Differential effects of benzyladenine and potassium on DNA, RNA, protein and chlorophyll contents and on expansion growth of detached cucumber cotyledons in the dark and light

Benzyladenine (BA) and KCl were applied to detached cucumber ( Cucumis sativus L. cv. Ohio) cotyledons in continuous light or in the dark with subsequent light. BA brought about an increase in fresh weight and in DNA, RNA and carotenoid contents in both treatments. KCl did not cause an increase in fresh weight and cellular constituents in the dark, but it did result in an increased fresh weight and DNA content after illumination or in continuous light. BA + KCl treatment resulted in increased carotenoid and DNA contents in the dark, and in increases in fresh weight and all cellular constituents upon subsequent exposure to light. The effects of BA and BA + KCl on growth and chlorophyll synthesis decreased with cotyledon age.
BA pretreatment in the dark eliminated the lag phase in chlorophyll synthesis and increased the rate of synthesis. Treatment in continuous light had little effect. KCl did not shorten the lag phase in chlorophyll synthesis, but it stimulated the rate of synthesis in the light. Dark pretreatment with BA + KCl markedly increased the effect of BA on chlorophyll synthesis. Chlorophyll content and fresh weight were higher in cotyledons treated with BA followed by KCl than in cotyledons treated in the reverse order. These results suggest that growth and greening in cucumber cotyledons are primarily controlled by BA and that KCl intensifies the BA effect after irradiation.     

Selective shift in the metabolic pathways of excised tomato cotyledons in response to mannitol induced water stress

Excised tomato cotyledons subjected to mannitol induced water stress had more total sugars than normal cotyledons during injury but less total sugars than normal cotyledons in the adaptive phase. During water stress injury, protein and UNA synthesis were reduced, activities of beta-fructofuranosidase and phosphofructokinase were reduced but activities of proteases, ribonuclease, hexokinase and glucose-6-phosphate dehydrogenase were increased. Additions of kinetin reversed the water stress effects on enzyme activities. It is concluded that during water stress injury, there was a fundamental reduction in cytokinin activities leading to the selective shift in the enzyme populations.     

Effect of UV-B (290–320 nm) irradiation on growth and metabolism of cucumber cotyledons

Cucumber ( Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV-B (290–320 nm) irradiation (equivalent to the UV-B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid-april on a weighted daily fluence basis) and a UV-B-free control condition. UV-B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV-B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV-B radiation. UV-B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV-B radiation at the ambient level may act as a physiological stress in some UV-sensitive plants.     

Changes in Mulberry Leaf Metabolism in Response to Water Stress

A series of experiments were conducted to characterize the water stress-induced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose phosphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls, carotenoids, starch, sucrose, amino acids, free proline, proteins and nucleic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progressively reduced the activities of RuBPCO and SPS in the leaf extracts, the chlorophyll content, and PS2 activity in isolated chloroplasts. Plants exposed to drought showed lower content of starch and sucrose but higher total sugar content than control plants. While the soluble protein content decreased under water stress, the amino acid content increased. Proline accumulation (2.5-fold) was noticed in stressed leaves. A reduction in the contents of DNA and RNA was observed. Reduced nitrogen content was associated with the reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compared to control plants.     

Phytohormonal changes in greening and senescing intact cotyledons of oilseed rape and pumpkin: influence of the growth retardant BAS 111 ˙˙ W

The triazole growth retardant BAS 111‥W delayed senescence in cotyledons of pumpkin ( Cucurbita maxima L. cv. Gelbe genetzte Riesenmelone) and stimulated chlorophyll synthesis in greening cotyledons of oilseed rape ( Brassica napus L. cv. Petranova) seedlings. In both cases, changes of phytohormone-like substances in the cotyledons were analyzed on a fresh weight basis by immunoassay.
After soil treatment with increasing retardant concentrations, a close correlation was observed in senescing cotyledons of pumpkin between a reduced loss in total chlorophyll and increasing levels of dihydrozeatin riboside (DZR) and trans -zeatin riboside (ZR)-type cytokinins. In contrast, the levels of isopentenyladenosine (IPA)-type cytokinins, 3-indoleacetic acid (IAA) and gibberellin (GA) did not change significantly. The levels of abscisic acid (ABA) were slightly elevated at low retardant concentrations but dropped considerably below those of controls at higher doses. Consequently, the molar ratio of total cytokinin to ABA content changed from approximately 1:40 in controls (50% of initial chlorophyll) to 1:3 in cotyledons treated with 3 mg BAS 111‥W plant⁻¹ (85% of initial chlorophyll). These changes, together with the known reduction of ethylene production by plants treated with nitrogen-heterocyclic retardants, can explain the delayed senescence in pumpkin cotyledons. Likewise, when etiolated, BAS 111‥W-treated seedlings of oilseed rape were exposed to light, the stimulation of chlorophyll synthesis in the cotyledons was accompanied by an accumulation of DZR- and, particularly, ZR-type cytokinins and IAA. In contrast, GA and ABA contents decreased slightly. We conclude that the influence of BAS 111‥W on cytokinin levels might be involved in the stimulation of greening.     

