Diurnal Variations in Leaf Fluorescence Induction Kinetics

Abstract

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]

Photosynthetic acclimation to high temperatures in wheat

“…It was also accompanied by enhanced photosynthetic performance as indicated by data of FR' Changes in F R have previously been used to assess thermotolerance in crop plants (Smillie & Hetherington 1983)and the reduction or loss ofFRwas considered to be a manifestation of heat injury on the donor side of photosystem II (Havaux & Lannoye 1984).Continuous monitoring of FRrevealed the presence of diurnal fluctuation in which high values of FR recorded during the night could be due to long dark incubation prior to stimulation. Diurnal fluctuations of the variable component of chlorophyll fluorescence have been attributed to changes in the stoichiometry of the amounts of electron carriers between the photosystems (Everson et al 1983). However, when measured at 25°C F R was higher in leaf segments of warm-grown plants than in those of cool-grown plants which reflects enhanced thermal stability of electron transport via photosystem II in warm-grown plants.…”

Light Scattering as an Indicator of the Energy State in Leaves of the Crassulacean Acid Metabolism Plant Kalanchoë pinnata

“…In 'malic enzyme type' CAM species, like Kalanchoe~pinnata, chloroplasts may have to generate up to 6.7 ATP and 2 NADPH to allow for the conversion of 1 malate to glucan in the light (4). Light-induced transport oftwo electrons from the water splitting system to NADP (linear electron flow) leads to the synthesis of two ATP at most (22 Recently, the kinetics of variable fluorescence were studied in several CAM species in relation to the degree of acidification of the tissues during day/night cycles (5,19). In the study presented here, we have used the light scattering method in combination with measurements of Chl fluorescence and CO2 exchange to obtain information on energization of leaves of the CAM plant Kalanchoe pinnata during a day/night cycle.…”