Hormonal responses to partial drying of the root system of Helianthus annuus

Plants of Helianthus annuus were pot-grown in soil, with approximately30% of the root system protruding through the base. After 7d, the upper part of the root system of half of the plants wasexposed to drought (internal roots) while the lower part waskept in aerated nutrient solution (protruding root). The treatmentrapidly reduced the internal roots' water content from 26.1to 21.9 g g^–1 dry weight (DW), while in protruding rootsof stressed plants it slowly and continuously decreased from31.9 to 25.2 g g^–1 DW. Leaf water content rapidly decreasedin treated plants from 7.4 to 6.4 g g^–1 DW in the first2d and then reached a plateau. In stressed plants leaf stomatalresistance was significantly higher in the first 3 d while leafwater potential was lower only on the last day. Abscisic acid (ABA) concentration in treated plants increasedsignificantly compared to the controls. In treated internalroots, ABA rose from the first day, reaching a maximum of 1.48±0.49nmol g^–1 DW after 3 d. In treated protruding roots a maximumof 0.99±0.09 nmol g^–1 DW was reached after 1 d.ABA concentration in the xylem sap increased 2 d and 3 d afterthe start of soil drying, with a maximum of 113±12nmoll^–1 during the third day. The ABA rise in the leaves oftreated plants was less significant. Indol-3yl-acetic acid (IAA) concentration in internal rootsof treated plants reached a maximum of 22.54±3.34 nmolg^–1 DW on the third day, then decreased dramatically.The protruding root system of control plants showed a maximumvalue of 16.05±1.77 nmol g^–1 DW on the sixth day. Little difference in cytokinin content of xylem sap was notedbetween control and treated plants. Hormonal variations in different parts of the plant are discussedin relation to drought stress. Key words: Soil drying, roots, ABA, IAA, cytokinins     

Characterization of phytohormonal and postharvest senescence responses of balsam fir (Abies balsamea (L.) Mill.) exposed to short-term low temperature

To fulfill the US Thanksgiving and Christmas tree markets, balsam fir (Abies balsamea (L.) Mill.) is generally harvested before the cold season, anecdotally leading to premature needle senescence. Accordingly, we tested the hypothesis that LT exposure before harvest induces specific hormonal changes and delays postharvest senescence and/or abscission in balsam fir. Two hundred and six seedlings exposed to two temperature treatments for 48?h, LT at 5?°C and controls at 22?°C were severed off roots and monitored for their postharvest needle senescence. Root and shoot (needles and buds) tissues were examined for major endogenous hormone metabolites. LT increased shoot ABA (2,007?ng?g^?1 DW) by 2.5× and decreased GA₄₄ (9.84?ng?g^?1 DW) by 3.5× over those in roots. LT did not alter cytokinins, auxins or any root hormonal concentration. With auxins, only IAA, IAA-Asp, IAA-Leu and IAA-Glu were detected and the concentrations of IAA and IAA-Asp in shoots were lower than those found in roots. Among cytokinins, shoot c-ZR (58.95?ng?g^?1 DW) and t-ZR (4.17?ng?g^?1 DW) were 3× higher than those in roots. Apart from GA₄₄, GA₉ (136.76?ng?g^?1 DW) was abundant in shoots. The PBL and PNL were 46 and 1.2?%, irrespective of treatments. LT seedlings held needles 11?days longer than the controls (122?days). In balsam fir, short-term LT exposure augmented ABA and decreased GA₄₄ levels in shoots and delayed postharvest needle senescence.     

