Plants & Human Affairs
Cherries.wmf (7140 bytes) Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

Vegetative Structures & Vegetables

 I. Major Vegetative Organs

  • roots – anchor, store nutrients, underground, positively gravitropic
  • leaves – photosynthesis, attached to stem, has a bud at its base
  • stems – supports leaves, flowers and fruits; usually negatively gravitropic, with buds

There is often no clear anatomical distinction between leaf and stem. The crown is the junction of the root and stem. A shoot is a stem with leaves. 

II. Plant Habit

  • herb - no woody tissue, soft stems
  • shrub - multiple stems, woody
  • tree – single stem, woody (oaks, maples)
  • succulent – very fleshy, juicy stem (cactus)
  • vine – stem that climbs or trails, requires support. Lianas are woody vines
  • forb - non-grass herbaceous plants.

III. Life Span/Duration

A.  Terms

  • annual – completes life cycle in a single year.
  • winter annual - completes life cycle in a year, spread out over two growing seasons; germinates late summer/early fall, over-winters as rosette, flowers next spring/early summer
  • biennial – completes life cycle in two years; the first year typically as rosette (like carrot) and the second year it bolts (produces a flowering stalk that grows quickly).  examples:  celery, carrot, cabbage, beet, turnip, rutabaga.
  • perennial – lives more than two seasons; can be woody or herbaceous; trees & shrubs are always perennials, herbaceous plants can be perennials (e.g., tulips, dandelions, Kentucky blue grass) or annuals.
  • evergreen – keeps its leaves year-round; e.g. pines, spruces, firs
  • deciduous – looses its leaves at the end of the growing season; e.g., oaks, maples, walnuts

B.  Food & Life Span
    We can make a few generalizations about the foods we eat and plant life span:  (a) Root crops are usually biennials.  These plants spend the first year accumulating nutrients in roots to prepare for flowering the following season; (b) Annual plants invest most of their energy in vegetative structures and producing seeds/fruits.  Thus, many of our important seed & fruit crops (e.g., corn, wheat, tomato) are annuals.  Similarly, many leaf crops are annuals; (c) Woody perennials are usually grown for fruit - they can get large enough to support and supply nutrients to developing fruits (e.g., apples, cherry, pear, avocado)

C.  Response to temperature

  • cold hardy/cold tender
  • warm season plants (sweet potato, muskmelon, tomato) vs. cool season (broccoli, peas)
  • Memorial Day - time to plant warm season crops
  • Pushing the envelope - "wall of water" (thermal buffer action of water)
  • USDA Cold Hardiness Zones

IV.  Cells - A Water Balloon in a Box - This is a good model for a plant cell. Thus, there are two major components to a plant cell:

A. The Box (= cell wall) 
    This part of the cell is analogous to the cell wall. Like a cardboard box, the cell wall is relatively rigid, it is non-living and highly structured. The wall is made up of a variety of carbohydrates including cellulose and some protein.  The more obvious functions of the wall are to support and protect the cell. It is produced by the living portion of the cell - called the protoplast.

    If you stack up a bunch of boxes you generally can’t make a very large tower before it comes crashing down. Since a plant is essentially constructed of numerous small boxes, why don’t they fall apart, too? The answer is glue! Plants glue their cells together with pectins. These carbohydrates, which make up the outermost layer of the plant cell wall (called the middle lamella), bind adjacent cells together. Cooks use pectins extracted from the middle lamella to solidify jams and jellies. One aspect of fruit ripening is that the fruit becomes softer, in part because enzymes digest the middle lamella (pectins).  Thus, immature or green fruits can be mixed with ripe ones when making jelly. 

    Pores or air spaces (called intercellular spaces) exist between adjacent cells because of the difficulty of packing of cells with rigid walls. Try and squeeze a bunch of irregularly boxes into a room without leaving any space between them! The intercellular spaces are important for gas exchange and water transport, some movements (i.e., sensitive plants - water moves into/out of theses spaces; nyctinastic movements - sleep movements) and freezing protection (i.e., water moves out of cells into the spaces to minimize cellular damage on freezing. Trivia note: prized ginseng roots have a translucent appearance - apparently obtained by freezing).

