (PAA). The Murashige and Skoog (MS) medium supplemented with 2.0 mg dm^-3 6-benzylaminopurine (BAP) and 1.0 mg dm^-3 PAA was used for induction of bud formation. Buds were elongated on MS medium supplemented either with only 0.75 mg dm^-3 gibberellic acid (GA₃) or 0.2 mg dm^-3 GA₃ + 0.6 mg dm^-3 PAA. The elongated shoots were then transferred onto rooting medium containing 1 mg dm^-3 PAA. The frequency of multiple shoot induction and rooting was higher in Annigeri as compared to ICCV-10. The complete plantlets with well-developed roots were transferred to pots containing sterilized soil and sand in the ratio 3:1 where they survived (74 %) and set normal seeds.

Oxidative stress plays an important role in plant ageing and in response to different stresses. Oxidative DNA damage, unless repaired, may have detrimental consequences and increase genetic instability. Therefore, we determined the role of heat-shock induced oxidative stress on induction and repair of DNA damage in relation to oxidative stress tolerance in senescent tobacco plants. One-month-old (young) and three-month-old (senescent) plants were exposed to 42 °C for 2 and 4 h and left to recover at 26 °C for 24 and 72 h. The progression of senescence was characterized by the lower soluble protein and malondialdehyde content compared to young plants. Immediately after the heat shock, an increase in lipid peroxidation and guaiacol peroxidase activity, as well as DNA damage measured by the Comet assay were induced to higher extent in the young plants than in the senescent ones compared to their respective controls. Moreover, after 24-h recovery, the DNA damage further increased in the young plants whereas tendency of DNA repair was observed in the senescent plants. Upon 72-h recovery, no significant differences were noticed in all parameters studied (regardless of plant age) compared to the controls. The random amplified polymorphic DNA (RAPD) analysis confirmed genetic stability of the tobacco plants during the heat-shock exposures as well as the subsequent recovery periods.

In vitro regeneration of Trifolium glomeratum, a leguminous forage species, was attempted through leaf, petiole, cotyledon, hypocotyl, collar and root explants and two media combinations. Root and collar explants showed no callus induction. Medium with 0.05 mg dm^-3 α-naphthaleneacetic acid (NAA) and 0.10 mg dm^-3 N⁶-benzyladenine (BA) was more effective for hypocotyl explant whereas cotyledon and petiole explant were more responsive to 5.0 mg dm^-3 NAA and 1.0 mg dm^-3 BA. Friable, green calli obtained from petiole explant on this medium showed organogenetic potential. Modified root-inducing medium having 0.21 mg dm^-3 indole-3-acetic acid and 2.5 % sucrose was successful for root induction and plantlets were successfully transferred to field after hardening and Rhizobium inoculation.

In vitro induction of haustoria from Castilleja tenuiflora Benth. was achieved by applying 25 μM catechin, 25 μM vanillin, or 25 μM H₂O₂. Of the treatments tested, 25 μM vanillin was the strongest inducer of haustoria in C. tenuiflora roots in vitro (up to 3 haustoria per root). Haustorium development occurred laterally and was observable 14 d after inducer application. It was characterized by elongation of the epidermal cells and division of the inner cortical cells which also possessed abundant nuclei. Histochemical analysis using 3,3-diaminobenzidine (DAB) and diphenylboric acid 2-aminoethyl ester (DBPA) indicated that the formation of haustoria was associated with the accumulation of H₂O₂ and flavonoids.

We have developed three protocols for the rapid micropropagation of Ruscus aculeatus. The primary explants utilised were immature embryos, aerial buds excised from rhizomes and shoot buds regenerated from organogenic calli. In order to increase the plant regeneration from the primary explants, we used organogenic calli from cladode, stem and rhizome segments. We tested more than 20 culture media for callus induction and shoot regeneration and the best results were obtained when rhizome segments were cultured on Murashige and Skoog medium supplemented with 0.5 mg dm^-3 2,4-dichlorophenoxyacetic acid and 1 mg dm^-3 kinetin.

Transgenic Podophyllum peltatum plants were successfully produced by Agrobacterium tumefaciens-mediated transformation. Embryogenic callus was co-cultivated with Agrobacterium tumefaciens harboring a binary vector pBI 121 carrying β-glucuronidase (GUS) and neomycinphosphotransferase (NPT II) gene. GUS-histochemical analysis revealed that, 50 µM acetosyringone treatments during Agrobacterium infection and 3 d co-cultivation with Agrobacterium showed enhanced transformation efficiency. Percentage of GUS positive callus increased rapidly as the subculture time proceeded on selection medium containing 100 mg dm^-3 kanamycin. Kanamycin resistant somatic embryos were formed from embryogenic callus after cultivation with 11.35 µM abscisic acid (ABA) for 3 weeks and then on hormone-free selection medium. Somatic embryos were germinated and converted into plantlets on medium containing 2.89 µM gibberellic acid (GA₃). The integration of GUS and NPT II gene into transgenic plants was confirmed by polymerase chain reaction and Southern analysis.

