Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Maltose Excretion by the Symbiotic Algae of Hydra viridis

Elsa Cernichiari, L. Muscatine and D. C. Smith
Proceedings of the Royal Society of London. Series B, Biological Sciences
Vol. 173, No. 1033 (Jul. 22, 1969), pp. 557-576
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/75789
Page Count: 20
  • Read Online (Free)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Maltose Excretion by the Symbiotic Algae of Hydra viridis
Preview not available

Abstract

The symbiotic algae (zoochlorellae) of Hydra viridis live inside the gastrodermal cells. When isolated into pure suspension free of animal tissue, zoochlorellae liberate maltose to the medium during photosynthesis. Maltose synthesis and excretion are very sensitive to external pH. At pH 4.0, about 40 to 50% of the carbon fixed in photosynthesis may be released from the cells as maltose, and a further 4 to 6% as other compounds (including alanine, glycollic acid, glucose, and an oligosaccharide provisionally identified as maltotriose). As the pH rises, excretion progressively diminishes, and at pH 7.0, only about 1% of the photo-synthetically fixed carbon is excreted, about half as maltose. Only traces of maltose are ever found within the cells, and sucrose is always the predominant intracellular soluble sugar. When cells previously labelled with 14C at pH 7.0 are transferred to non-radioactive media in the dark at pH 4.0, they immediately begin to synthesize and excrete [14C]maltose; the increase of [14C]maltose is closely correlated with a decrease of 14C-labelled hexose monophosphates and is not accompanied by any loss of 14C from the insoluble fraction. This suggests that maltose is synthesized from hexose monophosphates by a process which is not directly light dependent. In short-term photosynthesis experiments at pH 4.0, fixed 14C appears in sucrose within 20 s, but none appears in maltose until 60 s. This, together with the near absence of intracellular maltose and the marked sensitivity of maltose synthesis to external pH, suggests that the mechanism of synthesis is at or near the cell surface. The experimental results were consistent with the hypothesis that maltose synthesis is UDPG-dependent, but direct proof of this was not obtained. Although excretion of photosynthetically fixed 14C at pH 4.0 diminishes in the presence of external maltose, it could still continue at an appreciable rate when the external maltose concentration was as high as 10% (w/v). In 10% maltose media, some of the excreted 14C was still in maltose, but most was in compounds provisionally identified as maltotriose and maltotetrose, suggesting that a mechanism for transglycosylation may exist on the surface of the cells. Unlike symbiotic zooxanthellae and lichen algae, Hydra zoochlorellae show no signs of losing their ability of excreting carbohydrate during the first 24 h after isolation from the symbiosis. In the case of Hydra, it is suggested that the host might be able to control maltose excretion from its zoochlorellae by variations in the intracellular pH of the gastrodermal cells, but evidence for such changes is still lacking.

Page Thumbnails

  • Thumbnail: Page 
557
    557
  • Thumbnail: Page 
558
    558
  • Thumbnail: Page 
559
    559
  • Thumbnail: Page 
560
    560
  • Thumbnail: Page 
561
    561
  • Thumbnail: Page 
562
    562
  • Thumbnail: Page 
563
    563
  • Thumbnail: Page 
564
    564
  • Thumbnail: Page 
565
    565
  • Thumbnail: Page 
566
    566
  • Thumbnail: Page 
567
    567
  • Thumbnail: Page 
568
    568
  • Thumbnail: Page 
569
    569
  • Thumbnail: Page 
570
    570
  • Thumbnail: Page 
571
    571
  • Thumbnail: Page 
572
    572
  • Thumbnail: Page 
573
    573
  • Thumbnail: Page 
574
    574
  • Thumbnail: Page 
575
    575
  • Thumbnail: Page 
576
    576