Increased Synthesis of ABA in Partially Dehydrated Root Tips and ABA Transport from Roots to Leaves

Zhang, J. and Davies, W. J. 1987. Increased synthesis of ABAin partially dehydrated root tips and ABA transport from rootsto leaves.—J. exp. Bot. 38: 2015–2023. Isolated root tips of pea (Pisum sativum L. cv. Feltham First)and Commelina communis L. were air-dried until they lost between10% and 40% of their fresh weight, followed by a period of incubationat these reduced water contents. These treatments resulted inincreased ABA production, suggesting that root tips of bothspecies have the capacity to synthesize ABA in increased amountswhen water deficits develop in the root. The ABA concentrationin pea roots increased linearly as turgors fell below about0·15 M Pa and relative water contents (R WC) fell below90%. Commelina roots produced more ABA when RWC fell below asimilar value but the threshold turgor for increased ABA productionin Commelina roots was around 0·30 MPa. Roots of intact plants loaded with ABA as a result of incubationin solutions of varying concentrations provided ABA to leaveswhich resulted in increased ABA concentrations in the leaveswhen these were assayed several hours later. This occurred whenthese roots were not contributing substantially to transpirationalflux. Leaves on shoots that were enclosed and darkened and thereforenot transpiring, did not accumulate ABA from ‘loaded’roots. A role for root-sourced ABA in root-to-shoot communication ofthe effects of soil drying is discussed. Key words: ABA, roots, water relations     

Effect of alkaline and saline substrates on ABA contents,distribution and transport in plant roots

The distribution of the phytohormone abscisic acid (ABA) between plant and soil and within plants growing on an alkaline substrate has been studied in order to separate the true effect of high soil pH from any effects that might be a result of the high salinity normally observed in alkaline soils. Leaves of a range of plants grown in an alkaline and saline solid substrate (municipal solid waste incinerator bottom slag) exhibited higher ABA levels than leaves of control plants. In contrast, roots of most plants grown on alkaline and saline substrates, particularly those without an exodermis (various species of Fabaceae), had slightly lower than or comparable ABA contents to control roots. However, in corn roots (Zea maysL. cv. Garant FAO 240) which possess a well-developed exodermis, alkaline and saline conditions in the rhizosphere did not reduce the endogenous ABA concentration, because the leaching of ABA from corn roots into the rhizosphere was lower than that from Vicia faba (variety Dreifache Weisse) roots. ABA efflux from corn and Vicia roots into the soil solution was observed only during the first days of the experiments and thereafter became substantially decreased. Because the leaching of ABA from Vicia faba roots into the rhizosphere was higher than that from corn roots, the leaves of Vicia plants grown in alkaline soil at low salinity no longer exhibited an elevated ABA concentration. However, whilst the roots of corn plants grown on desalted slag retained ABA levels that were higher than those of the control, the ABA content of leaves was not significant higher than the controls. For this reason, root ABA retention must be enough to induce tolerance to alkalinity in corn plants and there is no need to implicate changes in ABA concentrations in the aerial parts of the plant as having a role in this tolerance. In alkaline soil substrates, considerable portions of the ABA synthesised in the roots leached out into the soil solution of the rhizosphere according to the anion trap concept. An exodermis substantially reduces this leakage. The transient nature of ABA efflux into the rhizosphere was a result of the fact that the salt stress itself was only a transient phenomenon due to a washout of salt by irrigation. The results match predictions of mathematical models describing the effect of alkaline pH on the distribution of abscisic acid within plants and between roots and the rhizosphere. Species that can retain root ABA in the face of its tendency to leach into the more alkaline compartment are able to tolerate these normally harmful sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hairy root cultures of Rehmannia glutinosa and production of iridoid and phenylethanoid glycosides

Hairy root lines through the infection of Agrobacterium rhizogenes strain (A4) were established from shoot tips and leaves of Rehmannia glutinosa Libosch. Ten lines of hairy roots were selected on the basis of biomass increase in half-strength Gamborg medium (¹/₂ B5). Transgenic status of the roots was confirmed by polymerase chain reaction using rolB and rolC specific primers. Iridoid glycosides (catalposide, loganin, aucubin and catalpol) and phenylethanoid glycosides (verbascoside and isoverbascoside) identified using HPLC?CESI?CMS, and their contents were compared with untransformed root culture and roots of 1-year-old field-grown plants of R. glutinosa by RP-HPLC. The growth and production of secondary metabolites in ten hairy root lines varied considerably as to the media. Woody plant (WP) medium displayed higher growth in terms of fresh (FW) and dry weights (DW) compared to ¹/₂ B5 medium. High-yielding hairy root lines produced higher amounts of loganin, catalposide, verbascoside and isoverbascoside in comparison to the untransformed root culture and roots of 1-year-old field-grown plants. The highest amounts of catalposide and loganin in transformed roots were 4.45?mg?g^?1 DW (RS-2 hairy root line) and 4.66?mg?g^?1 DW (RS-1 hairy root line), respectively. Aucubin and catalpol were detected in some lines in trace amounts. The highest amounts of verbascoside (16.9?mg?g^?1 DW) and isoverbascoside (3.46?mg?g^?1 DW) were achieved in RS-2 root line. The contents of catalposide, verbascoside and isoverbascoside in high-producing lines were several times higher than in untransformed root culture and roots of R. glutinosa plants grown in soil. Loganin and aucubin could not be detected in roots of field-grown plants. However, the levels of catalpol were much lower in the in vitro roots.     

