7: الجذور وحركة الماء - بنية الجذور وعلم التشريح - علم الأحياء

سرخس شجرة متحجرة عمرها 270 مليون عام

خلال العصر الكربوني ، منذ ما يقرب من 300 مليون سنة ، كانت الأرض تهيمن عليها غابات واسعة من Lycopods العملاقة (قسم Lycophyta) ، و Horestails (قسم Sphenophyta) وسراخس الأشجار (تقسيم Pterophyta). نشأ الكثير من احتياطيات الفحم على الأرض من رواسب ضخمة من النباتات المتفحمة من هذا العصر. تكشف جذوع متحجرة من البرازيل عن تفاصيل خلوية لسرخس شجرة منقرض (Psaronius brasiliensis) عاش قبل حوالي 270 مليون سنة ، قبل عصر الديناصورات. لا يحتوي الجذع المتحجر لسارونيوس على حلقات نمو متحدة المركز نموذجية للصنوبريات وكاسيات البذور. بدلاً من ذلك ، تحتوي على شاهدة مركزية تتكون من العديد من الأقواس التي تمثل الحزم الوعائية لنسيج نسيج الخشب. يحيط بالساق قواعد الأوراق. في الحياة ، ربما يشبه بسارونيوس سرخس شجرة Cyathea الحالية في نيوزيلندا.

أنواع امتصاص الماء في النباتات

تمتص النباتات الماء عادةً بالطريقتين التاليتين:

الامتصاص النشط للماء

يتطلب هذا النوع من امتصاص الماء إنفاق الخلايا الجذرية للطاقة الأيضية لأداء النشاط الأيضي مثل التنفس. يحدث الامتصاص النشط في النبات بطريقتين ، وهما امتصاص الماء التناضحي وغير التناضحي.

1. امتصاص الماء النشط الاسموزي: في هذا النوع ، يحدث امتصاص الماء من خلال التناضح حيث ينتقل الماء إلى نسيج الخشب عبر تدرج التركيز لخلية الجذر. تعود الحركة التناضحية إلى التركيز العالي للمذاب في عصارة الخلية وانخفاض تركيز التربة المحيطة.
2. امتصاص نشط غير تناضحي للماء: هنا يحدث امتصاص الماء حيث يدخل الماء إلى الخلية من التربة مقابل تدرج تركيز الخلية. وهذا يتطلب إنفاق الطاقة الأيضية من خلال عملية التنفس. ومن ثم ، مع زيادة معدل التنفس ، سيزداد معدل امتصاص الماء أيضًا. Auxin هو هرمون منظم للنمو ، مما يزيد من معدل التنفس في النباتات والذي بدوره يزيد أيضًا من معدل امتصاص الماء.

الامتصاص السلبي للماء

هذا النوع من امتصاص الماء لا يتطلب استخدام الطاقة الأيضية. يحدث الامتصاص عن طريق النشاط الأيضي مثل النتح. الامتصاص السلبي هو النوع الذي يتم فيه امتصاص الماء من خلال سحب النتح. هذا يخلق توترًا أو قوة تساعد في حركة الماء لأعلى في نسيج نسيج الخشب. أعلى هو معدل النتح ، وأعلى هو امتصاص الماء.

دور الشعر الجذري في امتصاص الماء

يحتوي الجذر على بعض الهياكل الأنبوبية التي تشبه الشعر وحيدة الخلية تسمى جذور الشعر. في نظام الجذر ، يُطلق على المنطقة التي تبرز منها شعيرات الجذر منطقة جذور الشعر. منطقة شعر الجذر هي المنطقة الوحيدة التي تشارك في نشاط امتصاص الماء. منطقة شعر الجذر هي منطقة نفاذ الماء. الشعيرات الجذرية هي النواتج التي تنشأ من طبقة البشرة المسماة طبقة شائكة.

