Influence of Drought,High Temperature,and Carbamide Cytokinin 4-PU-30 on Photosynthetic Activity of Bean Plants. 1. Changes in Chlorophyll Fluorescence Quenching

Fifteen-day-old bean plants (Phaseolus vulgaris L.) grown in a climatic chamber were exposed to water deficit (WD) and high temperature (HT) stresses applied separately or in combination. Changes in chlorophyll fluorescence quenching were investigated. Bean plants that endured mild (42 °C, 5 h for 2 d) WD separately or in combination with HT did not change their q_P and q_N quenching (measured at 25 °C) compared with those of the control. After 5 min testing at 45 °C, q_P in control and droughted plants strongly decreased, while q_P of plants that experienced combined WD+HT stress was insignificantly influenced, suggesting the acclimation effect of HT treatments. At more severe stresses (after 3 d-treatment), q_P measured at 25 °C was the lowest in WD+HT plants and q_N values were the highest. But when measured at 45 °C, q_P of WD+HT plants had practically the same values as at 25 °C. Under these conditions q_P of WD plants also showed an adaptation to HT. Twenty-four hours after recovery, the unfavourable effects of the stresses were strongly reduced when measured at 25 °C, but they were still present when measured at 45 °C. Positive effect of the carbamide cytokinin 4-PU-30 was well expressed only in droughted plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Exogenous Ca<Superscript>2+</Superscript> alleviates nitrogen and water deficit,and improves growth of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) seedlings exposed to high temperature

This study was designed to examine whether exogenous Ca²⁺ would improve nitrogen nutrition, water status and growth of high temperature (HT)-stressed wheat (Triticum aestivum) seedlings. Wheat plants were exposed to 35/30 and 25/20°C as temperature control. Some of HT-stressed plants were simultaneously treated with 4 mM Ca²⁺. External Ca²⁺ could obviously improve growth of HT-exposed wheat seedlings indicated by the biomass. Compared with Ca²⁺-untreated plants, total nitrogen content showed a significant increase in Ca²⁺-treated plants under HT stress, this primarily resulted from enhanced nitrate reductase activity and depressed loss of ammonium through photorespiration. External Ca²⁺ application could also increase leaf relative water content and alleviate osmotic stress via increased K⁺ ion and water-soluble carbohydrates in HT-stressed plants. Whereas free proline content showed remarkable decline in Ca²⁺-treated plants at HT stress.     

Effect of Cytokinins on Photosynthetic Pigments and Chlorophyllase Activity in in Vitro Cultures of Axillary Buds of Dianthus caryophyllus L.

The effect of benzyladenine (BA) and two phenylurea cytokinins, N-phenyl-N′-(2-chloro-4-pyridyl)urea (4-PU-30) and thidiazuron (TDZ), on the growth, photosynthetic pigment content, and activity of chlorophyllase (chlorophyll-chlorophylliodhydrolase, EC 3.1.1.14) of in vitro cultures of carnations was studied. All cytokinins caused a rise in the fresh weigth and a drop in the dry weight of leaf mass produced by the explanted buds. Both 4-PU-30 and TDZ increased the chlorophyll content and this correlated with changes in chlorophyllase activity. The effect of 4-PU-30 and TDZ was similar to that caused by BA but at 10-fold or 100-fold lower concentrations. The application of higher concentrations of the phenylurea cytokinins caused an increase in the chlorophyll a/chlorophyll b ratio. However, at equimolar concentrations, the purine and both phenylurea cytokinins had opposite effects, probably indirect and related to some malformations caused by phenylureas. 4-PU-30 increased, but TDZ decreased, photosynthetic membrane stability, which argues for a different molecular organization of the chloroplast membranes. Received February 26, 1996; accepted May 30, 1997     

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N¹-(2-chloro-4-pyridyl)-N²-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10⁻⁵ m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Received September 25, 1997; accepted August 10, 1998     

