Saburo Itoo

Variations in the levels of major free cytokinins and free abscisic acid during tuber development of sweet potato

Changes in two plant growth substances were examined throughout tuber development of sweet potato (Ipomoea batatas Lam. cv. Minamiyutaka). Major free cytokinins [t-zeatin riboside, N6-(Δ2-isopentenyl)adenosine and 6-(3-methyl-2-butenyl amino)purine glucoside] and free abscisic acid in tubers were determined by HPLC and GC-ECD. An increase int-ZR almost coincided with the onset of rapid tuberization 30–90 days after planting the vine cuttings. The levels of i6Ado and ABA were much lower than that oft-ZR throughout tuber development. The maximum level of i6Ado preceded the maximum oft-ZR. The level of iPG was higher than that oft-ZR, and the pattern of changes in the level was more complex. The maximum level of iPG reached about 270 μg kg−1 fresh weight. Varied changes in the low levels of ABA appeared not to be related to tuber development. Longitudinal distribution of the cytokinins and ABA in the developing tubers showed that levels oft-ZR were higher in parts of the proximal side of the stem than in other, lower parts of the tubers.

Membrane damage caused by exposure to t-butyl hydroperoxide

Abstract As well as red beet discs, turnip and sweet potato storage tissues exposed to t -butyl hydroperoxide ( t -BHP) showed leakage of several cellular components including potassium ions, reducing sugars and UV-absorbing materials. Even at the beginning of the eight hr-treatment period, leakage of potassium ions was accompanied by a decrease in respiratory activity. At the time when the respiration of turnip discs started to decrease, accumulation of lipid hydroperoxides was detected by four different methods. Just after t -BHP treatment started incorporation of t - BHP was observed and the amount increased linearly to a maximum after ca four hr and then decreased gradually. This disc experiment suggests that t -BHP, a model compound of oxygen stress, is incorporated into plant tissues and may cause directly or indirectly lipid peroxidation in various biomembranes which leads to a leakage of cellular components and a decrease in respiratory activity.