Can changes in root anatomical traits during stress enhance drought & Salinity tolerance ?


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There are array of ways of studying plant response to drought or any kind of stress, ranging from physiological, morphological, cellular level, biochemical, anatomical or even at molecular level. This presentation deals or shows how plant tissues can respond under stress at anatomical level and hence contribution to tolerance.

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  • Soil characteristics of a great biological importance like porosity, water capacity or penetration resistance are affected by compaction and they are also dependent on soil typesRoots under different soil conditions or belonging to different species show contrasting root traits in anatomy and morphology.In general, it is assumed that soil compaction affects negatively seedling establishment and development and processes mediated by root such as anchorage, water and nutrient uptake, or symbiotic relations
  • Suberin consists of two domains, a polyaromatic and a polyaliphatic domain. The polyaromatics are predominantly located within the primary cell wall, and the polyaliphatics are located between the primary cell wall and the plasmalemma. The two domains are supposed to be cross-linked. The exact qualitative and quantitative composition of suberin monomers varies in different species. Some common aliphatic monomers include α-hydroxyacids (mainly 18-hydroxyoctadec-9-enoic acid) and α,ω-diacids (mainly octadec-9-ene-1,18-dioic acid). The monomers of the polyaromatics are hydroxycinnamic acids and derivatives, such as feruloyltyramine.In addition to the aromatics and aliphatics components, glycerol has been reported a major suberin component in some species. The role of glycerol is proposed to interlink aliphatic monomers, and possibly also to link polyaliphatics to polyaromatics, during suberin polymer assembly. The polymerization step of aromatic monomers has been shown to involve a peroxidase reaction.The biosynthesis of the aliphatic monomers shares the same upstream reactions with cutin biosynthesis, and the biosynthesis of aromatics shares the same upstream reactions with ligninbiosynthesis. Lignin and suberin are the only known biological polymers that are irregular.
  • In the present study, we test the response to soil compaction of FraxinusangustifoliaVahl. seedlings in two soil types under greenhouse conditions. We used F. angustifolia as a model plant, as it is a woody species with a fast growth (Antúnez et al., 2001). We studied four categories of variables: root morphology, root anatomy, plant physiology and plant growth and architecture. The first objective of this study was to find out which of these groups of variables areaffected by soil compaction and/or soil type and to what degree by each one. The second objective was to build a causal model which aims to explain how soil compaction affects root traits and how these changes explain whole-plant level functioning.
  • Therefore, it seems that there is a strong causal relationship between root anatomy, morphology and physiology, which may explain traits at whole-plant level such as plant physiology, plant height and growth, and ecological aspects
  • Aquaprin are water channels found in plasmamembrane of root cell ,which effect cell to cell component radial water flow, and can vastly contribute to the symplast and transcellular of water transport in root.
  • No significant difference in shoot biomass between non stress water and stress water plants using NH+4. (AN and ANP)But under Nitrate ( NN and NNP) growth depressions in shoot biomass was observed with NNPWater stress increased the root/shoot ratio under ANP and NNPTillers also were depressed under NNP but no depression with Ammonium (AN and ANP)Despite of water stress, Shanyou 63 higher biomass and other parameters.
  • No significant difference in aerenchyma formation was observed between plants under the two N forms of nutrition in the non-water-stressed condition Water stress severely increased aerenchyma formation, and aerenchyma in NNP was heavier than that in ammonia +PEG (ANP)For example, root cortical aerenchyma is beneficial for drought tolerance in maize because it reduces the metabolic cost of soil exploration under water stress (Zhu et al. 2010). However, enhancement of drought tolerance by root cortical aerenchyma formation occurs only when the metabolic cost associated with root cortical aerenchyma formation is exceeded by the metabolic benefits of enhanced water acquisition (Lynch and Ho 2005).