Stimulation of cytokinins and chlorophyll synthesis in cucumber cotyledons by triadimefon

Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1,2,4-triazol-1-yl)-2-butanone] changes the morphology and partitioning of dry matter in cucumber ( Cucumis sativus L. cv. National Pickling) seedlings. The dry weights, potassium and cytokinin levels in the cotyledons and roots of the treated seedlings were higher, whereas the hypocotyl weights were lower than the controls. When etiolated intact seedlings or cotyledons excised from triadimefon-pretreated dark-grown seedlings were exposed to light, chlorophyll synthesis in the pretreated cotyledons was stimulated. Triadimefon does not have cytokinin-like activity in the cucumber cotyledon greening bioassay, but appears to induce the plants to produce more cytokinims, probably by stimulating root growth. Hence it is proposed that the stimulation of chlorophyll production by triadimefon in cucumber cotyledons is mediated by maintaining high levels of potassium and cytokinins in the cotyledons.     

Effects of fusicoccin on Fresh Weight and Chlorophyll Levels in Cucumber Cotyledons

Incubation of cucumber cotyledons with fusicoccin increasedtheir fresh weights and chlorophyll levels and this effect wasenhanced by KCl. Addition of fusicoccin to this combinationincreased fresh weights but decreased chlorophyll levels. Thissuggests that the effects of fusiccocin on these two processesare probably mediated via different mechanisms. (Received January 4, 1982; Accepted March 25, 1982)     

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。     

Brassinolide alleviates the drought-induced adverse effects in barley by modulation of enzymatic antioxidants and ultrastructure

In the present study, possible role of exogenously applied brassinolide (BL) in alleviating the detrimental effects of polyethylene glycol (PEG)-inducted drought stress in barley was evaluated. Barley seedlings were subjected to two PEG levels (0 and 8% w/v) for 2 weeks followed by a foliar spray of BL (0, 0.01, 0.1 and 1 µM) to assess the changes in growth, gas exchange, chlorophyll contents, antioxidant enzyme activities and ultrastructural changes. PEG-induced drought considerably inhibited the barley growth in terms of shoot and root length, shoot, root fresh and dry weights, and chlorophyll contents. Moreover, extensive decrease by PEG-induced drought in gas exchange attributes i.e. net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO₂ were also recorded. However, exogenous application of BL remarkably improved the gas exchange attributes, chlorophyll contents and plant growth under either drought or control condition. Furthermore, foliar spray of BL decreased the production of malondialdehyde (MDA) and reactive oxygen species (ROS) in the leaves and roots by increasing enzymatic antioxidant activities under drought stress. The microscopic examination indicated that exogenous application of BL improved the cell structure and enabled a clean mesophyll cell having a well-developed chloroplast with thylakoid membranes of the drought stressed plants. On the basis of these findings, it can be concluded that exogenous application of BL could alleviate drought stress to barley by ameliorating photosynthetic parameters, improving antioxidants enzyme activities, reducing ultrastructural changes in leaf mesophyll and finally maintaining the plant growth.     

Effects of juglone on growth of cucumber seedlings with respect to physiological and anatomical parameters

Effects of juglone on seedling growth of cucumber (Cucumis sativus cv. Beith Alpha) with respect to physiological and anatomical parameters were investigated. Growth parameters (seedling elongation, fresh and dry weights) were reduced by 1 mM juglone. Juglone also decreased chlorophyll a and b contents and reduced some anatomical tissues (xylem vessel and bundle radius of stem, stomata length and stomata number of the cotyledons). The anatomical changes in stem and cotyledon of the seedlings were related to growth inhibiting effect of juglone. On the other hand, increase in catecholase and tyrosinase activities by the effect of juglone were also recorded.     

