CHOOSING A MODEL SYSTEM FOR STUDIES OF LEAF RE-GREENING

Chloroplasts are the repository for the green color in plants. As leaves grow, age, experience stress and/or senesce, they change color. To select a system for a study of physiological mechanisms that allow yellowing leaves to regreen, leaves of 32 horticultural species were screened for chloroplast size, leaf thickness and ease of fresh frozen sectioning. Zantedeschia aethiopica, Dianthus caryophyllus, and Plectranthus australis all had thick leaves (range of 450-880+ µm), large chloroplasts and were easily sectioned at a thickness of 12-18 µm. Chrysanthemum x morifolium and Alstroemeria aurantiaca also had large chloroplasts and leaf thicknesses that were mid-range (250-450 µm) or thin (less than 250 µm). Of these plants, however, only Dianthus, Chrysanthemum and Plectranthus are easily, clonally propagated. Plectranthus was selected for the second phase of the study, with Chrysanthemum as an alternate. Attempts to vital stain Plectranthus chloroplasts with silver nitrate at concentrations of 1, 2, 5, or 10% at pH levels of 4 and 6.2 were unsuccessful. Thus, alternatives to stains such as fluorescence and scanning laser confocal microscopy of chloroplasts are being investigated.

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