يتكون جدار الخلية لشعر الجذر من غشاء مزدوج الطبقة. البكتين موجود في الطبقة الخارجية ، والسليلوز موجود في جدار الخلية & # 8217 s الطبقة الداخلية. تحت جدار الخلية ، هناك نفاذية انتقائية تذكر الذكريات. ستسمح الخلية أو الغشاء السيتوبلازمي لمواد معينة بالمرور عبر تدرج تركيز الخلية.

توجد الخلايا الجذرية والنواة والفجوة أو نسغ الخلية داخل الغشاء السيتوبلازمي. تحتوي مجاميع التربة على قطرات صغيرة من الماء تحملها شعيرات الجذر إلى نسيج الجذر من خلال آليات مختلفة ، يكون التناضح أكثر شيوعًا منها.

7: الجذور وحركة الماء - بنية الجذور وعلم التشريح - علم الأحياء

علم التشريح والتركيب لنبات الأزهار تمثل صفحة الويب التالية نسخة من ملاحظاتي التي شكلت أساس المحاضرات التي ألقيت خلال الجزء الأول من دورة محاضرة بيولوجيا النباتات (BOT 1103). يرجى الرجوع إلى الملاحظات الخاصة بك ، والنشرات ، وإلى الكتاب المدرسي (Stern، K.، R.، JE Bidlack، and SH Jansky. 2008. Entrepitory Plant Biology، McGraw-Hill. 616 pp. - مهام القراءة موجودة في المنهج الدراسي) للحصول على معلومات إضافية. لا تتضمن صفحة الويب هذه المعلومات الموجودة في العديد من النشرات والمواد ذات الصلة (على سبيل المثال ، الأفلام ، والرسوم البيانية ، والإسقاطات العلوية ، وما إلى ذلك) التي ستتلقاها خلال الفصل الدراسي. سيتم تقييمك على هذه المعلومات أيضًا. إذا لاحظت أي أخطاء في المستند التالي ، فسأكون ممتنًا لو لفتت انتباهي إلى هذا الأمر. عنوان البريد الإلكتروني: [email protected]

الجذور: التنظيم والتشريح

1. وظيفة
2. التشريح الخارجي
3. التشريح الداخلي
4. الجذور المتخصصة
5. الجذور وتغذية النبات

• تثبت الجذور النبات في الطبقة السفلية أو التربة.
• تمتص الجذور الماء والمغذيات المذابة أو المواد المذابة (النيتروجين والفوسفور والمغنيسيوم والبورون وما إلى ذلك) اللازمة للنمو الطبيعي والتطور والتمثيل الضوئي والتكاثر.
• في بعض النباتات ، أصبحت الجذور مهيأة للوظائف المتخصصة ، والتي ستتم مناقشتها في نهاية القسم الخاص بجذور النباتات.

1. قلنسوة الجذر
2. منطقة انقسام الخلايا
3. منطقة الاستطالة
4. منطقة التمايز أو النضج

• قلنسوة الجذر
  • كتلة من خلايا البرانشيما على شكل كشتبان عند طرف كل جذر
  • يحمي الجذر من الإصابة الميكانيكية
  • تطلق أجسام الجولجي أو ديكتوسومات مادة تشحيم صمغية (ميوسيجيل)
  • تدوم الخلايا أقل من أسبوع ، ثم تموت
  • ربما يكون مهمًا في إدراك الجاذبية (أي التوجه الجغرافي أو الجاذبية)
  • يبدو أن amyloplasts (وتسمى أيضًا statoliths) تتراكم في قاع الخلايا ، وربما يكون للنبات آلية لاستشعار ترسيب العضيات المغطاة بالنشا وتفسير ذلك على أنه اتجاه لأسفل.
  • نسيج قمي - تنقسم الخلايا مرة أو مرتين في اليوم.
  • تنشأ الأعمدة الانتقالية من أطراف الجذور والبراعم. وتشمل هذه:
    • الأديم الأولي (الذي يشكل البشرة)
    • الأرض الإنشائية (التي تشكل نسيج الأرض)
    • البروكامبيوم (يشكل اللحاء الأساسي والخشب).
    • تصبح الخلايا أطول وأوسع
    • root hairs develop as protuberances from epidermal cells
    • increase the surface area for the absorption of water
    • cuticle exists on root but not on root hairs
    • أ. epidermis (outermost layer of cells forming the initial covering on a root).
    • ب. cortex (ground tissue that surrounds the vascular cylinder or stele).
    • ج. endodermis with Casparian strip (regulates the flow of water and dissolved substances).
    • د. primary xylem (water-conducting tissue found in the vascular cylinder or stele)
    • E. primary phloem (food-conducting tissue found in the vascular cylinder or stele)
    • The ring of cells beneath the endodermis would be the pericycle (the origin point for the production of lateral roots)
    • The band of tissue between the phloem and xylem are remnants of procambium which could lead to the production of the vascular cambium and secondary growth, especially in a woody dicot root.

