ISHS Acta Horticulturae 171: I International Symposium on Water Relations in Fruit Crops
DAILY AND SEASONAL COURSES OF VALERIANELLA LOCUSTA STOMATAL APERTURES AND GUARD CELL POTASSIUM CONTENTS: FIELD MEASUREMENTS AND MODEL PREDICTIONS |
| Author: | R. Lösch |
| Abstract:
Daily courses of microclimate, stomatal apertures, and guard cell K+ contents were measured during the growing period of Valerianella locusta (L)Betcke (microscopic pore aperture assessment, Macallum staining for potassium detection). Midday stomatal closure accompanied by reduction of the potassium contents in guard cells was very pronounced in late summer and early autumn. During winter time and in the spring stomata were more or less widely open during the whole day. Measurements of stomatal apertures and potassium contents in a growth cabinet allowed the construction of response surfaces describing the dependence of the stomatal response pattern of Valerianella locusta to the microclimatic factors. The absolute potassium content of open and closed stomates was determined by non-aqueous disintegration of epidermal strips and assessment of the potassium content in a suspension of isolated pairs of guard cells by atomic absorption spectroscopy. By this method it was possible to calibrate the values of relative guard cell potassium contents obtained by the Macallum staining. From the data obtained under controlled conditions a model was constructed and applied in order to describe the stomatal apertures and potassium relations measured in the field. There was in general agreement between the predicted and the measured stomatal behaviour. Some discrepancies are discussed with emphasis on early morning light sensitivity of the guard cells, "afternoon fatigue", and the influence of the ontogenetic history of the guard cells on their behaviour. Guard cell potassium turnover is incorporated into this model description of stomatal behaviour. By this way a step is made to link mechanistically the biochemical processes at the cellular level with the description of the stomatal behaviour under field conditions. | |
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