Leaf Abscisic Acid Concentration Research Articles

Recently-released genotypes of naked oat (Avena nuda L.) out-yield early releases under water-limited conditions by greater reproductive allocation and desiccation tolerance

Naked oat (Avena nuda L.) is becoming increasingly popular because of its high nutritive value and increased yields. As naked oat is grown in marginal environments, one of the limitations to yield is drought stress. In this study conducted in the field and a rainout shelter, the yield, water relations, and physiological and biochemical responses to drought of six genotypes, three released since 2008 (recently-released, RR) and three genotypes released at least 60 years earlier (early-released, ER) were compared. The grain yield, harvest index (HI) and water use efficiency for grain were higher in the RR than ER genotypes under rainfed and irrigated conditions in the field and under drought and well-watered conditions in the rainout shelter. Aboveground biomass and HI had significant direct effects on grain yield, while leaf dry weight was negatively associated with grain yield in the rainout shelter. During a progressive soil drying experiment, the threshold soil water content (SWC) when stomatal conductance and photosynthesis began to decrease was lower in the RR [48–52% field capacity (FC)] than ER (54–58% FC) genotypes, but whole plant transpiration began to decrease when the leaf water potential and relative water content began to decrease at a threshold SWC of 31–44% FC in both the RR and ER genotypes. The beginning of the decrease in stomatal conductance and photosynthesis was associated with the increase in leaf abscisic acid concentration, but higher osmolyte accumulation, greater osmotic adjustment and less lipid peroxidation in the RR genotypes than the ER genotypes occurred at low SWC (below 30% FC) and are associated with greater desiccation tolerance in the RR genotypes. We conclude that the higher yields in the RR genotypes of naked oat are associated with selection for higher reproductive allocation and desiccation tolerance. The role of stomatal closure and osmotic adjustment on adaptation to drought are discussed.

Effect of the transgenerational exposure to elevated CO2 on the drought response of winter wheat: Stomatal control and water use efficiency

Climate change predicts more frequent drought spells along with an elevation in atmospheric CO2 concentration (e[CO2]). Although the responses of winter wheat (Triticum aestivum L.) plants to drought or a single generation exposure to e[CO2] have been well documented, the transgenerational effect of e[CO2] in combination of drought on stomatal behavior, plant water consumption and water use efficiency (WUE) have not been investigated. Seeds harvested from plants after two generations (2014–2015) continuously grown in ambient CO2 (a[CO2], 400μmolL−1) and e[CO2] (800μmolL−1) were sown in 4L pots, and the plants were grown separately in greenhouse cells with either a[CO2] or e[CO2]. At stem elongation stage, in each of the cells half of the plants were subjected to progressive drought stress until all the plant available soil water was depleted, and the other half were well-watered and served as controls. The results showed that transgenerational exposure of the winter wheat plants to e[CO2] could attenuate the negative impact of drought stress on dry biomass (DM) and WUE. The modulations of multi-generational e[CO2] on leaf abscisic acid concentration, stomatal conductance, and leaf water status could have contributed to the enhanced DM and WUE. These findings provide new insights into the response of wheat plants to a future drier and CO2-enriched environment.

Relationships between the Number of First-Flush Flowers and Leaf Water Potential or Leaf ABA Content Affected by Varying Degrees of Water Stress in Meiwa Kumquat (<i>Fortunella crassifolia</i> Swingle)

Relationships between the Number of First-Flush Flowers and Leaf Water Potential or Leaf ABA Content Affected by Varying Degrees of Water Stress in Meiwa Kumquat (<i>Fortunella crassifolia</i> Swingle)

Gene expression and physiological responses associated to stomatal functioning in Rosa × hybrida grown at high relative air humidity