Azospirillum brasilense ameliorates the response of Arabidopsis thaliana to drought mainly via enhancement of ABA levels

Production of phytohormones is one of the main mechanisms to explain the beneficial effects of plant growth‐promoting rhizobacteria (PGPR) such as Azospirillum sp. The PGPRs induce plant growth and development, and reduce stress susceptibility. However, little is known regarding the stress‐related phytohormone abscisic acid (ABA) produced by bacteria. We investigated the effects of Azospirillum brasilense Sp 245 strain on Arabidopsis thaliana Col‐0 and aba2‐1 mutant plants, evaluating the morphophysiological and biochemical responses when watered and in drought. We used an in vitro‐grown system to study changes in the root volume and architecture after inoculation with Azospirillum in Arabidopsis wild‐type Col‐0 and on the mutant aba2‐1, during early growth. To examine Arabidopsis development and reproductive success as affected by the bacteria, ABA and drought, a pot experiment using Arabidopsis Col‐0 plants was also carried out. Azospirillum brasilense augmented plant biomass, altered root architecture by increasing lateral roots number, stimulated photosynthetic and photoprotective pigments and retarded water loss in correlation with incremented ABA levels. As well, inoculation improved plants seed yield, plants survival, proline levels and relative leaf water content; it also decreased stomatal conductance, malondialdehyde and relative soil water content in plants submitted to drought. Arabidopsis inoculation with A. brasilense improved plants performance, especially in drought.     

自然干旱胁迫下长春花叶片和根部的激素和可溶性糖代谢变化

植物在离开生长环境较短时间内（1~6 h）会导致缓慢的表面水分散失,引起自然的干旱胁迫。本文以耐旱植物长春花（Catharanthus roseus）为材料,研究其在离土干旱胁迫中的脱落酸（ABA）及可溶性糖含量变化。结果表明,长春花根部ABA含量在正常条件下低于叶片中的含量,干旱胁迫促进了ABA在根部的积累,6 h时增加至最高值。蔗糖酸性转化酶活性可能受到ABA的诱导在胁迫6 h时最高,比对照高出30%左右。长春花叶片中总可溶性糖含量在对照条件下非常稳定,但在干旱胁迫过程中,其随着时间的延长呈现线性增加的趋势（r²=0.964）,蔗糖和已糖含量在胁迫过程中也呈增加的趋势,可能发挥着渗透调控节功能。     

The shikonin derivatives and pyrrolizidine alkaloids in hairy root cultures of Lithospermum canescens (Michx.) Lehm.

Hairy root cultures of Lithospermum canescens were established using three strains of Agrobacterium rhizogenes: ATCC 15834, LBA 9402 and NCIB 8196. Eight lines resulting from infection with A. rhizogenes ATCC 15834 demonstrated sufficient biomass increase and were submitted to further investigations. The contents of acetylshikonin (ACS) and isobutyrylshikonin (IBS) in transformed hairy roots made up ca. 10% of those observed in natural roots of L. canescens (24.35 and 14.48 mg g⁻¹ DW, respectively). One line, Lc1-D, produced the largest amounts of ACS (2.72 mg g⁻¹ DW) and IBS (0.307 mg g⁻¹ DW). Traces of pyrrolizidine alkaloids (PA), canescine and canescenine, were found in all lines of transformed hairy roots.     

