Photosynthetic properties of adaxial guard cells from Vicia leaves

Abstract

Photosynthetic properties of adaxial (ad GCP) and abaxial guard-cell protoplasts (ab GCP) from Vicia faba L. were compared. The CO 2 uptake was red light-dependent, and saturated at 400 μmol m -2 s -1 for ad GCP and ab GCP. The light dependency showed a half saturation at 55.4 for ad GCP and 22.5 μmol m -2 s -1 for ab GCP, on a protein basis. In SDS-PAGE, ad GCP and ab GCP showed almost similar profiles of protein including a similar content of Rubisco. From the electrophoretic analysis, the enrichment of particular 21 kDa protein was found in ab GCP. Chlorophyll (Chl) fluorescence transient also showed similar phases in both cell types. The transient changes were affected by DCMU, an inhibitor of photosystem II (PS II) activity and by methyl viologen, an electron acceptor from )photosystem I) PS I. The relative height of P from GCPs of both cell types depended on the exciting light intensity. Absorption spectrum of ad GCP showed similar profiles to that of ab GCP but two-fold higher content of flavonoid was found in ad GCP. Total Chl content was somewhat higher in ab GCP than in ad GCP. Chl a/b ratios were estimated to be 3.19 for ad GCP and 2.66 for ab GCP. From the results, adaxial guard cells had high photosynthetic capacity similar to abaxial ones, and a possible explanation on the responsiveness to red light (RL) is discussed.