Related Experiment Videos
A study of sieve element starch using sequential enzymatic digestion and electron microscopy.
The Journal of Cell Biology
|May 1, 1970
Summary
Sieve tube starch in bean plants has a unique chemical structure. Unlike ordinary starch, it contains numerous alpha-(1 --> 6) linkages, making it resistant to standard enzymatic digestion.
Area of Science:
- Plant Cell Biology
- Biochemistry
- Ultrastructural Cytochemistry
Background:
- Plastids and starch deposits are crucial in plant cell differentiation.
- Sieve elements are specialized cells in the phloem responsible for long-distance transport.
Purpose of the Study:
- To investigate the fine structure and chemical composition of starch in differentiating sieve elements of Phaseolus vulgaris L.
- To compare the molecular structure of sieve tube starch with starch from other plant cell types.
Main Methods:
- Ultrastructural cytochemistry using specific carbohydrases (alpha-amylase, diastase, pullulanase) on thin sections of bean hypocotyl tissue.
- Electron microscopy to observe the digestion patterns of starch grains.
- Enzymatic treatments targeted alpha-(1 --> 4) and alpha-(1 --> 6) glycosidic linkages.
Main Results:
- Ordinary starch grains were digested by alpha-amylase and diastase, which cleave alpha-(1 --> 4) bonds.
- Sieve element starch grains were resistant to alpha-amylase and diastase.
- Pre-treatment with pullulanase (an alpha-[1 --> 6] glucosidase) rendered sieve element starch digestible by alpha-amylase, indicating the presence of alpha-(1 --> 6) linkages.
Conclusions:
- Sieve tube starch is chemically distinct from ordinary starch due to a high degree of branching and numerous alpha-(1 --> 6) linkages.
- This unique structure influences the digestibility and potentially the function of starch within sieve elements.