An efficient regeneration system for Phaseolus vulgaris was developed from mature seeds germinated on Murashige and Skoog (MS) medium supplemented with thidiazuron or N⁶-benzylaminopurine (BA) for 6 d. Using cotyledonary nodes, multiple buds were induced on the MS medium supplemented with 5.0 mg dm^-3 BA with the induction frequency 71.9 % after 4-week culture. The buds were then transferred onto shoot formation medium containing 1.0 mg dm^-3 BA, 0.1 mg dm^-3 gibberellic acid and 2.0 mg dm^-3 silver nitrate. The addition of AgNO₃ enhanced the frequency of the shoot formation from 61.3 to 87.6 %. Root induction medium was half-strength MS medium with 0.75 mg dm^-3 indolebutyric acid and 0.02 mg dm^-3 BA. The average root frequency was 84.3 %. The regenerated plantlets with healthy roots grew successfully when transferred to soil. Using this system we obtained over 10 regenerated plantlets from one explant.

High frequency of shoot formation was achieved from Solanum nigrum L. leaves on Murashige and Skoog (MS) medium without any callusing stage. Shoot forming ability was more pronounced on leaves positioned dorsally. For shoot induction, 2.0 mg dm^-3 benzylaminopurine and 1.5 mg dm^-3 kinetin were observed to be the most effective plant growth regulators (PGRs). The present paper also describes first successful induction of in vitro flowering in S. nigrum. The leaf derived shoots were excised and treated with various root promoting PGRs and 0.25 mg dm^-3 indole-3-butyric acid produced maximum number of roots (15.2 per plant). Plants were later transplanted in field with 100 % survival. Solasodine content was higher in in vitro raised shoots and leaf derived callus, compared to ex vitro grown shoots.

Understanding the molecular basis of polarity induction in plant cells is a research aspect that extends from signal perception and transduction to morphogenesis. A gradient of cytoplasmic ion fluxes generated through ion channels plays a crucial role in subsequent events leading to polar growth. Convincing evidence is now available implicating temporal and spatial distribution of Ca²⁺ in cytoplasm, generated by localized activity of calcium channels, as the early biochemical events associated with polarity induction. Ion channel antagonists are common tools for studying ion channel structure and function. Coupled with a fluorescent dyes, calcium channel antagonists (phenylalkylamine and dihydropyridine), have been used to localize L-type calcium channels. Additionally, the advent of Confocal Laser Scanning Microscopy has made possible the visualization of Ca²⁺ channels in plant cells. Persisting problems of dye loading and their cellular compartmentation have been addressed by developing a variety of experimental protocols. Present article highlights the current state of our understanding of these concepts, methodologies and their applications in different aspects of plant development.

Cymbidium shoot buds grown under Mg²⁺ deficiency without naphthalene acetic acid (NAA) showed knotted appearance. Ultrastructure of the cortical cells showed a progressive disorganization and disintegration of chloroplast membranes. The growth of shoots was resumed with the addition of 10 μM NAA. Specific NO scavenger, cPTIO induced deformation in shoot growth in 80 % of cultures. In longitudinal sections of shoots treated with cPTIO, depositions of densely stained particles in cells were observed. These inhibitory responses of cPTIO were ameliorated by 10 μM NAA. The NO donor, sodium nitroprusside (SNP), treated shoot buds displayed rapid senescence followed by necrosis of leaves. Ultrastructure of cortical cells at this stage revealed the endocytosis of mitochondria along with membrane bound cytoplasmic inclusions in the vacuole. A sharp increase in H₂O₂ generation was observed with a little change in the activity of antioxidant glutathione disulfide (GSSG), suggesting NO mediated oxidative stress. Surprisingly, after 4 weeks these necrotic shoots were converted into a globular, embryo like shoot tip with numerous structures termed here as 'neomorph' in its base. Neomorphs were different from protocorm like bodies both anatomically and morphologically. Ultrastructure of the rhizome tip exhibited numerous amyloplast and round mitochondria. At this stage, the generation of high rate of H₂O₂ was masked by GSSG, and the generation of GSSG was proportional with the concentrations of SNP, and not observed in the control (without SNP). The neomorphs were further sub-cultured to medium with different concentrations of SNP or cPTIO. After 4 weeks of culture, only the neomorphs sub-cultured on medium with SNP developed into shoots and approximately ten shoots were observed to emerge from the axils of each rhizome. Ultrastructure of cells of regenerating green neomorphs showed different shapes of mitochondria and chloroplasts and presence of active dictyosomes. The obtained shoots subjected to the acclimatization in polyhouse, expressed good growth with 85 % survival. Therefore it is reasonable to suggest that the process of de-differentiation and re-differentiation leading to rhizome formation under the condition of Mg²⁺ deficiency is NO mediated.