Drought response of two bedding plants

Bedding plants are an important part of the urban public space and private gardens. However, they are not always properly watered and suffer from drought stress, especially when grown in containers. In this trial a response to water stress of two commonly used species, impatiens (Impatiens walleriana Hook) and geranium (Pelargonium hortorum L. H. Bailey) were compared. The former is highly herbaceous and prone to wilting whereas the latter has hairy leaves and is better adapted to drought. Plants were grown at three levels of soil water content (SWC): 80% (control), 60% (mild stress) and 30% (severe stress). Drought was maintained during three 10 day cycles, separated by 10 day periods of normal watering. In both species roots were significantly longer in plants grown at 30% SWC as compared to 80% SWC while plant height and flower number were reduced by drought only in impatiens. The initial relative water content (RWC) was lower in geranium and decreased less in response to drought than in impatiens. Ammonium content in leaves of both species increased significantly under stress but the ranges of increase were different in both species. There was a significant increase in the free amino acids content in leaves of impatiens as compared to geranium but this rise was more time than drought dependent. The reduction in the a + b chlorophyll concentration in leaves of impatiens was significantly time and stress dependent while no reaction in geranium was observed. The above results show that changes in leaf RWC merit further attention as a possible indicator of plant response to drought stress in ornamental plants but additional studies are needed before this or other parameters can be used to evaluate new bedding plants for introduction into urban growing conditions, or as selection criteria in breeding for adaptation to demanding growing conditions.     

Effect of cytokinins on the photosynthetic apparatus in water-stressed and rehydrated bean plants

Effects of the cytokinins 6-benzylaminopurine (BAP) and N-2-chloro-4-pyridyl-N′-phenylurea (4-PU-30) on the photochemical activity, oxygen flash yields, and thermoluminescence in bean plants under a water stress were studied. The cytokinins increased the photochemical (Hill reaction) activity and thermoluminescence "B"-band in control as well as in stressed and rehydrated plants, while the oxygen flash yields were affected only in the stressed and rehydrated plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of cytokinins on the photosynthetic apparatus in water-stressed and rehydrated bean plants

Effects of the cytokinins 6-benzylaminopurine (BAP) and N-2-chloro-4-pyridyl-N′-phenylurea (4-PU-30) on the photochemical activity, oxygen flash yields, and thermoluminescence in bean plants under a water stress were studied. The cytokinins increased the photochemical (Hill reaction) activity and thermoluminescence "B"-band in control as well as in stressed and rehydrated plants, while the oxygen flash yields were affected only in the stressed and rehydrated plants.     

NaCl对齿肋赤藓叶肉细胞超微结构的影响

齿肋赤藓(Syntrichia caninervis)是古尔班通古特沙漠苔藓结皮层中的优势物种,对荒漠生态系统的稳定性及功能多样性具有十分重要的意义。利用透射电镜技术对不同浓度Na Cl胁迫下齿肋赤藓叶肉细胞超微结构进行了观察。结果表明:齿肋赤藓叶肉细胞在未胁迫(0 mmol/L)处理下排列疏松,各种细胞结构完整,叶绿体基质排列均匀且叶绿体内含少量淀粉粒和脂质球。在轻度盐Na Cl胁迫(100 mmol/L)下,齿肋赤藓叶肉细胞结构依然保持完整,叶绿体基质均匀,叶肉细胞超微结构仅有较小变化。在中度盐Na Cl胁迫(200、300 mmol/L)下,齿肋赤藓叶肉细胞发生质壁分离,出现晶体结构,且中央大液泡发生破裂;叶绿体由梭形变成椭球形或圆球状,出现空泡化并伴随有轻微的解体;叶绿体类囊体肿胀,脂质球数量增加。在高度Na Cl胁迫(400、500 mmol/L)下,齿肋赤藓细胞的质壁分离加剧,叶肉细胞出现大量泡状结构和膜片层,叶肉细胞死亡;叶绿体片层结构消失,空泡化加重,脂质球数量增加且体积变大,叶绿体内外膜消失,叶绿体大部分解体,在叶肉细胞中几乎看不到叶绿体的存在。上述结果表明,叶绿体膜结构的损伤与盐胁迫下叶肉细胞死亡有密切关系。     

