CRASSULACEAN ACID METABOLISM IN THE SUCCULENT-C4 DICOT, PORTULACA-OLERACEA L UNDER NATURAL ENVIRONMENTAL-CONDITIONS
CRASSULACEAN ACID METABOLISM IN THE SUCCULENT-C4 DICOT, PORTULACA-OLERACEA L UNDER NATURAL ENVIRONMENTAL-CONDITIONS
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DOI：
10.1104/pp.69.4.757
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发表时间：
1982-01-01
期刊：
影响因子：
7.4
通讯作者：
KENNEDY, RA
中科院分区：
文献类型：
--
作者：
KOCH, KE;KENNEDY, RA
Crassulacean acid metabolism (CAM) was examined under natural environmental conditions in the succulent C4 dicot P. oleracea L. Two groups of plants were monitored: 1 was watered daily (well-watered), while the other received water once every 3-4 wk to produce a .PSI. [water potential] of -8 bars (drought-stressed). Gas exchange, transpiration rate and titratable acidity were measured for 24-h periods during the growing season. CAM activity was greatest in drought-stressed plants during late Aug., which had 13 h days and day/night temperatures of 35.degree./15.degree. C. Under these conditions net CO2 uptake occurred slowly throughout the night. Diurnal fluctuations of titratable acidity took place in leaves and stems with amplitudes of 17 and 47 .mu.equivalents/g fresh wt, respectively. Transpiration data indicated greater opening of stomata during the night than the day. CAM was less pronounced in drought-stressed P. oleracea plants in July and Sept.; neither dark CO2 uptake nor positive C balance occurred during the July measurements. Well-watered plants appeared to rely on C4 photosynthesis throughout the season, although some acid fluctuations occurred in stems of these plants during Sept. To determine the fate of the CO2 assimilated at night in drought-stressed Portulaca plants, exposure to 14CO2 during the night was followed by 9 h of ambient air in the light. Malate was the predominant compound labeled during the night, with some citrate and aspartate. No 14CO2 release was detected during the following day and by midafternoon the majority of the label was present in the insoluble fraction (predominantly starch). This supports earlier work with growth-chamber-grown plants and shows that limited CAM activity can occur in the succulent C4 dicot P. oleracea L. under certain natural environmental conditions.
