The transition from water to land required plants to develop efficient transport pipelines for water and nutrients to the leaves, and for energy-rich carbohydrates (from photosynthetic carbon dioxide fixation) to tissues that require energy (e.g. roots, storage organs etc.).

Xylem and phloem are found together in vascular bundles and transport water (unidirectionally) and photosynthates (bidirectionally), respectively. While these vascular bundles, or steeles, are arranged in a circle in dicots, they are scattered throughout the stem in monocots. This means that monocots can not perform secondary, or thickness, growth.

Thickness growth in dicots is due to the activity of a secondary, or vascular, cambium that produces xylem towards the inside, and phloem towards the outside. Old phloem eventually dies and contributes to the bark which protects the active phloem.

Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.

Stems II (handout)

Plant Science focusses on the green, silent, and motionless life forms we take for granted. Plants are amazing organisms. Literally rooted in one spot, they are able to cope with a wide range of environmental conditions, while at the same time using only light, carbon dioxide and water to generate energy-rich sugars that drive and support the vast majority of life on the surface of our planet.

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Over thousands of years, humans have "domesticated" wild type plants and animals through selective breeding. Examples from the plant world include the breeding of modern hybrid maize from teosinte, or the development of modern wheat from emmer.
As our knowledge of genomics and molecular technologies advances, we have developed much more precise and potentially more versatile ways to modify plants: genetic modification.

In these two lectures we have a brief look at what biotechnology actually means, and our challenges in the time of rapid population growth and climate change. Using the example of Bacillus thuringiensis toxin we explore the principles behind genetic modification, and follow that up with a brief description of the introduction of herbicide resistance into broad acre crops.

To conclude Plant Science in 2012, we move away from those input traits and take a look at Golden Rice, a genetically modified rice that produces beta-carotin in the grain. Golden Rice has the potential to save many thousands of children from blindness, and even death, caused by lack of vitamin A in the prevalent staple diet.

Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.

Stems II (handout)

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