Increase In ABA Research Articles

Exogenous nitric oxide delays salt-induced leaf senescence in cotton (Gossypium hirsutum L.)

Nitric oxide (NO) is a signaling molecule which plays an important role in delaying leaf senescence and increasing abiotic stress tolerance, but it is not clear if and how exogenous NO delays salt-induced leaf senescence in cotton. In this study, uniform cotton seedlings with five true main-stem leaves were cultured in hydroponics for 20 days and subjected to 150 mM NaCl. Seedlings were then treated with foliar spray of 300 μM sodium nitroprusside (SNP), a nitric oxide donor, and those with water spray were used as control. The effects of SNP on leaf senescence and expression of senescence-related genes were examined. Foliar spray with SNP significantly delayed leaf senescence in terms of the increased chlorophyll (Chl) content, photosynthetic (Pn) rate and expression of LHCB gene at 22 days after salt stress (DAS). The SNP significantly (p < 0.05) increased the expression of SOS1 and NHX1 genes and K+ content in leaves, but decreased leaf Na+ content. It also reduced (p < 0.05) the expression of ABA biosynthesis genes, NCED2, NCED9, and ABA content but increased the expression of cytokinin biosynthesis gene, IPT1 and ZR and iPA contents at 22 DAS. The overall results suggest that the delay in salt-induced leaf senescence by SNP was due to marked decrease in Na+ and ABA contents and increase in K+ and cytokinin through regulation of the expression of SOS1, NHX1, NCED2, NCED9 and IPT1 genes under salt stress. Foliar spray with SNP can be potentially useful in delaying leaf senescence, thereby increasing the economic yield of cotton under salt stress.

Increasing resistance of wheat to unfavorable environmental factors by pre-sown priming of its grains

Presowing priming involves soaking seeds under controlled conditions until complete saturation with water or essential components for thefurther development of plants, seeds followed by drying. AO (aldehydeoxidase) is involved in ABA biosynthesis, converting abscisic aldehyde toABA. Seeds of resistent cultivar – NAZ, soaked in a solution of 50 mMmolybdate, showed high activity of AО1, indicating that the maximum saturation molybdenum enzyme. Saratovskaya- 29 was shown that soaked of theseeds in 50 mMmolybdate solution for 24 hours, as these optimal conditions hydrating seed will increase in ABA content of the caryopsis. Excessive ROS formed in the conditions of application of priming, in embryonictissues during hypoxia induces increasing synthesis of ABA. In seeds during soaked in 50 mMmolybdate solution increased ABA content in 10.5times of Lutecsens 70 and 5.2 times by soaking the seeds in water. As aresult of the priming procedure, which is accompanied by the formationof excess free radicals induced defensive responses in plant cells. Incubation of seeds within 24 hours and 32 hours during this period increasedGR activity and almost no imbalance reduced and oxidized glutathione,wheat varieties. Views will data showed that pre-sowing seed priming bothvarieties NAZ and Saratovskaya 29 led to an increase in the content ofendogenous ABA in 2 times and 1.5 times the antioxidants and as a resulthas led to an increase in resistance to stress (adverse environmental factors)both varieties.This paper presents the results of the impact of pre-sowing grain priming maintenance plant hormone ABA, the activity of AO and antioxidantenzymes in two different varieties of wheat.Key words: priming, wheat, ABA, AO, abiotic stress, antioxidants

Water-Deficit Response Is Not Affected by Glutathione Deficiency in &amp;lt;i&amp;gt;Arabidopsis thaliana pad&amp;lt;/i&amp;gt;2-1 Plants

Changes in glutathione and ascorbate content, hydrogen peroxide and abscisic acid were studied in developing leaves in wild-type (Col-0) and glutathione-deficient mutant pad2-1 lines of Arabidopsis thaliana over a time period of 9 days of drought followed by re-watering. Glutathione deficient mutant (pad2-1) presents mechanisms of acclimation to water stress through the reduction of plant biomass and increase in endogenous concentrations of ascorbate and glutathione. These acclimation responses to stress appeared along with the first symptoms of stress and we suggest here that they are regulated by ABA and H2O2. Normally, wild type plants under conditions of stress require an initial response phase in which a decrease in antioxidants is observed before reaching acclimation through the increase in levels of antioxidants. pad2-1 is more sensitive to stress and reacts to it; however, it did not suffer more oxidative stress than Col-0 plants, even though pad2-1 had higher levels of endogenous H2O2 relative to wild-type. In both water stressed Col-0 and pad2-1 plants increases in ABA were observed, however, more sharply in wild-type stressed plants. Low levels of glutathione together with high levels of H2O2 may regulate endogenous ABA concentrations and could be related to the slow growth rates which were observed during the experiment. The results highlighted the double function of glutathione as an antioxidant and signal molecule and also, the different response patterns of wild-type and pad2-1 when faced with drought stress. The results bring new insights to the responses of pad2-1 under conditions of water stress.