    

    • Food storage (Carbohydrates)
      • manioc or cassava => the source of starch for making tapioca pudding
      • sugar beets => sucrose
      • Historical FYI: the original Jack O'Lanterns were carved out of rutabagas, turnips, and white potatoes. Americans introduced the practice of using the pumpkin of this purpose.
      • velamen roots of orchids: a thick epidermis to prevent water loss.
      • prop roots of corn for support
      • adventitious roots of ivies, aid in climbing
      • mycorrhizae or "fungus roots" where a symbiotic relationship forms between a plant and a fungus. In this partnership the fungus provides protection against some types of pathogens and increase the surface area for the absorption of essential nutrients (e.g. phosphorous) from the soil. The plant in return provides food for the fungus in the form of sugar and amino acids.
      • Legumes (e.g., pea, beans, peanuts) form root nodules. Mutualism between a plant and bacteium which allows for the fixation of atmospheric nitrogen to form that the plant can utilized. The bacterium is reward with food and a place to live

      V. ROOTS AND PLANT NUTRITION

      • Plants require large amounts of carbon, hydrogen, and oxygen. Majority arrives to the plant in the form of carbon dioxide and water.
      • Other elements are essential for growth include the macronutrients and micronutrients.
      • Soil is the source of minerals or nutrients used by plants.
      • nitrogen (proteins, nucleotides)
      • phosphorous (ATP, nucleic acids)
      • potassium (movement of materials across membranes)
      • calcium (associated with increasing sensitivity of tissues to different plant hormones)
      • magnesium (chlorophyll, assists functioning of certain enzymes).
      • sulfur (component of cysteine, an amino acid. sulfide bonding in proteins).
      • iron (electron transport system in photosynthesis and respiration)
      • boron
      • manganese
      • الزنك
      • copper (cytochromes in electron transport systems)
      • molybdenum (necessary for normal functioning of nitrate assimilation)
      • chlorine
      • For example, sodium/chlorine causes wilting (salt run off from streets that are treated to remove ice).
      • Excessive amounts of boron, copper, manganese, aluminum are toxic to plants.
      • Plant nutrition is linked to the chemical and physical attributes of the soil the plant is growing in.
      • Soil Particles - SAND, SILT, and CLAY - mix some soil in a jar with water, and allow it to settle out overnight. The sand will be on the bottom, the silt will be next, and the clay will be on top. Clay is the final product of weathering and is composed of the smallest particles. Loams contain approximately equal amounts of sand, silt, and clay. Cation exchange from the surface of negatively-charged clay particles to the plant is facilitate by trading a cation for a hydrogen ion. Anions do not attach to clay and are frequently leached from the soil before the plant can obtain them (sulfates and nitrates).
      • Humus is the decomposing organic matter in soil. Amount varies along a continuum MINERAL SOILS (1-10% humus) To ORGANIC SOILS (about 30 % humus).
      • Air -About 25-50% of the volume of soil is air. The amount of air is higher in sandy soils than in clay soils.
      • Water - Soil contains chemically bound (locked to minerals and clay particles - unavailable to plants) and unbound water (available to plants).

