Plant Science 1203L Laboratory 10

Prop roots and sheathing leaf bases (no petioles)

Identify the following illustrations from a corn plant as male or female. The figure on the right shows numerous hair-like (silk) structures. Botanically what are these structures? The figure on the left shows numerous floral structures. What are these structures? What is an inflorescence?

Inflorescence – is a group of flowers, in a definite arrangement on an axis

Each “kernel” on a corn cob is a separate one seed ovary termed a caryopsis. The caryopsis (or grain) is typical of many of the grain crops making them monocot or dicot plants? Monocot, other examples are rice, wheat, barley, sorghum,......

Observe the corn cobs on demonstration. Do the “silks” each lead to individual caryopsis? Name at least three other crops that produce a caryopsis.

Ancient Corn - Teosinte (shown above) is believed to be the ancestor to our modern day varieties of corn. Thankfully the early new world natives actually gave breeders a multi-century head start on the improvement of corn so that we have the modern high yielding plant we are familiar with today. Compare the illustration of teosinte and modern day corn from the first page. What are some obvious differences that you can observe?

Introduction to Photosynthesis

Photosynthesis and Carbohydrate Production “It is the business of agriculture to harvest the light energy that is used to produce food, fiber, and usable stuffs produced by agricultural plants and animals” National Academy of Science, 1975 Question of the Day – How does a corn kernel weighing 0.15 g, become a mature plant weighing 6-7 Kg in 90 days?

In Photosynthesis, always remember that light energy is being converted to chemical energy or food.

Photosynthetic Reaction – Generalized 6 CO H 2 O  C 6 H 12 O 6 + 6H 2 O + 6O 2 ^ green tissue ^ light

CO 2 from the atmosphere around the leaf, enters the stomate, travels to a photosynthetic cell where glucose is produced

Factors Affecting Photosynthesis Carbohydrate production via photosynthesis C3 vs. C4 photosynthetic pathways Slightly different pathways C4 experience less net respiration losses, they recycle much of the respired CO -2 Examples: C4 – corn, sorghum, bermudagrass C3 – soybean, barley, rice, cotton

C-3 Versus C-4 Plants - Corn is one of a small percentage of plants that uses a different and more efficient form of photosynthesis. While 95% of all plants use what is termed C-3 photosynthesis, corn uses what is termed C-4 photosynthesis. C-4 photosynthesis allows a plant to utilize very low levels of CO 2 that normal C-3 plants cannot. Since CO 2 is essentially the same in air anywhere why is this an advantage?

If water becomes limiting during daylight photosynthesis stomates will usually close and thereby reduce the movement of CO 2 into the leaf. At certain low CO 2 levels photosynthesis can no longer occur. C-4 plants can essentially capture the lower levels of CO 2 and “pump” this captured CO 2 into interior tissues of the plant where it is released at high enough concentration that photosynthesis can continue.

Anatomical differences in the leaf are what allows this to occur. C-4 plants have bundle sheaths around their veins that contain chloroplasts, while C-3 plant DO NOT! Additionally, C-4 plants have much of their mesophyll also arranged around (radially) the bundle sheaths. This gives the veins of C-4 plants a look that is somewhat similar to a “Christmas wreath”. The German botanist that first observed this used the term “Kranz” (wreath-like) to describe this anatomy. Consequently, it has been observed that all C-4 plants exhibit this Kranz anatomy.

Anatomical Difference between C-3 and C-4 Plants

The tight arrangement of mesophyll cells to the bundle sheath cell gives an appearance much like a corn cob in C- 4 plant leaves when seen in longitudinal view.