Leaf explants of Jatropha curcas cultured on Murashige and Skoog's (MS) medium supplemented with thidiazuron (TDZ; 0.90 μM) in combination with indole-3-butyric acid (IBA; 0.98μM) produced adventitious shoot buds directly on the surface of the explants without formation of intervening callus while shoot bud formation was accompanied with callus formation on medium supplemented with 6-benzylaminopurine (BAP; 13.3 μM) and IBA (2.46 μM). TDZ treatment resulted in more than twice higher rate of shoot bud induction than BAP. Shoot buds were multiplied and elongated following repeated transfers to medium containing BAP (2.22 μM) and gibberellic acid (GA₃; 1.44 μM). The effect of copper sulphate on differentiation of shoot buds from leaf segments was also investigated. Both shoot induction and multiplication media were supplemented with different levels of CuSO₄ (0-5 μM). Significant improvement in shoot bud induction was observed when the concentration of CuSO₄ was increased to 10 times the normal MS level. Healthy elongated shoots were rooted on half strength MS medium supplemented with IBA (2.46 μM). Rooted plantlets were transferred to field and survived. Histological analysis revealed direct formation of shoot buds from leaf explants.

Plant regeneration through indirect somatic embryogenesis was attempted from leaf, internode, node and shoot-tip derived callus of Leptadenia reticulata. Somatic embryos at the highest frequency was induced on Murashige and Skoog (MS) medium supplemented with 8.87 μM benzyladenine (BA) and 2.46 μM indole-3-butyric acid (IBA). From different explants, only shoot-tip and node explant derived calli induced somatic embryos. Transfer of the embryogenic callus to suspension cultures of the same concentration of growth regulators facilitated the development of embryos. Suspension cultures with reduced concentration of BA (2.22 μM) either alone or in combination with 0.49 μM IBA fostered maturation of embryos. Half-strength MS solid medium with 1.44 μM GA₃ and BA (0.22 or 0.44 μM) facilitated conversion of embryos into plantlets at higher rate compared to that on with BA alone. About 77 plantlets were recovered from 10 mg callus. Plantlets transferred to small cups and subsequently to field survived in 80 %. All the plantlets established in the field exhibited morphological characters similar to that of the mother plant.

The changes in the activities of antioxidant enzymes and amounts of proteins, phenols, and flavonoids in regenerating and non-regenerating calli during organogenesis of Sterculia urens were monitored. Maximum growth of calli and the most efficient regeneration of shoots occurred on Murashige and Skoog (MS) medium supplemented with 0.5 mg dm^-3 benzylaminopurine (BAP) + 2 or 4 mg dm^-3 naphtalene acetic acid (NAA). Peroxidase (POD), catalase, and superoxide dismutase activities increased in the regenerating calli but decreased in the non-regenerating calli. Six POD isoenzymes were detected. Protein content decreased in the non-regenerating calli and increased significantly during regeneration of shoots from callus. Total phenols and flavonoids increased in the non regenerating calli. SDS-PAGE analysis revealed a role of many proteins in organogenesis.

Gynogenesis of Chinese long cucumber (Cucumis sativus L.) was obtained from unpollinated ovules cultured on cucumber basal medium (CBM) supplemented with thidiazuron (TDZ) and in some experiments AgNO₃. High induction frequencies (7.85-12.14 %) were induced from unpollinated ovules at the time of anthesis at 0.03-0.07 mg dm^-3 TDZ. Histological analysis indicated that embryo sacs developed completely at the time of anthesis. Further, the highest plant regeneration rate was achieved at CBM supplemented with 0.05 mg dm^-3 a-naphthaleneacetic acid, 0.2 mg dm^-3 6-benzyladenine and 5-10 mg dm^-3 AgNO₃. Flow cytometry analysis showed that 80 % of the regenerated plants were haploid. Histological micrographs and ploidy level analyses clearly revealed initiation, development, and germination of embryos from the unpollinated ovules.

