Re: Can plants absorb starch?

Photosynthetic plants did not evolve to efficiently absorb carbohydrates from 
their environment, they manufacture them from water and carbon dioxide via 
photosynthesis. Photosynthetic plants adapted to an  autotrophic lifestyle, 
rather than the heterotrophic lifestyle of humans, animals and fungi. Plant 
roots cannot efficiently absorb even soluble carbohydrates. I believe the book 
by Hewitt discusses some of the early research on carbohydrate absorption by 
plants. 

Starch has low solublity so plants use it as a storage carbohydrate because it 
does not have the osmotic effect of soluble carbohydrates, such as sucrose. 
Leaves often form starch grains in chloroplasts. 

Irrigating plants with soda is a popular student science project based on the 
many questions MadSci gets on that topic. Plants are typically killed when 
irrigated with sugared sodas because of osmotic effects. Adding starch or 
sugars to soil would also promote microbe growth that could have detrimental 
effects on plants, e.g. roots harmed by toxic waste products of microbes, 
microbes competing with roots for mineral nutrients and possibly oxygen.   

If you want to get soluble sugars into plants, you can cut off the roots or 
leaf cuticle. Cut flower preservatives contain sucrose to provide energy to 
the flower. It is possible to keep albino corn seedlings alive by dipping the 
cut tips of leaves into a sucrose solution. 

Plant tissue culture usually uses sucrose as an energy source, not starch. The 
last website notes that "Other carbohydrates [besides sucrose, glucose and 
fructose] including lactose, maltose, galactose and starch are poor carbon 
sources." for plant tissue culture. 

References


Re: What is a good plant to test the effects of sugar or sweetener?

Hewitt, E.J. 1966. Sand and Water Culture Methods Used in the Study of Plant 
Nutrition. Commonwealth Bureau of Horticulture and Plantation Crops, East 
Malling, England. Technical Communication 22.


Re: Would watering a plant with sugar solutions positivly effect the grow of 
th


Photos of starch grains in chloroplasts


Basic Principle in Plant Tissue Culture Technique