锰胁迫对盐肤木种子萌发、幼苗生长及理化特性的影响

为揭示植物适应锰胁迫的生理机制,通过在不同Mn²⁺浓度(0、1、5、10、15、20 mmol/L)下开展盐肤木(Rhus chinensis)种子萌发以及幼苗生长实验,检测锰胁迫处理7、15、30 d后幼苗生理生化特性的变化。结果表明:(1)随着Mn²⁺浓度的升高,盐肤木种子发芽率变化不显著,在80.0%-81.6%之间,发芽势、发芽指数和活力指数则呈先升后降的趋势;其幼苗生物量也呈现先升后降的趋势;(2)随着Mn²⁺浓度的升高与胁迫时间的延长,盐肤木幼苗叶绿素a、叶绿素b含量均呈现先增加后降低的趋势,类胡萝卜素含量呈现下降的趋势;(3)胁迫7 d时,随着Mn²⁺浓度的升高,盐肤木幼苗超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性均显著上升;胁迫15、30 d时,高Mn²⁺浓度(15-20 mmol/L)下POD、CAT活性则均降低;(4)胁迫7 d时,随着Mn²⁺浓度的升高,可溶性糖、可溶性蛋白、游离脯氨酸含量升高;胁迫15、30 d时,在Mn²⁺浓度为20 mmol/L时可溶性蛋白与游离脯氨酸含量显著降低;(5)随着Mn²⁺浓度的升高与胁迫时间的延长,丙二醛(MDA)含量均升高。研究说明盐肤木具有较强的耐受锰胁迫能力,它可通过增强抗氧化酶活性、积累渗透调节物质含量来应对锰胁迫。     

Overexpression of transketolase gene promotes chilling tolerance by increasing the activities of photosynthetic enzymes,alleviating oxidative damage and stabilizing cell structure in Cucumis sativus L.

Despite being a key enzyme of Cavin cycle, transketolase (TK) is believed to be related to abiotic resistance in higher plants. However, how TK affects chilling tolerance still remains largely unknown. Here, we describe the effect of overexpression of the Cucumis sativa TK gene (CsTK) on growth, photosynthesis, ROS metabolism and cell ultrastructure under chilling stress. Low temperature led to a decrease of the photosynthetic rate (Pn), the stomatal conductance (Gs), the actual photochemical efficiency (ΦPSII) and the sucrose content, whereas there was an increase of the intercellular CO₂ concentration (Ci) and MDA content. These changes were alleviated in the CsTK plants after 5 days of chilling stress, however, inhibition of CsTK showed the opposite results. Furthermore, transgenic plants with overexpression of CsTK showed higher increase in leaf area and dry matter, higher activity of the enzymes and higher increase in the contents of metabolism substance involved in Calvin cycle and reactive oxygen scavenging system as well as lower ^?OH and H₂O₂ content, superoxide anion production rate compared with the control cucumber plants under chilling stress. At the end of the chilling stress, compared to wild‐type (WT) which exhibited dramatically destroyed cell ultrastructure, expanded chloroplast, broken cell and chloroplast membranes as well as the disappeared grana lamella, the CsTK sense plants showed a more complete cell ultrastructure, whereas, the damage of the cell ultrastructure was aggravated in CsTK antisense plants. Taken together, these results imply that CsTK promoted chilling tolerance in cucumber plants mainly through increasing the capacity to assimilate carbon, alleviating oxidative damage and stabilizing cell structure.     

Growth and Solute Composition in Two Wheat Species Experiencing Combined Influence of Stress Conditions1

The effects of environmental stress combinations on the soluble metabolites were investigated in several cultivars of Triticum aestivum and T. durum. The seedlings grown at optimum (24/16°C), low (5/–5°C) (LT), and high (40/30°C) (HT) day/night temperature conditions were exposed to waterlogging, drought, and salinity (0.7% NaCl, w/w) stresses for six days. Root and shoot fresh weight significantly decreased under waterlogging, drought and salt stresses. Fresh weight was most reduced at severe drought + HT combinations. The lowest relative water content was found under drought stress + HT combination. Soluble carbohydrate (SC) contents increased under LT conditions, but decreased under HT conditions. Under HT + salt combinations, T. aestivum genotypes showed higher SC content thanT. durum genotypes. Proline content significantly increased in the case of water deficit and salt stress. Under drought and salt stresses, T. aestivum genotypes had lower proline contents than T. durum genotypes. These results indicate that biochemical responses to drought, waterlogging, and salt stresses were significantly changed in wheat seedlings under LT and HT conditions.     

Effect of temperature stress on the endogenous cytokinin content in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh plants

The levels of three endogenous cytokinin equivalents: zeatin (Z), iso-pentenyladenine (iP) and dihydrozeatin (dZ) in two Arabidopsis thaliana (L.) Heynh genotypes — wild type (wt) and ethylene-insensitive mutant (eti5), were compared using enzyme immunoassay (ELISA). Cytokinin content was measured after exposure to low (4 °C for 24 h in darkness) or high temperature (38 °C for 24 h in darkness). Measurements were performed immediately and 24, 48 and 120 h after treatments. It was found that at normal growth conditions eti5 plants contained more endogenous cytokinins compared to the wild type. At both temperature treatments mutant plants had decreased total cytokinin levels. Wild-type plants treated with high temperature (HT) exhibited reduced total cytokinins (with the exception of rates at 48 h), while low temperature (LT) treatment resulted in elevated total amount of the studied equivalents (except at 24 h). The obtained results suggested that HT had greater effect on cytokinin levels than LT since it caused more profound changes in the total content. We assume that this was due to the natural chilling tolerance of Arabidopsis plants.     

