Plant System: How do plants store food?

Plant leaves produce food in the presence of sunlight, water and carbon dioxide. The plants use the food and store the excess within itself. Different plants store food (sugars/starch) in their roots (turnips, carrots, sweet potatoes, etc), stems (water chestnuts, gingers, yams, potatoes, etc), leaves, fruits and even seeds. 

Please refer to your textbook (pages 12 to 15) in addition to the following notes.

(Click on the links to learn more about the terms.)

A storage organ is any part of a plant specifically modified for storage of energy (generally in the form of starch), nutrients or water in order to be used for future growth.

A storage organ is any part of the plant in which excess of energy (generally in the form of starch, sugars, lipids or protein), nutrients or water are stored in order to be used for future growth (usually in biennial or perennial plants). In the first year biomass is added to the storage organ. Afterwards some of the biomass from the storage organ is returned to the rest of the plant. 

Storage organs often grow underground, where they are better protected from attack by herbivores. Underground storage organs are also characteristic of geophytes. They evolved as a mechanism for plant survival through adverse climatic conditions, and as a result, geophytes in their natural habitats are capable of perennial life cycles. In the geophyte - especially during temperature extremes and prolonged drought - the aerial portions die back, leaving only the storage organ in the soil until the temperature or water availability is appropriate for above-ground growth. This stage in geophyte development is often referred to as a dormancy period or resting stage. But the storage organ is never physiologically dormant even when aerial growth is halted. It continues to change and constantly senses its environment like a biocomputer.

In common parlance, underground storage organs may be generically called roots, tubers, or bulbs, but to the botanist these are specific, technical terms, which apply only more narrowly:

• True roots:
	▫	Tuberous root
	▫	Storage taproot
• Modified stems:
		Corm
		Tuber
		Rhizome
		Pseudobulb
		Succulent stems
• Modified  leaves
		Bulb
		Succulent leafs
		Leaf petioles (e.g. celery, onion)
• Seeds:
		Cotyledons
		Endosperm
• Others:
		Storage hypocotyl (caudex)
		Axillary buds (e.g. Brussels sprouts)
		Inflorescences (broccoli, cauliflower)
		Etc.

In some plants the storage organ are short-lived and serve as regenerative organ bearing a bud or buds (e.g. a tuber); in that case the plant dies back in the resting season, except for the underground storage organ with the buds, later utilised for regrowth; afterwards old tubers decay and new ones are formed. In addition some plants produce smaller reproductive storage organs (bulbils, small tubers, etc); plants growing from them resemble in morphology and size seedlings.

(extracts from CACTUS ART Nursery)