Jasmonic acid interacts with abscisic acid to regulate plant responses to water stress conditions

Phytohormones are key players in signaling environmental stress conditions. Hormone profiling together with proline accumulation were studied in leaves and roots of different mutant lines of Arabidopsis. Regulation of proline accumulation in this system seems complex and JA-deficient (jar1-1) and JA-insensitive (jai1) lines accumulating high levels of proline despite their very low ABA levels seems to discard an ABA-dependent response. However, the pattern of proline accumulation in jai1 seedlings parallels that of ABA. Under stress conditions, there is an opposite pattern of ABA accumulation in roots of jar1-1/coi1-16 (in which ABA only slightly increase) and jai1 (in which ABA increase is even higher than in WT plants). This also makes JA-ABA crosstalk complex and discards any lineal pathway that could explain this hormonal interaction.

Physiological characteristics and related gene expression of after-ripening on seed dormancy release in rice.

After-ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after-ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after-ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after-ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after-ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after-ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA(1)/ABA, GA(7)/ABA, GA(12)/ABA, GA(20)/ABA and IAA/ABA ratios significantly increased, while GA(3)/ABA, GA(4)/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after-ripening, thereby altering α-amylase activity during seed germination. Peak α-amylase activity occurred at an earlier germination stage in after-ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy-related genes was regulated by after-ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3-2, qLTG3-1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after-ripening. Dormancy release through after-ripening might be involved in weakening tissues covering the embryo via qLTG3-1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.

The role of ABA in the freezing injury avoidance in two Hypericum species differing in frost tolerance and potential to synthesize hypericins

Cold stress is a major environmental factor that limits the distribution of plants and determines the spectrum and amount of secondary metabolites with a protective function. The most studied representative of the genus Hypericum, H. perforatum L. (St. John’s wort), is known as a producer of the photodynamic pigment hypericin, the unique bioactive compound structurally belonging to naphtodianthrones. In relation to the cosmopolitan distribution, we hypothesised that low temperature stress could increase the content of naphtodianthrones as a part of the adaptive mechanisms. Two strategies in preventing the freezing injury in the genus Hypericum were defined. Based on a frost-killing temperature (LT50) in untreated (control) plants and more than a 10 °C decrease in LT50 in cold-acclimated plants, we demonstrated the freezing tolerance for H. perforatum. On the contrary, the freezing avoidance was preferable in H. canariense—the species endemic to (sub)tropical Canary Islands and Madeira. The freezing tolerance/avoidance was related to the course of ABA accumulation/depletion in H. perforatum/H. canariense under a subfreezing temperature of −4 °C; however, the effect of dehydration or application of 76 μM ABA on the level of endogenous ABA was comparable. The 48-h exposure of H. perforatum control plants to −4 °C resulted in a 1.6-fold increase in the content of naphtodianthrones, along with the 1.5-fold increase of ABA. On the contrary, neither dehydration nor exogenous ABA stimulated the biosynthesis of these compounds. Our findings indicate possible integration of ABA signalling into naphtodianthrones biosynthesis under subfreezing conditions; this mechanism could be modified by plant tolerance to cold environments.