Effect of drought stress on chlorophyll a fluorescence and electrical admittance of shoots in Norway spruce seedlings

Effects of mild and severe soil drought on the water status of needles, chlorophyll a fluorescence, shoot electrical admittance, and concentrations of photosynthetic pigments in needles of seedlings of Picea abies (L.) Karst. were examined under controlled greenhouse conditions. Drought stress reduced shoot admittance linearly with a decrease in shoot water potential (_w) and increase in water deficit (WD) and led to a decrease in concentrations of chlorophyll a, b and carotenoids. Severe water stress (shoot _w=–2.4 MPa) had a negative effect on chlorophyll a fluorescence parameters including PSII activity (F_v/F_m), and the vitality index (R_fd). Variations in these parameters suggest an inhibition of the photosynthetic electron transport in spruce needles. Water stress led to a decrease in the mobility of electrolytes in tissues, which was reflected by decreased shoot electrical admittance. After re-watering for 21 days the WD in needles decreased and the shoot water potential increased. In the re-watered plants, the chloroplast function was restored and chlorophyll a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in the seedlings triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. We conclude that the shoot electrical admittance and photosynthetic electron transport in leaves are closely linked to changes in water status and their decrease is among the initial responses of seedlings to water stress.     

Arabidopsis growth under prolonged high temperature and water deficit: independent or interactive effects?

High temperature (HT) and water deficit (WD) are frequent environmental constraints restricting plant growth and productivity. These stresses often occur simultaneously in the field, but little is known about their combined impacts on plant growth, development and physiology. We evaluated the responses of 10 Arabidopsis thaliana natural accessions to prolonged elevated air temperature (30 °C) and soil WD applied separately or in combination. Plant growth was significantly reduced under both stresses and their combination was even more detrimental to plant performance. The effects of the two stresses were globally additive, but some traits responded specifically to one but not the other stress. Root allocation increased in response to WD, while reproductive allocation, hyponasty and specific leaf area increased under HT. All the traits that varied in response to combined stresses also responded to at least one of them. Tolerance to WD was higher in small-sized accessions under control temperature and HT and in accessions with high biomass allocation to root under control conditions. Accessions that originate from sites with higher temperature have less stomatal density and allocate less biomass to the roots when cultivated under HT. Independence and interaction between stresses as well as the relationships between traits and stress responses are discussed.     

Transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> and tobacco plants overexpressing an aquaporin respond differently to various abiotic stresses

Despite the high isoform multiplicity of aquaporins in plants, with 35 homologues including 13 plasma membrane intrinsic proteins (PIPs) in Arabidosis thaliana, the individual and integrated functions of aquaporins under various physiological conditions remain unclear. To better understand aquaporin functions in plants under various stress conditions, we examined transgenic Arabidopsis and tobacco plants that constitutively overexpress Arabidopsis PIP1;4 or PIP2;5 under various abiotic stress conditions. No significant differences in growth rates and water transport were found between the transgenic and wild-type plants when grown under favorable growth conditions. The transgenic plants overexpressing PIP1;4 or PIP2;5 displayed a rapid water loss under dehydration stress, which resulted in retarded germination and seedling growth under drought stress. In contrast, the transgenic plants overexpressing PIP1;4 or PIP2;5 showed enhanced water flow and facilitated germination under cold stress. The expression of several PIPs was noticeably affected by the overexpression of PIP1;4 or PIP2;5 in Arabidopsis under dehydration stress, suggesting that the expression of one aquaporin isoform influences the expression levels of other aquaporins under stress conditions. Taken together, our results demonstrate that overexpression of an aquaporin affects the expression of endogenous aquaporin genes and thereby impacts on seed germination, seedling growth, and stress responses of the plants under various stress conditions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of GA3 and 4-PU-30 on Leaf Protein Composition, Photosynthetic Activity, and Growth of Maize Seedlings