  • They also invistigated whether aquaporin activity in rice roots will be affected by different water stress and different form of nitrogen, using aquaporin inhibitorRegardless of water stress and compared with the control (without HgCl2), the water uptake rates in all HgCl2 treatments decreased in both rice cultivars, and the water uptake rate in plants fed ammonium was lower than in those fed nitrateWater stress restricted water uptake in plants fed both N forms. Regardless of water stress, Shanyou 63 rice roots supplied with NH+4 exhibited a relatively higher water uptake ability than roots supplied with NO3. Although no significant differences in root water uptake ability of Yangdao 6 were observed between the AN and NN and the ANP and NNP treatments, water stress-induced inhibition of nitrate was higher than that for ammonium.
  • No casparian band detectation, hence no endodermins or immature endodermis.
  • It was reported that the growth envi- ronment could affect the amount and proportion of suberin in apoplastic barriers, by which plants can effectively regulate effi- cient uptake of water and solutes by regulating the amount of apoplastic barriers and their chemical compositionfound that more suberin deposited in soil-grown rice roots than those in hydroponically- grown roots, which might be responsible for the complete clogging of fine inter-microfibrillar spaces in cell walls. They also showed that Casparian bands of the endo- and exo-dermis developed much closer to the root tip in salt-stressed rice plants than in the controls
  • in root zones I and II were significantly lower than those in zone III, which corresponded to positions where lateral roots develop from the pericycle of adventitious roots and the continuity of endo-andexodermis was interrupted
  • Can changes in root anatomical traits during stress enhance drought & Salinity tolerance ?

    1. 1. Can changes in root anatomical traits during stress enhance drought & Salinity tolerance ? KABEYA Jerry Muamba Department of Crop Physiology, University of Agricultural Sciences, Bangalore, India
    2. 2. Roots  Usually underground individual functions:  anchor plant and hold upright  absorb water and minerals form soil and conduct to stem  store food & propagation
    3. 3. A better understanding of the basic mechanisms of root growth and development is necessary
    4. 4. Causes of plant’s action and reaction in her ever changing environment Drought Temperature Temperature High Salinity Soil compaction Others
    5. 5.  Plant’s rapid resilience to these unfriendly environments is thus crucial and matter of urgency to keep surviving. Resilience strategies Physiologicale.g. stomata and non- Anatomical. Biochemical. stomata water loss e.g. root diameter, etc. e.g. OA, proline level, check. etc. Morphological Molecular. e.g. leaf angle, root e.g. Genes expression , length, etc. etc.
    6. 6.  Plant roots are crucial for the absorption and translocation of water and nutrients through xylem to above ground for various cellular processes. Anatomical root traits such as;  cortex thickness  suberized exo and endodermis,  Casparian bands,  aerenchymatous tissues, great role in root functioning in termof hydraulic conductance, oxygenation,protective measures etc.
    7. 7. Root Cortex size  The size of cortex play important role in water conductivity and hence plant tolerance to stress  Thus, smaller cortex width results in higher conductivity because the distance of water to reach vascular cylinder is shorten, and better capacity to tolerance to stress
    8. 8. Casparian Bands The main role of this structure is to block non selective apoplastic bypass flow of ions and water through the cortex into vascular cylinder (no free water & ion movement through apoplast).
    9. 9. Suberin lamellae structure  Suberin structure consists of two domains,  Polyaromatic  Polyaliphatic • Permeability of apoplastic barriers to water or solute transport strongly to the amount and chemical composition of aliphatic and aromatic domains Polyaromatic Polyaliphatic Roles: a. It reduces ROL to the rizosphere and increase longitudinal diffusion in the aerenchyma b. It avoid partial absorption of phytotoxins from rhizosphere c. It diminishes the release of excess gases such as ethylene and methane in soil d. it decreases the intake of water and nutrients
    10. 10. Aerenchyma structure Submerged roots Aerenchyma and air spaces Irrigated condition Aerenchyma, gas or air-spaces, are formed either as part of normal development or in response to stress ( hypoxia or nutrient deficiency) by two main mechanisms I. Lysigeny : gas- spaces are formed via cell lysis II. Schizogeny : gas–spaces are formed during cell separation during tissue development The importance is to provide an internal pathway for oxygen transport between roots and the aerial environment. Along this pathway, O2 is supplied to the roots and rhizosphere, while CO2, ethylene, etc. move from the soil to the shoot and the atmosphere
    11. 11. Morphological Response of root of Fraxinus angustifolia seedling under compaction treatments(A) No compaction of loam soil, (B) high compaction of loam soil, (C) no compaction ofsandy-loam soil and (D) high compaction of sandy-loam soil. For each root, the value ofsoil bulk density is shown.
