| MadSci Network: Botany |
The plant kingdom is very diverse so it is difficult to make broad generalizations. When making generalzations in plant biology teaching, exceptions are often not taken into account. This seems to be the case in your situation. The first reference discusses the general problem of misconceptions in plant biology teaching. Most seeds do require oxygen for germination. Seeds of aquatic plants and plants that survive well in flooded soils, such as rice and some willows, can germinate underwater. That is not necessarily zero oxygen but it is low oxygen relative to most situations. Anaerobic respiration in seeds is usually a temporary process because once seedlings develop leaves, they can photosynthesize and produce oxygen gas. Many aquatic plants or those that survive well in flooded soils have stem and root tisues with abundant air spaces, termed aerenchyma. Aerenchyma allows photosynthetic oxygen to be stored and transported within the plant. It also allows for transport of air from aerial parts of the plant to submerged or underground parts. Plant species that survive well in anerobic conditions seem to accumulate malate via anaerobic respiration. Malate is nontoxic. Plant species that do not survive well in anaerobic conditions seem to accumulate alcohol via anaerobic respiration. Alcohol is toxic to plant species. Anaerobic respiration is much less efficient than aerobic respiration. Seeds that are able to use anaerobic respiration to germinate use their energy reserves much less efficiently than if they had oxygen available. However, it may give them a competitive advantage over other plants. For example, it may enable them to become established earlier in the season than species whose seeds have a higher oxygen requirement for germination. In waterlogged soils, plants may suffer more from toxic wastes created by anaerobic bacteria than from direct lack of oxygen. References Hershey, D.R. 2004. Avoid Misconceptions When Teaching about Plants. ActionBioscience.org original article. Comis, D. 1997. Aerenchyma—Lifelines for Living Underwater. Agricultural Research" 45(8):4-8. August US Army Corps of Engineers Wetlands Delineation Manual: APPENDIX C: VEGETATION Yamasue, Y. 2001. Strategy of Echinochloa oryzicola Vasing. for survival in flooded rice. Weed Biology and Management. 1: 28-36. Re: Why do oxygen bubbles come from the cut stem of Elodea, rather than leaves Plant Adaptations Evans, D.E. 2004. Tansley review: Aerenchyma formation. New Phytologist 161: 35-49
Try the links in the MadSci Library for more information on Botany.