Comparison of isoperoxide patterns in tobacco cell culture and in the intact plant

Analysis by ion-exchange chromatography of the enzymes from cultured tobacco cells and root or leaf tissues of the tobacco plant revealed that the cultured cells contain exclusively cationic peroxidases and the leaf tissues mainly anionic and neutral peroxidases.     

2,4-D和激动素对烟草愈伤组织IAA氧化酶和细胞分裂素氧化酶活性的影响

2,4-D和激动素(KT)均显著降低烟草愈伤组织中IAA氧化酶和细胞分裂素氧化酶的活性,KT的影响更显著.在MS中的愈伤组织IAA氧化酶活性最高,MS 2,4-D中的次之,MS KT和MS 2,4-D KT中的最低.愈伤组织在MS中继代6 d时,细胞分裂素氧化酶活性出现明显的高峰,在其它3种培养基中则没有.     

Significance of caffeic acid-O-methyltransferase in lignification of cultured tobacco cells

Caffeic acid-O-methyltransferase, activity was assayed in the callus and suspension cultured cells of tobacco. Lignification of cells was observed only in a kinetin (10^?5 M) culture and not in an auxin (10^?6 M 2,4-D or 10^?5 M IBA) culture. Enzyme activity in the kinetin cultured cells was much higher than in the stock culture and the rise in enzyme activity coincided with the onset of lignification.     

Isolation and characterization of two isoperoxidases from tobacco tissue cultures

Two isoperoxidases (A_f and C_n) from the medium of tobacco tissue suspension culture WR-132 grown in darkness have been purified to apparent homogeneity and partially characterized. C_n and A_f have MWs of ca 30 000 and 54 000, respectively. A_f has ca 5.1% carbohydrate, but none could be detected in C_n. Both isoperoxidases appear to follow simple Michaelis-Menten kinetics with respect to guaiacol as the substrate. The K_ms for guaiacol are 4 and 13.3 mM for Af and C_n, respectively, while both isoperoxidases have a pH optimum at 6.5. C_n, is dissimilar to other isoperoxidases from tobacco tissue cultures, but A_f is very similar to isoperoxidase A₃ from W-38 tobacco tissue culture.     

Isoenzymes of glucose-6-phosphate dehydrogenase from tobacco cells

Two anodic isoenzymes of glucose-6-phosphate dehydrogenase (G6PDH) were isolated from tobacco suspension culture WR-132, utilizing fractional ammonium sulfate precipitation and DEAE-cellulose chromatography. The pH optimum was 9.0 for isoenzyme G6PDH I and 8.0–8.3 for G6PDH IV. Isoenzyme G6PDH I exhibited Michaelis-Menten kinetics for both substrates, G6P and NADP⁺, with K_m's of 0.22 mM and 0.06 mM, respectively. G6PDH IV exhibited Michaelis-Menten kinetics for G6P with a K_m of 0.31 mM. The NADP⁺ double reciprocal plot showed an abrupt transition between two linear sections. This transition corresponds to an abrupt increase in the apparent K_m and V_max values with increasing NADP⁺, denoting negative cooperativity. The two K_m's for high and low NADP⁺ concentrations were 0.06 mM and 0.015 mM, respectively. MWs of the isoenzymes as determined by SDS disc gel electrophoresis were 85 000–91 000 for G6PDH I and 54 000–59 000 for G6PDH IV. Gel filtration chromatography on Sephadex G-150 showed MW's of 91 000 for G6PDH I and 115 000 for G6PDH IV. A probable dimeric structure for IV is suggested, with two NADP⁺ binding sites.     

