CHLOROPLAST ULTRASTRUCTURE CHANGES IN PISUM-SATIVUM ASSOCIATED WITH SUPPLEMENTARY ULTRAVIOLET (UV-B) RADIATION

Pea plants (Pisum sativum L. cv. Greenfeast) were grown and exposed to supplementary UV-B radiation from day 17 after planting under growth cabinet conditions. The effects of this exposure on the ultrastructure of chloroplasts and the total soluble sugar and starch concentrations were estimated. Supplementary UV-B radiation was shown to damage the structure of chloroplasts, as manifested by dilation of thylakoid memb ranes, a progressive disruption of the thylakoid structure and disinte gration of the double membrane envelope surrounding the chloroplast, a ccompanied by the accumulation of large starch grains. Diurnal changes observed in starch concentration suggest that the higher concentratio n of starch in supplementary UV-B-treated leaves is due to its immobil ization, rather than to any increase in starch synthesis: soluble suga rs accumulated and remained at a higher level and then later declined.