Studies in the Metabolism of Crassulacean Plants: The Behavior of Excised Leaves of Bryophyllum calycinum During Culture in Water

Abstract

A fundamental problem in experimental work with living tissues is the selection of samples in such a way that differences in composition which result from the treatment to which the material is exposed shall represent the effects of the treatment alone. There should be no opportunity for other processes to intervene and obscure the results. Complete isolation of the system under study can be effected, in the case of leaf tissue, only by excision from the plant. This has the disadvantage that the leaves are then merely "surviving organs" and soon begin to undergo changes that are ultimately lethal. Nevertheless, for a reasonable length of time, such leaves can be assumed to behave in a manner that reflects the normal course of metabolic events.The technique of excised leaf culture as applied in this laboratory (4, 5) consists in the selection at random of a group of approximately equal samples from a quantity of leaves picked from the plants at the same time, and therefore, presumably, in the same biological and chemical condition. One or more samples are at once prepared for analysis, in order to provide a point of departure for the series, and the others are subjected to treatment. Samples are subsequently withdrawn from time to time for analysis, the data obtained being computed in terms of equal quantities of fresh tissue as weighed at the start of the experiment. Biological variation is minimized by the use of moderately large numbers of leaves per sample. Although the results are expressed in concentration units, they refer to originally equal and similar lots of tissue. Accordingly, the differences from sample to sample furnish, within the limitations of biological and statistical variation, a measure of the actual magnitudes of the changes that have occurred. Errors arising from translocation are eliminated and, presumably, the only phenomena that affect the data are those associated with photosynthesis, respiration, absorption of culture solution, transpiration, and chemical transformations occurring within the cells.The diurnal variation of acidity characteristic of crassulacean plants is a phenomenon admirably suited for study by this general method. The entire cycle of changes is normally completed within 24 hours, a period sufficiently short to justify the assumption that irreversible catabolic changes which may be initiated are of minor significance in comparison with the 477 www.plantphysiol.org on August 5, 2020 -Published by Downloaded from

STUDIES IN THE METABOLISM OF CRASSULACEAN PLANTS: DIURNAL VARIATION OF ORGANIC ACIDS AND STARCH IN EXCISED LEAVES OF BRYOPHYLLUM CALYCINUM

“…In view of the unfortunate error that was made in computing the protein nitrogen (9) in three of the earlier papers of this series (6,7,8), special attention was devoted to this component in the present experiment. The data (table I, column 7) show that no significant change in the quantity of protein took place during culture in alternate light and darkness for three days.…”

Malate Synthesis in Crassulacean Leaves. I. The Distribution of C14 in Malate of Leaves Exposed to C14O2 in the Dark.

“…Thomas The lack of mobility of foliar applied calcium in a downward direction has been reported (1,2,3,7,8) and it has been suggested that polarity might play a role in this movement (3). By suspending polarity by mild anesthesis (10) …”

“…1) In the dark, after a period of strong illumination, detached leaves of Kalanchoe, Bryophyllum and some other plants undergo marked increases in free acid (1) associated primarily with increases in malic acid (2,3,4).…”

Dark Fixation of CO2 by Succulent Leaves: Conservation of the Dark Fixed CO2 Under Diurnal Conditions.

“…The flowers were picked each morning and 3 Deceased. 4 Appreciation is expressed to the Department of Floriculture and Ornamental Horticulture for granting research assistantships (to H. W. S. and C. T. C.) during the course of this investigation.…”

“…However, when the ribulose diphosphate pathway for CO2 fixation is saturated at high CO2 concentrations in the light, the acidification system involving phosphoenol-pyruvate carboxylase can be utilized. (3,4) that there is an inverse quantitative relationship between total titratable acids and net carbohydrate stores in succulent leaves subjected to diurnal conditions. The known pathways for the interconversion of Krebs cycle organic acids and carbohydrates depend upon decarboxylation and the reversal of glycolysis.…”