      STEMS: Organization and Anatomy

      • Stems support leaves and branches.
      • Stems transport water and solutes between roots and leaves.
      • Stems in some plants are photosynthetic (e.g., cacti - leaves are reduced to spines to protect against herbivory and reduce water loss).
      • Stems may store necessary materials for life (e.g., water [cactus, miscellaneous succulents] starch, sugar [sugarcane]).
      • In some plants, stems have become adapted for specialized functions, which will be discussed at the end of the section on plant stems.

      REFER TO FOLLOWING DIAGRAM OF A WOODY DICOT STEM:

      FYI: Apical dominance refers to the suppression of growth by hormones produced in the apical meristem. The Christmas tree pattern of pines indicates strong apical dominance. Bushy plants have weak apical dominance. If apical meristem is eaten or destroyed, plants may become bushy.

      ثالثا. INTERNAL ANATOMY IN FLOWERING PLANTS

      Dicotyledon (two seed leaves) and Monocotyledon (one seed leaf) flowering plants.

      • no vascular or cork cambium (secondary growth is rare)
      • vascular tissue in bundles (primary phloem, primary xylem, procambium, and sclerenchyma fibers) and distributed randomly through the ground tissue
      • ground tissue not divided into pith and cortex
      • intercalary meristems at base of nodes allow for elongation of stem (e.g., grass, bamboo) among some monocots
      • some secondary growth may or may not develop
      • vascular tissue in bundles (primary phloem, primary xylem, procambium, and sclerenchyma fibers) but arranged in a circular pattern when stem is observed in cross section
      • ground tissue is divided into pith and cortex
      • woody dicot stems start out like that in herbaceous dicots, but these develop secondary growth
      • lateral meristems allow the stem to increase in girth or diameter
      • lateral meristems: vascular cambium and cork cambium (phellogen)
      • Further discussion of secondary growth appears in a later section on secondary growth.
      • Rhizomes - horizontal stems that grow below the ground with adventitious roots examples are irises, grasses.
      • Stolons or runners - horizontal stem that grows above the ground with long internodes examples are strawberry, airplane plants.
      • Tubers - accumulation of food at the tips of underground stolons, after the tuber matures the stolon dies, the "eyes" of a potato are the nodes of a starch-ladened stem.
      • Rosette - stem with short internodes and leaves attached at nodes
      • Bulbs - large buds with a small stem at the lower end surrounded by numerous fleshy leaves, adventitious roots at base examples include onion, tulip, lily.
      • Corms - resemble bulbs but composed entirely of stem tissue surrounded by a few papery scale like leaves, food storage organs with adventitious roots at the base of corms examples include crocus and gladiolus.
      • Cladophylls - leaf-like stems examples include butcher's broom, asparagus.
      • Cacti - stout fleshy stems that are modified for food and water storage and photosynthesis.
      • Thorns - honey locust (modified stem), black locust and some species of الفربيون ( spines are stipules), roses (thorn or prickles arise from epidermis).
      • Tendrils - for climbing for example, grape and Boston ivy (English ivy - adventitious roots not stem).

      SECONDARY GROWTH IN STEMS AND ROOTS In woody plants, most of which are dicots, secondary growth may occur in the roots or the stems. As the plant develops functional lateral meristems, that is, the vascular cambium and cork cambium (the phellogen), the diameter of roots and stems increases as new tissues are produced. This increase in girth causes irreparable damage especially to the epidermis, phloem, and associated tissues.

      Please refer to the flow charts of primary and secondary growth in stems and roots that were handed out in lab. Vascular cambium produces secondary phloem and xylem. The study of woody plant growth over time by examining the annual rings created by secondary xylem is known as Dendrochronology .

