Plant Sciences Lab 2 2024 PDF

Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 Vegetative Growth Learning Objectives  List the major function of roots.  Explain the difference between root development in monocots and dicots.  List the basic func...

Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 Vegetative Growth Learning Objectives  List the major function of roots.  Explain the difference between root development in monocots and dicots.  List the basic function of stems.  Explain the difference between determinate and indeterminate growth patterns.  Identify the three main growth habits of dicot stems.  List the functions of leaves.  Explain how a monocot leaf differs from a dicot leaf.  Differentiate between a simple leaf and a compound leaf.  Differentiate between a leaf and a leaflet.  Identify leaves by their shape.  Identify the three main types of leaf arrangement.  Define annual, biennial and perennial life cycles. Key Terms and Concepts annual life cycle leaf type root apical meristem auricles leaf venation root hair axil leaflet ligule secondary adventitious root biennial life cycle linear sessile bud node sheath collar opposite leaf arrangement shoot apical meristem compound leaf palmate venation simple leaf compound palmate leaf perennial life cycle simple palmate leaf compound pinnate leaf petiole simple pinnate leaf culm petiolule stipules erect stem growth habit phyllotaxy taproot glabrous pinnate venation tendril herbaceous perennial primary root tiller internode prostrate stem growth habit trifoliolate leaf lamina pubescent twining stem growth habit leaf blade rachis whorled leaf arrangement leaf margin reticulate woody perennial leaf shape 1  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 The primary difference between monocot plants and dicot plants is summarized in the following table. Monocot Plants Dicot Plants PLSC LAB 1 One cotyledon (scutellum) per seed Two cotyledons per seed PLSC LAB 2 Parallel leaf venation Reticulate (net or branched) leaf venation PLSC LAB 3 Floral parts tending to be in units of Floral parts tending to be in units of three five or sometimes four Vegetative Growth Process Plant growth proceeds from areas where mitotic cell division occurs.  These areas are known as meristems.  Meristems responsible for increasing plant length are called apical meristems.  Plant growth proceeds upward from the shoot apical meristem (SAM) which gives rise to above ground plant structures such as leaves and flowers.  The root apical meristem (RAM) gives rise to primary meristematic tissues that develop into root components. Vegetative Plant Components The Root System Basic functions of the root system:  ABSORPTION – absorb and conduct the water and soil nutrients required for growth  ANCHORAGE – serve as an anchor for the above ground components of the plant  STORAGE – in some crops, the roots also serve as organs for food or water storage or as units of vegetative reproduction Because the root system is hidden from sight it is easy to under-estimate its size. In a typical cereal plant, the root system may represent ¼ to ⅓ of the total mass of the plant. The root of a carrot may represent over 90% of the total mass of the plant. Root hairs are small epidermal extensions on the root surface that increase absorption surface area for both water and nutrients (they exist in both monocot and dicot roots). Development of the Root System Monocot Roots (Cereal Crops)  The seedling’s first root or primary root (1° root) develops directly from the radicle.  At some point during the seedling stage, most grasses initiate a secondary adventitious root system.  Secondary adventitious roots (2° adventitious roots) are any roots on a monocot (cereal) plant that cannot trace their origin back to the radicle. 2  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 o Typically 2° adventitious roots erupt from lower stem nodes.  Adventitious is used to describe any plant structure originating in an unusual or unexpected location. Dicot Roots (Oilseeds and Pulses)  Most dicot crops have a taproot system derived from the radicle in the original seed. It becomes the primary root.  The taproot initially sends one major root directly downward, with only minor lateral branches emerging along its length.  The branches off the taproot are termed secondary roots (this is a distinct difference from grasses, which are monocots and have secondary adventitious roots). The Stem Basic functions of stems:  SUPPORT leaves and orient them in a manner that maximizes light capture  TRANSPORT – the stem functions as a pathway for movement of nutrients and water from the roots to the leaves and for movement of photosynthetic products in the opposite direction  STORAGE –stems may be modified to serve as organs of food storage or for vegetative reproduction (potato tubers) Stem Terminology  A node is the point of attachment of a leaf or branch to a stem. o An internode is the part of the stem between successive nodes  An axillary bud is the bud found in the leaf axil. The leaf axil area is the upper angle created between leaves at the point of its connection with a stem. Growth Pattern Determinate