High relative air humidity (RH≥85%) during growth disturbs stomatal functioning, resulting in excessive water loss in conditions of high evaporative demand. We investigated the expression of nine abscisic acid (ABA)-related genes (involved in ABA biosynthesis, oxidation and conjugation) and two non-ABA related genes (involved in the water stress response) aiming to better understand the mechanisms underlying contrasting stomatal functioning in plants grown at high RH. Four rose genotypes with contrasting sensitivity to high RH (one sensitive, one tolerant and two intermediate) were grown at moderate (62±3%) or high (89±4%) RH. The sensitive genotype grown at high RH showed a significantly higher stomatal conductance (gs) and water loss in response to closing stimuli as compared to the other genotypes. Moreover, high RH reduced the leaf ABA concentration and its metabolites to a greater extent in the sensitive genotype as compared to the tolerant one. The large majority of the studied genes had a relevant role on stomatal functioning (NCED1, UGT75B2, BG2, OST1, ABF3 and Rh-APX) while two others showed a minor contribution (CYP707A3 and BG1) and AAO3, CYP707A1 and DREB1B did not contribute to the tolerance trait. These results show that multiple genes form a highly complex regulatory network acting together towards the genotypic tolerance to high RH.

Development of screening method for drought tolerance in cotton genotypes based on ABA, chlorophyll stability index and drought tolerant index

Drought stress adversely affects the growth, development and ultimately yield of cotton. The growth and productivity of cotton plants depend largely on their vulnerability to environmental stress. Water stress is commonly attributed to situations where the water loss exceeds sufficient absorption intensity causing a decrease in plant water content, turgor reduction and, consequenctly, a decrease in cellular expansion and alterations of various essential physiological and biochemical processes that can affect growth or productivity. The experiment was conducted by adopting Factorial Randomized Block Design with three replications. The treatments comprised of water stress imposed at vegetative, squaring and boll development stages of crop growth.Withholding water at any growth stage significantly increased the leaf ABA content. Among the different treatments, stress at squaring had a major impact over the ABA quantity enhancement. Chlorophyll stability index is a measure of integrity of membrane or heat stability of the pigments under stress conditions. The genotype KC 2 X MCU 13 showed tolerance to water stress as it accumulated relatively higher ABA.

Different causes of photosynthetic decline and water status in different stages of girdling in Alhagi sparsifolia Shap. (Fabaceae)

Phloem girdling can cause decline of photosynthetic rate (Pn), and the reason for Pn decline had been attributed to the reduction of stomatal conductance (Gs) and end-product feedback inhibition. In order to explore the reason for Pn decline, the different stages of girdling—control, semi-girdling (SG), and full-girdling (FG)—were performed on Alhagi sparsifolia Shap. (Fabaceae) on the southern rim of the Taklamakan Desert. Our results showed that on the 1st day, abscisic acid (ABA) content and water use efficiency (WUE) increased, and Gs, Pn, and transpiration rate (Tr) decreased in the full-girdled leaf. On the 30th day, leaf ABA content, leaf starch content, and leaf soluble sugar content increased in the full-girdled leaf, and Gs, Pn, Tr, WUE, root starch content, root soluble sugar content, chlorophyll (Chl) content, maximum photochemical efficiency (Fv/Fm), and leaf water potential (Ψleaf) all decreased in the full-girdled leaf. SG showed no physiological change on the 1st day, whereas on the 30th day, the change was similar to FG, although the degree was less. The result of the present work implied that the reason for Pn decline in girdling may depend on time. In the short term, girdling (FG)-induced Pn decline was due to ABA accumulation, which resulted in the reduction of Gs. In the long term, however, Pn decline caused by girdling was due to many factors, including Gs reduction, which resulted from ABA accumulation, carbohydrate feedback inhibition, degradation of Chl content, decreasing of Fv/Fm, and deterioration of Ψleaf. In addition, a portion (half) of the phloem cannot undertake the transport work conducted by the whole phloem, and thus the girdled half circle of the phloem would lead to a similar effect to FG in the long term, although the degree was less.

Abscisic acid metabolic genes of wheat (Triticum aestivum L.): identification and insights into their functionality in seed dormancy and dehydration tolerance.