Lepidimoide Promotes Light-Induced Chlorophyll Accumulation in Cotyledons of Sunflower Seedlings

The effect of disaccharide lepidimoide on light-induced chlorophyll accumulation was studied in cotyledons of sunflower (Helianthus annuus L.) seedlings and detached cucumber (Cucumis sativus L.) cotyledons. From studies on the structure-activity relationships of lepidimoide, its analogs, and sucrose with respect to light-induced chlorophyll accumulation in the cotyledons of sunflower seedlings, both lepidimoide and the free carboxylic acid of lepidimoide (lepidimoic acid) showed the highest promoting activity, whereas the hydrogenated lepidimoide, which lacks a double bond in the C4, 5 position in uronic acid, showed lower activity than lepidimoide; however, sucrose exhibited very weak activity. These results suggest that lepidimoide acts as a new type of plant growth regulator, not simply as a carbon source providing energy. Lepidimoide promoted not only light-induced chlorophyll accumulation in sunflower cotyledons but also light-induced 5-aminolevulinic acid content, which is considered to be a rate-limiting step in chlorophyll biosynthesis. Lepidimoide with cytokinin stimulated the accumulation of chlorophyll and 5-aminolevulinic acid additively. In detached cucumber cotyledons, lepidimoide also promoted light-induced chlorophyll accumulation. These results indicate that lepidimoide, in cooperation with cytokinin, causes light-induced chlorophyll accumulation in the cotyledons of several dicot plant species by affecting the level of 5-aminolevulinic acid. Received April 4, 1997; accepted September 28, 1998     

The Relationship between the Effects of Cytokinin on the Expension and Metabolism of Excised Cucumber Cotyledons and Water Stress

Excised cucumber (Cucumis sativus, var. Jin-ian No. 4) cotyledons were incubated with 10 ppm of BA (benzyladenine) or water for 1 h, then thouroughly rinsed with water and grown in darkness on filter paper saturated with different concentrations of mannitol solution. Up to 24 h, the fresh weight, carotenoid, RNA, DNA and lipid contents of cotyledons were determined. Although mannitol solution reduced the effectiveness of BA treatment, in the same condition of osmotic potential, the increases of fresh weight, carotenoid, RNA and DNA contents, as well as the decrease of lipid per cotyledon were always much higher in BA treated tissues. BA enhanced the rate of water uptake by the cotyledons. The fresh weight of BA and 0.2 M mannitol treated cotyledons was equal to that of water control, but the increases of carotenoid and nucleic acid contents and the decrease of lipid were much higher in tho former than the latter. 0.3 M and 0.5 M mannitol solu- tions almost interrupted the water uptake of water and BA treated cotyledons respectively. However, the increases of carotenoid and nucleic acid contents as well as decrease of lipid were still occurred in these conditions. The different osmotic potential did nearly not affect the ratio of the increases of carotenoid and nucleic acid contents between BA treatment and control. It means the effectiveness of BA was almost the same under different osmotic potential It is evident that BA stimulated simultaneously the water uptake and metabolism of the cotyledons. They are probably different processes but closely related to each other.     

Gel electrophoresis patterns of proteins and peroxidases of excised tomato cotyledons subjected to mannitol induced water stress

Excised tomato cotyledonswere subjected to mannitol induced water stress solutions for three days. Extracts of proteins and the enzyme peroxidase were made and separated with polyacrylamide gel electrophoresis. The water stress injury caused increases in bigger protein molecules but decreases in smaller protein molecules. The small fastest moving peroxidase isozyme was almost completely eliminated. Applications of growth regulators to the stress solutions indicated that the protein and peroxidase changes could be explained on the basis of reduction in endogenous cytokinin activities by the water stress.     

Uniconazole-induced alleviation of freezing injury in relation to changes in hormonal balance, enzyme activities and lipid peroxidation in winter rape

Winter rape (Brassica napus L. cv. 601) seedlings were treated with 50 mg.l-1 of foliar-applied uniconazole and then exposed to freezing stress with a light/dark temperature regime of 2 °C/–3 °C for 5 days at the seedling stage. Stressed plants contained lower endogenous GA3 and IAA contents than the controls, while zeatin and ABA contents and ethylene levels were significantly increased. Uniconazole-treated plants had lower endogenous GA3 and IAA contents, and higher zeatin and ABA contents and ethylene levels. Leaf chlorophyll content and respiratory capacity of roots were reduced significantly after plants were subjected to freezing stress, and foliar sprays of uniconazole retarded the degradation of chlorophyll and increased respiratory capacity of roots. Uniconazole-induced freezing tolerance was accompanied by increased activities of various antioxidant enzymes, including superoxide dismutase, catalase and peroxidase. Foliar applications of uniconazole reduced electrolyte leakage and malondialdehyde accumulation caused by freezing stress, suggesting that uniconazole may have decreased freezing-induced lipid peroxidation and membrane damage.     