    12. 12. Pictures of root histology of Fraxinus angustifolia seedling under compactiontreatments: no compaction treatment of loam soil is shown in the left; high compactiontreatment of sandy-loam soil on the right.X, xylem; P, phloem; S, suber; R, rhizodermis; XV, xylem vessels D. Alameda and R. Villar, 2012
    13. 13. Causal relationships of the effects of soil compaction from root to whole plant functioning.
    14. 14. (January 2012) Drought-Induced Root Aerenchyma Formation Restricts Water Uptake in Rice Seedlings Supplied with NitrateXiuxia Yang, Yong Li, Binbin Ren, Lei Ding, Cuimin Gao, Qirong Shen and Shiwei Guo,The aims of the study were to investigate;1. Whether the root aerenchyma and water uptake of water-stressed rice are related to both nitrogen and water stress.2. Also analyze the relationship between root aerenchyma and root hydraulic conductivity in rice seedlings supplied with different forms of nitrogen under water stress.
    15. 15. Methodology Rice seeds (O. sativa L., cv. ‘Shanyou 63’ hybrid Indica China, and cv. ‘Yangdao 6’ Indica China) were disinfected in 10% H2O2 for 30 min and then immersed in saturated CaSO4 solution for 2 hrs. When the seedlings had developed an average of 2.5 visible leaves in distilled water, they were transplanted to 3 liter buckets and into a full-strength mixture of ammonium and nitrate nutrition (ANN) One week later, the seedlings were supplied with either ammonium (AN) or nitrate (NN) nutrition alone Two weeks after, water stress was conducted by adding 10% PEG (10%, w/v; mol. wt 6,000 Da) to the nutrient solutions ( -0.15MPa) for 1 week. Four treatments were applied: AN, NN, ANP and NNP (ANP and NNP represent the ammonium and nitrate nutrition with 10% added PEG6000, respectively).
    16. 16. Nutrient solutions were changed every 3 days and pH was adjusted to 5.50 ± 0.05every day with 0.1 mol l-1 HCl or 0.1 mol l-1 NaOH.Observations and measurementsXylem sap flow rate measurements plants were de-topped approximately 2 cm above the interface of the roots and shoots, and the exudation was immediately cleaned with filter paper to avoid contamination. Absorbent cotton was placed on the top of each piece of de-topped xylem and covered with plastic film to avoid evaporation. Xylem sap was collected from 20:0 h to 06:00 h, and the exudation rate was calculated from the differences in cotton weight.
    17. 17. Determination of water uptake rate and aquaporin activityWater uptake of intact plants, with or without addition of 0.1mM HgCl2 (aquaporin inhibitor) tothe hydroponic solutions, was determined by the depletion of nutrient solution (by weighing).The contribution of aquaporin to the water uptake rate was calculated from the difference inthe water uptake rate between the control and HgCl2-treated plants. Root aerenchyma measurements4mm to 5mm root pieces were cut from the middle of 7–8 cm long newly formed adventitiousroots using a razor blade.Root tissues were then fixed with 3% glutaraldehyde in 0.1M phosphate buffer (pH 7.0) for 3–5 h.The tissues were thereafter rinsed in with phosphate buffer and sections were dehydrated in agraded ethanol series and dried using a vacuum freeze-dryer.The dried root sections were coated with gold-palladium and glued onto specimen stubs.Finally, root samples were viewed and photographed with a scanning electron microscope (model3000N; Hitachi).Aerenchyma formation was calculated from the observed electron microscope images with MoticImages Plus 2.0 (China Group Co., Ltd.)