      Keep in mind that the periderm arises from the growth and production of cork (dead and suberized at maturity) and parenchyma (lenticels - allows for gas exchange) from the cork cambium . The periderm replaces the outer covering of the plant as it increases in girth. The bark includes the periderm and any other tissue (living or dead) from the outermost part of the tree to the cylinder of the vascular cambium in the stem and the root.

      LEAVES: Organization and Anatomy

      • Leaves are the solar energy and CO₂ collectors of plants.
      • In some plants, leaves have become adapted for specialized functions, which will be discussed at the end of the section on plant leaves.
      • Leaves possess a blade or lamina, an edge called the margin of the leaf, the veins (vascular bundles), a petiole, and two appendages at the base of the petiole called the stipules.
      • Arrangement of leaves on a stem = phyllotaxy.
        • whorled - three or more leaves at a node.
        • opposite - two leaves attached at the same node.
        • spiral or alternate - one leaf per node.
        • Simple leaf = undivided blade with a single axillary bud at the base of its petiole.
        • Compound leaf = blade divided into leaflets, leaflets lack an axillary bud but each compound leaf has a single bud at the base of its petiole.
          • pinnately-compound leaves: leaflets in pairs and attached along a central rachis examples include ash, walnut, pecan, and rose.
          • palmately-compound leaves: leaflets attached at the same point at the end of the petiole examples of plants with this leaf type include buckeye, horse chestnut, hemp or marijuana, and shamrock.
          • Netted-venation = one or a few prominent midveins from which smaller minor veins branch into a meshed network common to dicots and some nonflowering plants.
            • Pinnately-veined leaves = main vein called midrib with secondary veins branching from it (e.g., elm).
            • Palmately-veined leaves = veins radiate out of base of blade (e.g., oak, maple).
            • Epidermis = single layer of epidermal cells (containing no chloroplasts) that interlock with one another on the upper (adaxial - toward the leaf axis) and lower (abaxial - away from the leaf axis) side of the leaf blade the outer surface is often coated with a waxy substance called cutin to form the cuticle (to prevent excessive water loss) and the hair-like structures called trichomes.
            • In the epidermis are pores called stomata (pl.), stoma (singular), which allow for gas exchange. Stomata are formed by two guard cells, which regulate the opening and closing of such pores. In dicots, guard cells tend to be sausage-shaped, whereas in monocots, these tend to be shaped like a bone or a fattened capital letter I. Guard cells possess chloroplasts. When water is pumped into the guard cells, these tend to bend away from one another creating the opening when water is pumped out of these cells, the cells become more cylindrical in shape and the stomata close.
            • Beneath the upper layer of epidermis, are a rows of vertically-positioned chlorenchyma cells that form the palisade mesophyll. Just below this layer exists bag-like chlorenchyma cells that are loosely packed together which form the spongy mesophyll. The chloroplasts in these two layers of mesophyll are responsible for photosynthesis. Beneath the lower most portion of the mesophyll is the lower epidermis.
            • Veins = vascular bundles xylem (water-conducting tissue) oriented towards the upper side of the leaf, containing phloem (food-conducting tissue) oriented towards the lower side of the leaf, sclerenchyma fibers, and parenchyma tissue (which may form a bundle sheath surrounding the vein).
            • Collenchyma may be present in the midrib of the leaf or in the petiole just below the epidermis. Collenchyma serves as strengthening tissue to assist leaves in supporting their own weight and to prevent damage due to motion caused by the wind.
            • Many plants are deciduous (able to loose their leaves during cold or dry seasons).