The three homeologues of wheat NCED2 were identified; the wheat NCED2A and CYP707A1B affect seed ABA level and dormancy but not leaf ABA level and transpirational water loss in Arabidopsis. Biosynthesis and catabolism of abscisic acid (ABA) in plants are primarily regulated by 9-cis-epoxycarotenoid dioxygenases (NCEDs) and ABA 8'-hydroxylase (ABA8'OH), respectively. The present study identified the complete coding sequences of a second NCED gene, designated as TaNCED2, and its homeologues (TaNCED2A, TaNCED2B and TaNCED2D) in hexaploid wheat, and characterized its functionality in seed dormancy and leaf dehydration tolerance using the TaNCED2A homeologue. The study also investigated the role of the B genome copy of the cytochrome P450 monooxygenase 707A1 (CYP707A1) gene of hexaploid wheat (TaCYP707A1B), which encodes ABA8'OH, in regulating the two traits as this has not been studied before. Ectopic expression of TaNCED2A and TaCYP707A1B in Arabidopsis resulted in altered seed ABA level and dormancy with no effect on leaf ABA content and transpirational water loss. To gain insights into the physiological roles of TaNCED2 and TaCYP707A1 in wheat, the study examined their spatiotemporal expression patterns and determined the genomic contributions of transcripts to their total expression.

Improving agronomic water use efficiency in tomato by rootstock-mediated hormonal regulation of leaf biomass

Water availability is the most important factor limiting food production, thus developing new scientific strategies to allow crops to more efficiently use water could be crucial in a world with a growing population. Tomato is a highly water consuming crop and improving its water use efficiency (WUE) implies positive economic and environmental effects. This work aimed to study and exploit root-derived hormonal traits to improve WUE in tomato by grafting on selected rootstocks. Firstly, root-related hormonal parameters associated to WUE were identified in a population of recombinant inbred lines (RILs) derived from the wild tomato species Solanum pimpinellifolium. A principal component analysis (PCA) revealed that some hormonal traits were associated with productivity (plant biomass and photosynthesis) and WUE in the RIL population. Leaf ABA concentration was associated to the first component (PC1) of the PCA, which explained a 60% of the variance in WUE, while the ethylene precursor ACC and the ratio ACC/ABA were also associated to PC1 but in the opposite direction. Secondly, we selected RILs according to their extreme biomass (high, B, low, b) and water use (high, W, low, w), and studied the differential effect of shoot and root on WUE by reciprocal grafting. In absence of any imposed stress, there were no rootstock effects on vegetative shoot growth and water relations. Finally, we exploited the previously identified root-related hormonal traits by grafting a commercial tomato variety onto the selected RILs to improve WUE. Interestingly, rootstocks that induced low biomass and water use, ‘bw’, improved fruit yield and WUE (defined as fruit yield/water use) by up to 40% compared to self-grafted plants. Although other hormonal factors appear implicated in this response, xylem ACC concentration seems an important root-derived trait that inhibits leaf growth but does not limit fruit yield. Thus tomato WUE can be improved exploiting rootstock-derived hormonal signals which control leaf growth.

Nitrogen Sustains Seed Yield of Quinoa Under Intermediate Drought

AbstractQuinoa (Chenopodium quinoa Willd.) is a promising crop for food security in dry areas. Studies have been conducted to define nitrogen (N) fertilization levels and to understand the responses of quinoa to drought, but little is known about the response of this crop to N fertilization under drought stress. The aim of this study was to investigate whether N fertilization could improve quinoa yield and physiology under limited water. A greenhouse experiment was carried out with quinoa grown at four N fertilization levels (0, 0.2, 0.4 and 0.6 g N pot−1) and two watering treatments (progressive drought and full irrigation; 10 and 98 % of pot water holding capacity, respectively). Results of this experiment showed that N may confer a certain degree of drought tolerance to quinoa as seed quality and yield of N‐fertilized plants were not affected by drought stress. Responses such as faster stomatal closure, reduced leaf water potential, higher leaf abscisic acid (ABA) concentration and particularly an improved N remobilization in N‐fertilized plants may have played a role in sustaining seed yield in the drought‐stressed treatment. These results under controlled conditions serve as a basis to elucidate drought tolerance mechanisms activated with N fertilization and to define the use of N in management practices under semi‐arid environments.