The effect of stress on reproduction in Atlantic cod

This study imposed stress upon spawning cod Gadus morhua in the laboratory to evaluate the potential effects of trawl avoidance on their reproductive physiology and spawning behaviour. Plasma cortisol levels of stressed fish were significantly higher than controls. Stressed cod initiated fewer courtships and often performed an altered courtship sequence. Both control and stressed fish spawned and there was little difference in the production of eggs, fertilization rate, hatching success or time to starvation of larvae. However, stressed fish produced abnormal larvae more frequently. Cod exposed to a chronic stressor are able to spawn successfully, but there appears to be a negative impact of this stress on their reproductive output, particularly through the production of abnormal larvae.     

PSAG12-ipt嵌合基因转化樱桃番茄的研究

利用根癌农杆菌(Agrobacterium tumefacienst)介导法将嵌合基因P SAG12-ipt导人樱桃番茄,经双重PCR检测和基因组总DNA Southern杂交测验,共获得17株转基因植株。田间生长实验观察结果显示,这17株转基因植株生长发育及形态正常,但其中的14株长势明显好于对照。对14株中的2株进行叶片叶绿素、细胞分裂素检测结果表明,转基因植株基本定型叶下部,不同叶位叶片叶绿素、细胞分裂素含量明显高于对照,基本定型叶上部叶片与对照基本一致,同一叶位叶片比对照延缓衰老15～20d。     

Inter-organ Control of Chlorophyll Synthesis in Primary Leaves of Dark-grown Phaseolus aureus

The changing roles of the cotyledons and hypocotyl in the development of dark-grown Phaseolus aureus seedlings are described. The effect of the cotyledons on total chlorophyll synthesis declined with age, but on a chlorophyll per gram fresh weight basis this was less pronounced. In five-day-old plants the hypocotyl was more effective than the cotyledons in increasing the chlorophyll level, and together their effect was less than additive. The promoting factors in the cotyledons were at a saturating level at this stage. The relationship between the effects of the two organs is discussed with particular reference to the components which they supply to the leaves.     

The role of cytokinins in chloroplast lamellar development

The accumulation of chlorophyll, production of two specific lamellar chlorophyll-protein complexes, onset of O(2) evolution, and detection of P700 were examined in intact Jack bean (Canavalia ensiformis [L.] D.C.) leaves treated with 10(-5)m kinetin or benzyladenine and allowed to green under low (30-35%) and high (80-85%) relative humidity. In contrast to reports of the promotion of chlorophyll accumulation by cytokinin treatment in excised tissue or cotyledons, intact greening leaves showed neither promotion of chlorophyll accumulation nor alteration in formation of the lamellar chlorophyll-protein complexes or development of photosynthetic function. Furthermore, cytokinin was ineffective in relieving the consequences of low relative humidity water stress on chlorophyll accumulation and on the formation of at least one lamellar chlorophyll-protein.     

Effect of water stress on some oxidative enzymes and senescence in Vigna seedlings

Seedlings of Vigna catjang Endl. were subjected to water stress for 6, S and 10 days by withholding water to investigate the activities of some oxidative enzymes and the pattern of senescence in leaves of 17-day-old seedlings undergoing water stress. Increasing duration of stress produced a proportional increase in the activities of IAA-oxidase, AA-oxidase, peroxidase and glycolate oxidase but decreased catalase activity and the contents of both chlorophyll and protein, hastening senescence. Leaf water potential and relative water content were also lowered with incresing duration of stress. Permeability was increased in leaf tissue undergoing water stress for 8 days. Seed treatment with CaCl₂ (10⁻² and 10⁻¹⁴ M ) for 6 h improved the water status of leaves, decreased tissue permeability, activities of oxidative enzymes, decline of chlorophyll and protein contents and delayed senescence compared to untreated water stressed plants.