    18. 18. ResultsEffects of nitrogen form and water stress on shoot and root DW (g plant1), theroot/shoot ratio and tillers of rice plants (No. plant1) (cv. Shanyou 63 and cv.Yangdao 6)AN -ammonium , NN- nitrate (NN) under either non-water stress or water stress simulatedby adding 10% PEG6000 (NH4+ + PEG as ANP; NO3- + PEG as NNP). NH+4 nutrition improves water holding in rice seedlings and subsequently enhances their resistance to drought
    19. 19. Effect of nitrogen form and water stress on root aerenchyma formation in rice plants AN AN Aerenchyma formation (%) NN NN ANP ANP NNP NNP Aerenchyma formation during stress (either hypoxia or anoxia) promotes radial oxygen release from roots, leading to rhizosphere oxygenation Also facilitate methane diffusion from water-loggedShanyou 63 to the atmosphere. sediments Yamgdao 6 Shanyou 63 Yamgdao 6 The formation of root aerenchyma may be an adaptation to low P availability by reducing Rice plants were supplied with ammoniumP (AN) or nitrate (NN) under either 2010). the metabolic costs of soil exploration and recycling (Fan et al. 2003, Zhu et al. non-water stress or water stress simulated by adding 10% PEG6000 (NH+4 + PEG as ANP; NO 3 + PEG asNNP). ae, aerenchyma. of water stress on root aerenchyma development the electron Nevertheless, the effects Aerenchyma formation was determined from depend not micrographs in Fig. above. or the environment but also on the plant species. only on the nitrogen form
    20. 20. Effects of nitrogen form and water stress on root hydraulic conductance in rice plants (cv.Shanyou 63 and cv. Yangdao 6)Aerenchyma formation (%) Shanyou 63 Yamgdao 6 Shanyou 63 (26%) Yamgdao 6 (18%) Aerenchyma formation restrict water uptake ability in nitrate nutritionRoot aerenchyma increased significantly in water-stressed plants fed with nitrate. Root Water stress can enhance lignificationplants fed with of cell walls in in those fed withhydraulic conductivity was lower in and suberization nitrate than the endodermis andammonium, probably caused by the hydraulic water transport pathways in plants fed with exodermis where major apoplastic different resistance exists.nitrate and those fed with ammonium.
    21. 21. Effects of nitrogen form and water stress on water uptake rate (with or without HgCl2)based on per unit root FW for 2 h [gH2O (g root FW)-1] and decreased percentage afteraddition of 0.1 mmol-1 HgCl2 to rice plants (cv. Shanyou 63 and cv. Yangdao 6) This indicates that water transport occurs mainly through Hg-sensitive aquaporins (symplastic) in roots under ammonium-fed conditions, Whereas it occurs mainly through an apoplastic pathway in water-stressed plants fed with nitrate (aerenchyma formation is often accompanied by formation of apoplastic barrier)
    22. 22. Inference of the study The outcome of the study showed that rice growth, root aerenchyma formation, root hydraulic conductivity and root xylem flow rate in two water-stressed rice cultivars were affected by the different nitrogen forms Under the water-stressed condition, ammonium nutrition increased the tolerance of rice plants to water stress and resulted in higher water uptake rates and xylem sap flow rates than found in plants fed with nitrate This phenomenon was caused by lower root aerenchyma formation and relatively higher aquaporin activity Thus, water transport from the medium to the xylem varied between water-stressed plants fed with the two nitrogen forms and impacted the drought tolerance of rice seedlings.