Effect of supplemental irrigation on the relationships between leaf ABA concentrations, tiller development and photosynthate accumulation and remobilization in winter wheat

Drought after the jointing stage restricted the growth and yield formation in wheat. Supplemental irrigation (SI) at Z31 (Zadoks Stage 31) reduced the ABA concentrations in the leaves of the inferior tillers (T3 and T10) and improved the survival rate of the tillers. Additional SI at Z60 reduced the ABA concentrations in the flag leaves of ear-bearing stems after anthesis and increased the assimilate accumulation and the 1000-grain weight. These two SIs increased the yield by 16.7–32.2 % compared with a rainfed control (W0). Delaying the first SI from Z31 to Z34 or Z39 reduced the ABA concentrations in the leaves of the main stem and superior tillers (T1 and T2) but increased the ABA concentrations in the leaves of the inferior tillers at Z45 and reduced the survival rate of the tillers. Delaying SI from Z31 and Z60 (W1) to Z34 and Z69 (W2) increased the partitioning of the recent (14C-labelled) assimilate to the stems plus sheaths and stalk plus glume at anthesis and the grains at maturity and increased the 1000-grain weight and the grain yield significantly. However, if SI was applied too late, i.e., at Z39 and Z77 (W3), the redistribution of the recent assimilate from the vegetative organs to the grain after anthesis and the grain yield at maturity were reduced. These data suggested that: (1) a lower soil moisture at the early jointing stage elevated the ABA concentrations in the inferior tillers and inhibited their growth; (2) if SI was applied too late (W3) senescence of the inferior tillers could not be halted; and (3) low ABA concentrations in the leaves during the later grain filling following the late SI (W3) were correlated with a reduced transfer of assimilates from the vegetative organs to the grain, leading to a significant reduction in the grain weight at maturity.

Root-to-shoot ABA signaling does not contribute to genotypic variation in stomatal functioning induced by high relative air humidity

High relative air humidity (RH ≥85%) during leaf expansion hampers stomatal responsiveness to closing stimuli, a genotype-dependent effect. Genotypes with reduced stomatal closure in response to closing stimuli (i.e., sensitive genotypes) show low bulk leaf abscisic acid concentration ([ABA]). We hypothesized that the amount of ABA produced in the roots and delivered with the transpiration stream to the leaves is a critical step for a proper stomatal functioning in high RH-grown plants. Ten genotypes from a cut rose tetraploid population were grown at moderate (62%) or high (89%) RH. Stomatal anatomy and responsiveness to desiccation or ABA feeding were evaluated. Root and leaf petiole xylem sap [ABA] were quantified, and ABA delivery rate from root-to-shoot was estimated. High RH reduced stomatal responsiveness to both closing stimuli in the sensitive genotypes, whereas it had a non-significant effect in the tolerant ones. Estimates of [ABA] in root xylem sap at transpirational flow rate were not related to the genotypic differences in the sensitivity to high RH. However, high RH increased this concentration irrespective of the genotype, probably due to a reduced dilution of the [ABA] in the xylem sap as a result of a lower transpiration rate compared to moderate RH-grown plants. Leaf petiole xylem sap [ABA] was neither related to the genotypic differences in the sensitivity to high RH nor it was affected by RH. We concluded that genotypic differences in the stomatal sensitivity to high RH cannot be explained by changes in the [ABA] delivered with the transpiration stream from the roots to the leaves.

Differential Responses of Antioxidants, Abscisic Acid, and Auxin to Deficit Irrigation in Two Perennial Ryegrass Cultivars Contrasting in Drought Tolerance