    Putting a cell in a box presents one major problem - how do cells talk to one another since they are now effectively isolated in their own small compartment? Plants solved this problem by putting windows in the box! Or in other words, there are lots of specialized pores through the wall called plasmodesmata that provide a cytoplasmic connection ("cytoplasmic bridges") between adjacent plant cells. Thus, the cytoplasm of a plant is essentially contiguous throughout the entire plant. Imagine hopping on board a tiny submarine like in the films Fantastic Voyage or Innerspace. You can essentially travel from cell-to-cell throughout the plant without ever leaving the cytoplasm nor crossing any cell membranes. Cool!

B. The water balloon
    This is analogous to the protoplast. The protoplast is everything inside the cell wall. It is the "living" part of the cell and includes:

  • membrane - bound cells, regulates entry/exit materials
  • cytoplasm - gel-like material inside cell in which other organelles are suspended
  • vacuole - large, central water-filled sac; waste disposal, cell support, increases cytoplasmic s/v ratio
  • nucleus - cell 'brain', controls functions
  • chloroplast - site of photosynthesis, contain light absorbing pigments (chlorophylls), protective pigments (carotenes) and assortment of molecules necessary for photosynthesis
  • mitochondrion - cell powerhouse - produces ATP (energy currency to get work done)
  • ribosomes - sites of protein synthesis

V. Leaves

A . Parts

  • blade – main photosynthetic part
  • petiole – fancy term for the leaf stalk
  • stipules – appendage are base of petiole in some leaves. Stipules can be glandular, leafy, spiny, or scale-like. In many cases, the stipules fall off shortly after the leaf expands. Many plants completely lack stipules.

B. Leaf structure:  The leaf blade may be all one section (=simple leaf) or broken up into smaller sections (called leaflets = compound leaf).  Margins may be smooth (=entire), toothed (=serrate) or lobed.

C.  Function:  Photosynthesis (= food production).  Leaves are well-adapted for photosynthesis:

  • broad - light & carbon dioxide absorption
  • flat (thin) - light penetration, carbon dioxide diffusion
  • pores (stomata) - carbon dioxide uptake, minimize water loss.
  • guard cells - open/close the stomata; ultimately regulate carbon dioxide uptake and water loss (transpiration).  Anti-transpirants - prevent water loss by either causing guard cells to close stoma (e.g., ABA) or coat the pores/leaf with a layer of wax (like a cucumber)
  • cuticle - prevent water loss
  • veins (xylem/phloem) - water/nutrient transport
           - xylem structure & function - vessels, tracheid, fibers; transpiration
           - phloem structure & function - sieve cells/elements, companion cells

D. Leaf Arrangement – Leaves may be found only at the base of the plant (basal, rosette, as in dandelion) or along the stem or in some combination. Phyllotaxy - leaves avoid overlapping (think "Da Vinci Code")

E. Venation. This refers to the pattern of the main veins which can be pinnate (like a feather), palmate (like the fingers on your hand), parallel.

F. Specialized Leaves – leaves may be modified in a variety of different ways. For example, the leaves of carnivorous plants are modified into traps. Tendrils are common in vines and used for support. Tendrils can be derived from modified leaves or stems

GLeaves as food
Crops can be derived from the leaf blade ("greens") or petiole

  • Greens (leaf blade) - spinach, lettuce, parsley, endive, kale, beet greens, Swiss chard, dandelion, amaranth, watercress, etc.

  • Spices (leaf blade) - sage, rosemary, thyme, dill, etc.

  • Leaf Stalk (petiole) - celery, rhubarb

  • Onion group - onion, garlic, leek. The tubular leaves of chives and other onions are often eaten.  Also, a bulb, which we classified as a stem, is actually made up of the fleshy bases of the onion leaves attached to a small stem.  Thus, even though onions are described as modified stems, the leaf base is the major part that is eaten.