Bioreactor application on adventitious root culture of <Emphasis Type="Italic">Astragalus membranaceus</Emphasis>

Astragalus membranaceus is one of the most widely used traditional medicinal herbs in China, but the time required to generate a useful product in the field production is long. The growth of adventitious root cultures was compared between cultures grown in solid, liquid, or a 5-L balloon-type bubble bioreactor. The maximum growth ratio (final dry weight/initial dry weight) was determined for adventitious roots grown in the bioreactor. Studies carried out to optimize biomass production of adventitious roots compared adventitious root growth from various inoculum root lengths, inoculum densities, and aeration volume in the bioreactors. The maximum growth ratio occurred in treatments with a 1.5-cm inoculum root length, with 30 g (fresh weight) of inoculum per bioreactor or with an aeration volume of 0.1 vvm (air volume/culture medium volume per min). The polysaccharide, saponin, and flavonoid content of roots from bioreactor-grown cultures were compared to roots from field-grown plants grown for 1 and 3 yr. Total polysaccharide content of adventitious roots in the bioreactor (30.0 mg g⁻¹ dry weight (DW)) was higher than the roots of 1-yr-old (13.8 mg g⁻¹ DW) and 3-yr-old (21.1 mg g⁻¹ DW) plants in the field. Total saponin (3.4 mg g⁻¹ DW) and flavonoid (6.4 mg g⁻¹ DW) contents were nearly identical to 3-yr-old roots and higher than that of 1-yr-old roots under field cultivation.     

Effect of biotic and abiotic elicitors on production of betulin and betulinic acid in the hairy root culture of Betula pendula Roth

Abstract

Betulin (B) and betulinic acid (BA) are two triterpenoids with a wide range of biological and medicinal activities in different organs of Betula pendula. This research aimed to increase the accumulation of B and BA in the hairy root culture of B. pendula by seven biotic and abiotic elicitors. Hairy root was induced in the stem’s inner bark of B. pendula using the C58C1 strain in the WPM (Woody Plant Medium). The effects of different concentrations of elicitors and different time of root harvest in hairy root culture of B. pendula showed that highest level of growth index (GI), B, and BA was acquired in treated hairy roots with chitosan (CTS), chlorocholine chloride (CCC) and chitosan nano-fiber (CTS NF). Highest GI of B. pendula hairy roots was 13 that was obtained in the roots treated with CTS 150?mg l^?1 on the 8th day. The highest content of BA was 1.3?mg g^?1 DW after treatment with 1?mg l^?1CCC on the 4th and 6th days and 200?mg l^?1CTS NF on the 10th day. The highest B content (0.94?mg g^?1DW) was obtained in the treated hairy root by 2?mg l^?1 CCC after 4 and 6?days.     

The effects of exogenous ABA applied to maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) roots on plant responses to chilling stress

This work aimed to discuss the effects of exogenous abscisic acid (ABA) on the root growth regulation of maize seedlings under chilling stress. The roots of the maize cultivar Zhengdan 958 were irrigated with ABA (10^?7, 10^?6, 10^?5 and 10^?4 M) at the third true leaf stage under chilling duration (0, 2, 4, 6, and 8 days). The biomass, the phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) enzyme activities, total phenolic and flavonoid contents, the ferric reducing ability of plasma (FRAP) antioxidant capacity, and 2,2-azinobis (3-ethlbenzothiazo-line-6-sulfonic acid) diammonium salt radical (ABTS^·+) scavenging capacity of the roots of maize seedlings were measured after the treatment. The results showed that appropriate concentrations of exogenous ABA effectively enhanced root biomass, increased PAL and PPO enzyme activities, and significantly increased total phenolic contents and flavonoid contents. Moreover, the ABA markedly improved the FRAP antioxidant capacity and ABTS^·+ scavenging capacity under low-temperature stress. These results indicate that ABA-treated maize seedlings are resistant to chilling stress and that the optimum concentration of ABA is 10^?5 M. Exogenous applications of ABA have a concentration effect in alleviating chilling stress, in which low concentrations have a promoting effect and high concentrations have an inhibiting effect.     