The role of phytohormones in relation to bakanae disease development and symptoms expression

Fusarium proliferatum, the causal agent of bakanae disease was found to be up-regulated gibberellic acids (GAs) in bakanae diseased rice plants and thereby contributing to the different types of symptoms observed associated with the disease. The up- and down regulation of GAs, IAA and ABA were studied in susceptible (MR 211) and resistant (BR3) varieties artificially inoculated with F. proliferatum at different times after inoculation. The increase in GAs including fungiproduced GA3 and IAA were higher in inoculated MR 211 rice plants (GAs = 26%, IAA = 40.39%) as compared to resistant BR3 (GAs = 19%, IAA = 4.27%), 7 days after inoculation (disease score 1, S-1) in whole plant sample analysis. The increase were higher in both roots and leaves but not in the stem, thus the main symptom observed as stunting of the susceptible plants at disease score 1. However, 14 days after inoculation (disease score 3, S-3), both phytohormones were observed to increase in whole plant sample analysis as well as in all plant parts sampled. This increasing effect was found associated with elongation of internodes and chlorosis of leaves in susceptible plants of MR 211. As the symptoms progressed to disease score 5 (S-5, after 21 days of inoculation) susceptible plants of MR 211 were started to collapse and lodged due to over elongation, and finally dead followed by a decrease in GAs and IAA but an increase in ABA. In resistant variety BR3, marginal up regulation of GAs and IAA were observed only at 21 days after inoculation in stems with no typical symptom of bakanae disease.

Tissue-specific accumulation and regulation of zeaxanthin epoxidase in Arabidopsis reflect the multiple functions of the enzyme in plastids.

The enzyme zeaxanthin epoxidase (ZEP) catalyzes the conversion of zeaxanthin to violaxanthin, a key reaction for ABA biosynthesis and the xanthophyll cycle. Both processes are important for acclimation to environmental stress conditions, in particular drought (ABA biosynthesis) and light (xanthophyll cycle) stress. Hence, both ZEP functions may require differential regulation to optimize plant fitness. The key to understanding the function of ZEP in both stress responses might lie in its spatial and temporal distribution in plant tissues. Therefore, we analyzed the distribution of ZEP in plant tissues and plastids under drought and light stress by use of a ZEP-specific antibody. In addition, we determined the pigment composition of the plant tissues and chloroplast membrane subcompartments in response to these stresses. The ZEP protein was detected in all plant tissues (except flowers) concomitant with xanthophylls. The highest levels of ZEP were present in leaf chloroplasts and root plastids. Within chloroplasts, ZEP was localized predominantly in the thylakoid membrane and stroma, while only a small fraction was bound by the envelope membrane. Light stress affected neither the accumulation nor the relative distribution of ZEP in chloroplasts, while drought stress led to an increase of ZEP in roots and to a degradation of ZEP in leaves. However, drought stress-induced increases in ABA were similar in both tissues. These data support a tissue- and stress-specific accumulation of the ZEP protein in accordance with its different functions in ABA biosynthesis and the xanthophyll cycle.

Low sink-induced stomatal closure alters photosynthetic rates of source leaves in beans as dependent on H2O2 and ABA accumulation in guard cells

Low sink demand provided by pod removal and stem girdling of beans (Vicia faba, cv. Daqingshan) (-Sink) induced a significantly lower net photosynthetic rate (Pn), stomatal conductance (gs), internal CO2 concentration (Ci), and transpiration rate (E) compared with pod and root sink retention (CK). This depression in Pn was due to stomatal limitation. Low sink demand of -Sink plants resulted in a higher leaf sucrose content, but a lower sucrose content in guard cells. Moreover, the significant accumulation of H2O2 and ABA were observed in both leaves and guard cells of -Sink plants. The most intensive electron dense deposit of cerium perhydroxides, produced by H2O2 reaction with cerium chloride, was present in the cell walls, especially the dorsal walls of guard cells. Immunogold electron-microscopy localization of ABA showed that ABA was distributed in ventral walls of guard cells and the intercellular space of mesophyll cells of -Sink leaves in contrast to CK plants. Application of exogenous sucrose to isolated bean leaves increased H2O2 and ABA contents. H2O2 and ABA in leaves was likely generated by two independently regulated pathways, each affected by the high sucrose concentration induced by low sink demand. Increased sucrose in leaves in response to low sink demand may have caused the increase of H2O2 and ABA, and their accumulation in mesophyll cells and guard cells was likely the primary cause for stomatal closure under low sink demand.

