Journal Article

Water stress enhances β‐amylase activity in cucumber cotyledons

Daisuke Todaka, Hisashi Matsushima and Yukio Morohashi

in Journal of Experimental Botany

Volume 51, issue 345, pages 739-745
Published in print April 2000 | ISSN: 0022-0957
Published online April 2000 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jexbot/51.345.739
Water stress enhances β‐amylase activity in cucumber cotyledons

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Cotyledons detached from 4‐d‐old cucumber (Cucumis sativus L.) seedlings were subjected to water stress (air‐drying or PEG‐treatment) to examine the effects of the stress on carbohydrate metabolism. Amylolytic activity in the cotyledon was increased about 6‐fold by water stress within 1 d. The substrate specificity and the action pattern indicated that β‐amylase is responsible for the activity. Activities of azocaseinase, malate dehydrogenase and triose‐phosphate isomerase were not affected by water stress, indicating that the effect of the stress on β‐amylase is rather specific. Cycloheximide‐treatment strongly reduced the enhancement of β‐amylase activity. The hypocotyl of cucumber seedlings also exhibited an increase in the enzyme activity when subjected to water stress. The major free sugars in cucumber cotyledons were glucose, fructose, maltose, and sucrose; sucrose being the most abundant. Sucrose content in excised, unstressed cotyledons increased markedly during the incubation. Changes in other free sugars were small compared with that of sucrose. Starch also accumulated in unstressed cotyledons. In stressed cotyledons more sucrose and less starch accumulated than in unstressed ones. Such results were discussed in relation to the enhancement of β‐amylase activity.

Keywords: β‐Amylase; cucumber cotyledon; starch; sucrose; water stress.

Journal Article.  4043 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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