Water deficit is a major limiting factor for grass culture in many regions with physiological mechanisms of tolerance not yet well understood. Antioxidant isozymes and hormones may play important roles in plant tolerance to water deficit. This study was designed to investigate antioxidant enzymes, isozymes, abscisic acid (ABA), and indole-3-acetic acid (IAA) responses to deficit irrigation in two perennial ryegrass (Lolium perenne L.) cultivars contrasting in drought tolerance. The plants were subjected to well-watered {100% container capacity, 34.4% ± 0.21% volumetric moisture content (VWC), or deficit irrigation [30% evapotranspiration (ET) replacement; 28.6% ± 0.15% to 7.5% ± 0.12% VWC]} conditions for up to 8 days and rewatering for 4 days for recovery in growth chambers. Deficit irrigation increased leaf malondialdehyde (MDA) content in both cultivars, but drought-tolerant Manhattan-5 exhibited lower levels relative to drought-sensitive Silver Dollar. Superoxide dismutase (SOD) activity declined and then increased during water-deficit treatment. ‘Manhattan-5’ had higher SOD activity and greater abundance of SOD1 isozyme than ‘Silver Dollar’ under water deficit. Deficit irrigation increased catalase (CAT) and ascorbate peroxidase (APX) activity in ‘Manhattan-5’, but not in ‘Silver Dollar’. ‘Manhattan-5’ had higher CAT, APX, and peroxidase (POD) activity than ‘Silver Dollar’ during water limitation. Deficit irrigation increased mRNA accumulation of cytosolic cupper/zinc SOD (Cyt Cu/Zn SOD), whereas gene expression of manganese SOD (Mn SOD) and peroxisome APX (pAPX) were not significantly altered in response to deficit irrigation. No differences in Cyt Cu/Zn SOD, Mn SOD, and pAPX gene expression were found between the two cultivars under deficit irrigation. Water limitation increased leaf ABA and IAA contents in both cultivars, with Silver Dollar having a higher ABA content than Manhattan-5. Change in ABA level may regulate stomatal opening and oxidative stress, which may trigger antioxidant defense responses. These results indicate that accumulation of antioxidant enzymes and ABA are associated with perennial ryegrass drought tolerance. Activity and isozyme assays of key antioxidant enzymes under soil moisture limitation can be a practical screening approach to improve perennial ryegrass drought tolerance and quality.

Cold Acclimation Treatment–induced Changes in Abscisic Acid, Cytokinin, and Antioxidant Metabolism in Zoysiagrass (Zoysia japonica)

Zoysiagrass (Zoysia spp.), a warm-season turfgrass species, experiences freezing damage in many regions. The mechanisms of its cold acclimation and freezing tolerance have not been well understood. This study was designed to investigate effects of cold acclimation treatment on leaf abscisic acid (ABA), cytokinin (transzeatin riboside (t-ZR), and antioxidant metabolism associated with freezing tolerance in zoysiagrass (Zoysia japonica). ‘Chinese Common’ zoysiagrass was subjected to either cold acclimation treatment with temperature at 8/2 °C (day/night) and a photosynthetically active radiation (PAR) of 250 µmol·m−2·s−1 over a 10-hour photoperiod or normal environments (temperature at 28/24 °C (day/night), PAR at 400 µmol·m−2·s−1 and 14-hour photoperiod) for 21 days in growth chambers. Cold treatment caused cell membrane injury as indicated by increased leaf cell membrane electrolyte leakage (EL) and malondialdehyde (MDA) content after 7 days of cold treatment. Cold treatment increased leaf ABA and hydrogen peroxide content and reduced t-ZR content. Leaf superoxide dismutase (SOD), ascorbate peroxidase (APX) activity, and proline content increased, whereas catalase (CAT) and peroxidase (POD) activity declined in response to cold treatment. Cold treatment increased freezing tolerance as LT50 declined from −4.8 to −12.5 °C. The results of this study indicated that cold acclimation treatment might result in increases in ABA and H2O2, which induce antioxidant metabolism responses and improved freezing tolerance in zoysiagrass.

Overexpression of an ABA biosynthesis gene using a stress-inducible promoter enhances drought resistance in petunia.

The response of plants to drought stress includes reduced transpiration as stomates close in response to increased abscisic acid (ABA) concentrations. Constitutive overexpression of 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in ABA biosynthesis, increases drought resistance, but causes negative pleiotropic effects on plant growth and development. We overexpressed the tomato NCED (LeNCED1) in petunia plants under the control of a stress-inducible promoter, rd29A. Under water stress, the transgenic plants had increased transcripts of NCED mRNA, elevated leaf ABA concentrations, increased concentrations of proline, and a significant increase in drought resistance. The transgenic plants also displayed the expected decreases in stomatal conductance, transpiration, and photosynthesis. After 14 days without water, the control plants were dead, but the transgenic plants, though wilted, recovered fully when re-watered. Well-watered transgenic plants grew like non-transformed control plants and there was no effect of the transgene on seed dormancy.