Growth Pattern o The plant has a predetermined number of leaves or stem nodes, and then produces an inflorescence. o After a period of vegetative growth the plant switches to reproductive development, and vegetative growth ceases. o Plants flower and produce seed all at one time resulting in uniform maturity. Indeterminate Growth Pattern o The plant does not have a predetermined number of leaves or stem nodes. o Indeterminate plants flower and produce seed while continuing to grow and produce more flowers. o Mature seeds and unopened flowers can exist on one plant. Stem Growth Habit 3  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 A dicot plant’s growth habit is determined mainly by characteristics of the stem. The three principal growth habits we will find in this lab are: o Erect Stem Growth Habit  Stems grow upright and are strong enough to be self-supporting.  Sunflowers and trees are examples of plants with an erect stem growth habit. o Prostrate Stem Growth Habit  Stems are not strong enough to support the plant upright so they lie flat against the ground.  These stems may or may not root at nodes along their length where they come in contact with the soil.  Portulaca and prostrate pigweed are examples of plants with prostrate stem growth habit. o Twining Stem Growth Habit  Stems are too weak to support the plant upright but the stems have a unique ability to sense objects they touch and quickly wrap themselves around them for above ground support.  Wild buckwheat and clematis are examples of plants with twining stem growth habit. Growth of Stems Stems (Cereal Crops)  Initially cereal plants have extremely short above ground stems.  The first few leaves seem to arise from almost the same level because there are short internodes (stem segments) between each leaf that have not yet begun to elongate. As growth becomes progressively faster, upper internodes are extended to form longer stems.  The stem of a cereal crop is typically called a culm. o The culm is cylindrical and usually hollow except at solid nodes or joints (i.e. corn and sorghum do not have hollow stems).  Typically after four or five leaves have been produced, the cereal plant will begin to tiller.  A tiller is a side shoot that is produced when the axillary bud at a stem node breaks dormancy and begins to grow. o After a tiller has produced about three leaves, it generally begins developing its own secondary adventitious roots from its lower stem nodes. o Under favorable conditions, the tillers as well as the main shoot will flower and produce grain, making the plant more productive. o The number of tillers produced by a plant is a determined by:  genetic characteristics of the plant  availability of growing space, nutrients and water 4  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 Dicot Stems (Oilseeds and Pulses)  Above ground growth of dicot stems proceeds with elongation of internodes.  Like the tillering in monocots, branching in dicots increases productivity.  Branching occurs from axillary buds located in leaf axils.  There are two stem growth patterns characterized in dicots; determinate growth and indeterminate growth. Leaves The basic functions of leaves:  Capture light and conduct the basic reactions of photosynthesis.  Draw water and mineral nutrients from the root to the leaves and stems through the process of transpiration, which nourishes and cools the plant. Dicot Leaves (Oilseeds and Pulse Crops)  Dicot leaves typically consist of a blade/lamina and a petiole (the petiole may or may not be present). o The blade is the wide, flattened part of a leaf. o If present, the petiole is the stalk of a leaf and attaches the lamina/blade to the stem. o A leaf blade attached to the stem with a petiole is said to have petiolate leaf attachment. o A leaf blade attached directly to a stem, with no petiole is said to have sessile leaf attachment.  Sessile leaf attachment is characteristic of most monocots.  Dicot leaf veins branch forming reticulate (netted or branched) venation.  The two main types of reticulate leaf venation found in dicots are: o pinnate venation  each leaf has a main central vein known as the rachis (main central vein), with smaller veins arising from the rachis o palmate venation  several main veins emerge from a common central point at the bottom of the leaf blade  Divisions of a leaf blade/lamina determine the two basic forms of dicot leaves: a simple leaf and a compound leaf. o A simple leaf has an undivided blade. o A compound leaf has a subdivided blade consisting of several leaflets.  The division of the leaf blade on a compound leaf often leads to confusion because each leaflet on a compound leaf can appear to be a leaf blade/lamina of a simple leaf.  In order to differentiate between several small, simple leaves or the leaflets of a compound leaf, look for the presence of an axillary bud. 5  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024  An axillary bud is a bud found at the base of a true leaf at its point of attachment to the stem.  A true leaf will emerge from a node on the stem and an axillary bud will be present.  