The Photostability of Different Chlorophyll Forms in Dark Grown Leaves of Wheat

The stability against high intensity irradiation (red light, 700 W m²) was investigated for the chlorophyll(ide) pigments formed after photoreduction of the protochlorophyllide in dark grown leaves of wheat. Connections were found between changes in absorption spectrum in vivo (the Shibata shift and the late red-shift) and changes in photostability both in young (five-day) and old (12-day) leaves. The photostability of both the 684-form and the 673-form as well as the rate of the changes in photostability (the Shibata shift and the late red-shift) decreased with the age of the dark grown plants. It was concluded that the more pronounced decrease in the chlorophyll(ide) contents found at irradiation of older dark grown leaves mostly depended on the lower rate of the changes in the photostability of the pigment in old leaves. No resynthesis of protochlorophyllide occurred before the onset of the late red-shift. The results and their connection with the lag in chlorophyll formation are discussed. This lag is more pronounced in older dark grown wheat.