    23. 23.  Under unfavorable situations, root anatomical and Physiological traits have played immense role to plant resistance to salinity stress.  Rice is a very salt-sensitive crop species and damage from salinity on rice seedlings may result in an excess transport of NaCl through the root system to the leaves
    24. 24. The aim of this study was;  To assess net Na+ fluxes and shoot Na+ content by means of SIET analysis and atomic absorption spectrometry to elucidate the contribution of net sodium fluxes at anatomically distinct root zones of rice seedlings  To provide data for further interpretation of roles of Casparian bands in sodium fluxes.With regard to rice and this study, the assessment of the Na+ fluxes into plantsystem was carried out at three anatomically distinct regions in terms ofdevelopment of Casparian bands in a developing roots. SIET –Scanning ion-selective electrode techinique
    25. 25. Root distinct zonation 1. Close to root apex, - where no exo- or endo-dermal casparian bands are formed- Zone I 2. Further from the apex,- where casparian bands of either the endo –or exo- dermal or both, are mature- Zone II 3. More further from apex, - where root primodia are initiated and casparian bands are interrupted by developing lateral roots- Zone IIIMethods:  Seeds of rice (Oryza sativa L. cv.Nipponbare ) were germinated for 5 days on wet filter paper in the light at 27±2 ◦C.  Seedlings were transferred to an aerated hydroponic culture system and grown in the same growth chamber in which all of the following experiments were conducted  The solution contained the macronutrients 0.09mM (NH4)2SO4, 0.05mM KH2PO4, 0.05mM KNO3, 0.03mM K2SO4, 0.06mM Ca(NO3)2, 0.07mM MgSO4, 0.11mM Fe-EDTA and the micronutrients 4.6 M H3BO3, 1.8 M MnSO4, 0.3 M ZnSO4 and 0.3 M CuSO4, pH 5.5–6.0.
    26. 26. Root anatomy and microscopy measurementsTo examine Casparian bands in root exodermal and endodermal cells, sections weremade at different distances from the root tip (3, 6, 10, 12, 15, 18, 21, 25, 30, 35, 40, 50,60, 80, 90, 100, 120, 150, 180, 200, 250 mm) of 15 days-old rice.a. To localize suberin deposition, the sections were stained with Sudan III dissolved in ethanol/water (1:1; v/v).b. To localize casparian bands , the sections were stained with 0.1% berberine hemisulphate for 1 h and with 0.5% (w/v) aniline blue for another 1 h  The stained sections were observed under an epifluorescence microscope (Q 500 IW, Carl Zeiss, Göttingen, Germany)
    27. 27. Freehand cross-sections of rice roots At 15mm : no At 25mm : caspariancasparian detection detection in radial or morphological cell wall change At 30mm : casparian detection At 35mm : was observed in endodermal suberin exodermis lamellae first appearance At 60mm : At 25mm : lysis of endodermal suberin cortical cells into lamellae full aerenchyma development formation(A) Part of a cross-section at 15mm from the root tip where the endodermis was immature, stained with anilineblue. (B) Endodermal cell walls with Casparian bands were shown in root zone II, 25mm behind the root tip.(C)Exodermal cell walls with Casparian bands were shown in root zone II, 30mm behind the roottip.(D)Endodermal suberin lamellae were well-developed at 50mm (E) Exodermal suberin lamellae were welldeveloped at about 60mm. (F) Cortical cells started to collapse and aerenchyma gradually formed at a distance of25mm from the root tip, stained with Sudan III.