            رابعا. SPECIALIZED LEAVES

            • Cotyledons: embryonic or "seed" leaves. First leaves produced by a germinating seed, often contain a store of food (obtained from the endosperm) to help the seedling become established.
            • Tendrils - blade of leaves or leaflets are reduced in size, allows plant to cling to other objects (e.g., sweet pea and garden peas ).
            • Shade leaves = thinner, fewer hairs, larger to compensate for less light often found in plants living in shaded areas.
            • Drought-resistant leaves = thick, sunken stomata, often reduced in size
              • In American cacti and African euphorbs, leaves are often reduced such that they serve as spine to discourage herbivory and reduce water loss stems serve as the primary organ of photosynthesis.
              • In pine trees, the leaves are adapted to living in a dry environment too. Water is locked up as ice during significant portions of the year and therefore not available to the plant pine leaves possess sunken stomata, thick cuticles, needle-like leaves, and a hypodermis, which is an extra cells just underneath the epidermis.
              1. Transpiration and movement of water within the plant body
              2. Gutation
              3. Movement of food within the plant body

              I. Transpiration - evaporation of water from shoot.

              Movement of water and minerals in the xylem is a major process. For example, corn plants transpires almost 500 liters of water during its 4 month growing period.

              Water moves in tracheids and vessel members. Tracheids pass water laterally through simple and bordered pits. Vessel elements have an greater diameter and are stacked end to end, so water can flow for longer distances (a centimeter to a meter) before having to transverse a pit.

              II. Gutation results from root pressure (solutes moving into xylem cause water to also move into the xylem from surrounding root cells) when transpiration is negligible. Wet soils at night.

              Factors Affecting Transpiration

              Wind, Internal concentration of carbon dioxide (low concentrations in leaf cause the stomata to open), wind, air temperature, soil, and light intensity. (Light tends to cause stomata to open in the morning and close in the afternoon).

              ثالثا. Movement of food within the plant body - transporting organic solutes

              Transport occurs in the sieve-tube members of phloem. Very delicate and easily damaged. This fact has limited a lot of work done on phloem, since it releases callose (glucose polymer) and P-protein (proteinaceous slime) which clog up the sieve-tube plates (perforated).

              Process is initiated by active transport of sugars from the leaf cells to sieve-tube. SOURCE (leaves in summer and fall, roots in the early spring) AND SINKS (buds in the spring fruits, seeds, and roots in the summer and fall) AND THE BULK MOVEMENT OF WATER AND SOLUTES.

              
              

              Corn Roots

              Corn plants are unusual in that they have two distinct sets of roots: regular roots, called seminal roots and nodal roots, which are above the seminal roots and develop from the plant nodes.

              • ال seminal root system includes the plant's radicle (the first root emerging from the seed). These roots are responsible for taking up water and nutrients, and for anchoring the plant.
              • The second root system, the nodal roots, is formed about an inch or so below the soil surface, but above the seminal roots. The nodal roots are formed at the base of the coleoptile, which is the primary stem that emerges from the ground. The nodal roots are visible by the V2 stage of development. The seminal roots are important to the survival of the seedling, and damage can delay emergence and stunt development. This is because the corn plant depends on the nutrients present in the seed until the nodal roots are developed. As soon as the coleoptile emerges from the soil, the seminal roots cease to grow.

              Nodal roots that form above the ground are called brace roots, but they function similarly to the nodal roots below the ground. Sometimes brace roots actually penetrate the soil and take up water and nutrients. These roots may be needed for water uptake in some cases, as the crown of a young corn plant is only about 3/4" below the soil surface! Therefore, corn can be vulnerable to dry soil conditions as they don't have a deep root system.

              
              

              2) The Region of Cell Division (Meristematic Region)

              It is located a few millimeters above the root cap. The cells of the meristematic region are typically small, thin-walled, and contain dense protoplasm. Meristematic cells contain three layers: i) Dermatogen – the outermost layer, ii) Plerome – the middle layer, and iii) Periblem – the innermost layer.

              • Performing cell division to produce new cells for the developing root
              • Helping in root elongation
              
              

              شاهد الفيديو: الأحياء العامة. عملي. 7-1. أنواع الجذور في النباتات الزهرية (أغسطس 2022).

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