Comparison of tryptic peptide maps of eight isoperoxidases from tobacco tissue cultures

Eight isoperoxidases from tobacco suspension culture WR-132 (termed C_n, C₃, C₄, A_c, and A_f) and tobacco callus culture W-38 (termed A₁, A₂, and A₃) have been subjected to trypsin digestion followed by peptide mapping. The peptide maps of isoperoxidases A_f and A₃ are identical. All other isoperoxidases do not appear to be dramatically dissimilar in certain portions of their sequence, since many matching peptides have been found when various isoperoxidases are cross-compared. However, only two, and possibly three, highly homologous peptides are present in all of the isoperoxidases.     

Scopoletin: A substrate for an isoperoxidase from Nicotiana tabacum tissue culture W-38

Scopoletin was found to be a substrate for a single anodic isoperoxidase isolated from tobacco callus tissue W-38. Isolation of this peroxidase was accomplished using DEAE-cellulose chromatography. This isoperoxidase catalysed the destruction of scopoletin in the presence of H₂O₂ only. An enzyme assay for the scopoletin reaction was developed. The pH optimum of the enzyme was 5·5 and the apparent K_ms for scopoletin and H₂O₂ were 0·6 and 0·9 rnM respectively.     

营养胁迫诱导的油菜子叶衰老过程中IAA氧化酶和细胞分裂素氧化酶活性的变化

以离体油菜子叶为材料,研究了营养胁迫诱导的子叶衰老过程中吲哚乙酸氧化酶(IAA氧化酶)和细胞分裂素氧化酶活性的变化。在光照条件下,离体子叶在不含任何无机元素的0．8％的琼脂中培养9d后,出现明显的衰老迹象(叶绿素含量下降,丙二醛含量上升),15d时完全死亡。在营养胁迫诱导的衰老过程中,IAA氧化酶和细胞分裂素氧化酶的活性表现出相似的变化趋势,在诱导处理1d时,两种酶的活性均比处理前有明显下降,之后又随着衰老进程逐渐上升。IAA氧化酶活性在诱导处理11d时达到高峰,超出处理前30％以上;比对照高出1倍以上;而细胞分裂素氧化酶活性在诱导处理13d时达到高峰,比对照高出3倍以上,也超过了处理前的水平。衰老过程中IAA氢化酶和细朐分裂素氧化酶活性的上升可能是导致内源激素含量下降的重要原因。     

Enzymes of starch metabolism in Nicotiana tabacum callus

Activities of enzymes of starch metabolism were determined in tobacco callus grown in light or darkness and in the presence or absence of gibberellic acid. There was a higher rate of starch turnover in light-grown cultures, as judged by the activities of synthetic and degradative enzymes. Gibberellic acid-treated tissues contained a lower level of starch than the corresponding control tissue. This decrease could be correlated with the activity of phosphorylase. Cultured tissue and seedling material were found to have comparable levels of activity for the starch metabolizing enzymes.     

Persistence of differences between peroxidase isoenzymes of flax genotrophs in tissue culture

Anionic peroxidase isoenzymes from seedling root, hypocotyl and cotyledon regions of the large (L) and small (S) flax genotrophs were separated on acrylamide gels. Tissue cultures were initiated from each of these regions of the seedlings, and maintained for a 200-day period with six transfers. The differences in electrophoretic mobility of the peroxidase isoenzymes between L and S noted in seedlings, and also in main stems of adult plants, were still present in the tissue cultures.     

Comparison of tryptic peptide maps of two isoenzymes of 6-phosphogluconate dehydrogenase from tobacco tissue cultures

In a previous study by the authors, two isoenzymes of 6-phosphogluconate dehydrogenase were isolated from cultures of tobacco tissue Nicotiana tabacum W-38 and shown to be similar in their pH optima and MWs and in their affinities toward 6-phosphogluconate or NADP⁺. In an attempt to clarify the structural relationships between these two isoenzymes, peptide mapping of trypsin digests of the purified isoenzymes was performed. The maps were found to be similar, with at least 29 peptide groups from the trypsin digestion of each isoenzyme being alike. There were, however, definite minor differences in the peptide maps of the two isoenzymes.     