    28. 28. Lysigenous aerenchyma channels and lateral root primordium of rice roots. At 120mm : fully Aerenchyma caused developed main separation Aerenchyma between outer and inner root part No observation ofAt 60mm: Initiation either liginified nor of lateral root suberised exodermis primordia in direction of lateral root primordia formation (A) Well-developed aerenchyma of roots was observed at about 120mm from the root tip. (B) Well- defined OPR (the outer part of roots) comprised rhizodermis, exodermis, sclerenchyma and one central cortical cell layer. (C and D) A lateral root primordium was formed from the stele of the parent root. C, from a clearing material of roots, D, from an anatomical section of roots
    29. 29. Measurement of Na+ contents from different zones along roots  For each 15-day-old rice seedling, five adventitious roots were selected for experiments  Root were divided into three zones I. Zone I ( 0-20mm from the apex), neither exodermis nor endodermis is matured II. Zone II (40- 60mm) III. Zone III, basal root part, where lateral root primordia were initiated and lateral roots had emerged from parent root.  In order to measure net fluxes of Na+ in different zones, the seedlings were allowed to grow in a plastic box with three compartments.  Alternatively, the root zones were allowed to take up Na+ in the root xylem through the shoot, for 48hrs by subjecting the portion with NaCl. The whole shoot was harvested and Na+ content determined by atomic absorption spectrometry
    30. 30. Frequency distribution of shoot sodium content in plants under differenttreatment conditions and comparisons of Na+ transport between the three root zones of rice seedlings. A B  Considerable variation in individual Na+ content was observed in the plants from different treatments  The uptake of Na+ capacity in different treatments ranged from; 0.02-0.16 µmol (zone I), 0.01-0.23 µmol (zone II) and 0.06-3.10 µmol (zone III) D respectively.C  The average shoot Na+ contents in the plants from treatments I , II and III were 0.092±0.048 µmol, 0.074 ± 0.067 µmol and 1.382 ± 0.911 µmol, respectively (D)
    31. 31. Study summary The study revealed that Casparian bands in the endo-/exodermis started to form at a position about 25–30mm from the root tip and suberin lamellae started to develop at about 35mm from the root tip The anatomical data also showed that a region of the exodermis opposite to developing lateral root primordia lacked impregnation with lignin and suberin Studies have showed that Casparian bands of the endo- and exo-dermis developed much closer to the root tip in salt-stressed rice plants than in the controls Atomic absorption spectrometry revealed that the average Na+ contents entering the root were dependent on • Root zonation (lower in zone I & II than in III) • Amount and chemical composition of apoplastic barriers in root zonation.
    32. 32. Study inference  Casparian bands and suberin hampered with free water movement and ions through the apoplast of roots into stele or further into root, thereby offering tolerance at the root tip.  But, the regions of discontinuity in endodermal Casparian bands created during the development of lateral root primordia from the pericycle allowed significant apoplastic leakage of ions from the external medium into root tissues. THANK YOU
    33. 33. The nutrient composition of the solutions was as follows: macronutrients (mg l1): 40 N as(NH4)2SO4 or Ca(NO3)2, 10 P as KH2PO4, 40 K as K2SO4 and KH2PO4, and 40 Mg asMgSO4; micronutrients (mg l1): 2.0 Fe as Fe-EDTA, 0.5 Mn as MnCl24H2O, 0.05 Mo as(NH4)6Mo7O244H2O, 0.2 B as H3BO3, 0.01 Zn as ZnSO47H2O, 0.01 Cu as CuSO45H2O,and 2.8 Si as Na2SiO39H2O. The Ca content in AN was compensated for by adding CaCl2.A nitrification inhibitor (dicyandiamide) was added to each nutrient solution to maintainthe identified condition.
    34. 34. Basis sets for the partial independence constraints implied by each of the three models shown in Fig. 5. The notation ‘(X,Y)|{A,B,…}’ meansthat variables X and Y are hypothesized to be probabilistically independent, conditional on the set of variables {A,B,…} and the ‘φ’represents the null (empty) set. Pearson’s partial correlation coefficient (r), and probability (P) are given for each conditional independencestatement. Values in bold have a probability below 0.05. The overall model is tested with Fisher’s C statistic and the probability is shown inbrackets (below each model). In those models where the C value was not significant (P > 0.05), the model wasaccepted. Model 1 and 2 are rejected (P <0.05) and model 3 is accepted (P >0.05). CodesThe codes of the variables of the models are: 1, Photosynthetic rate; 2, Transpiration rate; 3, ψ, leaf water potential; 4, Soil compaction(soil bulk density); 5, Plant height (not used in the models); 6, Plant area; 7, Xylem vessels proportion; 8, Xylem vessels diameter; 9, SRL,specific root length; 10, Root tissue mass density (TMDR) (not used in the models); 11, Plant Biomass.