Differentiation of Photoperiod-Induced ABA and Soluble Sugar Responses of Two Quinoa (Chenopodium quinoa Willd.) Cultivars

Adaptation of quinoa (Chenopodium quinoa Willd.) to new regions demands acclimation to day-length, in addition to a host of other abiotic factors. To further elucidate the effects of photoperiod on development of quinoa, two differently adapted cultivars, Achachino (short day) from Bolivia and Titicaca (day-length neutral), were subjected to continuous long (17.5 h) and short (10 h) photoperiod conditions as well as a shift between the two to trigger possible adaptive mechanisms initiated by changes in leaf soluble sugar and ABA concentration. Our findings show both cultivars responding to an increase in photoperiod with significant increases in soluble sugar concentrations and a simultaneous increase in ABA. However, Titicaca exhibited a much stronger ABA response to increase in photoperiod, whereas the increase for Achachino falls within the range of natural diurnal variation. Achachino also showed increasing sensitivity to long photoperiods throughout all reproductive growth stages, resulting in continued flowering, stem elongation and disruption of seed formation, whereas Titicaca was capable of maintaining full seed set under all the photoperiod conditions. Discernible photoperiod-dependent chlorosis of the lower leaves of Titicaca was observed under long photoperiods compared to short photoperiods, implying multi-faceted adaptive responses to changes in photoperiod which may also involve nitrogen and carbon dynamics. Both ABA and sugar signals are possibly involved in regulating the photoperiod-adaptive capability of each cultivar, leading to pronounced differences in growth and reproductive development patterns between the contrasting cultivars.

Progress of snow mould infection in crowns of winter rye (Secale cereale L.) is related to photosynthetic activity during cold acclimation

Resistance to snow mould is a feature determined by multiple genes. Therefore, determining the phenotype of resistant plants is difficult as it requires an investigation over a long period of time from cold acclimation through pathogenesis. The aim of the present study was (i) to determine the characteristics of the resistant genotype and (ii) to clarify the connections between photosynthesis during cold acclimation and then pathogenesis caused by Microdochium nivale. Two inbred lines of winter rye (Secale cereale L.) differing in their susceptibility to snow mould were used in the study. After cold acclimation snow mould resistant (SMR) line was characterised by higher values of CO2 assimilation and electron transport efficiency but did not differ from snow mould susceptible (SMS) line in carboxylation rate of RuBisCO (Vcmax). Higher soluble carbohydrate accumulation, due to higher photosynthesis intensity, as well as an ABA increase at 5 days post infection (DPI) in leaves and crowns were found in SMR line during the pathogenesis period. Callose deposition was found around non-infected bundle sheets and in cortex cells at 5 DPI (at the same time point as ABA peak) only in SMR line, which probably prevented the infection of leaf initials. Early leaf initials infection in SMS line may be responsible for inhibiting leaf growth and plant regeneration after stress cessation. The results show different physiological and biochemical characteristics of the investigated lines, which can be applied in the selection of resistant genotypes and identifying genomic regions responsible for metabolic pathways increasing pathogen resistance.

Changes in the content of endogenous phytohormones and proteins caused by abiotic stresses on cotton

The dynamics of changes in the contents of endogenous phytohormones (ABA and IAA) in sprouts of a cotton line resistant to stresses were studied. A sharp increase of ABA and insignificant change of IAA were noted in the first hours of treatment by salinity and drought. These phytohormones decreased but remained above the control level under the effect of the abiotic stresses. A comparison of proteins in various parts of the sprouts (radicles and hypocotyls) of drought- and salinity-resistant line L-7010 showed that the phytohormones caused under stress both inhibition of the synthesis of several proteins and the induced synthesis of proteins de novo.

Wounding of potato tubers induces increases in ABA biosynthesis and catabolism and alters expression of ABA metabolic genes

The effects of physical wounding on ABA biosynthesis and catabolism and expression of genes encoding key ABA metabolic enzymes were determined in potato tubers. An increase in ABA and ABA metabolite content was observed 48h after wounding and remained elevated through 96h. Wounding induced dramatic increases in the expression of the ABA metabolic genes encoding zeaxanthin epoxidase (ZEP), 9-cis-epoxycarotenoid dioxygenase (NCED), and ABA-8′-hydroxylase. Although the patterns of wound-induced expression of individual genes varied, increased gene expression was observed within 3h of wounding and remained elevated through 96h. An apparent correlation between expression of the gene encoding ZEP and the increase in ABA content suggested that the wound-induced increase in ABA biosynthesis was regulated by both substrate availability and increased NCED activity. Suppression of wound-induced jasmonic acid accumulation by rinsing the wounded tissue with water did not inhibit the subsequent increase in ABA content. Exogenous ethylene completely suppressed the wound-induced increase in ABA content and dramatically reduced wound-induced up-regulation of ABA metabolic genes. This study is the first to identify the molecular bases for increased ABA accumulation following physical trauma in potato tubers and highlights the complex physiological interactions between various wound-induced hormones.

