As leaf irradiance is decreased in increments, a single transient CO2 burst is exhibited by C3 plant leaves. This post-lower illumination CO2 burst (PLIB) is sensitive to changes in irradiance, to changes in the concentrations of 02 and CC2, and to temperature. Increasing 02 concentrations above ambient produces a progressively larger PLIB while increasing CO2 concentrations above ambient produces a progressively smaller PLIB. The PLIB, which exhibits many responses to environment common with other methods for measuring photorespiration and photosynthesis, is proposed as a measure of photorespiration in illuminated leaves of C3 plants. Although the PLIB cannot be used as a quantitative measurement of photorespiration, we propose that the PLIB is a rapid, easy, relatively inexpensive, nondestructive method for evaluating photorespiration in intact illuminated C3 leaves in air.Leaves of some plants release a burst of CO2 immediately following illumination. This phenomenon was first referred to as a dark CO2 outburst by Decker (6,7) and is now commonly referred to as PIB.' A photo-stimulated dark 02 uptake also appears to be an expression of the same phenomena (13). The PIB was initially interpreted as being a remnant of light respiration (6, 7), and the same interpretation is widely accepted today (3,15,21). In relating the PIB to photorespiration, the amplitude of the PIB was shown to be a function of previous light intensity (7,17,18), temperature (8), atmospheric 02 concentration (1 1, 14, 17, 19), atmospheric CO2 concentration (7,9,13,16,21), leaf age, and photosynthetic CO2 assimilation pathway, i.e. C3 and CAM plants exhibit a PIB but most C4 plants do not (10-12, 15, 17-19). In some CAM plants such as pineapple, the PIB is exhibited as two peaks-the first associated with photorespiration, being sensitive to C02, 02, and light intensity but the second CO2 outburst attributed to decarboxylation of organic ' and Department ofBiochemistry (Z-P. T., S-S. C., C. C.acids during CAM (5). Multiple PIB peaks of CO2 release were observed in the earliest C3 plants studied (6,18) Biochemically, it is commonly accepted that photorespiration occurs during photosynthesis in the presence of 02 when the enzyme RuBP carboxylase functions as RuBP oxygenase. In its oxygenase capacity, it adds 02 to RuBP to produce P-glycolate and ultimately amino acids, glycine and serine, as transitory intermediates en route to completing the photosynthetic carbon oxidation cycle. The balance between carboxylation and oxygenation in leaves shows similar responses as does the PIB to environmental parameters such as 02, C02, and light intensity.We recently reported (20) a transitory release of CO2 from illuminated leaves when the illumination intensity was suddenly reduced. This post-lower illumination CO2 burst appeared to be a relatively simple means of measuring photorespiration at specific illumination intensities (20). These studies were conducted to document this hypothesis. In the initial work, a release of CO2 was detected follow...

The diurnal variations in volume and in specific weight were determined for green stems and leaves of Crassulacen acid metabolism (CAM) plants. Volume changes were measured by a water displacement method. Diurnal variations occurred in the volume of green CAM tissues. Their volume increased early in the light period reaching a maximum about mid-day, then the volume decreased to a minimum near midnight. The maximum volume increase each day was about 2.7% of the total volume. Control leaves of C3 and C4 plants exhibited reverse diurnal volume changes of 0.2 to 0.4%. The hypothesis is presented and supported that green CAM tissues should exhibit a diurnal increase in volume due to the increase of internal gas pressure from CO2 and 02 when their stomata are closed.Conversely, the volume should decrease when the gas pressure is decreased.The second hypothesis presented and supported was that the specific weight (milligrams of dry weight per square centimeter of green surface area) of green CAM tissues should increase at night due to the net fixation of CO2. Green CAM tissues increased their specific weight at night in contrast to control C3 and C4 leaves which decreased their specific weight at night. With Kalanchoe daigremontiana leaves, the calculated increase in specific leaf weight at night based on estimates of carbohydrate available for net CO2 fixation was near 6% and the measured increase in specific leaf weight was 6%. water vapor transfer to increase at night when stomata are open and to decrease during stomatal closure in the day (6-8). Thus, CAM plants conserve water and tend to hydrate during the day; then the tissues transpire and tend to dehydrate at night (7,8).Many of these characteristic diurnal aspects of CAM have been known for decades (8,11). By combining these known features with more recent data on CAM (6, 13), two hypotheses were developed which we have tested and are presented in this paper. First, we reasoned that the volume of green CAM tissues should increase during the day when stomata are closed due to the internal accumulation of gases such as CO2 from metabolism, e.g. decarboxylation of organic acids or the release of 02 from photosynthesis and possibly a small increase in the vaporization of H20. Second, we reasoned that the specific weight of green CAM tissues should increase at night due to the net fixation of CO2. We have partially tested these hypotheses by measuring the diurnal changes in volume and in the specific weight of green tissues from several CAM plants. These changes with green CAM tissues are compared to similar diurnal measurements made with leaves of a C:3 and a C4 plant. Plant Physiol. Vol. 71, 1983 mental plants were covered with cardboard at the stem base and sealed with tape. A stem was inserted upside down to a constant position on the stem into a cylinder containing H20. The change in H20 level was recorded by using a 0.l-ml pipette which had the H20 siphoned into it. The pipette was calibrated with the cylinder volume so we could determine the H20 d...

The variable fluorescence of leaves from Kalachoi daigrenwntiana and pineapple, Anaws comnosus, both CAM plants, was found to change over a 24-hour cycle and to exhibit high temperature-dependent maxima during the night period. The time course of the induced fluorescence was correlated with malic acid accumulation but not with other aspects of CAM such as with the nature of the decarboxylation pathway or with stomatal movements. The variable fluorescences of sunflower (Helanthus awuws L.) and corn (Zea mays L.) leaves were compared with the CAM plants diurnafly, both plants also exhibit high fluorescence maxima during the night period. We conclude that the assembly of the photosystems in the Light is a primary process in photosynthesis induction and may be influenced by other celiular metabolic processes, specifically in the case of CAM leaves by malic acid accumulaton.events associated with CAM CO2 metabolism and organic acid metabolism (13,14). We are not aware of other investigations on variable fluorescence induction during the night phase of a higher plant's diurnal cycle, so diurnal curves for a C3 and a C4 plant also were measured and compared with CAM curves.We have chosen the two CAM species as representing two different biochemical pathways of CAM. Kalanchoe utilizes malic enzyme for decarboxylating malic acid and pyruvate Pi dikinase in the regenerative phase of glycolysis; pineapple uses PEP4 carboxykinase for decarboxylation and PEP production. Furthermore, the two plants vary in the source of sugars as substrate for glycolysis during malic acid production. Pineapple utilizes fructose and glucose (cytosolic) plus glucans while Kalanchoe utilizes starch (chloroplastic) as their respective sources of carbon for producing the nighttime CO2 acceptor PEP (3, 13). MATERIALS AND METHODSPreviously darkened leaves display fluorescence which varies in intensity during continuous excitation with weak actinic light. This phenomenon first described five decades ago (11) has been studied more recently in relation to water potential, frost resistance, and photoinhibition of photosynthesis in leaves (6,20) as well as more extensively in laboratory studies on the coupling of photochemical and metabolic processes in chloroplasts and cells (2,17, 23, 24). Although the time course of this fluorescence has certain consistent features (for reviews, see Clayton [5]