In Phalaenopsis, lowering irradiance has been used to delay flower stalk development but the accompanying biochemical changes remain poorly understood. We cultured two commercial Phalaenopsis-type orchids, Phalaenopsis cv. Sogo Yukidian V3, and Doritaneopsis cv. Walnut Valley Halo ES09 under reduced irradiance by under-bench shading (approximately 15 % of mean control irradiance) for 15 weeks in a greenhouse under the natural photoperiod. Besides delaying flower stalk development as expected, the treatment greatly decreased the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase, and NAD⁺-malic enzyme, and reduced the nocturnal malate accumulation and daytime starch deposition, the typical diurnal metabolite fluctuations of crassulacean acid metabolism (CAM) plants. As well, the content of sucrose and starch was reduced at dawn and dusk whereas the content of glucose and fructose only at dawn. The persistent decrease in the sucrose content under shading may be an inhibitory signal of flower stalk induction.

This paper describes the effect of NaCl on the respiration of Citrus cell suspensions namely on the induction of the alternative oxidase. The exposure of two Citrus (cvs. Carvalhal tangor and Valencia late) cell suspensions to 200 or 400 mM NaCl lead to a reduction on cell respiration rates. Under these conditions, the respiration rate decreased less in the presence of KCN indicating a stimulation of the capacity of the alternative oxidase (AOX). In addition, immunoblots showed an increase on the amount of AOX protein. Antibodies raised against the Sauromatum guttatum enzyme recognized the reduced form of the enzyme near the 35 kDa band. The protein accumulation was correlated with the significantly higher AOX capacity observed for cv. Carvalhal tangor.

The effects of plant growth regulators (PRGs) on the induction of flowering and sex expression in micropropagated cucumbers are presented. The highest number of male flowers (6.0 ± 0.7 per plant) was produced by cv. Kmicic F1 on the Murashige and Skoog (MS) medium supplemented with 4.0 μM kinetin. The highest number of female flowers (3.1 ± 0.3) was also observed in cv. Kmicic F1 on either control (PRG-free) medium or medium supplemented with 6.4 μM indole-3-acetic acid (IAA). The MS medium supplemented with 4.4 μM benzyladenine inhibited flower formation. The highest percentage of flowering plantlets (67.5 ± 7.5) was observed on the control MS medium after 16 weeks of culture. Female-to-male flower ratio was influenced by the culture media and changed during cultivation. The highest pollen viability (60-70 %) was observed in anthers of plants cultured on the control medium and the medium with IAA.

In vitro morphogenetic ability of plant cells has been demonstrated in diverse species of angiosperms and gymnosperms but no such report is available in the genus Selaginella till date. We have established an in vitro morphogenic root culture where indole butyric acid (IBA) induced profuse branched and unbranched roots in Selaginella microphylla. We observed inter-convertibility of root apical meristem (RAM) to shoot apical meristem (SAM) in presence of IBA and showed that intact roots are also capable of transformation. Friable callus was obtained from roots on prolonged (∼50 weeks) root cultures. By isolating total RNA from each of the developmental stages, we performed cDNA synthesis followed by random amplification, sequencing, and BLAST analysis of differentially expressed transcripts to correlate morphological events with the changes on molecular level. The results revealed sequence matches to genes involved in diverse cellular processes such as transcription, translation, photosynthesis, replication, secondary metabolism, stress response, and plant defense suggesting ancient origins of such proteins and the evolutionary conservation of biological function.

An efficient, rapid, and reproducible plant regeneration protocol was successfully developed for Abrus precatorius L. using mature nodal explants excised from a 5-year-old field grown plant. The highest shoot regeneration frequency (87 %) with maximum number of multiple shoots (15.0) and shoot length (4.8 cm) were recorded on Murashige and Skoog (MS) medium amended with 2.5 μM thidiazuron, 120 mg dm^-3 polyvinylpyrrolidone, and 0.5 μM α-naphthalene acetic acid. The best treatment for maximum root (4.0) induction was half strength MS medium supplemented with 1.5 μM indole-3-butyric acid. The in vitro plantlets with well-developed shoots and roots were successfully transferred into plastic cups with Soilrite and acclimatized in a culture room under photon flux density (PFD) of 150 μmol m^-2 s^-1, thereafter transferred to a greenhouse with PFD of 300 μmol m^-2 s^-1, and finally to a field with 70 % survival rate. During the acclimatization period (0-49 d), leaf chlorophyll and carotenoid content increased whereas malondialdehyde and H₂O₂ content decreased probably due to increasing activities of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, and ascorbate peroxidase). Our work suggests that micropropagated plants developed an antioxidant enzymatic protective system to avoid oxidative stress during establishment under ex vitro environment.