Dehydration of isolated roots of seven <Emphasis Type="Italic">Lupinus</Emphasis> species induces synthesis of different amounts of free,but not conjugated,abscisic acid

Abscisic acid (ABA) is recognised as an important hormone involved in root-to-shoot communication of drought stress in plants. This study aimed to determine whether isolated roots can produce both free and conjugated ABA (ABA–glucose ester) and whether Lupinus species vary in the synthesis of ABA in the roots when dehydrated. The concentration of free and conjugated ABA at 100 and 50% root water content was measured in the distal 10 mm of the roots of 3- to 5-day-old seedlings of seven Lupinus species with and without 10⁻⁵ M tetcyclacis, an inhibitor of the oxidative breakdown of ABA. When the root tips were exposed to tetcyclacis, the concentration of free ABA increased by 20% on average, suggesting that oxidative breakdown of free ABA was limited in the isolated Lupinus roots. The concentration of free ABA of the fully hydrated plants varied significantly among genotypes and more than doubled on average across genotypes with dehydration of the root tips to 50% water content. The concentration of conjugated ABA also varied significantly with species, but was only one-tenth the concentration of free ABA in the roots and did not change significantly with root dehydration or the inhibition of oxidative metabolism. The production of free ABA in response to the water deficit varied with species from +470% in L. digitatus to +33% in L. angustifolius. The small concentration and lack of increase of conjugated ABA with water deficit suggests that it is unlikely to have an important role as a root signal in response to soil drying in Lupinus species.     

Effects of Combined Abiotic Stresses on Growth,Trace Element Accumulation,and Phytohormone Regulation in Two Halophytic Species

Trace element contamination of lands is a serious environmental problem that limits yield and threatens human health. To study the combined effect of high salinity and toxic levels of trace elements on halophytes, the performance of two marsh species, Atriplex halimus and Suaeda fruticosa, grown for 1 month with an irrigation solution supplemented with 200 mM NaCl and 400 μM Cd²⁺ or 400 μM Cu²⁺ was evaluated. The effect of the combined stress conditions on hormone signaling was also assessed. Biomass production and chlorophyll content decreased under Cd²⁺ stress in both species, whereas Cu²⁺ had a lower impact on plant performance. The different plant sensibilities to the two trace elements assayed indicate that each metal has a different effect on plants. Furthermore, the deleterious effect of metal toxicity was alleviated when NaCl was added to the irrigation solution, demonstrating that NaCl improves plant performance and tolerance of halophytic species to cope with trace element intoxication. Results show that both species accumulated important quantities of Cd²⁺ and Cu²⁺ in roots (Cd²⁺: 2,690–3,130 μg g^?1 DW and Cu²⁺: 2,070–2,770 μg g^?1 DW); this finding allows us to classify these species among the hyperaccumulator plants. Cd²⁺ and Cu²⁺ differently affected endogenous phytohormone contents in both species. Data suggest an essential involvement of roots on the regulation of tolerance to trace elements. Therefore, indole-3-acetic acid levels increased in roots of both species irrigated with high levels of Cd²⁺, which suggests that the auxin may stimulate root promotion and growth under these stress conditions. Other compounds, classically considered as “stress hormones” showed very different patterns of accumulation. Whereas, salicylic acid (SA) levels in roots and leaves increased in response to Cd²⁺, root contents of jasmonic acid (JA), and abscisic acid (ABA) decreased. In leaves, the rambling pattern of accumulation observed for JA and ABA suggested the lack of a specific role in regulation against trace element toxicity. Together, data suggest that SA could act as a specific signal that detects trace element toxicity, whereas JA and ABA promote general responses against abiotic stress.     