H.  Abscission - leaf drop in autumn

I.  Environmental Response. 
     Leaves must be adapted to their environment - particularly related moisture availability and temperature.  For example, plants in dry environments have leaves that are smaller, more succulent, with a thicker cuticle, etc. than other species. This is the topic of two of our labs (leaves & climate,& leaves and environmental conditions).   Other adaptations include drip tips, hairs, waxes on leaf surface, pigments in the leaves to help absorb light or reflect it back into the leaf. 

VI. Roots

A.  Structures

  • tap – one main root, carrot
  • fibrous – many roots, no one root is dominant, like grasses
  • tuberous roots - swollen clumped
  • adventitious – a root that develops from a part of the plant other than another root, like the prop roots of maize, or the tendrils of ivy
  • root hairs � tiny outgrowths of the epidermis designed to absorb water and minerals
  • mycorrhizae - fungi associated with plant roots

B.  Functions

  • support
  • anchoring plant
  • absorption of water and nutrients

C.  Roots as food

  • Some select root crops (cassava or manihot, parsnip, carrot, rutabaga, turnip)
  • Roots or stems? � A few crops, such as radish and beet, grow underground and appear to be a taproot.  These crops actually develop from the hypocotyl, part of the embryonic stem.  Thus, even though they look and act like taproots, they are probably best considered stems

VII. Stems
     Botanically, a stem is the structure to which the leaves and roots are attached.  The stem supports the plant and is characterized by having buds and leaves.

A. Structures:

  • node – region to which a leaf is attached
  • internode – region between nodes
  • bud – found at base of leaf, immature shoot system
  • axillary (or lateral) bud – bud at base of leaf, along stem
  • terminal bud – bud at end of stem
  • bud scales – protective covering over bud, modified leaves
  • bud scale scar – scar left on stem where the terminal bud scales fell off
  • leaf scar – scar left on stem where leaf detached
  • lenticel – areas on stem for gas exchange
  • vascular bundle scar – in leaf scar, where vascular bundle went into leaf

B. Specialized Types

  • rhizome (ginger)
  • runner or stolon (strawberry)
  • bulb (onion)
  • corm (gladiolus)
  • tuber (potato)
  • spur shoot - short shoot; e.g., apples
  • suckers -  shoots that arise from root tissues (common in raspberry, aspen, sumac).  (not on exam)
  • water sprouts - arise from latent buds, usually have large leaves, succulent, rapid growing. (not on exam)

C.  Stems As Food.
      We typically think of stems as growing above the ground, but as we discussed earlier, some specialized types of stems (e.g., tubers, rhizome, corm, bulb) grow underground.  How can you tell? - stems have buds and nodes.

  • Aerial stems - asparagus, bamboo, kohlrabi
  • Tubers � white potato, yams
  • Rhizomes � Jerusalem artichoke (type of sunflower), arrowroot (starch), ginger
  • Corm � water chestnuts, taro
  • Bulbs � onion, garlic, leek (technically we eat the leaf base rather than the true stem)

VIII. Meristems.
     Growth in plants is restricted to certain regions called meristems.  For more on meristems, click here.

  • Apical meristems - found at the tips of roots and stems; responsible for growth in length.

  • Vascular cambium - produces vascular tissue (xylem and phloem); responsible for growth in width. (not on exam)

  • Cork cambium - produces cork (bark) (not on exam)

  • Pericycle - lateral roots develop  (not on exam)

  • Meristems as food � cabbage, Brussels sprouts, head lettuce

IX.  Vegetables.

  • food derived from the "vegetative" or non-flowering parts of the plant (e.g., root, stem, leaf)

  • common usage may vary from botanical usage.  Lay usage:  vegetables are considered green, not usually sweet, eaten as part of main course vs. Fruits - typically sweet, eaten as dessert or as a salad course.  Thus, tomatoes, zucchini, garden beans, and peas are erroneously considered vegetables.  The simple way to distinguish fruits and veggies:  fruits have seeds, veggies don't.

X.  The Mustard Family (Cruciferae or Brassicaceae) - an important family of veggies

A.  Family characteristics

B.  Some important crucifers

C.  Why so important?

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Last updated:  02/28/2005   � Copyright  by SG Saupe