THE EFFECT OF GROWTH CONDITIONS AND THE STAGE OF LEAF DEVELOPMENT ON THE HILL REACTION IN HOMOGENATES OF PISUM SATIVUM LEAVES

Miller, John H. (Yale U., New Haven, Conn.) The effect of growth conditions and the stage of leaf development on the Hill reaction in homogenates of Pisum sativum leaves. Amer. Jour. Bot. 47(7): 532–540. Illus. 1960.—With plants grown under short-day conditions (8 hr. light and 16 hr. dark), crude chloroplast suspensions from young leaves have a higher Hill-reaction activity between 1 and 3 hr. after the beginning of illumination than suspensions from older leaves, while after 5–7 hr. of illumination, this activity difference is not found. These differences result from a marked diurnal rise and fall in the Hill reaction. The magnitude of the rise depends on the age of the leaf from which the chloroplast suspension is prepared. Peak activity occurs after the plants have received between 3 and 4 hr. of light and is highest in suspensions prepared from young leaves. Suspensions from the oldest leaves show no diurnal change in activity. No diurnal changes in activity are found in chloroplast suspensions from plants which are grown under continuous light, and the diurnal rise and fall is dependent on the plant receiving an alternation of light-dark-light.     

Changes in mRNA level rhythmicity in the leaves ofSinapis alba during a lengthening of the photoperiod which induces flowering

A previous study has shown that mRNAs exhibit complex patterns of diurnal rhythms in their quantity in the leaves ofSinapis alba during an 8 h light/16 h dark short day (SD). In order to determine whether this situation is rapidly modified in plants subjected to an extended light treatment, we have usedin vitro translation and two-dimensional polyacrylamide gel electrophoresis, together with a strict gel comparison procedure giving aP=0.03 certitude level, to analyse the mRNA complement at different times during a 22 h light/2 h dark long day (LD).During this LD, complex changes affected about 10% of the mRNAs. Thirty-four different patterns were observed. Some diurnal rhythms present in SD are not modified by the lengthening of the light period, but most are affected. Moreover, we have shown that some mRNAs presenting a constant quantity under a SD regime show an increase or a decrease during the first hours of the photoperiod lengthening.InSinapis, this LD also induces flowering. All the changes in mRNA quantity detected thus parallel the photoperiodic induction of flowering in the leaves and are quantitative; no mRNA was shown to appear or to disappear.