The effects of gibberellic acid (GA3) and N1-(2-chloro-4-pyridyl)-N2 phenylurea (4-PU-30) on maize seedling growth, photosynthetic parameters, and leaf protein composition were investigated. The agents used alone or in combination increased leaf growth and photosynthetic rate of the seedlings. Chlorophyll and total nitrogen contents in leaves as well as the quantity of individual protein fractions increased simultaneously. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins (albumins and globulins) revealed quantitative differences between 4-PU-30-treated plants and the other experimental variants. They differed in polypeptide composition associated with changes in soluble proteins and amino acids. However, GA3 did not induce similar changes in polypeptide composition of soluble proteins. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of Water Stress and High-Temperature Stress on the Structure and Activity of Photosynthetic Apparatus of Zea Mays and Helianthus Annuus

Effects of high-temperature stress (HTS) and PEG-induced water stress (WS), applied separately or in combination, on the functional activity and ultrastructure of the photosynthetic apparatus (PSA) of maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were investigated. In maize plant tissues WS provoked the decrease in RWC by 10.9 %, HTS by 7.0 %, and after simultaneous application of the both treatments the decrease was 32.7 % in comparison with control plants. Similar but more expressed changes were observed in sunflower plants. Sunflower was more sensitive to these stresses. Net photosynthetic rate decreased significantly after all treatments, more in sunflower. In mesophyll chloroplasts after separately applied WS and HTS the number of grana and thylakoids was reduced and electron-transparent spaces appeared. At combined stress (WS+HTS) granal and stromal thylakoids were considerably affected and chloroplast envelope in many of them was partially disrupted. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of water deficit and selenium on common buckwheat (<Emphasis Type="Italic">Fagopyrum esculentum</Emphasis> Moench.) plants

Two cultivars of common buckwheat (Fagopyrum esculentum), Pyra and Siva, were exposed to three treatments: water deficit (WD), foliar spraying by selenium (as Na₂SeO₄) (Se), and the combination of both. In WD-plants the stomatal conductance (g _s) was significantly lower, while WD+Se-plants of Siva had significantly higher g _s. None of the treatments resulted in significant differences of potential photochemical efficiency of photosystem 2 (PS2). A significantly higher actual photochemical efficiency of PS2 was obtained in Siva WD-plants and in Pyra Se-and WD-plants which was possibly due to improvement of plant water management during treatment. A significant interaction was observed between the effects of WD and Se on respiratory potential in Pyra. WD, Se, and the WD+Se combination resulted in shorter Pyra and Siva plants, with a reduced number of nodes. WD slightly negatively affected the yield per plant. The yield was highest in plants exposed to Se only. In Siva the number of seeds was triple while the average seed mass remained unchanged.     

干旱胁迫下镉处理对互叶醉鱼草幼苗生长、镉积累及光合生理的影响

为探究干旱条件下,互叶醉鱼草(Buddleja alternifolia Maxim.)幼苗对重金属镉胁迫的生长及光合生理响应机制,以两年生互叶醉鱼草幼苗为试验材料,设置对照与干旱两个水分处理组(土壤相对含水率分别为:65%—60%,35%—30%),每个水分处理条件下再分别设置3个镉处理浓度(0.28、(0.6+0.28)、(1.2+0.28)mg/kg),共6个处理。测定不同水分及镉处理对互叶醉鱼草生长、生物量、光合参数及体内重金属含量的影响。结果表明:干旱与镉复合胁迫下植物的存活率为100%。镉胁迫、干旱与镉复合胁迫均不同程度抑制了互叶醉鱼草幼苗生长、生物量积累、植株的光合作用及叶绿素含量,且其光合和叶绿素含量的降幅明显大于单一镉胁迫。镉胁迫下,互叶醉鱼草幼苗单株最高镉富集量为69.33 mg/kg,而复合胁迫下单株最高镉富集量为50.68 mg/kg。以上结果表明:干旱胁迫能够加重镉胁迫对植物的影响,使复合胁迫下互叶醉鱼草生长、光合生理及镉富集能力下降。但单一镉胁迫下,互叶醉鱼草对镉具有更强的耐受性,并有较高的生物富集能力,且干旱与Cd复合胁迫下互叶醉鱼草幼苗仍有一定的镉积累量。因此在干旱半干旱区园林绿化以及Cd污染地区的生态建设中,互叶醉鱼草是一种具有巨大应用潜力和前景的灌木树种。