ABA 처리를 통한 '홍이슬' 포도의 착색향상 및 적정 수확기 설정

본 연구는 ABA 처리를 통해 '홍이슬' 포도의 착색을 증진시키고자 하였으며 고품질 과실을 생산할 수 있는 적정 수확시기를 밝히고자 하였다. 변색 초기에 <TEX>$1000mg{\cdot}L^{-1}$</TEX> 의 외생ABA 처리는 내생 ABA와 당함량 증가를 가져왔으며 착색증진에 효과가 있는 것으로 조사되었다. ABA 처리 시 착색이 촉진되어 처리 후 15일인 만개 후 85일부터는 수확이 가능한 정도까지 착색되었으며 이후에도 계속적으로 안토시아닌 함량이 증가하였다. 과립성숙에 따른 가용성고형물의 증가와 산의 감소도 꾸준히 진행되었다. 만개 후 100일 이후에는 당도가 높고 산도는 낮은 수준으로 변화가 없으나 경도가 급격히 감소하였다. 따라서 지연 수확 시 과숙의 위험이 있어 과실의 상품성을 높이기 위해서는 만개 후 100일을 전후하여 수확하는 것이 바람직할 것으로 생각된다. 반면 무처리구의 경우에는 착색이 불량하여 만개 후 85일에는 수확이 불가능하였다. 만개 후 100일에도 당산비를 기준으로 한 수확은 가능하였으나 여전히 착색이 불량하였다. 착색을 기준으로는 만개 후 110일에서야 수확이 가능하였으나 과숙과 동시에 경도가 현저하게 낮았다. 따라서 무처리구의 경우 만개 후 100일을 기준으로 착색을 증진시키는 방법이 요구되었다. This study was carried out to improve the fruit color through ABA treatment and to determine the optimum harvest time for producing high quality fruits in 'Hongisul' grapes. Spraying of <TEX>$1000 mg{\cdot}L^{-1}$</TEX> exogenous ABA at early verasion (70 days after full bloom, DAFB) brought increase of endogenous ABA and soluble solid contents and enhanced fruit coloration. So, it was possible to harvest ABA treated fruits from 85 days after full bloom (15 days after treatment) by accelerated anthocyanin content which increased continuously until 110 DAFB. An increase of soluble solid and decrease of total acidity appeared steadily with the onset of berry ripening. After 100 DAFB, soluble solid content and total acidity did not change significantly, but the berry firmness was suddenly decreased. Consequently, it was suggested that ABA treated fruits need to be harvested at about 100 DAFB because of their short period of marketing by over ripening. On the contrary, harvesting of untreated fruit was totally impossible at 85 DAFB because of their poor berry coloration. But it was possible to harvest them at 100 DAFB based on the soluble solid/acidity ratio, whereas the berry coloration was progressed poorly. On the other hand, the fruits harvested at 110 DAFB showed acceptable berry coloration but their berry firmness was dropped significantly coincide with overripening. Therefore, it was needed to develop an altered production system for improving coloration at around 100 DAFB in 'Hongisul' grapes.

Common and distinct responses in phytohormone and vitamin E changes during seed burial and dormancy in Xyris bialata and X. peregrina