A leaflet never has an axillary bud. Dicot Leaf Types Leaf types are determined by:  the presence/absence of divisions in the leaf blade/lamina  the type of venation of a simple leaf  the leaflet orientation of a compound leaf Simple Pinnate Leaf o Composed of a single blade/lamina with pinnate venation (feather-like). Compound Pinnate Leaf o Pinnate (feather-like) orientation of the leaflets on the rachis (the rachis is the main central vein of a compound pinnate leaf).  The leaflets may be directly attached to the rachis – sessile attachment.  The leaflets may be attached to the rachis by a structure called a petiolule (petiolule leaflet attachment). o There is a single axillary bud for an entire compound pinnate leaf. Simple Palmate Leaf o Several major veins radiate from a central point, like fingers radiating outward from the palm of your hand. Compound Palmate Leaf o Leaflets radiate from a central point. o The leaflets may be directly attached to a single point – sessile attachment. o The leaflets may be attached to the rachis by a structure called a petiolule (petiolule leaflet attachment). o There is a single axillary bud for an entire compound palmate leaf. Trifoliolate (or Trifoliate) Leaf (Compound Leaf) o There are always exactly three leaflets per leaf (many pulse crops). o There is a single axillary bud for an entire trifoliolate leaf. The leaflets of a compound leaf may themselves have pinnate venation but it is the orientation of leaflets that determine whether a leaf is a compound pinnate leaf or a compound palmate leaf. Dicot Leaf Shape (Shape of the Leaf Blade)  This is the general outline of the leaf. o cordate leaves are heart-shaped, with the notch at the base of the leaf blade o deltoid leaves are shaped like an equilateral triangle (flat at the base of the leaf) 6  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 o linear leaves are long and narrow with more or less parallel sides o lanceolate leaves are much longer than wide, with the widest point of the leaf below the middle of the blade o ovate leaves are egg-shaped in outline with the point of attachment (or the petiole) at the broad end Dicot Leaf Margins (Edge Pattern of the Leaf Blade)  Leaf margins can often be used as a distinguishing characteristic among plants. o entire or smooth leaf margins are not toothed, notched or divided o lobed leaf margins are cut less than half way to the base or midrib of the leaf (lobes can be smooth or pointed) o serrate leaves have saw-like margins; the serrations (teeth) along the leaf margin are pointing forward toward the leaf apex  double serrate leaves have serrate margins with smaller serrations (teeth) on the margins of the larger serrations (teeth) Dicot Leaf Arrangement The arrangement of leaves on a stem is known as phyllotaxy. Alternate Leaf Arrangement o The leaf arrangement characterized by one leaf per node. o In the grasses, there is always one leaf attached per node. o This is a common leaf arrangement for dicot plants. Opposite Leaf Arrangement o The leaf arrangement characterized by two and only two leaves at a node, these on opposite sides of the stem. Whorled Leaf Arrangement o A circular leaf arrangement involving three or more leaves at a node. Special Leaf Characteristics (Dicots) Stipules o Appendages, usually seen as paired structures, inserted at the base of the petiole; stipules are part of the leaf. o Stipules function as protection for emerging leaves, photosynthetic support, and plant defense. o Many legumes have large stipules. Tendrils o A modified leaf or leaflet of a climbing plant that coils around suitable objects. o Often the compound leaves of a pea plant will terminate with the last three leaflets being modified as tendrils. Leaves (Cereal Crops)  Monocot/cereal leaves consist of two parts, the blade/lamina and the sheath. 7  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 2 2024 o The blade/lamina is the flattened, elongate portion of the leaf. o The cylindrical sheath portion arises from each node and encircles the stem.  Monocot leaf veins are always parallel. o leaf veins do not branch o leaf veins run parallel from the base of the leaf to the leaf tip (parallel veins converge at the tip of the leaf)  The point of junction between the leaf sheath (the portion of the leaf that encircles the stem) and the blade/lamina is called the collar.  While the basic leaf structure is similar for all cereals (presence of a leaf blade and leaf sheath), leaves differ from crop to crop in the characteristics present at the collar area.  Structures known as ligules and auricles may be present at the collar (the junction of the blade and sheath).  Ligules and auricles are useful for identifying various crops in the field. Not every grass species has ligules and auricles, but their absence is also useful for identification. Ligules o A ligule (tongue like) is a membranous flap of tissue just inside the collar. o If present it is oriented upward toward the leaf tip. Auricles o Auricles (ear like) are small membranous projections at the sides of the collar. o If present they are positioned at the two outward edges of the collar. o They have characteristic lengths and shapes on different species. 8