水分胁迫对棉花叶片中IAA从含量、IAA氧化酶和过氧化物酶活性的影响

整株干旱降低盐棉46号叶片中的IAA总量,叶龄愈小下降愈多。幼叶中IAA总量的下降主要是结合态IAA减少的结果。气干和-1.7MPa PEG溶液渗透胁迫处理也降低离体成熟叶片的IAA总量,其变化与叶片含水量呈直线相关(r=0.905)。整株干旱处理提高各叶片的过氧化物酶活性,叶龄愈小提高愈多,但IAA氧化酶活性无显著变化。离体和整株干旱时IAA总量的下降,可能是过氧化物酶活性增加所致。     

Effect of phenolic compounds on glucose-6-phosphate dehydrogenase isoenzymes

Effector studies with two isoenzymes (I and IV) of glucose-6-phosphate dehydrogenase (G6PDH) from tobacco suspension culture WR-132 revealed that chlorogenic acid, at 0.4 mM, inhibited both isoenzymes almost 100%, with the inhibition decreasing as the concentration of the acid was reduced. At 0.3 and 0.4 mM, the coumarin glucosides scopolin and esculin were inhibitory, whereas their aglucones scopoletin and esculetin were less inhibitory, and at low concentrations of glucose-6-phosphate (G6P), the latter two were actually stimulatory for G6PDH I. Of the possible effectors studied, only scopoletin and esculetin exhibited a significant activation of G6PDH I under these conditions. However, with G6PDH IV these two effectors do not show the same marked activation at the low G6P concentrations. The phenolic acids, caffeic and ferulic, were less inhibitory than the coumarins tested. The activation of G6PDH I by scopoletin, a compound which accumulates in tobacco under certain stress conditions, gives a possible clue as to the resulting enhanced activity of the hexose monophosphate pathway that has been reported for some plants subjected to stress conditions.     

Effect of N,N-diallyl-2,2-dichloroacetamide (R-25788) on efflux and synthesis of glutathione in tobacco suspension cultures

The low level of glutathione synthesis observed in tobacco suspension cultures grown under heterotrophic conditions was stimulated by the addition of t     

The effect of flow turbulence on plant growth and several growth regulators in Egeria densa Planchon

The effects of turbulence velocity on Egeria densa Planchon was studied for 12 weeks using mechanically oscillating grid-generated turbulence without mean flow. The root-mean-square of the turbulence velocity fluctuations (u′) ranged from 1.62 ± 0.44 to 2.86 ± 0.8 cm s⁻¹ (high turbulence), 1.36 ± 0.2 to 1.86 ± 0.78 cm s⁻¹ (medium turbulence) and 0.67 ± 0.12 to 0.81 ± 0.16 cm s⁻¹ (low turbulence). The control was subjected to gentle manual mixing once a day. Shoot elongation was significantly reduced with increasing turbulence intensity, and the endogenous indole acetic acid (IAA) concentration was significantly decreased with increasing turbulence intensity and exposure time. The plants exposed to high turbulence showed a 64.6% decrease in endogenous IAA concentration compared to the control, while it was decreased only 26.9% in plants exposed to low turbulence. IAA and cytokinin catabolism was increased, and there was an increase in the hydrogen peroxide concentration of the tissues, which triggered peroxidase activity. The total chlorophyll and chlorophyll a content decreased with the time of exposure. Although the flow turbulence negatively affected plant growth and metabolism, all of the plants survived for the experimental period.     

Glutathione in conditioned media of tobacco suspension cultures

Conditioned media of suspension cultures of Nicotiana tabacum var. Samsun contain 0.15-0.20 mmol/l glutathione. These concentrations correspond closely to the intracellular content of glutathione and represent about three to four times the amount of glutathione needed to maintain the intracellular level of glutathione. In contrast to the GSH:GSSG ratio inside the cells, the amount of GSSG in the media rises to 20% of the GSH content.