Chlorophyll-Protein Complexes in Salix sp. 'Aquatica Gigantea' under Strong and Weak Light II. Effect of Water Stress on the Chlorophyll-Protein Complexes and Chloroplast Ultrastructure

The effect of slowly-induced water stress on the distributionof chlorophyll among the chlorophyll-protein complexes and onthe chloroplast ultrastructure was studied in Salix sp. ‘aquaticagigantea’ grown under two different light regimes. Underhigh irradiance the proportion of chlorophyll was largest inthe P700-chlorophyll-a protein complex (CPI). With increasingwater stress the proportion of the light-harvesting chlorophylla/b-protein complex (LHCP) and the chlorophyll a-protein complex(CPa) decreased, and these changes corresponded with inversechanges in the amount of chlorophyll in the protein free pigment(FP) band. The CPI complex remained stable throughout the dryingperiod. Under low irradiance the LHCP complex was the largeststructural component and its proportion of the total chlorophyllremained constant with increasing water stress. Under theselight conditions CPI and the CPa complex appeared to be thelabile components of the chloroplast lamellae. The integrityof the chloroplast membranes, as judged by electron microscopicobservations, was preserved well under both light regimes andwith increasing water stress. This and the relative constancyof the chlorophyll content during the experiments suggestedthat no great changes had occurred in the lamellar structureduring water stress. In the chloroplast stroma area, however,large crystal formations were observed under the strong lightregime with increasing water stress. In weak light these crystalstructures could be seen in the well-watered controls, but seemedto disappear totally as water stress became severe. (Received February 1, 1982; Accepted May 10, 1982)