Chlorplast fluorescence of C4 plants : III. Fluorescence spectra and relative fluorescence yields of bundle-sheath and mesophyll chloroplasts.

In situ fluorescence emission spectra of mesophyll and bundle-sheath chloroplasts of Dichanthium annulatum (Forsk.) Stapf are measured by a microscopic technique using black and white infrared film as a detector. These spectra confirm the higher ratio of infrared to far-red fluorescence in bundle-sheath relative to mesophyll chloroplasts as predicted by infrared color film observations. The total relative fluorescence yield of bundle-sheath chloroplasts is ca. half that of mesophyll chloroplasts.The fluorescence emission spectra and yields of both mesophyll and bundle-sheath chloroplasts of Dichanthium annulatum are equally affected by Tris washing. Therefore, we conclude that both chloroplast types have approximately equivalent variable components of fluorescence. This variable fluorescence component has a strong infrared component, in addition to the expected far-red component. Similarly, the relative mesophyll to bundle-sheath fluorescence yeilds of these chloroplasts remains almost constant after DCMU, and after Tris followed by hydroxylamine treatments. The similar effects of the above chemical treatments on the fluorescence yields and spectra of the two chloroplast types is interpreted as evidence for the same relative proportion of photosystem I to photosystem II in bundle-sheath and mesophyll chloroplasts.