Screening for intrinsic water use efficiency in a potato dihaploid mapping population under progressive drought conditions

A drought screening experiment focusing on intrinsic water use efficiency (WUEi) was carried out among 132 clones belonging to a dihaploid potato mapping population. The clones were exposed to progressive soil drying during a five-day period in a greenhouse pot experiment. Analysis of the underlying variables was done based on a multivariate data analysis strategy. The strategy successfully divided the clones into WUEi performance categories. Differences between clonal WUEi responses were traced back to differences in the net photosynthetic rate. Stomatal conductance (gs) did not vary significantly between the clones. Leaf abscisic acid (ABA) concentration and leaf water potential were found to reflect known isohydric behaviour for potato, and a non-linear relationship could be established for gs and leaf ABA concentration across the WUEi groups. Similarly, a common non-linear relationship between leaf ABA concentration and soil water potential was found. The latter findings suggest that the investigated population did not harbour significant genetic variation as to ABA production as function of soil desiccation level or with respect to the sensitivity of stomatal aperture vis-à-vis leaf ABA concentration and soil water potential.

Differential physiological and biochemical responses to drought in grapevines subjected to partial root drying and deficit irrigation

The effects of two different irrigation methodologies, partial root drying (PRD) and deficit irrigation (DI), on grapevines (Vitis vinifera L., cv. Mavrodafni) physiological and biochemical parameters were studied using split-rooted potted plants. Five irrigation treatments were applied: fully irrigated (FI) at both parts of the rootzone to soil capacity; deficit irrigated (DI50 and DI25) receiving 50% and 25% irrigation water of FI plants, respectively, to the entire rootzone and partial root drying (PRD50 and PRD25) receiving 50% and 25% irrigation water of FI plants, respectively, which was successively applied to one and the other part of the rootzone. Compared with DI50, PRD50 plants exhibited higher stomatal conductance and photosynthetic rate maintaining more favorable plant water status throughout the experimental period. On the contrary, no significant differences in physiological parameters between PRD25 and DI25 plants were observed, suggesting that irrigation amount could influence different irrigation methodologies effects on plant's performance. Leaf abscisic acid (ABA) concentration at the end of the drought period was significantly higher in DI compared to PRD plants while the opposite trend was evident concerning cytokinins (Cks) concentration. Irrespective the irrigation amount applied, stomatal conductance (gs) in DI plants exhibited the strongest correlation with leaf abscisic acid (ABA) concentration among the treatments but this relationship was significantly weakened when gs was regressed against ABA/CKs ratio. PRD plant's stomatal conductance was also strongly correlated with leaf abscisic acid (ABA) concentration but this relationship was markedly improved when ABA/CKs ratio was used. These results imply a more pronounced role of CKs in mediating stomatal responses in PRD plants. In contrast in DI grapevines ABA concentration seemed to dominate stomatal responses to drought.

Physiological factors affecting intrinsic water use efficiency of potato clones within a dihaploid mapping population under well-watered and drought-stressed conditions

Optimizing crops water use is essential for ensuring food production under future climate scenarios. Therefore, new cultivars that are capable of maintaining production under limited water resource are needed. This study screened for clonal differences in intrinsic water use efficiency (WUEi) within a dihaploid potato (Solanum tuberosum L.) mapping population under well-watered (WW) and drought-stress (DS) conditions. The factorial dependency of WUEi on several plant bio-physiological traits was analyzed, and clonal difference of WUEi was compared. Significant differences in WUEi were found among the clones within the population. Under WW the two clones showing the highest WUEi were significantly different from the two lowest WUEi performing clones. This could only be seen as a trend under DS. Under WW, WUEi differences were closely associated to net photosynthetic rate (An) and nitrogen isotope composition (δ15N) in the leaf biomass, but did not relate to stomatal conductance (gs) and carbon isotope composition (δ13C) in the leaf biomass. An was found to correlate significantly with leaf nitrogen concentration ([N]leaf) and chlorophyll content index (CCI) under WW. Leaf abscisic acid concentration did not correspond to the changes in gs, indicating that other factors might have been involved in controlling gs among the different clones. Collectively, the clonal differences in WUEi were attributed mainly to the variation in An, which in turn was influenced by plant N metabolism. Clones with high WUEi could be potentially used as material in future breeding programs. Furthermore CCI seemed to be a reliable tool in estimating the clonal An and thereby WUEi.

