In:
Journal of Experimental Botany, Oxford University Press (OUP), Vol. 46, No. special_issue ( 1995-09-01), p. 1377-1388
Abstract:
Nocturnal fixation of CO2 and storage of carbon in the form of malic acid in vacuoles of photosynthetically active cells are key processes of crassulacean acid metabolism (CAM). A prerequisite for malate transport into the vacuole is the concerted action of primary-active H+ -pumps, i.e. the tonoplast V0V1-H+-ATPase and H+ -PPiase, and a secondary-active carboxylate transporter. During the transition from C3-photosynthesis to CAM the H+ -ATPase of the C3/CAM-inter-mediate plant Mesembryanthemum crystallinum undergoes particular structural changes indicating an adaptation of the enzyme to the requirements for an increased capacity of tonoplast transport systems. The role of the H+-PPiase in energization of carbon transport in CAM remains unclear. While in Kalanchoë blossfeldiana cv. Tom Thumb, where CAM is induced by shortening of daylength, there is a higher expression of the H+-PPiase in the CAM state as compared to the C3-state, the enzyme disappears in M. crystallinum when CAM is induced by salt stress. However, the H+-PPiase could also be involved in the regulation of the H+-ATPase as shown by the PPistimulated ATP-dependent H+-transport activity found in K. daigremontiana and K. blossfeldiana cv. Tom Thumb. Although the tonoplast carboxylate transporter has not yet been identified, the kinetic parameters of the enzyme were characterized after partial purification and functional reconstitution into proteo-liposomes. While the influx of malate into the vacuole is mediated by the co-operation of different enzymes, the regulation of the passive efflux of malic acid from the tonoplast during the day may depend on biophysical membrane properties, i.e. the degree of order of the vacuolar membrane, which seems to be modulated by Ca2+.
Type of Medium:
Online Resource
ISSN:
1460-2431
,
0022-0957
DOI:
10.1093/jxb/46.special_issue.1377
Language:
English
Publisher:
Oxford University Press (OUP)
Publication Date:
1995
detail.hit.zdb_id:
1466717-4
SSG:
12
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