Temperature and humidity are the main factors influencing seed viability, dormancy and longevity of buried seeds. Unfortunately, very little is known about such processes in species of tropical regions, where temperature does not show major seasonal variations. The extent to which germination capacity, phytohormones and vitamin E levels were altered after burial of seeds of Xyris bialata and X. peregrina (Xyridaceae), two species endemic to rupestrian fields of Brazil, was examined. After 2 months of burial, seed germination capacity remained constant, which is associated with decreases in ABA and IAA content in both species. During this period, zeatin levels also decreased in X. bialata, but not in X. peregrina, the latter showing much lower levels of ABA. During the summer (rainy season), seeds of both species experienced a progressive, but severe, decrease in germination capacity, which reversed at the end of the winter (dry season), thus suggesting secondary dormancy. This dormancy appeared to be caused by drastic decreases in GAs, rather than increases in ABA. Levels of GA(4) decreased to non-detectable values during dormancy in both species. Furthermore, zeatin levels decreased in X. bialata but not in X.peregrina during this period. Both species accumulated γ-tocopherol as the major vitamin E form, and levels of this antioxidant remained constant or even increased during seed burial; however, X. bialata seeds showed a significant decrease in α-tocopherol during seed burial and dormancy. It is concluded that in X. peregrina and X. bialata, (i) burial causes significant changes in the phytohormone levels of seeds; (ii) secondary dormancy is induced in seeds; (iii) a GA(4) decrease, rather than an ABA increase, seems to be involved in the induction of secondary dormancy; and (iv) reductions in α-tocopherol in buried seeds are not necessarily indicative of reduced germination capacity.

ABA Controls H2O2 Accumulation Through the Induction of OsCATB in Rice Leaves Under Water Stress

The production of both ABA and H₂O₂ is induced by drought and can act as signals under stress conditions. We investigated the relationships between ABA, H₂O₂ and catalase (CAT) in rice leaves when rice seedlings were treated with polyethylene glycol as water stress treatment. As a key gene in ABA biosynthesis, OsNCED3 was significantly induced in rice by water stress treatment and such induction preceded the rapid increase in ABA. Water stress inhibited the expression of CATA and CATC but substantially enhanced the expression of CATB. Exogenously applied ABA promoted the expression of CATB also and inhibited the expression of CATC in a concentration-dependent manner. When ABA production was inhibited by using ABA biosynthesis inhibitors nordihydroguaiaretic acid and tungstate, expression of CATB was also subdued while CATC was enhanced under the water stress. Accumulation of H₂O₂ was also reduced when endogenous ABA production was inhibited and showed a correlation with the total activity of catalases. Our results suggest that water stress-induced ABA prevents the excessive accumulation of H₂O₂, through the induction of the expression of CATB gene during water stress.

Root signalling and modulation of stomatal closure in flooded citrus seedlings

In this work, we studied the sequence of responses induced by flooding in citrus plants, with the aim of identifying the signals that lead to stomatal closure. One-year-old seedlings of Carrizo citrange, grown in sand under greenhouse conditions, were waterlogged for 35 d and compared with normally watered well-drained plants. Significant decreases in stomatal conductance and transpiration were detected between flooded and control seedlings from a week after the beginning of the experiment. However ABA concentration in leaves only started to increase after three weeks of flooding, suggesting that stomata closed in the absence of a rise in foliar ABA. Therefore, stomatal closure in waterlogged seedlings does not appear to be induced by ABA, at least during the early stages of flood-stress. The low levels of ABA detected in roots and xylem sap from flooded seedlings indicated that it is very unlikely that the ABA increase in the leaves of these plants is due to ABA translocation from roots to shoots. We propose that ABA is produced in old leaves and transported to younger leaves. Flooding had no effect on water potential or the relative water content of leaves. Soil flooding reduced root hydraulic conductance in citrus seedlings. This effect was already evident after a week of waterlogging, and at the end of the experiment, flood-stressed seedlings reached values of root hydraulic conductance below 12% of that of control plants. This reduction was related to down-regulation of the expression of PIP aquaporins. In addition, whole plant transpiration was reduced by 56% after 35 d under flooding conditions. Flood-stress also decreased the pH of sap extracted from citrus roots. Evidence is presented suggesting that acidosis induced by anoxic stress in roots causes gating of aquaporins, thereby decreasing hydraulic conductance. Additionally, stomatal closure finely balances-out low pH-mediated losses of root hydraulic conductance therefore maintaining stable leaf hydration.