Mesophyll conductance decreases in the wild type but not in an ABA-deficient mutant (aba1) of Nicotiana plumbaginifolia under drought conditions.

Under drought conditions, leaf photosynthesis is limited by the supply of CO2 . Drought induces production of abscisic acid (ABA), and ABA decreases stomatal conductance (gs ). Previous papers reported that the drought stress also causes the decrease in mesophyll conductance (gm ). However, the relationships between ABA content and gm are unclear. We investigated the responses of gm to the leaf ABA content [(ABA)L ] using an ABA-deficient mutant, aba1, and the wild type (WT) of Nicotiana plumbaginifolia. We also measured leaf water potential (ΨL ) because leaf hydraulics may be related to gm . Under drought conditions, gm decreased with the increase in (ABA)L in WT, whereas both (ABA)L and gm were unchanged by the drought treatment in aba1. Exogenously applied ABA decreased gm in both WT and aba1 in a dose-dependent manner. ΨL in WT was decreased by the drought treatment to -0.7 MPa, whereas ΨL in aba1 was around -0.8 MPa even under the well-watered conditions and unchanged by the drought treatment. From these results, we conclude that the increase in (ABA)L is crucial for the decrease in gm under drought conditions. We discuss possible relationships between the decrease in gm and changes in the leaf hydraulics.

Reprint of “Contrasting stomatal regulation and leaf ABA concentrations in wheat genotypes when split root systems were exposed to terminal drought”

Wheat grown in the Mediterranean-type environments of southern Australia is often exposed to end-of-season drought (terminal drought). During the development of terminal drought, soil dries from the top of the profile exposing the upper part of the root system to water stress while deeper roots may still be able to access deeper soil water for grain filling. It is hypothesised that the part of the root system exposed to drying soil signals abscisic acid (ABA) production and the corresponding rise in ABA concentration in leaves causes partial stomatal closure, regulating the extraction of available water at depth. In the first step to test this hypothesis, a glasshouse experiment was conducted to identify contrasting stomatal response to terminal drought and production of ABA using four wheat genotypes adapted to different soil moisture environments. Terminal drought was induced by withholding water from anthesis in one half (WD) or both halves (DD) of the root system using split pots. Stomatal conductance decreased in all four genotypes in WD plants, but leaf ABA concentration and leaf water status differed. The cultivar Drysdale had higher leaf ABA concentrations and lower stomatal conductance, but leaf water status decreased. Leaf ABA concentration did not increase in WD plants of the breeding line IGW-3262, but stomatal conductance decreased and leaf water status was unchanged. All the genotypes behaved similarly under DD conditions, with increased leaf ABA concentration, lower stomatal conductance and severely dehydrated leaves. The possible causes of the above differences in leaf ABA concentration despite similar stomatal behaviour in wheat genotypes are discussed.

The lose of juvenility elicits adventitious rooting recalcitrance in apple rootstocks

For perennial woody plants, softwood cutting is an efficient technique for larger scale propagation and adventitious rooting of cuttings is one of the most crucial steps. To evaluate the significance of juvenility on adventitious rooting, rooting rates was compared between softwood cuttings collected from apomictic seedlings (juvenile), in vitro cultured plants (rejuvenated), suckers (juvenile like) and canopy shoots (adult) of reproductively mature trees in Malus xiaojinensis. After pre-treatment with indole-3-butytric acid (IBA) (3,000 mg L−1) + H2O2 (50 mM), rooting rates in cutting from juvenile, juvenile like and rejuvenated donor plants were significantly higher (>90 %) than that from adult trees. The effects of IBA on adventitious rooting were enhanced significantly by exogenous H2O2. After 15 passages of in vitro subculture, the micro-shoots from adult phase explants were rejuvenated successfully, marked by the elevated expression of miR156 in the leaflets of the micro-shoots. But the rooting ability of rejuvenated micro-shoots was recovered delayed at the 18th or 21st passage of subculture. During the process of rejuvenation, the leaf indole-3-acetic acid contents and the expressions of rooting related genes CKI1, ARRO-1, ARF7 and ARF19 increased significantly. In contrary, the leaf abscisic acid contents decreased. A lack of juvenility is the most important limiting factor governing adventitious rooting of softwood cuttings in apple rootstocks.