The induction of pathogenesis-related (PR) proteins in sugarcane (Saccharum officinarum L.) leaves and suspension-cultured cells in response to treatment with a glycoprotein elicitor isolated from Colletotrichum falcatum (the red rot pathogen) was investigated. Treatment of leaves and cells with the elicitor resulted in a much marked increase in the activities of chitinase and β-1,3-glucanase in red rot resistant (BO 91) than susceptible (CoC 671) sugarcane cultivar. SDS-PAGE analysis revealed that C. falcatum elicitor induced the accumulation of several proteins in suspension-cultured cells of resistant cultivar (BO 91); among them the 35 kDa protein was predominant. Whereas, a 27 kDa protein was induced predominantly in the cells of susceptible cultivar upon treatment with the elicitor. When sugarcane leaves were treated with C. falcatum elicitor, two proteins with apparent molecular masses of 25 and 27 kDa were induced both in the resistant and susceptible cultivars. However, the induction was stronger in the resistant than the susceptible cultivar. Immunoblot analysis for chitinase indicated that a protein with an apparent molecular mass of 37 kDa cross-reacting with barley chitinase antiserum was strongly induced in the suspension cultured cells of both the cultivars. The induction of 37 kDa chitinase was more in the cells of resistant cultivar than in the susceptible cultivar. Western blot analysis revealed that a 25 kDa thaumatin-like protein (TLP) cross-reacting with bean TLP antiserum was strongly induced in leaves and cultured cells of both resistant and susceptible cultivars due to elicitor treatment.

Somatic embryogenesis (SE) in Arabidopsis was induced using various systems, including auxin treatment of in vitro cultured explants (immature zygotic embryos, IZEs) and transgenic plants overexpressing embryogenesis-related transcription factors, e.g. LEC2 together with the GUS reporter gene under control of the auxin-induced DR5 promoter. The study indicated that the SE-systems used gave different embryogenic capacities for the production of true embryos. The highest ratio of true embryos (75 %) was found among embryo-like structures in transgenic seedlings overexpressing LEC2. Analysis of in vitro induced SE systems indicated that in somatic embryos produced in response to exogenous auxin treatment the formation of root poles is frequently disturbed. A lack of a properly formed root meristem was observed in 35-80 % of in vitro induced somatic embryos, in dependence on auxin concentration and duration of treatment.

The influence of freezing treatment on plasma membrane (PM) H⁺-ATPase was investigated using plasma membrane vesicles isolated from calluses from Chorispora bungeana Fisch. & C.A. Mey. by the discontinuous sucrose gradient centrifugation. Freezing treatment (-4 °C) for 5 d resulted in significant increases in the ATPase activity and the activity of p-nitrophenyl phosphate (PNPP) hydrolysis, decreases in the K_m for ATP hydrolysis and PNPP hydrolysis, and the shift of optimal pH from 6.5 to 7.0. Also, the activity PNPP hydrolysis was less sensitive to vanadate after freezing treatment compared to control, while the inhibition of ATP hydrolysis by hydroxylamine was more sensitive. In addition, freezing treatment also decreased the activation effects of trypsin on PNPP hydrolysis, but increased the activation effects of lysophosphatidylcholine on ATP hydrolysis. Taken together, these results suggested that PM H⁺-ATPase might play an important role during adaptation to freezing and enhancing the frost hardness in C. bungeana.

We explored the interaction between radiation of different wavelength and jasmonic acid (JA) or brassinosteroids (BR) on leaf senescence-induced oxidative stress. Three approaches were used: 1) jasmonic acid insensitive1-1 (jai1-1) and brassinosteroid-deficient [dumpy (dpy)] mutants were treated with red (R) or far-red (FR) radiation; 2) phytochromedeficient aurea (au) and high pigment-1 (hp-1) (radiation exaggerated response) mutants were treated with methyl jasmonate (MeJA) or epibrassinolide (epiBL); and 3) double mutants au jai1-1 and au dpy were produced. Leaf chlorophyll content, lipid peroxidation, and antioxidant enzyme activities were determined. After senescence induction in detached leaves, we verified that the patterns of chlorophyll degradation of hormonal and photomorphogenic mutants were not significantly different in comparison with original cv. Micro-Tom (MT). Moreover, there was no significant change in lipid peroxidation measured as malondialdehyde (MDA) production, as well as catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities in the hormonal mutants. Exogenous BR increased CAT and APX activities in MT, au, and hp-1. As concerns the double mutants, severe reduction in H₂O₂ production which was not accompanied by changes in MDA content, and CAT and APX activities was observed during senescence in au dpy. The results suggest that JA and BR do not participate in light signaling pathway during leaf senescence-induced oxidative stress.