Chloroplasts in the stomata of Allium cepa L.
Shaw M. (1954)
Department of Biology, University of Saskatchewan, Canada
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in New Phytol. 53. 344-348 –
The stomata of Allium cepa are fully motile (Loftfield, 1921) and exhibit a genuine response to light and, by inference, to changes in carbon dioxide tension (Heath, 1952). They are, however, completely starch-free, as demonstrated by a number of investigators from Parkin (1899) to Heath. The former, having examined both alcohol fixed and living epidermis of some eight species of onion, including A. cepa and A. schoenoprasum, reported: ‘ No chloroplasts could be recognized, nor could I certainly detect any green colour in the guard cells.’ He noted, however, that refractive granules were sometimes present.
Heath also was unable to recognize chloroplasts in the stomata of A. cepa (var. Ebenezer) and obtained negative results with certain microchemical tests for chlorophyll (saturated KOH and the phaeophytin test: Molisch, 1921), but did not refer to the Molisch reaction (reduction of AgNOg by chloroplasts: Molisch, 1918). It may be noted that Sayre (1926) found that the stomatal plastids of Rumex patientia, though obviously green, did not give the microchemical tests {sic) for chlorophyll, a result he regarded as inconclusive in view of the small amount of pigment present.
PLANT STOMATA ENCYCLOPEDIA 