The occurrence of functional non-chlorophyllous guard cells in <i>Paphiopedilum</i> spp.

Abstract

Hypostomatous lady slipper orchids, Paphiopedilum spp., were found to have non-chlorophyllous epidermal cells, including guard cells. The lack of chlorophyll within the guard cells was demonstrated by fluorescence microscopy. A "normal" chlorophyllous mesophyll was present. The leaf resistances of intact leaves were about 5–10 s cm −1 in the light and were greater than 100 s cm −1 in the dark, indicating light opening and dark closure of the stomata. A CO 2 -dependent stomatal response (i.e., a tendency to close at elevated CO 2 levels) was demonstrated, as was a CO 2 -independent light response (i.e., greater opening in blue light than in red). This provides direct evidence to support the idea that guard cell chlorophyll is not necessary for stomatal functioning.