The two α-dox genes of Nicotiana attenuata: overlapping but distinct functions in development and stress responses

BackgroundPlant fatty acid α-dioxygenases (α-DOX) are oxylipin-forming enzymes induced by biotic and abiotic stresses, which also participate in developmental processes. In Nicotiana attenuata, herbivory strongly induces the expression of an α-dox1 gene. To determine its role, we silenced its expression using Agrobacterium-mediated plant transformation with an inverted repeat construct. More than half of the transformed lines showed a severe dwarf growth phenotype that was very similar to the phenotype of tomato plants mutated at a second α-dox isoform. This led us to identify the corresponding α-dox2 gene in N. attenuata and examine the regulation of both α-dox genes as well as the consequences of their silencing in plant development and anti-herbivore defense.ResultsThe transformed lines exhibiting a dwarf growth phenotype are co-silenced for both α-dox genes resulting in a nearly complete suppression of α-DOX activity, which is associated with increases in ABA, JA and anthocyanin levels, all metabolic signatures of oxidative stress. The other lines, only silenced for α-dox1, developed similarly to wild-type plants, exhibited a 40% reduction of α-DOX activity resulting in a 50% reduction of its main product in planta (2-HOT) and showed no signs of oxidative stress. In contrast to α-dox1, the expression of α-dox2 gene is not induced by wounding or elicitors in the oral secretions of Manduca sexta. Instead, α-dox2 is expressed in roots and flowers which lack α-dox1 expression, but both genes are equally regulated during leaf maturation. We transiently silenced α-dox gene copies with gene-specific constructs using virus induced gene silencing and determined the consequences for plant development and phytohormone and 2-HOT levels. While individual silencing of α-dox1 or α-dox2 had no effects on plant growth, the co-suppression of both α-dox genes decreased plant growth. Plants transiently silenced for both α-dox genes had increased constitutive levels of JA and ABA but silencing α-dox1 alone resulted in lower M. sexta-induced levels of JA, 2-HOT and ABA.ConclusionsThus, both α-dox isoforms function in the development of N. attenuata. In leaf maturation, the two α-dox genes have overlapping functions, but only α-dox2 is involved in root and flower development and only α-dox1 functions in anti-herbivore defense.

EFFECT OF PLANT HORMONES ON INVERTASE ACTIVITY AND ON PETAL GROWTH OF CUT ROSE

Cell expansion caused by water influx in petal cells is an important mechanism responsible for the flower opening process. It is believed that carbohydrates are key factors as an osmolite to draw water into cells. To clarify the mechanism of flower opening and to improve cut flower quality, we investigated sucrose metabolism in rose petals using attached and cut flowers. We have been probing into possibility that the quality of cut rose flowers can be improved by controlling the invertase activity in postharvest condition. In this present study, we tried to clarify the effect of plant hormones on invertase activity and on the petal growth of cut roses. First we used petal discs of Rosa 'FEbesa' for plant hormone (IAA, ABA, GA 3 , and JA) treatment. The results showed that IAA and GA 3 could increase the activity of cell-wall bound invertase, and IAA, GA 3 , and ABA increase that of vacuolar invertase. For applied experiments with plant hormones, we used a scent rose Rosa 'Meivildo', which has a short vase life. We found some of the plant hormones (IAA and JA) in vase solution affected the petal growth of cut rose. For example, flower opening was promoted by NAA treatment and delayed by JA treatment compared with control. We are now investigating about sugar metabolism including invertase activity in rose petal on each treatment.

Differences in stomatal responses and root to shoot signalling between two grapevine varieties subjected to drought

A comparative study on stomatal control between two grapevine varieties (Vitis vinifera L. cvs Sabatiano and Mavrodafni) differing in their ability for drought adaptation was conducted using 3-year-old own-rooted plants. The plants were subjected to prolonged drought stress by withholding irrigation water. The relationship between predawn water potential and maximum stomatal conductance indicated significant differences in stomatal sensitivity to drought between the two varieties. Stomatal closure occurred at higher values of predawn water potential in Sabatiano compared with Mavrodafni. No significant differences were found in plant hydraulic conductance and osmotic potential at full turgor (π100) between the two varieties. Leaf and root ABA concentrations increased more rapidly in Mavrodafni compared with Sabatiano at the beginning of the drought period. Furthermore, Mavrodafni also exhibited significantly higher xylem pH values as well as higher stomatal sensitivity to ABA and pH increase compared with Sabatiano. Results suggest that these two grapevine varieties might have evolved different strategies in order to adapt under drought conditions. In particular, the greater ability for drought adaptation in Sabatiano might be attributed to the more efficient regulation of stomatal closure. In contrast, chemical signalling in Mavrodafni seems to be the main mechanism for drought adaptation.