Valepotriates accumulation in callus, suspended cells and untransformed root cultures of Valeriana glechomifolia

Summary Valeriana glechomifolia is an endemic species of southern Brazil, capable of accumulating, in all of its organs, the terpene derivatives known as valepotriates, the presumed sedative components of the roots of pharmaceutically used species of Valeriana. In vitro cultures of the plant were established and the accumulation of acevaltrate, didrovaltrate, and valtrate in callus, cell suspension, and untransformed root cultures was studied. Leaves of in natura plants and roots of micropropagated plantlets were used as the explants for callus induction and root culture establishment, respectively, on Gamborg B5 basal medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) alone or with kinetin (KIN). Culture growth and secondary metabolite yields were enhanced with 2,4-D (4.52μM) and KIN (0.93μM). Maximum valepotriate contents, quantified by HPLC, of acevaltrate (ACE) 2.6mg g⁻¹ DW, valtrate (VAL) 10.2mgg⁻¹ DW, and didrovaltrate (DID) 2.9mg g⁻¹ DW were observed in root cultures after 7–8wk of culture.     

Most stomatal closure in woody species under moderate drought can be explained by stomatal responses to leaf turgor

Reduced stomatal conductance (g_s) during soil drought in angiosperms may result from effects of leaf turgor on stomata and/or factors that do not directly depend on leaf turgor, including root‐derived abscisic acid (ABA) signals. To quantify the roles of leaf turgor‐mediated and leaf turgor‐independent mechanisms in g_s decline during drought, we measured drought responses of g_s and water relations in three woody species (almond, grapevine and olive) under a range of conditions designed to generate independent variation in leaf and root turgor, including diurnal variation in evaporative demand and changes in plant hydraulic conductance and leaf osmotic pressure. We then applied these data to a process‐based g_s model and used a novel method to partition observed declines in g_s during drought into contributions from each parameter in the model. Soil drought reduced g_s by 63–84% across species, and the model reproduced these changes well (r² = 0.91, P < 0.0001, n = 44) despite having only a single fitted parameter. Our analysis concluded that responses mediated by leaf turgor could explain over 87% of the observed decline in g_s across species, adding to a growing body of evidence that challenges the root ABA‐centric model of stomatal responses to drought.     

Effects of varied water regimes on root length,dry matter partitioning and endogenous plant growth regulators in sunflower (Helianthus annuus L.)

Abstract

A field experiment was conducted to quantify the effect of varied water regimes on root length, partitioning of dry matter and plant growth regulators by using sunflower genotypes differing in maturity and drought tolerance. Significant depressing effect of drought stress was evident on traits (i.e., reproductive dry matter, leaf area index and cytokinin concentrations in leaves). However, root/shoot, reproductive/vegetative ratios and Abscisic acid (ABA) concentration were found to increase under drought stress. Drought stress also changed the dry matter accumulation pattern of genotypes. In most cases it reduced the days to reach the maximum peak showing early senescence.

ABA was identified as a multi-functional plant growth regulator under drought stress, causing early senescence of plants and translocation of assimilates to the roots and reproductive part while root growth under drought stress was explained by the indole-acetic acid (IAA) concentrations. Maintaining higher cytokinin contents were involved in accumulation of higher reproductive dry matter under drought stress. Although ABA and IAA were both involved in the development of defense responses during the adaptation and survival to drought stress but higher productivity under drought stress was only realized through maintaining higher cytokinin contents.     

Effect of Water Stress Induced by Polyethylene Glycol on Growth,Proline Accumulation in <i>Agave americana</i> L.

The effect of water deficit was determined on both in vitro and soil seedling as well as in cells in suspension of Agave americana L. In order to do the establishment of cells, the formation of callus was induced; for it two auxins were evaluated: 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-mino-3,5,6-trichloropicolinic acid (picloram) at three concentrations (0.25, 0.5 and 0.75 mg L⁻¹) in three explants (leaf, root and meristems) cultured in MS semisolid medium. The callogenesis response was related to the type and section of the explant, as well as the regulator used, and a cell suspension was established using 0.5 mg L⁻¹ naphthaleneacetic acid (NAA) + 0.5 mg L⁻¹ Benzylaminopurine (BAP). Seedlings were exposed to polyethyleneglycol (15% and 30% w/v) with a water potential of −0.87 and −2.67 MPa, respectively, under soil conditions. Water stress was applied through restricted irrigation. Fresh weight, root system growth, and chlorophyll concentration were some of the parameters that were affected by the effect of water deficit on A. americana L. Chlorophyll concentration values were significantly decreased by 15 at 30% PEG (19.6 SPAD units) compared to the control treatment. In in vitro plants, the highest concentration of proline was found in the roots, being the treatment with 30% polyethylene glycol where the highest concentration of this osmoregulator was obtained (62.5 mg g⁻¹ DW). Under restricted irrigation conditions, an increase in proline concentration was observed both in the aerial part (2.2 µg 100 g⁻¹ DW) and in the root system (1.8 µg 100 g⁻¹ DW). However, the concentrations found were approximately ten times greater, less than those found under in vitro conditions. Therefore, the accumulation of proline can be considered an indicator of stress in Agave Americana L. growth in vitro.     

Antioxidant Responses of Lentil to Cold and Drought Stress

The effects of cold and drought stress on antioxidant responses and growth parameters in shoots and roots of lentil (Lens culinaris M cv Sultan 1) seedlings were investigated. Ten-day-old hydroponically grown seedlings were subjected to drought and cold (4°C) stress for 5 days. The length and fresh weight of shoots decreased significantly under both stress conditions, contrary to the increase in these growth parameters for roots under the same conditions. The oxidative damage as generation of malondialdehyde and hydrogen peroxide, was markedly higher in shoots under cold. Both stress conditions caused a significant increase in malondialdehyde levels in root tissues. The increase in proline levels was more pronounced under cold stress in shoots and roots. The tested stress conditions had no significant effect on chlorophyll contents. Superoxide dismutase activity was differentially altered in shoot and root tissues under drought and cold stress. The catalase activity was higher in roots under drought stress. On the other hand, ascorbate peroxidase activity increased in root tissues under cold stress. The results indicate that improved tolerance to cold and drought stress in root and shoot tissues of lentil might be correlated to the increased capacity of antioxidative defense system.     

Distribution of IAA and ABA in gravistimulated primary roots ofZea mays. L.

The transport of¹⁴C-IAA and¹⁴C-ABA applied exogenously to root cap toward the elongation zone was investigated in gravi- and light-stimulated primary roots ofZea mays L. cv. Golden Cross Bantam 70. No significant difference of either IAA or ABA in radioactivities was observed between upper and lower halves of elongation zones during the latent period (0–60 min after the stimulation) of gravitropic response. When quantitative analysis of endogenous IAA and ABA by an internal standard method was carried out 60 min after gravi- and/or light-stimulation, no asymmetric redistribution of either IAA or ABA was observed between upper and lower halves of elongation zones. Light irradiation increased by 20% the contents of ABA in elongation zones. These results suggest that although both IAA and ABA are basipetally transportable and can transmit their information to the elongation zone during a latent period we cannot explain the gravitropic curvature by their redistributions between the two (upper and lower) halves of primary roots ofZea. On the basis of results from the present work and previous papers, the distribution of IAA and ABA in gravistimulatedZea roots is discussed. A part of this study was reported at the Eighth Annual Meeting of the IUPS Commission on Gravitational Physiology at Tokyo 1986.     

Water transport in sunflower root systems: effects of ABA, Ca2+ status and HgCl2

Excised 20-d-old sunflower roots (Helianthus annuus L. cv. Sun-Gro 380) with different Ca²⁺ status were used to study the effects of root Ca²⁺ status and abscisic acid (ABA) on the exudation rate (Jv), the hydraulic conductivity of the root (Lpr), the flux of exuded Ca²⁺ (JCa, and the gradient of osmotic pressure between the xylem and the external medium. Jv and Lpr increased in direct proportion to the Ca²⁺ status of the root. Addition of ABA (4 M) at the onset of exudation in the external medium made Jv and Lpr rise, and this effect also increased with the Ca²⁺ status. The effects of HgCl2 and its interaction with ABA on water transport in the root were also studied. Addition of HgCl2 (1 M) 2 h after the onset of exudation in the external medium quickly inhibited Jv, independently of the presence of ABA in the root medium. The results recorded here point to the involvement of ABA and Ca²⁺ in the regulation of root water flow, as well as the existence of aquaporins in the cell membranes of sunflower roots.